Patent GB-658724-A (GB)
Title: Improvements in or relating to recovery of caffein
IPC: C07D473/12
Filed: 1949-06-30
Abstract: 658,724. Coffee. GENERAL FOODS CORPORATION. June 30, 1949, No. 17325. Convention date, July 20, 1948. [Class 129] An aqueous coffee extract is decaffeinated by extracting it with a water-immiscible organic caffeine solvent, e.g. a chlorinated hydrocarbon solvent, redissolving the solute in water, adjusting the pH value of the resulting aqueous solution to at least 7.0. preferably 7.8, by the addition of an alkali case, and crystallizing the caffeine therefrom. The pH value is adjusted by adding basic compounds such as oxides, hydroxides, carbonates, bicarbonates of sodium, potassium, titanium, rubidium, and cesium, or ammonium bases such as ammonium hydroxide. Ground roasted coffee is extracted with hot water in an extractor 1. The resulting infusion being introduced into a liquid-liquid extraction column 2 supplied with about three times as much trichlorethylene. The decaffeinated infusion leaving near the top of the column 2 may be used to produce soluble coffee. The caffeine (and impurities) in the solution removed from the column 2 is redissolved in water, the bulk of the organic solvent being removed in an evaporator 3 and recovered in a condensing system (not shown). The concentrated solution then flows to a steam still 4 where the remaining solvent is removed, the vapours passing to said condensing system. The resulting solution passes to a concentrator 5, and, when the caffeine content is about 30 per cent by weight, it flows to a steam-jacketed mixing tank 6 where it is treated for about half an hour with carbon which absorbs a certain amount of the dissolved impurities. The spent carbon is filtered from the solution in a filter press 7, and wash-water is passed through the press to combine with the filtrate. The solution flows into a water-cooled crystallizing tank 8 where its pH value is adjusted to at least 7.0 by the addition of one or more of the previously mentioned alkali bases. Caffeine crystals formed in the tank 8 are separated from the mother liquor and washed in a continuous centrifuge 9, the diluted mother liquor thus obtained being further processed as described later. The caffeine from the centrifuge 9 can be further purified in a similar manner in ports 10 to 13, corresponding to ports 6 to 9, the crystals finally passing to a drier 14. The carbon from the filter press 11 is removed to the mixing tank 6, and the mother liquor and washings from the centrifuge 9 are conveyed back to the concentrator 5 to be recycled. The first mother liquor from the centrifuge 9 still contains a substantial amount of caffeine and may be returned to the concentrator through the line 15 and recycled, most of the impurities being precipitated in the concentrator. In another method the mother liquor is conveyed to a 'concentrator 16 and further concentrated until it contains about 30 per cent caffeine before being introduced into a water-cooled crystallizing tank 17; the crystals are separated from the mother liquor in a centrifuge 18, and the mother liquor is discarded. The crystals may be purified by recrystallization procedures, or may be returned via the line 19 to the concentrator 5 and recycled. In a preferred method of handling the mother liquor from the centrifuge 9, the caffeine is separated from the bulk of the impurities and then recycled. The mother liquor flows to a mixing tank 20, and the impurities are precipitated by adjusting the pH value to 6.0 or less, preferably 4.0, by gradually adding an 'acid such as H2SO4, HCl, H2SO3, or H3PO4; the suspension is passed through a filter press 21, the washings from which are combined with the filtrate. This filtrate may be conveyed to the concentrator 5 via the line 22 and recycled, but is preferably heated in a heater 23 and then extracted in a column 24 with at least three times its volume of a water-immiscible, organic caffeine solvent, the spent mother liquor leaving the top of the column and being discarded. The sol- 'vent is preferably the same as that used in the column 2 so that the solution leaving the bottom of the column 24 may be passed to the evaporator 3. Extracts of whole roasted or whole green beans, or flaked green coffee or the like may be used instead of ground roasted coffee, but where green coffee decaffeination is followed by the production of a beverage from such coffee then whole beans must be used'since the flaked green coffee cannot be roasted to give the proper flavour. Specification 625,349 and U.S.A. Specification 2,309,092 are referred to.