Patent GB-389534-A (GB)
Title: Improvements in or relating to the manufacture of ether derivatives of carbohydrates, particularly cellulose
IPC: C08B11/20
Filed: 1931-08-14
Abstract: Hydroxyalkyl ethers of carbohydrates which are incompletely soluble in caustic alkali solutions at above 0 DEG  C. have their solubility increased by mixing the ether with a solution of caustic alkali and refrigerating until a mass of crystals forms. The caustic soda may be of about 2-10 per cent, and preferably of 4-6 per cent strength.  The process is particularly applicable to the treatment of hydroxyalkyl ethers of cellulose in which substantially less than one hydroxyl hydrogen atom in each cellulose unit is replaced by an hydroxyalkyl radicle, for example, those made according to the process of Specification 392,206, or similar products obtained by the use of alkylene oxides or chlorhydrins as etherifying agents.  When the refrigeration is carried out continuously with production of the ether from alkali cellulose and an alkylene oxide, it is necessary to dilute the ether obtained until the strength of the caustic soda solution is about 2-10 per cent, and preferably 4,75 per cent.  The solution is then refrigerated until a mass of crystals appears, i.e. at about -20 DEG  C., which is the most effective temperature, although lower temperatures may be used.  The mass is melted and, if necessary, caustic soda added to prevent gelling of the ether, the lower the hydroxyalkyl content of the ether, the more caustic soda being required, e.g. an ether containing 7 per cent ethylene oxide requires at least a 6 per cent caustic soda solution to dissolve it. This results in an ether concentration (5-6 per cent) which is too low for many purposes, and an alternative method consists in removing one-third of the reaction product after etherification, neutralizing the alkali and returning to the bulk of the reaction product, after which the mass is diluted to a caustic soda strength of 4,75 (less water being required than before), refrigerated and dissolved in the manner already described.  This gives a solution containing 8-8,5 per cent of ether.  Again, the entire reaction mass may be acidified, washed, and then refrigerated in the desired amount of caustic soda solution.  The following examples are given: (1a) Wood pulp in sheets is mercerized in 30 per cent caustic soda solution, squeezed, shredded, and caused to react with about 7 per cent of its weight of gaseous ethylene oxide.  The product is diluted to bring the caustic soda solution strength down to 4,75 per cent, and the mass refrigerated at -20 DEG  C.  The frozen mass is allowed to melt and enough caustic soda is added to produce a final 6 per cent caustic soda solution.  (1b) After etherification as in (1a), one-third of the reaction mass is removed and neutralized, returned to the two-thirds portion, the mass is then diluted with water to bring the caustic soda concentration to about 4,75 per cent, and the freezing carried out as before. The final solution may be extruded into an acid coagulating bath to produce films, filaments, &c.  (2) The procedure is as in (1) except that 12 per cent of ethylene oxide is used, and the product dissolved in a 4-5 per cent caustic soda solution.  (3) Alkali cellulose made as in (1) is caused to react with 12,4 per cent of its weight of propylene oxide.  The refrigeration and isolation of the product proceed in the manner of the first example.  (4) Wood pulp is treated with a 40 per cent caustic soda solution, squeezed, shredded, and caused to react with 18 per cent of anhydrous ethylene chlorhydrin.  The process may be continued as in (1), or the reaction mass diluted to bring the caustic soda concentration to 6-10 per cent after which it is neutralized, and the precipitated ether washed and refrigerated in a 4,75 per cent caustic soda solution in amount sufficient to produce an 8,5 per cent ether concentration.  (5) The ethylene chlorhydrin of example (4) is replaced by 22,5 per cent of anhydrous glycerol monochlorhydrin.  (6) Alpha-cellulose pulp containing 8,5 per cent of moisture is mercerized in 30 per cent caustic soda, squeezed to 3,5 times its weight, shredded, aged for 21 hours, and reacted with 12 per cent of ethylene oxide.  The ether is then agitated with 15 per cent of benzoyl chloride in the presence of benzol, and the cellulose hydroxyethyl ether benzoate dissolved in 4,75 per cent caustic soda solution, frozen, and thawed as in (1) or (2).  A 7,5 per cent solution of the product in 7,5 per cent caustic soda solution may be used in the preparation of films, filaments, and the like.  The alkali cellulose may be first benzoylated and then etherified.  In the drawings (not shown) a number of curves are given showing the effect of refrigeration on the solubilities of various hydroxyalkylethers in caustic soda and caustic potash solutions. The solutions of the products may be extruded in the form of filaments, films, tubes, &c. into coagulating baths, or made into bottle caps, plastic mixtures, insulating goods, sizes, adhesives, and the like. The Specification as open to inspection under Sect. 91 refers also to the production of hydroxyalkyl-ethers from starches or sugars such as cane sugar and glucose, and states that the refrigeration process may be applied to the starch ethers.  This subject-matter does not appear in the Specification as accepted.