Microwave Assisted Catalytic Pyrolysis Of Lignite For Gas Production

Coal resource-based multi-generation model is one of the promising trends of coal industry,contributing to achieving full utilization of coal resources,as well as clean energy structure adjustment.Hydrogen-rich gas,high-valued coal tar and semi-coke could be derived from coal pyrolysis process,which makes it suitable for the initial step of polygeneration model,attracting wide attention.Microwave assisted pyrolysis as a new type of heating method has been widely applied to the thermal conversion process of biomass,coal and urban sludge and has achieved satisfying results.To enhance the pyrolysis process and increase the yield and concentration of H₂ and CO,microwave assisted catalytic pyrolysis were conducted in this study.First,the effect of inherent minerals on the pyrolysis process under microwave irradiation was studied.The results showed that Fe₂O₃ could increase the yield of H₂,CO and CO₂;the emission of CO₂ was suppressed by CaO significantly.In the TG-MS experiments,the apparent activation energy of H₂ and CH₄ were decreased by 18.1%and5.5%respectively after impregnation with Fe³⁺,suggesting that Fe element had catalytic effect on the breakage of side-chains and dehydrogenation reaction.Considering the feature of microwave heating,Fe₂O₃ on the one hand enhanced the process mentioned before,on the other hand,‘hot spot'was formed and facilitated the cracking of primary pyrolysis products.Then Ca/Fe@Al₂O₃ catalysts with different Ca/Fe ratio was synthesized,and their catalytic effect on the production of H₂ and CO in the manner of microwave heating and conventional heating was studied.The results suggested that 12Ca/Fe@Al₂O₃ had better catalytic effect under microwave irradiation with the yield of H₂ and CO of 310.7 ml·g^-1?STP?and 225.3 ml·g^-1?STP?.The yield of H₂ and CO were also improved dramatically under conventional heating method with a summation of 105.6 ml·g^-1?STP?,still far less than that by microwave heating.Thus,microwave assisted catalytic pyrolysis was more efficient for the production of H₂ and CO.Under microwave irradiation,10%Fe₂O₃@ZSM5 catalyst had better catalytic effect compared with 12 Ca/Fe@Al₂O₃,with H₂ of 342.1 ml·g^-1?STP?and CO of 255.7 ml·g^-1?STP?.Differently,5%Fe₂O₃@ZSM5 showed better catalytic effect than other ratios.It was due to that the catalytic effect under microwave heating was related to the ability of absorbing microwave energy and the structure of catalyst.With the amount of Fe₂O₃ of10%,the overall catalytic effect was better.However,the catalytic effect of catalyst only depends on the pores structure and active sites.Thus,the appropriate amounts were different under two heating method.