Published 09/07/2018
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A simple and timesaving method for the mass-transfer assessment of solvents used in physical absorption

P.Biard , A.Couvert , A.Coudon , S.Giraudet

Consequently, up to now, the assessment of organic solvents for VOC absorption is often based only on the VOC/solvent affinity evaluation through the gas-liquid partition coefficient measurement. The VOC/solvent partition coefficients and overall liquid-phase mass-transfer coefficients were deduced from the breakthrough curves using a numerical procedure developed in this work.
A simple dynamic absorption procedure to assess the mass-transfer performances of a solvent toward a selected gaseous solute is presented. Absorption was operated semi-continuously at transient state until the equilibrium was reached without solvent recirculation. Four volatile organic compounds more or less hydrophobic were absorbed in water and two heavy organic solvents adipate DEHA and polydimethylsiloxane PDMS). A numerical resolution procedure was developed to simulate the gas-liquid mass-transfer and to deduce the VOC partition coefficients, expressed as the Henry's law constants, as well as the overall liquid-phase mass-transfer coefficients. The overall liquid-phase mass-transfer coefficients were correlated to the diffusion coefficients using the Higbie penetration theory. The results confirm the high selectivity of water whereas the two organic solvents, especially DEHA, exhibit rather good affinity with all VOC even if the Henry's law constants of the most soluble and the less soluble compounds for those solvents differ by 1 or 2 orders of magnitude. The liquid-film mass-transfer coefficients in the two organic solvents, even being more viscous, are larger than in water which confirms their good potential for hydrophobic VOC treatment.
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