The effects of continuous- and stop-flow gas streams on adsorptive removal of benzene vapor using type – II covalent organic polymers

Abstract

Various materials have been investigated for the adsorptive removal of volatile organic compounds (VOCs, such as benzene). However, most materials proposed for the adsorptive removal of gaseous benzene (and other VOCs) perform relatively poorly (e.g., an impractically low-service 10% breakthrough volume [BTV10] at < 100 ppm). The adsorbent uptake rate (mg g(-1) min(-1)) can also be assessed as a function of the gas-stream flow rate (or space velocity). The main aim of this study is to explore the effect of two different gas-stream supply modes - stopped flow (at a fixed stream flow rate of 330 mL atm min(-1)) vs. continuous flow (a variable-stream flow rate of 100, 200, or 330 mL atm min(-1)) on the adsorption metrics of gaseous benzene on 5 mg of two types of - II covalent organic polymers (COPs: CBAP-1 [DETA], CD; or CRAP-1 [EDA], CE). The sorbent tube outlet stream was sampled by two respective sampling methods (i.e., a large-volume injector [LVI] for stopped flow vs. syringe injection [SI] for continuous flow) for sample quantitation by gas chromatography flame-ionization detection (GC-FID). The observed BTV10 values in the two sampling modes were similar when tested using 10 ppm benzene, irrespective of sorbents: 56/60 (CD) vs. 620/624 L atm g(-1) (CE). BTV10 values increased systematically with decreasing stream-flow rates to reflect the importance of space velocity in adsorptive removal of benzene. The overall assessment of adsorption performance between stopped flow (LVI) and continuous flow (SI) revealed that the performance of the adsorbent is independent of flow mode (e.g., when performance was compared at flow rate of 330 mL min(-1)).