GB567893A - Improvements in the production of organic esters of cellulose - Google Patents

Abstract

Cellulose is esterified in presence of an inorganic acid esterification catalyst and a solvent for the cellulose ester and the solution so obtained is subjected to ripening after the inorganic acid has been eliminated and replaced by an organo-mineral acid. The acid esterification catalyst may be neutralized by adding oxides, carbonates, or organic salts of metals, which can combine with the catalyst without liberating any other mineral acid. Magnesium acetate or carbonate, calcium acetate or carbonate, zinc acetate, or zinc oxide, may be used. A sulphuric acid catalyst may be neutralized in two stages with different neutralizing agents, e.g. part may be neutralized with a mixture of magnesium acetate and calcium acetate and the remainder with magnesium acetate alone. The organo-mineral acid may be methyl sulphonic, ethyl sulphonic, propyl di-sulphonic, benzyl sulphonic, benzene sulphonic, phenyl sulphonic, naphthalene sulphonic, toluene sulphonic, xylene sulphonic, or methyl or ethyl phosphinic acid, or ethyl hydrogen sulphate. The amount of organo-mineral acid may be 5-50 per cent of the weight of the original cellulose. The water required for ripening may all be added before ripening begins or part may be added before and part at one or more stages during the ripening. Ripening may be carried out at 30-100 DEG C. Before esterification, the cellulose may be pre-treated with acetic, or formic acid, or a mixture of these, with or without sulphuric acid. In an example, cotton is esterified with a mixture of acetic anhydride, acetic acid and sulphuric acid, the mixture being allowed to reach a peak temperature of 35 DEG C. When the acetylation is complete, water is added to destroy unreacted anhydride. A mixture of magnesium and calcium acetates is added to neutralize half of the sulphuric acid present. The rest of the sulphuric acid is then neutralized by adding magnesium acetate. Toluene sulphonic acid and water are added and the solution is kept at 35 DEG C. for 96 hours. The ripened cellulose acetate is precipitated by adding a large amount of water. Instead of sulphuric acid, there may be used phosphoric acid or mixtures of phosphoric and sulphuric acids, as the catalyst.