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MTO is a very promising new technology for alternative oil routes SAPO-34 molecular sieve is widely recognized for its good catalytic performance of the MTO reaction. The MTO technology lies in research and development of a high activity, good selectivity, long life, low manufacturing costs catalyst. Various metal elements introduced the SAPO-34 zeolite skeleton was modified in order to improve the selectivity of light olefins, is the focus of current research. The subject in the MTO process under production conditions, simulation SAPO-34 and metal-modified SAPO-34 zeolite diffusion and adsorption process, the shape-selective properties of molecular sieves, in order to improve the selectivity of light olefins, SAPO-34 zeolite modified to provide strong support. Based molecular sieve adsorption theory, Monte Carlo simulation method MTO process reactants methanol, the main product of ethylene and propylene in the molecular sieve adsorption properties, to compare the performance of molecular sieve adsorption through the adsorption capacity and the heat of adsorption analysis of the molecular sieve to explore the modified low carbon olefin selectivity. The results showed that, methanol, ethylene and propylene is SAPO-34, and Fe, Co, and Ni modified molecular sieve had significant adsorption, methanol, ethylene and propylene, single-component on the studied by molecular sieve adsorption capacity with increasing temperature decreases, the maximum adsorption amount of propylene under the same conditions; ethylene and propylene in the adsorption amount of Fe, Co and Ni, the modified SAPO-34 molecular sieve has obvious decline compared to the SAPO-34 adsorption, adsorption The heat is also decreased. After modification of the catalyst, is conducive to product lower olefin desorption thereon, compared to propylene, ethylene desorption easier. At atmospheric pressure ,400-500 ° C for the MTO reaction byproducts n-butene the amount of adsorption in the molecular sieve with the temperature change is very small, the adsorbed amount is substantially stable in a numerical value, but greater than the propylene and ethylene; modified zeolite byproducts n-butene adsorbed amount is decreased, the frequency can be reduced the catalyst pore blockage inactivation. On the basis of the study adsorption, diffusion theory based on molecular sieve configuration, the MD simulation method simulation calculation of the diffusion of the reactants and products in modified zeolites energy barrier, analysis of the diffusion properties of the reactants and products in different zeolites. The results showed that the diffusion energy barrier of small to large sequence of methanol, ethylene, propylene; methanol, ethylene and propylene in the diffusion of Ni-modified SAPO-34 zeolite in the energy barrier average minimum on the same kind of modified molecular sieve. Combining the results of adsorption and diffusion studies, can be drawn, the use of Fe, Co and Ni metal of SAPO-34 molecular sieve was modified beneficial to improve the selectivity of light olefins in the MTO reaction, particularly the selectivity to ethylene, where, Ni change optimal sexual effects. Experimental and molecular simulation methods in order to verify the reliability of the simulation method, were used to study atmospheric ,80-160 ℃ methanol SAPO-34 molecular sieve adsorption behavior, adsorption and temperature diagram. The results showed that both numerical or less, and the amount of adsorption temperature diagram has basically the same trend, and therefore the use of molecular simulation technology to simulate the behavior of small molecules in the molecular sieve adsorption is reliable and feasible. The methods and findings of the study can provide useful guidance for that the system catalyst performance optimization.
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