Improvements in the nitration of aromatic hydrocarbons

摘要

Metaphosphate catalysts, suitable for nitrating aromatic hydrocarbons in the vapour phase using nitric acid or nitrogen dioxide, are prepared by dissolving the metallic oxides, hydroxides, oxalates or carbonates and sometimes the metals themselves in orthophosphoric acid, evaporating to dryness and drying the solid catalyst at 250 to 400 DEG C. Phosphoric acid catalysts, for the same purpose, are made by calcining a mixture of a phosphoric acid, e.g., o- or pyro. phosphoric acid and a solid absorbent g. Kieselguhr, at 180 to 400 DEG C. Specification 463,272 is referred to.ALSO:Mono-nitro derivatives of aromatic hydrocarbons are obtained (in a process which may be used continuously) by nitrating the corresponding hydrocarbon in the vapour phase using nitric acid or nitrogen dioxide and a catalyst selected from the metallic metaphosphates, boron phosphate, solid and sup ported phosphoric acid catalysts. Specified products are: mono-nitrobenzene and mononitro alkyl benzenes such as mono-nitrotoluenes, mono-nitro xylenes and mono-nitroethylbenzenes. Specified catalysts are: calcium, magnesium, cadmium, nickel, ferric, ferrosoferric, strontium, copper and potassium metaphosphates. The nitrogen dioxide may be used as such, or after having been made in situ by using nitric oxide and oxygen, nitrogen trioxide and oxygen, or nitrogen pentoxide. Advantageously in the production of mononitro benzene, the molar ratio of benzene to nitric acid ranges from 3 : 1 to 1 :. Generally, the reaction temperature ranges from 130 DEG to 430 DEG C., and ordinary or elevated pressure is used. In examples: (1) an apparatus illustrated schematically, in the Figure comprises nitric acid and benzene feed tanks: (1) and (2) connected to separate vaporisers (3) and (4) leading to a converter (5) of stainless steel provided with a glass liner and connected to a condenser (6). The condensate-comprising aqueous nitric acid and an oily layer, collects in catch pot 7 while the gaseous products are passed to oxidiser (8) in which the nitric oxide is oxidised to nitrogen dioxide by means of oxygen (e.g. air) and then to the absorber (9) in which the nitrogen dioxide is absorbed in water. The condensate in 7 is passed to the decanter 10 and there separated into an oily layer and an aqueous nitric acid layer which are passed respectively to the benzene stripping still 12 attached to a condenser 13 (or two condensers in series) for the stripped benzene which is recycled to the feed tank 2; and to the still 17 (to which also that from absorber 9 is led) for concentrating the nitric acid to constant boiling strength and thence to feed tank 1. In example (2) benzene and 98 per cent nitric acid are vaporised in separate glass vessels and the vapours are heated in a glass converter filled with granules of calcium metaphosphate at a maximum temperature of 175 DEG C. The benzene and nitro benzene in the oily layer of the condensate are separated by distillation. Specification 463,272, [Group III], is referred to.