Monolithic Catalytic Reactor For Direct Coupling Of Dehydrogenation Of Long Chain Alkane And Catalytic Combustion Of Methane

As a new technique in chemical process intensification,monolithic catalysts have obvious advantages over conventional pellet catalytsts, such as low pressure drop through the catalyst bed,favorable heat and mass transfer properties,and radially uniform distribution of reactant local flow.Especially,the application of the metallic monolithic catalysts with favourable heat transfer property to direct coupling of endothermic and exothermic reactions not only can intensify reaction process,but also reduce energy consumption,environment impact and equipment size. Therefore,we try to directly couple the endothermic reaction of long chain alkane dehydrogenation with the exothermic reaction of methane catalytic combustion by using the metallic monolithic catalysts,which highly miniaturizes reactor size and significantly increases heat efficiency.In this paper,catalytic combustion of methane is chosen as an exothermic reaction to couple with long chain alkane dehydrogenation,as an endothermic model reaction system.A series of metallic monolithic catalysts applied to these two reaction systems were firstly prepared, respectively.The activities and stabilities of the catalysts were evaluated, and the properties of the catalysts were characterized by XRD,SEM, TEM,N₂ adsorption-desorption,TPR and XPS.Secondly,a tubular jacket reactor packed with the metallic monolith catalysts for directly coupling the methane catalytic combustion with the long chain alkane dehydrogenation was devised and constructed,and its operation performance was experimentally studied.Lastly,modeling and simulation for direct coupling process of the endothermic and exothermic reactions were carried out to evaluate the reactor performance,as a supplement to the experimental study.The main research contents and the results are listed as follows:For the endothermic reaction of long chain alkane dehydrogenation,the Pt-Sn-K/γ-Al₂O₃ and Pt-Sn/SBA-15 catalysts were prepared.The performances of these catalysts and a Pt-Sn-Li/Al₂O₃ industrial catalyst were evaluated.The results showed that the Pt-Sn-Li/Al₂O₃ industrial catalyst has the best performance of long chain alkane dehydrogenation, compared with prepared Pt-Sn-K/γ-Al₂O₃ and Pt-Sn/SBA-15 catalysts. Pt-Sn-Li/Al₂O₃/FeCrAl metallic monolithic catalyst was prepared by using Pt-Sn-Li/Al₂O₃ industrial catalyst as the active coating.The reaction performance of Pt-Sn-Li/Al₂O3/FeCrAl catalyst was measured,and the properties of the catalyst were characterized.It was found that reaction temperature,LHSV and the molar ratio of hydrogen to alkane have greatly affected on the catalytic performance of the Pt-Sn-Li/Al₂O₃/FeCrAl catalyst.Under a set of optimal reaction conditions,at 0.1 MPa,470℃,the molar ratio of hydrogen to alkane of 4 and LHSV of 0.14 mL·m^-2·h^-1,the dodecane conversion is 6%,and the dodecene selectivity is about 72%.The adhesiveness between the Al₂O₃/FeCrAl support and the Pt-Sn-Li/Al₂O₃ active coating of Pt-Sn-Li/Al₂O₃/FeCrAl catalyst is very good.For the endothermic reaction of methane catalytic combution,firstly, Pd-Zr/SBA-15/Al₂O₃/FeCrAl metallic monolithic catalyst was prepared by using Pd-Zr/SBA-15 catalyst as the active coating,since Pd-Zr/SBA-15 catalyst has the best catalytic performance compared with hydrothermally synthesized catalysts of Pd/SBA-15 and Pd/SBA-16. Secondly,according to other related work completed by our team,the catalytic performance of Pd/5 wt.%ZrO₂/SBA-15/Al₂O₃/FeCrAl catalysts with different Pd content were evaluated,and the relationships in the performance,composition and textural properties of catalysts were investigated.The results indicated that 0.5 wt.%Pd/5 wt.%ZrO₂/SBA-15 catalyst has the highest activity and the stability compared with the hydrothermally synthesized catalysts of 1 wt.%Pd/SBA-15 and 1 wt.%Pd/SBA- 16.0.5 wt.%Pd/5 wt.%ZrO₂/SBA-15/Al₂O₃/FeCrAl catalyst represented the high activity and the stability,and T₉₀is 395℃and the methane conversion has no variation during 700 h of reaction under adopted conditions.The active coating of 0.5 wt%Pd/5 wt%ZrO₂/ SBA-15/Al₂O₃/FeCrAl catalyst maintained the mesoporues structure of SBA-15,and Pd and Pd oxides had been incorporated into the channels of SBA-15.The ZrO₂ could promote redox process of Pd-Zr/SBA-15/Al₂O₃/ FeCrAl catalyst,and consequently improved the stability.Additionally,a tubular jacket reactor packed with metallic monolithic catalysts for direct coupling of long chain alkane dehydrogenation and methane catalytic combustion was devised and developed.The direct coupling performance of the two reactions in this reactor was experimentally studied.The primary results suggested that the heat needed for long chain alkane dehydrogenation came directly from that produced by methane catalytic combustion reaction,and the direct coupling of highly endothermic and exothermic reactions was successfully demonstrated.Under an optimal condition,the conversion of methane in combustion reaction was about 100%when methane catalytic combustion reaction directly provided heat for long chain alkane dehydrogenation.Finally,modeling of the tubular jacket reactor packed with metallic monolithic catalysts and process simulation for direct coupling of the endothermic and exothermic reactions in this reactor are carried out.The influences of the operation conditions and the structural parameters of the reactor on the reactor performance will be studied in the further simulation.