Study On Supported Palladium Catalysts For Synthesis Of Vinyl Chloride Via The Acetylene Method

Vinyl chloride monomer (VCM) is mainly used for synthesis of polyvinyl chioride (PVC) which is the one of the five general synthetic resins (polyethylene, polypropylene, polyvinyl chloride, polystyrene and acrylonitrile-butadiene-styrene copolymer) and is used in all walks of national economy widely. In china, due to special energy structure, the main technology of producing VCM is acetylene hydrochlorination method based on the calcium carbide as raw material. The toxicity of mercuric chloride catalyst used in this method does a lot of harm to environment and human being. Besides, a scarcity of mercuric resources makes the supplies decrease year by year. Therefore, the research and development of non-mercury catalyst have been a challengeable task and one of the core topics in the field of the PVC technology.In this work, based on carbon-supported lower content Pd catalyst, the effect of pretreatment of activated carbon, addition of auxiliaries and different kinds of carbon carriers on reactivity were mainly researched. Monometallic palladium and bimetallic Pd-based catalyst were prepared by the isovolumetric impregnation using ultrasonic or rotary evaporation. Catalytic activity (acetylene conversion) and vinyl chloride selectivity of catalysts were investigated via the acetylene hydroehlorination. And structure, physicochemical properties of catalysts and dispersion of activate component on the surface of activated carbon were characterized. The following contents are included:(1) The effect of pretreatment not only influences on the physical structure of activated carbon, but also increases the contents of surface oxygen-containing grounps of activated carbon which are useful to adsorb palladium precursor. The improvement of performance of activated carbon affected the activity of supported Pd catalyst directly. The Pd catalyst supported on activated carbon pretreated with H3PO4(PC-HP catalyst) exhibits the best performance. Acetylene conversion and vinyl chloride selectivity were96.55%and98.15%respectively, and the service life can reach over4hours. Characterizations proved that the content of surface oxygen-containing grounps of activated carbon pretreated with HNO3was the highest, interaction between activated carbon carriers pretreated with HNO3and H2O2(C-HN, C-HO) and PdCl2was also strengthened. The main deactivated reason of catalysts was generate heavily carbon deposit which result in blocking of pore cannel.(2) Catalytic activity of activated carbon treated with several pretreatment reagent supported Pd catalyst was compared, it was found that activated carbon pretreated with H3PO4supported Pd catalyst has a good activity and stability. Therefore, activated carbon pretreated with different concentrations of H3PO4supported Pd catalysts were studied systemically, Of which acetylene conversion of activated carbon pretreated with20%H3PO4as carrier supported Pd catalyst (PC4catalyst) was more than97%, the service life can reach over5hours. The phosphoric acid material as pretreatment medium could exert a tremendous influence on catalytic activity of acetylene hydrochlorination, while the concentration did not affected catalytic activity remarkably. Which one hand due to H3PO4treatment changed the physicochemical properties of activated carbon, which was useful to improve concentration and dispersity of Pd-containing species on the surface of activated carbon, on the other hand, it introduced PO43-on the surface of activated carbon and can provided proton which can form π-complex with C2H2, thereby forming carbocation enhanced activity and thermal stability of Pd catalyst.(3) Three different kinds of activated carbon carriers, supported Pd catalysts were prepared by the isovolumetric impregnation using ultrasonic or rotary evaporation. The catalysts were used for the acetylene hydroehlorination, the order of catalytic activity is:Pd/YC>Pd/GC>Pd/MC. The surface of cocoanut shell has very rich microchannel and shows open, honeycomb sructure.(4) HgCl2, BiCl3, BaCl2, CuCl2, FeCl3, LaCl3, CeCl3were taken as additives added Pd/C catalysts owing to synergetic actioin of between metals, and ofen showed the superior catalytic performance than monometallic Pd catalyst. Among them, catalytic performance of Pd catalyst doping with Fe was the best, then Pd catalyst doping with La and Ce, which can maintained the high-activity and stability in long terms.