Investigation On HPW Modified Catalyzer Development And Technical Optimization For Ethylene Preparation Catalyzed In Fluid Bed Dehydration Of Bioethanol

This paper mainly studied catalyzer development and technical optimization for ethylene preparation catalyzed in fluid bed dehydration of bioethanol (containing ethanol or low concentration ethanol). First, developing two catalyst systems by impregnation method:phosphotungstic acid modified HZM-5 and phosphotungstic acid modified activated clay. Secondly, evaluating their catalytic performance on dehydration of bioethanol (containing ethanol or low concentration ethanol) in "a fluidized bed reactor for ethanol dehydration to manufacture ethylene" obtained patent grand by our project team(patent authorization number is:200710009681.8) to manufacture ethylene. Thirdly, according to the investigation of catalyst's physical and chemincal structure and association of their structure and catalytic performance, preliminary studing the catalytic mechanism of phosphotungstic acid modified HZM-5 catalyst. Finally, putting forward a process route suitable for low concentration bioethanol dehydration to ethylene based on experimental results.The following results and conclusions were obtained from these studies.(1) According to the catalytic performance of phosphotungstic acid modified HZM-5 catalyst on ethanol dehydration to ethylene reaction, screened out the optimum modified conditions:the dipping concentration of phosphotungstic acid was 0.04mol/L, the dipping time of phosphotungstic acid was 24h, the calcination temperature of catalyst was 350℃, the calcination time of catalyst was 4h. When the catalyst was applied in the following conditions:reaction temperature was 220℃, ethanol flow velocity was 0.1ml/min, catalyst amount was 3g, it could play the optimum catalytic performance, the ethanol conversion and ethylene selectivity could reach 98.1% and 97.1%, respectively. Further more, the service life of the catalyst could reach more than 700h. The effects of ethanol concentration on catalytic behaviors were investigated, the results showed that even the ethanol concentration was 20%(volume fraction), the ethanol conversion and ethylene selectivity could reach 95.7% and 95.3%, respectively.(2) Phosphotungstic acid modified HZM-5 catalyst could be used in bioethanol dehydration to ethylene reaction, using the distilled pachyrhizus-derived ethanol and rice alcohol as original reactants, the following results could be obatined:when the reaction temperature was 220℃, ethanol flow velocity was 0.1mL/min, the bioethanol conversion and ethylene selectivity could reach over 90%, where the bioethanol conversion and ethylene selectivity of rice alcohol could reach 97.6% and 96.7%, respectively. (3) Tentatively propsed the catalytic mechanism of phosphotungstic acid modified HZM-5 catalyst in ethanol dehydration to ethylene reaction:on the modified process, phosphotungstic acid could be firmly loaded on HZM-5 zeolite, when in low phosphotungstic acid concentration, it could show a monolayer dispersion, with increase of phosphotungstic acid's concentration, it could formed secondary structure, namely multilayer dispersion,the number of secondary structure increased with increase of phosphotungstic acid's concentration, the behavior of "pseudo-liquid phase" also would be stronger, this behavior could absorb molecular in bulk phase structure to occur reaction, which could improve catalytic activity, but over large loading concentration would make specific surface area decreased seriously, which resulted in be unable to provide the effective contact space and decrease the catalytic activity, therefore it needed suitable loading concentration. (4) Putting forward a process route suitable for low concentration bioethanol dehydration to ethylene based on experimental results. (5) Investigating the catalytic performance of modified bentonite on dehydration of ethanol to ethylene, using phosphotungstic acid,sulfate,nitrate lanthanum and nitrate cerium as modifiers. The results showed that there had some catalytic action of modified bentonite in this reaction, the optimal modification conditions and application conditions needed further exploration. If we could develop a new catalyst system based on the abundant bentonite resource of our province, and explore a process route suitable for industrialization, the production cost of bio-ethylene would greatly reduced.