Preparation Of NiMoC/h? Catalyst And Its Application In Low Temperature Coal Tar Hydrogenation

It can be known that modern coal chemical industry is an effective way for the clean and efficient use of coal.Coal,which has been used cleanly and efficiently,is clean energy.As an important intermediate product in the coal pyrolysis and coking process,coal tar has the characteristics of large output and high utilization value.At present,rational and efficient utilization of low temperature coal tar can promote the clean and efficient conversion of coal,which main processing and utilization method is hydrogenation of low temperature coal tar to produce fuel oil,partially replacing petroleum resources in China.Meanwhile,in view of the strict environmental regulations,reducing the content of aromatics in fuel oils has become a key step for processing fuel oil,and conductive to reducing environment pollution during fuel utilization.However,hydrogenation of large amounts of aromatics in low temperature coal tar into cycloalkanes or hydrogenated aromatics,both of which are ideal blending components of coal-based jet fuels.Therefore,in order to convent aromatic components in low temperature coal tar into the blending components of the coal-based jet fuel as much as possible,the development of an efficient and highly selective hydrorefining catalyst in this study is significant to the clean conversion of coal tar.Porous H?zeolite supported Ni Mo bimetal carbides catalyst was proposed and prepared in the research of low temperature coal tar hydrogenation,based on extensive literatures research and preliminary experimental exploration.Hydrogenation of model compounds including naphthalene and phenanthrene,as well as real oils to evaluate the catalyst hydrogenation performance.On the basis of previous exploratory experiments,the effects of support preparation conditions on catalysts physical and chemical,as well as aromatics hydrogenation performance were studied.The preparation conditions include Si/Al ratio,crystallization time,and using PDADMAC template agents with different molecular weight.The prepared of samples were characterized by XRD,N₂adsorption-desorption,XRF,NH₃-TPD,H₂-TPR,Py-FTIR,SEM,HRTEM,XPS,etc.Meanwhile,using GC-MS,GC and elemental analyzer to analyze the liquid products produced by hydrogenation.The gas products produced by hydrogenation were analyzed by GC and hand-held NH₃ tester.Furthermore,the hydrogenation reaction mechanism of catalyst was revealed,and the structure-activity relationship of the catalyst was clariefied by analyzing the experimental results.In the final,the effects of reaction temperature and pressure on the hydrogenation performance of aromatics from low temperature coal tar were studied.Meanwhile,compared the aromatics hydrogenation performance of NiMoC/H?catalyst with traditional catalysts including Ni Mo S/H?,Ni Mo S/Al2O3,NiMoC/Al2O3,and the prepared NiMoC/H?catalyst was verified to have superior aromatics hydrogenation performance and heteroatom resistence.The main conclusions of this study are as follows:(1)In this work,the novel NiMoC/H?catalysts prepared exhibit excellent selectivity for aromatic hydrogenation.It can be found that the catalyst NiMoC/H?has higher naphthalene hydrogenation activity from the blank control experiments.The optimum temperature is 225°C for the naphthalene hydrogenation,and the decalin will undergo ring opening and isomerization reactions at higher reaction temperature.The catalyst exhibited better hydrogenation performance for phenanthrene and low temperature coal tar hydrogenation.In according to the analysis of the low temperature coal tar hydrogenation products,it was found that hydrodenitrogenation is difficult to hydrodesulfurization for NiMoC/H?catalyst.(2)The changes of initial Si/Al ratio during the preparation of H?zeolites affects the physical and chemical properties of H?zeolites and NiMoC/H?catalysts,as well as aromatics hydrogenation performance of NiMoC/H?catalysts.It can be found that the change of the Si/Al ratio has little on the specific surface area and pore structure distribution of the NiMoC/H?catalyst.The total acidity and B/L ratio of H?-x and NiMoC/H?-x decreased as the initial Si/Al ratio increased.The active metal phase consisted of Ni,Ni₃Mo₃C,Ni₆Mo₆C,fcc?-Mo C_x and hcp Mo₂C for all the prepared NiMoC/H?-x catalysts,all of which interacted with the B acid sites of the H?zeolites and its adjacent framework oxygen atoms.Meanwhile,the interactions between the active metals and the supports decreased as the initial Si/Al ratio increased,resulting in the dispersion of the active metals decreasing in the same order.Therefore,the higher density of B acid sites of the supports enhanced the metal dispersion and reduced the electron density of d orbitals,both of which improved the hydrogenation activity and tolerance to N atoms of the catalysts.Menawhile,the trend of catalytic activity was in accordance with both the dispersion of active metal and the acidity of the catalyst in the hydrogenation reaction of naphthalene and quinoline.The NiMoC/H?-18 catalyst exhibited the highest aromatics hydrogenation performance.Furthermore,the pure H?phase had a better tolerance to nitrogen-containing compounds than the H?-ANA mixed phase.(3)Different crystallization time has important effects on the pore size distribution,particle size and acidity of H?zeolites,and affects the physical and chemical properties,as well as the aromatics performance of NiMoC/H?catalyst.The relative crystallinity and grain size of the H?zeolites increased with the increase of crystallization time,while the BET surface area and total pore volume of NiMoC/H?-Tx catalysts slightly decreased.The total acidity of NiMoC/H?-Tx catalysts increased with the increase of crystallization time,and the NiMoC/H?-T5 catalyst with the crystallization time of 240h and the H?-T4support with crystallization time of 168h exhibited higher B/L ratio.The active metal phase of NiMoC/H?-Tx catalysts are composed of Ni,hcp Mo₂C,fcc Mo C_x,Ni₆Mo₆C,and Ni₃Mo₃C,which composition affected by the crystallization time of H?zeolites,and most of them interacted with strong B acid sites of supports.The NiMoC/H?-T5 catalyst displayed higher catalytic activity of naphthalene hydrogenation.Additionally,quinoline prefer to hydrogenate than naphthalene by calculating the reaction rate constant where naphthalene and quinoline coexist.Meanwhile,the NiMoC/H?-T4 catalyst exhibited higher resistance to nitrogen atoms and hydrogenation activity.It could be concluded that the higher B/L ratio of catalysts gives rise to an increase in hydrogenation activity of naphthalene.Additionally,the higher amount of B acid sites of supports and appropriate amount of Ni_xMo_yC composition will enhance the nitrogen atoms tolerance of catalysts,while bigger grain size of supports is not conducive to resistance to heteroatoms compounds and hydrogenation of naphthalene.(4)Using different molecular weight of PDADMAC as template,H?zeolites and NiMoC/H?-Mx catalysts with different pore size distribution were successfully prepared.Meanwhile,the prepared NiMoC/H?-Mx catalysts exhibit excellent aromatic hydrogenation performance.With the increase of PDADMAC molecular weight,the mesoporous pore size and volume of the prepared H?-Mx zeolites and NiMoC/H?-Mx catalysts increase.The NiMoC/H?-M3 catalyst with the PDADMAC of 400000-500000,exhibited the highest pore size and volume.While the larger molecular weight not conductive to the formation of more acid sites for H?-Mx zeolites.Meanwhile,the difference in the molecular weight of the template will cause different interactions between the active metal and the support of the corresponding catalyst.The NiMoC/H?-M3 catalyst with the highest dispersion of active metal,which determined by the physical structure including specific area,pore size and volume and acidity of H?supports.The B/L ratio of total acid sites and strong acid sites,and the dispersion of active metal,play the important role in hydrogenation of model compounds including naphthalene and quinoline.Especially,the higher B/L ratio of strong acid sites will enhance the tolerance to nitrogen atoms.The mesopore diameter of catalysts play a dominant role in the hydrogenation of real oil,and the effect of diffusion limitation is more prominent in the hydrogenation of real oil.The NiMoC/H?-M3 catalyst exhibited excellent aromatics hydrogenation performance in hydrogenation of real oils,which was attributed to its higher total volume and bigger pore size,as well as higher dispersion of active metal.(5)The prepared NiMoC/H?-M3 catalyst shows excellent hydrosaturation and hydrodesulfurization performance in hydrogenation of arenes from low temperature coal tar.It can be found that the aromatics hydrogenation activity increased first and then decreased with the increase of the reaction temperature.The aromatics hydrogenation performance of NiMoC/H?catalyst is best at the temperature is 275?,and the content of cycloalkanes and hydrogenated aromatics is close to 70%,and the content of aromatics is 15.33%.From the perspective of thermodynamics and kinetics,all of them reach the optimal operating poont at the temperature is 275?,which makes the catalyst exhibite the best hydrogenation performance.The analysis of hydrogenated gas products and liquid products suggest that the hydrodenitrogenation activity is affrected by many factors.The denitrification effect is not simply increased with the increase of cracking degree,which is also affected by hydrodesulfurization and hydrodeoxidation reactions.From the perspective of reaction acticity and operating cost,the optimal reaction pressure is 3 MPa and the optimal reaction temperature is 275?.Correspondingly,the content of cyclokanes and hydrogenated aromatics is higher,while the aromatics content is almost zero.The metal carbide catalysts including NiMoC/H?and NiMoC/Al₂O₃ catalysts exhibite better hydrogenation performance than the metal sulfide catalysts including Ni Mo S/H?and Ni Mo S/Al₂O₃ catalysts.Meanwhile,the strong acidity of support is not conductive to the vulcanization of active metal componenets for the metal sulfide catalyst,which is not conductive to enhance the aromatics performance.Therefore,the hydrogenation performance of Ni Mo S/H?catalyst is weaker than the Ni Mo S/Al₂O₃catalyst.