Experimental Study On Fe-based Catalysts For Cracking Of Biomass Tar Under Microwave Irradiation

At present,the use of traditional energy can no longer meet people's demands for industrialization and environmental protection.Biomass energy has attracted the attention of researchers due to its wide-ranging sources,environmental friendliness,and renewable characteristics.In the process of biomass gasification,the production of biomass tar greatly affects the operation of gasification equipment and the use of biomass energy.Among the methods for the disposal of tar,catalytic pyrolysis can effectively decompose tar into small-molecule gaseous compounds.Fe-based catalyst is an attractive metal catalyst which is environmentally friendly and economical.Microwave heating can be coupled with Fe(metal discharge,plasma effect,etc)to promote the decomposition of biomass tar.Therefore,in this paper,toluene was selected as the model compound for biomass tar and microwave was used as the heating method.SiC powder and biomass char were used as carriers in view of their splendid microwave absorption properties.We investigated the effects of microwave power,Fe content,and space velocity on the toluene cracking rate and the gas production rate;then characterized the carbon deposition of the catalyst after the reaction,and carried out carbon elimination test on the catalyst through reforming experiment.First of all,using homemade Fe/SiC and Fe/C catalysts,respectively,to investigate the cracking rate of toluene and gas production rate in different conditions.For Fe/SiC catalysts:With the increase of specific microwave power,the toluene cracking rate and hydrogen production rate both increased first and then decreased.When the specific microwave power was 70 W/g,the two reached their maximum values,which were 86.3%and 84.5%,respectively.With the increase of the Fe content,the toluene cracking rate and the hydrogen production rate both increased first and remained unchanged.When the Fe element content was 10%,both reach the maximum.Both the toluene cracking rate and the hydrogen production rate decreased with the increase of the space velocity,while the hydrogen production rate decreased more slowly(7.9%)than the toluene degradation rate(19.6%).For Fe/C catalysts:The trend of toluene cracking rate and gas production rate under the three working conditions was the same as that of Fe/SiC catalyst,but in the best working condition(specific power 300W/g,Fe content 8%,space velocity 637h-1),the cracking rate of the Fe/C catalyst was only 81.5%.However,the Fe/C catalyst didn't show sintering in the test and its service life was longer than that of the Fe/SiC catalyst.Changing the temperature of preparation of cob coke,and it was found that as the coking temperature increased,the toluene cracking rate increased significantly.When the coking temperature increased from 500? to 700?,the toluene cracking rate increased from 81.5%to 86.1%.The prepared corn cob was subjected to acid elution ash treatment.It was found that the toluene cracking rate and gas production rate decreased significantly after deashing.Secondly,the process characteristics and deposition of toluene using Fe/SiC catalysts were analyzed.In the preheating stage of 5 minutes before the reaction,toluene didn' participate in the reaction.From the 6th min to the 12th min of the formal reaction,the toluene cracking rate and the hydrogen production rate have been increasing,and at the 10th to 12th minutes,the two reached their highest values(94.4%and 85.8%,respectively),and then both began to decline.The XRD showed that the catalyst has obvious carbon deposition after the reaction,while the SEM-EDS and TPO showed that the type of carbon deposition were mainly spherical carbon and filamentous carbon.The TG analysis could accurately measure the catalyst's carbon deposition rate of 2.25%.The steam and carbon dioxide were introduced into the system to perform the reforming reaction.It was found that when the steam carbon ratio was 0.75,the cracking effect was the best.The cracking rate and gas production rate were 92.8%and 89.6%,respectively,and the carbon deposition rate was 0.67%.When the flow ratio of C02 to N2 was 0.75,the cracking rate and gas production rate reached maximum(90.1%and 91.6%,respectively),and the carbon deposition rate was 0.89%at this time.The introduction of water vapor or carbon dioxide into the system regenerates the catalyst.It was found that the toluene cracking rate gradually decreases with the increase in the use time of the catalyst and then remains stable.Finally,it is stable at 63.2%and 60.6%,respectively.