| The development and utilization of biomass is of great significance due to its priorities of abundance, renewability and environmental friendship. Considering the bio-oil characteristics of high oxygen content and strong acidity, biomass and three components (cellulose, hemicellulose and lignin) were pretreated by calcium formate before pyrolysis in this paper. And the effect of pretreatment on the characteristics of biomass pyrolysis was studied.Firstly, four kinds of biomass (corn straw, rice straw, wheat straw and sawdust), as well as the three components, were employed as raw materials and then pretreated by calcium formate. The effect of pretreatment on functional groups was investigated by Fourier transform infrared (FT-IR) analysis. FT-IR analysis showed that the structure stabilities of cellulose and hemicellulose were reduced while the benzene ring of lignin remained intact after calcium formate pretreatment. Furthermore, a strong carbonyl vibration (C=O) absorption peak and the deformation vibration of COO-1 indicated the presence of carboxylate in the pretreated biomass.In order to study the effect of calcium formate pretreatment on pyrolysis characteristics of the three components, pyrolysis experiments of untreated and pretreated cellulose, hemicellulose and lignin were carried out in a tube furnace. The results illustrated that the bio-oil yield of cellulose was the highest while the char yield of lignin was in the first place. The maximum bio-oil yields of cellulose, hemicellulose and lignin reach 0.613,0.395 and 0.373 (g/g), respectively. With the temperature rising, the char yields of three components were gradually reduced, and the gas yields were increased, while the bio-oil yields were enhanced first and then decreased. As for pyrolysis performances of the pretreated components, the yields of char and gas were enhanced whilst the bio-oil yield was reduced. Compared to the untreated samples,the maximum bio-oil yields of cellulose, hemicellulose and lignin, decreased by 19.1%,6.1% and 37.3% separately. However, the variation trend of pyrolysis product distribution remained same with temperature changing. In addition, calcium formate pretreatment led to a decrease in the contents of levoglucosan and furfural in cellulose bio-oil, however the contents of acetic acid and hydroxyl-acetone were enhanced. A notable reduction of the acetic acid and furfural contents in hemicellulose bio-oil while a significant increase of cyclopentene compounds were also caused by the pretreatment. This resulted in weakening the acidity, with the pH value of hemicellulose bio-oil increasing from 1.1～1.4 to 4.2-4.7. As for lignin, the pretreatment raised phenol content and promoted the demethoxy reaction, resulting in the content of methoxy-based phenols decreasing.Finally, the pyrolysis experiments of untreated and pretreated corn straw, rice straw, wheat straw and sawdust were conducted in the tube furnace, to investigate the effect of calcium formate pretreatment on biomass pyrolysis characteristics. Results showed that the bio-oil yield of 0.496(g/g) for sawdust was the highest, and the bio-oil yield of 0.447(g/g) for com straw was the first place among three kinds of straw biomass. Calcium formate pretreatment increased the yields of char and gas, but reduced the bio-oil yield. Compared to straw biomass, more saccharide and phenols were contained in the bio-oil of sawdust Calcium formate pretreatment significantly reduced the relative contents of acetic acid, furfural and levoglucosan in bio-oil, increasing the contents of hydroxy acetone and cyclopentanones. Moreover, the pretreatment was prone to weaken the acidity of bio-oil, pH value of the bio-oil derived from pretreated sawdust was raised from 4.1～4.3 to 5.6～5.8, with the value for wheat straw enhanced from 2.4～2.7 to 5.0～5.3. The acidity of bio-oil obtained from acid demineralized biomass, with calcium formate pretreatment performed, was inferior to that of the ones without acid demineralization. |
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