Patent GB-690688-A (GB)
Title: Improvements in the production of cellulose esters
Inventor: GROOMBRIDGE WALTER HENRY
IPC: C08B3/06
Filed: 1949-08-31
Abstract: Organic acid esters of cellulose are produced by treating cellulose, until it is substantially completely esterified, with an esterification liquor which comprises the organic acid anhydride corresponding to the ester to be produced, a diluent therefor which is a non-solvent for the cellulose ester and is present in amount such that the cellulose ester formed is not dissolved in the liquor, and a catalyst for the esterification, and as the reaction proceeds withdrawing esterification liquor from the esterification zone and fortifying it by the addition of the appropriate ketene in amount sufficient to regenerate substantially all the anhydride consumed, the liquor withdrawn being at once replaced by fortified esterification liquor.  The cellulose may be cotton linters or wood or straw pulps, especially those having an alpha-cellulose content over 90 and preferably over 95 per cent and a pentosan content not over 1.5 per cent. The cellulose may be given an activating pre-treatment at ordinary or raised temperatures with a lower fatty acid, preferably acetic, which may contain a certain amount of the esterification catalyst and/or sufficient acetic anhydride to combine with the moisture in the cellulose.  Alternatively the pre-treatment liquor may be fatty acid containing some water, e.g. aqueous acetic acid of concentration above 75 per cent, with or without acetylation catalyst.  The anhydride used may be that of an aliphatic acid containing 2-4 carbon atoms, and the process described below in connection with cellulose acetate may be similarly applied to the production of the propionate and butyrate, In the production of cellulose triacetate the acetylation liquor may contain over 50, e.g. 55-70 per cent by weight of acetic anhydride and the diluent is preferably an aromatic hydrocarbon such as benzene, toluene, ethyl benzene, or one or more of the xylenes.  The liquor also preferably contains a swelling agent for cellulose, preferably acetic acid, although others, such as methylene chloride, ethylene dichloride or sulphur dioxide, may also be used.  The catalyst may be sulphuric acid or preferably perchloric acid and the esterification may be carried out between about 25 DEG  and 40 DEG  C. or even up to about 55 DEG  C.  The acetylation of the cellulose is preferably carried out continuously, the cellulose undergoing acetylation and the acetylation liquor being passed in opposite directions through reaction vessels such as those described in Specifications 556,942 and 614,149, [both in Group II].  It may also be carried out on a semi-continuous basis in acetylators through which the liquor is caused to flow continuously or intermittently but into which the cellulose is introduced batchwise and from which the cellulose triacetate formed is similarly removed.  In the example cotton linters pre-treated with acetic acid are fed continuously into one end of a reactor, into the other end of which is fed a cooled acetylation liquor at a rate about 20 times that of the cellulose, the cellulose and liquor travelling in counter-current.  The liquor has the approximate composition acetic anhydride 65, acetic acid 15, benzene 20 and perchloric acid 0.05 per cent and the temperature reached in the reactor is 40 DEG  C.  The cellulose triacetate formed is washed successively with benzene mixed with a little glacial acetic acid containing an excess of sodium acetate to neutralize the catalyst and with benzene alone; finally it is immersed in water and freed from benzene by steaming.  The acetylation liquor leaving the reactor is cooled and mixed with ketene and sufficient acetic acid, benzene and catalyst to compensate for the liquor removed from the reactor with the cellulose triacetate.  The fortified liquor is then returned to the reactor.  The cellulose triacetate obtained may be ripened, e.g. as described in Specification 690,700.  Specification 637,267 also is referred to.