Preparation Of Ni-Mg₂Si/γ-Al₂O₃ And Application For Catalytic Hydroconversion Of Yinggemajianfeng Lignite

Since catalysts play a key role in lignites direct liquefaction,it is particularly important to develop a difunctional catalyst for converting lignite into clean liquid fuel under mild conditions.In this paper,Ni-Mg₂Si/γ-Al₂O₃ of different Ni and Mg₂Si contents were prepared using nickel carbonyl as nickel precursor,Mg₂Si as alkali source,and γ-Al₂O₃ as carrier.According to multiple characterizations,Ni and Mg₂Si are successfully loaded on the γ-Al₂O₃,the loading of Mg₂Si is relatively low,and nickel nanoparticles are uniformly distributed on the surface of Mg₂Si/γ-Al₂O₃ and interact with both Mg₂Si and γ-Al₂O₃,and the prepared Ni-Mg₂Si/γ-Al₂O₃ own strong alkalinities.The activities of Ni-Mg₂Si/γ-Al₂O₃ were examined using oxydibenzene（ODB）as reactant.As the result,the suitable loadings of Ni and Mg₂Si are 33 and 20 wt% in Ni-Mg₂Si/γ-Al₂O₃,respectively,and the optimal reaction conditions are 4 MPa of initial hydrogen pressure,240 ℃,and 2 h,under which ODB was almost completely converted to cyclohexane.Ni-Mg₂Si/γ-Al₂O₃ was proposed to have 3 functions,i.e.,activating H2 to biatomic active hydrogen（H…H）,release H-,and heterolytically splitting H…H to release H-as well,resulting in the hydrogenation of aromatic rings and the hydrocracking of C-O bonds,respectively.The reactivity of lignite is often affected by the soluble molecules in lignite structure,which can be removed through solvent extraction and thermal dissolution by methanol of Yinggemajianfeng lignite（YL）to afford extraction（E）and extraction residue（ER）,and methanol-soluble portion（MSP）and thermal dissolution residue（TDR）,respectively.The catalytic hydroconversions（CHCs）of E,MSP,ER,and TDR were examined under the optimal reaction conditions to realize the comprehensive utilization of YL,and the soluble portions（SPs）were analyzed by FTIR and GC/MS.As the result,both E and MSP contain a large number of alkanes,arenes,and oxygen-containing compounds,most of which were converted to cyclanes after CHC,and hardly any aromatic compounds containing benzene ring are detected in the catalysate.The conversions of CHCs for both ER and TDR are significantly higher than those of noncatalytic hydroconversion（NCHC）.SPER-NCHC contains abundant arenes,ketones,esters,nitrogen-containing compounds,and sulfur-containing compounds,while SPER-CHC contains a large number of cyclanes,and scarcely any nitrogen-containing or sulfur-containing compounds are detected in SPER-CHC,implying that most of the aromatic compounds were dissolved via the cleavage of bridged linkages in ER by Ni-Mg₂Si/γ-Al₂O₃,and subsequent heteroatom removal and hydrogenation,and eventually converted to saturated hydrocarbons.However,the NCHC of TDR was not converted at all even for 15 h,but SPTDR-CHC contains not only a lot of alkanes and cyclanes but also arenes and oxygen-containing compounds,revealing that the strong C-C and C-O bridged bonds in TDR,which are connecting condensed aromatic rings,have been cracked by Ni-Mg₂Si/γ-Al₂O₃.In conclusion,the catalysis of Ni-Mg₂Si/γ-Al₂O₃ are catalyzing the cleavage of bridged linkages in YL,and subsequently catalyzing hydrogenation,hydrogenation reduction of carbonyl,dehydroxylation,denitrification,and desulfurization,which are considered as a new method with industrial application value to convert lignites into high added value and clean fuels.