GB737439A - A process for preparing terephthalic acids - Google Patents

Abstract

In a process for preparing terephthalic acid, para-diisopropyl benzene is oxidized by means of oxygen or a gaseous mixture containing free oxygen, such as air, in a medium consisting mainly of an organic acid in which para-diisopropyl benzene is soluble and in the presence of a catalyst comprising a manganese compound together with either a cobalt compound or a barium compound or both a cobalt compound and a barium compound. Organic acids mentioned include saturated fatty acids with from 2 to 8 carbon atoms, e.g. acetic, propionic and butyric acids. Preferred salts of manganese, cobalt and barium for use as catalysts are those of the same acids as constitute the solvent or naphthenates may be used. Further para-diisopropyl benzene may be added during the reaction. The process may be carried out continuously, further catalyst being added during the reaction. The reaction may be carred out at atmospheric or superatmospheric pressures and vapours leaving the reaction mixture may be partially or completely condensed and recycled. In examples terephthalic acid is obtained by passing oxygen into a mixture of para-diisopropyl benzene, propionic acid and manganese and cobalt acetates at elevated temperature, low boiling products, e.g. aldehydes and esters, being distilled off during the reaction and the precipitate separated and worked with alcohol (1); in a similar process some terephthalic acid is removed intermediately (2); terephthalic acid is obtained by passing air into a heated mixture of diisopropyl benzene, glacial acetic acid and manganese and cobalt acetates in a V2A steel autoclave at elevated pressure, so as to maintain an elevated pressure (3); in a process similar to (1) fresh diisopropyl benzene and catalyst is added during the reaction and terephthalic acid is filtered off (4); in a similar process butyric acid is employed (5); and in a process similar to (1) para-diisopropyl benzene dissolved in acetic acid is treated in a stainless steel autoclave at elevated temperatures with air at various elevated pressures in the presence of various proportions of cobalt and manganese acetate catalysts. The rates of para-diisopropyl benzene consumption and terephthalic acid production in examples (4) and (5) are expressed in graphs.