纤维素木聚糖和木质素含量对生物质热解特性及产物的影响

采用热重法研究了纤维素、木聚糖和木质素含量对生物质热解特性的影响,分析了三组分相互混合热解时的交互作用规律,及其对热解动力学参数的影响;同时,在生物质真空热解液化系统上考察了三组分含量对热解液化产物分布及生物油组成的影响。结果表明,纤维素热解较为剧烈,生物油中芳香族、糖类、醛类和醇类含量较高;木聚糖的热稳定性较差,生物油中芳香族、酮类和酸类物质较多;木质素热解较为平缓且固体残留物较多,生物油成分主要为芳香族化合物。纤维素对活化能和指前因子的影响较大,木聚糖和木质素对反应级数的影响较大;纤维素的热解有利于减少固体残留物,而木质素的热解产物有利于促进糖类的分解;木聚糖对纤维素的热解具有明显的抑制作用;木聚糖能促进木质素的低温热解,两者混合热解对生物油组成影响较小。因此,高纤维素含量的生物质可以获得更高的生物油产率,且适量的木质素有利于促进纤维素的分解,为进一步提高生物油产率和品质提供了理论依据。

Effects of cellulose, xylan and lignin content on biomass pyrolysis characteristics and product distribution

Abstract: This paper investigated the effect of cellulose, xylan and lignin content on biomass pyrolysis characteristics and analyzed the interaction rules of the 3 biomass components. The proportions of the 3 components i.e. cellulose, xylan and lignin were reasonably designed, and there were 7 experimental samples according to different quality proportions. The Thermo TGA/DSC 1 was used to analyze the thermo-gravimetric processes of the samples composed of the 3 components. And the pyrolysis characteristics of the cellulose, xylan and lignin were studied. Supposing that the 3 components' thermo-gravimetric processes were isolated with each other, the overall weightlessness process of the mixed samples was attributed to the superposition of every single component's weightlessness. By comparing the experimental and calculated values, the three components' interaction rules when they were mixed and pyrolyzed were analyzed. The Coats integration method was adopted to calculate and analyze the three components' pyrolysis dynamic parameters. At the same time, on the basis of the biomass vacuum pyrolysis liquefaction system, the vacuum pyrolysis experiments of each component and the mixed samples were carried out. Taking biomass as a benchmark, oil and solid production rate and production rate of gas were calculated at the end of the pyrolysis. The production rate of mixed samples' pyrolysis products could be acquired by the superposition of the production rate of single component pyrolysis products according to the mixed proportion. The (GC-MS) Agilent 7890A were adopted to analyze the composition of bio-oil which was obtained through vacuum pyrolysis and liquefaction of 7 samples. By comparing the experimental and calculated value, the influence of those 3 components content on the distribution of pyrolysis product and bio-oil composition was also evaluated. The results indicated that cellulose had good thermal stability, the pyrolysis range was narrow, and its pyrolysis was relatively intense which generated less solid residues, and bio-oil production rate was higher which generated more aromatics, sugars, aldehydes and alcohols. Xylan with a poor thermal stability could generate more aromatics, ketone and acid in bio-oil, and the initial pyrolysis temperature was lower which could generate more gases. Lignin with a poor thermal stability could generate aromatic compounds, the pyrolysis range was narrow and the pyrolysis was relatively mild which generated more solid residues. By analyzing the three components' pyrolysis dynamic parameters, it could be concluded that cellulose had considerable effect on the activation energy and pre-exponential factors while xylan and lignin had greater effects on reaction order. By comparing the experimental and calculated value, it could be concluded that cellulose pyrolysis was beneficial to the reduction of the solid residue while lignin pyrolysis products could promote the decomposing of sugars. Xylan had a negative effect on the cellulose pyrolysis and could benefit the low-temperature pyrolysis of lignin. The co-pyrolysis of xylan and lignin had little influence on the bio-oil composition. Therefore, biomass with high cellulose content could foster the bio-oil yield and a certain amount of lignin could promote the decomposing of cellulose. The results provide a theoretical basis for further improving the yield and quality of the bio-oil.