Hydrate formation and re-formation in nucleating THF/water mixtures show no evidence to support a memory effect

There are many reports in the chemical engineering literature citing a 'memory' effect in association with nucleation of clathrate hydrates. Some researchers appeal to this memory effect in order to explain the apparent reduction in induction time for hydrates formed repetitively from supercooled solutions. It is suggested that for various species of clathrate in liquid-liquid or gas-liquid systems, such as THF/water, CO2/water and hydrocarbon gas/water, the 'memory' effect results from water which is obtained from melted hydrates possessing a modified structure which allows easier hydrate re-formation. We provide here data from several series of measurements of the stochastic nature of THF-water hydrate formation using an automatic lag time apparatus. Our data supports the existing molecular understanding of nucleation and does not require any appeal to a memory effect. (C) 2010 Elsevier B.V. All rights reserved.