Effects of eco-friendly cyclodextrin on the methane hydrate formation in the complex systems

Due to the increasing demand for natural gas, solidified natural gas (SNG) technology provides an attractive option for natural gas storage and transportation. However, the use of sodium dodecyl sulfate (SDS) to promote hydrate formation will have a negative impact on the environment. To overcome this difficulty, the compounding system of environmentally friendly additives with SDS was intended to find the synergistic promotion effects aiming to reduce the usage of SDS in this study. Three kinds of cyclodextrins including alpha CD, beta CD, hydroxypropyl-beta CD (HPCD) with SDS were compounded to study the effect of their interaction on hydrate formation kinetics. The result showed that when used with SDS, the formation of hydrates was promoted by alpha CD and beta CD but inhibited by HPCD. It is emphasized that the promoting effect depended on the water channel (completely hydrophilic zones) formed by H-bonds between cyclodextrin and SDS self-assembled channel-type complexes. Compared with 500 ppm SDS used along, it was possible to reduce the dosage of SDS by 40%. Finally, by observing the morphology of hydrate formation, it is found that the addition of cyclodextrins would affect the driving force for hydrate growth in the horizontal direction during hydrate formation. This study provides theoretical support for further understanding of cyclodextrin and surfactant compounding and shows an effective way for the application of SNG industry.