Influence of the carbon chain length of a sulfate-based surfactant on the formation of CO2, CH4 and CO2–CH4 gas hydrates

Abstract

Influence of the carbon chain length of a sulfate-based surfactant on the formation of CO 2 , CH 4 and CO 2 -CH 4 gas hydrates, Chemical Engineering Science, http://dx. AbstractThis study investigates how the length of the carbon chain of homologous surfactants affects the amount and growth rate of gas hydrates formed in quiescent CO 2 /CH 4 /water systems. The 1 Present address: PDVSA Intevep, Los Teques -Edo. Miranda, Apto 76343, Caracas 1070-A, Venezuela 2 hydrate formation experiments were conducted using sodium alkyl sulfates with different carbon-chain lengths (C 8 , C 10 , C 11 , C 12 , C 13 , C 14 , C 16 and C 18 ), at a concentration of 10.4 mol.m -3 .The CO 2 :CH 4 ratios investigated were 0:100, 25:75, 75:25, and 100:0. Hydrate formation was studied in a batch reactor at an initial subcooling of about 5 K. It was observed to be efficient only for those surfactants that promoted the formation of a water-wettable porous hydrate structure, which spreads over the inner sidewalls of the hydrate-formation cell. For the CO 2 :CH 4 ratios of 0:100, 25:75, 75:25 and 100:0, hydrate formation was efficient for the surfactants with respectively 8 to 14, 11 to 13, 11 to 12, and 12 carbon atoms in their alkyl chain. Only the surfactant with 12 carbon atoms was found to promote and accelerate hydrate growth for all the gas-phase compositions tested. The much lesser surfactant effect on hydrate growth rate observed with the increase in the initial CO 2 fraction in the gas phase is ascribed to a modification of the adsorption behavior of the surfactant molecules on the hydrate surface, which, as already suggested by Zhang et al. (2010), is probably due to competitive adsorption between the surfactant anions and bicarbonate.

Clathrate hydrates: recent advances on CH4 and CO2 hydrates, and possible new frontiers

“…Ionic surfactants also affect the morphology of the resultant hydrate particle, suggesting that a capillary-driven pattern occurs during hydrate growth when the gas is CH4 and SDS or AOT are present, while a rapid growth of a non-permeable hydrate 'skin' grows in the other cases. The results summarised are consistent with previous observations, 61 -63 including those reported by Dicharry et al, 64 who studied hydrate formation triggered by tetrahydrofuran (THF), where the effect of the alkyl chain length of sodium alkyl sulfates (from 8 to 18 carbon atoms) was studied explicitly. It has been argued that surfactants are not effective in CO2-rich systems because of a competitive adsorption between CO2 and the surfactants at the water-gas interface.…”

Experimental investigations on tetrahydrofuran – methane – water system: Rapid methane gas storage in hydrates

“…However, experiments conducted with continuous stirring have shown significant gas consumption due to the phase change even with lower THF concentrations [14,16]. Furthermore, the addition of surfactants like sodium alkyl sulfates (C8-C16) along with low mol% THF, helps in faster hydrate nucleation and higher gas uptake [28,29]. Additionally detailed structural studies indicated that the hydrates formed with lesser amounts of THF are crystallised into mixtures of both sI and sII, while the hydrates with stoichiometry crystallise into sII [30,31].…”

Biopromoters for Gas Hydrate Formation: A Mini Review of Current Status

“…As shown in Figure 1C, LS molecules can adsorb on the surface of forming hydrate particles under the action of hydrogen bonds between partial hydrophilic groups and hydrate molecules. Meanwhile, partial hydrophilic groups, such as sulfonic acid group and carboxyl group, are exposed to the outside surface of forming hydrate particles, which leads to mutual repulsion among forming hydrate particles under electrostatic action (Dicharry et al, 2016). And the hydrate particles become more wettable for water molecules due to hydrophilic groups.…”