The Process And Mechanism Of The Selective Hydrogenation Of Acrylonitrile

Propionitrile is widely applied in chemical industry as a useful solvent,reagent and intermediate.The selective hydrogenation of acrylonitrile is one of the greenest processes to produce propionitrile.Acrylonitrile is a kind of ?,?-unsaturated nitrile and it has both C=C and C?N bonds,so it is important to control the hydrogenation process according to analysing samples to avoid the hydrogenation of C?N bond.But it is dangerous to sample in this reaction because of the highly toxic of the reagent and product.Futhermore,it is lack of kinetic and mechanism studies of this reaction,but both of them are significant to the industrialization and understanding of the selected hydrogenation of acrylonitrile.Firstly,we test some kinds of hydrogenation catalysts,and we found Raney Ni,Pd/C and Pt/C show high reactivity.By analysing samples in the reactions over different catalysts,we found the C=N bond will not be hydrogenated if the acrylonitrile remains in the reaction mixture when we use Raney Ni as catalyst,but when we use Pd/C or Pt/C as catalyst the C?N bond can be easily hydrogenated which causes the bad selectivity.Therefore we chose Raney Ni as the hydrogenation catalyst of this reaction,but it is important to control the hydrogenation process to avoid the excessive hydrogenation.In this dissertation,we took advantage of detecting the hydriding rate and the hydrogen uptake to determine the reaction end point which is more safety and accurate than the sampling method.On the basis of the Raney Ni catalyst,the optimum reaction process were determined through the parallel experiment and the results were as follows:90.0?,4.00MPa,none solvent,1.8wt%catalyst dosage and stopping the reaction when the hydriding rate reduce to 25%.Under the optimum reaction process,the yields of the propionitrile was 93.7%and the average yield was 91.0%through 15 times recycle of the catalyst.Then,we studied the kinetic of the hydrogenation of the acrylonitrile with the catalysis of Raney Ni.Through analyzing the mass transfer processe and the kinetic experimental data,a macro kinetic model of the reaction was set up and then the model parameter was determined,the apparent activation energy of this reaction is 31.3kJ/mol.This reaction is controlled by the chemical process on the Raney Ni surfaces.The apparent rate is a zero-order reaction to acrylonitrile and one-order reaction to liquid hydrogen concentration.Lastly,we investigated the reaction of acrylonitrile on Raney Ni and Pd/C by first-principles density-functional calculations.We found the hydrogenation of propionitrile had a larger barrier than the hydrogenation of acrylonitrile on the Raney Ni surface,contrary to the results on the Pd/C surface.These calculated results implied the propionitrile was much more stable when the reaction was catalyzed by Raney Ni than Pd/C,which explained the sampling results before and support the method of detecting hydriding rate and the hydrogen uptake to determine the reaction end point.