Catalytic Depolymerization And Directional Transformation Of Organic Matter In Xinjiang Dahuangshan Lignite

Lignites are abundant fossil resources in China.They are rich in aromatic rings and heteroatomic units,which have the natural advantage of obtaining value-added products from them.Based on this characteristic,understanding the existence forms of organic oxygen and developing the non-fuel utilization technologies are essential to achieve the efficient use of such fossil resources.Converting the organic matter from lignites into derived soluble portions under relatively mild conditions and directional upgrading based on the compositional feature differences are the key links.In this thesis,based on the concept of“hierarchical and directional utilization of derived light/heavy fractions and residues”,3 catalysts were designed,including Ni/M?metal-metal oxide composite?,CoMoS_xO_y@C?metal sulfide-oxide composite?,and NiFe₂O₄?bimetallic oxide?.Taking the Xinjiang Dahuangshan lignite?DL?as the research object,3 catalytic depolymerization strategies were proposed,including the catalytic ethanolysis of DL,the two-step cascade catalytic depolymerization of DL,and the catalytic hydrocracking of extraction residues from DL.In addition,the compositional features of derived light/heavy fractions and residues were analyzed and evaluated in detail.Based on the differences in characteristics,molecular dynamics simulation and density functional theory?DFT?calculations were used to investigate the relevant extraction or reaction mechanisms.?1?For the catalytic ethanolysis of DL:Ni/M can effectively activate ethanol and promote the transfer of various active species including hydrogen proton?H⁺?,hydrogen radical?H·?,ethyl radical?·CH₂CH₃?,and ethoxy radical?·OCH₂CH₃?.The introduction of Ni/M significantly increased the yield of DL-derived soluble portions,including light fraction?ESP_C,32.4 wt%?and heavy fraction?34.1 wt%?.More abundant alkanes and arenes were detected in ESP_C,indicating that Ni/M could effectively promote the in-situ removal of oxygen atoms in solubles,especially light fractions.For the catalytic hydroconversion?CHC?of ESP_C,H₂ can be effectively activated to biatomic active hydrogen?H···H?over Ni/M.Both H₂ and H···H can be further activated to H·with the synergy of metal-metal oxide.Therefore,there are synergetic transfers of 3 active hydrogen species,i.e.,H⁺,H·,and H···H,during this period.The aromatic ring-and heteroatom-containing species in hydrogenated oil were significantly reduced,while the proportion of alkanes and cyclanes increased.In addition,the rearrangement of hydrogenated products can be induced by acidic catalysts to form bicyclic cyclanes.A ternary mixed solution consisting of petroleum ether,methanol,and water?5%water content?can be used to rapidly enrich hydrocarbon-rich and phenol-rich light oils from light fraction.The results of molecular dynamics simulation further confirmed that various interactions including van der Waals,H-?and H-H,together promote the rapid enrichment of hydrocarbons and arenols in petroleum ether phase and methanol/water phase,respectively.?2?For the two-step cascade catalytic depolymerization of DL:a new metal sulfide-oxide composite,CoMoS_xO_y@C,was designed by in-situ co-pyrolysis and pre-vulcanization strategy.CoMoS_xO_y@C with highly dispersed bimetals and rich hierarchical pores can effectively activate H₂ and ethanol in different systems and promote the cleavage of multiple bridged bonds including>C-O-without hydrogenation of the aromatic rings.The two-step cascade of catalytic hydrocracking and ethanolysis can not only improve the utilization efficiency of the catalyst,but also increase the yield of soluble portion?from 42.7 to 70.0 wt%?.Among them,the total yield of light fractions increased from 17.5 to 27.0 wt%.The CHC of two-stage light fractions further confirmed that the hydrogenation of aromatic rings is easier than the removal of heteroatoms.During the CHC,heteroatom removal is one of the rate-controlling steps.After comprehensive analysis and evaluation,the derived light fractions in the first-stage?thermal dissolution/catalytic hydrocracking?are more suitable for upgrading to clean liquid fuels through the CHC,while those rich in heteroatom compounds in the second-stage?ethanolysis/catalytic ethanolysis?are more suitable for obtaining value-added chemicals from them by rapid enrichment,column chromatography separation,and/or purification.?3?For the catalytic hydrocracking of extraction residues from DL:a one-pot hydrothermal method for the rapid preparation of nickel ferrite?NiFe₂O₄?nanospheres was designed.NiFe₂O₄,which can be recovered by an external magnetic field,has good>C-O-bridged bond cleavage activity,which is related to its characteristics of effectively activating H₂ and H···H as well as promoting the transfer of H·.Raising the temperature and reducing the initial H₂ pressure can effectively reduce the formation of hydrogenated and/or rearranged products,and improve the selectivity and yield of arenes.In addition,NiFe₂O₄ has good cycle stability.After the introduction of NiFe₂O₄,the yield of soluble portion increased from 13.6 to17.7 wt%.Among them,the yield amplifications of the light and heavy fractions are 9.8%and46.7%,respectively.The yield of arenes in the catalytic hydrocracking-derived light fraction?SP_C?was significantly improved,further confirming the ability of NiFe₂O₄ to remove heteroatoms in situ from the soluble portions.Compared to the ethanolysis-derived light fractions,the content of heteroatom species in extracts?EP?and SP_C is relatively low,so the time required for the CHC procedure of EP or SP_C is shorter.In addition,the deoxygenation is easier to perform than the denitrification or desulfurization,and the hydrogenation catalyst is more resistant to oxygen atoms than nitrogen/sulfur atoms.The composition of EP and SP_C is different,and both of them can be effectively converted into derived hydrogenated oils rich in alkanes and cyclanes.Such hydrogenated oils have the potential to be upgraded to clean liquid fuels.?4?For the analysis of the compositional features of heavy fractions:the derived heavy fractions obtained by 3 different strategies,including DL thermal dissolution in cyclohexane?AP_C?,ethanolysis?AP_E?and two-step sequential thermal dissolution in cyclohexane and ethanol(AP_CE),were analyzed and evaluated in detail.The microstructural characteristics of AP_C and AP_E/AP_CE are significantly different.In addition,AP_C may contain more-OH,>C=O,and>C-O-functional groups,and may still contain some medium/small molecules and weak/medium strength covalent bond units,including the structure of bridged bonds.AP_E and AP_CE are mainly composed of macro/super macromolecular groups,and the aromaticity of AP_CE may be higher than that of AP_E.The analysis results with a CPP-GC/MS show that compared with the thermal dissolution in inert solvents,alkanolyses have better cleavage effect on nitrogen and sulfur bridged bonds in macromolecular groups.Based on the analysis of ruthenium ion-catalyzed oxidation,AP_CE may be dominated by cata-condensed aromatic and polyaryl units,followed by a small number of peri-condensed aromatic units,long-chain saturated ring units,aromatic ring units with longer aliphatic side chains,and polymethylene linkage units.?5?For the analysis of the structural difference of DL-derived residues:alkyl-substituted naphthalenes and phenols may be present in the nested groups of DL.With increasing the destructive degree,the aromaticity of organic matter from the derived residues increases.The>C-OH and>C-O-moieties dominate the surface of all the samples,while the pyrrolics and SO₄^2-,SO₄^2-,and-SO₃H are the most abundant nitrogen-and sulfur-containing species,respectively.The cleavage of medium strength covalent bonds,i.e.,>C_al-X bonds(X=H/C_al</O-/N</S-),should be the main reaction during the DL extraction and degradation.Based on the differences in characteristics,the derived residues can be applied to different processes,including pyrolysis,sequential thermal dissolution/alkanolysis,catalytic hydrocracking,and preparation of carbon materials.?6?For the DFT calculation:under the premise of inhibiting the H···H transfer and effectively obtaining H·,lowering the temperature is favorable for the cleavage of>C_ar-O-bridged bonds.Properly increase the acidity of the support to ensure the release of sufficient H⁺,which is conducive to the cleavage of>C_al-O-bridged bonds,especially>C_al-OH bonds.The introduction of one of the 3 catalysts may lower the energy barrier for*C_al-O-bond cleavage.In addition,ethanolysis can also induce the cleavage of>C_al-O-bridged bonds,which involves the transfer of H·and·OCH₂CH₃,not·OH.This thesis contains 135 Figures,141 Tables,and 355 references.