A Study Of Sulfonated Activated Carbon-supported Gold Catalyst For Acetylene Hydrochlorination

Polyvinyl chloride(PVC)is one of the widely used raw materials in the plastics industry.In China,vinyl chloride monomer(VCM),the key material that PVC is made,is mostly produced by hydrochlorination of acetylene using activated carbon supported mercury chloride(Hg/AC)as the catalyst.It is known that mercury chloride is a kind of volatile and highly toxic chemical.In addition,our country has made it clear that,in 2020,to reduce the amount of mercury usage to half of the level in 2010,and in 2030,to obsolete the PVC process involving Hg.Therefore,it is imperative to efficient and mercury-free catalyst for the VCM production.The study found that the AC-supported Au catalysts(Au/AC)are most likely to replace Hg/AC,but there are still several problems to be solved before the Au/AC catalysts are practical.In particularly,these are including:(1)to solve the catalyst deactivation caused by the aggregation of Au particles due to easy reduction of active Au3+ species to Au0 during the reaction and the carbon deposition on the catalyst surfaces;(2)to develop the Au catalyst preparation method for ultra low loading with high activity due to the high price of gold.This thesis,based on previous studies,proposed a new method for the preparation of supported Au catalyst by using sulfuric acid modified AC(sulfonated AC)as the carrier.The results indicate that the catalyst has excellent performance for the acetylene hydrochlorination to produce vinyl chloride.The structures of the supports and the catalysts are investigated by means of a series of spectroscopic techniques.On this basis,combining with theoretical calculation,the reaction mechanism of acetylene hydrochlorination over the sulfonated AC supported Au catalyst is discussed for the purpose of developing novel efficient gold catalysts for the acetylene hydrochlorination.The preliminary experimental results indicated that the Au supported on a potassium peroxydisulfate(K2S2O8)modified AC showed considerable promoting effect for the hydrochlorination of acetylene.The finding,after in-depth analysis,was believably caused by the fact that the S2O82-species had been changed to SO42-on the AC surfaces in the process of catalyst preparation.Then,the sulfuric acid modified AC was used as carrier to prepare the supported gold catalyst(denoted as Au/n-SO3H-AC,n as the mass fraction of S).The results showed that the Au/n-SO3H-AC catalyst could greatly improve the performance of hydrochlorination of acetylene,affording a volcano type change for the acetylene conversion with the increase of sulfuric acid.When the dosage of sulfuric acid was set at n = 1.5%,the catalyst performed the best and the most stable.The characterization results of the related catalysts proposed the following conclusions:(1)the presence of-SO3H species can effectively inhibit the aggregation of Au particle size,increase the surface defects of AC carrier,so as to improve the active sites;(2)-SO3H species can effectively stabilize Au3+ and thus improve the stability of the catalyst;(3)the introduction of-SO3H can effectively inhibit the performations of coke and oligomers on the catalyst surface,prevent covering the active sites of catalyst,thus increasing the activity of the catalyst.Based on the above results,the method was further extended to the preparation of other catalysts such as Pd,Pt,Ru and Cu for the acetylene hydrochlorination.The results showed that compared with the conventional Au/AC catalyst,the sulfonated AC supported other metal catalysts also presented higher catalytic activity,indicating that the sulfuric acid modified AC can effectively stabilize the high valence metal.In addition,studies with theoretical calculation were employed to deepen the understanding of the structure-performanece relationship and catalytic mechanism.The results showed that the key species of Au/n-SO3H-AC catalysts with high reactivity is ascribable to the presence of-SO3H;-SO3H and Au can form a specific AC-SO3-AuCl3 chelate species which effectively stabilize the active Au in high valence Au3+.DFT calculation proposed a plausible reaction machine for the acetylene hydrochlorination over the Au/n-SO3H-AC atalyst.The use of sulfonated AC supported Au the catalyst can lower the activation energy of hydrochlorination,benefiting to the catalytic cycle.Finally,the calculation results also pointed out that both sulfinic and sulfonic groups are capable of enhancing the activity of the Au catalysts for the acetylene hydrochlorination.