Studies on the Catalytic Synthesis of Aromatic Nitriles (Part 1)

Abstract

A vapour phase catalytic ammoxidation reaction using SO2 as an oxidizing agent was investigated as follows: C6H5CH3+NH3+SO2→C4H5CN+2H2O+H2S+2.0kcal/mole. This reaction is a little exothermic and the equilibrium constants are very large at wide range of temperatures (Kp=4×108: at 300-500°C). Therefore, the reaction is thermochemically very favourable and is free from trouble of deep oxidation as SO2 is a weak oxidizing agent.In consequence of the investigation with various catalysts it was found that the reaction was promoted even by γ-Al2O3 alone into benzonitrile at a yield of Ca. 70(mole)%/fed toluene and moreover the activity of γ-Al2O3 improved by the addition of CuO, Fe2O3, Cr2O3, MoO3, WO3 and V2O5. The conversion of 93.9 (mole) %/fed toluene and the selectivity of 99.2 (mole)% to benzonitrile were obtained by the γ-Al2O3-V2O5-MoO3 catalyst at 430°C.The preferable molar ratio of reactants was NH3_??_SO2_??_toluene. The maximum yield of benzonitrile was observed at 440-470°C. The activity of catalyst changed with the reaction time. In the case of γ-Al2O3 the activity increased gradually during the period of Ca. 1.5hrs after the start of reaction and then began to decrease after 26-27hrs. This decay of catalyst can be explained by the deposition of sulphureous and carbonaceous matters over the catalyst surface. The decayed catalyst was regenerated to 98% of the activity before the decay by means of slow burning of these matters in the air current.