Preparation And Performance Of Zeolite-supported On Supported Palladium Catalysts For Acetylene Hydrochlorination

Vinyl chloride monomer （VCM） which is widely used in all walks of life is thebasis of the synthesis of a variety of chemical products, and VCM is mainly used forthe production of polyvinyl chioride （PVC）. Currently, acetylene hydrochlorinationmethod （acetylene method）, ethylene method and ethane method are mainly used forVCM in industry. In China,where coal resources are vast but oil and gas is poor,acetylene hydrochlorination is still a main technology of producing VCM. However,the industrial catalyst for this process is based on mercuric chloride supported onactivited carbon （HgCl₂/C）, which brought troubles in pollution to environment andhealth to human beings with the highly toxicity and the loss of volatile activecomponents （HgCl₂, Hg） during the reaction. Moreover, the mercury resources are inshort supply recently. Hence, exploring a new cost-effective and environment friendlynon-mercury catalyst is needed for the sustainable PVC production.Nonmercuric catalysts for hydrochlorination of acetylene were designed, in orderto eliminate and reduce the pollution for chlor-alkali industry, based on sufficientstudies and references. A series of PdCl₂/MY catalysts, in which precious metals andmolecular sieves were used as active components and supports, respectively, wereprepared with incipient wetness impregnation. Catalytic performances of the catalystswere investigated and process conditions were optimized. The surface morphology,structure parameters and related physical and chemical properties of supports andcatalysts were characterized. The comparative study of these catalysts for thehydrochlorination of acetylene is described and the deactivated reasons are discussed.The following conclusions are included:（1） Different zeolites were investigated and MY zeolite is discovered to be activeto the acetylene hydrochlorination. The potential of the catalyst for the acetylenehydrochlorination was explored at temperature160℃, V（HCl）/V（C2H2）=1.25and gas hourly space velocity of C2H2=110h^-1. The PdCl₂/MY catalyst exhibited highcatalytic properties: acetylene conversion is about99.78%, vinyl chloride selectivityis about90%and the lifetime is about140min. On the basis of the results, the loadingof Pd, reaction temperature and space velocities were studied in detail. The optimizedreaction conditions were obtained: the loading of Pd is no less than0.5wt%,temperature is from90-160℃, the total gas hourly space velocity is around110h^-1.After characterization, Analysis results showed that the active component Pd isuniformly dispersed on the catalysts’ surface. The generation of polymers, carbondepositions, and the decrease of the catalysts’ BET surface areas might course thedeactivation of the catalyst.（2） Different treatment methods were influences on the catalytic performance inacetylene hydrochlorination. After the treatment of B and N, the initial activity of thecatalyst are increased: acetylene conversion is about99.89%, vinyl chlorideselectivity is about95.66%; the lifetime of the K-HY catalyst is extended to3hours.The changes of the catalysts’ surface acidity is maybe related to the activity of thecatalyst; After calcination in different temperature, the activity of the catalysts whichwere calcinated is worse than the catalyst which is untreated. This can be explainedthat the structure of the zeolites were destroyed and collapsed in the process ofcalcination, leading to the catalyst deactivation. Besides, the coke on its surface isanother reason.（3） Different metal chlorides as promoters were studied generally in acetylenehydrochlorination. K、C、L、Z are discovered to have better effects. The resultspointed that the catalytic activity order is: K1> C2> C1> L> Z> K2. Due to addingK, the dispersibility of Pd and the synergistic interation between metals are improved,which make the activity of catalysts increasing. The selectivity of catalysts isenhancing with the increased the concentration of K solutions. Under the reactionconditions of T=160℃, V（HCl）/V（C2H2）=1.25and gas hourly space velocity of C2H2=110h^-1, acetylene conversion and vinyl chloride selectivity are99.84%and99.86%, the life of the catalyst is more than320min. The results of characterizationare showed that the relative content of K solution is little relevant to the activity ofcatalysts. The generation of carbon depositions and the decrease of relative content ofPd might course the deactivation of the catalyst.