Study On The Preparation And Performance Of Tin Based Catalysts For Acetylene Hydrochlorination

Three significant synthetic resins in world include polyvinyl chloride（PVC）,polycarbonate（PC）and polyurethane（PU）.Particularly,the output and demand of PVC has long been the largest.Because it is light weight,low cost,and chemical resistance,PVC is widely applied in many fields.Vinyl chloride monomer（VCM）is the main material to produce PVC and can be manufactured by three methods:acetylene hydrochlorination method,ethylene chlorination method and ethylene oxychlorination method.The bulk of chemical enterprises（vinyl chloride）in china mainly use carbon-based mercury chloride as catalysts for acetylene hydrochlorination.Although Hg Cl₂/AC catalysts has an excellent catalytic activity,the active ingredient mercuric chloride is easily sublimate during the acetylene hydrochlorination,resulting in impacting human health and causing severe pollution.Additionally,the production and imports-export of mercury-containing products in Contracting States（the Minamata Convention）will be prohibited after 2020.Therefore,it is of great significance to explore non-mercury catalysts for acetylene hydrochlorination.Based on the practical applications,tin-based catalysts were prepared by the tin precursor（Sn Cl₂or Sn Cl₄）and additives（organotin,nitrogen compounds,organic ligand,boron compounds and alkali metal salts）and have the better catalytic performance.Furthermore,the catalytic performance,deactivation reason and catalytic mechanism of tin-based catalysts in acetylene hydrochlorination were systematically studied by characterization techniques（XPS,FT-IR,C₂H₂-TPD,TEM,BET,XRD,H₂-TPR etc）.The main content of conclusion is as follow:The third chapter mainly studies the catalytic performance of tin-based(Sn⁴⁺)catalysts in acetylene hydrochlorination.The main contents include the following three parts:（1）when the single-organotin loading in catalysts was fixed at 20 wt%,the optimum acetylene conversion of 20%Ph₃Cl Sn/AC and20%C₁₆H₃₄Cl₂Sn/AC reached 84.0%and 89.1%,respectively(reaction condition:Temperature=200°C,C₂H₂-GHSV=30 h^-1,and V_HCl/V_C2H2=1.1:1.0).The acetylene conversion of 20%Sn Cl₄/AC was 91.9%,respectively,under the same condition.Moreover,the vinyl chloride selectivity of 20%Sn Cl₄/AC was over 98.0%in the hydrochlorination of acetylene.（2）The Kocheshkov redistribution reaction of Sn Cl₄and organotin(Ph₃Cl Sn or C₁₆H₃₄Cl₂Sn)can further improve the catalytic performance of tin-based catalysts.Through a series of optimization experiments,the optimum acetylene conversion and vinyl chloride selectivity of 12%（1.0Ph₃Cl Sn+3.5Sn Cl₄）/AC-200 was 98.2%and98.5%,respectively.Additionally,the catalytic mechanism of organotin catalysts in acetylene hydrochlorination was investigated by FT-IR.It is showed that organotin firstly makes a ligand with C₂H₂（transition state）,and then adsorb HCl to generate vinyl chloride.（3）In order to further reduce the cost,toxicity and prolong the lifetime of tin-based catalysts,tin-nitrogen based catalysts for acetylene hydrochlorination were synthesized using nitrogen-containing compounds（hexamethylenetetramine,urea or dicyandiamide）,C₁₆H₃₄Cl₂Sn and Sn Cl₄.According to the analysis of the experiments（XPS,BET,C₂H₂-TPD etc）,it is noted that the existence of Sn-N_xcan improve the reactant adsorption capacity,thermal stability and anti-coking ability of tin-based catalyst,resulting in the improvement of catalytic performance.The fourth chapter mainly studies the catalytic performance of tin-based(Sn²⁺)catalysts in acetylene hydrochlorination.The main contents include the following three parts:（1）The effect of alkali metal chlorides（Li Cl,Na Cl,KCl,Rb Cl or Cs Cl）on the catalytic performance of Sn Cl₂/AC in acetylene hydrochlorination was systemically studied.The optimum acetylene conversion of Li Sn Cl_n/AC,Na Sn Cl_n/AC,KSn Cl_n/AC,Rb Sn Cl_n/AC and Cs Sn Cl_n/AC reached 98.3%,88.9%,89.4%,60.4%and 78.1%,respectively,under the same condition.Particularly,while for the modification of Li Cl,the acetylene conversion of 98.3%can be achieved over 1.0Li Sn Cl_n/AC（10%）catalyst,which decrease to 79.8%after 50 h reaction.After studying the experimental results（FT-IR,XPS,ICP etc）,the conclusions are as follows:1)HSn Cl₃as the transition state of Sn Cl₂/AC catalysts in acetylene hydrochlorination reacts with C₂H₂to produce vinyl chloride.2)The existence of Li-Sn（IV）can strengthen the anti-coking ability,reduce the loss of Sn⁴⁺and inhibit the oxidation of Sn²⁺,thereby improving the catalytic performance of Sn Cl₂/AC.（2）A series of tin complexes were prepared using Sn Cl₂and different organic ligands（phthalic acid,isophthalic acid,terephthalic acid and 2-methylimidazole）.（3）The vinyl chloride production is based on the carbon-supported tin complexes as catalysts for acetylene hydrochlorination.Furthermore,the optimum acetylene conversion of 10%Sn MOF-L/AC and 10%Sn（Im）_n/AC was 93.5%and 98.8%,respectively,under the same reaction condition.Based on the XPS and experimental results,it is showed that Sn-O-C and Sn-N_xare the main active sites of Sn MOF-L/AC and Sn（Im）_n/AC,respectively.Chapter 5 is based on the results of Chapters 3 and 4((1.6Sn Cl₄+1.0C₁₆H₃₄Cl₂Sn),Li Sn Cl_n,Sn MOF-L,and Sn（Im）_n)for study that the effect of NAC and BNAC support on the catalytic performance of Sn-based catalysts.Particularly,the initial acetylene conversion of Sn（Im）_n/（BNAC-800）reaches 99.2%,which decrease to 85.1%after 40 h reaction.According to the results of XPS,C₂H₂-TPD and HCl adsorption/desorption experiments,it is demonstrated that the coexistence of Sn-N_xand BN in Sn（Im）_n/（BNAC-800）not only can effectively improve the reactant adsorption capacity,but also strengthen the anti-coking ability,thereby improving the catalytic performance of tin-based catalysts.