New surfactant combination to improve potential of gas hydrates
doi:10.1038/nindia.2017.62 Published online 30 May 2017
By synthesizing surfactant micelles at low hydrate forming temperatures, scientists from the CSIR-National Chemical Laboratory, Pune and Indian Institute of Technology Madras claim to have finally settled the long-simmering debate on whether surfactant micelles actually enhance gas hydrate formation kinetics.
Gas hydrates are ice-like crystalline materials formed when small gas (guest) molecules come in contact with water (host) molecules at low temperature in high pressure conditions. The guest molecules, such as methane and carbon dioxide, get trapped in hydrogen bonded water cages thus stabilizing these cages.
Massive hydrate deposits of natural gas have been formed under the seabed or in permafrost over millions and millions of years and have lately come under widespread scrutiny due to their enormous potential as a clean energy source. India is estimated to have 2000 TCM (trillion cubic metres) of natural gas in the form of hydrate reserves, sufficient to meet the country’s total energy demand for the next ~200 years. The Indian deposits constitute only 10% of the world’s total estimated reserves, making this clean source of energy one of the most exciting frontiers of science and engineering in recent times. Apart from their viability as a future energy source, gas hydrates also boast huge potential in technological applications such as gas capture, separation and storage. The most attractive is as method for methane storage. To put its potential in context, 1 volume of gas hydrate can store up to 170 volume of methane at STP.
Employing gas hydrates for methane storage requires rapid hydrate formation kinetics which usually requires specific additives called as surfactants. It was long hypothesised that surfactant micelles promote hydrate formation by acting as nucleation sites. The hypothesis however, was later discounted because the surfactant used in most of the studies, sodium dodecyl sulfate (SDS) does not form micelles at the typically low hydrate formation temperatures.
Researchers have now used a hybrid surfactant mixture made up of anionic surfactant SDS and zwitterionic surfactant cocoamidopropyl betaine (CAPB) to synthesize surfactant micelles at methane hydrate forming temperatures and investigated this effect of the same on the kinetics of gas hydrate formation.
The study proves for the first time that the presence of surfactant micelles enhances hydrate formation kinetics.
1. Bhattacharjee, G. et al. Effects of micellization on growth kinetics of methane hydrate. Ind. Eng. Chem. Res. (2017) doi: 10.1021/acs.iecr.7b00328