Study On Catalytic Conversion Of Crude Methanol To Dimethyl Ether And Light Olefins

Focusing on the direct catalytic conversion and utilization of crude methanol,according to the characteristics of crude methanol components,the thesis proposes to carry out the research work of crude methanol?methanol and water?to dimethyl ether and crude methanol?methanol,water and ethanol?to light olefins.In the process of preparing dimethyl ether from crude methanol?methanol and water?,in view of the poor reactivity and stability of the?-Al₂O₃ catalyst in hydrothermal environment,the paper proposes to use ZSM-5 molecular sieve with good hydrophobic properties due to its low surface charge density as the modifier to modify the hydrophilic?-Al₂O₃.In the process of preparing light olefins from crude methanol?methanol,water and ethanol?,combining the catalytic cracking reaction mechanism of methanol and ethanol,during the ZSM-5 molecular sieve catalytic conversion process,the reaction temperature required for the conversion of methanol and ethanol is different,and the catalyst is easy to deposit coke,which reduces the reaction efficiency.The paper proposes to use mesoporous?-Al₂O₃ with L?Lewis?acid properties to compound the microporous ZSM-5 molecular sieve with B?Br?nsted?acid properties.In the process of preparing dimethyl ether from crude methanol?methanol and water?,?-Al₂O₃ was composite modified with ZSM-5 as modifier,and the preparation,characterization and catalytic performance evaluation of ZSM-5/?-Al₂O₃ composite catalyst were investigated.With the help of XRD,SEM,NH3-TPD,BET,TEM,Py-FTIR,XPS,XRF and other characterization methods,the physicochemical effects of composite processes such as liquid phase precipitation coating method,hydrothermal coating method and physical blending method were compared and analyzed.The influence of the properties and catalytic performance;the influence of the liquid phase precipitation coating preparation factors such as ZSM-5 content,ZSM-5 silicon-to-aluminum ratio,precipitation pH value and calcination temperature on the physicochemical properties and catalytic performance of the composite catalyst was systematically investigated.The research results show that the ZSM-5/?-Al₂O₃composite catalyst prepared by the liquid-phase coating chemical composite method exhibits excellent catalytic properties and hydrothermal stability in a hydrothermal reaction environment using crude methanol as a raw material.The ZSM-5/?-Al₂O₃composite catalyst reached an excellent methanol conversion of 91.9%and DME selectivity of 100%.The DME yield was increased by about 13%compared to only using?-Al₂O₃.Partial desiliconization and dealumination of the ZSM-5 molecular sieve effectively reduced the surface acid center strength and increased the mesoporous ratio.The special composite phase interface effectively decreased surface charge density of?-Al₂O₃ and formed the B?Br?nsted?-L?Lewis?synergistic active centers.All these factors contribute to improving the catalytic performance,hydrothermal stability and resistance to deactivation of ZSM-5/?-Al₂O₃ during the conversion of crude methanol to DME.In the process of preparing light olefins from crude methanol?methanol,water and ethanol?,and improving methanol catalytic cracking activity at lower reaction temperature,The thesis is the first to focus on the structure-activity relationship study of the?-Al₂O₃/ZSM-5 composite catalyst at 350?for the methanol-to-olefin?MTO?reaction.ZSM-5 was composite modified with?-Al₂O₃ as modifier.The composite processes such as liquid phase precipitation coating method,hydrothermal coating method and physical blending method were investigated.The influence of liquid phase precipitation coating preparation factors such as?-Al₂O₃ content and ZSM-5 silicon-to-aluminum ratio on the physicochemical properties of the composite catalyst and the catalytic performance of MTO.The reaction process conditions were optimized and the catalytic activity of methanol at 350?was improved.The?-Al₂O₃/ZSM-5 composite catalyst reached an excellent methanol conversion of 94.5%,the selectivity and yields of light olefins reached 86.7%and 81.9%,respectively.The light olefins yield was increased by about 35.9%compared to only using ZSM-5.On this basis,the influence of the content of water and ethanol on the catalytic performance of the methanol-to-low-carbon olefins process was investigated.Finally,the?-Al₂O₃/ZSM-5 composite catalyst with high activity,high selectivity and good hydrothermal stability suitable for the catalytic conversion of crude methanol?methanol,water and ethanol?to light olefins was successfully prepared.At 350?,?-Al₂O₃/ZSM-5 composite catalyst reached an excellent methanol conversion of 94.6%,the ethanol conversion rate was 100%,the selectivity and yields of light olefins reached 86.1%and 82.3%,respectively.The light olefins yield was increased by about 21.1%compared to only using ZSM-5.L?Lewis?acid characteristics mesoporous?-Al₂O₃ composite modified ZSM-5 molecular sieve structure formed?-Al₂O₃/ZSM-5 has L?Lewis?-B?Br?nsted?synergistic active center and meso-microporous system.This is the key to the excellent catalytic performance of?-Al₂O₃/ZSM-5 in a hydrothermal reaction environment containing methanol,water and ethanol.