GB748124A - Improvements in the treatment of alkaline liquors which have been used in the purification of cellulose - Google Patents

Abstract

Aqueous alkaline liquor which has been used in the purification of cellulose of alpha-cellulose content already above 85 per cent, particularly cotton, has its content of dissolved organic matter reduced by heating it under substantially constant volume conditions (such that, at all temperatures below the critical temperature, the greater part remains in the liquid phase as a result of the vapour pressure developed) to a temperature above 300 DEG C. The liquor may be heated up to the critical temperature, or even above it, but generally temperatures between about 350 DEG C. and 375 DEG C. are preferred. The process is particularly applicable to liquors containing below about 5 per cent of caustic soda, but may be used in connection with solutions of other alkalies and with solutions of higher alkali concentration, e.g. 25 to 30 per cent or higher. In the example a 3 per cent caustic soda solution in which cotton linters have been boiled is heated in an autoclave up to 350 DEG C. during 2.5 hours, held at this temperature for a further 10 minutes, cooled and the resinous solids which have precipitated are allowed to settle. The liquor is decanted off, fortified with soda ash and recausticized with lime, after which it is used for the purification of further cellulose.ALSO:Aqueous alkaline liquor which has been used in the purification of cellulose of alpha-cellulose content already above 85 per cent, particularly cotton, has its content of dissolved organic matter reduced by heating it under substantially constant volume conditions (such that, at all temperatures below the critical temperature, the greater part remins in the liquid phase as a result of the vapour pressure developed) to a temperature above 300 DEG C. The liquor may be heated up to the critical temperature, or even above it, but generally temperatures between about 350 DEG C. and 370 DEG to 375C DEG . are preferred. The process is particularly applicable to liquors containing below about 5 per cent of caustic soda, but may be used in connection with solutions of other alkalies and with solutions of higher alkali concentration, e.g. 25 to 30 per cent or higher. In the example a 3 per cent caustic soda solution in which cotton linters have been boiled is heated in an autoclave up to 350 DEG C. during 2 hours 30 minutes, held at this temperature for a further 10 minutes, cooled and the resinous solids which have precipitated allowed to settle. The liquor is decanted off, fortified with soda ask and recausticized with lime.