Study On The Preparation Of Propane Dehydrogenation Pt Catalyst And Its Catalytic Performance

In recent years,propylene consumer market in our country is of great vitality.How to improve propylene yield has become a popular topic.Among all technologies for the production of propylene,propane dehydrogenation technology has fewer by-products and lower the separation cost,thus attracting much attention of the petrochemical industry.The main propane dehydrogenation process introduced in China are Oleflex process and Catofin process.However,both of the processes are foreign technologies,they entails high transfer cost,expensive catalysts and high degree of purity of raw material.Compared to the moving bed and fluidized bed processes,the fixed bed reactor requires less investment and is easy to operate,hence it is more suitable for industrial production.Therefore,there is a need to prepare a low cost and highly stable catalyst that is suitable for fixed bed reactor.In this paper,the preparation method,the active component Pt and the additives Sn and K loadings,the alumina carrier and the carrier calcination temperature were investigated by using the impregnation method.The effects of different additives and loadings on the catalyst structure and propane dehydrogenation performance were studied.The prepared catalysts were characterized by XRD,mercury intrusion,H₂-TPR and NH₃-TPD.Propane was used as the raw material to evaluate the catalytic performance and process conditions of the optimized catalyst in a fixed bed reactor.The Pt-Sn-K/?-Al₂O₃ catalyst was prepared by one-step impregnation method and fractional impregnation method.The effects of preparation method,active component Pt,additive Sn,K loadings,alumina carrier and carrier calcination temperature on the catalyst structure and propane dehydrogenation performance were investigated.The results showed that the catalyst prepared by one-step impregnation had better dehydrogenation performance;the preferred composition of the catalyst was:0.3wt%Pt,0.8wt%Sn,0.2wt%K?calculated according to the loadings of the elements,the same below?;Compared with the catalyst prepared by pseudoboehmite 1 and 2,the Pt-Sn-K/?-Al₂O₃ catalyst prepared by using pseudoboehmite 3 as the alumina precursor had a large specific surface area,pore volume and pore diameter,and its acidity was weaker.So the propane dehydrogenation activity and propylene selectivity of Pt-Sn-K/?-Al₂O₃ catalyst prepared by using pseudoboehmite 3 as the alumina precursor were better;increasing the calcination temperature of the carrier could increase the pore size and pore volume of the catalyst,and the calcination temperature was preferably 800°C?900°C.In order to further improve the stability of the catalyst,the catalyst carrier was modified by introducing the third additives Ba,Ni,Ga,Ce and B,based on the Pt Sn-K/?-Al₂O₃ catalyst prepared by one-step impregnation method.The effects of additives and loadings on the catalyst structure and propane dehydrogenation performance were studied.The results showed that the introduction of the additive B stood out in improving the stability of the catalyst.Compared with the Pt-Sn-K/?-Al₂O₃ catalyst,the initial propane conversion of the B-modified catalyst was 36.22%,propane conversion only dropped by12.73%after react 8h.The proper loading of the B could enhance the interaction between the component and the carrier,and it could also reduce the surface acidity of the catalyst.The optimum loading of B was 0.4wt%.The pseudo-boehmite 3 was selected as the alumina carrier precursor,and the loadings of each component of the best catalyst was:Pt-0.3wt%,Sn-0.8wt%,K-0.2wt%,B-0.4wt%.Then,using propane as the raw material,the effect of process conditions on the catalytic performance of propane dehydrogenation in a fixed bed reactor was investigated.The results showed that the optimum process conditions were:catalyst reduction temperature 450°C,reaction temperature 580°C,propane feed space velocity GHSV=600h^-1,feed ratio hydrogen/propane=1:3.Experiments targeting at stability were carried out under such reaction conditions to compare the self-made catalyst and an industrial catalyst,showed that the propane conversion of the catalyst prepared in the laboratory decreased from 34.67%to 25.3%,and the propylene selectivity remained at97.5%throughout the continuous operation of 25 hours.The propane conversion of the industrial catalyst decreased from 33.32%to 24.85%,and the propylene selectivity varied from 95.5%to 97%throughout the continuous operation of 25 hours.The catalysts prepared in the laboratory were superior to industrial catalysts in both propane conversion and propylene selectivity.