GB585713A - Improvements in the production of cellulose esters - Google Patents

Abstract

To the primary acylation solution resulting from the esterification of cellulose in an excess of a lower fatty acid anhydride in a solvent for the ester, and in presence of a catalyst, ice is added to convert the excess of anhydride into the corresponding acid without substantially increasing the temperature of the solution, and the amount of ice added is sufficient to provide water for effecting conversion of the anhydride and hydrolysis of the cellulose ester. Preferably, the temperature is maintained not in excess of 30 DEG C. throughout the esterification of the cellulose and subsequent hydrolysis of the primary ester in solution. Sufficient ice may be added to reduce the concentration of the total organic acid to about 95 per cent with respect to water. The process may be applied to the production of cellulose acetate, propionate, butyrate, or aceto-butyrate. The cellulose may be cotton, cotton linters, wood pulp, or reconstituted cellulose. It may be activated by pretreatment with formic or acetic acids, or with alkali, and part or all of the catalyst required for esterification may be present in the pretreating liquid. The catalyst may be sulphuric acid, zinc chloride, sodium bisulphate, or methyl sulphate. The solvent for the cellulose ester may be acetic acid, propionic acid, butyric acid, or methylene chloride. In an example, 100 parts of cellulose are pretreated by soaking in 50-100 parts of acetic acid. The cellulose is then acetylated at 25-30 DEG C. in a medium consisting of 300 parts of acetic anhydride and 2 parts of sulphuric acid. After the reaction has taken place; 60 parts of ice are added to convert the excess of anhydride to acetic acid and to reduce the acetic acid concentration to 95 per cent with respect to water. The solution is allowed to stand until the cellulose acetate has been hydrolysed to a product which is soluble in acetone.