Modification Of SAPO-34 Molecula Sieves And Its Catalysis Performance In Synthesis Of Light Olefins From Carbon Dioxide Hydrogenation

In recent years, with the rapid development of industry, the demand of ethylene and propylene had been increased rapidly. The commercial light olefin production obtained mainly from fractional distillation and cracking of gasoil could not meet the market demand. For this reason, it got more attention to synthesize light olefin by developing new chemical technology such as no-petroleum process. Carbon dioxide is one of the richest C1 resources in the nature and the main greenhouse gases. Utilizing of carbon dioxide has attracted widespread attention by researchers from global chemical industry and environmental protection agency. The chemical process of carbon dioxide hydrogenation to light olefins is considered a potential method instead of convention oil route. The catalyst of Methanol-to-olefins?MTO? has received wide attention in the past years. At present, SAPO-34 molecular sieve is a potential catalyst for MTO reaction. In this thesis, based on the review, preparation and modification of SAPO-34 catalyst and its performance in catalytic synthesis of light olefins from carbon dioxide hydrogenation were studied systematically.1. SAPO-34 molecular sieves were hydrothermally synthesized using pseudoboehmite, silica sol and phosphoric acid as the source of aluminium, silicon and the phosphorus, respectively, and tetraethylammonium hydroxide as template. The influencing factors on the synthesis of SAPO-34 were investigated systematically. The CuO-ZnO-Al₂O₃/SAPO-34 bifunctional catalyst was prepared by mechanical mixing method and its catalytic activity for carbon dioxide hydrogenation to light olefins was investigated. Under the reaction pressure at 3.0 MPa, temperature at 400 °C and volume ratio of CO₂ to H2 at 1 : 3, the conversion of CO₂ and selectivity of light olefins are 52.6 % and 60.0 %, respectively.2. Imidazol, ferric nitrate, zinc nitrate and nickel nitrate modified SAPO-34 zeolite were prepared by hydrothermal synthesis method, respectively. The samples were characterized by the methods of XRD, SEM, EDS. The CuO-Zn O-Al₂O₃/modified-SAPO-34 bifunctional catalysts were prepared by mechanical mixing method and its catalytic activity for carbon dioxide hydrogenation to light olefins was investigated. The results shows that nickel nitrate modified SAPO-34 molecular sieves have the highest catalytic activity. Under the reaction pressure at 3.0 MPa, temperature at 400 °C and volume ratio of CO₂ to H2 at 1 : 3, the conversion of CO₂ and selectivity of light olefins are 71.1 % and 70.4 %, respectively.3. Imidazole and nickel nitrate modified SAPO-34 molecular sieves were hydrothermally synthesized and were characterized by the methods of XRD, SEM and BET. The CuO-ZnO-Al₂O₃/modified-SAPO-34 bifunctional catalyst was prepared by mechanical mixing method and its catalytic activity for carbon dioxide hydrogenation to light olefins was investigated in a fixed-bed reactor. Under the reaction pressure at 3.0 MPa, temperature at 400 °C, volume ratio of CO₂ to H2 at 1 : 3 and mole ratio of imidazole to nickel nitrate at 1 : 1, the conversion of CO₂ and selectivity of light olefins are 73.8 % and 74.0 %, respectively.