Study On Hydrogen-supported Composite Catalyst For Cyclohexane Dehydrogenation

Organic liquid hydrogen storage technology is a safe and economical way to store and transport hydrogen.Its basic principle is to achieve the storage and transportation of hydrogen through the reversible reaction of hydrogenation and dehydrogenation of organic liquids,which has good prospects for industrial applications.However,the catalysts used in the catalytic dehydrogenation process of organic liquids are not suitable for large-scale application due to their low-temperature activity and high-temperature instability,as well as the cost of organic liquid hydrogen storage media.Extensive studies have been conducted to solve this problem,and it was found that the design of catalysts and a low-cost hydrogen storage medium are the core of the solution.This paper uses several complex substituted cyclohexanes in naphtha as hydrogen storage media,which are first thermodynamically calculated.The catalyst and dehydrogenation process are optimized using methylcyclohexane as a model compound（MCH）.Finally,the optimal catalyst and dehydrogenation process are applied to the dehydrogenation of complex substituted cycloalkanes.（1）The standard molar enthalpy of formation and absolute entropy of benzene,toluene and ethylbenzene were firstly calculated thermodynamically for several complex substituted cycloalkanes in naphtha,and the standard molar enthalpy of reaction,standard molar Gibbs free energy change and equilibrium constants were calculated for the dehydrogenation reactions of cyclohexane,methylcyclohexane and methylcyclohexane at different temperatures and pressures.The results showed that the standard molar enthalpies,standard molar Gibbs free energies and equilibrium constants of the dehydrogenation reactions of cyclohexane,methylcyclohexane and methylcyclohexane were all heat-absorbing reactions;the trends of the standard molar enthalpies,standard molar Gibbs free energies and equilibrium constants of the three dehydrogenation reactions were similar with pressure and temperature;under the conditions of 300-1000 K and 0.5-30 MPa,increasing the temperature was favourable to the dehydrogenation reactions,and increasing the p（2）The model compound MCH was studied for dehydrogenation and Ni-X/γ-Al₂O₃,Ni-Cu/M catalysts,Ni-Cu/α-Al₂O₃with different solvent systems and Ni-Cu/α-Al₂O₃with different metal loadings were prepared using the impregnation method.The catalysts were characterized by X-ray diffractometer analysis,scanning electron microscopy and Fourier infrared using a fixed site.First,the catalyst design was optimized by using an MCH dehydrogenation reaction as a probe reaction.The MCH dehydrogenation process was optimized.Finally,the MCH dehydrogenation products were also analyzed to determine the by-products and the reaction route of MCH in the dehydrogenation reaction.The results showed that the Ni-Cu/α-Al₂O₃catalyst in the ethanol system was used at a reaction temperature of 673 K,a reaction pressure of 0.2 MPa,a carrier gas flow rate of 2 m L/min,and an MCH feed rate of 0.1 m L/min,and the dehydrogenation conversion of MCH was94.90%,and the selectivity of toluene was 90.10%.The products of MCH dehydrogenation were toluene,benzene,p-xylene and m-xylene.（3）Naphtha’s theoretical hydrogen storage capacity was calculated,naphtha dehydrogenation was tested,and the best catalyst and catalytic reaction conditions were used for MCH dehydrogenation.The results showed that the dehydrogenation of cyclohexane,methylcyclohexane,methylcyclohexane and propyl cyclohexane in naphtha occurred.The reaction conversion decreased gradually with the increase of the length of the substituent.