Patent GB-332608-A (GB)
Title: Improvements in or relating to the treatment of cellulosic materials and the production of cellulose esters therefrom
IPC: C08B1/02
Filed: 1929-04-17
Abstract: 332,608. British Celanese, Ltd., (Celanese Corporation of America). April 17, 1929. Addition to 332,607. Cellulose esters; preparatory treatment of cellulose.-The process of the parent Specification for rendering cellulosic materials more reactive towards esterification is modified in that the cellulosic materials are first treated with one or more organic acids alone or mixed with inert diluents and then with one or more organic anhydrides with or without organic acids. The organic acids may be employed in liquid or vapour form either alone or mixed with inert substances, for example air or carbon dioxide in the case of employing the acid in vapour form, or benzene in the case of employing the organic acid in liquid form. After the pretreatment with organic acids the latter may be wholly or partly removed, for example by passing air or other inert gas through the material. Formic acid except when employed in small quantities, see for example Specification 288,657, should be removed or substantially removed either after the first stage of the preliminary treatment or after the second stage. The second stage of the pretreatment is effected with the aid of an organic acid anhydride or mixture thereof with an organic acid, preferably with a mixture which can in presence of a condensing agent constitute a suitable esterifying mixture. The second stage is preferably effected in the absence of condensing agents, but small quantities of condensing agents insufficient to produce substantial esterification may be present, particularly at the beginning of the second stage. This condensing agent is neutralized or eliminated before the end of the second stage. As in the first stage, the reagents employed may be in liquid or vapour form and may be diluted with inert diluents. As initial materials' there may be employed cotton or other celluloses or near conversion products thereof or other cellulosic materials. The cellulosic materials may be dry or may contain the usual amounts of moisture, for example 4-8 per cent. Wood pulp or bamboo, esparto, or other materials containing encrusting matter from which the lignin, pentosan, resin, and like constituents have been substantially removed, as for example in sulphite pulp, soda pulp, or sulphate pulp, may be employed, but in the case of such materials the two-stage pretreatment preferably follows an alkaline purifying treatment, for example as described in Specification 249,173. The pretreated material mav be esterified. If a sufficient quantity of anhydride and if desired solvent or diluent be already present with the cellulose, only a suitable catalyst need be added, but further reagents, for example anhydride or acetic acid, may be added together with the catalyst. The esterification may be effected in presence of a solvent for the cellulose ester produced, particularly acetic acid in the preparation of cellulose acetates. The acetic acid or equivalent solvent may be present in any desired quantity, such as 4-6 times the weight of the cellulose, but cellulose esters of especially high viscosity can he obtained if the acetic acid or equivalent solvent is present in amount greater than six times, for example 6-20 times or more the weight of the cellulose as described in Specification 207,562. Alternatively the acetylation or esterification may be conducted in suspension in liquid diluents, for example benzene, toluene, or ether, and if desired solvents, for example acetic acid, may be present in addition to the liquid diluent. The esterification may, however, be conducted substantially in absence of liquid solvents or diluents by employing vapours of acetic anhydride or other esterifying agent as described in Specification 264,937. Any suitable catalyst may be employed in the esterification, for instance sulphuric acid, organically substituted sulphuric acids, e.g. benzene sulphonic acid, bisulphates, e.g. sodium bisulphate, sulphuryl chloride, or the various catalysts forming the subject matter of Specification 308,322, 309,201, 311,790, 312,095, and 312,096. The primary cellulose acetate or other cellulose esters produced may be used in their esterification solutions or in solutions of the primary esterification products, or they may be subjected to secondary treatment for the purpose of charging their solubilities either in the primary esterification solutions or suspensions or after separation of the esters therefrom. In conducting the secondary treatment in the esterification solutions or suspensions any excess anhydride may first be destroyed and the secondary treatments may be performed with the aid of the catalyst employed in the esterification. The cellulose acetates or other esters, either as primary or secondary esters, may be employed for the production of artificial silks or fibres, films, celluloid substitutes, or other thermoplastic masses, moulding powders, or other compositions or articles. In one example, cotton linters, dried or moist, are sprayed with 75-85 per cent formic acid, the mass allowed to stand for some hours and then transferred to an acetylator charged with a mixture of glacial acetic acid and acetic anhydride cooled to 5‹ C. After stirring in the acetylator for 2 hours sulphuric acid dissolved in acetic acid is added. Stirring is continued, if necessary with cooling, until solution is complete. The acetate may be precipitated and ripened to acetone solubility or the ripening may take place in the acetone solution. In another example, cotton linters, dried or moist, are moistened by spraying with 30-40 per cent or 60-70 per cent formic acid and the mass allowed to stand for 4 hours after which it is transferred to an acetylator charged with a mixture consisting of glacial acetic acid, acetic anhydride, and a very small amount of sulphuric acid. After half an hour sodium carbonate is added to the mass and stirring continued for one and a half hours. Sulphuric acid dissolved in glacial acetic acid is then added and the further treatment conducted as in the first example. Specification 263,938 also is referred to.