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Kinetic and Morphology Study of Equimolar CO2-CH4Hydrate Formation in the Presence of Cyclooctane and l -Tryptophan
Gaikwad N., Bhattacharjee G., , , Linga P.
Published in ACS Publications
Volume: 35
Issue: 1
Pages: 636 - 648
This study investigates the kinetics and morphology of an equimolar CO2-CH4 gas mixture by inducing sI and sH hydrates in gas-water and gas-liquid hydrocarbon (LHC)-water systems using pure water and sH hydrate former cyclooctane (Cyclo-O) at 274 K and 5.0 MPa in a quiescent system. Further, the effect of promoter l-tryptophan in enhancing the kinetics is evaluated for both systems. The visual morphology observations provide mechanistic insights into the hydrate crystal nucleation and growth kinetics in the presence of pure water, 1 wt % tryptophan, 2.86 mol % Cyclo-O, and 1 wt % tryptophan with 2.86 mol % Cyclo-O. Distinct variations in the kinetics and morphology of hydrate crystal growth in aqueous bulk solution depend on the type of additive used. Swordlike elongated polygons were observed in the pure water system at the gas-liquid interface. As time progressed, the smooth polygonal shape was observed in the gas phase, and the evolution of swordlike to larger polygons was observed at the gas-liquid interface. The addition of 1 wt % tryptophan to the gas-liquid system led to significant gas uptake and rapid hydrate formation rate compared to the pure water system and that was evident by morphology study as well. Whereas, in the case of the gas-LHC-water system, the presence of water-insoluble Cyclo-O provides resistance to mass transfer between the gas and the bulk water phase; however, hydrate formation involves only dissolved guest gas molecules that could travel through the Cyclo-O layer in quiescent conditions, showing cloudlike hydrate formation. The addition of 1 wt % tryptophan with 2.86 mol % Cyclo-O aids inducing a growing front by bridging the hydrophobic Cyclo-O layer and enhances gas uptake and hydrate formation rate significantly compared to the water-Cyclo-O system. The significant increase in gas uptake in the presence of tryptophan was assigned to the porous hydrate formation, which enhanced the gas-water contact. ©
About the journal
JournalEnergy and Fuels
PublisherACS Publications
Open AccessNo