Study On The Application Of Nickel-based Catalyst In The Hydrogenation Of Acetylene To Ethylene

As an important chemical raw material,ethylene is one of the indicators to measure the level of industrial development of a country.At present,the production of ethylene in China is mainly through the cracking of naphtha.As China is short of oil resources but rich in coal resources,and the process of producing ethylene by calcium carbide acetylene method is mature,the use of calcium carbide acetylene method to obtain acetylene and its partial hydrogenation to produce ethylene can not only alleviate the problem of oil shortage in China,but also make better use of coal resources.The current research on acetylene hydrogenation to ethylene is divided into two main categories,hydrogenation of acetylene in ethylene-rich streams;and hydrogenation of acetylene at high concentrations.Ni,a non-precious metal of the same group as Pd,is also active in the hydrogenation of acetylene to ethylene,but it is less active than Pd,and Ni can also lead to over-hydrogenation of acetylene and has the problem of ethylene selectivity.The second problem is that Ni can also lead to over-hydrogenation of acetylene and has a low ethylene selectivity.In this thesis,catalyst preparation methods were explored by comparing different nitrogen sources and doping methods.To address the problem of nitrogen loss in the preparation process,phosphorus,which is homologous to nitrogen,was chosen as a nitrogen substitute for phosphorus doping of Ni catalysts to investigate the application of nickel phosphide in the acetylene hydrogenation to ethylene reaction.The main studies are as follows:The Ni/SiO₂-C₁₈ catalyst was prepared by using oleylamine as a complex obtained by coordination of oleylamine with Ni²⁺,inducing the assembly and shaping of siloxatetrahedra generated by the hydrolysis of tetraethyl silicate around it,and then removing the template by roasting in air(as the oleylamine carbon chain has 18 carbon atoms,C₁₈ for short,the remaining primary amines are also named after the number of carbon atoms),and by increasing the chain length of the template molecular chains,modulating the specific surface area of the catalyst,Ni/SiO₂-C₁₈ showed good activity and stability under optimised reaction conditions.At GHSV（C₂H₂）=10000 m L g^-1 h^-1,T=180°C and V（H₂）/V（C₂H₂）=6,the acetylene conversion was still able to reach 85%and the ethylene selectivity was stable at 50%-60%after 129 h of the reaction.TEM characterisation of the catalysts revealed that the catalysts prepared by the non-template method showed significant agglomerative clustering of the metal Ni and the catalysts prepared by the template method had a better dispersion of the high specific surface area,which was consistent with the XRD characterisation results.The experimental results indicated that the catalysts prepared by the template method had better dispersion of Ni metal and better activity and stability of the catalysts.In order to improve the selectivity of ethylene,the Ni catalysts were modified with melamine,4-hydroxypyridine and butanedione-oxime as nitrogen sources,and Ni/SiO₂-4-hydroxypyridine-phenolic resin,Ni/SiO₂-melamine-phenolic resin and Ni/SiO₂-butanedione-oxime catalysts were prepared by impregnation,roasting and reduction,and it was found that Ni/SiO₂-butanedione-oxime had the optimal selectivity for the acetylene hydrogenation reaction with optimum selectivity and optimal catalytic performance at the optimum conditions GHSV（C₂H₂）=10000 m L g^-1 h^-1,T=200°C and V（H₂）/V（C₂H₂）=4.The ethylene selectivity was improved to 74.6%relative to the 50-60%selectivity of the Ni/SiO₂-C₁₈catalyst.Characterisation by BET,XRD and TEM showed that the reason for the better selectivity presented by butanedione oxime as a nitrogen source was the complete preservation of the pore channel during nitrogen doping and the better dispersion of metallic nickel.To enhance the catalyst stability,Ni₂P/SiO₂ catalysts were prepared by roasting NiO/SiO₂ and sodium hypophosphite under argon atmosphere.The catalytic performance was optimized at the optimum conditions of 10000 m L g^-1h^-1,240°C and V（H₂）/V（C₂H₂）=4.Compared to Ni/SiO₂-butanedione-oxime,the time taken to reduce the acetylene conversion to 85%was increased from 16 h to 30 h and the ethylene selectivity was increased from 74.6%to 80.0%.XRD characterisation demonstrated the formation of Ni₂P/SiO₂ and no agglomeration of Ni₂P occurred by roasting at 350°C.