GB825429A - Process for the oxidation of organic compounds - Google Patents

Abstract

In a process for the oxidation of organic compounds in the liquid phase by means of molecular oxygen or ozone, wherein the overhead vapours are condensed, water is decanted from the condensate and the non-aqueous condensate is returned to the reactor, the concentration of organic compounds in the vapour over the liquid in the reactor is maintained either below the lower limit or above the upper limit of the explosive concentration range by (a) introducing an incombustible inert gas, such as nitrogen or steam, into the space over the liquid in the reactor; or (b) introducing a volatile organic liquid, which is more resistant to oxidation than the compound being oxidized, into the liquid in the reactor and maintaining a suitable rate of boiling; or (c) blowing vapours of such a volatile organic liquid over the surface of the liquid-mixture in the reactor. The oxidation may be carried out in two stages, the concentration of organic compounds in the vapour being above the upper explosive limit in one reactor and below the lower explosive limit in the other reactor. Where operation is above the upper explosive limit, the concentration of the organic compound in the gas may often, after condensation, fall within the explosive range. Provision is therefore preferably made for the admission of inert diluent, e.g. nitrogen or carbon dioxide, in the exit gas line after the condenser.ALSO:In a process for the oxidation of organic compounds, e.g. the oxidation of p-xylene to terephthalic acid, in the liquid phase by means of molecular oxygen or ozone, wherein the overhead vapours are condensed, water is decanted from the condensate and the non-aqueous condensate is returned to the reactor, the concentration of organic compounds in the vapour over the liquid in the reactor is maintained either below the lower limit or above the upper limit of the explosive concentration range by (a) introducing an incombustible inert gas, such as nitrogen or steam, into the space over the liquid in the reactor, or (b) introducing a volatile organic liquid, which is more resistant to oxidation than the compound being oxidized, into the liquid in the reactor and maintaining a suitable rate of boiling, or (c) blowing vapours of such a volatile organic liquid over the surface of the liquid-mixture in the reactor. In Example 1, o-xylene is dissolved in molten benzoic acid containing benzene and catalytic amounts of manganese bromide and cobalt bromide, and is oxidized at 150 DEG C. by passing oxygen into it through a high-speed cruciform stirrer. Simultaneously, steam is blown over the liquid reaction surface. The reactor is provided with a packed reflux column and a decanter; and the benzene/o-xylene layer of the condensate is returned to the reactor by overflow. When the oxidation is complete, the reaction mixture is hydrolysed by refluxing it with water; and phthalic acid is isolated from the product. In Example 2, p-xylene is dissolved in propionic acid containing catalytic amounts of MnBr2 and CoBr2, and is treated at 137 DEG C. with oxygen. The reactor is provided with a packed reflux column and decanter; and the p-xylene/propionic acid phase of the condensate is returned to the reactor. The boil-up rate is maintained so that the concentration of propionic acid in the vapour is such that the vapour is above the higher inflammability limit. Colourless terephthalic acid is isolated from the reaction product by filtration. Example 3 relates to the same reaction as Example 2, but a lower boil-up rate is employed; and propionic acid vapour at 150 DEG C. is blown over the surface of the reaction mixture. The oxidation may be carried out in two stages, the concentration of organic compounds in the vapour being above the upper explosive limit in one reactor and below the lower explosive limit in the other reactor. Where operation is above the upper explosive limit, the concentration of the organic compounds in the gas may often, after condensation, fall within the explosive range. Provision is therefore preferably made for the admission of inert diluent, e.g. nitrogen or carbon dioxide, in the exit gas line after the condenser.