Patent GB-391802-A (GB)
Title: Improvements in or relating to the manufacture of aliphatic anhydrides
Filed: 1931-11-03
Abstract: Aliphatic anhydrides and ethers are produced by thermally decomposing esters of glycols or other polyhydric alcohols in which not more than one oxygen atom is attached to any individual carbon atom.  The reaction may be effected at 200-1000 DEG  C. at any suitable pressure, such as atmospheric or subatmospheric pressure, and catalysts may be employed such as a salt of the acid whose anhydride is to be produced, zinc halides, sulphuric or phosphoric acid, surface catalysts such as pumice, silica gel or kieselguhr, and catalysts which promote the production of aliphatic anhydrides from the corresponding acids.  When catalysts are employed a moderate or low temperature should be used such as 350 DEG  C.  The reaction tubes may be made of or lined with copper, fused silica, chrome-nickel steels or earthenware, and whether catalysts are used or not the apparatus may contain balls of wire or cellular structures of copper or other metal of high conductivity.  The ester may be diluted with nitrogen, carbon dioxide or the like.  The reaction may be effected by passing the ester vapour through baths of liquid or molten materials which may consist of or contain catalysts, such as molten zinc chloride such as promote the production of anhydrides from the corresponding acids; or the ester may be sprayed or injected into the reaction zone or dropped on to heated surfaces which may be catalytic. When the vapour of the ester is to be used, it may be preheated in tubes preferably containing filling materials of good conductivity such as copper wire or turnings or by passage through a bath of molten or liquid material or by heat exchange with the reaction products.  The reaction may be effected as a batch process by heating the ester with a dehydrating or etherifying catalyst at 200-300 DEG  C.  The process may be used for the concentration of aqueous aliphatic acids by reacting acetic acid with ethylene oxide if desired in presence of zinc or aluminium chloride, the resulting glycol diacetate being preferably concentrated (which may be done by decantation, centrifuging, or distillation with or without azeotropic liquids) and then thermally decomposed; any water present may be separated before allowing the anhydride to condense as described in Specifications 289,972, 298,667, 303,772, 310,863, [all in Class 2 (iii), Dyes &c.], and 354,199, or the water may be allowed to combine with the anhydride (with or without the addition of more water) to produce acid of the concentration desired.  The ethylene oxide or other ether produced may be separated from the anhydride in any suitable way; for instance, if highly volatile it may be recovered after condensation of the anhydride and water if present.  It is preferred to concentrate very dilute acids up to 50-70 per cent by other methods before using them for the preparation of the glycol ester.  In examples (1) ethylene diacetate vapour is passed rapidly at 400 DEG  C. through a copper tube containing pieces of iron-free pumice coated with phosphoric acid, the product being condensed and fractionated; (2) ethylene diacetate vapour is fed through jets into molten zinc chloride at 380 DEG  C., the product being treated as before.  Specifications 256,663 and 279,916, [both in Class 2 (iii), Dyes &c.], also are referred to.