Study On The Catalyst For Dehydration Of Bioethanol To Ethylene

Ethylene is a basic organic chemical raw material,mainly used in the production of polyethylene,ethylene glyco and many other chemicals.At present,traditional ethylene is mainly produced by cracking light naphtha,which relies heavily on petroleum resources.As the international energy situation becomes increasingly tense,oil resources are decreasing and non-renewable,which urgently requires us to develop new oil alternative energy sources.In the field of alternative energy development,the technology of bioethanol dehydration to ethylene has attracted extensive attention at home and abroad.The dehydration of ethanol to produce ethylene has great potential to replace part or all of the ethylene obtained from petroleum.Therefore,ethanol dehydration to ethylene has great economic value and strategic significance.In this paper,the goal is to prepare an activated alumina catalyst for the dehydration of bioethanol to ethylene,in order to solve the problem that the alumina catalyst activity decreases significantly and the stability is not good when low concentration ethanol is used as a raw material.In this paper,different solid acid catalysts were screened,and their catalytic activities under different conditions were investigated.The results show that the HZSM-5 catalyst has good catalytic performance at 280℃,but after 38 hours of reaction,the ethylene yield of the catalyst decreases by 10%;and after theγ-Al₂O₃catalyst reacts at 380℃for 118 hours,the ethylene yield of the catalyst The rate decreased by only 10%,which shows thatγ-Al₂O₃catalyst was a kind of ethanol dehydration catalyst with better stability.By adding different types and proportions of pore-expanding agents to adjust the pore structure of alumina catalysts,different alumina catalysts were prepared respectively.The specific surface area and pore structure were characterized by mercury intrusion method,and their performance was investigated through the reaction of ethylene production.The results showed that carbon powder,polyethylene glycol,polyacrylamide,polyvinyl alcohol and other pore-expanding agents can effectively expand the pore volume and average pore size of the catalyst;through evaluation experiments,it can be seen that the yield of alumina catalyst ethylene added with 20%carbon powder was 96.5%,and the catalytic activity of the catalyst decreased only5.41%after 216 hours of reaction.Its effect was significantly better than that of catalysts with other pore-enlarging agents.The pore size of the catalyst was mainly distributed between 1000 and 7000 nm.It can be seen from this that the pore size of1000-7000 nm was more conducive to the progress of the ethanol dehydration reaction.The 20% carbon powder expanded alumina under the optimal preparation conditions was used as the carrier.Using Ce,La and Fe metals as active component precursors and citric acid as a competitive adsorbent,the modified catalyst were prepared by different impregnation methods.XRD,NH₃-TPD and other characterization methods were used to study its acidity and crystal form,and its catalytic performance was investigated by dehydration of bioethanol to ethylene.The results show that adding a certain amount of citric acid as a competitive adsorbent and excessive impregnation can effectively improve the ethanol conversion rate of the catalyst.It was presumed that this method improves the dispersion of the active component on the catalyst.The effect of Ce modified catalyst was the best,whose ethylene yield was 96.9%,followed by La,the ethylene yield was 94.62%,the catalytic activity of the Fe-modified catalyst has decreased to only 82.24%,which shows that Ce-modifiedγ-Al₂O₃was the best catalyst.The characterization results show that the metal modification does not destroy the crystal structure of the catalyst,and the acidity of the metal-impregnated catalyst was mainly weak acid,with medium to strong peaks.The process conditions of the optimized catalyst were investigated,and the best process conditions were determined:using 50～95wt%ethanol aqueous solution as raw material,reaction temperature 380℃,reaction pressure 0.1MPa,and mass space velocity 6h^-1.Under this process condition,the ethanol conversion rate of the catalyst was 99.50%,and the ethylene selectivity was 97.37%.