KREBITZ PROCESS.
The Krebitz process which has been used to some extent in Europe is based upon the conversion of the fat or oil into lime soap which is transformed into the soda soap by the addition of sodium carbonate. To carry out the process a convenient batch of, say, 10,000 pounds of fat or oil, is run into a shallow kettle containing 1,200 to 1,400 pounds of lime previously slaked with 3,700 to 4,500 pounds of water. The mass is slowly heated with live steam to almost boiling until an emulsion is obtained. The tank is then covered and allowed to stand about 12 hours. The lime soap thus formed is dropped from the tank into the hopper of a mill, finely ground and conveyed to a leeching tank. The glycerine is washed out and the glycerine water run to a tank for evaporation. The soap is then further washed and these washings are run to other tanks to be used over again to wash a fresh batch of soap. About 150,000 pounds of water will wash the soap made from 10,000 pounds of fat which makes between 15,000 and 16,000 pounds of soap. The first wash contains approximately 10 per cent. glycerine and under ordinary circumstances this only need be evaporated for glycerine recovery.
After extracting the glycerine the soap is slowly introduced into a boiling solution of sodium carbonate or soda ash and boiled until the soda has replaced the lime. This is indicated by the disappearance of the small lumps of lime soap. Caustic soda is then added to saponify the fat not converted by the lime saponification. The soap is then salted out and allowed to settle out the calcium carbonate. This drops to the bottom of the kettle as a heavy sludge entangling about 10 per cent. of the soap. A portion of this soap may be recovered by agitating the sludge with heat and water, pumping the soap off the top and filtering the remaining sludge.
While the soap thus obtained is very good, the percentage of glycerine recovered is greatly increased and the cost of alkali as carbonate is less. The disadvantages are many. Large quantities of lime are required; it is difficult to recover the soap from the lime sludge; the operations are numerous prior to the soap making proper and rather complicated apparatus is required.