A low carbon footprint method for converting low-rank coals to oxygen-containing chemicals

Abstract

Due to the urgent need to reduce CO2 emission and the shortage of petroleum, using coals especially low-rank coals as raw materials for producing chemicals has attracted much attention. Thermal extraction and oxidation in aqueous solution are efficient approaches for obtaining oxygen-containing chemicals from low-rank coals. However, yield of chemicals is limited and/or large amount of CO2 is released solely using either of the two technologies for converting low-rank coals. In this paper, a low carbon footprint method combining thermal extraction (TE) and oxy-cracking in dilute alkali aqueous solution for efficiently depolymerizing three low-rank coals, i.e., Xiaolongtan lignite (XLT), Xilinguole lignite (XLGL), and Shenfu sub-bituminous coal (SF), was proposed. The results indicate that considerable oxygen-containing compounds such as phenols, esters, and humic acids along with little CO2 emission can be obtained via the two-step depolymerization process. TE temperature significantly effects the dissolution of small molecular compounds. Comparing with XLT and XLGL, SF has lower TE and oxy-cracking activity. A good correlation between the oxy-cracking conversion of TE residues and their DTG peak temperature for the low-rank coals can be found. Therefore, the aforementioned approach is promising for high-value and low-carbon utilization of low-rank coals.