Pretreatment of lignite by acidic bronsted ionic liquid [B(SO3H)mim]OTf for lignite pyrolysis

The effect of pretreatment with acidic bronsted ionic liquid 1-sulfonic acid butyl-3-methylimidazolium trifluoromethanesulfonate ([B(SO3H)mim]OTf) on Shengli lignite (SL) pyrolysis behavior and its pyrolysis products distribution were investigated in this paper. In order to study the mechanism of [B(SO3H)mim]OTf pretreatment on the dissolution of SL, [B(SO3H)mim]OTf treated-SL was also analyzed by the Fourier Transform Infrared Spectroscopy (FTIR), Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT) and TG-DTG. It is found that the pretreatment temperature and the ratio of [B(SO3H)mim]OTf to SL have a significant impact on the pyrolysis of SL. The pretreatment of SL with [B(SO3H)mim]OTf can not only result in the increase of the yield of total tar and light oil fraction but also improve the quality of tar. After the pretreatment at 200 °C and [B(SO3H)mim]OTf/SL at 1, the tar yield, light fraction content, arenes, and phenolics content in tar is 1.6, 2.4, 6.3 and 3.2 times higher than that from raw SL pyrolysis, respectively. Pretreatment with [B(SO3H)mim]OTf leads to the fracture of the coal network, resulting in the increase of the content of CO and COC bonds and the disruption of hydrogen bonds.