离子液体溶胀对煤直接液化残渣结构及热解性能的影响

Effect of swelling treatment by ionic liquid on the structure and pyrolysis performance of the direct coal liquefaction residue

采用四种相同阴离子不同有机链长阳离子的离子液体([EMIM][MeSO4]、[BMIM][MeSO4]、[HMIM][MeSO4]和[OMIM][MeSO4])对煤直接液化残渣(DCLR)进行溶胀处理,通过SEM、FT-IR和TG-DTG表征,分析了各离子液体溶胀对煤直接液化残渣溶胀效果、表面形貌、官能团分布、主体结构和热解性能的影响。溶胀结果表明,不同链长离子液体对煤直接液化残渣具有不同的溶胀效果,[HMIM][MeSO4]对残渣溶胀效果最好,其溶胀度高达1.78。FT-IR表明,不同链长离子液体会不同程度地破坏煤中C-H键,使得脂肪族和芳香族类化合物的相对含量有所差异。由TG-DTG可知,不同链长离子液体溶胀对残渣热解性能的影响具有较大差异,其中,以离子液体[OMIM][MeSO4]溶胀对残渣的热解最为有利,失重率高达47.5%;而离子液体[BMIM][MeSO4]溶胀在一定程度上抑制了残渣的热解,其失重率低于未经溶胀处理的残渣。基于Coats-Redfern法的热解动力学分析表明,煤直接液化残渣及其溶胀残渣在低温段(180-480℃)的热解过程均符合二级反应动力学,高温段(480-825℃)均以三级和四级反应动力学为宜。另外,不同链长离子液体溶胀处理明显改变了残渣的热解活化能,其链越长残渣的热解活化能越高。

Direct coal liquefaction residue(DCLR) was swelled by four kinds of ionic liquids with the same anion and different organic chain length cations, [EMIM][MeSO4], [BMIM][MeSO4], [HMIM][MeSO4] and [OMIM][MeSO4], and the effects of swelling treatment with ionic liquids on swelling degree, surface morphology, functional group distribution, the main structure and pyrolysis performance of the direct coal liquefaction residue were analyzed by SEM, FT-IR and TG-DTG characterizations. The swelling results show that different chain length ionic liquid has different swelling degrees for the DCLR, and [HMIM][MeSO4] presents the best swelling effect with the swelling degree of 1.78. The FT-IR results indicate that the ionic liquid could destroy C-H bond in DCLR, leading to a change in relative content of aliphatic and aromatic compounds. The TG-DTG characterization demonstrates that the pyrolysis performance of the residue is greatly affected by the different organic chain length ionic liquid. And the [OMIM][MeSO4] ionic liquid is more favorable for the pyrolysis of the residue than others, with the weight loss rate of 47.5%. However, the pyrolysis performance of the residue is restrained by the [BMIM][MeSO4] ionic liquid, in which the weight loss rate is lower than that of DCLR(without swelling treatment). The pyrolysis kinetic data based on Coats-Redfern method show that the pyrolysis reaction for the direct coal liquid residue and the swelled ones at low temperature(180-480 ℃) obeys a second order law, while the third and fourth order law of reaction is more suitable for the residue pyrolysis at high temperature section(480-825 ℃). In addition, the activation energy of the pyrolysis process for the DCLR is altered obviously by swelling treatment with different organic length ionic liquid, the longer the chain length, the higher the pyrolysis activation energy.