| Rice husk,as a widespread agriculture waste,has high silicon content,which hinders its effective utilization.In this paper,high ash rice husk was effectively utilized by pyrolysis poly-generation technology.Biochar,bio-oil and pyrolytic gas are simultaneously generated from biomass via pyrolysis poly-generation,and the purpose products of different pyrolysis poly-generation processes are not consistent.The purpose products of this paper are low-oxygen bio-oil（water-free basis）,porous carbon materials,amorphous Si O2and CO-rich syngas with high calorific value.In order to achieve the above objectives,the torrefaction temperature and the selection of catalyst type should be determined,and the appropriate treatment method of biochar should be determined subsequently.In this paper,torrefaction and catalytic pyrolysis experiments were carried out in a two-stage fixed-bed pyrolysis reactor.Firstly,rice husk was torrefied at 210℃,250℃and 300℃.The effects of torrefaction temperature on the pyrolysis behavior of rice husk were studied to determine the appropriate torrefaction temperature based on the migration route of carbon and oxygen elements.Then,the synergistic effects of Zr O2/n-ZSM-5 and Zr O2/n-ZSM-5/ATP catalysts and torrefaction extent（210℃,250℃and 300℃）were studied.The quality improvement of bio-oil during torrefaction and catalytic pyrolysis was evaluated by deoxygenation,bio-oil（water-free basis）yield,hydrocarbons yield and energy yield.Finally,the effects of three different torrefaction temperatures and desilication treatments at210℃,250℃and 300℃on the adsorption of phenol by biochar were studied,and the corresponding pyrolysis poly-generation process path was proposed.The results of this paper are as follows:（1）Torrefaction pretreatment has a great influence to the pyrolysis behavior of rice husk,with the torrefaction temperature rising,the yield of biochar increases gradually.However,excess torrefaction temperature will result in sharp reduction of liquid and gaseous products and obvious increase in the yield of biochar.The phenomenon is a high correlation between the thermostability of hemicellulose,cellulose,and lignin.Due to the rich Si O2 in rice husks,the lower torrefaction temperature has little effect on the surface of rice husks,and only the higher torrefaction temperature can damage the outer surface of rice husks.Due to the rich Si O2 in rice husk,the low torrefaction temperature has little effect on the surface of rice husk,and only the high torrefaction temperature can damage the outer surface of rice husk.Torrefaction pretreatment reduces the oxygen content in pyrolysis bio-oil,and this effect gradually increases with the increase of torrefaction temperature.The deoxygenation in torrefaction process is mainly dehydration,followed by decarboxylation and decarbonylation.With the increasing of torrefaction temperature,the water content in pyrolysis bio-oil decreases gradually.Torrefaction has a good effect on the chemical compositions of pyrolysis bio-oil.For rice husk pyrolysis,the optimal torrefaction temperature should be between 210-250℃.（2）There were good synergistic effects between mild torrefaction（210℃）and acid catalyst Zr O2/n-ZSM-5 or acid-base catalyst Zr O2/n-ZSM-5/ATP.However,only the combination of mild torrefaction（210℃）and acid-base catalyst Zr O2/n-ZSM-5/ATP could be improved in four different evaluation parameters,including deoxygenation,bio-oil（water-free basis）yield,hydrocarbons yield and energy yield.In addition,Zr O2/n-ZSM-5/ATP has uniform distribution of acid and base sites,which is conducive to the deoxygenation reaction,and significantly increases the generation of hydrocarbon substances.The results of catalytic pyrolysis showed that the acid-base catalyst Zr O2/n-ZSM-5/ATP had better deoxygenation ability,which was also related to the uniform distribution of acid-base sites.Torrefaction-catalytic pyrolysis experiment showed that the synergistic effects of mild torrefaction pretreatment and acid-base catalyst was beneficial to balance the quality and yield of bio-oil（water-free basis）.Among them,the acid catalyst is beneficial to reduce the oxygen concentration of bio-oil（water-free basis）,and the acid-base catalyst is beneficial to the productivity and hydrocarbon generation of bio-oil（water-free basis）.The combination of mild torrefaction at 210℃and acid-base catalyst Zr O2/n-ZSM-5/ATP is the best combination of rice husk torrefaction-pyrolysis process.（3）The torrefaction pretreatment had a certain negative effect on the specific surface area of rice husk biochar,but increased the proportion of intermediate pores in the pore structure of biochar,which was beneficial to reduce the resistance in the adsorption process.torrefaction pretreatment had little effect on the types of chemical groups on the surface of biochar,but reduced the number of chemical groups to some extent,and this effect was positively correlated with torrefaction temperature.For different concentrations of phenol solution,including the key factors of adsorption capacity is not the same,when the concentration is low,is the specific surface area of adsorption material and decisive,when the concentration is higher,the adsorption capacity is the specific surface area and adsorption resistance between the coupling effect,when high concentration,adsorption capacity depends on the coupling action between adsorption and chemical adsorption resistance.The desilication treatment significantly increases the porous properties of biochar as a porous carbon material,and still retains a large number of chemical groups.The adsorption experiments of porous carbon materials showed that,compared with no desilication treatment,desilication treatment significantly increased the adsorption capacity of porous carbon materials.For biochar torrefied at 210℃and desilication treatment,good balance was formed between the pore structure and the number of chemical groups at this time.Therefore,the biochar torrefied at 210℃and desilication treatment is the best adsorption material in high concentration phenol solution. |
