Senlin Tian

Reversibly enhanced aqueous solubilization of volatile organic compounds using a redox-reversible surfactant.

Surfactant-enhanced remediation (SER) is an effective method for the removal of volatile organic compounds (VOCs) from contaminated soils and groundwater. To reuse the surfactant the VOCs must be separated from the surfactant solutions. The water solubility of VOCs can be enhanced using reversible surfactants with a redox-acive group, (ferrocenylmethyl)dodecyldimethylammonium bromide (Fc12) and (ferrocenylmethyl)tetradecanedimethylammonium bromide (Fc14), above and below their critical micelle concentrations (CMC) under reducing (I+) and oxidative (I2+) conditions. The CMC values of Fc12 and Fc14 in I+ are 0.94 and 0.56 mmol/L and the solubilization of toluene by Fc12 and Fc14 in I+ for toluene is higher than the solubilization achieved with sodium dodecyl sulfate, cetyltrimethylammonium bromide and Trition X-114. The solubilization capacity of the ferrocenyl surfactants for each tested VOCs ranked as follows: ethylbenzene > toluene > benzene. The solubilities of VOCs by reversible surfactant in I+ were 30% higher than those in I2+ at comparable surfactant concentrations. The effects of Fc14 concentrations on VOCs removal efficiency were as follows: benzene > toluene > ethylbenzene. However, an improved removal efficiency was achieved at low ferrocenyl surfactant concentrations. Furthermore, the reversible surfactant could be recycled through chemical approaches to remove organic pollutants, which could significantly reduce the operating costs of SER technology.

Vapour–liquid equilibrium relationship between toluene and mixed surfactants

Micellar partitioning of volatile organic compounds (VOCs) in surfactant solutions and its effects on vapour–liquid equilibrium is fundamental to the overall design and implementation of surfactant-enhanced remediation. Knowledge of the vapour–liquid equilibrium partitioning coefficients for VOCs, especially in contaminated soils and groundwater in which they exist, is required. Headspace experiments were performed to quantify the effect of three mixed surfactants, cetyltrimethyl ammonium bromide (CTMAB) with tetrabutylammonium bromide (TBAB), sodium dodecyl sulph ate (SDS) with Triton X-405 (TX405), and CTMAB with Triton X-100 (TX100), on the apparent Henrys constants (H c ) of toluene at temperatures ranging from 25 °C to 40 °C. The H c values were significantly reduced in the presence of all three mixed surfactants at concentrations above their critical micelle concentrations (CMC). Mixed micellar partitioning, showing effects on the vapour–liquid equilibrium of toluene, was primarily responsible for the significant reduction of H c in their mixed systems. The mixed surfactants CTMAB–TX100 had the greatest effect on H c above the CMC, followed by SDS–TX405, then CTMAB–TBAB. Mixed systems of CTMAB–TX100 decreased H c at concentrations significantly lower than the SDS–TX405 and CTMAB–TBAB concentrations, because of to the lower CMC of CTMAB–TX100. Vapour–liquid equilibrium data were also tested against the model (H c =H/(1+K(X−CMC)) that described the partitioning of VOCs in vapour–water–micelle phases. The correlation of H c with mixed surfactant concentrations (X) and CMC can be utilized as an effective tool to predict the H c by mixed surfactants.

Solubilization Absorption of Toluene Vapor by Formation of Oil-in Water Microemulsions with Cation Surfactants

Absorption reactors to remove volatile organic compounds from gas streams can be retrofitted, as volatile organic compounds act as oils and form microemulsions. Using the region of microemulsion in the phase diagram as the indicator, the main influences on the solubilization capacity of various microemulsion systems were investigated. When the mass ratio of the surfactant (cetyltrimethylammonium bromide) to the cosurfactant (tetrabutylammonium bromide) was 1:1, the microemulsion was the best absorbent. Comparative absorption tests of microemulsion, distilled water, and surfactants were performed in a double-stirred reactor. The results indicate that the microemulsion has a relatively higher absorption rate and absorption capacity than the other absorbents.