Two-Dimensional Modeling of the Effect of Relative Humidity on Volatile Organic Compounds Adsorption in a Fixed Bed Adsorber
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Abstract
Water vapor can affect adsorption of volatile organic compound (VOC) onto activated carbon. In this research, a two-dimensional heterogenous computational fluid dynamics model was developed and validated to understand the mechanism and kinetics during competitive adsorption between VOC and water vapor in a beaded activated carbon (BAC) fixed-bed adsorber. The model comprised of a VOC-water vapor multicomponent competitive adsorption isotherm and governing transport phenomena equations. The multicomponent competitive adsorption isotherm was based on Manes method, which requires only single-component adsorption isotherms of adsorbates as inputs. Consequently, a modified Dubinin-Radushkevich (MDR) isotherm equation and Qi-Hay-Rood (QHR) isotherm equation were used to describe the pure single-component adsorption equilibrium of VOC (type I) and water vapor (type V), respectively. The MDR and QHR isotherm equations fitted the experimental data of pure VOC adsorption and water vapor adsorption on BAC with an overall r2 value of 0.998 and 0.999 respectively. The governing transport phenomena component of the model consists of macroscopic mass, momentum, and energy conversation equations. The model predicted the competitive adsorption isotherms, breakthrough and bed temperature profiles of selected VOCs (2-propanol, acetone, toluene, n-butanol, 1,2,4-trimethylbenzene) with a mean relative absolute error (MRAE) of 3.6%, 15.4% and 2.2% respectively. Sensitivity analysis was also conducted to test the robustness of the model in detecting the impact of relative humidity (RH) on VOC adsorption with change in adsorption temperature and inlet adsorbate concentration; and an overall MRAE of 6.6% was observed between the experimental and simulated results. The model, hence, can be used for optimizing adsorber design and operating conditions to minimize the impact of RH during adsorption of contaminants from gas streams.