Patent GB-332607-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: 332,607. British Celanese, Ltd., (Celanese Corporation of America). April 17, 1929. Cellulose esters; preparatory treatment of cellulose.-Cellulosic materials are rendered more reactive to esterification by treating them with organic acid anhydrides, particularly acetic anhydride or propionic anhydride. The anhydride may be employed as liquid either alone or mixed only with a liquid lydrocabon, for example benzene, or as a vapour, if desired diluted with an inert carrier, for example air, nitrogen, or carbon dioxide. The pretreated materials may be subjected directly to esterification, for example bv immersion in acetic anhydride, glacial acetic acid, and a suitable catalyst, for example sulphuric acid, but it is preferred to subject the material to a further preliminary treatment with organic acids, particularly .lower fatty acids, or with a mixture of an organic acid with an anhydride, preferably with a mixture which can in the presence of a condensing agent constitute a suitable esterifying mixture. This 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 in the early stages. This catalyst may be neutralized or eliminated before the end of the second pretreatment. As in the first stage, the reagents employed in the second stage 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 pre-treatment processes preferably follow an alkaline purifying treatment, for example as described in Specification 249,173. The pretreated material may 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 producd, 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 be obtained it 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, mav 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 agents 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, sulphonyl chloride, or the various catalysts forming the subject matter of Specifications 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 changing 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 catalysts 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, moist bleached willowed cotton linters are sprayed with acetic anhydride and turned occasionally during three hours, whereupon the pretreated mass is introduced into a mixture of acetic anhydride and glacial acetic acid cooled to 5‹ C. and stirred for two hours, after which sulphuric acid dissolved in acetic acid is added. Stirring is continued until solution is complete. The acetate may be preciptated and subsequently ripened or the ripening may take place in the esterification solution. In a second example, moist cotton linters are treated with acetic anhydride for three hours, and the pretreated mass charged into a mixture of glacial acetic acid, acetic anhydride, and a very small amount of sulphuric acid previously cooled to 5‹ C. After a period sodium carbonate is added, the stirring continued and the acetylation finally conducted by adding to the mixture sulphuric acid dissolved in a mixture of acetic anhydride and glacial acetic acid until solution is complete, whereupon the acetate may be treated as in the first example. In a third example, air is drawn through liquid acetate) anhydride maintained at 75-85‹ C. under reduced pressure and the mixture of air and acetic anhydride vapour drawn through moist cotton linters contained in a jacketed drum provided, if desired, with baffles and maintained for example at 60‹ C. or on perforated or non-perforated trays, for example, so that fresh gaseous mixture acts on already treated material and then passes on to treat material which has been treated for a shorter time. The gaseous mixture is withdrawn by means of a suction pump and reintroduced into circulation. After treatment for 3-6 hours the cellulose is acetylated as in the first example. Specification 263,938 also is referred to.