Study On Directed Pyrolysis Of Lignocellulose Biomass

Biomass resources, the only renewable carbon resources, can be turned into conventional liquid, gaseous fuels and other chemical raw material or product by thermo-chemical, biological and other methods. As the only renewable energy directly translated into liquid fuels, biomass with the advantages of huge output, storage and the carbon cycle has attracted widespread interests all over the world. Fast pyrolysis technology is a new type of technologies of biomass thermochemical conversion for the purpose of. preparing the liquid products. The main problems of impeding the development of preparing chemicals from biomass are the pyrolytic products extremely complex and unstable. The general idea of this paper is to investigate the behavior of directed pryolysis from biomass by Curie-point Pyrolysis -gas chromatography-mass spectroscopy(CP-GC-MS),reveal the mechanism of directionally controlling the products pyrolyzed from lignocellulose biomass,study the dynamics of biomass pyrolysis by TG-FTIR and establish the kinetics models of biomass pyrolysis, exploit the technology of comprehensive utilization of pyrolytic products including high heating value gas, high quality liquid oil and high performance carbon material by the method of the super-high temperature medium pyrolysis in order to provide the theoretical basis of high value, comprehensive utilization of biomass. The main research content and results of the paper were as follows:1. The curie-point pyrolysis behavior of biomass major componentsThe lignocellulose biomass resources are the greatest amount of biomass resources on the earth, mainly composed of cellulose, hemicellulose, lignin. And its pyrolysis behavior can be attributed to the summation of its major components pyrolysis. In this paper, the curie-pyrolysis behaviors of the three main components of biomass and the levoglucosan as the intermediate products pyrolyzed from cellulose were investigated by the apparatus of CP-GC-MS from the microcrystalline cellulose,xylan and Alkali-lignin,which were considered as the model compounds of cellulose, hemicellulose and lignin. The differences of the pyrolysis behavoir of biomass basic components and the composition of major pyrolysis products were analyzed. The research results indicated that the curie-point pyrolysis behavior of biomass major components has obvious differences. The levoglucosan is the main component of pyrolysis products from cellulose all the time. The intermediate step of levoglucosan was experienced in the process of preparing the furfural, levoglucosenone and HMF from cellulose pyrolysis. The process of xylan curie-point pyrolysis could be broke into two region: At the area of less than 300℃, xylan by random glycosidic cleavage was pyrolyzed into furan derivatives and saccharidic compounds,furfural content reaches to 54.38 % in the pyrolysate. At the area of more than 300℃, the kind and content of chemicals of small molecular aldehyde,ketone were improved greatly with the enhancement of pyrolysis temperature. The carbon dioxide and guaiacol unit compounds were produced from the lignin pyrolysis. The cause of that guaiacol always was the main products in the process of lignin curie-point pyrolysis was more easy rupture of the bond between guaiacol and methoxy resulted from the electronic effect of methoxy and phenolic hydroxyl group. The carbon dioxide was prepared from the rupture of C-O-C.2. The directionally catalytic curie-point pyrolysis behavior of celluloseThe technology of catalytic pyrolysis is a directionally controlling techniques in order to get high value products and the high yield of the target product. In this paper, the directed pryolysis behaviors of cellulose catalyzed by Fe₂(SO₄)₃,CuSO₄,ZnCl₂,H₃PO₄ were investigated by the apparatus of CP-GC-MS. The variation of pyrolysate such as furfural, levoglucosenone and levoglucosan was reviewed. the pathway and mechanism of selectively controlling levoglucosenone and levoglucosan were brought forward. The research results indicated that the catalysts of Fe₂(SO₄)₃,CuSO₄,ZnCl₂,H₃PO₄ can play the role of selectively controlling the forming pathway of cellulose pyrolysate such as furfural, levoglucosenone and levoglucosan. The catalysts can enhance the dehydration and decarbonylation of cellulose. The distinctness of the dehydration and decarbonylation between four catalysts resulted in the dissimilarity of furfural, levoglucosenone and levoglucosan contents. The levoglucosenone was made from the levoglucosan by dehydrating two molecules H₂O. And the furfural was prepared from the levoglucosenone by decaronylation. It is a very effective method of selective pyrolysis cellulose catalyzed by H₃PO₄ and CuSO₄ to reduce the content of the levoglucosan and enhance the content of levoglucosenone and furfural. The directed pyrolysis of cellulose catalyzed by ZnCl₂ is a very good way to selectively prepare the furfural.They were very good means of selectively reducing the content of levoglucosan and enhancing the content of levoglucosenone and furfural by treating the cellulose by the adsorption of the Fe₂(SO₄)₃ solution,directionally preparing high levoglucosan and low levoglucosenone by treating the cellulose by the complexation of the Fe₂(SO₄)₃ solution3. The directed pyrolysis behavior of lignocellulose biomassThe lignocellulosic biomass composed of three major components of lignin, cellulose and hemicelluloses is supramolecular polymer with complex spatial structure. In this paper, the directed pryolysis behaviors of lignocellulose biomass including bamboo,willow and caragana catalyzed by ZnCl₂,H₃PO₄ with low cost were investigated by the apparatus of CP-GC-MS. The regulation mechanism of biomass pyrolysis products such as furfural, levoglucosenone,levoglucosan and phenolic compounds was ananlyzed. The research results indicated that the species and content of lignocellulose biomass pyrolysate could be regulated by the catalysts of ZnCl₂ and H₃PO₄ selectively, which was the effective method of reducing the content of acetic acid and phenolic compounds and enhancing the content of the sugar compounds and furan compounds directionally. The enhancement of the dehydration and decarbonylation of the levoglucosan intermediate by treating the lignocellulose biomass with ZnCl₂ and H₃PO₄ resulted in preparing more furfural and levoglucosenone, promoting the lignin to form carbon rather than phenolic compounds. and restraining the production of acetic acid. The catalyst of H₃PO₄ made for the selectively forming of levoglucosenone. The catalyst of ZnCl₂ helped to selectively prepare the levoglucosan and furfural. The ability for the inhibition of the acetic acid and phenolic compounds was ZnCl₂>H₃PO₄.4. The pyrolyis behavior of lignocellulose biomass via the super-high temperature mediumThe super-high temperature medium pyrolysis was a new type technology of pyrolysis,existed the bottle-neck of obtaining the super-high temperature medium with low cost. In this paper, the super-high temperature medium with low cost was obtained by the technology of the honeycomb ceramic heat exchanger. The pyrolysis behavior of super-high temperature medium(steam and nitrogen) and the influence of it on the pyrolysis products were investigated in the fixed bed pyrolysis reactor. The research results showed that the technology of super-high temperature steam pyrolysis helped to prepare high value solid carbon materials,high heating value gas and high quality bio-oil. The solid carbon product with low volatile content and big specific surface area can be got by high-temperature steam pyrolysis. The influence of high temperature steam pyrolysis on pyrolytic gas such as H₂, CO, CH₄, CO2 and C2Hy was remarkable. The contents of various gas components by high temperature steam pyrolysis are significantly higher than nitrogen. With the improvement of pyrolysis temp. the contents of the major gases in the process of high temp. steam pyrolysis were increased and the times of various gas components appear were moved up. Specially, the contents of high heating value gas such as H₂,CH₄ and C2Hy were improved significantly. As the same time, it was in favor of preparing high heating value gas because of not existing the diluted phenomena of a great deal of nitrogen during the steam pyrolysis and condensing steam after cooling the pyrolytic gas.The characterization depending on the analysis of the bio oil obtained from high temperature steam pyrolysis has shown that a low O/C and high H/C ratio product can be obtained. Heating value of the liquid fraction based on GC-MS data was calculated and found equal to 33.54 MJ kg-1. These facts imply that this product can be used as a potential source of renewable fuel and chemical feedstock.5. The pyrolysis mechanism of biomass by TG-FTIRThe study of the biomass pyrolysis mechanism includes two aspects of the forming pathway of pyrolytic products and pyrolysis kinetics. In this paper, the pyrolysis characteristic parameters, kinetics parameters, reaction pathway and the evolutions of pyrolytic products were investigated by TG-FTIR and the kinetics model of biomass pyrolysis reaction was simulated. The research results showed that the pyrolysis characteristic parameters, kinetics parameters, reaction pathway and the evolutions of pyrolytic products could be varied effectively by catalysts.The kinetics analysis of three major components such as cellulose,xylan and lignin showed that the reaction pathways of cellulose and xylan pyrolysis are attribute to the parallel and competitive reaction, and that of lignin is attribute to first forming medium and occuring the competitive reaction subsequently. The FTIR peak(3016cm-1) of CH₄ appeared in the process of lignin pyrolysis. The mass loss scope of cellulose pyrolysis under H₃PO₄ and ZnCl₂ catalysts moved to low temperature region, the activation energy of cellulose was reduced in effect. The characteristic absorbance peak of CO was broadened and the second absorbance peak of CO appeared. The catalyst of H₃PO₄ made the cellulose pyrolysis for the competitive reaction pathway of forming medium.The mass loss scopes of bamboo,willow and caragana pyrolyzed under H₃PO₄ and ZnCl₂ catalysts moved to low temp. region. The kinetics analysis showed the activation energy of bamboo pyrolysis reaction was reduced,but that of willow and caragana pyrolyisis reaction were enhanced under the catalysts. The pyrolysis of bamboo experienced one step pathway.The reaction pathway of bamboo pyrolysis under H₃PO₄ was not changed. The catalyst of ZnCl₂ made the bamboo pyrolysis for the competitive reaction pathway of three steps.The pyrolysis of willow experienced one step pathway too.The reaction pathway of willow pyrolysis under H₃PO₄ was not changed. The catalyst of ZnCl₂ made the willow pyrolysis for the competitive reaction pathway of two steps.The pyrolysis of caragana experienced the competitive reaction pathway of two steps. The catalyst of H₃PO₄ made the caragana pyrolysis for the one step reaction pathway. The reaction pathway of caragana pyrolysis under ZnCl₂ was not changed. The FTIR absorbance peak of CO,CH₄ in the pryolysate from the lignocellulose biomass pyrolyzed by catalysts showed a significant drag. It was resulted from the secondary cracking of rich oxygen functional groups in carbon surface and the branched ring cracking of benzene at the high temperature. The catalyst of ZnCl₂ helped to restrain the forming of gaseous products.