Catalytic thermal dissolution of Zhaotong lignite and composition and structural characterization of its soluble portions
Thermal dissolution(TD)under mild conditions is an effective way to obtain organic species from lignite.However,the conven-tional TD affords low yield of soluble portions(SPs).Herein,a series of Al2 O3-loaded metal catalysts prepared by co-precipitation meth-od were used to investigate the catalytic thermal dissolution(CTD)behavior of Zhaotong lignite in isopropanol.For comparison,TD of Zhaotong lignite was conducted under the same conditions.The physicochemical properties of the catalysts were investigated by XRD,H2-TPR,TEM and XPS,and the compositions as well as structural features of SPs obtained from TD and CTD were analyzed by GC/MS,FTIR and MALDI-TOF-MS.The results show that NiCu/Al2O3 exhibites superior performance to other catalysts on CTD of Zhaotong lig-nite,in which the active components exist in the form of NiCu alloy with interaction between Ni and Cu.The yields of SPs obtained by TD and CTD first increases and then decreases with the elevation of temperature,and the highest yields of SPs from TD and CTD at 320℃ are 27.69％ and 50.54％,respectively.The introduction of the catalyst can increase the yields of asphaltene(AS),preasphaltene(PAS)and oil in SPs,in which the enhancement of the latter two components is more obvious than that of AS.Phenols are the main group compo-nents in the TD derived oil with a relative content of 64.44％,while the CTD derived oil mainly consists of arenes,phenols,alcohols and ketones,indicating that the catalyst promotes the cleavage of covalent bond in the soluble organic fragments and the hydrogenation of phenols.Compared with the AS and PAS obtained from TD,those acquired from CTD possess a narrower molecular weight distribution range,and the intensity of adsorption peaks assigned to the hydroxyl group and ether bonds in the FTIR spectra become weaker or disap-peared,suggesting that CTD facilitates the hydrogenolysis of C—O bonds.CTD can directly get soluble organic species with high yield from lignite under relatively mild conditions,and the results of the study may provide a reference to develope process for directly acqui-ring chemicals from lignite.
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