Enhanced methane hydrate formation using l-leucine and cyclodextrin

Abstract

Recently, solidified natural gas (SNG) technology has been suggested as a promising method for storing and transporting natural gas (NG), however, it is hindered by the slow formation kinetics of hydrate. Sodium dodecyl sulfate (SDS) is currently the most efficient kinetic promoter, unfortunately, it has a high environmental impact and poor recycling potential due to its high foaming properties. Thus, this work investigated for the first time the effect of environmentally friendly and non-foaming l-leucine, α-cyclodextrin, and β-cyclodextrin and their complex systems on hydrate formation. The results showed that l-leucine could effectively promote hydrate formation, and its promotion effect was concentration-dependent. Higher concentrations (3000–8000 ppm) of l-leucine increased the methane uptake of the system by an average of 696.5 %, with an optimal concentration being 5000 ppm. A synergistic effect occurred between l-leucine and cyclodextrin, where the optimal concentration of cyclodextrin was 100 ppm. β-cyclodextrin was more effective than α-cyclodextrin in promoting hydrate formation. The addition of 100 ppm of β-cyclodextrin to l-leucine solution resulted in a 29.6 % reduction in T90. According to morphological observations, cyclodextrins strengthen the dendritic features of the hydrate to enhance mass transfer. This work aids in the advancement of SNG and environmentally friendly fast hydrate formation technology.