Integrated Process Of Coal Pyrolysis With CO2Reforming Of Methane For Tar Production

Coal tar, the high quality liquid fuel and important chemical raw material, has been widely studied. In this work, the effect of technological conditions, coal properties and preparation conditions of Ni/MgO and Ni/Al2O3-MgO catalysts on integrated coal pyrolysis with CO2reforming of methane was studied and the properties of char from the integrated process were analyzed. Besides, coal pyrolysis under CH4/CO2/O2and simulated coal gas was also discussed. The major works and results are as follows:The effect of pyrolysis temperature, holding time, CO2/CH4ratio, CH4flow rate and coal properties on the integrated process was investigated in a fixed-bed reactor containing upper catalyst layer and lower coal layer, and the appropriate reaction conditions were determined. The results indicated that the tar yield increases with the increase of pyrolysis temperature, holding time, CO2/CH4ratio and CH4flow rate. Pingshuo coal has higher tar yield under CH4/CO2than Shendong, Lingwu and Hami coals, which is1.6and1.8times as that under H2and N2, respectively, at the appropriate reaction conditions. And the high tar yield is related to the CHx groups produced in CO2reforming of methane. The influence of pyrolysis temperature and O2/CH4ratio on Pingshuo coal pyrolysis under CH4/CO2/O2was also discussed. The results showed that the tar yield enhances with increasing pyrolysis temperature, and has a maximum with increasing O2/CH4ratio.Thermogravimetric analyzer, infrared spectrometer and intelligent sulfur tester were used to analyze the properties of char from coal pyrolysis. Thermogravimetric analysis showed that coal pyrolysis under CH4/CO2is relatively completed and the volatile matter content of char is lower than that from pyrolysis under N2. FTIR spectra showed the intensities of stretching vibration peaks of organic functional groups in char from pyrolysis under CH4/CO2decrease compared with those in coal. The sulfur content in char from pyrolysis under CH4/CO2is lower than that from pyrolysis under N2. And the char from pyrolysis under CH4/CO2with lower volatile matter content is less reactive than that from pyrolysis under N2.Ni-based and Co-based catalysts were prepared by incipient wetness impregnation. The effect of catalyst active component and support, Ni loading, calcination and reduction temperatures of Ni/MgO catalysts on the integrated process was discussed and the appropriate preparation conditions of Ni/MgO catalyst were determined. Among all the catalysts, Ni/MgO catalyst provides higher tar yield and lower carbon deposition on the catalyst. With the increase of Ni loading and reduction temperature of Ni/MgO catalyst, the tar yield increases. And Ni/MgO catalyst prepared at appropriate conditions shows high and stable activity, which can be ascribed to the high dispersion of reduced Ni species and the basicity of the support surface.Industrial Ni/Al2O3catalysts modified by MgO, CaO and BaO were prepared. The effect of catalyst promoter, MgO content, calcination and reduction temperatures of Ni/Al2O3-MgO catalysts on the integrated process was investigated and the appropriate preparation conditions of Ni/Al2O3-MgO catalyst were determined. Higher tar yield and lower carbon deposition over Ni/Al2O3-MgO catalyst are obtained than those over Ni/Al2O3-CaO and Ni/Al2O3-BaO catalysts. With increasing MgO content from1to8wt.%, and reduction temperature from550to850℃, the tar yield enhances. And Ni/Al2O3-MgO catalyst prepared at appropriate conditions displays high activity and stability in the integrated process, which results from the formation of NiO-MgO solid solution.The effect of pyrolysis temperature, gas flow rate and coal properties on coal pyrolysis under simulated coal gas containing25%CH4and CO2, respectively, was studied. With the increase of pyrolysis temperature and gas flow rate, the tar yield increases. Shenmu coal shows higher tar yield compared with other coal samples. And the tar yield of Shenmu coal pyrolysis under catalysed simulated coal gas is1.8and2.9times as that under H2and N2, respectively.