INTRODUCTION Gas hydrates, or clathrate hydrates, are ice-like crystalline compounds formed by the inclusion of low molecular diameter non-polar or slightly polar molecules inside cavities formed by water molecules 1 . Currently, gas hydrate technology is being widely used in the fields of storage and transportation of natural gas, seawater desalination, carbon dioxide seques- tration and cold storage air-conditioning. Therefore, it is substantially important to perform studies on gas hydrate 2 . Slow formation rate of natural gas hydrate is a critical problem hindering the industrial application of this technology. One way to increase the hydrate formation rate is using of surfac- tants. At our previous works, we have used various surfactants for increasing the rate of dissolution and hydrate formation 3-5 . Electrospraying is a method of droplet production. Droplets, which produced by this method are highly charged, that prevents their coagulation and promotes self-dispersion. In electrospraying method the size of the droplets can be controlled to some extent by voltage and flow rate 6 . The kinetic modeling of hydrate formation so far has been developed based on a stirred tank batch, where a reactor containing water main- tained at hydrate forming conditions is injected with gas and agitated to produce hydrates systems 7,8 . Recently, advanced observation and measuring methods have been adopted in the researches of hydrate formation kinetics worldwide 9-13 . Lee et Kinetic of Methane Hydrate Formation in Micro- and Nanodroplets MEHRDAD MANTEGHIAN * , REZA DOROSTI and ABOLFAZL MOHAMMADI Department of Chemical Engineering, Tarbiat Modares University, Tehran, Iran *Corresponding author: Fax: +98 21 88005040; Tel: +98 21 82883333; E-mail: manteghi@modares.ac.ir (Received: 20 December 2011; Accepted: 12 October 2012) AJC-12274 In this research, the kinetic of hydrate formation from a microdroplet or nanodroplet is investigated. The shrinking core model is used for predicting of hydrate growth on a droplet. In this model, it assumed that the nucleation was started on the outer surface of water droplet and the direction of hydrate growth is into the center of the droplet. Diffusion of the gas molecules through the gas film surrounding the droplet, diffusion through the hydrate layer and reaction with the outer surface of unreacted water is the steps of hydrate formation in shrinking core model. The reaction rate constant of methane molecules with water droplet (k) is extracted from literature. Using shrinking core model showed that, in nanodroplets and droplets smaller than 1 μm, reaction of gas molecules with water droplet is the main resistance in the hydrate formation. By increasing the size of water droplets, the resistance of diffusion through the hydrate film was increased and in droplet larger than 100 μm, the main resistance of hydrate formation was diffusion of gas molecules. By increasing the temperature, the effect of chemical reaction in hydrate formation resistances was increased. Key Words: Nanodroplet, Microdroplet, Hydrate, Kinetic, Shrinking core model, Mass transfer, Methane. Asian Journal of Chemistry; Vol. 25, No. 4 (2013), 2038-2042 al. 14 studied the gas hydrate formation and decomposition of water droplets using methane-ethane and methane-propane mixtures. Ohmura et al. 15 reported the visual observation of the formation and growth of structure-H hydrate crystals on a water droplet. In this research, we will investigate the kinetic of hydrate formation from a micro- and nanodroplet. EXPERIMENTAL Fig. 1 shows the proposed mechanism of hydrate forma- tion from a droplet surrounding by gas molecules. Fig. 1. Proposed mechanism of hydrate formation from a water droplet; a) Initial droplet that surrounded by gas molecules; b) A thin film of hydrate that is formed from the outer surface of initial droplet; c) Growth of hydrate layer from surface to the center of droplet In shrinking core model, hydrate formation of a water droplet consist of three steps 16 : (1) Diffusion of the gas http://dx.doi.org/10.14233/ajchem.2013.13298