Effect of pH on the Stability of Water in Heavy Crude Oil Emulsions Stabilized by Saponin and RhamnolipidBiosurfactants

Biosurfactants are used widely in the oil and petroleum industries such as the production, transportation, and storage process of oil. This application of biosurfactants is due to the biodegradability of these biomaterials. This study investigated the effect of pH on stabilized water-in-oil emulsions using rhamnolipid and saponin biosurfactants. The phase separation was determined by measuring the volume of the water phase separated. The obtained results showed the introduction of HCl significantly affects the stability of emulsions stabilized by rhamnolipid and saponin but had no significant effect on the mixture of biosurfactant contents because of the synergistic effect. Also, the results showed that the maximum separation yield for rhamnolipid, saponin, and mixed biosurfactants at pH=1 and after 1 hour of sonication was 61, 57, and 20%, respectively. The water droplet sizes of the emulsion after sonication and before phase separation at pH of 5, 3, and 1 were around 100, 200, and 1000 µm for 40–60% of w/o emulsion stabilized by the mixture of rhamnolipid and saponin biosurfactants using DLS analysis. The results demonstrate that at low pHs the dramatic instability of w/o emulsion was obtained and significantly increased the rate of the Ostwald ripening process and coalescence rate of water droplets.