Kinetic promotion of non-ionic surfactants on cyclopentane hydrate formation

Abstract

Clathrate hydrates are among the most important cold storage materials studied which are known to enhance the coefficient of performance in air conditioning systems. In the present work, the kinetics of cyclopentane (CP) hydrate formation is investigated in an atmospheric stirred reactor, with and without additives. The effects of 14 surfactants and polymers on hydrate promotion are experimentally investigated. These surfactants and polymers belong to the family of Nonyl Phenol ethoxylates (NPE), Lauryl Alcohol Ethoxylates (LAE), Poly Ethylene Glycols (PEG), Ethylene Oxide/Propylene Oxide copolymer (EO/PO), polyoxyethylene sorbitan monopalmitate (Tween), butyl phenol ethoxylates (TritonX-100), and sodium alkyl sulfate. The results indicate that while the CP/water system exhibits high induction time and low formation rate, addition of surfactants can highly decrease the induction time and increase the formation rate. Among the studied surfactants, LAE8EO, TritonX-100 and NPE6EO were the best. The rate of hydrate formation is increased 1533% and the induction time is lowered to 0.04 its original value. Also our studies show that surfactants that form oil in water emulsions in general can promote hydrate formation better than surfactant that forms water in oil emulsions. For better understanding of the promotion mechanism, the interfacial tension (IFT) of CP/water, in the presence of some surfactants, is measured. Results show that addition of TritonX-100 can lower the CP/water IFT from 31.6 to 2.1mN/m. The IFT data along with a simple mass transfer analysis are utilized to uncover the CP hydrate promotion mechanism.