Selective Hydrogenation Of 4-Chloronitrobenzene With Supported Nickel Catalysts

Chloroaniline,as a considerable organic intermediate,has been generally applied to the synthesis of fine chemicals such as pesticides,dyes and medicines.However,the highly-cost and complicated industrial process of chloroaniline along with low selectivity are obstacles to be resolved.This paper adopts precipitation deposition method to prepare nickel-supported catalysts,exploring the relations between catalyst types,preparation methods,preparation conditions and catalytic activity and selectivity.In addition,the physical structure and surface chemical properties of catalysts are characterized by XRD,TEM,XPS,H₂-TPR and TGA-DSC.The experiments systematically detected how the types of carrier and precursor salt,active metal nickel loading amounts and the temperature of reduction and drying affected the performance of catalysts through exploring 4-chloronitrobenzene hydrogenation reaction.It has been demonstrated that when selecting TiO₂ as the carrier,Ni?NO₃?₂ as the nickel precursor,?NH₄?₂CO₃ as the precipitation,after dried at 60°C for 24 h,reduced under hydrogen atmosphere at 500°C for 4 h,the efficiency of best performance product Ni/TiO₂ is able to reach 0.91 mol _4-CAN·g_Ni^-1·h^-1 which is the best in the current literature.On the basis of existing progress,separately applying above catalysts to tank reactors and trickle bed reactors in order to investigating optimal reaction conditions.In the tank reactor,when choosing THF as solvent,reacting 40 min under 130°C and 1.0 MPa hydrogen pressure,the conversion of 4-chlorobeneze can achieve 99.9 percent,with a 4-chloroaniline selectivity of 99.8%,more importantly,dechlorination by-product formation is completely suppressed.When it comes to trickle-bed reactor,the reaction is able to reach the same conversion of 4-chlorobeneze and the same 4-chloroaniline selectivity when still selecting THF as solvent,using 20 to 40 mesh catalyst particles,reacting under 80°C and 0.3 MPa hydrogen pressure with a space velocity of 5 h^-1 and a 100 ratio of hydrogen to oil.What's more,continuous 72 h reactions will not impact the performance of catalyst.