Coal-based Endothermic Hydrocarbon Fuel And Its Catalytic Dehydrogenation Endothermic Reaction

The dehydrogenation of alkanes is highly endothermic,which can be applied for the absorption and removal of heat generated during the aviation of hypersonic vehicles to alleviate the thermal barrier as well as to promote the fuel’s enthalpy.Plentiful cycloalkane structures are required for the endothermic hydrocarbon fuel’s dehydrogenation,which can be obtained by kerosene derived from coal-to-liquid fuel after its desulfurization,hydrogenation and fraction cutting.Precious metal catalysts that are sensitive to sulfur are widely used in the hydrogenation saturation,so ultra deep desulfurization is necessary.Hence,highly efficient desulfurization catalysts were developed following two pathways,i.e.,oxidation desulfurization and hydrodesulfurization to achieve the ultra-deep desulfurization of coal-to-liquid fuel.Coal-based endothermic hydrocarbon fuel was achieved by hydrogenation saturation and fraction cutting.Furthermore,highly efficient catalysts were prepared by the introduction of framework heteroatoms and by the deep dealumination of supports.The dehydrogenation of alkanes with different structures was explored.Finally,the dehydrogenation performance and influence of different molecules were examined for mixed fuel,and excellent catalytic dehydrogenation and endotherm were realized under supercritical condition for coal-based endothermic hydrocarbon fuel.The main research contents are as follows:Supported Ti/MCM-41 catalysts were synthesized by adsorption,hydrolysis and calcination under Ar atmosphere,which were applied in the extractive and catalytic oxidation desulfurization of model fuel.The turnover frequency（TOF）in this work was higher than that of reported Ti O₂ catalysts,and ultra-deep desulfurization was achieved at mild conditions.The extractant methanol’s promotion effect and highly active Si-O-Ti structure were discovered and the reaction mechanism of bis-hydroperoxo Ti species for the oxidation desulfurization was proposed.Ni Mo S/CNTs catalysts were prepared by citric acid-assisted hydrothermal method.Ultra-high loading of active species and controllable nanoflake arrays with plentiful stepped sites make it highly active,stable and selective to hydrogenolysis pathway,and the sulfur content decreases from 439ppm to 8.4 ppm for coal-to-liquid fuel.Hydrogenation saturation was realized catalyzed by Pd/Al₂O₃ after desulfurization.Coal-based endothermic hydrocarbon fuel with plentiful cycloalkanes was obtained.Mesoporous MCM-41 supports were synthesized with in-situ incorporated Si-O-Zr structure.Moderate interaction between framework Zr and Pt Sn species is advantageous for the metal species’dispersion and the formation of highly active Pt₃Sn/Pt species.The activity and stability for dehydrogenation of ethane were improved thereafter.Promotor Sn is the key factor for the improvement of dehydrogenation selectivity.The dehydrogenation characteristics of components of endothermic hydrocarbon fuel were studied.Equilibrium conversion was obtained for dehydrogenation of light hydrocarbons such as ethane and propane,while its catalytic ability for dehydrogenation of longer chain alkanes was poor.Deactivation is a problem for dehydrogenation of cycloalkanes,in which methylcyclohexane（MCH）and bicyclohexyl（BCH）exhibited better in dehydrogenation degree and reaction stability.Microporousβzeolites were modified by deep dealumination and the medium and strong acid sites were totally removed.The catalytic activity and stability were further improved.The generated silanol nests are the generation sites of highly efficient Pt Sn active species.Si O₂/Al₂O₃ ratio,dealumination degree,Pt precursor’s charge,Pt and Sn’s impregnation sequence,molar ratio and loading amount greatly influence the catalytic activity.When Si O₂/Al₂O₃=74,dealuminated twice,H₂Pt Cl₆ as Pt precursor,Sn Cl₄ as Sn precursor,co-impregnation of Pt and Sn or step impregnation of Sn first then Pt,0.8 wt%Pt loaded and Pt/Sn=0.5（mol/mol）,the obtained catalyst can achieve equilibrium conversion for ethane’s dehydrogenation to ethene（GHSV=30000m L/（gcat·h））and conversion higher than 95%for dehydrogenation of cycloalkanes（LHSV=30 m L/（gcat·h））at 600°C,0.1 MPa and running time≥120 min.Long chain alkanes and polycyclic alkanes were mixed with MCH separately for the research of their catalytic dehydrogenation characteristics.Dehydrocyclization can be achieved for long chain alkanes.But the catalyst trends to deactivation and MCH’s dehydrogenation is restrained.Dehydrogenation of cycloalkanes is easier and more stable,and the activity sequence is BCH>decalin>MCH.The catalytic dehydrogenation characteristics of coal-based endothermic hydrocarbon fuel were examined at supercritical conditions.Inspiring improvement of dehydrogenation degree and endothermic performance at high temperature（700～750°C）was achieved compared with that at atmospheric pressure.Fuel’s stability can be improved notably.Aromatic content was 88.3 wt%in liquid product and heat sink as high as 4.63 MJ/kg was achieved at 750°C,3.0 MPa and LHSV=240 m L/(g_cat·h).