Mass Transfer and Warming during Adsorption of High Concentrations of VOCs on an Activated Carbon Bed: Experimental and Theoretical Analysis

Abstract

An experimental and theoretical study was carried out to predict the warming and the mass-transfer rate during adsorption of high concentrations of volatile organic compounds (VOCs) in an activated carbon bed. A linear driving force (LDF) model is found to provide an acceptable fit to the measured data. An empirical correlation of the mass transfer rate is proposed as a function of the strength of adsorbent−adsorbate interactions and the gas velocity to design the adsorption process without using any adjustable parameter. The model was validated for an adsorption unit with high loadings (up to 100 g.m-3) of seven kinds of VOC and within the velocity range 0.139−0.556 m.s-1. The prediction of the temperature rise inside the adsorber is improved by the use of the differential heat of adsorption instead of the integral heat. A theoretical parameter sensitivity test indicates that the temperature rise is strongly dependent on the molar VOC concentration, the adsorption heat, and the volumetric heat capacity of the carrier gas. The warming of the activated carbon bed can be well predicted from these variables. The relation obtained appears to be a practical means for designing the safety of an adsorber and preventing carbon bed ignition.

Non-Calorimetric Determination of the Adsorption Heat of Volatile Organic Compounds under Dynamic Conditions

“…The choice of these materials rather than activated carbon is mainly due to the exothermic phenomenon associated with values of VOC adsorption enthalpy, usually ranging between 40 and 90 kJ.mol −1 [4,14]. This can yield to high temperature increases depending on levels of treated VOC concentration and may induce significant local warming to start combustion of either the adsorbate or the adsorbent itself, particularly if activated carbon is used [15,16]. Thus additional consideration of safety conditions is required for appropriate engineering and safe operating of adsorption facilities, which in turn needs accurate knowledge of the evolved heat effect values.…”

Statistical quantification of the influence of material properties on the oxidation and ignition of activated carbons

“…Ignition risks are commonly found for activated carbons packed in filters, mainly caused by certain types of contaminants that are filtered or adsorbed. Extensive literature sources are available for incidents of fires and thermal runaways encountered with activated carbon beds in service, idle condition and also during the handling and regeneration of the spent carbon (Naujokas 1985;Delage et al 2000;Zerbonia et al 2001). Fires were also reported during transit on board ship for chemically activated carbons (Bowes and Cameron 1971).…”

Potential use of a combined ozone and zeolite system for gaseous toluene elimination

“…Porous media such as activated carbon and zeolite possess large specific areas and have high adsorption capacity. They are frequently employed in traditional adsorption air purification systems to adsorb gases or odours [6][7][8][9]. Pollutant adsorption by activated carbon provides a cost-effective and feasible way to minimize the pollutant level.…”