Catalytic Hydroconversion Of Naomaohu Lignite Over Magnetic Solid Superbase/Superacid Catalysts

Coal is abundant fossil resources on the planet and will be the main energy subatitute for oil in the future.In China,most of the coal is used for combusition.However,lignites are regarded as low-quality fuel because of their high moisture content,low calorific value,and easy spontaneous combustion.On the other hand,many chemicals,especially oxygen-containing compounds are high value-added chemicals,could be obtained from lignites due to their high oxygen content and volatile matter.Therefore,it is necessary to develop non-fuel use technology for realizing vale-added utilization of lignites.The key issue is to understand molecular compositional features and mild conversion mechansisms.Direct coal liquefaction is one of the effective ways to realize the efficient utilization of coal resources.The preparation of highly active catalysts is the key technology in coal liquefaction.A large of C_ar—O,C_alk—O,and C_ar—C_alk bridges are present in the lignite macromolecular structure.Therefore,the selective cleavage of C_ar—O,C_alk—O,and C_ar—C_alk bridges is of great significance for coal liquefaction and the acquisition of high value-added chemicals.In this paper,a novel magnetic solid superbase?MSSB?and a novel magnetic solid superacid?MSSA?were prepared.A series of characterizations for the above two kinds of catalysts were performed.Transmission electron microscopy?TEM?,Scanning electron microscopy?SEM?,Energy dispersive spectroscopy?EDS?,X-ray photoelectron spectroscopy?XPS?,X-ray diffraction?XRD?,N₂ adsorption,CO₂ and NH₃ temperature programmed desorption?CO₂/NH₃-TPD?and sample vibrating magnetic meter?VSM?analyses.The characterization results showed that MSSB and MSSA catalysts all had large specific,surface area,mesoporous structure,superparamagnetism,recycle and all have high strength alkali or acid respectively.Hydrocracking of oxybis?methylene?dibenzene?OBMDB?and di?1-naphthyl?methane?DNM?were used as probe reactions to investigate the activities of MSSB and MSSA under the different temperature,time,initial hydrogen pressure,and catalyst dosages,respectively.The extraction residue?ER?was obtaind from Naomaohu lignite?NL?exraction with isometric acetone/carbon disulfide mixed solvent in order to avoid the subsequent analysis of small molecule compounds attached to the surface of NL.The ER was subjected to catalytic hydroconversion?CHC?over MSSB and MSSA,in sequence.The non-catalytic hydroconversion?NCHC?were used as contrast experiments.The soluble portions?SPs?from CHC and NCHC were analyzed with a gas chromatograph/mass spectrometer?GC/MS?qualitatively and quantitatively to investigate the catalysis on the hydroconversion of lignite.The yields of products from CHC over MSSB?16.31%?was close to from MSSA?18.65%?.However,the yields of products from sequential CHC over MSSB/MSSA?27.38%?were significant higher than from sequential CHC over MSSA/MSSB.The analysis with GC/MS shows,phenols,alcohols,and esters are the predominant group components in SPs from CHC over MSSB,the SPs from CHC over MSSA are rich in arenes and phenol.These results confirmed that MSSB selectively catalyzed the cleavage of C_ar—O and C_alk—O bonds,whereas MSSA tended to cleave C_ar—C_alk and C_alk—O bonds.In addition,MSSA can also promote many hydrogenation compounds to release from ER.Based on the characteristics of large molecular structure of coals,benzyloxybenzene?BOB?was selected as coal-related model compounds to compare the CHC mechanism of MSSB and MSSA,and combine the group distributions of SPs from CHC and NCHC,the formation mechanisms of arenes and phenols from CHC were revealed,providing a reference for the directional depolymerization mechanisms of coals.