CO2 and CH4 adsorption on different rank coals: A thermodynamics study of surface potential, Gibbs free energy change and entropy loss

2021

AIChE Journal

Self Cite

The isothermal adsorption curves for water vapor on montmorillonite were measured by a gravimetric adsorption system. Dent's model was employed to estimate the adsorption behaviors of water vapor on primary adsorption sites and secondary adsorption sites. The thermodynamics analysis of water vapor adsorption was performed. At low vapor pressure region, primary adsorption predominates, and with increasing vapor pressure, secondary adsorption becomes notable. Primary adsorption sites have an evidently stronger adsorption affinity than secondary adsorption sites. With increasing vapor pressure, Gibbs free energy variation rapidly increases and then reduces slowly. Although increasing vapor pressure raises adsorption spontaneity on primary adsorption sites, the enhancement in vapor pressure decreases the spontaneity of water vapor adsorption on secondary adsorption sites. As adsorbed loading increases, isosteric heat of adsorption and entropy loss decrease first and then increase quickly. The gradually growing water clusters are responsible for the increase of entropy loss at late stage.

Section: Introductionmentioning

confidence: 99%

Investigation into adsorption equilibrium and thermodynamics for water vapor on montmorillonite clay

2021

AIChE Journal

Self Cite

“…e pressure rise rate of 45 s-60 s diffusion space's pressure is lower than that of 0 s-10 s diffusion space's pressure [32,33]. e reason is that the adsorbed gas on micropore surfaces within the coal matrix is rapidly desorbed to free gas under the action of gas pressure gradient and concentration gradient [25][26][27][28].…”

Section: Resultsmentioning

confidence: 99%

“…It is revealed that the gas desorption and desorption rates of the coal samples decrease with the increase of the moisture content of the coal samples in the same time period, regardless of the degree of metamorphism coal [24,25]. e adsorption-water-desorption experiment was carried out to obtain the conclusion that the desorption rate decreased with the decrease of the critical pore scale [26]. e analysis of outburst prevention effect of coal seam water injection comes to the conclusion that the higher the original water content of the coal seam, the less the risk of coal and gas outbursts [27].…”

Section: Introductionmentioning

confidence: 99%

Moisture Content on Methane Desorption Characteristics in Coal and Its Effect on Outburst Prediction

Cao

Advances in Civil Engineering

et al. 2021

Coal and gas outburst is a dynamic phenomenon with violent eruptions of coal and gas from the working coal seam. It has been proved that rapid desorption within a short period is necessary for the occurrence of an outburst. Due to the limitation of the present test condition, gas desorption characterization in coal with different moisture content for the first several seconds (0–60 s) has not been researched sufficiently. In this study, initial desorption characterization of gas in coal with different moisture content is studied by experiments with methane. The most remarkable characteristic of the experimental setup is the application of a self-developed real-time data acquisition system with a time interval of about 10 ms, which achieves the goal of collecting enough pressure data for analysis and calculation. The data is used to study gas pressure variation and calculate the initial amount of desorbed gas and index (ΔP) of initial velocity diffusion of coal gas. From the experimental results, the new proof has been found to verify that coal with lower moisture content and methane outburst is more dangerous than coal with higher moisture content and outburst. The degree of coal and methane outburst is exponentially decaying with increasing moisture content.

“…Liu [26] believed that the effects of the temperature and the pressure on the CO 2 adsorption by coal reservoirs with different burial depths were mainly concentrated in the micropore range of high-grade coal and the macropore range of low-grade coal. Du [27] studied and analyzed the thermodynamic characteristics of CO 2 and CH 4 adsorption by three different grades of coal (anthracite, bituminous coal and lignite) sampled from China and considered that low temperature increased the adsorption capacity of CO 2 and CH 4 and had a greater impact on CO 2 adsorption.…”

Section: Discussionmentioning

confidence: 99%

Experimental Investigation on Strain Changes during CO2 Adsorption of Raw Coal Sample: Temperature and Effective Stress

Zhang

et al. 2021

Energies

Through laboratory simulation experiments, this paper studies the influence of different temperature and stress conditions on strain changes of raw coal samples induced by the CO2 adsorption with tri-axial creep-seepage and adsorption-desorption experimental system. Comparing and analyzing the experimental results, the study shows that: (1) within a certain time, the axial and radial strain of the raw coal sample induced by CO2 adsorption both show a growing trend as the adsorption time increases and the strain of the raw coal sample for CO2 adsorption is obvious anisotropy; (2) at the same point in time, the greater the axial effective stress, the smaller the axial strain increasing rate of the loaded coal sample during CO2 adsorption process and the smaller the value of axial deformation; (3) during the adsorption process, the volume strain of raw coal sample decreases with the increasing of temperature, namely, the adsorption capacity of raw coal sample decreases with the increasing of temperature.