GB630937A - Improvements in the manufacture of esters of cellulose - Google Patents

Abstract

Cellulose is substantially completely esterified in the presence of an inorganic acid catalyst under conditions such that a primary cellulose ester is obtained; to the solution there is added a neutralizing agent, other than an alkali metal or ammonium compound, in an amount at least equivalent to the total amount of inorganic acid employed in the esterification; ammonium bisulphate is added to the neutralized solution, preferably in a proportion of 3-10 per cent of the weight of the cellulose, and the cellulose ester is ripened in the solution at a temperature above 60 DEG C. Secondary cellulose esters of good stability are thus obtained. The neutralizing agent may be an acetate of magnesium, zinc, aluminium, calcium, barium, or strontium, or strontium oxide or hydroxide, barium oxide or hydroxide, or magnesium carbonate. In an example, cotton linters are pretreated with acetic acid containing sulphuric acid and water at 35 DEG C. The activated cellulose is treated with acetic anhydride, acetic acid, and sulphuric acid cooled to -6.5 DEG C. The reaction proceeds for 2 hours, a peak temperature of 43 DEG C. being reached. At the end of the reaction, aqueous magnesium acetate solution is added to neutralize all the sulphuric acid and provide a 10 per cent excess, and at the same time to convert unchanged acetic anhydride to acetic acid. The solution is then heated to 60 DEG C. and then steam is injected until 100 DEG C. is reached. Ammonium bisulphate is added and the cellulose acetate is allowed to ripen, the temperature dropping gradually to 90 DEG C. After 12 hours, the cellulose acetate is precipitated by adding water. The process is applicable to the production of cellulose propionate, butyrate, aceto-butyrate, and other cellulose esters.