Catalytic Alcoholysis Of Xilin Gol Lignite And Catalytic Hydrogenation Of Its Product

China is rich in lignite resources,which have high oxygen,ash,and water contents,and low calorific value,making them unsuitable as fuel.However,lignite can still be of high added value through its utilization as a raw material.The organic oxygen atoms in lignite are mainly found in aromatic ring side chains and bridge bonds that connect these rings.The bond energy of the C-O bridge bonds is low,which allows for the depolymerization of the organic macromolecular structure of lignite by cracking these bonds.Catalytic hydrogenation of the soluble small molecule products can further increase the value of lignite.Therefore,this paper focuses on the preparation of a catalyst for cracking C-O bonds,the two-stage depolymerization of lignite,and the catalytic hydrogenation of the depolymerized products.The catalyst used is Ni/HZSM-5,which was prepared by the deposition-precipitation method.Ethanol was used as a hydrogen donor for the catalytic alcoholysis of（benzyloxy）benzene（BOB）and dibenzyl ether（DE）in an H₂-free system.The results show that the C-O bridge bond cracks most efficiently with a Ni loading of15%.BOB was fully converted at 240℃ for 2 hours,producing toluene and phenol as the main pyrolysis products with selectivity above 80%.DE was fully converted at180℃,producing toluene with a selectivity of nearly 100%.This research demonstrates that Ni/HZSM-5 can efficiently crack C-O bridge bonds in an H₂-free system.The possible cracking path of BOB was also speculated,which involves the activation of ethanol by Ni/HZSM-5 to produce CH₃CH₂O·and H·,with the active free radicals transferring to the C-O bond for cracking.Xilinguol lignite was subjected to a two-stage depolymerization process to obtain soluble small molecule compounds.The lignite was first ethanolysed and then subjected to catalytic alcoholysis using Ni_15%/HZSM-5 catalyst.The yields of the two-stage depolymerization products were 47.8 wt%and 15.1 wt%,respectively,demonstrating the significant effect of the catalyst on the catalytic depolymerization of the lignite’s organic macromolecular structure.The soluble products were analyzed by gas chromatography/mass spectrometry,and the results revealed that the alcoholysis products of lignite consisted mainly of esters,alcohols,and phenols,while the catalytic products were primarily composed of esters,aromatic hydrocarbons,and alkanes.Aromatic hydrocarbons accounted for a relatively high proportion of the catalytic products,indicating that the catalyst contributed to the cleavage of C-O bonds in the lignite’s macromolecular structure.Infrared spectrum,thermogravimetric analysis,and X-ray photoelectron spectroscopy analyses of the raw coal,alcoholysis residue,and catalytic alcoholysis residue revealed a significant reduction in the content of the C-O bond in the catalytic alcoholysis residue.Furthermore,Ni-Co/NC catalysts were prepared using ZIF-67 as a sacrificial template by deposition-precipitation method to catalyze the separation of phenolic components from alcoholysis products.The catalytic performance of the catalyst was tested with model compounds such as phenol and guaiacol.The hydrogenation effect of the Ni_5%-Co/NC-600 catalyst was remarkable.Phenol was entirely converted to cyclohexanol at 140℃ and 2 MPa H₂ for 40 min.When the initial hydrogen pressure was 3 MPa,guaiacol was completely converted to cyclohexanol and 2-methoxycyclohexanol at 160℃ for 60 min,with a total selectivity above 99%.Based on this exploration,Ni_5%-Co/NC-600 was used for the catalytic hydrogenation of phenolic components,resulting in the successful conversion of the phenolic components into cyclohexanols.