GB589480A - Improvements in and relating to the nitration of hydrocarbons - Google Patents

Abstract

In the continuous production of nitroparaffins from paraffins and nitrogen tetroxide or nitric acid in the vapour phase, a process comprises subjecting the reaction products to at least one sequence of the following operations: removing the nitroparaffins and water by condensation, oxidizing the nitric oxide in at least a portion of the remaining gaseous products to nitrogen tetroxide by means of an oxygen-containing gas and further reacting the so treated gaseous mixture under nitrating conditions. Preferably, and especially where a single nitrating zone is used, a portion of the gaseous products remaining after removal of nitroparaffins and water is purged from the system and the remainder after the oxidation step is recycled to the nitrating zone, generally together with fresh nitrating agent and paraffins. If desired, several reaction zones may be used in series with means situate between each pair of zones for removal of nitroparaffins and water, for oxidizing the nitric oxide and for preheating; fresh nitrating agent and paraffins may be introduced before any of the zones. The oxidation may be effected at temperatures up to 200 DEG C., but preferably not above 150 DEG C.; the oxidizing gas may be air, but is preferably oxygen which, if desired, may contain nitric acid to serve as the nitrating agent. To avoid explosion risks, make-up paraffin should be added to the gaseous mixture prior to the oxidation treatment and desirably the gas in the oxidation space should not contain less hydrocarbon than that in the nitration zone; the amount of gas recycled to the latter zone should preferably be such that the reaction mixture contains about 50 per cent diluents. When using paraffins containing up to 5 carbon atoms it is preferred to operate under super-atmospheric pressure. According to the Provisional Specification, a higher temperature is used when nitrating with nitric acid than with nitrogen tetroxide. The final purged gas may be treated for recovery of paraffins and oxides of nitrogen. An example illustrates the continuous nitration of propane by nitrogen tetroxide at 370 DEG C. and 75 lbs. pressure using a single converter in the manner described above, part of the nitroparaffin-free exit gases being purged and the remainder passed to an oxidation space maintained at 100 DEG C. and then recycled to the converter; the results are compared with those obtained when no recycle gas is used.