Clathrate hydrates for hydrogen storage: The impact of tetrahydrofuran, tetra-n- butylammonium bromide and cyclopentane as promoters on the macroscopic kinetics Hari Prakash Veluswamy, Weng Inn Chin, Praveen Linga* Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore 117 576, Singapore article info Article history: Received 28 September 2013 Received in revised form 25 December 2013 Accepted 9 January 2014 Available online 10 February 2014 Keywords: Gas hydrates Hydrogen storage Hydrogen hydrate Promoters Formation kinetics Decomposition kinetics abstract Hydrogen hydrate formation and decomposition kinetics using tetrahydrofuran (THF), tetra-n-butylammonium bromide (TBAB) and cyclopentane (CP) as promoters under similar experimental conditions was studied. First set of experiments on hydrate forma- tion were conducted at same promoter concentrations, experimental pressure and experimental temperature and the second set of experiments were conducted at same experimental pressure, same driving force and varying promoter concentrations. Hydrogen storage capacity of THF/Hydrogen hydrate was the highest amongst the three promoters under the experimental conditions studied. Hydrogen uptake of 0.0173 mole of gas/mole of water was obtained for the 3.5 mol% THF solution and it was about 2 times higher than hydrogen uptake obtained for 3.5 mol% TBAB solution under similar experimental condi- tions. With the same amount of heat supplied, TBAB/Hydrogen mixed semi-clathrates took longer time to dissociate compared to THF/Hydrogen hydrates under similar decomposi- tion conditions. It was very difficult to form CP/Hydrogen hydrates even at a very high driving force. Copyright ª 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Clathrate hydrates are crystalline compounds in which host water molecules form cages around guest molecules and enclose them under favourable formation conditions of temperature and pressure [1,2]. The driving force for the kinetics of hydrate formation can be either the difference in operating temperature or operating pressure from the equilibrium conditions. These cage inclusion compounds are non-stoichiometric and depending on the guest mole- cules can form different crystalline structures. The common structures observed are structure I (sI), structure II (sII) and structure H (sH) formed by 46, 136 and 34 water molecules respectively [2]. Apart from these common structures there are semi-clathrates, wherein the guest molecule is ionic in nature with the cationic part occupying the cages of hydrate structure like a guest and the anionic part takes part in the cage formation along with water [3,4]. * Corresponding author. Tel.: þ65 6601 1487; fax: þ65 6779 1396. E-mail address: praveen.linga@nus.edu.sg (P. Linga). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 39 (2014) 16234 e16243 0360-3199/$ e see front matter Copyright ª 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijhydene.2014.01.054