Removal of heat of adsorption from adsorbent by forced convection

Desiccants are used in the process industry for the drying of technical gases. An emerging application is fresh water production from water vapor of atmospheric air using adsorbents in a day-night cycle. Water adsorption is performed at night and desorption using solar heat during daytime. In this paper a non-isothermal kinetic model of a packed bed of desiccant pellets is developed to determine possible uptake improvements by elucidating the complex mass and heat transfer interdependent resistances. Shallow beds thinner than 1 cm are required to handle bed diffusion and thermal conduction effects. Options for improvements regarding intragranular water vapor diffusion are limited. The adsorption process quickly becomes convection and radiation limited by the strong exothermicity of water adsorption.

Section: Simulation Methodsmentioning

confidence: 99%

Section: Simulation Methodsmentioning

confidence: 99%

Non-Isothermal Kinetic Model of Water Vapor Adsorption on a Desiccant Bed for Harvesting Water from Atmospheric Air

Peeters

Verbruggen

Rongé

et al. 2021

“…24 It is also shown that flow of gas over the adsorbent at a moderate to high rate for removing (or supplying) the heat of ad(de)sorption during the kinetic test may not achieve a true isothermal process when the kinetics of sorption is relatively fast. 24,25 d. Random Nature of Data Generation. Many of the traditional methods for measurement of multicomponent equilibrium adsorption data do not have control over the final equilibrium state at the end of the test.…”

Section: Traditional Experimental Methodsmentioning

confidence: 99%

Recent Developments in Macroscopic Measurement of Multicomponent Gas Adsorption Equilibria, Kinetics, and Heats

Sircar

2006

Self Cite

Most practical applications of adsorption technology for gas separation and purification deal with multicomponent feed gas mixtures. The key input variables for the design and optimization of such separation processes are the multicomponent gas adsorption equilibria, kinetics, and isosteric heats. Recent advances in the measurement of these properties for multicomponent systems by macroscopic methods are discussed. The isothermal isotope exchange technique for measurement of multicomponent gas equilibria and kinetics, and micro-calorimetry for direct measurement of component isosteric heats from gas mixtures are recommended.

Section: Equilibrium Isotherm Modelmentioning

confidence: 99%

“…The flow rate of the gas mixture flowing to the column was set to a high rate (∼350 mL/min) to keep temperature changes due to the adsorption heat effects negligible. According to Sircar, although the flow of feed gas facilitates heat removal from adsorbents, small temperature increases are expected even at high flow rates. While negligible temperature changes of adsorbent result in considerable changes of the adsorption kinetic rate constants, in this study, small temperature effects on the adsorption equilibria, e.g., uptake amounts, were considered negligible.…”

Section: Experimental Sectionmentioning

confidence: 99%

Novel Differential Column Method for Measuring Multicomponent Gas Adsorption Isotherms in NaY Zeolite

Shirani

Eić

2017

Separation and purification of gas mixtures using selective adsorbents is widely used in different industries such as gas drying, air separation, and H2 purification. Equilibrium analysis involving adsorption of binary gas mixtures provides important information related to the adsorbent performance in the separation of gases. In this study, a novel technique termed “differential column technique” was developed for binary isotherm measurement employing streams containing carbon dioxide, carbon monoxide, and ethylene at different compositions. This technique is based on measuring the gas desorption by changing equilibrium pressure conditions. The isotherm curve was generated by summing desorption amounts desorbed at each pressure step. Through the application of this technique, the single-component isotherms of CO2, CO, and ethylene on zeolite NaY were measured, and the isotherms were compared to the results obtained by a standard gravimetric technique. (The average relative deviation is less than 6%.) The main advantage of the technique is the significant time savings, e.g., one experimental run is required to generate an isotherm compared to multirun experiments using a standard breakthrough technique, in addition to using a simpler experimental setup and generally smaller amount of sample (agglomerated or in a powder form). Another important feature of this technique is the relatively simple extension that allows measurements of gas mixture equilibria. As such, the proposed technique has the potential to be used as a fast screening technique for adsorbent selection based on single-component or mixture analysis. To investigate the consistency of the proposed technique, the binary isotherms of competitive, CO2–C2H4, and noncompetitive, CO2–CO, mixtures were investigated at different gas compositions. In addition, the effects of sorbate concentrations in the gas phase and interactions with the NaY zeolite active surface were investigated in relation to the adsorption selectivity and capacity, i.e., strong interaction of both CO2 and ethylene with NaY site resulted in close adsorption selectivity 0.8 ≤ S CO2/C2H4 ≤ 1.7, while CO2 adsorbed more selectively compared to CO, 14 ≤ S CO2/CO ≤ 30, as a result of weak CO interaction with the adsorbent sites. Finally, the binary adsorption isotherms and selectivity were predicted by the multisite Langmuir model using the single component’s isotherm parameters. Modest agreements (error ≤ 28%) were obtained between the predicted and experimental results.