纤维素与半纤维素热解过程的相互影响

Interaction during the Pyrolysis Process of Cellulose and Hemicellulose

以微晶纤维素为纤维素模型物,以木聚糖为半纤维素模型物,采用同步热分析仪(STA)及热重和傅立叶红外光谱仪联用技术(TG-FT-IR)对微晶纤维素、木聚糖以及两种成分不同比例的混合组分进行了研究,以考察纤维素和半纤维素在热解过程中的相互影响。结果表明微晶纤维素和木聚糖均有一狭窄的快速热解温度区间,而且两者热解区间不重合。在微商热失重(DTG)峰对应温度区间微晶纤维素热解有一明显的吸热峰,吸热量为547.98 J/g,木聚糖热解则有一个比DTG峰较晚出现的小吸热峰,吸热量为45.01 J/g。木聚糖与微晶纤维素的混合组分的热解研究中发现,在DTG曲线上有两个分别由它们热解引起的失重峰,随着组分中比例的变化两个热失重峰此消彼长。微晶纤维素的热解失重峰不仅往高温区移动,而且热解速率减缓,热失重范围变宽。在DSC曲线上有两个分别由木聚糖和微晶纤维素热解所引起的吸热峰,木聚糖的吸热峰受组分中比例的变化影响较小,而微晶纤维素吸热峰随着纤维素比例的下降而明显减小。FT-IR检测到的主要有气体产物为H2O、CH4、CO2和CO。木聚糖与微晶纤维素的混合组分热解产物析出规律总体上是两者热解产物析出的叠加,与单独热解相比组分的混合有利于CH4、CO的生成,而CO2的产量则有较大幅度的下降。

Simultaneous thermal analyzer （STA） and Thermogravimetric analyzer coupled with a Fourier transform infrared spectroscopy （TG-FT-IR） were used to investigate the pyrolysis characteristics of microcrystalline cellulose（MCC）, xylan and their mixtures. The results showed that both MCC and xylan were fast pyrolysis in a narrow temperature ranges with separated pyrolysis ranges. An obvious endothermic peak has been observed from MCC pyrolysis. The temperature area was corresponded to the peak of DTG curve and the absorbed heat was indicated as 547.98 J/g. When xylan was pyrolyzed, there was a small endothermic peak in DSC curve later than DTG peak. This indicated the absorbed heat was 45.01 J/g. There are two weight loss peaks found in different ratios of xylan and MCC mixture. They were induced by MCC and xylan respectively. These two weight loss peaks were inversely proportional according to the ratio of the two conponents. There are two independent endothermic peaks existing in DSC curve, which are caused by pyrolysis reaction of xylan and MCC. The peak of xylan did not influence by ratio of xylan, but the peak of MCC decreases largely with the ratio of MCC decreasing either in DTG or in DSC curves. In addition, the peaks of MCC are shifting to higher temperature. The FT-IR observed that H2O,CH4 ,CO2 and CO are the mainly gas products from biomass components and mixed components pyrolysis. During xylan-MCC mixtures pyrolysis, the products released from pyrolysis reaction is approximately sum of the pyrolysis reaction of xylan and MCC pyrolysis individually, it was found that pyrolysis of mixture has benefit to generate CH4 and CO, while CO2 yield decreases drastically at the same time.