Study On The Pretreatments Of Shenhua Coal And Its Catalytic Hydro-liquefaction By A Novel Solid Acid

Direct liquefaction of coal will be one of effective paths to compensate the shortage of petroleum sources and ensure the energy supplement. At present, it has becoming main research issues to improve the liquefaction reactivity of feed coal, to moderate the liquefaction conditions and increase the oil yield. Therefore, the aim of this dissertation is to research the pretreatment of feed coal and develop a novel solid acid with higher catalytic cracking activity in order to explore a high efficiency liquefaction technology under moderated conditions. Shenhua coal was used as a feedstock in this dissertation. The effects of hydrothermal treatment and swelling treatment on the hydro-liquefaction behavior of Shenhua coal were studied by the liquefaction experiment in a batch autoclave. Meanwhile, a series of SO₄^2-/ZrO₂ solid acids were prepared by precipitation and impregnation, and characterized by FTIR,NH₃-TPD techniques as well as batch hydro-liquefaction experiments. The impacts of the preparation conditions of catalyst on its structure, acidity and hydro-liquefaction properties were investigated. The catalytic liquefaction mechanism of solid acid was explored. In addition, the kinetics of the hydro-liquefaction of Shenhua coal was studied and a kinetic model was proposed.Results of thermal and hydrothermal pretreatments of Shenhua coal suggest that the cross-linking structure of Shenhua coal, especially the strength and distribution of non-covalent bonds such as hydrogen bond, were changed. The swelling ratio and extraction yield of thermal treated coal are lower than those of raw coal due to the formation of new non-covalent and covalent bond cross link in the process of thermal treatment under higher temperature, in which the devolatilization and the pyrolysis occured obviously. Because of obviously existing hydrogenation during hydrothermal treatment at certain temperature, the CS₂/NMP extraction yield and liquefaction conversion of Shenhua coal were improved. For example the conversion of treated coal at 250℃is 6.3% more than that of raw coal.The results of swelling pretreatment demonstrate that the principal structure of Shenhua coal consists of a large molecular network with covalent bond and the content of small molecular compounds bonding with non-covalent interactions is lower. The CS₂/NMP extraction yield and liquefaction conversion of Shenhua coal can be improved by swelling pretreatment with NMP or THN. The swelling kinetics studies suggest that the swelling process of Shenhua coal between 40℃and 160℃fits to a first order kinetic equation and the apparent activation energy of swelling in NMP and THN are respectively 0.77 KJ/mol and 5.23 KJ/mol.For the hydro-liquefaction of Shenhua coal, the SO₄^2-/ZrO₂ solid acid displays good catalytic activity, especially for the catalytic cracking of coal and its heavy products. Its catalytic activity on the coal liquefaction is related to the strength of acid site and the content of strong acid site. Strong acid site is favorable to catalyze the cracking of coal matrix and large molecular structural units, therefore increasing liquefaction conversion. In addition, the SO₄^2-/ZrO₂ solid acid shows also a good catalytic activity for the hydrogenation reactions. For the hydro-liquefaction of Shenhua coal, the optimal preparation conditions of SO₄^2-/ZrO₂ solid acid are 1 mol/l H2SO4 used as impragnant and calcination at 650℃for 3 hours. The conversion of Shenhua coal reached to 76.77%,when 5%(wt, to coal) SO₄^2-/ZrO₂ and 5.0 MPa H2 were used for the hydro-liquefaction under 400℃for 30min. In addition, the strength of acid site and catalytic properties of SO₄^2-/Fe₂O₃ loaded on SiO₂ are similar to SO₄^2-/ZrO₂, and it gives higher yield of oil+gas compared to that of SO₄^2-/ZrO₂ used as catalyst.The studies of hydro-liquefaction kinetics indicate that the proposed kinetic model is suitable to describe the hydro-liquefaction process of Shenhua coal catalyzed by solid acid between 375℃and 450℃. For all reactions in the model, the rate constants are in the range of 0.2¹8.9×100 min-1 and the apparent activation energies are in the range of 90～145KJ/mol-1. The hydro-liquefaction of preasphaltene and the element analyses and 1H-NMR spectra of liquefied products also further confirmed that this model is reasonable.