Patent GB-784514-A (GB)
Title: Improvements in solvent extraction processes
Inventor: WEBB EDWIN THOMAS
IPC: C10G33/04
Filed: 1954-04-13
Abstract: <PICT:0784514/III/1> A solvent extraction process comprises treating a stock (which is a liquid or a material which can be caused to flow) in a number of successive stages with a different batch of solvent in each stage, and separating the solvent and stock after each stage. The solvent in each stage is progressively enriched to a predetermined extent by repeatedly mixing the same batch of solvent with the stock, as the stock flows through the stage. When this enrichment has been obtained, the batch of solvent is transferred for use in an earlier stage with a richer stock, the solvent from the first stage being run off for recovery.  An embodiment of the invention is described with reference to the diagram, which illustrates an extraction process in three stages, I, II, and III, in each of which there is provided a tank of solvent S1, S2, S3, a mixer M1, M2, M3, and a centrifuge C1, C2, C3.  The path of flow o the stock and solvent is governed by valves V1-V17.  Assume, initially, that fresh stock is passing through pipe 10 to M2, the valves being set so that the path of flow of stock is pipe 10, past V1, V2, V8 to M2, then to C2, thence past V13 to M3, then to C3, past V17 and through pipe 30 to M1, so to C1, and finally past V6 to pipe 26 and out through evacuation pipe 28.  In this particular cycle of operation solvent in S1 will be fresh solvent, that in S3 will be partly charged, and that in S2 will also be charged but to a greater extent than that in S3.  The path of the solvent in Stage II is from S2 through pipe 14, past V10 and pipe 16 to M2, where it is mixed with the stock, thence to C2, where stock and solvent are separated, and from there through pipe 24 and so back to S2.  The solvent from tanks S1 and S3 follow precisely similar paths.  Thus, as the stock passes (in order) through stages II, III, and I, it meets solvent, which is continually being re-cycled within that stage, and which at each stage is of lower solute content than that of the previous stage.  The above cycle of operation is continued until a state of equilibrium is about to be reached, at which point no further extraction would occur. V10 is then closed, V11 opened and solvent S2 is evacuated through pipe 20 to recovery plant 32.  Tank S2 is recharged with fresh solvent and V10 and V11 restored to their previous settings.  Valves V8 and V6 are closed, and V9 opened so that stock passes directly to M3 and thence to M1 and M2.  V13 is closed, and V12 is opened so that on leaving C2, the stock passes out of the plant to waste through pipe 28.  The extraction process is then restored, the cycle of operations being stages III, I, and II. The procedure is repeated cyclically as and when the solvent in S1, S2 or S3 reaches the desired high level of concentration, and in one complete overall cycle, each tank S1, S2, and S3 is discharged once. Th process, which is of particular application in the recovery of glycerol from soapstock and in the extraction of oil from crushed seeds with trichlorethylene, also finds application in the petroleum industry, in such processes as the sweetening of petrol by aqueous caustic soda, or by a solutizer solution, in the purification of lubricating oils by means of aqueous phenol, furfural, or methyl ethyl ketone, in deasphalting or dewaxing lubricating oils by means of petrol or gasoline, and in the improvement of kerosene and jet fuels by solvent extraction with liquid sulphur dioxide.ALSO:A solvent extraction process, for the extraction of thioglycollic acid from aqueous solutions containing salts, comprises treating the thioglycollic acid stock in a number of successive stages with a different batch of methyl iso-butyl ketone in each stage, and separating the solvent and stock after each stage.  The solvent in each stage is progressively enriched to a predetermined extent by repeatedly mixing the same batch of solvent with the stock, as the stock flows through the stage. When this enrichment has been obtained, the batch of solvent is transferred for use in an earlier stage with a richer stock, the solvent from the first stage being run off for recovery.  An embodiment of the invention is described with reference to the diagram, which illustrates an extraction process in three stages, I, II and III, in each of which there is provided a tank of solvent S1, S2, S3, mixer M1, M2, M3 and a centrifuge C1, C2, C3.  The path of flow of the stock and solvent is governed by valves V1-V17.  Assume initially, that fresh stock is passing through pipe 10 to M2, the valves being set so that the path of flow of stock is pipe 10, past V1, V2, V8 to M2 then to C2, thence past V13 to M3, then to C3, past V16 and through pipe 30 to M1, so to C1, and finally past V7 to pipe 26 and out through evacuation pipe 28.  In this particular cycle of operation solvent in S1 will be fresh solvent, that in S3 will be partly charged, and that in S2 will also be charged, but to a greater extent than that in S3.  The path of the solvent in stage II is from S2 through pipe 14, past V10 and pipe 16 to M2, where it is mixed with the stock, thence to C2 where stock and solvent are separated, and from there through pipe 24 and so back to S2.  The solvent from tanks S1 and S3 follow precisely similar paths. Thus as the stock passes (in order) through stages II, III and I, it meets solvent, which is continually being recycled within that stage, and which at each stage is of lower solute content than that of the previous stage.  The above cycle of operation is continued until a state of equilibrium is about to be reached, at which point no further extraction would occur. V10 is then closed, V11 opened and solvent S2 is evacuated through pipe 20 to recovery plant 32.  Tank S2 is recharged with fresh solvent and V10 and V11 restored to their previous settings.  Valves V8 and V6 are closed and V9 opened so that stock passes directly to M3 and thence to M1 and M2.  V13 is closed, and V12 is opened so that on leaving C2 the stock passes out of the plant to waste through pipe 28.  The extraction process is then restarted, the cycle of operations being stages III, I and II.  The procedure is repeated cyclically as and when the solvent in S1, S2 or S3 reaches the desired high level of concentration, and in one complete overall cycle, each tank S1, S2 and S3 is discharged once.