Influence of mixed anionic-nonionic surfactants on methane hydrate formation : suppression of foam formation

Abstract

Solidified natural gas (SNG) via clathrate hydrate is a new technology for natural gas storage with high energy content per unit volume, extremely safe, and ease to recover. Although SNG has several advantages, its limitation is low rate of hydrate formation. Sodium dodecyl sulfate (SDS) is well known as a kinetic promoter used to increase the hydrate formation rate. However, using SDS resulted in a large amount of foam during gas recovery. In order to alleviate this problem, mixtures of SDS with nonionic surfactants were investigated. Polyoxyethylene (n) lauryl ether (EO₃ and EO₅) and alkyl poly glycol (APG) were mixed with SDS in different concentrations for the formation at 8 MPa and 4 ℃ in the quiescent condition. The experiment was investigated for the effects of these mixed surfactants in both kinetics and morphology studies. The result showed that the addition of EO₃ resulted in the gradual increase in the induction time with the addition of higher concentration of EO₃, while there was no difference for the NR₃₀. Adding EO₅ showed the stochastic phenomenon on the induction time and NR₅₀. In the presence of APG, the induction time increased up to ten times, while the NR₅₀ was lowered compared to only 0.25 wt% SDS. Interestingly, there was no significant different on the methane uptake with all conditions. The morphology showed similar hydrate formation and dissociation patterns with all investigated solutions. However, the different foam height at 8 hr was observed. The addition of EO₃ showed a gradual decrease in the foam formation with the higher concentration of EO₅. Adding the highest EO₅ concentration showed the optimum foam reduction compared with all conditions, while lower concentration cannot lower the foam generated. Moreover, the presence of APG showed the similar effects of foam reduction with EO₅. Furthermore, all experiments maintained the average hydrate yield and the amount of gas recover as 83 and ≥ 90%, respectively.