title: Dissolution kinetics of volatile organic compound vapors in water: An integrated experimental and computational study.
abstract: In this study we performed batch experiments to investigate the dissolution kinetics of trichloroethylene (TCE) and toluene vapors in water at room temperature and atmospheric pressure. The batch systems consisted of a water reservoir and a connected headspace, the latter containing a small glass cylinder filled with pure volatile organic compound (VOC). Results showed that air phase concentrations of both TCE and toluene increased relatively quickly to their maximum values and then became constant. We considered subsequent dissolution into both stirred and unstirred water reservoirs. Results of the stirred experiments showed a quick increase in the VOC concentrations with time up to their solubility limit in water. VOC vapor dissolution was found to be independent of pH. In contrast, salinity had a significant effect on the solubility of TCE and toluene vapors. VOC evaporation and vapor dissolution in the stirred water reservoirs followed first-order rate processes. Observed data could be described well using both simplified analytical solutions, which decoupled the VOC dynamics in the air and water phases, as well as using more complete coupled solutions. However, the estimated evaporation (ke) and dissolution (kd) rate constants differed by up to 70% between the coupled and uncoupled formulations. We also numerically investigated the effects of fluid withdrawal from the small water reservoir due to sampling. While decoupling the VOC air and water phase mass transfer processes produced unreliable estimates of kd, the effects of fluid withdrawal on the estimated rate constants were found to be less important. The unstirred experiments showed a much slower increase in the dissolved VOC concentrations versus time. Molecular diffusion of the VOCs within the aqueous phase became then the limiting factor for mass transfer from air to water. Fluid withdrawal during sampling likely caused some minor convection within the reservoir, which was simulated by increasing the apparent liquid diffusion coefficient.
authors.affiliation: Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands; Department of Watershed and Rangeland Management, Gonbad Kavous University, Iran. Electronic address: m.gharehmahmoodlu@uu.nl.
authors.forename: Mojtaba G
authors.initials: MG
authors.lastname: Mahmoodlu
authors.affiliation: Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands; Department of Nuclear Engineering, Federal University of Rio de Janeiro, UFRJ, Rio de Janeiro, Brazil.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Pontedeiro
authors.affiliation: Radioactive Waste Division, Brazilian Nuclear Energy Commission, CNEN, Rio de Janeiro, Brazil.
authors.forename: Jesús S
authors.initials: JS
authors.lastname: Pérez Guerrero
authors.affiliation: Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Amir
authors.initials: A
authors.lastname: Raoof
authors.affiliation: Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Majid Hassanizadeh
authors.affiliation: Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands; NIDES Interdisciplinary Centr for Social Development, Federal University of Rio de Janeiro, UFRJ, Rio de Janeiro, Brazil.
authors.forename: Martinus Th
authors.initials: MT
authors.lastname: van Genuchten
mesh_terms: D004058:Diffusion; D005740:Gases / Q000032:analysis* / Q000737:chemistry; D007700:Kinetics; D008962:Models, Theoretical; D012995:Solubility; D014050:Toluene / Q000032:analysis* / Q000737:chemistry; D014241:Trichloroethylene / Q000032:analysis* / Q000737:chemistry; D055549:Volatile Organic Compounds / Q000032:analysis* / Q000737:chemistry; D014835:Volatilization; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry
chemical_list: D005740:Gases; D055549:Volatile Organic Compounds; D014874:Water Pollutants, Chemical; D014241:Trichloroethylene; D014050:Toluene
keywords: Dissolution; Kinetics; Molecular diffusion; Salinity; Volatile organic compounds