GB738808A - A method for the oxidation of cycloalkanes - Google Patents

Abstract

A method of oxidizing cycloalkanes comprises the steps of subjecting a cycloalkane containing at least four cyclic carbon atoms to oxidation by means of a free-oxygen-containing gas at a temperature of from 100 DEG to 200 DEG C. and at a pressure at least sufficient to maintain the cycloalkane in the liquid phase, separating the resultant reaction mixture into an upper liquid hydrocarbon-rich phase and a lower phase rich in oxy-compounds containing water and some dissolved hydrocarbons, distilling the liquid oxy-compound-rich phase so as to remove hydrocarbons and water therefrom, withdrawing the residual material containing the oxy compounds from which the water and hydrocarbons have been removed from the distillation step; and further oxidizing this residual material by <PICT:0738808/IV (b)/1> means of a free-oxygen-containing gas at a temperature of from 100 DEG to 170 DEG C. and at a pressure at least sufficient to maintain the residual material in the liquid phase. Cycloalkanes mentioned are cyclohexane, cyclopentane, cyclobutane or homologues such as the methyl-, dimethyl-, ethyl-substituted cyclic hydrocarbons or their homologues with the production of the corresponding dibasic acids such as adipic, glutaric or succinic acids or their homologues. The products also include ketones and alcohols, e.g. from cyclohexane adipic acid, cyclohexanol and cyclohexanone are obtained. Catalysts which may be used include polyvalent metals of atomic weights between 50 and 200 which may be used in the finely divided state or as organic or inorganic salts or oxides. Specific metals include cerium, cobalt, copper, manganese and uranium. Specific catalysts mentioned include vanadium, cerium and cobalt chlorides, manganese naphthenate, manganese acetate alone or together with barium or cobalt permanganate, sodium cobaltinitrite or mixtures of two or more of such compounds. Promoters which may also be present include salts of alkali- and alkaline-earth metals, e.g. barium, magnesium and potassium acetates, butyrates and propionates. In the apparatus in the drawing preheated liquid cyclohexane and air are fed through lines 1 and 3 into tower 2 maintained at elevated temperature. Spent air, entrained cyclohexane vapours and water are taken overhead through line 5 and cooled in heat exchanger 6. The condensate is passed to separator 14 and spent air vented through line 7. The reaction product is withdrawn through line 4 from tower 2, cooled in chiller 29 and filtered on rotatory filter 30. Adipic acid is collected in hopper 31 and the filtrate is fed to separator 9 through line 32 where separation takes place into a hydrocarbon-rich layer which is recycled through lines 10, 33 and 1 to tower 2 and an oxy-compound-rich phase which is passed to stripper tower 12 where cyclohexane and water are distilled off through line 13, water is removed in separator 14 and hydrocarbon is recycled to the oxidation tower. The oxy-compounds are further oxidized with air in tower 17 introduced through line 19 and the oxidation product is removed through line 18 and combined with the reaction product from tower 2, the combined reaction products then being cooled and the adipic acid filtered. Excess water may be introduced into tower 12 to permit recovery of dissolved cyclohexane as an azeotropic mixture. In the example air is blown through cyclohexane at elevated temperature and pressure and the product separated into a hydrocarbon-rich upper layer and an oxy-compound-rich slurry, the former being recycled. The oxy-compound-rich slurry is chilled and filtered to remove most of the adipic acid produced, dissolved cyclohexane and water are removed from the filtrate which is then further oxidized with air under pressure at elevated temperature to obtain additional adipic acid.