This section is from the book "A Practical Treatise On Friction, Lubrication, Fats And Oils", by Emil F. Dieterichs. Also available from Amazon: A practical treatise on friction, lubrication, fats and oils.
The clarifying and bleaching process must necessarily vary, as some oils may be more or less colored or mixed with impurities than others. The animal oils and fats require bleaching or clarifying only when obtained from impure material or offal. The vegetable oils, however, are generally more or less colored and permeated with vegetable and albuminous matter. In many cases it will suffice to blow hot dry air of a temperature of from 120° to 130° F. through the oil to remove the undesirable color and impurities. Others may be bleached by exposure to the sunlight in bright, shallow vessels, or by agitating the oil mixed with animal charcoal, at a temperature of about 120° F., and then filtering it. In many cases, however, one or the other of the following processes may be required:
Oils are clarified by the admixture of from five to ten per cent of fuller's earth, stirring well at a temperature of 140° to 150° F.. The mixture is then allowed to rest and settle. The fuller's earth carries down with it all impurities in suspension, and the sediment can be treated with benzine to recover any oil remaining mixed with the fuller's earth.
Oils are also refined by treatment with sulphuric acid, which destroys all extraneous vegetable matter. The oil is heated to about 110° to 115° F., and from one to two per cent of sulphuric acid, usually previously diluted with an equal proportion of water, is added, with constant agitation for about half an hour. It is then allowed to rest and settle for about twenty-four hours. From twelve to fifteen gallons of water, heated to about 150° F., to every twelve gallons of oil, is then stirred with the oil and the oil allowed to rest and settle for a few days, when it is drawn off and washed with water to remove all traces of acid.
Oils and fats, especially cottonseed oil, are also refined with caustic soda, which, like acid, destroys all extraneous vegetable, mucilaginous and resinous matter, and all acidity in the oil. A caustic lye of from fifteen to twenty degrees Baume is used for cottonseed oil, from eight to twelve degrees for most other fatty oils, and a lye from five to six degrees strength is generally found sufficient for cocoanut and like oils, and often a lye of from one-half to one per cent strength only will be sufficient for the purpose.
Oils containing much of free fatty acids can be effectively treated with weak solutions of caustic or carbonate of soda, or with milk of lime or magnesia, and the oil filtered from the lime and magnesia soap thereby formed.
Strong solution of chloride of zinc, from one, to two per cent of the oil, is also used. It destroys and precipitates all albuminous and vegetable matter suspended, without injury to the oil, but is more expensive than sulphuric acid.
It is advisable to avoid treating oils to be bleached with too large proportions of chemicals at once, as repeating the operation with smaller proportions will generally secure better results.
Oils can be bleached and thereby also deodorized with chlorine, a powerful bleaching agent.
The oil is heated to a temperature of about 140° to 150° F., and a solution of chloride of lime, "bleaching powder," in the proportion of about one pound to a thousand pounds of oil, is mixed with the oil. Hydrochloric (muriatic) acid is then added in about twice the quantity of the bleaching powder used, and the oil is thoroughly agitated. It is then allowed to settle, and the oil and fat are then drawn off. Chloride of potassa or peroxide of manganese, with hydrochloric acid, can also be used in the same manner as the chloride of lime.
Oil can also be deodorized by shaking 1,000 parts of it with 120 parts of water, holding in solution 3 parts of permanganate of potassa, keeping it warm for some hours, and then filter. For bleaching lard oil, palm oil, and similar oils and fats, the bichromate of potassa process is much used. The oil or fat is heated to a temperature of about 130° to 140° F., and a concentrated solution of bichromate of potassa in the proportion of about 10 to 12 pounds of the bichromate to a thousand pounds of the oil or fat is added and thoroughly stirred into the oil. Hydrochloric acid in the proportion of from two to three per cent of the oil is then added, and the whole well stirred for from ten to fifteen minutes. The oil, which at once assumes a reddish-green color soon changes to a pale-green one. Boiling water is then added, and the agitation continued for a few minutes more, or live steam is blown through the oil and then allowed to settle. The oil is then drawn off and washed with water to remove all traces of acid.
Degras is bleached and deodorized in the following manner: The degras is melted by heating with live steam and thoroughly agitated by paddling, or blowing with air. A solution of bichromate of potassa in water - one pound or more of bichromate of potassa for a hundred pounds of degras - is added, and after agitating for a few minutes a solution of two pounds of sulClarifying, Refining And Bleaching. 45 phuric acid, previously diluted with six pounds of water, is poured in. Next three pounds of black oxide of manganese are added and agitated for half or three quarters of an hour. The blower is then turned off and the acid and water allowed to separate, and are drawn off from underneath the fat. The grease is now sprayed with hot water, which is again allowed to settle, and is drawn off. This is repeated until all sour taste is removed. When cold, stir thoroughly and allow still adhering water to run off.
Tallow and other fat can be cleaned and bleached by boiling some fifty pounds of the fat with about five to ten pounds of alum dissolved in about ten gallons of water for about an hour, constantly stirring and skimming. Draw off the clear fat and add one pound of sulphuric acid diluted with three pounds of water. Boil and add some eight ounces of bichromate of potassa; continue boiling, and if necessary add a little more acid ; then allow to settle, draw off and wash with boiling water; finally spray with a little cold water to accelerate the clearing of the fat.
To clean and bleach and deodorize train oil boil with salt water, consisting of about one-fourth its weight of sodium chloride (common salt), and stir briskly for about half an hour ; then allow to settle, draw off the oil and mix with a decoction of nutgalls. After briskly stirring for about fifteen minutes or so, add about four ounces aqua fortis (nitric acid) to every hundred pounds of the oil; stir for a little while longer and allow to settle; draw off the clear oil and wash with water.
Grease is bleached by melting and agitating with about three per cent of sulphuric acid and two per cent of a saturated aqueous solution of bisulphite of soda. The mixture is then run into a narrow cylindrical vessel and violently agitated with dry steam for half an hour, and is then run off and allowed to cool slowly, and while still fluid the fat is drawn off without disturbing the sediment. It is again agitated with steam and about 20 per cent water and left standing to separate and harden.
Mineral lubricant has no effect whatever on tin and copper, attacks brass least and lead most. Olive oil attacks copper most, zinc least. Rape oil does not act on brass and tin, while copper is attacked most by it, and iron least. Tallow oil acts most vigorously on copper and least on tin, while lard oil attacks copper most and zinc least. Cotton-seed oil acts most vigorously on zinc and least on lead. Spermaceti oil attacks zinc most and brass least. Whale oil has no effect whatever on tin, least on brass, and most on lead, while seal oil attacks brass least and copper most. On the other hand,
Clarifying, Refining And Bleaching. 47 the experiments have shown that iron is most vigorously attacked by tallow oil and least by seal oil, while rape oil has no effect on it whatever. Tin is not attacked by rape oil, only slightly by olive oil, and most by cotton-seed oil. Lead is least acted on by olive oil and most vigorously by whale oil, while lard oil and spermaceti oil have almost the same effect as whale oil. Zinc does not appear to be attacked by mineral lubricants, while lard oil acts on it least and whale oil most. Copper is attacked least by spermaceti oil and most by tallow oil.