Influences of different co-promoters on the mixed methane hydrate formation with salt water at moderate conditions

Effects of co-promoters on the mixed methane-THF hydrate formation in the presence of 3.5 wt% NaCl and 5.56 mol% THF solution were investigated at 8 MPa and 288.2 K in an unstirred reactor. The addition of NaCl resulted in the two-step hydrate formation, and it is the first stage that adversely affected the hydrate formation rate. However, the final gas uptake in this system was similar to that without NaCl. The synergistic effects on the kinetic promotion by adding a co-promoter including sodium dodecyl sulfate (SDS) and amino acids (valine, leucine, and methionine) were then studied. The results showed that the addition of the co-promoters reduced the induction time, minimized the length of the first stage formation, and increased the hydrate formation rate. Moreover, the induction time and the length of the first stage formation decreased along with the increase in the co-promoter concentration. However, the addition of SDS had the adverse effects by decreasing about half of the final gas uptake and the water to hydrate conversion for the system without SDS. Moreover, the addition of methionine resulted in the best performance as a kinetic promoter on the hydrate formation in the system with THF and NaCl. Up to 95 % of methane gas can be recovered from the hydrates formed with and without the co promoters. The hydrate formation morphology illustrated the same pattern in all cases.

Automated summary

The effects of co-promoters on mixed methane-THF hydrate formation were investigated, and it was found that the addition of co-promoters reduced the induction time, minimized the length of the first stage formation, and increased the hydrate formation rate. However, certain co-promoters had adverse effects on the final gas uptake and water to hydrate conversion.