| The yield of food wastes and the CO2 are increasing with the improvement of the living standards of urban residents and the rapid development of industry.A large amount of carbon-containing resources need to be recycled.Microwave pyrolysis,as a new type of solid wastes pyrolysis technology,has become a research hotspot in the environmental field since it can simultaneously treat solid wastes(such as food wastes)and CO2 for energy and resource treatment.In this study,firstly,the effects of pyrolysis temperature and CO2 on the bio-gas,bio-oil,bio-char were explored via optimizing the microwave input power and regulating the CO2 concentration,in which the food wastes and the CO2 were respectively used as the materials.The generation pathway of CO2and organic matters to produce high-quality syngas was investigated in detail.Then,the effects of different ferrite catalysts on the changes of thermal conversion performance and the yield,composition,and characteristics of products were further studied.At last,the catalysis of ferrite catalysts in microwave pyrolysis reaction was investigated via analyzing the changes of key products and the crystal structure of catalysts.This study investigated the effects of different microwave input power and reaction atmosphere(CO2 or N2)on microwave pyrolysis of food wastes.Results showed that the increase of microwave input power(from 800W to 1400W)contributed to an increase in the heating rate.The heating rate and the final pyrolysis temperature of the food wastes in the N2 atmosphere(1070?)were higher than that of the CO2 as the reaction gas(1020?)when the microwave power was 1400W.This difference may be due to the CO2 reacted with volatile organic compounds and bio-char in the pyrolysis process,which consumed thermal energy,resulting in reducing the pyrolysis temperature.The yield of bio-gas was significantly increased,while the yield of bio-oil and bio-char was decreased under the CO2 reaction atmosphere.The yield of bio-gas in the CO2 atmosphere increased to 69.70 wt.%,which was 25.29%higher than that in the N2 atmosphere,indicating that CO2 promotes the pyrolysis reaction of food wastes.With the increase of the concentration of CO2 reaction gas(from 0 vol.%to 100 vol.%),the content of CO increased from 18.35%to 27.86%,and the yield of light bio-oil decreased from 6.56%to 4.24%,while the specific surface area of bio-char increased from 3.12 m~2/g to 205.71 m~2/g.This was because CO2 could react with light bio-oil and bio-char to improve the yield of syngas and promote the development of pore structure of bio-char.The addition of ferrite catalysts contributed to improve thermal conversion performance and reduce the activation energy in the process of food wastes microwave pyrolysis.The results showed that Fe3O4 catalyst could improve the quality of bio-gas.The yield of syngas and lower heating value increase by 43.22%and 34.53%,respectively,compared with Fe2O3.However,Fe2O3 catalyst could improve the quality of bio-oil.The relative content of hydrocarbon compounds in bio-oil was the highest,and the relative content of polycyclic aromatic hydrocarbons was the lowest.Different ferrite oxygen catalysts had different catalytic properties during the microwave of food wastes due to the formation of non-stoichiometric defect structures.The change of the crystal structure would change the thermal conversion performance of catalysts,resulting in the decomposition and dehydrogenation reaction of food wastes and generate a large amount of syngas.In addition,the oxygen atoms in the lattice of ferrite catalyst would detach from the surface of catalyst to form an active site in the catalytic process to improve the decomposition efficiency of the organic matters and promote the formation of H2,CO and light bio-oil. |
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