Patent GB-303135-A (GB)
Title: Improvements in the esterification of cellulose
IPC: C08B3/06
Filed: 1928-08-03
Abstract: 303,135. Ruth-Aldo Co., Inc., (Assignees of Barthelemy, H. L.). Dec. 20, 1927, [Convention date]. Cellulose carboxylates.-For the acetylating of cellulose, the cellulosic material which may be wood cellulose or cotton, is submitted to a preliminaty softening treatment with at least 50 per cent of its weight of hot vapours of acetic acid preferably containing a small amount of halogen as described in Specification 303,134, and the softened, cellulosie material is subjected to ac.etylation by means of successive additions, of which there are at least four, of acetylation baths each comprising acetic anhydride, acetic acid, and a strong catalyst such as sulphuric acid, the composition of the baths and the quantities thereof being such that in the early stages of the acetylation the catalyst is introduced in small but gradually increasing quantities, and being such that the acetic anhydride after the first small addition is in subsequent additions progressively reduced in quantity until the later stages when, after the mass has attained the necessary degree of homogeneity, the bulk of the anhydride is added whereby acetylation can be completed at increased temperatures without the necessity for employing a too great excess of this reagent; and in any case the additions are so chosen that in the earlier stages acetylation proceeds without the formation of cellulose sulphates and with only a limited rise of temperature, each successive addition being made only after the reaction resulting from the preceding addition has terminated or practically terminated. The temperatures to be maintained during the several stages of the acetylation are,-for the stages up to the formation of monoacetate (C12), 18-26‹ C.; for the next stages up to tetracetate, 20-35‹ C. and for the final stage, the temperature may be raised to 55- 60‹ C., so avoiding the necessity for employing a large excess of anhydride. Sulphuric acid is the catalyst more particularly employed, and in the early stages of the acetylation this is preferably used in conjunction with halogens such as bromine or with oxidizing agents as described in Specification 282,793; by the use of halogen, the proportion of sulphuric acid may be reduced, thereby ensuring against the formation of cellulose sulphates in the initial stages of the acetylation. The apparatus used for the acetylation is preferably that described in Specifications 282,791 and 303,009. Fig. 1 shows a typical temperature curve for the acetylation, the acetylation baths being added at the points a - - e, while Fig. 3 shows on one diagram curves representing the general rate at which the several reagents may be regarded as being added. After the acetylation has been completed, the acetate may be precipitated in water, before or after filtration; and the cellulose acetate so obtained may be subjected to saponification, preferably by employing the process of Specification 282,789. Specification 282,788 also is referred to. The Specification as open to inspection under Sect. 91 (3) (a) includes the manufacture of cellulose esters other than acetates; it refers to a process of acetylation or other esterification in which at least four successive acetylations &c. are carried out, each one of which is deferred until an earlier one has terminated, and it refers also to the esterification of cellulose which has been treated with an oxidizing agent as described in Specification 282,794, or which has been partly esterified as by treatment with nitric or formic acid, or partly etherified by the introduction of benzyl or ethyl groups; and Specification 190,732 also is referred to. This subject-matter does not appear in the Specification as accepted.