Patent GB-688486-A (GB)
Title: Manufacture of cellulose ethers
IPC: C08B11/08
Filed: 1950-05-31
Abstract: Hydroxyalkyl cellulose ethers are made by mixing cellulose material in particulate form with a secondary 3-carbon or a secondary or tertiary 4- or 5-carbon aliphatic alcohol or a mixture thereof in the presence of an alkali, reacting the cellulose material in the presence of the alkali and the alcohol with a hydroxyalkylating agent, and obtaining the hydroxyalkyl cellulose ether thus produced in substantially the same particulate form as the cellulose starting material.  The latter may be chemical cotton (i.e. chemically-purified cotton), cotton linters, or wood pulp, and it may be bulk dried, sheet dried, or pretreated with alkali to form alkali cellulose in order to prepare it for size reduction to particulate form.  The alcohols used may be 2-propanol, 2-butanol, 2-methyl-2-propanol, 2-pentanol, 3-pentanol, 3-methyl-2-butanol or 2-methyl-2-butanol. They are taken in at least a proportion sufficient to prevent the cellulose ether formed from dissolving in the reaction mixture, e.g. at least about 2 parts by weight of alcohol for each part by weight of water in the reaction mixture.  In general the alcohol : cellulose ratio used corresponds to about 2-50 c.cm. and preferably 10-25 c.cm. of alcohol to one gram of cellulose. The alcohol may be anhydrous or hydrous, e.g. in the form of the constant boiling mixture in which it is obtained on separation from water.  The alkali used is usually sodium hydroxide, but any of the strong alkali hydroxides, including potassium hydroxide, is suitable. Ordinarily the ratio of caustic alkali to cellulose should be about 0.05 to 10, and preferably about 0.2 to 0.5, parts of caustic alkali per part of cellulose.  The water content of the reaction mixture may be one part by weight to about 0.02 to 3.0 and preferably about 0.04 to 1.0 parts by weight of caustic alkali.  The hydroxyalkyl ethers which may be prepared as above include all those which are alkali-soluble and water-soluble such as hydroxyethyl, hydroxypropyl and hydroxybutyl cellulose.  The hydroxyalkylating agent may be ethylene oxide, propylene oxide, butylene oxide, glycide alcohol, epichlorhydrin, butadiene monoxide, or ethylene-chlorhydrin.  At least 0.1 mole., and preferably about 0.4-20 moles., of hydroxyalkylating agent is used per anhydroglucose unit of the cellulose.  With ethylene oxide at least 0.025 part and preferably about 0.1-5.0 parts ethylene oxide are used per part of cellulose by weight.  The degree of substitution of the cellulose ethers produced is at least about 0.05 and preferably about 0.10-2.0 hydroxyalkyl groups for each anhydroglucose unit of the cellulose.  The reaction temperature may be about 20-150 DEG  C. and, for preparing hydroxyethyl cellulose, preferably about 50-75 DEG  C. with a reaction time of about 5-6 hours.  In an example a suspension of 30 grams of shredded cotton linters and 850 c.cms. of anhydrous tertiary-butyl alcohol are vigorously agitated at room temperature with 60 grams of 20 per cent by weight aqueous sodium hydroxide solution, and the mixture is then agitated with a solution of 17.8 grms. of ethylene oxide in 50 c.cms. of tertiary-butyl alcohol for 6 hours at 29-34 DEG  C.  The mixture is allowed to stand at room temperature for about 16 hours.  The liquor is drained off and the hydroxyethyl cellulose residue mixed with a 70 per cent by weight solution of methanol in water, neutralized with acetic acid, washed free of salts with 70 per cent methanol, dehydrated with anhydrous methanol and dried at 70 DEG  C.  An example is given also of the preparation by a similar method (but using a higher reaction temperature under pressure and longer reaction time) of hydroxypropyl cellulose, tertiary butyl alcohol being the diluent and propylene oxide the etherifying agent.