| Tar,the main by-product coal,has made up a large proportion in coal pyrolysis process,and its amount can reach several ten million tons.Reasonable utilization of coal tar and accelerate the progress of lighter oil products have a positive effect on alleviating the shortage of oil resources in China.In view of the situation,this topic proposes a dolomite catalytic system process coupled with an existing coal pyrolysis/CFB combustion system.Catalytic hydrocracking of two kinds coal tar fractions,anthracene oil and washing oil,was studied with the high-efficiency and inexpensive dolomite catalysts on a fixed-up bed reactor.The impacts of operating conditions(temperature,water/oi1 ratio and space velocity)on the distribution and yield of pyrolysis products,technological conditions and experimental equipment were investigated systematically.The influence of calcination temperature,additives types and its addition amount were investigated in the modification process of dolomite.In addition.four sulfur-containing compounds,such as l-octanethiol,methylthiobenzene,diphenyl disulfide and benzo[b]thiophene(BT)were selected sulfur sources to investigate sulfur resistance and hydrodesulfurization of 0.5%Ni/1%Fe-dolomite catalyst.The contents of gas products were analyzed by GC,catalysts were characterized by XRD,SEM and TG,and pyrolysis oil was analyzed using GC-MS.The main research conclusions are as follows:(1)The main cracking products of anthracene oil and washing oil fractions catalytic cracking was the pyrolysis oil,and main gas products were H2,CO,and CO2.Alkyl aromatics in anthracene oil underwent dealkylation reaction and generated hydrocarbon gases such as CH4.The phenyl fragments produced by the cracking reaction were condensed into biphenyl and terphenyl and PAHs,resulting in an increase in the content of fused aromatic hydrocarbons.In addition acenaphthene in wash oil underwent ring-opening cleavage reaction,and generated small molecule gaseous hydrocarbons,alkanes and biphenylenes.achieving the higher H/C ration of cracked oil.Biphenyl and alkyl benzene compounds were intermediate compounds during cracking reaction,and their relative contents did not change significantly.(2)Among these operating conditions(temperature,water/oil ratio and space velocity),the temperature has a great influence on dolomite catalytic cracking activity.High temperature condition could promote side-chain breakage reaction of tar components,while damaging catalyst activity as a result of some CaO converting into CaCO3 phase.The water/oil ratio mainly affected carbon deposition on catalyst surface,high water vapor atmosphere reduced the amount of carbon deposited on catalyst.Space velocity mainly regulates the possibility and contact time between tar molecules and catalyst active center.The influence of space velocity on distribution and yield of pyrolysis products was larger than that on the change of cracked oil components.(3)Calcination temperature mainly affected the calcination degree of dolomite and the distribution of metal components on catalyst surface.Additives Fe can promote the water gas conversion reaction in the pyrolysis process,which leading to more HZ and CO converted to CO2.Additives Ni and Fe can form Ni-Fe alloy,improving anti-carbon deposition ability of catalyst;and NiO can improve catalyst ability of aromatics decomposition,especially the bond cleavage reaction of C-C and C-H bond.(4)0.5%Ni/1%Fe-dolomite catalyst behaved different selectivity toward sulfur-containing compounds,such as 1-octanethiol,thioanisole,diphenyl disulfide,and benzothiophene.The two former with simple structure were completely cracked during the cracking process;and diphenyl disulfide were partially cracked;while BT with complex structure and higher aromaticity degree almost did not undergo hydrodesulfurization reaction.H2S generated by hydrodesulfurization reaction can react with dolomite and the Ni to produce CaS and NiS,resulting in deactivation of catalyst poisoning. |
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