Improved formation kinetics of carbon dioxide hydrate in brine induced by sodium dodecyl sulfate

Abstract

Due to high efficiency and low cost, hydrate-based desalination is investigated as a pretreatment method for seawater desalination. To improve the formation rate of hydrates, the effect of sodium dodecyl sulfate (SDS) on CO2 hydrate formation from a 3.5 wt.% NaCl solution was measured at 275 K and 3 MPa. X-ray diffraction (XRD) and cryo-scanning electron microscopy (cryo-SEM) were used to measure the crystal structure and micromorphology of the formed hydrates. The results showed that the induction time of CO2 hydrate formation reduced from 32 to 2 min when SDS concentration increased from 0.01 to 0.05%, the hydrate conversion rate increased from 12.06 to 23.32%, and the remaining NaCl concentration increased from 3.997 to 4.515 wt.%. However, as the SDS concentration surpassed 0.05 wt.%, the induction time increased accompanied by a decrease in the hydrate conversion rate. XRD showed that the CO2 hydrate was a structure I hydrate, and SDS had no influence on the hydrate structure. However, cryo-SEM images revealed that SDS promoted the formation of hydrates by increasing the specific surface area of the formed hydrates and folds; rods and clusters could be found on the surface of the CO2 hydrate. Thus, the best SDS concentration for promoting CO2 hydrate formation was approximately 0.05 wt.%; desalination was most efficient at this concentration.