Study On Cu-Based/γ-Al₂O₃ Catalysts For Ethane Oxychlorination To Vinyl Chloride

Vinyl chloride monomer (VCM) is one of the main raw materials to product Polyvinyl chloride (PVC). PVC is one of the five general plastics in the world and has been widely used in many fields. So far, the monomer of PVC, vinyl chloride is produced by three processes in the world:acetylene hydrochlorination, ethylene oxychlorination and ethane oxychlorination. Ethane oxychlorination is a new way to produce vinyl chloride. Ethane derives from the by-product of coal-bed gas or natural gas, which changes waste materials into things of value. Meanwhile, ethane oxychlorination is a simpler process scheme. As a result, to carry out the study of ethane oxychlorination and make this commercialized to become commercialized are beneficial to resolve problems such as environmental pollution and energy crisis in our country.In this work, copper-based catalysts were prepared by a impregnation method, a sol-gel method and a mechanical mixing method. The catalysts were characterized by means of XRD, XPS,H2-TPR, O2-TPD, BET, SEM and XRF etc. to investigate the relationship between the phase compositions, structure, surface species, redox properties and the catalytic performance. The effect of the different accessory ingredient to copper-based catalysts for ethane oxychlorination is also investigated. The main experimental results and conclusion are as follows:1. Chromium-doped CuCl2-KCl-CeO2-Crx/γ-Al2O3 with different content (Cr 0,1,3,5,7 and 9 wt.%) were synthesized by co-impregnation method and the effect of Chromium for the catalysts is investigated. It is found that the addition of chromium species affects the crystal size of CeO2 on the surface (under the circumstances of each catalysts possess the same content of cerium species); Meanwhile, the addition of chromium species increases a large amount of surface-adsorbed oxygen species on the catalysts surface, reduces the reduction activation energy of Cu2+â†' Cu+ process efficiently. The best catalyst is CuKCeCr3 with Cr (3 wt.%), which exhibited highest conversion of C2H6(97.8%) and best selectivity to C2H3Cl (68.2%). The selectivity to C2H3Cl nearly maintains about 60% and no deactivation of catalyst was detected after the reaction for 120h.2. Supported perovskite catalysts were prepared by an impregnation method, a sol-gel method and a mechanical mixing method. It is found that when the x=0.3, the weight percent of perovskite-type oxides in the modified supported catalysts is 30%, the catalyst possesses best C2H6 conversion of 100% and the C2H3Cl selectivity to 59.4%. The addition of K species leads to a larger lattice distortion for La1.7K0.3CuMnO6 than that of K-free catalyst, and therefore the catalyst Lai.7Ko.3NiMn06 (30wt.%)-CuCl2/γ-Al2O3 possesses a large amount of surface-adsorbed oxygen species. The transformation of a larger amount of Mn3+ species to Mn4+ species were attributed to K+ substitution into the perovskite structure in La2NiMnO6 composite oxide to balance the total charge. The a large amount of surface-adsorbed oxygen species may accelerate the oxidation of Cu+ due to the spillover effect. Mn4+ and surface-adsorbed oxygen species both accelerate the oxidation of Cu+ by a circular reaction and therefore promote the conversion of C2H6 and the selectivity to C2H3Cl.3. The experiment of substitution in Ni site of La1.7K0.3CuMnO6/γ-Al2O3 by Fe and Co indicates that catalyst La1.7K0.3CuMnO6/γ-Al2O3 possesses more surface-adsorbed oxygen species than that of La1.7K0.3CuMnO6/γ-Al2O3 catalyst. There is Fe3+ species on the La1.7K0.3CuMnO6/γ-Al2O3 catalyst surface, and Co4+ species on the La1.7K0.3CuMnO6/γ-Al2O3 catalyst surface. Therefore, the La1.7K0.3CuMnO6/γ-Al2O3 catalyst possesses a large amount of Mn4+ species to balance the total charge of catalyst. The Mn4+ species could accelerate the oxidation of Cu+, hence, enhance the catalytic performance of catalyst.4. K-doped La2CuMnO6/γ-Al2O3 catalysts were prepared by an impregnation method with citrate acid as the chelating agent. It is found that the addition of K influences the BET specific surface area, pore volume, content of surface-adsorbed oxygen species and copper species. The La1.7K0.3CuMnO6/γ-Al2O3 catalyst possesses a large amount of surface-adsorbed oxygen species and copper species, lager BET specific surface area and pore volume. Therefore, the catalytic performance of this catalyst is better than the catalysts with other K content.5. KC1 and CeO2 modified catalysts were prepared by an impregnation method. It is found that when the weight percent of Ce is 1.9wt.% in La1.7K0.3CuMnO6/γ-Al2O3 sample, the catalyst possesses a large amount of Mn4+ and surface-adsorbed oxygen species, which accelerate the oxidation of Cu+ and stop the catalysts form deactivation. Meanwhile, the catalyst possesses more activity Cu2+ species. The conversion of C2H6 and best selectivity to C2H3Cl for this catalyst is 98.5% and 66.9%, respectively. The conversion of C2H6 and selectivity to C2H3Cl nearly maintain steady during the 100h time-on-stream.