| In the modern chemical industry, ethylene and propylene as the important organic chemical raw materials have a pivotal position. Currently, ethylene and propylene has been obtained by cracking of naphtha mainly. Shortage of oil resource would restrict the development of China’s ethylene and propylene industrial. In order to break the constraints of the sleepy oil resources, we could proceed from the rich coal resources, coal into methanol, and then methanol to light olefins (MTO), which had great significance to ensure national energy security and to achieve sustainable development of encornemy. The research of catalyst was the core technology of the MTO. SAPO-34which has been considered the most suitable catalyst in MTO was a focus of research.In this thesis, SAPO-34was synthesized firstly by the hydrothermal method whose performance was evaluated in a continuous flow fixed-bed reactor to selecte the most suitable synthesis scheme of SAPO-34. A series of X%CoAPSO-34modified molecular respectively was modified by means of adding a single metal salt cobalt nitrate. The catalyst performance of these zeolites made MTO was evaluated taking methanol to olefins (MTO) as the model reaction to select the optimum salt concentration. Then the ratio of synthetic materials was optimized through changing single factor. Methods of XRD, SEM, BET and FT-IR and other characterization techniques were used to systematic study of the effects of Co modification on the physical and chemical characteristics of SAPO-34molecular sieve catalyst. The results showed that:1) Synthesis of SAPO-34catalyst obtained by the preliminary optimization:phosphoric acid, pseudo-boehmite (high viscosity), TEOS, morpholine were as phosphorus source, aluminum source, silicon source, template. The molar ratio is Al2O3:P2O5:SiO2:MOR: H2O=1:1:0.6:3:100. The water, the phosphorus source, aluminum source, a silicon source, the template was added to the reaction kettle successively. The ageing time was2hours, then stirred at200℃under autogenous pressure for crystallization of24h. The obtained solid was washed with deionized water to neutral, separated by centrifugation and then dried in an oven, calcined at600℃for6hours in a muffle furnace to remove the template agent. The synthesis scheme of synthesis of SAPO-34molecular sieves MTO performance tests showed the methanol conversion about97%, the ethylene yield about48%, the propylene yield about39%, the total olefin yield of (C2=+C3=) about87%, and these were stable performance. Detected by XRD and SEM synthetic molecular sieve was proved to be SAPO-34.2) The different concentrations of cobalt nitrate solution were prepared, SAPO-34catalyst synthesis scheme used, cobalt nitrate solution instead of water, a series of x%CoAPSO-34(x=0.05,0.1,0.2,0.3,0.4)modified molecular sieve were obtained. The results of MTO performance test showed performance parameters of0.1%CoAPSO-34MTO as the methanol conversion was99.9%, the ethylene yield was51.5%, the propylene yield was42%, the total olefin yield of (C2=+C3=) was93.5%. Molecular sieve color changed; a new peak was found in XRD image; FT-IR absorption peak shifted; specific surface area and pore volume had changed; all of this proved Co contained within the modified molecular sieve.3)The molar ratio of phosphorus source, aluminum source, silicon source and template agent as the raw materials of0.1%CoAPSO-34molecular sieves was optimized by the method of changing single factor, and the best molar ratio was Al2O3:P2O5:SiO2:MOR:H2O=1:0.85:0.6:3:100. The performance parameters of0.1%CoAPSO-34MTO as the methanol conversion was99.9%, the ethylene yield was51.3%, propylene yield was43.2%, the total olefin yield was94.5%.4) After0.1%CoAPSO-34as the best catalyst was choosed, the methods of changing single factor was used to inspect the effects of reaction temperature, WHSV of methanol, water molar ratio of MTO. And the best catalyst for the reaction conditions was selected as reaction temperature450℃, WHSV of methanol4h-1, water-alcohol ratio5:1. |
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