GB510959A - Improvements in the manufacture of acetic anhydride - Google Patents

Abstract

510,959. Acetic anhydride. DREYFUS, H. Feb. 10, 1938, No. 4202. [Class 2 (iii)] Acetic anhydride is prepared by oxidising acetaldehyde by means of free oxygen in the presence of liquid aliphatic hydrocarbons in amount sufficient to dissolve all the anhydride formed and hold it in a substantially non- aqueous phase, removing the water while maintaining the anhydride in its non-aqueous phase, and separating the anhydride from the hydrocarbons, thereby reducing the loss by hydrolysis of the anhydride. As hydrocarbons there may be employed petroleum fractions, e.g. benzine and fractions boiling, e.g. up to 150-200‹C., and individual hydrocarbons, e.g. the pehtanes and hexanes. The oxidizing gas may be oxygen, air or oxygen diluted with, e.g. 5 to 30 times its own volume of an inert diluent gas, e.g. nitrogen, carbon dioxide, methane. An oxidising catalyst, e.g. copper, cobalt, nickel, manganese as acetates, 'oleates, stearates of linoleates, may be used. Pressure is preferably superatmospheric, e.g. 25-65 lb. sq. in., and the'temperature range is generally between 35-75‹C. Reaction may be made continuous by separating the aqueous andhydrocarbon layers, distilling off the hydrocarbon and returning it to the reaction zone together with fresh acetaldehyde. The oxidising gas may be led into the hydrocarbon, acetaldehyde mixture, or acetaldehyde vapour and oxidising gas is led into the hydrocarbons, the gases or vapours preferably being forced through fine jets or a series of narrow reaction tubes. Some of the hydrocarbon may be distilled off during oxidation, when part or all of the water is entrained. In examples (1) air is forced into a mixture of acetaldehyde and benzine containing .2 per cent. copper oleate heated in an autoclave under 60 lb. sq. in. pressure, to about 65‹C.; the hydrocarbon layer is separated from the aqueous layer which contains acetic acid, and acetic anhydride is recovered by distillation ; (ii) air is forced into a mixture of acetaldehyde and a petroleum fraction boiling about 80-110‹C. containing copper oleate in a number of narrow tubes heated to 60-65‹C. and under 65 lb. sq. in. pressure ; (iii) air and acetaldehyde vapour is fed into benzine containing copper oleate in a set of narrow tubes as in (ii).