The effects of CO₂ on organic groups in bituminous coal and high-rank coal via Fourier transform infrared spectroscopy

Abstract

The interactions between supercritical CO 2 and coal and their effects on changes in the coal pore structure and organic groups play a critical role in the CO 2 geological storage-enhanced coalbed methane recovery. To investigate the effects of supercritical CO 2 on organic groups in coals of different ranks and its mechanisms under different temperature and pressure conditions, CO 2 sequestration processes in bituminous coals and high-rank coals were replicated using a highpressure reactor. Four coal samples of different ranks were exposed to supercritical CO 2 and water under three temperatures and pressures for 240 h. Fourier transform infrared spectroscopy was used to provide semiquantitative ratios and Fourier transform infrared spectra of coal samples before and after the supercritical CO 2-H 2 O treatment. The results show that interactions between supercritical CO 2 and coal were controlled by the coal macromolecular structure, and semianthracite is the inflection point of interaction characteristics for coal samples of different ranks. Bituminous coal, including high-and low-volatility bituminous coal, has a low degree of condensation of its aromatic structure, and its aromatic nuclei can facilitate addition reactions. Swellings primarily break cross-links between aromatic nuclei in the same aromatic layer. These characteristics favor the polymerization addition of aliphatic side chains of aromatic nuclei, causing an increase in the degree of condensation of the aromatic structures in bituminous coal. Highrank coals including semianthracite and anthracite have a high degree of condensation of their

The permeability of shale exposed to supercritical carbon dioxide

“…Over the years, numerous studies have been conducted to investigate the impacts of CO 2 on shale. Thickened liquid carbon dioxide fracturing fluid, reflux better, less damage to the reservoir, and low adsorption performance, can more effectively penetrate into the reservoir and thickened liquid carbon dioxide fracturing fluid also prevents leakage of methane in the reservoir 14 , Adsorption of SC-CO 2 in shale specimens caused expansion 15 , which can break cross links between aromatic nuclei in coal 16 and lead to the reduction in permeability 17 . The interaction with SC-CO 2 caused the greater changes in mechanical properties compared with sub-CO 2 18 .…”

The structural transformation and reburning characteristics of gas coal in Ningwu coalfield fire

“…At present, researchers mostly use thermogravimetric analysis to study the reaction characteristics of coal pyrolysis and combustion (Hameed et al, 2020;Jayaraman et al, 2017;Kanca, 2020;Lin et al, 2014;Liu et al, 2020b;Seo et al, 2011). The changes of groups during coal pyrolysis and combustion were analyzed by in-situ Fourier transform infrared spectroscopy (Chen et al, 2020;Dou et al, 2014;Feng et al, 2006;Liu et al, 2018;Niu et al, 2016;Qi et al, 2019;Zhang et al, 2021;Zhao et al, 2020). The TGA-DSC was used to study the effect of metal oxides on the catalytic combustion of flame coal (Zhang et al, 2020a).…”

The evolution characteristics of organic sulfur structure in various Chinese high organic sulfur coals

“…Since the emergence of infrared spectroscopy, it has become an indispensable tool for the identification, quantitative determination and structural study of organic compounds. Infrared spectroscopy studies of organic solids such as coal, oil shale, and kerogen have made great progress since the 1960s (Bent and Brown, 1961;Cline Ii et al, 2018;Guo and Bustin, 1998;He et al, 2017;Jos e et al, 1996;Lis et al, 2005;Liu et al, 2018;Mastalerz and Bustin, 1993;Painter et al, 1978Painter et al, , 1981Painter et al, , 1985Tang et al, 2018;Wang et al, 2011;Zhao et al, 2015). At present, Fourier Transform Infrared Spectroscopy (FTIR) is often used to obtain chemical structural parameters and also an important means for studying the molecular structure of coal (Chen et al, 2012;He et al, 2017;Jiang et al, 2019;Liu et al, 2018;Supaluknari et al, 1988;Tang et al, 2018;Yan et al, 2020).…”

“…In some special cases the sulfur content in coal is high and the organic sulfur content exceeds 50% of total sulfur (Dai et al., 2008, 2017, 2018; Li and Tang, 2013, 2014; Li et al., 2015; Medunić et al., 2016b; Sinninghe Damsté et al., 1999; Smith and Batts, 1974; Torres-Ordonez et al., 1990; White et al., 1990; Zhao et al., 2014). Studying the evolution characteristics of organic sulfur compounds, the source of the organic sulfur, and the relationship between organic sulfur and the coal-forming environment in these special cases can provide guidance for the rational utilization and removal of organic sulfur to achieve clean utilization of coal (Ken and Nandi, 2018; Kumar et al., 2019; Kumar and Kumar, 2018; Liu et al., 2019; Shen et al., 2019; Singh et al., 2012a, 2013, 2018; Medunić et al., 2019).…”