Mechanism of methane formation during toluene pyrolysis using DFT calculation

Abstract

Abstract:

The greater part of macromolecule aromatic structure unit of low-rank coal contains mainly 1—2 rings. In order to understand the mechanism of methane formation during coal pyrolysis, the thermodynamics and kinetics calculation were conducted for toluene pyrolysis using DFT method. The results showed that the rate-control step is the dehydrogenization or demethylation process for all routes of methane formation. The energy barrier of toluene demethylation can be significantly reduced by the participation of hydrogen free radical. When temperature is lower than 675 K, the formation of methane is mainly through the following steps: firstly, breaking of the C—H bond in methyl of toluene; secondly, the hydrogen free radical formed adds to the toluene in ipso position and then demethylation; finally, formation of methane is from the formed methyl that captures a hydrogen atom in side chain of toluene. When temperature is higher than 975 K, methane is mainly from toluene demethylation first and then the formed methyl captures a hydrogen atom in side chain of toluene. When the temperature is between 675 K and 975 K,formation of methane is a competitive result of the two routes mentioned above.

Key words: FONT-SIZE: 10.5pt, mso-bidi-font-size: 11.0pt, mso-bidi-font-family: 宋体, mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA, mso-ascii-font-family: Calibri">甲基苯hansi-font-family: 宋体" lang=EN-US>, FONT-SIZE: 10.5pt, mso-bidi-font-size: 11.0pt, mso-bidi-font-family: 宋体, mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA, mso-ascii-font-family: Calibri">热解机理hansi-font-family: 宋体" lang=EN-US>, FONT-SIZE: 10.5pt, mso-bidi-font-size: 11.0pt, mso-bidi-font-family: 宋体, mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA, mso-ascii-font-family: Calibri">密度泛函hansi-font-family: 宋体" lang=EN-US>, FONT-SIZE: 10.5pt, mso-bidi-font-size: 11.0pt, mso-bidi-font-family: 宋体, mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA, mso-ascii-font-family: Calibri">煤大分子结构芳香结构单元

摘要：

低煤级煤大分子芳香结构单元以1～2个环的芳香体系为主, 为了理解煤热解甲烷的生成机制, 利用量子化学密度泛函理论方法(DFT)对甲基苯热解甲烷的生成机理进行了热力学和动力学计算，计算结果表明，在生成甲烷的所有反应路径中，其控速步骤是甲基苯的脱氢或脱甲基的过程;氢自由基的参与可以显著的降低甲基苯脱甲基的能垒。在温度低于675 K时，生成甲烷的主反应路径为：甲基苯上甲基脱氢，然后由氢通过本位（ipso）加成到甲基苯然后脱甲基，最后由甲基夺取甲基苯侧链上的氢生成甲烷。当温度高于975 K时，生成甲烷的主反应路径为：甲基苯脱甲基，然后由甲基夺取甲基苯侧链上的氢生成甲烷。在675～975 K之间则为这两条反应路径的竞争反应。

关键词: FONT-SIZE: 10.5pt, mso-bidi-font-size: 11.0pt, mso-bidi-font-family: 宋体, mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA, mso-ascii-font-family: Calibri">甲基苯hansi-font-family: 宋体" lang=EN-US>, FONT-SIZE: 10.5pt, mso-bidi-font-size: 11.0pt, mso-bidi-font-family: 宋体, mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA, mso-ascii-font-family: Calibri">热解机理hansi-font-family: 宋体" lang=EN-US>, FONT-SIZE: 10.5pt, mso-bidi-font-size: 11.0pt, mso-bidi-font-family: 宋体, mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA, mso-ascii-font-family: Calibri">密度泛函hansi-font-family: 宋体" lang=EN-US>, FONT-SIZE: 10.5pt, mso-bidi-font-size: 11.0pt, mso-bidi-font-family: 宋体, mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA, mso-ascii-font-family: Calibri">煤大分子结构芳香结构单元

JIA Jianbo, ZENG Fangui, LI Meifen, XIE Kechang. Mechanism of methane formation during toluene pyrolysis using DFT calculation[J]. CIESC Journal, 2010, 61(12): 3235-3242.

贾建波, 曾凡桂, 李美芬, 谢克昌. 用密度泛函理论研究煤中甲基苯生成甲烷的反应机理 [J]. 化工学报, 2010, 61(12): 3235-3242.

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Mechanism of methane formation during toluene pyrolysis using DFT calculation

用密度泛函理论研究煤中甲基苯生成甲烷的反应机理

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