Aggregation and static adsorption behaviour of Achromobacter sp. TMB1 produced rhamnolipids on sandstone core in relation to microbial enhanced oil recovery

In this article, the adsorption characteristics of bacterial surface-active rhamnolipids produced by Achromobacter sp. TMB1 were studied on sandstone core collected from Upper Assam oil field, India with emphasis on adsorption equilibrium and kinetics. Studied rhamnolipid reduced the interfacial tension between aqueous phase and oil to 0.9 mN/m from 39.1 mN/m. Micelle formation and aggregation behaviour of the rhamnolipids were also evaluated along with their wettability alteration properties. Gibbs free energy and surface area per molecules of rhamnolipids were found to be -22.592 kJ/mol and 106.45 Ao2, respectively. The adsorption was confirmed through FTIR patterns of pure and rhamnolipid treated sand particles, which indicated the chemisorption mechanism of the process. Orcinol test was used to quantify the biosurfactant adsorbed on sandstone. In batch experiments, temperature, pH, salinity and adsorbent dose effect on adsorption efficiency were found to be significant. Further, the observed adsorption data were fitted with different isotherm models and found better fits with Freundlich isotherm after determined parameters of each models. The isotherm exhibited monolayer adsorption behaviour on the substratum bellow the CMC concentration. Above CMC value, the adsorption process tends to be associated with the formation of monomer <-> micelle <-> vesicle mechanism. Among four kinetic models, second-order model exhibited better predictions and was the most suitable kinetics model for rhamnolipids adsorption predictions. The adsorption equilibrium and kinetic behaviour of rhamnolipid onto sandstone corroborated chemisorption and involvement of functional groups during the process.

Automated summary

The study focused on the adsorption characteristics of bacterial surface-active rhamnolipids on sandstone cores from the Upper Assam oil field in India, revealing a significant reduction in interfacial tension between aqueous and oil phases. The adsorption process was confirmed to be chemisorption mechanism, forming a monolayer adsorption on the sandstone substrate.