The interactive roles of space velocity and particle size in a microporous carbon bed system in controlling adsorptive removal of gaseous benzene under ambient conditions

Abstract

The performance of an air filtration system is commonly evaluated using laboratory-scale studies under optimal, but unrealistic, experimental conditions (e.g., high pollutant loading, slow feeding rate, and fine particle size). It is, therefore, important to assess the role of key variables affecting performance from a practical perspective. To this end, a series of dynamic adsorption tests were carried out to evaluate the uptake behavior of gaseous benzene (at 1 Pa) by a filter bed system made of a commercial activated carbon (AC) in relation to two key variables: particle-size range (granular AC [GAC]: 0.212 to 5 mm vs. powdered AC [PAC]: 0.6 to 2.36 mm) and space velocity (flow rates: 100 to 3000 mL min−1). The effects of these two key variables on capturing of benzene were assessed in terms of key performance metrics (e.g., breakthrough volume [BTV]: L g−1 atm−1, partition coefficient [PC]: mol kg−1 Pa−1, and adsorption capacity [Q]: mg g−1). It was verified that GAC outperformed PAC at a low flow rate (100 to 500 mL min−1), in particular in the 5% BTV region. In contrast, PAC performed better at a 100 L BTV (PC: 0.49 to 0.98 mol kg−1 Pa−1) under high flow conditions (1000 to 3000 mL min−1). The results of isotherm/kinetic analysis revealed the dominant role of the surface/pore diffusion in the multilayer adsorption of benzene onto GAC adsorbent (relative to PAC adsorbent). With the increases in space velocity, the flow patterns crossed from a laminar to transitional mode to promote advection transport (relative to diffusion transport) of benzene molecules through the GAC-bed filter (relative to the PAC-bed filter). These findings are expected to help open new paths for optimization of air filtration system under real environmental conditions, particulary with respect to space velocity and particle diameter (of adsorbent).