Effect Of Ionic Liquids On Catalytic Electroreduction Of Coal

China is a country lacking of oil but riching in coal, and most of energy comes from coal. However, pulverized coal combustion is the main process of coal use today,which leads to severe environmental pollution and waste. So liquefaction of coal is of great importance to energy security and environmental protection. Direct coal liquefaction is usually carried out at temperature above 400℃ and under high H2pressure(6-10MPa). In order to reduce the cost of coal liquefaction, simple and inexpensive methods of coal liquefaction under easy-operating reaction conditions should be pursued. Electrochemical hydrogenation of coal is a novel method for coal liquefaction, which applies electrical energy instead of high temperature and pressure to liquefy coal on cathode. The electrochemical method has advantages of mild reaction conditions, simple equipments, and low cost in comparison of the industrial coal liquefaction. In this paper, ionic liquids are introduced to the electrochemical method for direct coal liquefaction to enhance the current efficiency and liquefaction yield.Firstly, ionic liquids have been employed to pretreat coal to modify its network structure. Among the pretreatment agents, 1-butyl-3-methylimidazolium chloride([Bmim]Cl) exhibits the best performance of coal extraction and swelling. Extract yield of the coal sample in [Bmim]Cl reaches to 18.51% and the swelling ratio in[Bmim]Cl is 1.73, which are both the highest among the solvents including other ILs and NMP at the same temperature. The coal sample is pretreated by [Bmim]Cl at optimized temperature(150 ℃), then the pretreated coal is analyzed and characterized by scanning electron microscopy, gas chromatograph, infrared spectroscopy and linear sweep voltammetry. The results show that the coal network is fractured, resulting in a loose and porous structure. The mechanism for pretreatment of coal in ionic liquids has also been proposed.Secendly, catalytic electrode Cu/Ni-W-B is prepared through electrodeposition for electrocatalytic reduction of coal. Characterizations of the layered nanoporous Cu/Ni-W-B electrode have been performed using techniques including X-ray diffraction, inductively coupled plasma and linear sweep voltammetry. The results indicate the Ni-W-B catalysts have typical amorphous structure and the composition(atomic percent) of Ni, W and B in the sample is 59.21%, 17.47% and 23.32%,respectively. In a Na OH + H2 O + tetrabutylammonium bromide mixed system with the pretreated coal sample, a liquefaction yield of 57.6% is obtained after electrolysis on the prepared electrode for 24 h at-1.7 V. The electroreduction mechanism of coal is also investigated. IR and 1H nuclear magnetic resonance results show that active hydrogen(H*) reacts with functional groups in the coal such as C=O,-C-O- and C=C etc, leading to the reduction of unsaturated bonds and breakage of bridge bonds during the electroreduction of coal.Lastly, we prepared ionic liquids modified Ni B amorphous alloy catalyst(IL-Ni B)and applied it in the electrocatalytic liquefaction of coal. The catalyst is characterized by scanning electron microscopy, infrared spectroscopy and X-ray photoelectron spectroscopy. Results show that the catalyst is dispersed well on the Si O2 support. The addition of IL helps electron transformation from B to Ni, leading to B electron-deficient and Ni electron-riched structure, which may facilitate the coal electrochemical liquefaction. From Linear Sweep Voltammetry result, it can be seen that the current of the system with IL-Ni B catalyst is significantly enhanced compared with that of the system with Ni B. The enhanced performance may be owing to that the cover of ionic liquid prohibits the reunion and oxidation of nanoparticles.