CATALYTIC SYSTEM FOR THE ACYLATION OF CELLULOSE AND A PROCESS FOR PRODUCING AND USING SAID CATALYTIC SYSTEM

摘要

A catalytic system for the acylation of cellulose comprises the addition product of sulphuric acid and N,N-dimethyl acetamide as well as free sulphuric acid or free N,N-dimethyl acetamide in the following ratios by weight (in moles): addition product of sulphuric acid with N,N-dimethyl acetamide 1.0; free sulphuric acid, not more than 0.49; or free N,N-dimethyl acetamide not more than 0.40. The process for obtaining such a catalytic system involves allowing sulphuric acid to react with N,N-dimethyl acetamide in the absence of water at a temperature of 0 to 25 °C and in the following proportions by weight (in moles): sulphuric acid 1.0; N,N-dimethyl acetamide not more than 1.4. A method of acylating cellulose in the presence of the proposed catalytic system involves treating the cellulose with acetic acid, following which the activated cellulose thus obtained is treated with an aliphatic acid anhydride at a temperature of 10 to 90 °C in the presence of the proposed catalytic system whose proportion by weight is 1.5 to 30 % that of the weight of cellulose calculated in respect of sulphuric acid, the weight ratio of the liquid phase to cellulose being accordingly 3 to 7:1. The process for obtaining acetone-soluble primary acetates of cellulose using the proposed catalytic system and acylation method disclosed involves activating the cellulose with acetic acid, acetylating the activated cellulose using acetic anhydride in the presence of the proposed catalytic system which contains 0.2 to 0.4 moles of free N,N-dimethyl acetamide to 1.0 mole of the addition product of sulphuric acid and N,N-dimethyl acetamide, and is applied in an amount equal to 20 to 30 % by weight of the weight of the cellulose calculated in respect of sulphuric acid. The weight ratio of the liquid phase to cellulose is 4 to 7:1 and treatment of the cellulose acetate thus formed with aqueous acetic acid takes place in two stages: in the first stage, treatment is carried out at a temperature of 70 to 85 °C for one to two hours with aqueous acetic acid containing 4.0 to 5.0 % by weight water and a neutralizing agent in an amount such that the free sulphuric acid content in the system will be equal to 5.0 to 10.5 % by weight of the cellulose; in the second stage, treatment is carried out with aqueous acetic acid containing 14.0 to 15.0 % water at a temperature of 65 to 70 °C for 1 to 2 hours.