| As the shortage of fossil fuels and the deterioration of global greenhouse effect,it is imminent to develop renewable energy alternative fuels.The use of biomass as a substitute fuel has been developed rapidly.The conversion of biomass into clean fuels by pyrolysis and gasification is considered as one of the most promising conversion technologies.However,in addition to obtaining useful biofuels,biomass pyrolysis will produce bad by-products,especially the tar in combustible gases,and the storage of tar will limit the subsequent utilization of biological gas.It also leads to pollution of downstream equipment,blockage of pipelines and corrosion.Therefore,tar removal is of great importance to biomass pyrolysis/gasification process,and there is no efficient way to remove it at present.The interaction of microwave and metal can induce the discharge phenomenon and produce plasma and photocatalysis effect.In this paper,a method of efficient catalytic conversion of tar is established by using the above two effects.Toluene is used as a model compound of biomass tar.The characteristics of toluene cracking,steam reforming and photocatalysis degradation under microwave metal discharge are mainly studied.The effects of electrode type,gas flow velocity,toluene concentration,reaction time,water carbon ratio(S/C)and anatase Ti02 photocatalyst on the conversion efficiency and reaction path of toluene were investigated.The experiment draws the following important conclusions:The effect of microwave induction on tungsten electrode is the best.It can effectively break the toluene into useful gas(H2,C2H2,CH4)and solid carbon,and the conversion efficiency is above 90%.The velocity of gas,the concentration of toluene and the reaction time have an effect on the cracking efficiency of toluene.With the increase of the velocity/toluene concentration,the cracking efficiency of toluene first decreases and then increases.The effect of reaction time on toluene cracking efficiency is mainly due to the hot effect of coke which accumulated over time.When coke accumulates to a certain extent,it will shield microwave to affect the metal discharge,so it is necessary to remove the coke.The introduction of water vapor can produce hydroxyl radicals and oxygen particles in the discharge area,and promote the conversion of toluene under certain conditions.It can be used for the removal of coke.In terms of carbon removal effect and composition of gas products,the steam to carbon ratio(S/C)plays an important role.Under the condition of low concentration of toluene(17-25 g/Nm3),the best S/C is 1.7,and the best S/C under the high concentration of toluene(154 g/Nm3)is 2.It is calculated that more than 80%of the carbon in toluene is converted to CO and CO2 after the introduction of water vapor.In this study,the photocatalysis effect of Microwave metal discharges for the destruction of tar was investigated by comparing the conversion of a model tar compound under Microwave metal discharges alone and under the synergetic effect of Microwave metal discharges and a photocatalysis on the synergism of steam reforming and photocatalysis for the degradation of toluene.The anatase-type TiO2 was used as the photocatalysis.The experimental results show that the anatase-type Ti02 can utilize the UV light emitted by Microwave metal discharges to assist in the decomposition of toluene.Moreover,the discharge atmosphere plays an important role in discharge light characteristics.Compared with pure nitrogen and pure argon atmospheres,the addition of a small amount of argon to the nitrogen gas strengthens ultraviolet light emission.Correspondingly,the application of photocatalysis enhanced toluene destruction efficiency when the carrier gas was a mixture of nitrogen and argon.The toluene conversion efficiency under the synergetic effect of Microwave metal discharges and anatase-type TiO2 can amount to 98.4%when the N2/Ar ratio was 5. |
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