Pyrolysis And Liquefaction Behavior Of Shenhua And Baiyinhua Coal

Direct coal liquefaction(DCL),as one of the efficient ways to convert coal into liquid fuels and chemicals,is of strategic importance to fulfill the energy needs of our society and balance energy structure.Although a high demand of energy exists,the severe reaction conditions of DCL have limited its large-scale application.Shenhua coal used in Shenhua Group liquefaction plant and a typical lignite(Bainyinhua coal)were used in the dissertation.In order to realize mild reaction conditions of DCL and promote oil yield and quality,the pyrolysis and liquefaction behaviour of Shenhua and Baiyinhua coal were investigated with pyrolysis time-of-flight mass spectrometry(Py-TOF-MS)and autoclave reactor.The main research works and results of this thesis are mainly as follows:Coal pyrolysis is the initial step for coal liquefaction,and deep insight into pyrolysis reaction is vital to liquefaction process.The evolution characteristic and distribution of initial pyrolysis products from Shenhua and Baiyinhua coal were online investigated with Py-TOF-MS.The coal pyrolysis products including alkanes,phenols and aromatics were detected.The results reveal that the species and distribution of volatile products largely depend on coal structure.The formation of phenols is related to the thermal decomposition of aromatic Car-O,and Baiyinhua coal releases more phenols.The formation of aromatic compounds can be attributed to two aspects:the dissociative molecules of mobile phase and thermal decomposition of coal structure.The higher condensation degree's Shenhua coal can product more aromatic compounds than Baiyinhua coal.Baiyinhua coal was subjected to catalytic pyrolysis over HZSM-5 and Ni/HZSM-5 for upgrading pyrolysis products.With the assistance of acid sites on the surface and pore structure of HZSM-5,phenols are converted to aromatic products through dehydroxylation reaction.Long-chain alkane undergo catalytic cracking reaction to form alkenes.With the assistance of HZSM-5 and Ni/HZSM-5,the amount of toluene generated increased by 44%and 175%.The introduction of Ni leads to the remarkable increase of catalytic activity toward dihydroxylation reaction.Baiyinhua coal is characteristic as high content of oxygen,which leads to high hydrogen consumption in BYH coal liquefaction reaction.Hydrothermal treatment have been proposed toward upgrading of Baiyinhua coal.Results reveal that oxygen content and volatile matter in treated sample reduce and carbon content increases.CO2 and CO account for the overwhelming majority of gaseous products from hydrothermal treatment,which can be attributed to the significant decrease of carboxyl and carbonyl content.Due to suppress the cross-linking reactions between oxygen containing functional groups and decrease of pyrolysis reactivity,a desirable upgraded coal was obtained by hydrothermal treatment of BYH raw coal at 250 ?.The oil yield increases from 32.9 wt%of raw coal to 37.8 wt%of BYH-250,and hydrogen consumption decreases from 4.8%of raw coal to 4.1%of BYH-250.Coal maceral structure is one of the key factors to coal liquefaction.Shenhua coal and its macerals were analyzed by FT-IR and Solid-State 13C NMR.The results indicate that vitrinite contains more weak covalent bonds(including Cal-Cal,Cal-0 and-COOH)in comparison with raw coal and inertinite,and the aliphatic structure of vitrinite is longer and less branch.The inertinite is of higher aromaticity and has larger cluster size than vitrinite and raw coal.The type and content of covalent bonds lead to different liquefaction behavior of Shenhua coal macerals.The conversion and oil yield in liquefaction process are in the order vitrinite>raw coal>inertinite.More CO2,CO and alkane gases were released from liquefaction process of vitrinite in comparison with inertinite and raw coal.Hydrogen transfer is of great importance to coal liquefaction.The effect of mass ratio of solvent to coal and catalyst on coal liquefaction was studied with autoclave reactor,and mechanism of hydrogen transfer is investigated by comparing the result of solvent free reaction and reaction with aromatic compounds without hydrogen-donation ability as solvent.Results show that:higher mass ratio of solvent to coal can enhance coal conversion and products yield,and the conversion of tetralin droped.There exists the competition between hydrogen transfer from H2 or donation solvent during coal liquefaction.Catalyst obviously promotes the H2 activation and decreases hydrogen transfer from donation solvent.When pyrite and Ni/Al2O3 were used,aromatic compounds play a "bridge" role in hydrogen transfer.When Mo-Ni/Al2O3,H2 can be directly transferred into coal radical fragments.Vitrinite exhibited higher ability of hydrogen acceptability than raw coal and inertinite.Even with low activity catalyst used,H2 can be directly transfered into the vitrinite radical fragments.However,when highly activity catalyst used,H2 can be directly transfered into the inertinite radical fragments,not via shuttle effect of solvent.Aromatic compounds with larger rings show higher hydrogen transfer efficiency.