Effect of biosurfactants produced by Bacillus subtilis and Pseudomonas aeruginosa on the formation kinetics of methane hydrates

Microorganisms play an important role in the formation of methane hydrate in subsea environment. Studies involving the effect of biosurfactants produced by microorganisms on methane hydrate formation kinetics are not well understood. The present work investigates the influence of cell free solution containing biosurfactant obtained during the cultivation of microorganisms on the formation kinetics of methane gas hydrate. Two microorganisms, viz., Pseudomonas aeruginosa CPCL and Bacillus subtilis YB7 have been used to produce biosurfactants namely, rhamnolipid and surfactin, respectively. The performance of the cell free solution containing various concentrations (200, 400, 600, 800 and 1000 ppm) of biosurfactant to form the methane gas hydrate was analyzed by adding it into the pure water system and compared with synthetic surfactant, sodium dodecyl sulfate (SDS). It has been observed that the introduction of biosurfactant into pure water system improves the formation kinetics of methane hydrate and reduced the induction time. Addition of 200 ppm of rhamnolipid solution in pure water system has resulted in 47.3% of methane gas to hydrate conversion with an induction time of about 0.23 h, whereas pure water showed 45.1% conversion with an induction time of about 5.77 h. The same concentration of surfactin and SDS have resulted in 42.7 and 33.3% of methane gas to hydrate conversion, respectively. Biosurfactants studied here shows efficient and better performance than their chemical counterpart, namely SDS. This study also provides information on the optimum biosurfactant concentration for the improved formation kinetics of methane hydrate. The results suggest that the utilization of environment friendly biosurfactant can be used as an effective kinetic promoter for the methane hydrate formation suitable for optimum storage and transportation of natural gases.