Upgrade Of Lignite By Catalytic Hydro-liquefaction In Sub/Supercritical Water

The energy structure of our country is "rich coal, less gas, lean oil", sustainable development and utilization of energy has become one of the most important issues in the 21st century, particularly, to obtain combustible gas and liquid fuels from those coal which in low rank can reduce our dependence on fossil fuels and natural gas, and contributed to sustainable energy development. Lignite is a typical low rank coal, although China with rich lignite resources, however its efficient conversion and utilization has been troubled us for a long time because of its high moisture content (30 %-60 %), high volatile, low calorific value (<2000 kcal/kg) and low ignition.Sub/supercritical water catalytic hydro-liquefaction is an effective method for the efficient utilization of resources like lignite et al. Among of them, the optimization of the liquefaction process, catalytic hydrogenation reaction mechanism, oil upgrading and coke quality control is our facing problems in this area. Because sub/supercritical water hydrogenation liquefaction is also a high-energy consumption process, therefore, analyze and explore effective methods to reducing this energy consumption of the process is also our focus that needed to be settled. The study first systematic analysed the influence of the different catalysts’ efficiency on catalytic hydrogenation of lignite at a specific temperature to providing the foundations of upgrading fuels and optimizing catalytic liquefaction process.Studies have shown that 380 ℃,40 min,50 wt% of catalyst loadings conditions, the efficiency of lignite catalytic hydrogenation with the order of Ru/C>Ni/SiO2/Al2O3>Pd/C>Pt/C, a maximum oil yield of 60.23 wt%; The main gases from gasification are H2, CO2 and CH4, and a small amount of CO, C2H4, C2H6; The liquid product components by GC-MS analysis showed that long-chain alkanes and polyphenolic compounds of these two types are the main oil components, different catalysts with different selective to the catalytic hydrogenation of various oil products. The condition of catalytic hydrogenation lignite has advantages of improving oil yield and upgrading oil quality compared to the control group,In order to obtain efficient method of hydrogenation liquefaction of lignite in Sub/supercritical water, this study systemtically analyzed this process under catalyst and investigated the impacts of the reaction parameters:reaction temperature, reaction residence time and catalyst loading etc. on the oil yield and oil quality in the supercritical batch reactors. Finally, qualitativly and quantitativly analysed of the three-phase products. The main conclusions are as follows:(1) In the studies of impact factors, we obtained the conditions of lignite catalytic hydrogenation liquefaction rapidly at low temperature: 320 ℃,2.3MPa (initial H2 pressure), water density of 0.3 g/cm3, 10 min retention time, coal-water ratio of 1:20, 50 wt% of Ni/SiO2/Al2O3 catalyst loading, the oil conversion was 45.61 wt%, total gas conversion of 9.92 wt%and the solid residue in a yield of 41.34 w%.(2) In the optimization study of the liquefaction process, we found that temperature and reaction residence time are the main factors affecting oil yield, the higher the temperature the higher the oil yields in same reaction residence time; oil yield had first increased then decreased after with extension of residence time in the same reaction temperature; low water density conducive to liquefaction while high water density conducive to gasification; While controlling the temperature and reaction time is the key to improve the oil yield;(3) At 320-400 ℃ milder reaction conditions, the gas yield is low, the main gaseous products as H2, CO2, CO, CH4, and trace amounts of C2H4, C2H6; the long-chain alkanes and polyphenols are the two main substances with GC-MS analysis to the oil; combined with FTIR, elemental analysis and SEM analysis to the solid residues, we inferred the mechanism of catalytic hydrogenation liquefaction process;(4) By analyzed and calculated of a three-phase products, oil quality improvement mainly through the following three ways:O heteroatom decreased with CO2, CO and water vapor in gaseous form part; N, S hetero atom transfer to solid components; oil with large number of long-chain alkane-based, low acid, alcohols, ketones content which contribute higher H/C, and the heat value, viscosity has been significantly improved;Based on the above, upgrade of lignite by catalytic hydro-liquefaction in sub/supercritical water can be expected at milder reaction temperatures and in shorter residence time. The higher the temperature, the more significant this effect will be. Through by optimized controled of the key factors that affecting the reaction will absolutely provide reference amplification to engineering production.