Assessment of interfering/synergistic effects in the adsorption between polar and non-polar VOCs on a commercial biomass-based microporous carbon

Abstract

This research has been carried out to investigate unique relationships in adsorption behavior between polar and non-polar volatile organic compounds (VOCs: formaldehyde (FA) versus toluene) using commercial macadamia nutshell (MNS)-based microporous activated carbon (i.e., Procarb-900: namely, P900). The breakthrough (BT) volume, adsorption capacity, and partition coefficient of P900 are estimated for 100 ppm FA as a single component and as a binary phase with 100 ppm toluene. The contrasting features of adsorption (such as interfering/synergistic relationships) for VOC mixtures with different polarities are accounted for in terms of interaction between the key variables (e.g., pore size distribution, adsorbent particle size, surface element compositions, and sorbent bed mass). Accordingly, the powdered P900 (0.212–0.6 mm: 150 mg) exhibits an adsorption capacity of 5.7 mg g⁻¹ and a partition coefficient of 0.19 mol kg⁻¹ Pa⁻¹ for single-phase FA at the 10% BT level. Interestingly, its FA adsorption performance is synergistically improved in the presence of toluene (e.g., > 150%) in the early stage of adsorption (e.g., 10% BT), although their competition reduced its performance at 99% BT. The apparent synergistic trend in the early BT stage may possibly reflect diffusion resistance of the adsorbent (e.g., small particle size and developed ultra-micropore structure) and natural attributes of FA (e.g., low affinity and smaller kinetic diameter). The overall results of this study are expected to offer a better understanding of the mechanisms underlying the interactions between the mixed VOC system and microporous adsorbents.