Patent GB-789212-A (GB)
Title: Production of organic acid esters of cellulose
IPC: C08B3/22
Filed: 1956-03-05
Abstract: Solutions of organic-acid esters of cellulose in water-immiscible solvents which contain water-soluble impurities are purified by passing them over one surface of a permeable or semi-permeable membrane and passing a solvent for the impurities over the other surface of the membrane.  When the solvent for the impurities is aqueous, e.g. water or a mixture of water and a water-soluble solvent such as methanol, ethanol, n- or iso-propanol, ethyl acetate, pyridine, acetone or methyl ethyl ketone, a permeable membrane may be used, e.g. filter paper or a porous ceramic, but it is preferred to use a semi-permeable membrane, e.g. coated or uncoated regenerated cellulose, animal or vegetable parchment paper or polyvinylidene chloride.  The passage of water through the membrane may be reduced or prevented by applying pressure to the cellulose-ester solution. Nonaqueous liquids, e.g. nitromethane, m-cresol, cyclopentanone, pyrrole, furfural, trichlorethanol, tetrachlorethane, trichlorethane, methylene chloride or chloroform, may also be used for extracting the impurities.  The process is preferably effected continuously and in counter-current.ALSO:Solutions of organic-acid esters of cellulose in water-immiscible solvents which contain water-soluble impurities are purified by passing them over one surface of a permeable or semipermeable membrane and passing a solvent for the impurities over the other surface of the membrane.  When the solvent for the impurities is aqueous, e.g. water or a mixture of water and a water-soluble solvent such as methanol, ethanol, n- or iso-propanol, ethyl acetone, pyridine, acetone or methyl ethyl ketone, a permeable membrane may be used, e.g. filter paper or a porous ceramic, but it is preferred to use a semi-permeable membrane, e.g. coated or uncoated regenerated cellulose, animal or vegetable parchment paper or polyvinylidene chloride.  The passage of water through the membrane may be reduced or prevented by applying pressure to the cellulose-ester solution.  Non-aqueous liquids, e.g. nitromethane, m-cresol, cyclopentanone, pyrrole, furfural, trichlorethanol, tetrachlorethane, trichlorethane, methylene chloride or chloroform, may also be used for extracting the impurities.  The process is preferably effected continuously and in counter-current, and may be applied to solutions obtained by esterifying cellulose in the presence of a cellulose-ester solvent.  In the preparation of such solutions, the cellulose may be pretreated in known manner, e.g. with an aliphatic acid, with or without a part or all of the catalyst to be used in the esterification, and may then be esterified with an organic acid anhydride in the presence of a water-immiscible solvent for the ester, e.g. nitromethane, m-cresol, cyclopentanone, pyrrole, furfural, trichlorethanol, methylene choride, tetrachlorethane, trichlorethane or chloroform, and an esterification catalyst, e.g. sulphuric or perchloric acid, ferric chloride, or an alkyl or aryl sulphonic acid.  When esterification is complete the ester may be ripened by addition of water to the solution, with or without a mineral acid.  Whether ripening is effected or not, the solution is preferably neutralized before it is purified, and this may be effected by addition of ammonia or an organic base, as described in Specification 789,210.  The purified solutions, after drying, if necessary, and preferably after concentration, may be used directly for the production of filaments, films and like products, or their composition may first be adjusted by adding a second solvent.  Thus, the spinning properties of a solution of cellulose triacetate in methylene chloride may be improved by adding a small proportion of a lower aliphatic alcohol, e.g. methanol, ethanol or n- or iso-propanol.  The solutions may also be decolorized by treatment with activated charcoal, diatomaceous earth or fuller's earth.  The process may be applied to the treatment of solutions of cellulose acetate, propionate, butyrate, acetate-formate, acetate-propionate, acetate - butyrate or benzoate.  Specification 779,802 also is referred to.