GB630388A - Improvements in the production of cellulose esters - Google Patents

Abstract

Stable organic esters of cellulose having a very low content of combined sulphuric acid or other inorganic acid are prepared by esterifying cellulose in the presence of an inorganic acid catalyst, neutralizing all the free inorganic acid, injecting steam into the solution to raise the temperature to at least 60 DEG C., acidifying the hot solution with a further quantity of inorganic acid and maintaining or further raising the temperature of the solution for a short time. The free acid is then neutralized and the cellulose ester ripened at an elevated temperature to the desired acyl value. A compound of magnesium, zinc, aluminium or an alkaline earth metal is used as the neutralizing agent, the temperature of the steam heating may be from 60 DEG to 90 DEG C., the proportion of free sulphuric acid after the hot solution has been acidified is preferably less than 1 per cent, the ripening temperature may be about 100 DEG C., and the amount of neutralizing agent added before the ripening may be more than that theoretically required to combine with all the free sulphuric or other inorganic acid in the solution. In an example, cotton linters are pretreated with a small quantity of sulphuric acid, water, and glacial acetic acid for about 2 hours at 25 DEG C. and then acetylated with acetic acid, acetic anhydride and sulphuric acid at -10 DEG C., a peak temperature of 40-50 DEG C. being ultimately reached. More than sufficient aqueous magnesium acetate is then added to neutralize all the free sulphuric acid and live steam injected into the solution until its temperature reaches 90 DEG C. Sulphuric acid in solution in acetic acid is then added until the solution contains 0.5 per cent of free sulphuric acid calculated on the weight of the cellulose starting material, and steam injection continued until the temperature rises to 100 DEG C. The free sulphuric acid is then completely neutralized by aqueous magnesium acetate and the solution allowed to ripen at 100 DEG C. When the desired acetyl value is reached, the solution is cooled rapidly to 35 DEG C., and the ripened cellulose acetate precipitated, washed, and dried. The process may be used for the production of cellulose propionate, butyrate, acetate-propionate, and acetate-butyrate. Specifications 538,913, 568,051, 568,098 and 597,295 are referred to.