A novel technique for interface analysis: behaviour of sophorolipids biosurfactant obtained from Meyerozyma spp. MF138126 during low-salinity heavy-crude experiments

A novel technique for interface behaviour and thermodynamic properties analyses of sophorolipids (SLs) biosurfactant obtained from Meyerozyma spp. MF138126 under high-pressure high-temperature (HPHT), for low-salinity heavy-crude experiments is presented. An experimental rig for production of biosurfactant and determination of interfacial tension (IFT) under HPHT is developed specially for the purpose of this investigation. A reduction of a factor of seven and nine in IFT was obtained for experiments between brine and heavy-crude at temperatures of 45°C and 65 °C respectively. Furthermore, with increasing temperature, the degree of SLs adsorption at the interface increases leading to a total collapse in the profiles of the adsorption graphs. The minimum area per molecule of SLs monomers for different conditions suggested that the interface weakens occupying more surface area as the temperature increases. The degree of counter-ion binding for SLs is obtained to be 0.86. The computed Gibbs free energy of micellisation is −1940 KJ/mol; which is exergonic depicting favourable reaction and spontaneous in forward direction. At a fixed temperature of 25 °C and pressure of 45 bar, IFT value of 0.251 mN/m was obtained. It is concluded that the produced SLs retained its molecular integrity and IFT reduction effectiveness under both unconfined and confined HPHT systems.