Microemulsions for remediation of light non-aqueous-phase liquids in aquifer rocks

Abstract

In this study, the formulation of microemulsions as cleaning systems is studied using model hydrocarbons to simulate light non-aqueous-phase liquids (LNAPL). The effects of the type of surfactant, the size of the LNAPL compound chain, the type of co-surfactant, salinity, pH, and temperature on the phase behavior of LNAPL-water-surfactant were investigated. Using pseudo-ternary diagrams, the effects of these variables on the microemulsion domain size were analyzed. The results show that choosing a co-surfactant with a shorter carbon chain length significantly increases the microemulsion domain. The microemulsion domain increases with the decrease in the length of the LNAPL compounds. Decreasing the salinity, pH or temperature increased the microemulsion domains. A sandstone core flooding experiment was carried out using kerosene as LNAPL and solution of Triton X-100 or LAS/iso-amyl alcohol as surfactant/co-surfactant. The results of the flooding experiment with low concentration of surfactant showed a total recovery of 50% of LNAPL by 14 bed volumes (7 of water and 7 of the Triton X-100/iso-amyl alcohol and 60% of the LNAPL by analogous injection of LAS/iso-amyl alcohol. The results of the flooding experiment with high concentration of surfactant showed a recovery of 67% of the LNAPL by 3 bed volumes of water injection and an extra 36% by 2 bed volumes of the surfactant/co-surfactant solution injection. This shows the strong effect of the microemulsion in the mobilization of the residual LNAPL from an aquifer rock using an appropriate formulation of surfactant solutions.