离子液体预处理对桉木热解半焦结构和反应性的影响

doi:10.11949/0438-1157.20201133

摘要/Abstract

摘要：

生物质是可再生能源的理想原料，由于生物质有坚硬的木质素外壳保护而难以被有效利用。离子液体（IL）是一种绿色溶剂，可用于木质纤维素预处理从而提高其利用的效率。为了研究IL水溶液预处理对桉木热解产半焦的结构及其反应性的影响，将桉木粉经2%、4%和8%（质量）离子液体（[Bmim]Cl、[Bmim]OAc和[Bmim]H₂PO₄）水溶液在120℃下预处理2 h，然后将预处理后的桉木粉在650℃下热解。采用SEM、FTIR、XRD和Raman分析表征热解半焦的结构变化，利用热重分析仪（TGA）测定半焦与空气在450℃下的反应性。结果表明，随着预处理IL浓度的增加，半焦产率下降，半焦的晶化程度提高，在拉曼光谱中，I_D1/I_G变小，I_G/I_all变大，这表明IL预处理使半焦结构有序增大，并促进半焦中小芳香环向大芳香环聚并，因而降低了半焦的反应性。IL预处理可便捷调节热解半焦的反应性，为生物质的高值化利用提供有效的制备方法。

关键词: 离子液体, 桉木, 热解, 半焦, 反应性

Abstract:

Biomass is an ideal raw material for renewable energy, and it is difficult to use effectively because of its hard lignin shell protection. Ionic liquid (IL) was a green solvent which could be used in pretreating and improving the use efficiency of the biomass. To investigate the effects of IL on the pyrolytic char structure and its reactivity, eucalyptus powder was pyrolyzed in quartz reactor under 650℃. After being pretreated by IL ([Bmim]Cl, [Bmim]OAc and [Bmim]H₂PO₄) with a concentration of 2%, 4%, 8% at 120℃ for 2 h, the structure of char obtained was characterized by SEM, FTIR, XRD and Raman spectrum. The reactivity of char with air at 450℃ was also evaluated with thermal gravimetric analysis (TGA). The results showed that the yield of the char decreased with the increasing of the IL concentration, while the crystallinity was enhanced. The decrease in I_D1/I_G and an increase of I_G/I_all in Raman spectrum indicated an improvement in the order of the char structure, and the promotion of the transformation of small aromatic ring system into the large one, which led to a decrease reactivity of the biochar. IL pretreatment can adjust the reactivity of the pyrolytic biochar conveniently, and can provide effective way in using biomass with high value added.

Key words: ionic liquid, eucalyptus, pyrolysis, biochar, reactivity

中图分类号:

TK 6

黄中艺, 史刘宾, 冯亚军, 李立硕. 离子液体预处理对桉木热解半焦结构和反应性的影响[J]. 化工学报, 2021, 72(4): 2267-2275.

HUANG Zhongyi, SHI Liubin, FENG Yajun, LI Lishuo. Effect of ionic liquid pretreatment on eucalyptus char structure and its reactivity[J]. CIESC Journal, 2021, 72(4): 2267-2275.

图/表 9

图1 实验装置

Fig.1 Experimental device

图2 不同浓度离子液体预处理下热解半焦的产率

Fig.2 Yield of biochar pretreated with different concentrations of ILs

图3 不同 ILs及浓度预处理热解制备半焦SEM图

Fig.3 SEM image of biochar prepared by different IL and concentration

图4 不同IL预处理热解制备半焦的红外光谱图

Fig.4 FTIR spectrum of char prepared by different IL pretreatment

图5 不同IL预处理桉木热解制备半焦的XRD曲线

Fig.5 XRD of char obtained by pyrolysis of eucalyptus pretreated by different IL

图6 未经处理及IL预处理桉木热解产半焦的拉曼光谱图

Fig.6 Raman spectra of untreated and IL pretreated eucalyptus pyrolysis to prepare biochar

图7 经2%[Bmim]Cl预处理产半焦拉曼光谱分峰图

Fig.7 Curve-fitting of the Raman spectra of biochar from pretreated with 2%[Bmim]Cl

图8 不同IL浓度下半焦拉曼光谱的ID1/ IG及IG/ Iall的比值

Fig.8 Band ratio of ID1/ IG and IG/ Iall of biochar from eucalyptus pretreated with different concentration ILs

图9 不同IL预处理热解制备桉木半焦的反应曲线

Fig.9 Reaction curve of pyrolysis of eucalyptus coke prepared by different IL pretreatment

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