Insight into KOH activation mechanism during biomass pyrolysis: Chemical reactions between O-containing groups and KOH
Insight into KOH activation mechanism during biomass pyrolysis: Chemical reactions between O-containing groups and KOH
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深入了解生物质热解过程中KOH的活化机制：含O基团与KOH之间的化学反应
DOI：
10.1016/j.apenergy.2020.115730
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发表时间：
2020-11-15
期刊：
影响因子：
11.2
通讯作者：
Chen, Hanping
中科院分区：
文献类型：
--
作者：
Chen, Wei;Gong, Meng;Chen, Hanping
了解生物质热解过程中特定的化学活化机理对于更有效地利用生物质和生物炭是至关重要的。研究了KOH/生物质比(1：8~1：1)和温度(400~800℃)对生物质热解的影响。在实验和量子计算的基础上，通过揭示气态产物、生物油、生物炭和氢氧化钾的演化机理，探讨了氢氧化钾的化学活化机理。结果表明，KOH能与生物质中的活性含氧物种发生反应，在较低的比例(1：8~1：2)或较低的温度(400~600℃)下反应是主要的。在这里，KOH完全转化为K2CO3，导致大量气态产物和酚类的形成(达到75%)。然而，在较高的比例(>；1：2)或较高的温度(700-800℃)下，KOH与更稳定的碳碎片之间的反应被加强，从而成为主要反应。随着酚类和O-物种的显著减少，碳氢化合物成为优势物种(含量达到57.43%)。对于生物炭，KOH、含氧物种和碳碎片之间的反应在生物炭中产生了大量的空位。来自KOH的OH-迅速进入这些空位，形成大量新的含O基团(即C=O、-OH、C-O、O-C=O和-COOH基团)。这也导致了生物炭中氧含量的增加(达到23.68wt%)。在较高温度下，KOH与生物质之间的反应显著增强，比表面积急剧增加(达到1351.13 m(2)/g)。含氧基团进一步转化为更稳定的-OH、C-O和-COOH基团。基于热解产物和KOH的演化机理，揭示了生物质热解过程中KOH的化学活化机理，首次提出了KOH与含氧基团之间可能的化学反应途径。
Understanding the specific chemical activation mechanism during biomass pyrolysis is critical for the more efficient use of biomass and biochar. In this study, the effects of KOH/biomass ratios (1:8 to 1:1) and temperatures (400-800 ?C) on biomass pyrolysis were investigated. The KOH chemical activation mechanism was explored by revealing the evolution mechanisms of the gaseous product, bio-oil, biochar, and KOH, based on experiments and quantum calculations. Results showed that KOH can react with active O-containing species in biomass, which was the main reaction at lower ratios (1:8-1:2) or lower temperatures (400-600 degrees C). Here, KOH was completely transformed to K2CO3, leading to the formation of large amounts of gaseous products and phenols (reaching 75%). The reaction between KOH and more stable carbon fragments, however, was enhanced at higher ratios (>1:2) or higher temperatures (700-800 ?C), such that it became the main reaction. With a significant decrease in the phenols and O-species, the hydrocarbons became the dominant species (reaching a content of 57.43%). For biochar, the reactions among KOH, O-containing species, and carbon fragments generated an abundance of vacancies in the biochar. The OH- from KOH rapidly entered these vacancies, forming a large amount of new O-containing groups (i.e., C=O, -OH, C-O, O-C=O, and -COOH groups). This also caused an increase in oxygen content (reaching 23.68 wt%) in biochar. At higher temperatures, the reactions between KOH and biomass were significantly enhanced, along with a sharp increase in the specific surface area (reaching 1351.13 m(2)/g). O-containing groups further transformed to more stable -OH, C-O, and -COOH groups. Based on the evolution mechanism of pyrolytic products and KOH, the KOH chemical activation mechanism during biomass pyrolysis was revealed, allowing us, for the first time, to propose a possible chemical reaction pathway between KOH and O-containing groups.