Study On Co-based Catalysts For Dehydrogenation Of Isobutane

As an important basic chemical raw material,isobutene has a wide range of market needs.Currently,the main sources of isobutene are steam cracking in refinery oil,cracking of naphtha,etc.These traditional sources are not only difficult to meet the increasing demand of the market,but also the purity of the product is not high.Therefore,a process for dehydrogenating isobutane which is inexpensive and rich in reserves to obtain isobutene has been widely concerned.At present,the isobutane dehydrogenation technology has been realized in the industry,and the Pt-based catalyst and the Cr-based catalyst mainly used have good catalytic dehydrogenation activity.However,the precious metal Pt has high cost,harsh operating conditions,and the catalyst is easy to be coked and deactivated to make the stability poor,and the Cr-based catalyst will produce high-toxic hexavalent chromium,which will hinder the subsequent treatment and other problems,which limits the development of the catalyst.Therefore,the development of environmentally friendly and low-cost catalysts with high dehydrogenation activity and high stability is a research hotspot in the field of isobutane dehydrogenation to isobutene,and is also the goal of this paper.In this paper,a Co-based catalyst was prepared by an equal volume impregnation method,and the catalyst was used in the direct catalytic dehydrogenation to isobutene reaction of isobutane by means of a fixed bed micro-reactor.The main contents are as follows:（1）The loading of the Co-based catalyst and the carrier were screened,and the calcination temperature of the catalyst was examined.The experimental results show that the dehydrogenation activity of the catalyst is best when the alkaline alumina with 120²00 mesh is used as the carrier and 10 wt.%of Co₃O₄ is loaded and calcined at 600°C.The characterization method was used to investigate the effect of metal oxide loading and calcination temperature on the performance of the catalyst.It was found that with the increase of metal oxide loading,the stronger the interaction between the catalyst and the support,the more difficult it is to reduce the catalyst;When the calcination temperature of the catalyst higher,the crystal form on the catalyst is destroyed,and Co₂AlO₄ is formed at the same time,which is not conducive to the dehydrogenation reaction.（2）The effects of process conditions on the dehydrogenation activity of the catalyst were investigated,and the optimal reaction conditions were determined.When the reaction temperature was 600°C,the feed space velocity was 1200 h^-1,and the ratio of nitrogen to isobutane was 8:2,the catalyst had The higher dehydrogenation activity,the conversion rate to isobutane can reach 31%,the selectivity to isobutylene can reach 70%,and the yield of isobutene can exceed 20%.At the same time,the catalyst has good stability and still maintains70%selectivity after 100 h of continuous reaction.（3）Investigating the deactivation of the catalyst and the active components,it is found that the main cause of the decrease in catalyst activity is carbon deposition,which can be treated by oxygen regeneration;the carbon nanowire structure formed on the catalyst surface helps to enhance the dehydrogenation activity;The reduced Co element is favorable for the cracking of isobutane and reduces the selectivity of the catalyst,and the Co₃C formed during the reaction can greatly shorten the induction period of the catalyst.