Coking behaviors and kinetics on HZSM-5/SAPO-34 catalysts for conversion of ethanol to propylene

The coke deposition on HZSM-5/SAPO-34 composite catalysts has been studied in the conversion of ethanol to propylene. The HZSM-5/SAPO-34 composite catalysts were synthesized by hydrothermal method（ZS-HS） and fully blending（ZS-MM）. The used catalysts were characterized by XRD, N;adsorption–desorption, TGA, TPO, elemental analysis, FTIR and XPS. The coking kinetics on both ZS-HS and ZS-MM has been investigated and their coking rate equations were obtained. The used ZS-MM catalyst had higher amount of coke and lower nC:nHthan the used ZS-HS. 90% of the coke was deposited in the micropores of ZS-HS, while almost 45% of the coke located in the micropores of ZS-MM. The coke deposited on ZS-HS catalyst was mainly graphite-like carbon species, whereas dehydrogenated coke species was the major on ZS-MM. The coking activation energy of ZS-MM was lower than that of ZS-HS, and the coking rate on ZS-MM was faster than on ZS-HS. In addition, the regeneration of ZS-MM catalyst showed that it had a good hydrothermal stability. The differences on coking behaviors on the two catalysts were due to their different acidic properties and textures.

乙醇制丙烯反应热力学及HZSM-5/SAPO-34复合分子筛的催化性能

采用平衡常数法计算了乙醇制丙烯的主、副反应在不同温度下的反应热、Gibbs自由能变和热力学平衡常数,以及不同反应温度和乙醇分压下产物的热力学平衡组成。热力学分析结果表明,降低反应温度和提高乙醇分压有利于提高丙烯的平衡组成。研究了复合分子筛HZSM-5/SAPO-34催化剂的乙醇制丙烯性能以及催化剂的结构和酸性。实验结果表明,反应温度和乙醇分压对HZSM-5/SAPO-34催化剂上丙烯收率的影响与热力学计算结果略有差别,这是因为热力学分析未考虑烯烃齐聚物和芳烃的二次反应及催化剂的酸催化和择形催化作用。HZSM-5/SAPO-34催化剂的酸量和酸强度分布与其活性密切相关。在773 K、乙醇分压0.020 MPa时,m(HZSM-5)∶m(SAPO-34)=4的HZSM-5/SAPO-34催化剂上丙烯收率最高(34.5%),主要归因于该催化剂具有适宜的酸量和酸强度分布。