Composition Analysis Of Coal Based Liquid And Its Aromatics Catalytic Hydrogenation

In China more than 40% of the total coal reserves are medium/low rank coal and they contribute 30% to the total output of coal. Along with worldwide rapid energy revolution and the government?s strengthening management on air pollution, the processing and utilization of low rank coal draws more and more attention. At present, ways of processing and utilization of low rank coal include direct liquefaction, gasification, low temperature pyrolysis and so on. The direct coal liquefaction oil(DCL oil) is aimed to be used as liquid fuels and chemical raw materials, while one of the main utilization ways of low temperature coal tar(LTCT) is to prepare for gasoline and diesel through catalytic hydrogenation. The methods mentioned above are to utilize the DCL oil and LTCT as alternative energy of petroleum. However, DCL oil and LTCT, as coal-based liquid have their own unique characteristics and advantages, some of which even crude oil doesn’t own. Therefore, it is practically significant to develop a processing route in which the unique characteristics of DCL oil and LTCT are taken advantage of to achieve clean and efficient conversion of coal-based liquid as well as to further improve the added value of two kinds of coal-based liquid products.Considering the DCL oil contains a large number of aromatics and hydroaromatics, while the LTCT contains a lot of two rings and three rings aromatics, this paper aims to convert DCL oil and aromatics from LTCT to products with abundant hydroaromatics and cycloalkanes which could be used as ideal blend composition of jet fuel through catalytic hydrogenation. During the process of this research, separation and analysis of DCL oil and LTCT were first implemented. By referencing the technology of preparative liquid chromatograph, the silica-gel column chromatography technology(SGCC) was improved. A pressure pump was used to improve the elution efficiency and a UV-absorbance detector was installed at the end of the column to verify the elution completion of each fraction. Utilization of large volume column in which more stationary phase could be packed is to separate more sample. In order to separate the fractions of DCL oil and LTCT more precisely according to their different properties, n-pentane, dichloromethane, ethyl acetate, methyl cyanide and methanol are chose as mobile phase. The eluted fractions were analyzed by GC-MS, GC×GC-TOFMS, FTIR, 1H NMR, XPS, etc. The components of the two kinds of coal-based liquid were acquired and compared. Basing on the composition of the two kinds of coal-based liquid and the research target, the enriched aromatics from LTCT was used as feed for hydrogenation, while the full range of DCL oil was hydrogenated without any pro-processed. During the experiments of hydrogenation of aromatics from LTCT into hydroaromatics and cycloalkanes, three series of catalysts were prepared based on the properties of LTCT. The hydrogenation properties of the Ni W/γ-Al2O3 catalysts which were modified with different contents of phosphorus by sequentially impregnation and co-impregnation method were investigated and compared. The hydrogenation properties of the Co Ni W/γ-Al2O3 catalysts added with different content of Co were investigated. The catalysts were characterized by N2 adsorption, H2-TPR, XRD, NH3-TPD, SEM and so on. With a fixed-bed reactor under certain conditions,the hydrogenation reaction pathways and the catalytic performance on naphthalene were investigated. For the Co Ni W catalyst, the hydrogenation reaction path and the catalyst performance on benzothiophene and quinoline were investigated additionally. According to the hydrogenation performance on model compounds, catalysts with high performance were selected for the hydrogenation of aromatics from LTCT and its effect on converting aromaics into hydroaromatics and cycloalkanes were investigated. At the same time, some catalysts’ effect on HDN, HDS and carbon deposit were also investigated. Besides, the conversion feasibiliy of full range DCL oil into jet fuel and the catalytic hydrogenation reaction mechanism were also discussed.The main conclusions are as follows:(1) Utilizing the preparative liquid chromatograph technology, the DCL oil and LTCT were separated by four kinds of mobile phase. The main components in LTCT are aromatics, O-containing compounds and N-containing compounds, followed by the heteroatomic compounds. Alkanes and alkenes are the least. The detailed contents of each component are as follows: 5.63% of alkane, 7.97% of alkene, 22.47% of aromatics, 31.19% of O-containing compounds, 17.66% of N-containing compounds and 10.79% of heteroatomic compounds. The dominant components in DCL oil are hydroaromatics, followed by aromatics, N-containing compounds and O-containing compounds. The detailed contents of each component are as follows: 9.06% of alkanes, 36.32% of hydroaroamtics, 17.85% of aromatics, 15.39% of O-containing compounds and 16.21% of N-containing compounds. Comparing the two kinds of coal-based liquid, it could be concluded that DCL oil contains more hydrocarbons, in which the dominant content is hydroaromatics and it contains no alkene, while the LTCT mainly contains O-containing compounds, N-containing compounds and aromatics, with certain alkenes but little hydroaromatics. DCL oil and LTCT, both of which contains high amount of(hydro)aromatics with 2-4 rings, have a good potential to be used as the source of jet fuel.(2) The Ni W catalysts modified with different content of P were prepared by co-impregnation method. The results show that P could expand the pore diameter and promote the dispersion of active metal components on the surface of the catalyst. 1%~1.5% of P could lower the reduction temperature, promote the generation of Ni-W-O phase and increase the content of weak acid on the surface of catalyst. When using the catalyst with 1% of P, the reaction conversion rate of naphthalene is more than 75%, while the content of decahydronaphthalene reaches the maximum in the hydrogenation products, which is more than 50%. The trans-/cis-decalin ratio is also relatively high when the catalyst added with 1%~2% of P. Ni W+1.0%P catalyst was used for the hydrogenation of enriched aromatics from the LTCT with the boiling point from 210℃ to 360℃。1% of aromatics was dissolved into the cyclohexane for the reaction. Results from GC-MS show that the hydrogenation reaction and the removal of heteroatoms are remarkable, with most of the aromatics transformed into cycloalkanes. GC×GC-TOFMS analysis method was used to classify and quantify the feed and the products. Results show that the aromatics consist 40% of the feed, while it only consist 4.93% of the product, of which the two-ring aromatics was merely 0.75%. These contents are far less than the national standard, in which the aromatics is required less than 20% and the naphthalene is less than 3%. At the same time, the content of one-ring cycloalkanes in the products is 43.25%, which is higher than the content of the one-ring cycloalkanes in the petroleum-based jet fuel by catalytic cracking. Meanwhile, the content of heteroatom compounds is reduced from 38.27% to 6.64% by hydrogenation. By comparing the requirements in the national standard of jet fuel No.3, the production through hydrogenation reaction could be used as the bending components for jet fuel.(3) By the sequentially impregnation method, the catalysts were prepared by impregnation of P on the γ-Al2O3 support first and then by the active phase of Ni and W. It could be found that effect of P on the performance of the catalyst is more obvious and the hydrogenation property is higher than co-impregnation. The reduction temperature of catalyst was obviously reduced by sequentially impregnation of P and the reducing in reduction temperature is higher than that of the co-impregnation method adding catalysts with P. Adding P by the sequentially impregnation, the total acid amount was increased. The conversion rate of naphthalene shows a reverse U shape with the increasing content of P, and the maximum reaches to 90% when using the catalyst with optimal hydrogenation performance(P2), while the conversion rate of naphthalene is about 75% when using the catalysts of PNi W prepared by co-impregnation. Besides, the content of decahydronaphthalene in the products is higher than 52% with high trans-/cis- ratio. The aromatics components from LTCT dissolved in toluene(with a mass fraction of 10%), was catalytically hydrogenated with Ni W/γ-Al2O3 catalysts which were modified with P by sequentially impregnation method. Results show that, with the content of P increasing, the hydrogenation performance has a reverse U shape, reaching its peak when the content of P is 1%. At this point, the content of aromatics decreases from initially 60% to 2%, and hydroaromatics in the product reaches nearly 70%. Meanwhile, the catalyst shows good performance on HDS and HDN, of which the rate is 71.6% and 99%, respectively.(4) The addition of Co in Ni W/γ-Al2O3 catalysts has a very limited impact on the dispersion of active metal components, reduction temperature, surface acidity, pore volume and pore diameter. Results from the hydrogenation of naphthalene show that, with the addition of Co, the conversion rate of naphthalene first increases and then decreases. The addition of Co has an inhibiting effect both on the generation of decahydronaphthalene and its trans-/cis- isomerism ratio in the products. Results from the hydrogenation of benzothiophene dissloved in cyclohexane(with a mass fraction of 0.4%) and quinoline dissloved in cyclohexane(with a mass fraction of 4%) show that both benzothiophene and quinoline were completely converted. The hydrogenation products of benzothiophene are bascially alkylbenzene(60%~70%) and alkyl cyclohexane(20%~25%), while the hydrogenation products of quinoline are alkylbenzene, alkyl cyclohenxane and hydroquinoline. The catalytic hydrogenation of aromatics components of LTCT, using SCo-1 catalyst which has a high performance in selective reaction activity, hydrogenation, HDS and HDN, shows that SCo-1 catalyst could reduce the content of aromatics from 60% to 36% and improve the content of hydroaromatics in the products to 35% as well as generate certain cycloalkanes. In the mean time, the content of alkane in the products increases, indicating that some ring-opening reactions happened during the catalytic hydrogenation. The catalyst also shows good performance on desulfurization and denitrogenation.(5) As the DCL oil contains low content of S, N and O, high content of hydroaromatics and owns low boiling point range, the full range of DCL oil was hydrogenated. The effect of reaction temperature and hydrogen pressure on the distribution of gas and liquid products were investigated, while the reaction machenism were also studied. There are four key conclusions:(1) With the reaction temperature rising, the content of hydroaromatics has a reverse U shape. At 300℃,the content of the aromatics in the products reaches maximum, which is 51%. Then with the temperature continuous rising, the content of hydroaromatics and alkanes decreased rapidly and the aromatics increased sharply, while the yield of liquid products reduced. The change of gas products could be divided into three stages, when temperature was at 200℃-400℃, all the five kinds of gas were produced with little amount; at 400-500℃, the methane and ethane in the products increased obviously; while higher than 500℃,all five kinds of gas products generated prominently, expecially the methane and ethane.(2) The change of the content of gas products and liquid products is decided by the main reaction type under different reaction temperature. The main reaction under 400℃,is hydrogenation. At 400-500℃, the mian reaction is hydrocracking. When the temperature is higher than 500℃,the main reaction is thermal cracking, the strong reactions will lead to generate lots of methane and ethane.(3) Keeping the temperature at 300℃,the main reaction is hydrogenation. The content of hydrocarbons increases with the pressure rising, but after the pressure surpasses 4MPa, the increasing tendency decreases. The content of methane and ethane increases with the pressure rising, while other gases have very limited response to the change of pressure.(4) At the best reaction condition(300℃, 4MPa), the catalyst activities of HDN, HDS and HDO were 35.56%, 72.73% and 24.20%, respectively. The H/C ratio in the liquid oil increased from 1.37 to 1.52. The results indicated that the catalytic reaction has a good performance on the removal of heteroatoms.(5) At the best reaction condition(300℃, 4MPa), the distillate with boiling point between 100-280℃ increased,and the increased compounds(hydroaromatics with 2~3 rings and cycloalkanes) are high quality blend components for jet fuel. The hydrogenated products still need to be cut to acquire the appropriate blend components of jet fuel.