Study On Rice Husk Catalytic Pyrolysis And Catalytic Cracking Of Tar Over The As-produced Char Product

The depletion of primary energy and the pollution caused to the ecological environment in the process of its utilization force countries to invest a lot of money and manpower to find a new alternative,sustainable and renewable energy.Biomass energy has been widely developed for its advantages of zero net emission of carbon dioxide,recycling,low nitrogen and low sulfur,and easy storage and transportation.Pyrolysis,as a promising biomass energy utilization technology,can not only produce biomass coke,syngas,pyrolysis oil and other heterogeneous fuel products for industrial production,but also is the basis of many thermochemical conversion technologies,such as pyrolysis liquefaction and gasification.One of the most important problems limiting the development of this technology is the presence of tar in syngas,which condenses at room temperature and can clog heat exchanger pipes,engines and other equipment,seriously affecting the safe and stable operation of the system.The most promising method of tar removal is catalytic cracking,which can not only reduce the temperature of tar cracking,but also catalyze the transformation of tar into small molecules such as H₂ and CO.?1?Rice husk was selected as biomass materials in this paper.Firstly,the pyrolysis and product characteristics of rice husk were studied by TGA and fixed bed.It was found that the main pyrolysis stage of rice husk occurred between 200?and 450?,and the pyrolysis process ended at 800?.With the increase of temperature,char production rate decreases and tends to remain unchanged at 800?;tar production rate reaches its maximum value at 600?;gas production rate increases gradually with the increase of temperature,especially H₂,CH₄ and CO.?2?The kinetic characteristics of rice husk pyrolysis was studied by using a micro-fluidized bed reactor,during which CuCl₂ and ZnCl₂ were added as catalysts,and the kinetic parameters of pyrolysis were obtained by using the equivalent conversion rate and the model fitting method.The results show that the presence of copper and zinc significantly affects the release characteristics and conversion rates of gas components.The addition of CuCl₂ reduced the activation energy of H₂,CH₄,CO₂ and CO.The addition of ZnCl₂ also reduces the activation energy required to produce H₂,CH₄ and CO₂.Through the analysis of coke after pyrolysis,it can be seen that copper nanoparticles were formed on the surface of rice husk char,and the pore structure of char under the action of ZnCl₂ was greatly improved.?3?Based on the pore expansion effect of ZnCl₂,three typical activators of KOH,H₃PO₄ and ZnCl₂ were used to prepare the rice husk cahr catalyst,and the dual-temperature zone fixed bed was used to study the effect of catalysts on cracking of tar.The results show that the coke catalyst can effectively convert biomass tar into combustible gases,significantly increase the yield ratio of H₂,CO and CH₄.The addition of activators improves the pore structure of coke and the content of metal elements,thus improving the catalytic efficiency,and RHC-KOH>RHC-H₃PO₄>RHC-ZnCl₂.After 5cycles,the tar conversion rate only decreased slightly,indicating that the catalyst had good cycle stability.?4?By combining the two improvement strategies of improving the catalyst's pore structure and increasing the active site,the influence of the rice husk char catalysts prepared under the combined action of CuCl₂ and ZnCl₂ on the catalytic cracking of tar was further studied.The results showed that the primary biomass tar was mainly decomposed into oxygen-containing aromatic compounds and light tar compounds after catalysis.With the enhancement of the catalyst's pore structure,the agglomeration of copper nanoparticles decreased,with an average particle size of about 17.2nm.At the same time,the tar conversion efficiency increased with the increase of metal load.At the reforming temperature of 800?,when RHC-1.0Cu1.0Zn was used as catalyst,the tar conversion efficiency reached 94.5%.This paper has 48 pictures,15 tables,and 145 references.