基于模型化合物反应路径解析淖毛湖褐煤萃取残渣的甲醇醇解机理

Mechanism analysis of methanol alcoholysis of Naomaohu lignite extraction residue based on model compound reaction path

  • 摘要: 以淖毛湖褐煤(NL)超声辅助萃取残渣(ER)作为研究对象,在300 ℃下采用甲醇对ER进行醇解,并考察添加KOH对醇解过程的影响。通过GC-MS分析MP(未添加KOH)和MPKOH(添加KOH)两种醇解产物的组成信息。选取苯甲酸苄酯(BB)和乙酸苯酯(PA)作为ER的两种模型化合物(MER),醇解后得到产物BBP、BBPKOH、PAP和PAPKOH。结果表明,MPKOH收率高达93.39%,而MP收率仅有5.25%,说明KOH的加入明显提高了醇解产物的收率。MP中酚类化合物、酯类化合物和烷烃类化合物的相对含量分别为17.92%、34.83%和5.98%,而MPKOH中的上述三类化合物相对含量分别为38.85%、10.17%和8.71%,在KOH存在下醇解过程发生了酯交换或酯的还原反应,还伴有一定程度的烷基化反应。模型化合物醇解产物分析结果显示,BBP中以苯甲酸甲酯和苯甲醇为主,而BBPKOH中苯甲酸甲酯基本消失,且苯甲醇相对含量占91.85%;PAP中仅检测到了酚类化合物,且苯酚相对含量占87.97%,而PAPKOH中甲基取代的苯甲醚和苯酚含量高达85.64%。两种模型化合物的醇解过程均表明,未添加KOH的醇解过程主要发生酯交换或酯还原反应,添加KOH后,不但加速了上述反应,还强化了后续产物与甲醇间的烷基化反应。

     

    Abstract: Ultrasonic assisted extraction residue (ER) from Naomaohu lignite (NL) was taken as the research object. ER was subjected to methanolysis at 300 ℃, and the effect of KOH was investigated. Composition of the two alcoholysis products, MP (without KOH) and MPKOH (with KOH) was analyzed by chromatograph/mass spectrometer (GC-MS). Benzyl benzoate (BB) and phenyl acetate (PA) were selected as model compounds (MER) for ER, and the alcoholysis products (BBP, BBPKOH, PAP and PAPKOH) were obtained. Results showed that the yield of MPKOH was 93.39%, while that of MP was only 5.25%, indicating that the addition of KOH greatly improved the yield of alcoholysis product. MP consisted of phenols, esters and alkanes with the relative contents of 17.92%, 34.83% and 5.98%, respectively, while the contents of the above three compounds in MPKOH were 34.8%, 10.17% and 8.71% respectively, indicating that transesterification or ester reduction reaction occurred in the alcoholysis process with the addition of KOH accompanied by alkylation reaction. Analysis of alcoholysis products of model compounds showed that methyl benzoate and benzyl alcohol were predominant in BBP, while methyl benzoate disappeared in BBPKOH, and the relative content of benzyl alcohol accounted for 91.85%; phenols were only detected in PAP, and the relative content of phenol was 87.97%. Whereas, the content of methyl substituted anisole and phenol accounted for the largest share in PAPKOH with the contents of 85.64%. Alcoholysis process of the two model compounds showed that, without KOH, transesterification or ester reduction reaction was occurred in the alcoholysis process. And the addition of KOH not only accelerated the above reaction, but also strengthened the alkylation reaction between the subsequent products and methanol.

     

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