Patent GB-264937-A (GB)
Title: Improvements in or relating to the manufacture of cellulose derivatives
IPC: C08B3/00
Filed: 1925-10-30
Abstract: 264,937. Dreyfus, H. Oct. 30, 1925. Cellulose acetates and other carboxylates.-For the manufacture of cellulose acetates or other esters of cellulose by a dry process, that is, in the absence of liquid diluents or solvents, the cellulose employed as the starting material is pretreated with organic carboxylic acids, such as acetic or formic acid, according to the processes described in Specifications 207,562 or 263,938, and the reaction is performed by passing over or through the pretreated materials the vapours of acetic anhydride or other esterifying agent either alone or in admixture with air &c. or with the vapours of acetic acid or other solvent. The acetylation &c. is preferably conducted with the aid of a condensing agent, although a condensing agent may be omitted; the condensing agent such as sulphuric acid, may be introduced by first moistening the cellulosic material therewith or it may be admixed, as in the case of hydrochloric acid, with the vapours &c. with which the material is treated, or it may be applied as a solution or acetic acid, the water or acetic acid being removed by pressing out, drying &c., although some dilute acetic acid or water mav be left in the material. The impregnation with the condensing agent may be combined with or form part of the process of pretreatment, the acetic acid &c. being wholly or partly removed before the acetylation &c. stage. The amount of condensing agent employed may be 0.5-3 per cent calculated on the cellulosic material. Acetylation &c. is preferably carried out while the cellulosic material is subjected to constant moving or mechanical agitation as by the use of rotary drums; heat may also be applied. The escaping vapours may be treated for the recovery of the acetic anhydride &c., or they may be re-circulated over the materials either with or without the addition of acetic anhydride &c. The material to be subjected to the pretreatment referred to above may be mercerized or unmercerized cotton, or wood pulps, for instance wood pulp that has been subjected to treatment with alkali, especially that described in Specification 249,173. The cellulose acetates &c. produced may be subjected to secondary or further treatment for the purpose of changing their solubilities, either before or after elimination or neutralization of the condensing agents. Such treatment may be performed by a dry process or while the acetate is in solution, or in suspension, but it is preferred to perform it by subjecting the dry acetylation &c. product to the action of formic or acetic acid vapour containing sufficient water to destroy any anhydride &c. remaining in the product, the latter being preferably agitated during the process. Further, other vapours such as those of hydrochloric acid or nitric acid may be added to the vapours with which the materials are treated; in this case it is preferred to conduct the process in the cold, whereas when acetic &c. acid is used alone the temperature may be raised to 70-100‹ C. The secondary treatments, when carried out in solution or in suspension may be performed according to the methods of Specifications 20977/11, 20852/12, and 207,562, and in such further treatment any remaining anhydride is removed, pre ferably by adding agents capable of esterification without forming water, for example lactic acid. Specifications 6463/15, 14101/15, 100,009, 101,555 and 263,939 also are referred to.