Patent GB-886138-A (GB)
Title: Method of separating fatty acids
Inventor: RUDDICK RONALD BRAN
IPC: C11C1/00
Filed: 1960-03-30
Abstract: <PICT:0886138/III/1> Saturated and unsaturated fatty acids are separated from mixtures by a process in which the mixture is dissolved in a normally liquid organic solvent, particularly a lower alcohol or ketone such as ethanol, isopropanol, or methyl ethyl ketone, but preferably methanol or acetone, the resulting solution subjected to a reduction of pressure under adiabatic conditions so as to cause the evaporation of a substantial proportion of the solvent whereby a rapid chilling of the solution results with the saturated acids forming easily filterable interlocking agglomerations of crystals, filtering off such crystals, and subsequently removing solvent from the residual solution of unsaturated acids.  The solvent to be used should not contain more than 5% water, but a little water below this quantity may assist separation.  Ax shown, a suitable system comprises an acid storage tank and a solvent storage tank which feed the acid mixture and solvent to mixing tank 14, suitably in such amounts that the acid mixture does not exceed 30% by weight of the solution resulting, and preferably so that the volume ratio of solvent to acids is 3:1 to 6:1.  The solution then passes by line 20 to one of the crystallizers 22 which are used alternately and which are thoroughly insulated.  The inlet valve 21 or 23 is then closed and exhaust valve 25 or 27 opened to connect the crystallizers with a vacuum source 26 through line 24; the pressure applied is 10-50 mm. Hg abs., but preferably less than 40 mm. Hg abs., under which conditions maximum agglomeration of crystals occurs within 60 minutes and most preferably within 20-40 minutes, and 15-25% of the solvent is evaporated, the temperature of the mixture falling to 0-14 DEG F. The agglomerates are kept in suspension by means of gentle agitation until crystallization is complete, after which the suspension containing 8-12% by volume of solids is passed by gravity flow by line 32 to tank 34, the discharge of the crystallizer being assisted by the use of compressed air passed by line 29 and valves 33 and 35. Both tank 34 and filter 38 to which the suspension next passes are maintained at a temperature below 14 DEG F.  The filter cake in filter 38 consisting of solid saturated fatty acids is washed with cold solvent recovered from the vapour evaporated off in the crystallizers 22; this vapour is condensed in condenser 28 and passed to refrigerated hold tank 42 before passing by line 40 to filter 38. The washed filter cake is passed to melt tank 44 maintained at 250 DEG F and thence to flash evaporator 46 (at 280 DEG -320 DEG F), residual amounts of solvent being removed in stripper 48 from the residual solid saturated fatty acids by means of inert gas such as nitrogen.  The filtrate from filter 38 is passed successively through heater 50, evaporator 52 and stripper 54 to recover the liquid unsaturated fatty acids.  The process may be applied to the separation of fatty acid mixtures derived, for example, from animal fats, bone fats, vegetable tallows, cottonseed, soyabean, palm, coconut, menhaden and whale oils.