Gas−Liquid Partition Coefficients and Henry's Law Constants of DMS in Aqueous Solutions of Fe(II) Chelate Complexes Using the Static Headspace Method

Abstract

Total reduced sulfurs quartet (H2S, CH3SH, CH3SCH3 [DMS]), CH3S2CH3 [DMDS]) is part of a spiny environmental problem afflicting the pulp mill industry exploiting the Kraft sulfate pulp process. Utilization of the ferric chelate complex of trans-1,2-cyclohexanediaminetetraacetic acid (CDTA) for the oxidative scrubbing of H2S and CH3SH in the Kraft mill atmospheric effluent streams is beneficial from the standpoints of iron protection against precipitation and oxygen-mediated regenerative oxidation of ferrous chelate CDTA. The remaining DMS and DMDS, considered non-oxidizable in CDTA−Fe(III) aqueous alkaline solutions, undergo physical absorption so their solubility is a crucial parameter for the design of the scrubbing−absorption process. The solubility of DMS in pure water, aqueous iron-free CDTA solutions, and CDTA−Fe(II) complex solutions was measured at atmospheric pressure between (288 and 308) K and for chelate concentrations between (38 and 300) mol·m-3. As experimental results revealed that DMS destabilized ferrous chelates at very large CDTA−Fe(II) concentrations, a maximum chelate concentration presenting practical interest was established. The static headspace method was used with an estimated uncertainty of ±2 %. It was shown that DMS solubility decreases with increasing temperature for all systems studied. CDTA concentration does not considerably affect DMS solubility; moreover, the concentration effect is negligible at 308 K. The solution pH was uninfluential on DMS solubility over the covered concentration and temperature ranges. CDTA concentration less than 100 mol·m-3 is recommended for use in absorption scrubbing equipments.