Study On Stabilization Mechanism And Catalytic Performance Of Low Mercury Catalyst For Acetylene Hydrochlorination

The production of vinyl chloride monomers is mainly based on calcium carbide process in China.At present,mercury chloride catalyst supported on activated carbon is used in the industrialization of this process.Mercury chloride is a covalent compound and the intermolecular force is van der Waals force,which is very volatile.The volatilization of mercuric chloride in catalyst can not only cause catalyst deactivation,but also cause serious environmental pollution.Although mercury-free catalysts have attracted extensive research,it is difficult to obtain large-scale promotion when the cost and performance of mercury-free catalysts can not be taken into account.Therefore,in the immature stage of mercury-free catalytic technology,the development of low mercury catalysts with high stability has become the key to the green and sustainable development of vinyl chloride industry by calcium carbide process.1.Firstly,the stabilization mechanism of ultra-stable low mercury catalysts was systematically studied by Density Functional Theory?DFT?calculation and experiment.It is found that the carbon defect sites near the C=O can form strong chemical bonds with HgCl₂ molecules.The binding energy can reach up to 120-130kJ/mol.The existence of chemical adsorption can greatly improve the thermal stability of the catalyst,thus reducing the volatilization of HgCl₂ in the catalyst.The stabilization mechanism of ultra-stable low mercury catalysts was first analyzed theoretically,which provided theoretical basis and reference for the development of low mercury catalysts with high activity and high stability.2.Secondly,nitrogen-doped activated carbon was prepared by a simple heat treatment method and the effect of nitrogen-doping on the performance of activated carbon supported HgCl₂ catalysts was investigated.It is found that the catalytic activity of low mercury catalyst can be significantly improved by adding nitrogen into activated carbon.The acetylene conversion over low mercury catalyst supported on nitrogen-doped activated carbon can reach more than 76%under 180 ^oC,1000 h^-1condition.The higher nitrogen content of the carrier,the higher activity of the catalysts is.3.Finally,the comprehensive performance of low mercury catalyst produced in ton scale was evaluated and the reaction conditions were optimized.The optimum reaction conditions of the catalyst were 140-160 ^oC and 20-40 h^-1.The catalyst has been used in industrial converter for more than 12000 hours,which showed excellent performance of acetylene hydrochlorination.Each ton of PVC production consumed34.00 g of mercury,which met the highest standard of Class C in the"Demonstration Project of Mercury Reduction and Minimization for PVC Production in China".