Patent GB-727441-A (GB)
Title: Organic acid esters of cellulose
IPC: C08B3/22
Filed: 1953-02-20
Abstract: A cellulose organic ester, which has been made by a solution process using sulphuric acid as catalyst, is subjected to a stabilizing and ripening operation comprising neutralizing a portion of the sulphuric acid in the esterification solution with an alkaline compound of an alkaline-earth metal, heating the esterification solution with added water to a temperature and for a time at least sufficient to split off from the cellulose ester substantially all sulphate or other sulphur-containing groups which are combined with it, neutralizing a further portion of the sulphuric acid with an alkaline compound of an alkali metal, and heating the esterification solution until the cellulose ester has the desired acyl value.  The process is applicable to the production of cellulose acetate, propionate, butyrate, aceto-propionate and aceto-butyrate.  Magnesium is included in the term "alkaline-earth metal."  Magnesium acetate, carbonate or oxide, or calcium, strontium or barium acetate, oxide or hydroxide may be used.  Cellulose may be esterified with an organic anhydride in the presence of at least 12 per cent of its weight, e.g. 12-17 per cent, of sulphuric acid as catalyst, using acetic acid or other lower aliphatic acid as solvent for the ester.  When the esterification is complete, water is added sufficient to convert any organic acid anhydride into the corresponding acid and to provide an excess of water which is preferably 25-60 per cent by weight, calculated on the weight of the cellulose.  To the acid dope there is added sufficient of an alkaline-earth metal compound to neutralize a substantial proportion, e.g. 54-68 per cent, of the sulphuric acid originally employed, and the free sulphuric acid may be reduced to 0.8-2.0 per cent of the weight of the cellulose.  The water may be added in the form of a dilute aqueous solution of a lower aliphatic acid which contains the required amount of the alkaline-earth compound.  The acid dope is then heated, e.g. at 60-75 DEG  C., for 60-150 minutes. During this period, the concentration of free sulphuric acid rises as a result of the splitting off from the cellulose ester of the sulphate or other sulphur-containing groups.  On completion of this stage, sodium acetate, formate, propionate or carbonate, or other alkaline compound of an alkali metal, is added to neutralize a further proportion of sulphuric acid, e.g. 8-25 per cent of that originally employed, and the free sulphuric acid may be reduced to 1.8-2.2 per cent by weight of the cellulose.  A further amount of water may be added at this stage, e.g. 5-15 per cent of the weight of the cellulose.  Ripening is continued at an elevated temperature, preferably higher than that of the first stage.  The acid dope may be held at a temperature between 80 DEG  and 90 DEG  C. for 50-200 minutes.  When the cellulose ester has been brought to the desired acyl value, all the remaining sulphuric acid is neutralized, e.g. with sodium acetate or carbonate, and the ripened ester is precipitated by means of water or other non-solvent.  Each of the main stages of the treatment may be effected in two or more sub-stages.