Adsorption and breakthrough characteristics of major odorants on a variety of surfaces

Abstract

The sorptive loss patterns of vapor-phase semi-volatile organic compounds [SVOCs (n=10): acetic acid (ACA), propionic acid (PPA), i-butyric acid (IBA), n-butyric acid (BTA), i-valeric acid (IVA), n-valeric acid (VLA), phenol (PhAl), p-cresol (p-C), indole (ID), and skatole (SK)] were evaluated. A gaseous standard of target species (48~406 ppb) in polyester aluminum (PEA) bags was passed through an empty impinger in 1 L steps and exiting SVOCs were collected on three-bed sorbent tubes for subsequent analysis by thermal desorption gas chromatography-mass spectroscopy (TD-GC-MS). Sorptive losses in PEA bags were also investigated. Adsorption saturation of these targets on inert impinger inner glass wall was quantified in the range of 0.02 to 0.39 µg cm-2. The 10% breakthrough volumes (BTV) of ACA, PPA, IBA, BTA, IVA, VLA were 1.8, 2.4, 3.0, 3.7, 5.5, and 7.0 L, respectively, while those of PhAl, p-C, ID, and SK were 0.2, 1.0, 1.8, and 3.5 L, respectively. The computed average adsorption capacity of the impinger glass surface was 4.05 ng cm-2 (at 10% BTV) for all target odorants. The observed sorptive patterns suggest that the sorptive losses of VFAs, phenols, and indoles can occur very effectively at low ppb levels onto glass surface in a highly predictable manner. To explore more about appropriate sampling, a simple dynamic headspace (HS) system was employed to generate vapor-phase volatile organic compounds (VOCs) from a liquid slurry sample placed in an impinger under steady-state conditions. To measure sorptive removal of odorants generated from slurry, a total of 13 VOCs ((methyl ethyl ketone (MEK), isobutyl alcohol (i-BuAl), benzene (B), toluene (T), p-xylene (p-X), m-xylene (m-X), o-xylene (o-X), styrene (S), o-cresol (o-C), phenol (PhAl), p-cresol (p-C), indole (ID), and skatole (SK)) were quantified before and after the treatment. The sorptive rate of odorants was evaluated against MOF-199 and two reference sorbents (zeolite and activated carbon (AC)). Adsorption capacity expressed between different studies was computed at 5, 10, and 50% BTV for all 13 odorants, while it was computed as 0.70±1.08, 11.0±18.3, and 22.6±42.3 µg g-1 (at 10% BTV) for zeolite, AC, and MOF-199, respectively. All adsorbents showed higher sorptive removal for phenolic and indolic compounds (o-C, PhAl, p-C, ID, and SK) compared to other VOCs (MEK, i-BuAl, B, T, p-X, m-X, o-X, and S). MOF-199 showed the best adsorption performance for o-C (0.31±0.04), PhAl (61.6±4.98), p-C (140±7.95), ID (27.8±2.23), and SK (63.9±1.55), while AC showed the best for MEK (5.02), i-BuAl (0.36), B (0.54), T (3.89), p-X (0.45), m-X (0.08), o-X (0.06), and S (1.57 µg g-1) at 10% BTV.