GB342738A - Improvements in or relating to the manufacture of cellulose esters and cellulose ester products therefrom - Google Patents

Abstract

In the preparation of cellulose acetates, propionates, butyrates, &c. the esterification is carried out, at least in part, in the presence of a ferric chloride or bromide catalyst containing iron in the ferric form in a greater quantity than is equivalent to the chloride or bromide present in the catalyst or catalyst mixture. The excess of ferric iron may be introduced directly by the addition of ferric oxide or ferric hydroxide to the ferric chloride or bromide, or alternatively, the ferric chloride or bromide already present in the esterifying mixture may be reacted with an alkali; in the latter case, the sodium chloride or other salt resulting from such reaction does not constitute part of the catalyst or catalyst mixture. As a further alternative, the catalyst may be introduced directly in the form of a basic ferric halide. The total ferric iron present in the catalyst varies from less than 1 per cent up to 50 per cent or more, calculated on the weight of the cellulose. As starting materials for the esterification, cotton or other celluloses, or near conversion products, wood pulps, or the like, may be employed. Chemical pulps are preferably subjected, before esterification, to an alkaline purifying treatment followed by a treatment with organic acids, as described in Specification 249,173, [Class 2 (ii), Cellulose &c.]. Other forms of pretreatment specified are pretreatment with organic acids, as for example, in the manner described in Specification 263,938, [Class 2 (ii), Cellulose &c.]; pretreatment with hydro-halide acids or salts, or mixtures thereof, as in Specification 312,098, [Class 2 (ii), Cellulose &c.], ferric chloride or bromide being especially valuable. According to a modification of the process, the early stages of the esterification may be conducted in the presence of ferric chloride (or bromide) and hydrochloric (or hydrobromic) acid, and at a later stage the whole or part of the hydrochloric (or hydrobromic) acid is neutralized, and at a still later stage the whole or part of the chloride (or bromide) radicle is neutralized. In such a multi-stage process, the temperature may vary from stage to stage. The secondary treatment or ripening process may be carried out in the presence of the catalyst used in the esterification, or other ripening agents may be added. In examples, (1) cotton linters are pretreated with formic acid, and then esterified by means of acetic anhydride for 2 to 3 hours in the presence of glacial acetic acid and ferric chloride; freshly precipitated ferric hydroxide is then added and the esterification completed. (2) Cotton linters pretreated with glacial acetic acid and ferric chloride are acetylated for 2 hours by introducing acetic anhydride; at this stage, freshly precipitated ferric hydroxide is stirred in and the reaction completed. (3) Cotton linters pretreated with glacial acetic acid and concentrated hydrochloric acid are acetylated with acetic anhydride in the presence of a mixture of ferric chloride and ferric hydroxide; additional ferric hydroxide is added after 3 to 4 hours, and the reaction carried to completion. The products may be used in the preparation of artificial silk, fibres, films, moulding powders, thermoplastic masses, &c. Specifications 264,937 and 312,095, [both in Class 2 (ii), Cellulose &c.], also are referred to.