Adsorption kinetics of CO2, CO, N2 and CH4 on zeolite LiX pellet and activated carbon granule

Abstract

The adsorption uptake curves of CO 2 , CO, N 2 and CH 4 on zeolite LiX and activated carbon were measured using a volumetric method at 293, 308 and 323 K and pressure up to 100 kPa. The experimental uptake curves were correlated with a non-isothermal kinetic model because the adsorption kinetics was controlled by heat generation and transfer, and an isothermal model showed large deviation from experimental uptake. The adsorption rates of the gases on zeolite LiX and activated carbon were affected by the isosteric heat of adsorption, heat transfer rate and adsorption affinity. At the same pressure and temperature, the sequence of effective diffusion time constants was CO 2 ( CO \ N 2 \ CH 4 for zeolite LiX and CO 2 ( CH 4 B N 2 \ CO for activated carbon. The adsorption rate of CO showed the largest difference between the two adsorbents. Effective diffusion time constants (D/R 2 ) for all cases were provided, which depended on pressure and temperature.Keywords Activated carbon Á Zeolite LiX Á Adsorption kinetics Á Heat of adsorption Á Non-isothermal model List of symbols a External surface area divided by the volume of the adsorbent (m -1 ) c p Concentration in the particle (mol kg -1 ) C s Heat capacity of the sample (J g -1 K -1 ) D/R 2 Effective diffusion time constant (s -1 ) D Diffusivity (m 2 s -1 ) D c /r c Micropore diffusion time constant (s -1 ) D p /R p Effective macropore diffusion time constant (s -1 ) hOverall heat transfer coefficient (J m -1 s -1 K -1 ) K Henry constant (-) P Pressure (kPa) Q Adsorbed amount (mol kg -1 ) Q st Isosteric heat of adsorption (kJ mol -1 ) R Ideal gas constant (J mol -1 K -1 ) R 2 Coefficient of determination (R 2 ) (-) T Time (s) T Temperature (K) V g Volume occupied by the gas (m 3 ) V s Volume occupied by the adsorbent (m 3 ) a Dimensionless parameter defined by nonisothermal model (-) bDimensionless parameter defined by nonisothermal model (-) q s Density of the adsorbent (g m -3 )

Adsorption equilibria and kinetics of CH4 and N2 on commercial zeolites and carbons

“…In principle, adsorption kinetics can be measured experimentally using a variety of techniques, for example, by monitoring the time-dependence of volumetric or gravimetric sorption capacity [17,18], by the combined pressure-swing and volume-swing frequency response technique [19,20], using a dynamic column breakthrough apparatus [21], and via zero length column (ZLC) experiments [22,23].…”

“…A survey of literature ( Figure 1) revealed that the reported effective sorption rates for N2 and CH4 on commercial adsorbents similar to those measured in this work have large variations, ranging in some cases over two orders of magnitude. Figure 1 Variations in effective sorption rate (D/r 2 ) reported in the literature for N2 and CH4 on activated carbon (AC) [18,21,24,25], zeolite 13X [26][27][28], carbon molecular sieve (CMS) [17,20,29] and zeolite 4A [30][31][32] One possible reason for the large deviations present in the literature data is that kinetic measurements are often analysed under the assumption of a constant temperature throughout the adsorbent, usually on the basis that the sample mass is small ( 1 g). However, the adsorption rate observed in such measurements is generally non-isothermal because heat is evolved during the process and cannot be removed instantaneously due to heat transfer limitations.…”

Adsorptive cyclic purification process for CO2 mixtures captured from coal power plants

“…Adsorption equilibria of N 2 and CO 2 were measured on activated carbon at several temperatures (293–323 K) using a volumetric technique . The adsorption isotherms of N 2 and CO 2 on activated carbon were correlated to the partial pressure of each component at the maximum feed pressure (650 kPa).…”

“… Adsorption isotherms of (a) CO 2 and (b) N 2 on activated carbon at (○) 293 K, (△) 308 K, and (□) 323 K …”

Temporal Coupling of Subsurface and Surface Soil CO2 Fluxes: Insights From a Nonsteady State Model and Cross‐Wavelet Coherence Analysis

“…Previous studies have attributed increased R soil following precipitation events to physical mechanisms (e.g., displacement of CO 2 stored in dry soil pores (Huxman et al, 2004;Kim et al, 2012;Marañón-Jiménez et al, 2011)) or biological mechanisms (e.g., increased microbial metabolism (Kim et al, 2017)). R soil can also decrease following precipitation events, which has also been attributed to physical (e.g., decreased D gs (Davidson et al, 2000;Kim et al, 2012;Rochette et al, 1991;Šimůnek & Suarez, 1993)) and biological processes (e.g., shift from aerobic to anaerobic decomposition (Ball et al, 1999;Davidson et al, 2000;Kim et al, 2012)).…”