Effects of non-ionic surfactants on formation kinetics of structure H hydrate regarding transportation and storage of natural gas

Abstract

Clathrate hydrates are one of the proposed mediums for transportation and storage of natural gas. Among the known hydrate structures, structure H seems the most fitting crystal due to its moderate formation pressure and high storage capacity. In the present work, the kinetics of methane hydrate formation is investigated in a high pressure batch stirred reactor with and without additives. Methylcyclohexane (MCH), methylcyclopentane (MCP) and tertbutylmethylether (TBME) were used as large molecule guest substance (LMGS). The effects of one anionic and five non-ionic surfactants on hydrate promotion at 2 °C and 55 bar pressure are experimentally investigated. These surfactants belong to the family of Nonyl Phenol Ethoxylates (NPE), Lauryl Alcohol Ethoxylates (LAE), Ethylene Oxide/Propylene Oxide copolymer (EO/PO), polyoxyethylene sorbitan mono palmitate (Tween®), Butyl Phenol ethoxylates (Triton™X100) and Sodium alkyl sulfate. The results show that while the system with MCH and MCP exhibit high induction times and low formation rates, addition of surfactants can intensely decrease the induction times and increase the formation rates. Among the studied surfactants, Triton™X100 and NPE6EO are the best kinetic promoters of structure H methane hydrate, resulting more than 500% increase in the hydrate formation rate. Also effects of non-ionic surfactants on MCP and TBME follow the same trend. Finally, systems containing two LMGSs (e.g. MCH+TBME) were tested and proved to be better candidates for storage and transportation of natural gas in sH hydrated form.