(232w) Cyclopentane Hydrate Formation Equilibria with Varying HLB Numbers in Sorbitan Monoester Surfactants

Sorbitan monoesters are nonionic surfactants having sorbitan functional group as a hydrophilic head. Their hydrophilic-lipophilic balance numbers (HLB numbers) can be determined by carbon numbers or structure of hydrophobic tails. The hydrophobicity of surfactants is one of the important factors on the emulsion formation, and thus it is significant that the variation of the HLB number of surfactants affects the hydrate formation equilibria from the water-in-oil emulsion. Span 20, 40, 60, and 80, which have the HLB number as 8.6, 6.7, 4.7, and 4.3, were utilized in this study, then we analyzed the effect of HLB numbers on the size of emulsion droplets and equilibrium temperature of cyclopentane hydrate formed from water-in-cyclopentane emulsion. The size of emulsion and equilibrium temperature of cyclopentane hydrate monotonically increased with increasing the HLB number of sorbitan monoesters. Especially, these values were suddenly decreased at the 4.3 of HLB number, because Span 80 uniquely have cis double bond on their hydrophobic tails. With 3.5 wt% sodium chloride, the trend of equilibrium temperature of cyclopentane hydrate was removed due to the significant effect of salt ions on the interaction between surfactant and water molecules.