Patent GB-814831-A (GB)
Title: Production of organic acid esters of cellulose
IPC: C08B3/22
Filed: 1956-08-16
Abstract: Water-containing solutions of organic acid esters of cellulose in water-immiscible solvents are dewatered by bringing the solution into contact with a solid dehydrating agent that is insoluble in the solution, and then separating the solution from the dehydrating agent.  The process may be applied to the treatment of solutions obtained by esterifying cellulose in the presence of a water-immiscible solvent, followed by extraction of the solution with an aqueous medium, as described in Specification 779,802.  In preparing such solutions, cellulosic material which has preferably been pretreated with, for example, an aliphatic acid, e.g. formic, acetic, propionic or butyric acid, or mixtures of such acids, is treated with the desired organic acid anhydride in the presence of a catalyst, e.g. sulphuric or perchloric acid, anhydrous ferric chloride or an aromatic or alkyl sulphonic acid, added either during or after pretreatment, and of a water-immiscible solvent for the ester, e.g. nitro-methane, m-cresol, cyclopentanone, pyrrole, furfural, trichloroethanol or a chlorinated hydrocarbon such as methylene chloride, tetrachloroethane, trichloroethane or chloroform or mixtures of such solvents.  When esterification is complete, the cellulose ester may be hydrolysed or ripened by adding sufficient water not only to convert unchanged anhydride to the corresponding acid, but also to provide an excess which may, for example, be between about 50 and 100 parts by weight for each 100 parts of the cellulose starting material, the solution being kept at room temperature or higher until the process is complete.  An alkaline material may then be added to neutralize part or all of the mineral acid present.  This may be a nitrogenous base, e.g. ammonia or an aliphatic or aromatic primary, secondary or tertiary amine, e.g. dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine or aniline, or a compound in which the nitrogen atom forms part of a heterocyclic ring, e.g. piperidine, quinoline or pyridine.  The solution is then subjected to solvent extraction with an aqueous medium, which may be water itself or a mixture of water and an organic solvent, e.g. methanol, ethanol, n-propanol, isopropanol, ethyl acetate, pyridine, acetone or methyl acetate.  At the end of the extraction a solution of the cellulose ester in the water-immiscible solvent is obtained which is saturated with water, and the water is removed by contacting the solution with a solid dehydrating agent, e.g. silica gel or a hygroscopic salt which may be of alkaline reaction, e.g. anhydrous sodium carbonate, magnesium sulphate, sodium sulphate or calcium chloride, which is used in excess, preferably in a particulate form, and removed from the solution, for example by filtration or centrifuging.  The dewatering process may be carried out on a batch basis, with stirring if desired, or in a continuous manner, by passing the solution through a bed of the dehydrating agent, which is preferably wetted with the solvent in which the cellulose ester is dissolved before passing the solution through the bed. The solution may be used directly for the production of filaments, films and like-shaped products after the addition of pigments, dyes, plasticizers and de-colourizing agents, e.g. charcoal, diatomaceous earth or fuller's earth, if desired. Specified cellulose esters to which the process may be applied are cellulose acetate (including the triacetate), propionate, butyrate, acetate-propionate, acetate-butyrate and benzoate.  Specification 789,210 also is referred to.