GB893498A - A method of purifying cellulose - Google Patents

Abstract

Purified cellulose poor in pentosans and containing over 96% of alpha cellulose is produced from high viscosity cellulose, obtained from wood in a conventional manner with subsequent bleaching, by treating the bleached cellulose with an aqueous solution of hydrochloric acid of 30-35% concentration at room temperature for a sufficient time, e.g. 15-60 minutes, to hydrolyse the non-cellulose carbohydrate constituents thereof to water-soluble sugars, and thereafter separating the aqueous solution of hydrochloric acid and soluble sugars from the cellulose and washing the cellulose. Cellulose containing between about 96 and 98% of alpha cellulose and less than 0,8% of pentosans may thus be obtained in nearly theoretical yields even from hardwood. The aqueous solution of hydrochloric acid and sugar may be repeatedly used without modification for further refining and may finally be evaporated under vacuum in a triple effect evaporator, as described in Specification 835,645. The resultant concentrated sugar solution may be re-hydrolysed, de-ionized and further concentrated to form a water-white syrup. The cellulose may be given a final treatment with a 1-10% solution of an alkali metal hydroxide to effect a further increase in its alpha cellulose content and to improve its vactivity. In an example, bleached cellulose, obtained from beechwood chips by heating with sulphite cooking acid containing 1% of CaO and 6% of SO2 at a temperature not exceeding 135 DEG C. and bleached by treatment with chlorine, and alkaline intermediate wash and sodium hypochlorite, is washed and treated in a continuous process at 20 DEG C. with 32% hydrochloric acid, the proportion of hydrochloric acid to cellulose being maintained at 30:1 and the contact period not exceeding 15 minutes. The treated cellulose is washed with water and treated at 20 DEG C. for 30 minutes with an 8% aqueous solution of caustic soda.