The Extraction Effect of Supercritical CO2 on Coal Organic Matter Based on CO2 Sequestration in Unmineable Coal Seam

On the basis of the effect of extraction components of supercritical CO2 (Sc-CO2) from coal on groundwater in the fields of greenhouse gas CO2 sequestration into deep and unmineable coal seams, Sc-CO2 extracts from coals were analyzed using GC/MS to investigate the compositions and their contents of the extracts under different experimental conditions. The results show that Sc-CO2 extracts from coals contain hydrocarbons and organic compounds containing heteroatoms. The main compound in the extract is hydrocarbons which include a large concentration of acyclic alkanes and alkenes and a small concentration of cycloalkanes and aromatic hydrocarbons. Even-numbered n-alkane dominates in the extract, and hexacosene is the main alkene in the extracts from lignite and bituminous coal. The aromatic hydrocarbons are more difficult to extract and their concentration decreases with the increase of coal rank. The main oxygen-containing compounds are esters and carboxylic acids which are more easily extracted from lignite. The concentrations of nitrogen-containing compounds are very small and are more difficult to extract from coal with the rank increase. A small concentration of sulfur-containing compounds is extracted from coal. The results demonstrate that Sc-CO2 has the potential to mobilize organic compounds from coal seams, which affect the transport of CO2 in coal seams and cause groundwater pollution.

Automated summary

Supercritical CO2 (Sc-CO2) extraction from coal results in the extraction of hydrocarbons, oxygen-containing compounds, and sulfur-containing compounds. The main components are hydrocarbons, specifically acyclic alkanes and alkenes. Oxygen-containing compounds include esters and carboxylic acids, while sulfur-containing compounds are present in low concentrations. Extraction becomes more difficult with higher coal ranks.