Adsorption behavior of surfactants and mass transfer in single‐drop extraction

Abstract

Abstract Three surfactants—SDS, Triton X‐100, and DTMAC—were used to study effects of surfactants on the mass transfer in liquid–liquid extraction. Single‐drop extraction apparatus was used to obtain the mass‐transfer coefficient of acetic acid from dispersed CCl 4 droplets to the continuous water phase. The excess mass‐transfer resistance was related to the adsorption behavior of surfactants on the interface. All of these surfactants significantly reduced the mass‐transfer rate. Mass‐transfer coefficient, K R , decreases rapidly with increasing surfactant concentration and reaches a minimum at concentrations less than 0.04 mM. The effectiveness of the surfactants in decreasing the mass‐transfer rate increases in the order: DTMAC<SDS = Triton X‐100. This effectiveness has no direct relation with the ionic types of surfactants, but is affected by the adsorption rate and adsorbed surface concentration on the interface. A slight increase in the mass‐transfer coefficient was found at higher concentrations of Triton X‐100 due to its higher adsorption kinetics. The excess mass‐transfer resistance exerted by the surfactant mainly resulted from the obstruction of the adsorbed barrier layer. The contribution of the inhibition of interfacial flow to the mass‐transfer resistance was considered to be minor.