Lubricants, Greases and Petrochemicals are most versatile on the Industrial Plateau now a days. The significance of Lubricants, Greases and specialty products in the day-to-day functioning of nearly every machine part, instrument, appliance & device can not be over emphasized lubricants reduce friction & wear between rubbing parts, there by enhancing their life.
Raw Material for Lubricants
The basic raw materials for the manufacture of lubricants are: (1) Saponifiable fats and oils, (2) Saponifying agents, and (3) the base lubricating oil. But to improve the quality and grade of the manufactured lubricants, the following are added to make standard: (1) Performed soaps, (2) densifiers, (3) stabilizers, (4) chemical additives, (5) fillers, (6) dyes, and (7) perfumes. Densifiers may be employed in the presence or in the absence of soaps.
Saponifiable fats and oils. Theoretically any fat or oil may be converted into a lubricant or grease, but generally animal fats are used, because they are cheap, next comes vegetable oils, and other synthetic or non-synthetic materials: rosin-oil, naphthenic acids, sulphonic acids, synthetic fatty acids, montan wax, and wool grease. Wool grease is a good substitute for fats. Other substitutes are: tallow; olein, corn oil, repessed oil, cotton seed oil, etc.
While purchasing raw materials, the following points should be kept in mind.
(1) For the manufacture of lubricating greases with good storage stability or long life in service, fatty materials of low iodine value or containing little or no polyunsaturates are recommended. This points to animal fats or chemically or physically modified fats of low iodine value, for this purpose.
(2) For the same type of product, fatty acids are preferable to glycerides, or if the latter are used, they should constitute not over 20% of the total fatty acids.
(3) More translucent calcium base lubricating greases can be made by employing fatty acids rather than fats.
(4) The length of fiber in sodium base lubricating greases can be varied by a change in titer to the fatty ingredients. Thus a very long fibre results if vegetable oils or fats containing a large proportion of unsaturated fatty acids are employed.
(5) Conversely, short fiber sodium base lubricating greases result from the use of predominertately saturated fatty acids such as hydrogenated tallow.
(6) Long chain fatty acids from soap with the greatest solubility. For this reason, if a sodium base lubricating grease of a smooth nature is desired, hydrogenated fish oil fatty acids should be used.
The following are the chief fats fatty acids used in this industry:
Fatty Acids: Lauric, Myristic, Myristoleic, Palmitic, Stearic, Oleic, Linoleic, Linolenic, Arachidic, Gadoleic, Arachidonic, Behenic, Clupanodonic.
Fats: Lard, Beef tallow, Hydrogenated grease, Herring oil, Menhden oil, Sardine Oil, Hydrogenated Herring, Hydrogenated Sardine.
Oils: Com, Castor, Coconut, Cotton seed, Linseed, Olive, Palm, Palm Kernal, Peanut, Repeseed, Soyabean, Tung, Hydrogenated, Castor. Fatty acids are preferable to fats, because they have the following advantages:
- Better control of fat composition.
- Greater ease of saponification.
- Completeness of saponification.
- Greater yield of anhydrous soap, 4.5% increase in soda products from 100 pounds of fatty acids over that from the same weight of fat.
- Greater uniformity of finished product.
Test for Good Fatty Acid
To 25 gms. Of liquid fatty acids in a clean beaker add 25 ml. Of alcohol, free, from indicator warming again if necessary to have the mixture liquid. To the above add, while stirring, 15 ml. Of a 50% solution of KOH in distilled water. A good fatty acid will show very slight colour change. A bad acid will be a dark raddish brown.
Preformed Soaps
Nearly all manufacturers of lubricating greases Employ preformed soaps to some extent. Since such soaps have a variety of other uses they are manufactured by a number of suppliers and stocked by most chemists. Soaps of almost any metal are available, but the manufacturer of lubricating grease is normally interested only in aluminium, calcium, barium, lithium sodium, lead and zinc soaps.
Advantages and the Use of Preformed Soaps
Compounding of lubricating greases is simplified by employing preformed soaps rather than manufacturing soaps from raw materials. Fewer ingredients need be stocked and weighed or measured. Since the saponification step is eliminated, the time required for the preparation of a batch of lubricating grease should be less when preformed soaps are employed than when fat and alkali are used. Moreover, elimination of the saponification step and the time consumed result in a lower heat demand.
Lubricating Oil
Lubricating oil constitutes the largest proportion of the total raw material required for the compounding of lubricating greases. Selection of the proper lubricating oil is important both from the standpoint of lubrication and of the structure and stability of the finished product.
Gravity of Lubricating Oils
The gravity of lubricating oil is a numerical value with an index of the weight of a measured volume of the product. Readings are made on a hydrometer. Tables are available for the conversion of such readings to specific gravity and weight per gallon.
The gravity of lubricating oils is interest to the manufacturer of lubricating greases because of its influence upon costs. Oils are purchased by the gallon and lubricating greases are sold by the pound. Therefore, if instead of purchasing an oil of 28 gravity, weighing 7.387 pounds per gallon; an oil of 20 gravity, weighing 7.778 pounds per gallon, is purchased, over 5% more weight would be secured for the same volume.
Pour Point of Lubricating Oil
Since the pour point of an oil indicates the temperature below which it is not possible to pour the fluid (Liquid) from a container, it is also indicative to a degree, of the temperature at which lubricating greases, made from such oil, can be forced through pipes or fittings. However, too much dependence cannot be placed upon the correlation of pour point and apparent viscosity at low temperatures.
Dyes for Colour
Most lubricating greases depend upon the natural colour of the mineral oils to provide colour to the finished product. But to make them attractive certain colouring is necessary and dyes are frequently employed for giving vivid colours, which otherwise (naturally) not possible.
Almost all the dyes used for colouring lubricating greases are oil soluble materials. Some colours are sold especially to provide fluorescent green or reds for mineral oils and such colours are also effective in lubricating greases. In selecting a dye, its stability towards light and heat as well as toward free alkali or fatty acids should be checked.
The predominating colours employed in lubricating geases are green, orange, red, and yellow. Less than a pound of dye should be required for 10,000 pounds of finished lubricant. It is well to dissolve the dye in warm oil before adding to the batch of lubricant.
Perfume
A small percentage of lubricating greases have perfumes added particularly in the case where an oil is of low grade and smells badly. Perfumes should be added when the product is as cool as possible. Perhaps less than a quarter of a pound of perfume base is sufficient for over 10,000 pounds of finished lubricant.
Fillers
A great variety of solids of various types are added to lubricating greases to give bulk, provide resistance to removal of the lubricants, and, according to some workers, to increase the lubricating value.
They are: Graphite, Asbestos, Mica, Talc, Vermiculite, Metal Oxides, Powdered metals, Metal Sulphides and similar Solids, Carbon Black, etc.
Synthetic Lubricants
Include Silicones, Olefin Polymers, Polyakylene Glycols and Derivatives, Esters, Silicone Fluids, Chlorinated Compounds Halogeno-hydrocarbons, etc.
Silicones are organosilicon oxide polymers. Silicones are available as liquids, semi-liquids, and solids. One of their-outstanding properties is that their viscosity is much less ssensitive to temperature than that of mineral oils. For example, even a relatively insensitive mineral oil, when lowered in temperature from 120ºC to 25ºC., becomes about a thousand times more viscous, whereas the corresponding figure for a silicone fluid is only about seventeen times. Other properties are : good oxidation stability, very low pour point, and low volatility.[]
Fluorosilicone: By careful control of the polymerization conditions and the use of suitable end-blocking agents e.g. hexamethyl disiloxane, various degress of polymerization can be gained to yield any desired viscosity of fluorosilicone oil.
Fluorosilicones fluids are used mainly for defoaming of solvent based wash solutions or processes and lubrication.
The chemical stability and heat stability of fluorosilicone oils, coupled with their good lubricity, accounts for their use as lubricating oils in chemical compressors and in vacuum pumps exposed to chemical fumes. Fluorosilicone fluids are also formulated with various thickeners to make grease-like sealing compounds and lubricating greases.
Synthetic esters are now produced in considerable variety. Esters, which are compounds of acids and alcohols, occur widely in nature, for example in fatty oils, but other types of ester, with special properties are now synthesized. One type (of which di-2-etlhyl hexyl sebacate is an example) is characterized by good viscosity-temperature characteristics, together with better boundary properties and lower volatility than mineral oils of similar viscosity. Its chief advantage is the very low flammability.
Polyalkylene glycols are a group of non-hydrocarbon polymers produced in a wide range of viscosities, and in water-soluble and water-in-soluble qualities. They possess good temperature-viscosity characteristics and find application as hydraulic oils and in special greases.
Halogeno-hydrocarbons are hydrocarbons in which hydrogen atoms have been partly or wholly substituted by fluorine or chlorine atoms, or in some cases by a mixture of both. The outstanding merit of the liquid varieties is their high chemical and thermal stability-their demerits are poor viscosity-temperature characteristics and high volatility.
Synthetic lubricants also includes solids materials consisting of carbon and halogan, of which Teflon is the best known. Teflon and Fluon are commercial names for Polytetra fluoroethylene (PTEE), which gives remarkably low coefficients of friction as a metal lubricant, and is effective up to the usefully high temperature of about 320ºC. This is particularly valuable on a small scale when particularly low friction is desired, as for example instrument work. One method of use is as a surface coating in conjunction with a liquid, which may be oil or water.
Equipments for Lubricants Manufacture
Introduction
There are two chief processing methods: (1) Batch method, (2) Continuous method. These both methods have a number of steps in common. Therefore, the equipments required will be the same in many cases. Steps in processing are as follows, and the equipments are required to fulfill these processing needs:
(1) Material storage and handling.
(2) Material measuring, either by weighing, or gauging.
(3) Saponification, which involves: (a) Mixing, (b) Heating. This step is eliminated if preformed soaps or bodying agents other than soaps are employed.
(4) Dispersion of bodying agent in the lubricating fluid. If this bodying agent is the soap formed in step 3, the dispersion may take place as the soap is formed. Normally, the dispersion will require additional heat, agitation, and perhaps shear.
(5) Dehydration, which may take place during saponification or at any other point in the processing. In some processes the final removal of water occurs by vacuum treatment of the finished or semi-finished product.
(6) Cooling of the soap dispersions. This may take place during agitation or in a static state. In the case of lubricants in which the bodying agent is dispersed by shear only, this step is not required.
(7) Milling.
(8) Removal of entrained air or of volatile materials. Only a portion of finished lubricant greases are subjected to such a step. Some dehydration may take place during the step.
(9) Handling finished product, which may include packaging and storage: No mention has been made of handling in connection with the equipment by which the various steps are carried on.
Most of this handling will be by means or pipelines and pumps, therefore, certain notices may be kept in mind:
(1) Pipelines should preferably be welded and equipped with long redius bends.
(2) Apparatus in which heating is carried out in which rot material is handled should be well insulated.
(3) Individual drives for each piece of equipment should be provided.
(4) Flow of material into finished product and in a package should be downward and toward shipping or storage.
Equipments
(i) Material Storage and handling
In most plants manufacturing lubricants, oil account for probably 85 to 90% of the total tonnage of raw materials. Fats and Fatty acids are next in volume. Raw materials, other than those above are seldom received or stored in bulk; but rather in the original containers. Raw material storage, therefore, involves both tank storage and warehouse storage. The space for tanks is devoted to fluid lubricants and to some type of fatty products, while the warehouse stock consists of a variety of materials in bags, cartons, and barrels.
(ii) Oil Storage and Handling
Oil handling in a lubricating grease plant is little different from that in a refinery, except that lesser amounts are handled. Most plants prefer vertical storage only, since horizontal tanks require more space for an equal gallonage than vertical tanks. No set correlation between the capacity of a plant and the amount of oil storage is possible. This will depend upon the location of plant and the variety of the products manufactured. Thus a lubricant plants adjacent to or located on a refinery property will probably require less oil storage.
In some cases oils must be blended before use. When this is done in storage tanks, the mixing is generally done by the use of dry air. Proportioning pumps can also be employed for preblending ad delivering to storage. In humid climates condensation may occur inside storage tanks and as a prevantative, some tanks use calcium chloride drying units on breathers of oil storage tanks. Other plants simply provide a ½ to 1 inch drain, flush with the bottom of the tank, so that water which collects can be drawn off.
(iii) Fat Storage and Handling
Fats, unless of high titer, are handled in either drums or tanks, both such materials are of steel, as a rule.
It should also be kept in mind that fat held in storage and subjected to heat and moisture will tend to hydrolyze and if agitated, to oxidize or polymerize to some extent.
Pumps for handling melted fats may be either reciprocating or centrifugal types. Pipelines, valves, and pumps used to handle fatty acids, should be of stainless steel. Where a positive displacement pumps is required for such service, bronze end pumps are satisfactory. Duriron pumps will also serve, but of course consideration most be given to the fact the such metal is quite brittle.
(iv) Storage and Handling of Caustic Soda
Solution of solid caustic soda may be accomplished in an ordinary steel tank by placing the solid cakes on grids which will hold them off the bottom. The drum metal can either be stripped from the solid cake of caustic or number of slits can be made in the drum with an axe before placing in the tank. A centrifugal pump can be connected to the bottom of the tank, and after water has been added, circulation will aid solution.
Flake caustic soda may also be dissolved by suspending it in the upper part of a tank of water. Since the rate of solution of flake is much more rapid than that of solid caustic, a short period of mechanical agitation will suffice for complete solution. Large single additions of flake caustic may heat the water above the boiling point, and caustic solution may be thrown out of the tank by the sudden evolution of steam.
While handling caustic soda or its solutions workmen should be protected by gloves, goggles, and preferably cotton clothing. In case of accidental contact of caustic with any part of the body, the afflicted surface should be flushed with copious quantities of water.
50% liquid caustic soda may be unloaded by pumping, by gravity flow, or by air pressure, but pumping is the most commonly used method. Since the solidification point of this solution is 54% F it should be handled and stored at temperature above this. Ordinarily steel will serve for storage and handling of this grade of caustic soda. If the temperature of the caustic solution does not exceed 140ºF, welded tanks will be satisfactory. Above this temperature caustic embrittlement may set in at the welds. For higher temperature it is usually more economical to construct riveted storage tanks.
Since 74% liquid caustic soda freezes at 144ºF, special provision must be made for handling this grade. In view of this high solidification temperature, the general practice is to dilute the liquor to 50% strength or less before storing. The matter of dilution is not as simple as might appear, since the heat of dilution may raise the temperature of the solution to the point where caustic embrittlement of the steel storage tank occurs. With nickel-clad equipment such embrittlement does not occur. It is best to cool the diluted caustic solution to 150ºF or below before placing it in storage. An alternative is to have a stock of diluted caustic soda from a previous shipment which has cooled naturally, into which the freshly diluted liquid can be mixed. Addition of a calculated amount of water to a tank car of 74% caustic soda may be made by adjusting a steam through a meter or by proportioning equipment. After unloading either grade of liquid caustic the pipelines and pump should either be blown free or washed with dilute caustic.
For handling caustic soda solutions, standard black iron pipe is satisfactory preferably equipped with flanged joints, since coupling tends to leak in service. Asbestos gaskets will resist hot caustic solution. If the lines are to be exposed to temperatures below the freezing point of the solution they should be traced with a steam line inside a common insulation. All iron stopcocks are preferable to valves for such service and if high temperature are to be encountered, nickel-iron cocks are best. Brass or bronze valves or fittings should not be used for caustic soda solutions. If valves are desired, they should be of all-iron or of iron trimmed with nomel, nickel, or an alloy of this metal. All iron centrifugal pumps with extra deep stuffing glands and graphite-asbestos packings are satisfactory for handling caustic solutions. For high temperatures, nickel or monel shafts will give better service than iron.
Handling Packaged Raw Material
Packaged raw material received by a plant manufacturer of lubricant and greases will include bags, barrels, or cartons in loads. How such packages are stored and handled will of course depend upon the storage facilities of the plant in question. A better plant is to provide a weighing hopper, carried by suspended scales, into which the bag and carton material for a single charged are dumped.
Fillers generally go into the finishing kettles and may be handled by one of the above methods. Since addition of fillers will cause considerable dust, some plants provide a closed room where an oil slurry of materials such as graphite are prepared preliminary to addition to kettles. One supplier of graphite now offers graphites which have been coated with oil so that the dust problem is entirely eliminated.
Preformed soaps, such as aluminium stearate, are also likely to cause considerable dust when handled into vessles. Dust is a source of contamination in other products and increases the work of housekeeping but soap dust is also a fire or explosive hazard. Every effort should therefore be made to reduce such dust. By having all open kettles covered and kept under a slight suction, dusting can be reduced materially.
Equipment for Saponification
The most satisfactory equipment for saponification is that which will permit complete reaction of the ingredients in as short a time as possible. The main factors which influence the time of this reaction are probably temperature, concentration, presence of catalysts, and intimate contact of reacting ingredients. Equipment for saponification therefore should be selected which will provide the best heat transfer possible and which will provide intimate contact of the ingredients.
Equipment for Batch Saponification at Atmospheric Pressure
Almost any kettle with an agitator and some heat will do some sort of job of saponification. The older kettles, some of which are still in use, were of riveted construction with agitators consisting of straight bars 21/2" or 3" wide, bolted to a shaft at about 18-inch intervals. These agitators were driven through bevel gears, by belts from a line shaft, tight and lose pulleys being provided. In some cases flat bottom vessles used, but modern kettles have either cone or dished bottoms. Fire-heated vessels are single walled.
The source of heat used to promote saponification varies. If direct fire is used, the fuel may be coke, fuel or gas. Steam is the most common source of heat, being used at the pressure available, which is normally 100 to 125 psi. An increasing number of saponification vessles are heated by circulation of hot oil through the jacket. Some installations have been made employing Dowthern as a heating medium. Where temperatures much above 300ºF are desired, something other team should be employed for heating.
Since practically all open type saponification vessles are vertical, a shaft will extend vertically from the driving gear with probably a step bearing in the bottom of the vessel and occasionally an intermediate bearing between this bottom bearing and the one at the top. The most simple agitators design consists of flat, bars bolted or welded to the shaft at intervals of 15 to 24 inches. Such "paddles" can be made of 3" by 1/3" steel bars twisted so that they will give a down thrust. Since better mixing is accomplished by double motion agitators, many installations stimulate such motion by having a set of stationary blades and another set rotating. Simpler still, breaker bars can be welded to the shell at intervals intermediate to the paddles. Of course such bars will be off-centre so that they miss the shaft. Actual double motion agitators complicate the design but are frequently worth the added expense.
Scrapers to clean the inner shell of saponification vessel not only insure better heat transfer and thus a shorter reaction time, but also improve mixing. When fat, mineral oil, and alkali are first charged to a kettle and warmed, the mass is quite fluid, and as long as agitation takes place, the fluid next to the vessel wall will be displaced by turbulence and reasonable heat transfer will result. However, as soon as part of the fat or fatty acids is converted to soap, the mass becomes more viscous, and heat transfer will be retarded if the portion next to the kettle wall is not removed mechanically.
If the same vessel is also used to finish lubricating grease, scrapers have an additional advantage. Without such equipment heavy material would stick to the sides of the kettle and in later stages of the process might become loosened and then break into particles which would remain as lumps and never disperse. Some scrapers consist of a flat bar carried by the ends of the paddles. In some cases the bar is changed to an angle which is so mounted that it is on a swivel and actuated by a spring to hold it against the kettle wall.
A saponification vessel can be used with a minimum of instrumentation, but a certain amount is desirable. Of course a gauge to indicate the pressure on the jacket should be installed. In addition a regulating valve is often provided on the steam inlet so that processing can be carried on at different pressures at various stages of manufacture. Most kettles used for saponification are provided with connections to a recording thermometer. The recorder may be used for one or several kettles, and an individual kettle may have thermocouples must be so placed that they will not interfere with the operation of the agitators or the scrapers and yet they should not become coated with lubricating grease or soap which would act as an insulator and thus prevent a true reading. If the bulb is inserted through the jacket of a vessel, clearance or air spacing should be provided so that the jacket temperature does not influence the reading. In some instances paddle blade near the bottom of the vessel will be slotted so that a bulb can be inserted in the space provided by the slot. In kettles which have a beaker bar attached to the inside of the shell, the bulb can be fastened to this bar so that a rigid location is provided. In still other cases the thermocouple is inserted through a bottom opening near to shaft. When a pump and circulating line are provided for a kettle, it is advantageous to have a thermocouple in such as line.
A ammeter for the operator to watch is desirable in connection with processing lubricating greases which pass through a very heavy stage. Ammeter readings can then be made of a part of the compounding instructions so that the operator will know when to shift to a different speed of agitation or to add oil.
Equipment for Dispersion of Thickening Agents
Agents employed for thickening lubricating fluids to produce lubricating grease structure can be divided into two classes, those which undergo phase changes and which require heat or a chemical method of dispersion and those which require heat or a chemical method of dispersion and those which do not undergo phase changes with heat and which can be dispersed in lubricating fluids mechanically. The first class consists primarily or soaps and it remains to be demonstrated that they can successfully be mechanically dispersed in liquids to form lubrication greases. Perhaps if applied energy were sufficiently concentrated, so as to be converted to heat momentarily, soaps could be dispersed in lubricating fluids by such means.
Milling Equipment
Milling or shearing equipment is often used as an aid in soap dispersion. The simplest arrangement is to provide screens in the circulating line. One plant has such screens progressively smaller, starting with 10 mesh and finishing with 60 mesh. While this aids in soap dispersion, the screens must be screens is rather laborious procedure, modern practice is to use various types of mills for this purpose.
Manufacture of Lubricating Oils
As shown in Fig. 2 the conventional steps in lubricating oil manufacture, are pretreatment of the crude oil charge, as required, followed by distillation of the crude in two steps, deresining or deasphalting, dewaxing, solvent extraction, finishing and blending, including mixing various additives with the final lubricating oil. The recovery and refining of asphalts, resins and waxes are important to the overall economy of lubricating oil manufacture.
The chemical composition of lubricating oils is exceedingly complex the number of carbon atoms varying from approx. 20 to 70. Well refined lubricating oils contain very little olefenic un aturation but do contain some aromatic un aturation. The compounds contained in lubricating oils include paraffins, cyclo paraffins the aromatics.
Waxes generally are paraffin compounds, both straight and branched and also contain 3-25% cycloparaffins, depending upon the source of crude oil.
Petroleum resins are hydrocarbons of very high molecular weight containing small amounts of oxygen, sulphur and nitrogen compounds, which can be found in bridge compounds or in ring compounds. The hydrocarbons include the paraffin, cycloparaffin and aromatic types in varying amounts and configurations.
Asphalt is physically made up of brown solids called asphalters, i.e. asphaltic resins of high molecular weight viscous compounds with a degree of unsaturation and oils. The asphalters are believed to contain condensed aromatic ring compounds with oxygen, sulphur and nitrogen in ring compounds with oxygen, sulphur and nitrogen in ring compounds or in bridge positions.
Where (1) Atmospheric tower
(2) Vacuum tower
(3) Deresining
Pretreatment of crude: In order to remove inorganic salts from the crude oil charge to the crude distillation unit, chemical or electrostatic desalting is used. Salts in the crude oil cause fouling of heat exchangers, corrosion in the distillation units and increased coking of the furnances.
Distillation: Crude oil after pretreatment, is charged to the atmospheric tower, where the crude oil is separated into light products. The bottoms of the atmospheric tower, to reduced crude, are charged to the vacuum tower.
The prime object in the manufacture of lubricating oil is the initial separation of the light products and the separation of wax distillate and cylinder stock without any decomposition or cracking of the lubricating fractions; thus a vacuum distillation unit is used to separate the wax distillate and cylinder stock at a lower temperature.
Deresining or Deasphalting: Asphalts, which contained in asphalter crudes can be constituted into different properties by further distillation or by air blowing. Resins occur in paraffin or low-asphaltic crudes.
Propane is used as a solvent and at different temperatures and ratios causes asphalts or resins to separate from the oil due to a difference in solubility. This process requires a tower for separation of the oil and the asphalt or resin.
Dewaxing: Wax is probably the most troublesome product in the manufacture of lubricating oil. Its presence in lubricating oils prevents free movement at lower temperatures.
Usually, methyl ethyl ketone (MEK) and an aromatic solvent, such as toluene are used for dewaxing purposes. The MEK causes the wax in the oil to crystallize, and the toluene is used to dissolve the oil. The solvent mixture, at a carefully controlled temperature, is added in measured amounts at points in the chilling to produce proper crystallization of the wax. Both the wax solution and the oil solution are distilled for removal of solvent (to be reused) and to provide solvent free wax and oil. Thus the two products are a wax-free oil and an oil-free wax.
Solvent Extraction: To upgrade or improve the quality of neutral or bright stock, solvent extraction is carried out. It can be performed before or after dewaxing, but most solvent extraction is performed after wax removal in order to prevent any interference from wax in the charge oil. Solvents such as chlorex, nitrobenzene, phenol, benzene, and sulphur dioxide are used. The improved oil (or raffinate) and solvent are taken overhead from the treating tower, and unsaturated material of extract and solvent are removed from the bottom. Solvent is removed from both the raffinate and extract in recovery equipment and reused.
Filtration: Bauxite is the common filtering medium or absorbent for the removal of asphaltic and resinous undesirables or simply for light filtration or finishing. The bauxite is placed in a vertical steel tank, and the oil is permitted to gravitate through the bauxite in the filter. A screen in the bottom head of the filter prevents the bauxite from being removed from the filter with oil.
Blending of additives: Additive blending is done after bauxite filtration, since filtering will remove the additives. Additives are used according to the severity of the operating conditions for which the lubricating oil is intended and the quality of the base lubricating oil. Naturally, a high quality lubricating oil base requires fewer additives than a lower quality base. Fully formulated lubricants contain additives to boost their properties. Wise choice of additives can increase the biodegradability of the full formation.
Reclamation of used Lubricating Oil
Lubricating oil deteriorates, and becomes contaminated with foreign materials, in service. In circulating systems, where a quantity of oil is involved, it is desirable to maintain the oil as clean as possible to provide maximum lubrication efficiency, and to keep wear and damage of lubricated parts to a minimum.
When the lubricating oil reaches the end of its life in the engine, what most probably happens is additive depletion. Because of the engine operation, these chemicals, slowly lose their effectiveness. This is the time to change the oil. This used oil can be re-refined for use. Technically speaking, re-refined oil can be used to replace some of the original base stocks. For some applications, in fact, they are better. But the usages depends heavily on the process used to manufacture the re-refined oil and so many other things like the chemical compatibility etc.
Reconditioning of a used oil may be accomplished by full flow, by pass, of batch methods or combination of these. In the full-flow system, the entire flow of oil form the main pressure line is continuously filtered. In the by-pass system, a fraction of the total of flow is continuously filtered and returned to the oil reservoir. In the bath system, as the name implies, all the oil is removed from the lubrication system and is reconditioned as a batch.
Nature of Contaminants in Used Lubricating Oil
Contaminants in a used oil may be divided into two classes:
(1) Products resulting from chemical action within the system, including effects due to fuels; and
(2) Foreign material which enter the system.
Products resulting from chemical action within the system are as follows:
(a) Carbon, and other products of partial decomposition of oil or of incomplete combustion of fuel;
(b) Oxidation products (which may be either soluble or insoluble in the oil), due to chemical action at high temperatures;
(c) Gummy product, both soluble and insoluble, resulting from polymerization (combining) of unsaturated components in the oil; and
(d) Sulphur compounds, formed by sulphur in the oil or fuel.
Foreign materials may include some of the following:
(I) Dirt and dust from the air;
(II) Metal particles resulting from wear of operating parts of the machine, or left over from machining operation during an overhaul;
(III) Foundry core-sand from castings;
(IV) Water condensed from air moisture or products of fuel combustion; and
(V) Fuel dilution.
Purification of Oils
Three basic methods of treating contaminated oils are used, both singly and in combinations:
(1) Gravity purification,
(2) Filteration, and
(3) Reclamation
Gravity Methods of Purification
Gravity methods which are based on the relative weights of clean oil and the contaminants to be separated out, include the use of settling tanks and of centrifuges.
Settling Tank
In a settling tank method, a batch of dirty oil is allowed to stand for ten or more days in a tank, and insoluble matter (including water), which is heavier than oil, settles to the bottom under the influence of gravity. The tank should be free from vibration and the oil is undisturbed. Small particles and dispersed oxidation products are not removed in this process. Best result are obtained when the oil is heated to the range of 120ºF to 160ºF reduce the oil viscosity, thus facilitating settling.
Drawbacks to the settling tank method of purification are : the time element, the space requirements for tanks, extra oil charge for the engine during settling process, and the fact that impurities are only removed periodically.
This method is adaptable to straight mineral oils, but is generally unsatisfactory with heavy duty additive-type oils.
Centrifuge
A centrifuge works on the principle of separation by centrifugal force. This force, supplied by the high-speed rotation of the bowl containing the contaminated oil, is several thousand times the force of gravity. As a result, the centrifuge is much faster and more efficient than the settling tank. Substances having a higher density than the oil, such as water ad heavy particles, are thrown out against the walls of the centrifuge with greater force than the oil. As a result, a stable oil water leave by separate outlets, the oil discharge tube being nearer the center. The sediment is removed from the walls by cleaning at regular intervals. For some types of centrifuge; special arrangements are provided to prevent mixture of purified oil with incoming contaminated oil, in the vicinity of the oil water boundary.
"Through-put" capacity is the maximum number of gallons of contaminated oil which can be sent through the centrifuge each hour, with no regard for the degree of purification. The effective capacity of the centrifuge, which is much more meaningful, is the rate at which contaminated oil may be processed to give the desired degree of purification. This rate depends upon prevailing conditions and what is deemed to be a desirable degree of purification in each case.
In so-called wet centrifuging, water is intentionally added to the entering stream of contaminated oil. This added water may have a washing effect on the oil and a tendency to carry away more of the lighter solid, as well as some acids which are more soluble in water than in oil.
A centrifuge is especially well adapted to a by-pass system, in which part of the oil being circulated is by-passed through the centrifuge each cycle. Centrifuge is also suitable for the batch system of purification.
Filteration
Filters may be applied on full-flow, by pass or batch systems where there is sufficient pressure to overcome the internal resistance of the filter. There are three principal types of filters:
(1) Mechanical, (2) Absorption, (3) Adsorption. Where a filter is installed in the lubrication system of machinery, such as an engine, a relief valve is provided to cut off flow to the filter at a predetermined pressure. This is for the protection of the engine against loss of oil supply. Filters may be integral units composed of a filter element in a sealed container, in which the entire unit must be replaced. When blocked with filtered material, or they may be replaceable element type, wherein the container can be opened for the replacement of the used element.
Regenerating Process of Used Lubricating Oils
Lubricating oils are discarded after a specific period of use, to give engines longer life and better performance. These are either drained into rivers or burnt in air, causing pollution of air and water. Thus the re-refining of used lubricating oil is another way of tackling the disposal problem through reutilization. The 80-90% of used lubricating oils remain unchanged, these can be economically regenerated.
India depends mostly on the foreign market to meet her requirements of lubricants and greases. The deficit in indigenous availability of lube stock is fulfilled through import. As such, the import of base stock and lubricant technology is making the important product "Lubricant" costilier, with the passing of each day. The economic factor alone is the most critical factor for industry to recognize the conservation of lubricant as an important area.
Regeneration of lubricating oil, a practice in many oil rich countries, should be popularized as this will stop drainage of foreign exchange and conserve our existing stock.
Contaminants Present in Used Lubricating Oil
Contaminants present in used lubricating oils can be classified as :
(1) Volatile, (2) Oils soluble compounds, (3) Oil insoluble compounds. Unburnt fuel and water constitute volatile component while in use in the engines, lubricating oils from primary oxidation products which polymerize and finally converted to asphalts by pyrolysis. These constitute oil soluble compounds. The third category of compounds includes dust, metallic particles, soot, degraded additives; metal soaps, etc.
Principles of Used Lubricating Oil Regeneration
Re-refining and reclamation are the two procedures used in regeneration. Re-refining may involve the following steps:
(1) Settling and Dehydration.
(2) Acid treatment.
(3) Clay treatment of acid treated oil.
(4) Removal of clay by filteration.
(5) Distillation or fractionation.
(6) Blending with bright stock and incorporation of additives.
Re-refined oil compares well with the virgin oil. Reclamation, on the other hand, involves steps like settling, dehydration, removal of asphalts and other solid bodies. It does not remove diluents and certain oil degraded products.
Existing Process for Regeneration of Used Lubricating Oils
Processes employed in United States:
1. In the process followed at Mohawk Refinery Co. Newark N.J. a 10,000 gall. Dish bottomed tank is charged with feed stock which is heated to 82ºC (dispersant filled oils require higher temp.) with 98% sulphuric acid and settled, leaving mainly saturated naphthenic and paraffinic molecules. After acid and settling treatment 82-84% of the feed remains. This is followed by heating to 316ºC in the clay contact step. In a flash chamber, clay and residue drop down while overheads are pulled down to reflux with a product steam joining the second tower. Here the lighter ends are gathered for process fueling, and the bottoms are recycled. Two lubricants products result a 350-SSU at 37.8ºC stream and 110/120 SSN at 37.8ºC light distillate.
2. S and R oil co. Houston Tex. re-refiner process (i) 300,000 gal./mo. Of crank case drainings. First the waste oil runs through a pipe still for dehydration. Next, acid treatment in air blown agitator is followed by clay containing at 204ºC. Then filteration takes place using sweetland filters, rotary vacuum filters or even plate and frame presses. The final step is blotter pressing to remove any remaining clay.
3. Diamond Head Oil Refining Co. Keramey N.J. does not use acid in its re-refining processes but employs more severe clay treatment, coupled with higher temperatures.
4. A new re-refining method for lubricating oils is said to offer favourable economies and eliminate refiner's own water pollutants acid sludge and filter cake. The process has been developed at Villanova University.
The new process has five basic steps:
1. After the moisture content is reduced to less than 0.1 percent by heating to 138ºC the acidic contaminants are neutralized by sodium hydroxide or other undisclosed agents.
2. Dilution with light naphtha as a coagulant followed by solids removal.
3. Atmospheric distillation to recover the light naphtha for recycle.
4. Vacuum fractionation to recover product and splilt out No. 1 heating oil.
5. Clay treatment. The oil is heated with clay to 338ºC for about an hour under a nitrogen blanket and with mechanical agitation. The mix is then colled to 149ºC and the clay is removed via a rotary vacuum filter.
By products of the process are a carbonaceous material similar to carbon black and a potential rubber extender oil. Out of total lubricating market in U.S. reclaimed oil accounts for about 6%.
In the field or re-refining of used lubricating oils, acids treatment is being replaced by light hydrocarbon treatment (propane and naphtha) resulting in better yields and obviating the problem of the disposal of acid sludge.
Research is being carried out in different countries of the world to evolve further cheaper methods of used oil regeneration.
Characterstics of a Used and Regenerated Heavy Duty Motor Oil.
| Properties | Used Oil | Regenerated Oil |
| Appearance | Dark | 0.890 |
| Density D420 | 0.892 | 0.890 |
| Flash point, open cup ºC | 260 | 236 |
| Kinematic viscosity, cs at 37.8ºC | 165.4 | 162.4 |
| 98.8ºC | 17.66 | 17.3 |
| Viscosity Index | ---- | H6.5 |
| Acidity, mg KOH/gm. | 3.0 | ---- |
| Conradson carbon | 0.805 | 0.26 |
| Residue % wt. | | |
| Ash sulphated, % wt. | 0.36 | ---- |
A flow diagram for a process on regeneration of used lubricating oil is given in figure : below 7.1 which gives complete idea.
Plants are said to be running on this process.
Process developed at the Regional Research Laboratories, Jorhat Assam (Indian Patent No. 127751) consists of the following steps.
1. Clay Treatment
Used lubricating oil together with activated fuller's earth and water is heated to suitable temperature in a closed vessel with constant stirring.
2. Filteration
Oil from (step 1) is cooled and then passed through a filter press.
3. Distillation
Filtered oil (step 2) is then subjected to vacuum distillation. Some portion of the distillate collected is discarded as heating oil. Distillation is continued upto a still temperature ensuring more or less complete recovery of the oil. Distillation residue comprises most of the spent additive and is discarded.
4. Blending
Distilled lubricating oil (step 3) is blended with additives to improve viscosity index and other properties.
Novelty of the Process
Novelty of the process lies in the elimination of sulphuric acid treatment a severe clay treatment step thereby avoiding acid sludge handling and disposal problem and in turn making the whole process more enonomical.
Lubricant Recycling
Considerable effort is underway to improve and expand recycling of lubricating oils. Although typical processes result in 80-90% yield, questions remains regarding the initial collection and the separation of the used oil from water and other contaminants. Subsequent treatment varies from simple cleaning to essentially the complete refining process used with virgin oil. The following are typical steps involved in reprocessing used petroleum lubricating oils are indicated schematically in the figure.
Reprocessing
It involves simple separation of contaminants by gravity setting of water and dirt, centrifuging, filtering and membrane techniques. Chemical emulsion brakers are first added and consist of sulphuric acid and then aluminium sulphate as a coagulant. Polymers sometimes are used to speed up the process. The separated oil is then decanted, skimmed or centrifuged and commonly is burned. 1-5% reprocessed waste oil generally may be added to fuel.
Reclamation
It involves flash distillation in an evaporator at about 100-200ºC in partial vacuum to remove water and low boiling contaminants e.g. gasoline and solvents.
References
1. Chemical Engineering, Vol. 75, Sept. 9, 1968.
2. Industry and Commerce, May 1, 1970, Vol. VII, Nov. 9.
3. Joshi T.C. and Goes P.K. Re-refining of Used Motor Oils, Seminar on Import Substitution in Petroleum Products, process and Other Know-how, Indian Institute of Petroleum, Dehradun, May 10, 1969.
4. Proceedings of a Seminar on Modern Trends in the Production and Utilization of Lubricants. Chemical Age of India, Jan. 1971.
5.Lubricants Production and Utilization in India in the Seventies, P. K. Goel and M.G. Krishna, Indian Institute of Petroleum, Dehradun, Chemical Age of India, Jan. 1971.
Greases
In the modern industrial year, greases have been increasingly employed to cope with a variety of difficult lubrication problems, particularly those where the liquid lubricant is not feasible. Over the last several decades, grease making technology throughout the world; has undergone rapid change to meet the growing demands of the sophisticated industrial rapid change to meet the growing demands of the sophisticated industrial environment. With automation and mechanization of industry, modern greases, like all other lubricants, are designed to last longer, work better under extremes of envirnment and generally expected to provide adequate protection against rust, water, humidity and dust. Industrial development and advances in the field of greases have been geared to satisfy all these diverse expectations.
Primary components of grease are mineral oils and soaps. The mineral oils consist of varying proportions of paraffining, napththenic and aromatic hydrocarbons. Soaps used in grease may be derived from animal or vegetable oils or fatty acids, wool grease, rosin or petroleum acids. Apart from this, variety of other compounds are added to lubricating greases to improve specific properties. Such components are - corrosion and rust inhibitors, film strength agents, antioxidants, passivators, colour stabilizers. V.I. improvers wear prevention agents. A grease thus produced is properly thickened in order that it remains in contact with the moving surfaces and does not leak out under gravity or by centrifugal action, or be squeezed out under pressure. Grease acts as real against dirt, dripping and spattering is eliminated, minimizes starting friction on journal bearing.
Greases are essentially solid or semi-solid lubricants consisting of a gelling or thickening agent in a liquid lubricant.
However, in general, greases are the substances whose basic components are soaps and mineral oils. Mineral oils comprise varying proportions of paraffining, naphthenic and aromatic hydrocarbons, whereas soaps used in greases may be derived from animal or vegetable oils or fatty acids, wool grease, rosin, etc. Besides, a number of other components are added to lubricating greases so as to improve specific properties, such components are antioxidants, corrosion and rust inhibitors, film strength agents, passivators colour stabilizers, wear prevention agents, etc. The grease thus produced is properly thickened in order that it remains in contact with the moving surfaces and does not leak out under gravity or by centrifugal action or be squeezed out under pressure.
However, one of the basic characteristics of most solid lubricants is that they reduce friction and remain in place longer than oils.
Solid Lubricants
Most solid lubricants reduce friction because their molecules from very thin plates or sheets that slide over one another very easily.
The main advantage of solid lubricants is that they remain in place longer than oils or greases. Parts that are not easily reached are often lubricated with solid lubricants so that they will not have to be lubricated as often. The most important solid lubricant is graphite, a form of the element carbon. Graphite is the black material used to make the "lead" in lead pencils.
Semi-Solid Lubricants
A semi-solid lubricant, or grease, consists of a thickening agent in a mineral oil or synthetic liquid base. Most industrial greases have mineral oil base. The most common thickening agents are metallic soaps made with aluminium, calcium, sodium, barium, or lithium. Animals and vegetable fats, saponified fats, gels, resins, waxes, fatty acids, and naphthenic acids can also be used as thickening agents. The metal soap-based greases have good water resistance and a high melting point. Greases are used as chassis and wheel-bearing lubricants. In many cases, oils are preferred to greases because they are better coolants and are easier to handle and apply. However, greases are preferred for applications where it is essential that the lubricant does not run out or drip and for higher temperature operations.
Greases for some special applications have a synthetic-liquid base. Fluorocarbon liquid bases greases offer good resistance to fire and oxidation and are used where acids, hydrogen peroxide, and other corrosive agents may be present. Silicone liquid-based greases are used at high temperatures and for show-moving machinery.
Solid Lubricants
Solid lubricants are used when the operating conditions of pressure and temperature are too severe to be met by liquids.
There are many forms of solid lubricants. Among them are powders, which are used either alone or with binders. They are found as dispersions in non-volatile carriers as soaps, fats or waxes, and as soft metal films.
The most common powdered lubricants are inorganic materials, such as graphite, molybdenum disulfide, tungsten disulfide, boron nitride, and zinc oxide. They are able to function continuously at temperatures up tp 650ºC, and are used as lubricants in such metal working operations as wire drawing, extrusion, forging, and machining. These solids are often used as additives to mineral oils, synthetic liquid lubricants, and greases, where they increase the load carrying capacity of the material. Powdered solid lubricants and soft metals are used as additives to other solids and metals to improve frictional properties. For example, graphite and graphite metal mixtures are fabricated into bearings and brushes used in motors and generators.
Gaseous Lubricants
Gases are used as lubricants where their circulation ability, high and low temperature properties, and resistance to reaction cannot be duplicated. They are used in ultracentrifuges, nuclear reactors, gyroscopes, gas turbines, and jet engines. The principal gas lubricant is air, but halogenated hydrocarbons, sulphur hexafluoride, and nitrogen are also sometimes used.
Types of Greases
The metallic radical of the soap largely determines the characteristics of the grease, the fatty radical having a secondary effect. Greases are, therefore, classified in terms of the metal they contain. Normally a great proportion, nearly about 90 per cent of greases contain lithium, calcium or sodium soaps. "Other soaps" (such as potassium, barium or strontium) are of minor importance.
Calcium Soap Greasese
The conventional type of calcium soap grease has smooth buttery texture and are water resistant, with drop points acound 90-100ºC. They are water stabilized, i.e. the water is present in the soap crystals as water of crystallization. The optimum amount of water varies considerably with the type of formulation, fatty material, and mineral oil used, but is usually within the range of 0.4-1.0 per cent wt. At high temperatures, the water is gradually lost and the soap structure is weakened. Consequently, calcium soap greases are restricted to use at fairly low maximum temperatures (about 50-60ºC). Such greases turn fluid after exposure to high temperatures and many separate into the oil and soap phases. Only those which contain other stabilizers besides water (e.g. wool grease or fatty acid) will regain their structure on cooling.
There is also a type of calcium soap grease made with hydroxyl-fatty acids which is anhydrous and does not depend on water for stabilization. Such greases have drop points around 145ºC and do not suffer from the limitations of water stabilized greases.
Sodium Soap Greases
These are usually more or less fibrous in texture depending mainly on the nature of the fatty material, high unsaturation yielding very fibrous greases. They have drop points usually not less than 150ºC and sometimes as high as 200ºC and are useful for relatively high temperature service. Owing to the solubility of the soaps in water, they are not water resistant.
Lithium Soap Greases
These greases first appeared during World War II and were made from lithium stearate pre-formed soap. Now-a days, lithium hydroxystearate greases made by saponification in situ from hydrogenated castor oil predominate. Depending on the composition lithium greases are smooth or slightly grainy in appearance. They have the highest droppoints (about 190ºC) of the conventional greases and the highest service temperatures. They are water resistant, mechanically stable and can be made with a greater variety of types of oil than most other greases. Their versatility and wide operational scope (especially in high speed service) had led to their use as multi-purpose greases to the displacement or earlier types of more specialized greases.
Aluminium Soap Greases
They have an attractive translucent, smooth and polished appearance. The drop points are low (about 90ºC), the mechanical stability is poor and the greases tend to become rubbery at high temperature. They are almost invariably made from high viscosity oils and often incorporate polymers. Such products are water resistant, stringy and adhesive and find application as chassis and gear lubricants. They are not recommended for rolling bearings.
Mixed Soap Grases
A variety of mixtures are used, the commonest being sodium/calcium, and the greases are generally manufactured by saponifying the fatty material with mixed alkalies derived from different metals. One of the soaps usually predominates and determines the general character of the grease, while the other modifies the structure in same way. This results, for example, in change in texture and improved mechanical stability.
Complex Soap Greases
The normal soaps can be complexed with various inorganic salts, usually salts of aliphatic acids with carbon chain lengths varying from C2 (acetate) to C14 (myristate) or mixtures thereof. Calcium complex greases (same including lead compounds) have been made for many years. More recently, aluminium complex greases have been introduced using benzoate as the complexing salt. Lithium complex greases have also made their appearance. The greases are water resistant and have very high drop points, in the range 200º-300ºC. Modern greases of these types are suitable for multi-purpose use.
Non-Soap Greases
There are two main types, those intended for general industrial use are those for specialized applications. The former include greases thickened with silica, clay or carbon black and organic derivatives such as terephthalates, diamino dicarbonyl and aryl-substituted areas. Published data (high service temperatures, mechanical stability, water-resistance, etc.), suggest that they are multi-purpose greases with a wider scope than soap greases. However, the rather far-reaching chains have not been supported by any notable impact on the market. The type used for specialized applications (mainly for very wide temperature ranges) includes greases made from the dyestuffs indanthrene and phthalocyanic, which are generally combined with synthetic fluids such as diesters, silicones, polyesters and polyethers and hence are very expensive.
Properties of Greases
The properties of greases depend upon the composition of grease and nature of its constituents. The gelling agents determine to a large extent the texture and mechanical stability of the system. The liquid phase on the other hand influences flow properties particularly at very low and high temperatures.
By virtue of being semi-solid or semi-fluid greases exhibit unique properties which are not shown by other fluid lubricants. Salient among these properties is the ability of greases to retain their position in a mechanism without significant leakages and yet release sufficient quantity of liquid lubricant for reducing friction and wear during usage. That greases can do so over a wide range of operating conditions over long durations of time, is an advantage which cannot be matched by lubricating oils. It is for this reason that for many industrial applications where oils have traditionally been used, greases are now emerging as superior and more effective alternative.
Mechanical Properties
The ability of a grease to resist changes in consistency as a result of a severe mechanical working is important in relation to service in rolling bearings.
Loss of Evaporation
If the grease loses significant amount of oil on evaporation, its lubricating properties would be seriously affected and the life of grease curtailed.
Oxidation Stability
Oxidation stability of greases is dependent on the oxidation stability of the oil. Oxidation of oil leads to acidity development, increase in viscosity, blackening caused by asphalt like bodies, and ultimately to the formation of bituminous mass.
Heat Stability
Heat stability is the ability of the grease to hold the oil at elevated temperature (below the drop point) for extended period. This is measured in terms of the oil separated from grease in a standard test at a fixed temperature (usually 100ºC) after a fixed period (usually 30 hours). The grease which gives less oil due to separation is more stable.
Temperature Limits for Different Greases
| Grease Type | Max. temp. for 100 Hrs. | Lowest Temp. for 100 g cm. Torque in 204 bearing ºC |
| Petroleum | 120 | --29.0 |
| Polyglycol | 120 | --34.5 |
| Silicon diester | 138 | less than--73.5 |
| Polyester | 150 | --41.5 |
| Special Silicone | 232 | --73.5 |
| (with non-soap additives) | | |
Typical Properties of Lubricating Greases
| Kind | Oil Thickener % | Worked Penetration | Viscosity SUS | Dropping Point ºC |
| Sodium soap | 9-10 | 318-240 | 300 to 38 | 160 |
| 11-13 | 265-295 | 300 to 38 | 165 |
| 14-18 | 220-250 | 300 to 38 | 171 |
| Calcium Soap | 8-10 | 355-385 | 300 to 38 | 080 |
| 10-12 | 310-340 | 300 to 38 | 082 |
| 12-14 | 265-295 | 300 to 38 | 088 |
| Calcium soap | 4-6 | 355-385 | 150 to 100 | 165 |
| 8-10 | 352-385 | 150 to 100 | 165 |
| 14-18 | 220-250 | 150 to 100 | 165 |
| Lithium Soap | 5-7 | 365-385 | 300 to 38 | 171 |
| 7-9 | 310-340 | 700 to 38 | 182 |
| 9-11 | 255-295 | 700 to 38 | 182 |
Typical Properties of Synthetic Greases
| Type of fluid | Types of Thickeners | Dropping point (ºC) | Serviceable Temp. Range ºC |
| Diester | Fine silica | None | --74 to 150 |
| Lithium Soap | 193 | --54 to 150 |
| S Poly alkylene | Fine silica | None | --54 to 150 |
| Glycol | Lithium Soap | 188 | --35 to 177 |
| Carbon Black | None | --18 to 232 |
| Silicones | Fine Silicon | None | --74 to 177 |
| Lithium Soap | 193 | --54 to 150 |
| Fluoro Carbon | Fine Silicon | None | --18 to 177 |
Grease Applications
Greases and lubricants are one of the important products derived from crude petroleum.
The particular virtues of grease that make it preferred to oil in many cases, and especially for rolling bearings, are ease of application and simplicity in use, while oil can carry away heat from the lubrication point and in general will lubricate rolling bearings more efficiently, it needs goods seals and relatively elaborate means of application such as circulation systems. Grease, on the other hand, can be used in simpler housing designs because it can be retained easily and therefore, seals against contamination, and requires much less attention and maintenance. Consequently, the majority of rolling bearings are now lubricated with grease. For similar reasons, plain journal bearings not operating under critical conditions are also commonly grease-lubricated.
However, in general, grease applications vary from high loaded ballbearings on small electric motors motors and fans to heavy duty plain and antifriction bearings on the largest of steel mill rolling equipment. Owing to their many advantages over oil, greases are now the first choice for the lubrication of ball and roll bearings in electric motors, household appliances, etc. They are also used for the lubrication by small gears drives and for many slow speed sliding applications.
Naturally enough the less critical conditions can be met by the cheaper products, i.e. the conventional calcium soap greases, which are mostly used for plain bearings and for low-speeds rolling bearings. For rolling bearings operating at high temperature and speed, the choice can be made from the remaining types of grease depending on service conditions, the more severe conditions requiring high quality inhibited greases. These latter have a multipurpose character and are increasingly used in many plants, with benefits in stock holding and freedom from misapplication, in place of the variety of cheaper greases that would otherwise be needed. Extreme temperatures, say from 150ºC upwards, call for greases made from the non-soap thickeners. They are also needed for critical mechanisms in nuclear power plants where soap greases cannot withstand conditions involving exposure to nuclear radiation.
It is important to use the right amount of grease in bearing, especially for high speeds too much can cause churning and over-heating, which may result in the grease breaking down and running out of the bearing. Too little can result is dry running and damage to the bearing. Best practice is to pack the bearing full and leave enough free space in the covers to accommodate excess grease working out from the bearing during the initial running. This can be achieved by packing the covers between about two-thirds and three-quarters of the total capacity.If external contamination is severe and the bearing speed is fairly low, effective sealing can be maintained by packing fully.
The mechanism whereby grease lubricates a rolling bearing is somewhat controversial. It is accepted that under settled conditions the bulk of grease within bearing and housing is stationary and that only a very small amount of grease is actually circulating on the moving parts, this being rapidly degraded by the mechanical action of the rolling elements. Some consider that this alone does the job of lubrication and that the soap itself plays a valuable part. Others consider that the lubrication and that the soap itself plays a valuable part. Others consider that the lubrication is done by slow oil release from the stationary bulk of grease. It seems probable that both mechanisms of lubrication may operate to a greater or lesser extent, depending on the nature of the grease and the applicational conditions, particularly temperature.
Market Position
The consumption of lubricating oils and greases in India has been increasing steadily in the wake of economic and industrial development.
The change in their consumption pattern is governed by the supplies and partly by change in maintenance and lubrication practices (i.e. oil drain period, maintenance, conservation/re-refining, etc.) of industries in the wake of change in prices.
The consumption pattern of lubricating oils and greases show an increase. Also, the import figures show that there is a drastic demand for greases in India. As India is progressing towards self-sufficiency in the field of petroleum and allied products, the import of greases is diminishing but the demand for greases is increasing as the industrialization in our country is on full swing in general and automobile in particular.
Fillers
Fillers may be considered as solid materials which add bulk, and if present in sufficient amount, decrease the penetration of a lubricating grease. Most fillers consist of inorganic compounds and normally such material are powders or flakes rather than granules.
Types of Fillers
These are:-
1. Carbons in various forms
Such as: Graphite, carbon black or lamp black.
2. Silicates
Such as: Asbestos, a magnesium silicate, bentonite, a form of clay, calcium silicate, mica, a potassium aluminium silicate, talc or soapstone.
3. Metal Powders or Flakes
Such as: Aluminium powder, copper powder or flakes, lead powder, zinc dust.
4. Metal Oxides
Such as: Alumina or aluminium oxide, hydrated alumina, magnesia, litharge or lead monoxide, zinc oxide, titanium dioxide.
5. Metal Carbonates
Calcium carbonate, lead carbonate, basic lead carbonate, white lead.
6. Metal Sulfides
Antimony trisulfide, antimony pentasulfide, lead sulfide.
7. Metal Sulfates
Barium sulfate, lead sulfate.
Graphite
It is the most widely used filler. Natural graphite may have some impurities, and if 100% pure graphite is to be used, artificial graphite is generally employed. These may be in the form of powder or flake.
Graphite is presumably absorbed on metal surfaces. The utility of graphite, the small plates of graphite lying with their large surfaces parallel to the metal surfaces. Thus, the solid surface is much smoother and more uniform than before such adsorption. Also the layer of graphite has a tendency to absorb oil and to be wetted of it. This action, therefore favours the stability of a thin oriented layer of lubricant.
Graphite may be used in any lubricant, but it is particularly recommended in anti-seize compounds, spring lubricants, thread sealing compounds and valve lubricants.
Grades of Graphite Recommended
Type % through 200 mesh % max ash % minimum Graphite Carbon
Artificial Powder 99 0.2 99
Artifical Flake 98 1.9 99
Natural Powder 96 15.0 90
Natural Flake 90 15.0 85/90
Preparation of Graphite Lubricating Greases
The addition of graphite to lubricating greases best made when the product is partially or almost completely finished, for if the addition is made before the soap structure forms, settling of the filler may result. If possible, one mixing kettle should be set aside for the manufacture of graphited products because it is difficult to entirely free a vessel of the filler once it has been used in equipment.
The addition of powdered graphite is accompanied by dust which settles on the sides of the mixing vessel, and if the mixer is not covered, escapes to soil the surroundings and perhaps to contaminate other products.
For general purpose lubricating greases, graphite is seldom added in concentrations greater than 5%, and 3% or less is more common. These products include graphite cup greases, graphite chassis lubricants, graphite fibre greases and graphite axle greases.
Carbon Black
Because of the fineness or small particle size of carbon black or lamp black, it has been often used as a filler in lubricating greases. To obtain the full value of carbon blacks, when employed as a filler, through dispersion is essential. Simple mixing will not suffice, but should be followed by some type of milling. Greater trouble will likely be encountered from dusting with carbon black than with fine graphite. In addition to acting as fillers, carbon black are inert and resistant to the solvent action of fluids with which they may come in contact.
A formulation of such a lubricating grease in which this filler used is described in a U.S. Patent 2,486,674 in which 8.94% of carbon black, having an average particle size diameter of 250 A, is dispersed in a silicon polymer having a viscosity at 25ºC of 140 centistokes. Dispersion consists of stirring, heating to 115ºC, and finally passing through a three roll paint mill.
Asbestos
The type of asbestos normally used as a filler in lubricating greases is a grade known as "asbestos floats". Such a product should not have any particles held on a 20 mesh screen and not over 16% held on a 30 mesh screen. While this grade is presumably recovered by air separation from heavier particles, grit can generally be detected by rubbing a small amount of the asbestos between two glass plates.
Most of the asbestos fitted lubricating greases are made by simply mixing the asbestos with a suitable oil. The asbestos is fed through a shaker screen into the oil, which is agitated during the compounding. No heat is required unless a cylinder stock of high pour point is used. Most of the oils for such lubricants had viscosities within the range of 175 to 210 SUS at 210ºF. Such oil varied from bright stocks to black oils, but in most cases consisted of well refined cylinder stocks. Most producers of such lubricants give them a rough screening by passing them through a coarse screen or a perforated disc with 1/8 inch holes before packaging.
Mica
Mica in flake form is sometimes used a filler in lubricating greases, in horse drawn vehicles or such other vehicles, axle grease containing flake mica has such a reputation for service that the name "Mica Axle Grease" was copyrighted in America, from a fraction of percent to 5% of mica is employed for much the same purpose as flake graphite.
In bearing wear tests by experts, while mica did not show the abrasion which asbestos did, scratching and scoring of the bearing surface is evident, and the material is thus placed in a questionable class as far as lubrication of antifriction bearing is concerned.
Vermiculite
Vermiculite has somewhat the same form and nature as mica and thus can be expected to serve much the same purpose as a filler. The flakes of this material have a yellow golden colour which make it evident when added to light coloured lubricating greases. Such a filler can be expected to be of doubtful value in lubricants for use in antifriction bearings.
Lubricants are being prepared for use on metallic moving parts by completely expanding vermiculite by heating to 300ºC, and grinding and mixing it with lubricating greases. Oxides of zinc or cadmium could also be included in such lubricating greases.
Talc
The slippery nature of talc (known also as soapstone) has made it attractive as a filter in some lubricants.
A hot neck lubricating grease for use after the rolls are warmed up in older steel mill equipment consists of petroleum pitch (125º C.M.P.) 47%, degras 7% talc 27% and cylinder stock, of 500 flash, 19%.
Both talc and asbestos used to be employed in Ford spring compounds as below:
| Ingredient | % by Wt |
| Ice Machine oil | 44.4 |
| Foundry Talc | 8.4 |
| Asbestos pulverized | 2.8 |
| Cup grease | 44.4 |
A stainless, emulsifiable, grease-like composition, suitable for pipe bending and wire drawing opetrations, has been suggested. The base oil for this product contained 10 to 15% of alkali metal petroleum sulfonates. The proportions of ingredients used : 25 to 75% of the base oil, 0.5 to 2.0% of tall oil, 0.5 to 2.0% of diethylene glycol, 0.3 to 1.0% of cyclohexylamine, 0.05 to 0.2% of stearic acid and about 38% of either talc or mica.
It is well to keep in mind that talc or mica are often preferable to graphite in die or drawing lubricants because the latter material is difficult to clean off after drawing.
Various Clays or Silicates
Bentonite, calcium silicate, magnesium silicate, magnesium aluminium silicate for their wear or abrasiveness when included in 10% concentrations in a soda base lubricating grease. The tests were on tapered roller bearings which were run for 200 hours at 1000 rpm under a load of 75% of thrust. Of above compounds only calcium silicate should be rated as non-abrasive.
Metal Powders
Metals in powdered or flake form are employed as fillers in certain types of lubricating greases, the softer metals generally being used.
A lubricant for die-forming magnesium and its alloys may be prepared from the following combinations : 50 to 70 parts of comminuted aluminium of 120 to 400 mesh size, 20 to 30 parts of potassium or sodium palmitate or stearate, and 10 to 20 parts of either hydrogenated cottonseed, lard oil, or peanut oil.
Finely divided lead is employed as filler in lubricating greases for more than one purpose. Thus, US Patent 2,383,148 provides a formula described below:
| Ingredient | % by Wt |
| Dark green petrolatum | 68.64% |
| Lithium stearate | 8.80% |
| Aluminium tristearate | 1.76% |
| Lead oleate | 0.40% |
| Tributyl phosphite | 0.40% |
| Leaf lead | 20.00% |
Some powdered metals, particularly aluminium and zinc, are used in various lubricants. Thread lubricants are made with proportions of zinc powder varying from 10 to 60%. It is well to introduce the zinc dust when the cup grease is as cool as possible, since it hydrogen is to be generated, the reaction will be accelerated by heat.
The most promising compounds contained a mixture of 2 to 4% flake copper, 18% graphite, and 42 to 44% of mixture of powdered lead and zinc (consisting of 2.35 to 3.17 parts by weight of lead to 1 part of zinc) dispersed in 34 to 36% of vehicle.
The copper is said to function as an active thread lubricant. An increase in copper content, from 2 to 4% by weight, resulted in a 10% decrease in make up torque.
Metal Oxides
Oxides of a number of metals have been and are being employed as fillers in lubricating greases. In selecting oxides care should be observed that they are of a physical nature which will not be abrasive. As these oxides act as anti-acids, they are suitable in many machineries, such as canning machinery, etc. A lubricant which is to be used on canning machinery contained magnesium oxide in order to neutralize any acids derived from fruit or vegetables.
Zinc oxides is sometimes added as a colouring aid in calcium base greases. For this purpose 1 to 2½% of a lead free, fully zinc oxide is employed.
A suitable zinc oxide for use as a filler in lubricating greases has the following specifications:
| % |
| Minimum through a 325 mesh screen | 99.85 |
| ZnO content | 99.3 |
| Lead content | 0.07 |
| Sulfur content | 0.04 |
| Cadmium content | 0.04 |
| Loss of ignition | 0.40 |
| Specific gravity | 5.65 |
| Apparent density-grams per cu.in. | 4.00 |
Manufacturing Processes for Grease
Manufacturing Details-In industry lubricating grease is manufactured by two processes:
1. Batch Process
2. Continuous Process
Following steps are used in processing:
(a) The required materials are properly weighted.
(b) For saponification mixing and heating of ingredients is involved.
(c) Dispersion of bodying agent in the lubricating fluid.
(d) Dehydration by vacuum treatment of the finished or semi-finished product.
(e) Cooling of the soap.
The value of lubricating grease in service depends upon the following physical characteristics:
1. Stability to working or shear
2. Thermal stability
3. Body or consistency
4. Viscosity or low
5. Structure
6. Syneresis
7. Texture and appearnce.
Following types of greases are manufactured and used in industry:-
1. Sodium, calcium, aluminium, barium, lithium, strontium, and lead base lubricating greases.
2. Mixed base lubricating greases.
3. Miscellaneous metal soap as components of lubricating greases.
4. Complex soap lubricating greases.
5. Non-soap thickeners for lubricating fluids.
Description
There are two main processes : (1) Batch Process, and (2) Continuous Process. Most lubricants are produced by the Batch process, which is still popular, particularly for a small scale manufacturer. In this process the amount of lubricants made in one lot may be from few hundred pounds to 60 or 100 barrels. Batch process may further be divided into two parts : (1) Open kettle, and (2) Closed kettle manufacture.
Simply, this process have the following successive steps in the production of lubricants:
(1) Open Kettle Manufacture:
(a) Saponification and finishing carried out in one vessel.
(b) Dispersion of preformed soap and finishing or product performed in the same kettle.
(c) Saponification and dispersion of soap carried out in one vessel, followed by cooling in auxiliary equipment.
(d) Dispersion of preformed soap in one vessel, followed by cooling auxiliary equipment.
(e) Saponification conclude in one kettle and finishing done in another.
(f) Preformed soap dispersed in one vessel and finishing carried out in second vessel.
(g) Fatty materials preferably fatty acids or rosin acids, mixed with a portion of the total oil in one vessel and the alkali mixed with the remainder of the oil in another vessel. The two mixtures are then brought together to the package where saponification takes place.
(2) Closed Kettle Manufacture:
(a) Saponification carried out under pressure and finishing done in a second vessel.
(b) Saponification carried out in a pressure vessel, soap dispersion in a second vessel and cooling in auxiliary equipment.
Open Kettle Process
The simplest process for the manufacture of lubricants is that in which the soap is made in the same vessel in which the finished product is completed. This entails the use of only one vessel for complete greasemaking and requires no auxiliary equipment, either for transfer of partially completed lubricants, or for cooling or milling of the completely formed lubricants.
In this process, though the vessel used is only one, but the whole process is divided into several steps, they are:
(1) Weighing or measuring materials for the formation of soap.
(2) Mixing and heating such a mixture of ingredients to form soap.
(3) Dispersion of the resulting soap in portion of the total oil.
(4) Hydration of the soap oil mixture.
(5) Introduction of additional oil, which oil may act as a coolant or serve to reduce the mixture to the desired consistency. Additives or modifiers may also be introduced in this step.
(6) Cooling which may be accomplished in step 5 or following that step.
(7) Filling of containers or delivery to storage. This step will include screening of the finished product.
It is evident that all the steps outlined can be carried out in one vessel. Such a simple process is not applicable to al types of lubricating greases but this method will permit the manufacture of most calcium and sodium based lubricants and greases. Lubricants and greases will have the most satisfactory structure provided that the crystallization of soap takes place while the mass is still dormant.
Use of more than one vessel in manufacturing lubricants and greases is the very common practice, and probably the most economical method of production. The two vessles, as far as possible, should not be identical in construction, so that provision can be made for one vessel which will permit dispersion and hydration to the best advantage. Thus, the saponification vessel can have a much smaller capacity than the finishing kettle. Two stage manufacturing processes permit greater through put and flexibility than one stage procedure.
When preformed soap is employed, one of the most time consuming steps in open kettle processing is eliminated, namely saponification, so that processing of preformed soaps is normally confined to one vessel and any auxiliary equipment.
The process by which soap formation takes place in the container is employed to a limited extent. Axle grease is made by such a process and mention will be made of this when continuous processes are described. One disadvantage of such a process is that any moisture present in the reacting mixtures, or formed by reaction of acids and alkali, remains in the finished product.
Raw Materials
1. Mineral oil (Turpentine Oil)
2. Rosin Oil
3. Hydrated lime [Ca(OH)2]
Plant & Machinery
1. Mixing vessel made of mild steel or carbon steel jacketed for steam heating.
2. Baby Boiler Cap. 100 Kg/Hr.
3. Storage Tank (M.S.) capacity 1.5 cu. Mt.
4. Weighing Scale.
5. Instrumentation, process control & Lab. Testing equipment
6. Pipes, fitting, pumps, valves and other miscellaneous equipments.
Industrial Grease
Manufacturing Process
Modern plants are normally arranged for gravitational flow, with raw materials received at the top, saponification and finishing processes on intermediate flows and filling and packaging on the ground floor materials are usually metered in a fluid condition as far as possible rather than weighed for processing. For example, fatty materials in bulk are stored in heated tanks, calcium hydroxide is used in concentrated aqueous solution.
Principles
The first step in making soap greases is to specify the fatty material by heating with a chemically equivalent amount of alkali in the presence of a proportion of the oil. A small amount of water must also be present to ionize the alkali and so facilitate the reaction when saponification is complete, more oil is added and the soap/oil mixture is conditioned by a more or less critical adjustment of heating, cooling and stirring in order to control the crystallization of the soap fibers and hence the properties of the finished grease. The balance of oil and any additives are added at suitable stages depending on the type of grease, the process used and the nature of the additives. The grease is finally stirred or milled to obtain uniformity and correct consistency and then filled into packages.
Processing
Most greases are made by batch processes that involve stages of heating (saponfication) and cooling (finishing). Heating may be by steam, which allows the possibility of water cooling in the same vessel, by direct firing with oil, gas or solid fuel, by hot oil or Dowtherm circulation systems or by electric induction heating vessels heated by direct firing or hot-oil circulation cannot be water-cooled and are generally coupled wilth water-jacketed finishing vessels (kettles).
The kettles are fitted with stirrers which should give a good wall-scraping action to assist heat transfer and good circulation to avoid dead spots. Provided that the stirring is efficient (particularly during cooling), the product is normally satisfactorily uniform and does not require any further treatment to ensure satisfactory properties. In some circumstances a more vigorous shearing is needed during finishing and can be provided by pumping or circulating through mills or homogenizers. Such equipment is of two main types, with the grease pumped either between stationary and rotaing surfaces set close together or through special valves set to lift at high pressure.
Now-a-days closed pressure vessles (i.e. autoclaves) are almost universally used for saponification and frequently also for finishing, although open kettles are still common for this part of the process. Saponification is much easier and quicker at the higher temperatures obtainable in autoclaves, which are generally operated at 50-80 psig, corresponding to temperatures of about 148º - 162º C. With some greases, it is also necessary to provide for heating the autoclave contents to over 200ºC.
Modern practice is to prepare soap concentrates in an autoclave, this being coupled to one or two larger finishing kettles (typical capacities are 1-2 tons for autoclaves and 2-5 tons for kettles). The general layout of a typical modern grease plant is shown in the figure. On this system much of the oil can be added cold to the soap concentrate in the finishing kettle, thus shortening the time otherwise needed for cooling. After saponification, the soap mixture is generally "blown down" under its own pressure into the finishing kettle, during which time practically all of the water is lost as steam. Alternatively, the autoclave may be vented and heated to higher temperatures if required before discharge into the kettle at the higher temperatures obtainable in autoclaves, which are generally operated at 50-80 psig, corresponding to temperatures of about 148º-162ºC. With some greases it is also necessary to provide for heating the autoclave contents to over 200ºC.
The finishing process is designed to develop soap fibers of the desired properties by suitable thermal and mechanical treatment. This involves a proper choice of heating and cooling rates, process temperatures and stirring speeds at different stages. These factors vary so greatly according to the size and design of the kettle, and particularly the stirrer, that each plant must work out its own process for a given type of grease according to the equipment available.
Instead of kettles, other forms of equipment can be used that involve rapid circulation of grease through narrow channels between heated or cooled surfaces. Such equipment, popular in U.S.A., but not widely used elsewhere, can be applied to continuous or semi-continous manufacture.
Some pre-made soaps, particularly aluminium, require a different type of process. The soap is heated with the mineral oil to form an isotropic solution which is then cooled statically at controlled rates in thin layers, generally in shallow pans of convenient size. This results in the formation of a stiff gel, which is then broken down into the normal plastic state by suitable stirring or milling.
With non-soap thickeners the manufacturing process is fairly simple; the thickener is first dispersed in the oil (heated it necessary) and the mixture is then milled. Milling is an important part of the process since intensive shear is needed in order to obtain the best properties and maximum yield of grease.
Current trend in grease manufacture are towards better instrumentation of the operations. In principle, automatic control of heating, cooling and shearing together with the use of ingredients with uniform properties, would give complete control over product quality. Despite the considerable practical difficulties, satisfactory progress is being made towards this objective.
Types of Grease
The metallic radical of the soap largely determines the characteristics of the greases, the fatty radical having a secondary effect. Greases are therefore classified in terms of the metal they contain.
(i) Aluminium
(ii) Calcium
- Conventional
- Anhydrous
- Complex
(iii) Lithium
(iv) Sodium
(v) Sodium
(vi) Non-soap (organic-inorganic)
Nearly 90 per cent of greases contain lithium, calcium or sodium soaps. "Other soaps" (such as potassium, barium or strontium) are of minor importance and will not be discussed here.
Manufacturing Process of Greases in General
The manufacturing processes for all types of greases is nearly the same. The mineral oil and other fatty materials are heated in fire heated kettle. When all the fatty materials melt, then mix them with the help of an agitator. Now to this melted fats add the required quantity of alkali with continous agitation. The complete saponification is around 400ºF. After complete saponification the batch is kept for cooling. After cooling the grease is filled in desired packings viz. 1 kg, 2 kg, 4 kg, etc.
COST ECONOMICS INDUSTRIAL GREASES
Basis: 300 kg/day grease; 90000 kg/annum grease
| 1. | Total land area required | 1000 sq. mts. |
| 2. | Covered area required | 600 sq. mts. |
| 3. | No. of employees | 12 |
| | Rs. in Lakhs |
| 4. | Land and building | 9.00 |
| 5. | Plant and machinery | 2.00 |
| 6. | Other, fixed assets | 2.00 |
| 7. | Fixed capital | 13.00 |
| 8. | Working capital for one month | 2.00 |
| 9. | Working capital for 2 months | 6.00 |
| 10. | Margin money for working capital | 1.50 |
| 11. | Cost of project | 14.50 |
| 12. | Total capital investment | 19.00 |
| 13. | Cost of production per annum | 25.00 |
| 14. | Receipt per annum | 31.50 |
| 15. | Profit per annum | 7.00 |
| 16. | Profit sales ratio | 21.00% |
| 17. | Rate of return | 37.19% |
| 18. | Break even point | 53.00% |
Resources of finance
| | Rs. in Lakhs |
| 1. | Fixed capital from Financial Institutions | 10.00 |
| 2. | Working Capital from Banks | 4.00 |
| 3. | Self Raised Finance | 5.00 |
| | Total 19.00 |
Practical project execution know-how report is available for those dynamic entrepreneurs who are genuinely interested to implement this project.
This report is prepared by team of engineers, and market research analysis supported by a panel of experts, equipped with an industrial computerized data bank.
Fire Hazards in the Manufacture
As saponification and soap dispersion, normally involve heating, it may be pointed out that enough care should be taken to avoid fire hazards in these processes. The material which is used in the manufacture of such items are almost entirely inflammable.
Since standard fire prevention practices, such as all steel or concrete construction in new plants, installation of sprinkler systems, division of the plant by fire-walls and doors, and cleanliness must always be retained in this regard, so fire hazards may be reduced at least to a certain point.
While the use of open obviously increases fire hazards they need not endanger a whole plant. If fire-heated vessels are employed in place of those heated by hot oil or "Dowthern" to obtain temperatures above 320ºF, such equipment should be segregated by fire walls going through the top of the building. It should also be possible to install barriers or diversions to keep overflow from a vessel away from a fire.
Saponification
Saponification is actually an alkaline hydrolysis of esters, which in this case are mixed triglycerides of higher fatty acids. While water has been considered a pre-requisite for such a reaction, very likely this compound may simply provide for more intimate contact of the reacting ingredients, since soaps have been formed in anhydrous systems by the reaction of fats and fatty acids with finely divided dispersions of various alkali mineral oils. Since water alone, under proper conditions, will hydrolyze fats, it is possible that during saponification hydrolysis takes place preliminary to combination of the resulting fatty acids with the base.
Such a reaction may take place step-wise, so that the first product formed is a diglycerde, followed by a further reaction to produce a monoglycerine. Finally, the mono-glyceride reacts with still more alkali so that upon completion of saponification, glycerol and soap are the products.
Soap formation, by combination of a fatty acid and a basic compound, while actually a neutralization, is also considered as saponification by people in this industry, such a reaction results in the formation of water in addition to the soap. Since almost all inedible fats and fatty oils contain some free fatty acids, neutralization of such fatty acids no doubt precedes the hydrolysis of the fats, so that the remainder of the reaction proceeds in the presence of both additional water and some soap.
Certain metals will react with fatty acids to form soaps. In this case hydrogen is produced in addition to the soap. Since the soap thus formed may be deposited on the surface of metal particles, the reaction will be arrested.
Processing of aluminium base lubricants and greases
This first step in the manufacture of aluminium base lubricating greases consists in weighing or measuring the primary ingredients, which consist of oil and soap. Since the soap will be in standard packages, generally holding 50 pounds or more per carton or bag, weighting is simple. As in all other types of lubricating greases, the oil may be either weighed, metered, or measured. In any event 20 to 25% of the total oil is added to the mixing kettle, followed by the aluminium soap. Some plants prefer to sieve the soap as added but in most cases this is not necessary. The oil should be below 150ºF when the soap is introduced, otherwise fusion of the outside of lumps of soap may take place and such lumps may be difficult to disperse later.
An intense mixing is desirable at this stage so that a good "Cream" results with no lumps of soap present. In some operations it is preferred to mix and heat at a temperature just below the gelling point, which is perhaps 150 to 160ºF, for one to two hours, in the belief that some of the moisture present may be removed before the soap is dispersed in the oil.
After the soap and the initial oil are thoroughly mixed, the soap is dispersed by the application heat. This dispersion can take place in the initial portion of oil but preferably more oil is added before gelling takes place. The temperature required for complete dispersion of the soap will vary with the specific oil and the type of aluminium soap employed, but it should fall within a range of 250 to 300ºF. If the hot mass is to be removed from the processing vessel, the top temperature may be required so that the mixture will be thin enough to handle. Modifiers and additives are to be mixed before the batch cools.
Cooling processes vary. In a few cases the hot grease is filled intocontainers and allowed to cool. In another case the mass is cooked in the kettle by means of water jacket. Another method is in shallow pans or trays to which the hot lubricating grease is delivered by pipes.
A flowsheet of a process for the production of aluminium base lubricants and grease, employing homogenizer, is shown previously. The first step in this process consists of preparations of soap oil slurry, in an open kettle, using half of the final mineral oil. This slurry is warmed to about 150ºF and passed through what is termed the hot grease homogenizer. This homogenizer consists of a rotating disc, housed in a vacuum chamber, with the inlet feed at the center of the disc and an outlet scoop out the circumference of the disc. Here, as the slurry travels continuously through the equipments, air and moisture are removed from the mixture and a thorough dispersion of the powdered soap is effected.
The next step consists of delivery to the heating kettle, where the batch is brought to 220 to 240ºF. After the heating step, the material is pan cooled and held until it gels.
The cool batch, plus an equal weight of oil, is then added to a mixing kettle where agitation breaks the cooled mass into small lumps. The final step consists of passing this slurry of soap gel lumps and oil through a cold homogenizer. As the mixture passes through this piece of equipment it is smoothed out, so that no lumps, graininess, or free oil remains.
Because the fact that moisture is removed before the soap and oil are heated to dispersion temperature, and also because the homogenizers are said to thoroughly disperse the soap, a smaller soap percent for a given consistency is claimed for this method than for other methods of manufacture aluminium base lubricating greases. A saving heat is also claimed because of the fact that the temperature required in the process is 240ºF.
This process has also been employed for the production of lithium base lubricants and greases, in which a higher temperature is used to disperse the soap. Likewise, instead of starting with preformed lithium soap, the lithium soap could be prepared in the initial kettle.
In employing the above process it is possible to have an oil-soap mixture exhibiting a brittle soap gel and free oil, which can subsequently be smoothed out by mechanical means to form a satisfactory lubricating grease. A recent procedure is applicable in processing preformed soaps of aluminium, barium, calcium, lithium, and sodium with mineral oil to form work-stable lubricants and greases.
The first step in this process consists of heating the soap-oil mixture, while agitating, until the entire mixture is liquefied and preferably until the oil and soap are miscible, which is said to be 365ºF, or above, for most mixtures. This step may be conducted in either open or closed vessels.
The next stage, cooling, is accomplished by discharging the hot soap oil dispersion into a cooling tank where cool oil is constantly supplied from an oil cooler. Here the soap separates as lumps of soap gel. The cooling time is usually 10 to 300 seconds. This cooled mixture is discharged to a separator consisting of either a centrifuge or a s
