GB625135A - Nitration process of toluene - Google Patents

Abstract

Tri-nitrotoluene is prepared by a process in which toluene is nitrated continuously in at least three steps by mixed acid containing at least 30 per cent free SO3, fresh acid being used in the last step and the spent acid from each step being used in the preceding step with the addition of fresh moderately concentrated, 60 per cent nitric acid. The nitrated product from each step is separated from the spent acid and treated in the next step with the stronger acid of that step. Preferably, three nitration steps are used and the conditions are adjusted so that the product from the first step is predominantly mono-nitrotoluene, that of the second is a mixture of mono- and di-nitrotoluene and that of the third tri-nitrotoluene. The fresh acid supplied at the last step should contain at least 30 per cent of free SO3 and at least 30 per cent of nitric acid and the supply is adjusted so that the spent acid contains only a few per cent of free SO3 or at most 8 per cent of water. Part of this spent acid may then be introduced into the second and another part into the first step of the process after adjustment of the nitric acid content and the residuum may be utilized if desired in the Glover tower of a sulphuric acid plant. The tri-nitrotoluene is separated in the final stage by cooling and crystallisation. A preferred embodiment of the invention is illustrated with reference to drawings.