Katarzyna Zarębska

The competitive sorption of CO2 and CH4 with regard to the release of methane from coal

Abstract It is generally acknowledged that beds of hard coals are an important medium with regard to their capacity to act as a reservoir for mine gases. At present, in Poland, the problem of extracting “coal-based methane” is at the stage of prospective investigation and the search for optimum extraction procedures under the specific conditions existing in this country. During the extraction of coal, methane is liberated by the desorption of CH 4 contained in the micropores of the coal, prior to which its release is hindered by sorption forces and the restricted and small dimensions of the transport paths. The aim of these investigations is to determine the thermodynamic conditions for the release of CH 4 from the coal microstructure by means of displacement sorption with CO 2 . The paper presents a study of the sorption/desorption kinetics and equilibrium states with displacement of sorbate gases, as well as the expansion/contraction of coal accompanying the sorption processes. It was found that the total equilibrium content of the mixture of gases in coal, desorption of the mixture of gases and the composition of the desorbed gas depend mainly upon the type of coal and on the initial equilibrium composition of the gas during desorption. The composition of the gaseous phase, in equilibrium with the adsorbed phase, does not reflect the composition of the sorbed phase.

Expansion and Contraction of Variable Rank Coals During the Exchange Sorption of CO2 and CH4

The influence of the physical and chemical properties and the composition of the sorbed gas on the sorption capacity of hard coal must be taken into account in an analysis of such coals as specific collectors of mine gases. The analysis presented was based on a comparison of the results of sorption and expansion studies of single gases (CO2 and CH4) and their mixtures on two hard coals (Vdaf: 40.87% and 22.32%). The work presented was undertaken in an attempt to determine the influence of the sorptive deformation of the coals, caused by the pre-sorption of CO2, on the variation of their external dimensions during CH4 sorption and vice versa, and during sorption of a mixture of these gases. In addition, it was anticipated that the work could answer the question as to which of these gases would enrich the desorbed gas. Knowledge of these effects should facilitate further exploration of the relationship between the properties of a hard coal and methane evolution to establish those factors that enhance the rate and effectiveness of the process.

Energy Aspects of CO2 Sorption in the Context of Sequestration in Coal Deposits

This paper summarises the results of experimental testing of carbon dioxide sorption on five coal samples. Sorption tests were done at the temperature 288, 298, 313 and 323 K, in the pressure range 0–5 MPa. The analysis of sorption isotherms and the effects of temperature on sorption capacity reveal that in the case of samples NR1, Pn, Tu, Be the temperature increase from 298 to 323 K led to 1.3-fold decrease of the sorption value. In the case of coal Th the decrease of sorption capacity was 3-fold. It appears that the analysis of maceral content plays a major role. In the case of coals, porosity is associated with the petrographic composition. The values of the isosteric heat of sorption and the work of expansion and desorption were derived for the investigated sorption systems. Test data reveal that for hard coals the isosteric heat is inversely proportional to the “reserve” of volumetric work—a major parameter triggering the sudden release of gas from the coalbed, thus enabling us to assess the potential risk involved in rapid unsealing of the coalbed.

Kinetic models assessment for swelling of coal induced by methane and carbon dioxide sorption

The ability of five kinetic equations to describe the sorption kinetics and expansion rate of solid coal samples was investigated. The conducted experiment included the measurements of sorption of methane and carbon dioxide on cuboidal hard coal samples at high pressure using volumetric method. Simultaneously the kinetics of coal sorption induced swelling was monitored. All of the approaches used to fit the experimental sorption and dilatometric data were literature-based equations. Two equations represent the traditional approach for sorption on powder and grain fractions based on the bidisperse gas transport model, and have been used to interpret and quantify the observed gas uptake rates in coal. The other three kinetic equations are the pseudo-second-order kinetic equation, Elovich equation, and stretched exponential (SE) equation. Four of the five equations are suitable to describe the kinetics of methane and carbon dioxide sorption in the porous structure of solid coal samples and the kinetics of coal expansion that accompany the sorption processes. The SE equation gave the best fit to the experimental data.

Hard coal as a potential low-cost adsorbent for removal of 4-chlorophenol from water

The potential use of raw hard coals as low-cost adsorbents for the removal of 4-chlorophenol (4-CP) from aqueous solutions was examined. The effect of experimental parameters such as the pH and salt presence was evaluated. The kinetic studies showed the equilibrium time was found to be 2 h for all of the adsorbents and that the adsorption process followed the pseudo-second order kinetic model. The adsorption isotherms of the 4-CP on the hard coals were fitted to the Langmuir, Freundlich, Langmuir-Freundlich, Sips and Redlich-Peterson equations. Based on the results obtained, hard coals appear to be a promising adsorbent for the removal of some hazardous water pollutants, like 4-CP and related compounds.

Effect of Li+ stabilization on smectite intercalate properties

Smectites are widely used minerals whose structure and properties can be modified and controlled. The aim of this study was to improve the sorption capacity and accessibility of interlayer (interpacket) spaces by reducing the pillar density in Chmielnik smectite. The micropore volume increases by increasing one of their dimensions, which is determined as the distance between pillars. This aim was achieved by lowering the resultant packet charge. Changes in intercalate structure and microporosity were studied using X-ray diffractometry and Ar sorption at–196°C. The Li/Na smectite ratio is crucial for modifying the smectite properties, particularly those associated with mineral microporosity. The behavior of the samples with the same interlayer cation composition exhibited two distinct trends. The first one is a decrease in the specific surface value (volume of micropores) accompanied by an increase in the amount of Li in the ion interlayer composition. The second one is a decline in the specific surface (volume of micropores) when the calcination temperature rises.

The use of mathematical models for modelling sulphur dioxide sorption on materials produced from fly ashes

2 Nicolaus Copernicus University in Toruń, Gagarin Street 7, 87-100 Toruń, Poland Fly ash-derived zeolites may become an attractive alternative for natural zeolites as well as for zeolites produced out of pure chemicals. A growing awareness of the need to protect the environment is an incentive for the use of waste materials as raw materials for production of microporous, multi-application materials – zeolites. Additionally, environmentally friendly actions undertaken in order to reduce air pollution intensify needs to search for new options for capturing hazardous air pollutants out of flue gases. Zeolites can be used as air pollutants sorbents. In this work there are presented results of sulphur dioxide, one of flue gases components, sorption experiments. The adsorbent used was zeolite synthesized form fly ash from a selected Polish power plant. For the purpose of investigation there were chosen fly ash zeolite samples synthesised with the use of different methods. Parameters were selected in such a way that one type of zeolite material was received. For the purpose of description of received results the mathematical model was used. As a result of experiments carried out it was found that the synthesized materials may be used as sulphur dioxide sorbent. It was found that the sorption capacity is highly connected with the zeolite synthesis method. Despite the fact that the same type of zeolite was received, samples presented differentiated values for capture, due to different conversion factors of fly ash into zeolite materials.

Evaluation of surface chemistry of selected hard coals

This paper presents the experimental and theoretical investigations of the sorption of water vapour in hard coal samples from Polish collieries (Sośnica, Jaworzno and Pniówek). Analysis of the sorption isotherm of water molecules gives information on specific interactions with surface groups, especially oxygen radicals. Detailed considerations of experimental results and theoretical simulation estimates let us to indicate changes in the surface composition for the different samples of coals and its dependency on the petrography or metamorphism.

Development of temperature-induced strains in coal–CH4 and coal–CO2 systems

Expansion/contraction of coal, induced by the sorption of carbon dioxide and methane in isothermal and non-isothermal conditions, was measured. The investigation is of great importance in the context of validating the potential CO2 sequestration in unmined coal seams. Changes in temperature in underground coal beds can influence the sorption balance, resulting in strains in coal strata, which could lead to the desorption of gas and leaks to the ground surface. The research shows that the strains induced by CO2 sorption are about twice the size of those resulting from the sorption of CH4. The linear strains are anisotropic and greater in the direction perpendicular to the bedding plane. The results of the non-isothermal experiments show that a temperature increase gives rise to the sample swelling in the presence of methane, but a different pattern is observed for coal–CO2 systems, where sample contraction occurs. This behaviour is explained by the different mechanism of CH4 and CO2 deposition and by the diversity in the maceral composition of the samples.

CO2 adsorption properties of char produced from brown coal impregnated with alcohol amine solutions

Carbon dioxide (CO2) emission reduction is critical to mitigating climate change. Power plants for heating and industry are significant sources of CO2 emissions. There is a need for identifying and developing new, efficient methods to reduce CO2 emissions. One of the methods used is flue gas purification by CO2 capture through adsorption. This study aimed to develop CO2 adsorbent out of modified brown coal impregnated with solutions of first-, second-, and third-order amines. Low-temperature nitrogen adsorption isotherms and CO2 isotherms were measured for the prepared samples. The results of experiments unexpectedly revealed that CO2 sorption capacity decreased after impregnation. Due to lack of strait trends in CO2 sorption capacity decrease, the results were closely analyzed to find the reason for the inconsistencies. It was revealed that different amines represent different affinities for CO2 and that the size and structure of impregnating factor has influence on the CO2 sorption capacity of impregnated material. The character of a support was also noticeable as well for impregnation results as for the affinity to CO2. The influence of amine concentration used was investigated along with the comparison on how the theoretical percentage of the impregnation on the support influenced the results. The reaction mechanism of tertiary amine was taken into consideration in connection to no presence of water vapor during the experiments. Key findings were described in the work and provide a strong basis for further studies on CO2 adsorption on amine-impregnated support.