Catalytic Hydrocracking Of Xilinguole Lignite And Its Model Compounds

In this paper,Ni/N-C-T and Co/Al₂O₃-T catalysts were synthesized by pyrolysis of Ni-containing metal organic framework（Ni-MOF）and calcination-reduction of cobalt-aluminum hydrotalcite（Co Al-LDH）.The physicochemical properties such as pore structure,elemental morphology and micromorphology of the catalyst were analyzed by N₂ adsorption-desorption,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscope with X-ray energy spectrometer and transmission electron microscope.The catalytic hydrocracking performance of Ni/N-C-T and Co/Al₂O₃-T towards C-O bonds in lignite was evaluated in detail using diphenyl ether（DPE）and 2-naphthyl ether（NE）as model compound,respectively,then the catalytic hydrocracking conditions of DPE and NE were further optimized.Fourier transform infrared spectroscopy（FTIR）,XRD and XPS were used to characterize the structure characteristics of organic matter in Xilinguole lignite（XL）and gas chromatography mass spectrometry（GC/MS）was used to analyze the soluble portion（SP）in methanolysis of XL to comprehensively understand the composition and structural characteristics of soluble organic species.The Ni/N-C-T and Co/Al₂O₃-T with high activity were used for catalytic hydrocracking（CH）of XL.FTIR and GC/MS were used to analyze the composition of SP.Thermogravimetry and curie point pyrolysis with gas chromatography/mass spectrometry（CPP-GC/MS）were used to characterize pyrolysis reactivity and volatile emission characteristics of XL and residues from catalytic and non-catalytic hydrocracking（NCH）of XL.The results show that the Ni/N-C-T and Co/Al₂O₃-T are spherical particles with high loading of Ni and Co,as well as good dispersion.Both catalysts contain micropores and mesopores and the specific surface area of Ni/N-C-T and Co/Al₂O₃-T are in range of 39.9-88.3 and 67.2-89.6 m²/g,respectively.The pyrolysis temperature of Ni-MOF and the reduction temperature of Co Al-LDH directly affect the hydrocracking activity of the catalyst.Among them,Ni/N-C-450 and Co/Al₂O₃-700show highest activity in the CH of DPE and NE,respectively.Under the conditions of200 ^oC,0.5 MPa H₂ and 3 h,DPE was completely converted over Co/Al₂O₃-700 and the selectivity of monomers generated by cleaving the C-O bond in DPE reached99.1%.Under the conditions of 250 ^oC,2 MPa H₂ and 90 min,NE was completely converted into monomers.Under the optimal conditions,the direct cleavage of the C-O bond in DPE affording phenol and benzene is the major reaction pathway.During the CH of NE,hydrogenation to 6,6’-oxybis（1,2,3,4-tetrahydronaphthalene）,followed by C-O bond cleavage to generate tetrahydronaphthalene and5,6,7,8-tetrahydronaphthalene-2-naphthol is the major reaction pathway.XL is rich in-OH,C=C and C-O functional groups.The aromatic carbon ratio in XL is 0.65 and the C atoms in XL mainly exist in the form of C-C.The conpounds in the methanol SP of XL are dominated by alkyl and alkoxy substituted phenols,while the relative content of arenes is only 5.08%.Under the conditions of 300 ^oC,2 MPa H₂,4 h and 20 m L n-hexane,the yields of SP in CH of XL by Ni/N-C-450 and Co/Al₂O₃-700 are 12.5%and 15.4%,which are significantly higher than that in NCH of XL（6.4%）,indicating that the two catalysts effectively promote the depolymerization of XL.Using isopropanol as the solvent,the yield of SP in Co/Al₂O₃-700 CH of XL is 52.6%,indicating that the solvent has great influence on the CH of XL.The weight loss of XL,residue in NCH of XL(R_NCH)and residue in CH of XL(R_CH)decrease successively,which is related to the dissolution of more volatile organic matter during CH of XL.CPP-GC/MS analysis shows that arenes are the main compounds in the volatiles of XL,R_NCH and R_CH and the content increase sequentially,while the phenol content decrease sequentially.