GB475466A - Improvements in or relating to the preparation of cellulose ethers - Google Patents

Abstract

Lower alkyl ethers of cellulose are separated from the mixture obtained by reacting alkali cellulose with an etherifying agent at elevated temperature under super-atmospheric pressure by a process which includes the step of discharging the reaction mixture from the etherifying chamber into water maintained at its boiling point under super-atmospheric pressure, the cellulose ether being precipitated from solution in the form of an aqueous suspension. The pressure on the aqueous cellulose ether suspension may then be released in order to flash distil the volatile constituents of the mixture. The cellulose ether may be separated from the aqueous liquid by filtration in a rotary or centrifugal filter, and washed with hot distilled water. The process is particularly useful in the manufacture of ethyl or methyl cellulose. The reaction product may be discharged under pressure into a moving current of steam-hot water mixture, and mixing is preferably carried out in a small chamber in which the ingredients are violently agitated, the discharge being forced through a perforated pipe. In an example, alkali cellulose and ethyl chloride are heated under pressure, and the reaction mixture is fed through a perforated pipe into a steam-water mixture at elevated temperature and pressure. The ethyl cellulose is precipitated in the water as fine snow-white spongy fibres. The aqueous suspension is led to an expansion chamber wherein the ethyl chloride, ethyl ether, and ethyl alcohol constituents are flashed off. The vapours from the expansion chamber are condensed. The hot ethyl cellulose suspension is centrifuged, and washed with distilled water to remove salt.