Investigation of adsorption-diffusion behaviors of elementary O2, CO2, and N2 in coal particles: influence from temperature

Abstract

Adsorption-diffusion behaviors of gases (i.e., O 2 , CO 2 and N 2 ) in coal are directly related to the coal spontaneous combustion (CSC), in which the temperature is the key factor affecting the gas migration process in coal. In this work, isothermal adsorption experiments of O 2 , CO 2 and N 2 under different temperatures were carried out on bituminous coal and anthracite coal samples at 0.5 MPa, respectively. Based on the free gas density gradient diffusion (FDGD) model, the microchannel diffusion coe cients of different gases at different temperatures were calculated, and the effects from temperature were quantitatively evaluated. The results acquired from the experiment and simulation show that (i) the adsorption capacity of these three gases decreases as the temperature increases, and the adsorption capacity at the same temperature satis es CO 2 > O 2 > N 2 ; (ii) the FDGD model is veri ed to be still applicable at high temperatures, indicating that the adsorption-diffusion behavior of O 2 , CO 2 and N 2 in coal particles at different temperatures is still consistent with the free gas density gradient diffusion; (iii) the microchannel diffusion coe cient K m of the three gases gradually increases when the temperature goes up. The present work contributes to the understanding of the gases migration process in the development of CSC.

A review on agrowaste based activated carbons for pollutant removal in wastewater systems

“…Their purpose is to provide useful information for evaluating the performance of adsorbents [24]. The adsorption diffusion model involves a three-step process: the transport of solute through the liquid film surrounding the adsorbent to reach its external surface (known as film diffusion), the bulk transfer of diffusing molecules (solute) within the adsorbent particle (referred to as intra-particle diffusion), and finally, adsorption/desorption occurring at the surface-active sites during the liquid/solid adsorption process [17,18]. The adsorption diffusion model was developed under the premise that mass action plays a negligible role in determining the overall rate of the adsorption process.…”

“…Unmodified agricultural wastes (biomass), when used as alternative adsorbents, demonstrate partial to moderate adsorption capacities, rendering them ineffective for treating polluted wastewater. However, modifying agricultural wastes through physical methods (such as thermal activation) or with chemical reagents (like chemical activation) enhances their adsorption capacity by creating a well-organized crystalline structure and improving pore texture in the resulting solid carbon [16,17].…”