Catalytic Hydroconversion Of Low Temperature Coal Tar Residue Over A Bifunctional Catalyst Derived From Coal Gasification Fine Slag

Coal gasification is an effective way for clean utilization of coal.Due to poor performance or operation level of coal gasification equipment,a large amount of coal gasification slag will inevitably be produced.At present,the main treatment methods of coal gasification slag are stacking and landfill,which occupies a lot of land resources and also pollutes the soil and groundwater.Coal gasification slag contains rich Si,Al and C resources.If its high added value can be effectively utilized,it can not only reduce the adverse impact on the environment,but also produce good economic benefits.In this paper,the research on impurity removal and activation process of coal gasification fine slag in northern Shaanxi was carried out.ZSM-5/porous carbon（PC）composite was prepared by hydrothermal method,and then supported nickel-based bifunctional catalyst was obtained by ion exchange and modified deposition-precipitation method.The low-temperature coal tar residue was extracted with the same volume of carbon disulfide/acetone mixed solution,and then petroleum ether soluble portion（SP_E）was obtained by the re-extraction of petroleum ether.Under the action of bifunctional catalyst,SP_Ewas catalytic hydroconversion into clean liquid fuel.The main research contents and conclusions are as follows:（1）The effects of alkali slag ratio,calcination temperature and calcination time on the activation effect were discussed.The results show that the activation effect is the best when the ratio of alkali to slag is 0.5,the calcination temperature is 800℃ and the calcination time is 120 min.（2）The effects of pH value,silicon aluminum ratio n（SiO₂/Al₂O₃）,amount of template（TPABr）n（TPABr/SiO₂）,crystallization time and crystallization temperature on the synthesized products were discussed.The results show that when pH=12,n（SiO₂/Al₂O₃）=100,n（TPABr/SiO₂）=0.1,crystallization temperature of 160℃and crystallization time of 48 h,a high purity ZSM-5/PC composite material can be obtained.After ion exchange and Ni loading of the composite material,a bifunctional catalyst(Ni_10%@HZSM-5/PC)with a Ni loading of10%can be obtained.Its analysis and characterization show that Ni nanoparticles are uniformly dispersed on the surface of ZSM-5/PC composite,and a small amount of nickel oxide on the surface can be reduced to Ni by H₂ under certain conditions.and Ni_10%@HZSM-5/PC has more B acid and L acid centers.（3）The catalytic hydroconversion experiment of the model compound benzyloxybenzene（BOB）showed that Ni_10%@HZSM-5/PC had the highest catalytic hydroconversion activity and selectivity for BOB.Under mild conditions,H₂ was easily converted into diatomic active hydrogen（H···H）under the action of metal Ni,and further homolysis into hydrogen free radicals（H·）.Under the synergistic effect of H·and proton hydrogen（H⁺）released from the carrier,the purpose of aromatic ring hydrogenation and oxygen atom removal has been achieved.（4）The SP_E was subjected to catalytic hydroconversion at 180℃,an initial hydrogen pressure of 5 MPa,Ni_10%@HZSM-5/PC and n-hexane in a high-pressure reactor for 24 hours resulted in the catalyzed hydrogenation product（SP_C）.According to GC/MS analysis,SP_Emainly contains chain alkanes,polycyclic aromatic hydrocarbons and oxygen-containing compounds,and a small amount of alkenes,nitrogen and sulfur-containing compounds.While SP_C mainly contains chain alkanes and cycloalkanes,with a relative content（RC）of 78.75%.In addition,there are incompletely saturated hydrogenated aromatic hydrocarbons,accounting for 16.92%,and the RC of heteroatom containing compounds is significantly reduced.