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

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 MP_KOH (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, BBP_KOH, PAP and PAP_KOH) were obtained. Results showed that the yield of MP_KOH 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 MP_KOH 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 BBP_KOH, 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 PAP_KOH 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.