Catalytic thermal dissolution of Zhaotong lignite and composition andstructural characterization of its soluble portions
ZHAO Yunpeng;WU Fapeng;QIU Lele;XIAO Jian;CAO Jingpei;WEI Xianyong
Thermal dissolution (TD) under mild conditions is an effective way to obtain organic species from lignite. However, the conventional TD affords low yield of soluble portions (SPs). Herein, a series of Al2O3-loaded metal catalysts prepared by co-precipitation method were used to investigate the catalytic thermal dissolution (CTD) behavior of Zhaotong lignite in isopropanol. For comparison, TD ofZhaotong lignite was conducted under the same conditions. The physicochemical properties of the catalysts were investigated by XRD, H2TPR, 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 lignite, in which the active components exist in the form of NiCu alloy with interaction between Ni and Cu. The yields of SPs obtained by TDand 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 components in the TD derived oil with a relative content of 64.44%, while the CTD derived oil mainly consists of arenes, phenols, alcoholsand ketones, indicating that the catalyst promotes the cleavage of covalent bond in the soluble organic fragments and the hydrogenation ofphenols. Compared with the AS and PAS obtained from TD, those acquired from CTD possess a narrower molecular weight distributionrange, and the intensity of adsorption peaks assigned to the hydroxyl group and ether bonds in the FTIR spectra become weaker or disappeared, suggesting that CTD facilitates the hydrogenolysis of C—O bonds. CTD can directly get soluble organic species with high yieldfrom lignite under relatively mild conditions, and the results of the study may provide a reference to develope process for directly acquiring chemicals from lignite.
Zhaotong lignite;catalytic thermal dissolution;soluble portions;oil;asphaltene;preasphaltene