Pyrolysis Characteristics Of Corn Stalk And Its Main Components And Quantitative Analysis Of Major Components Of Bio Oils

Biomass is the only renewable energy that is able to provide gas, liquid and solid fuels.Utilization of biomass energy can partially replace fossil fuels, slow the greenhouse effect,improve the energy supply situation, and ensure the security of national energy strategy.Therefore, it has far-reaching practical significance to national energy security, sustainableeconomic development, and environmental protection by develop great efforts to biomassenergy. Focusing on the basic research of biomass fast pyrolysis that should be strengthened,the present work mainly studies the pyrolysis characteristics of corn stalk and its threecomponents hemicellulose, cellulose and lignin, as well as quantitation and comparison ofpyrolysis bio oil composition, intending to provide theoretical basis and technical support forpreparation of high quality fuel and chemicals obtained by biomass staged pyrolysis.First, hemicellulose was isolated from corn stalk by the procedures of organic solventextraction-hypochlorite delignification-5%KOH extraction-ethanol precipitation; cellulosewas purified at the same time; and lignin was separated by enzymatic/mild acidolysis methods.Then the structure characterization and chemical composition of each single component wasstudied in detail by using the methods of FTIR,1H-NMR,13C-NMR, and IC, etc. The resultsshowed that the proposed separation method is feasible and superior, and the yield of theisolated hemicellulose and lignin was more than75%and50%, respectively, the puritiesreached about90%. These would lay the foundation to explain their thermochemicaldecomposition mechanism from the structural level.After obtained the representative single component of corn stalk, their decompositionmechanism and pyrolysis products distribution law under different thermochemical conditionswere thoroughly investigated by using TG-FTIR, TG-MS, and Py-GC/MS techniques. Thepaper mainly discussed the factors of temperature, composition, and staged pyrolysis or not,and particularly focused on the formation mechanism of the hemicellulose pyrolysis productsacetic acid and furfural, cellulose pyrolysis products levoglucose (LG) and small moleculealdehyde, lignin pyrolysis product2,3-dihydro-benzofuran (DHBF) and phenols. It is foundthat hemicellulose pyrolysis yielded the highest acid, and the acid content decreased with an increase in temperature; the furfural content achieved the maximum value of9.02%(peakarea%) at420°C. The typical cellulose pyrolysis product LG usually had a higher yield whentemperature≤420°C. As the temperature further increased, it was ease to secondarydecomposed and further generated small molecule aldehydes and ketones. The phenols fromlignin pyrolysis reached its maximum of47.68%at600°C; the benzene, and toluene couldemerged in the products when the temperature was800°C. From the related results, it couldconclude that the competition and the continuous reaction mode existed in the main productgeneration process; the staged pyrolysis could reduce the acid content, and improve thecontent of high value-added chemicals such as furfural, LG, phenols, etc.To further enhance the understanding of the actual pyrolysis process, the pyrolysischaracteristics of corn stalk and its three components were further investigated in a tubularreactor at different temperatures between300°C and900°C, with focus mainly on thereleasing profiles and forming behaviors of pyrolysis products (gas, char, and tar). It wasfound that the tar yields of each component pysolysis increased with an increase intemperature at first, and then decreased gradually. The tar yield of hemicellulose pyrolysisreached the maximum value of48.20%at450°C, while that of cellulose, lignin, and cornstalk were all emerged at500°C, with the maxima was70.46%,44.89%, and53.99%,respectively. A higher reactor temperature was conducive to the yield of gas products, butaccompanied by a reduction of char. Among the three components, hemicellulose yielded thehighest H2and CO2, lignin yielded the highest CH4, while cellulose produced more CO. Thecomposition and content of each component pyrolysis tar identified by GC-MS was consistentwith that of the Py-GC/MS results.Finally, in order to more accurately grasp and compare the components content of bio-oil,based on the results of qualitative analysis, about20kinds of standard compounds werepurchased, and the quantitative methods of these characteristic components of bio oil wereestablished by external standard method and standard addition method. On this basis, theinfluence of pyrolysis conditions on bio oil composition and their content were discussedin-depth. It was shown that all of material type, pyrolysis temperature, and pretreatmenttemperature had great impact on the chemical composition of bio oils. Within theexperimental, bagasse bio oil had the highest acetic acid content of4.8%(wt.%of the bio oil); corn stalk bio oil had the highest furfural yield of0.52%; fir and pine bio oils had highercontent of phenolic compounds, whose yield was5.09%and4.70%respectively; while LGcontent in the pine bio oil was much higher than that of other materials, which could reach upto about4%. As the pyrolysis temperature (between480°C and580°C) increased, the contentof aldehydes and acid increased, the phenols decreased, while that of ketones, anhydrosugars,and furans showed a decreasing trend after they first reached a maximum value. Stagedpyrolysis had a good effect on the enrichment of the chemicals in bio oil. The contents ofmain compounds such as phenols, ketones, furans, and anhydrosugars were all greatlyimproved, but when the pretreatment temperature>280°C, the increment of some majorproduct would decrease, such as acetic acid, furfural, furfuryl alcohol, etc. The experimentalresults and related conclusions in the present work may provide useful data for enhance thequality of bio oil and regulate its target chemicals during biomass pyrolysis.