Experimental study on extraction of organic matter from coal by liquid CO2

Abstract

Liquid CO2 injection into coal seam for CH4 displacement is one of the important means to strengthen gas extraction and carbon sequestration in recent years. Liquid CO2 is a non-polar solvent, based on the principle of “similar phase solubility”, part of non-polar or weakly polar organic matter can be dissolved in liquid CO2. By controlling the key parameters of liquid CO2 in the extraction process, small molecular organic matter can be dissolved and migrated from the pore structure of coal as far as possible. In order to clarify the main factors affecting the process of liquid CO2 extraction of coal body, the experimental platform of liquid CO2 extraction of organic matter in coal body was built by ourselves, the single factor experimental design method was used to analyze the evolution law of organic matter components in the process of liquid CO2 extraction of coal body. The experimental results showed that: the macromolecular structure of coal was not significantly damaged by liquid CO2 extraction; after liquid CO2 extraction, the relative contents of aliphatic hydrocarbon and aromatic hydrocarbon are positively correlated with pressure, the dissolution of ketones, alcohols, ethers and esters has the characteristics of stage, time sequence and explosion; at the initial stage of extraction, the dissolved compounds are free in the structure of the macromolecular network. With the increase of extraction pressure and time, the small molecular compounds of hydrocarbons and non-hydrocarbons in the embedded state are dissolved.