GB709430A - Improvements in the pretreatment and esterification of cellulose - Google Patents

Abstract

Cellulose which initially contains less than 5 per cent. of water is pretreated with a lower aliphatic acid, i.e. one containing 1-4 carbon atoms in the molecule, in two stages, in the first of which there are present 4-9 per cent. of water, calculated on the dry weight of the cellulose, but no esterification catalyst, this stage lasting for at least 2 minutes, and in the second of which there is used a further quantity of lower aliphatic acid containing an esterification catalyst in an amount of 3-15 per cent. of the dry weight of the cellulose, this stage lasting for not more than 15 minutes and being effected under conditions of temperature such that at the end of the pretreatment part or all of the lower aliphatic acid is frozen. cellulose containing the frozen aliphatic acid is immediately subjected to esterification with an organic acid anhydride. The process may be used in the production of cellulose acetate, acetic acid being used as the pretreating acid and also as the solvent for the cellulose acetate, sulphuric acid being used as the catalyst, and acetic anhydride as the esterifying agent. The process may also be used in the production of cellulose propionate, butyrate, aceto-propionate, and aceto-butyrate. The cellulose may be cotton linters, purified wood-pulp, or pulp from flax. hemp, grasses, peanut hulls, and bark. The cellulose may be treated in the form of loose fibres or in sheet form. The temperature during the first stage of pretreatment may be 25-55C. The second stage may last for 2-5 minutes and there may be present 100-600 per cent. of the lower aliphatic acid calculated on the dry weight of the cellulose. When acetic acid is used, the temperature may be reduced to 15 DEG C. to cause freezing. In an example, cotton linters are dried at 100 DEG C. until they contain 0.3 per cent. of water. Acetic acid, containing 6 per cent. of water, calculated on the dry weight of the cellulose, is sprayed on to the linters, which are then allowed to stand for 3 minutes. The linters are then sprayed with acetic acid containing 15 per cent. of sulphuric acid, based on the cellulose, and during 4 minutes the temperature of the mass is reduced to 15 DEG C. so that a large proportion of the acetic acid is frozen. The linters are then acetylated by treatment with acetic anhydride, the temperature rising to 35 DEG C. The primary triacetate is ripened in the solution and then precipitated. Specifications 688,580, and 706,522 are referred to.