The Preparation Of Aromatic Nitriles By Ammoxidation

Ammoxidation is the most widely used method to preparing the nitriles in industry now,of which the main byproduct is water.The aromatic nitriles are generally prepared by the gas-solid phase catalytic ammoxidation of methyl aromatic compounds,but there is not a kind of ammoxidation catalyst that can be used in the ammoxidation of multiple methyl aromatic compounds.Cyanopyridine compounds are widely used in medicine,pesticide and so on,which is an important part of aromatic nitriles,but the existing ammoxidation catalysts for the ammoxidation of 2-picoline is not ideal for a lot of by-product pyridine generated.So the development of high selectivity ammoxidation catalyst is necessary.Firstly,the vanadium-titanium catalyst was prepared by mixing method,in which the content of vanadium pentoxide and titanium dioxide were 9.4%and 90.6%,respectively,and was evaluated by the ammoxidation of 2-picoline,3-picoline and 4-picoline,but the result of 2-picoline wasn’t ideal among them.The vanadium-titanium catalyst was improved by the calcination to change the pore structure of catalyst and adding another active component of molybdenum,denoted by the V-Ti-O-c catalyst and the V-Mo-Ti-O-b catalyst,and the yields of 2-cyanopyridine were raised to 86.1%and 85.6%,respectively.In addition,it was found that the stability of the catalyst was ideal.Then,the V-Ti-O-c catalyst and the V-Mo-Ti-O-b catalyst were applied in the ammoxidation of different methyl aromatic compounds,and the yields of all substrates were beyond 75%.By comparison of the reaction results of o-,m-,p-xylene,it was found that the steric effect has a big influence on the ammoxidation.While electronic effect has little impact on ammoxidation by comparing the results of toluene,4-chlorotoluene and 4-methylanisole.On the basis of the prepared catalyst,the optimum reaction process of two kinds of catalysts were determined through the orthogonal experiment with the ammoxidation of 2-picoline as a template,and the results were as follows:370℃,1:7:3:25(2-picoline/NH3/H2O/Air,molar ratio),0.18h-1 and 375℃,1:6:3:22.5,0.165h-1,respectively.Under the optimum reaction process,the yields of the V-Ti-O-c catalyst and the V-Mo-Ti-O-b catalyst were 86.8%and 86.5%,respectively.Lastly,the pilot test on the ammoxidation of 2-picoline was carried out.First of all,the adjustment of the reactor catalyst bed layer,molten salt temperature control system and cooling collection system was done.Then,the process of the ammoxidation of 2-picoline was simulated by using PR equation in the Aspen Plus to obtain the results of material balance,energy balance and the vapor generation.On basis of the optimum conditions,the yield of 2-cyanopyridine in the pilot test was 85.1%,and the vapor generation under preheating raw material and not were 0.21kg/hr and 0.69kg/hr,respectively.In the end,the production capacity of reaction single tube was estimated,and the result was 3.3 tons/year.