Degradative solvent extraction of subbituminous coal with deep eutectic solvent and effect of reaction conditions on products

A degradative solvent extraction method for upgrading low-rank coal was performed at 200-350◦C for 90 min to obtain a substance dissolved in the solvent at room temperature(Soluble).Because the resulting mixture exhibited a high carbon content without ash,it could be readily used as a fuel.Furthermore,deep eutectic solvents(DESs)have attracted attention for improving the Soluble yield and decreasing the oxygen content in Soluble.DES is known to cleave oxygen-containing functional groups in biomass and is considered effective for deoxidizing low-rank coal.Herein,DES was prepared by mixing choline chloride,FeCl3⋅6H2O,and Adaro subbituminous coal(AD)and then added to 1-methylnaphthalene(1-MN)in a non-polar solvent,followed by degradative solvent extraction in the range of 200-350◦C.The effects of reaction temperature and added DES amount on the product yield and the composition were evaluated.As the reaction temperature and amount of DES added increased,the Soluble yield and carbon content increased.It was also found that the thermal decomposition temperature and oxygen content decreased with the increasing DES amounts.This decrease indicates that DES promotes the deoxygenation and decomposition of AD and increases the soluble yield of the fuel source.

Degradative solvent extraction of low-rank coal:Role of water on pyrolysis mechanism of low-rank coal in a highly-dispersed medium

A degradative solvent extraction(DSE)method was proposed to upgrade low-rank coals(LRC)for their cascaded utilizations in a highly-dispersed medium.The derived products exhibited well improved properties in comparison to the raw LRCs.Previously,the LRCs were pre-dried to eliminate the potential impact of the varied water content of raw LRCs,but in light of the abundant water in fresh coals,the hydrolyzing effect of water on coals under heating,and the energy cost to pre-dry the LRCs,it is consequently essential to clarify the effect of water so as to verify the necessity of pre-drying process.In this study,the roles of inherent water and extra-added water were respectively investigated,using dried,raw and wet coals from two typical LRCs.The results show that increasing the moisture content of raw LRCs contributed to the extraction ability of DSE method without noticeably changing the elemental composition,chemical structure and thermal decomposition behavior of extractable products,thus pre-drying of LRCs before DSE treatment was proven unnecessary.Additionally,the roles of the inherent water were concluded as:1)leading to the formation of stable covalent bond during drying process;and 2)acting as H donor to promote extraction ability,while the added water can only function as H donor.Since excessive water will increase the pressure during DSE treatment and lead to the waste water treatment,the LRCs with a water content between 10%and 30%were consequently recommended for the practical application of DSE treatment.