Research Article Increasing the Storage Capacity and Selectivity in the Formation of Natural Gas Hydrates Using Porous Media Formation of a gas hydrate with two different gas compositions (natural gas and a mixture of methane-ethane-propane) was investigated using a special method of producing the hydrate from ice. Gas uptake, splitting the fraction of each com- ponent between the gas phase and hydrate phase, and purification of methane were studied in the presence of silica-based porous media. Addition of a small amount of colloidal silica media increased considerably the gas storage capacity of the hydrate phase. In the presence of silica-based porous media, the purifica- tion factor of CH 4 became significantly higher. The results can provide the basis for the storage of natural gas in hydrate form and application of the hydrate- based gas separation technology to achieve methane with high purity from natur- al gas. Keywords: Gas hydrate, Gas separation, Methane, Nanoporous media, Natural gas storage Received: February 15, 2012; revised: June 01, 2012; accepted: July 18, 2012 DOI: 10.1002/ceat.201200089 1 Introduction The storage and transportation of natural gas are of great interest with respect to the ever-increasing demand for natural gas as a clean and low-cost energy source. Compressed natural gas (CNG) is the most common method currently used for storage and transportation. Compressing gas up to 20 MPa is expensive and unsafe [1]. Adsorbed natural gas (ANG) and natural gas hydrate (NGH) are two methods that necessitate a lower storage pressure [2, 3]. ANG requires considerable lower storage cost compared with CNG [4]. Furthermore, NGH, as an alternative method in gas storage and transportation, can increase the storage capacity of natural gas up to 184 volumes of natural gas per volume of hydrate [5]. Hydrate formation is potentially influenced by temperature, pressure, salinity, gas composition, and interfacial surface area, which can be affected by the presence of porous media [5–8]. The effects of different types of porous media such as silica, activated carbon, carbon nanotubes, and silica gel on hydrate formation are considerable, depending on the specific area, pore volume, and pore size distribution [9–13]. Liu et al. studied hydrate formation in the presence of the ordered mesoporous carbon consisting of silica nanoroads with a pore size distribution ranging from 2 to 5 nm [4]. This porous media with high surface area (approximately 1100–1200 m 2 g –1 ) stored 41.2 wt % of methane per unit mass of carbon at 275 K and pressures < 7 MPa [4]. Zhou et al. investigated the effect of the amount of water on the sorption/ desorption equilibrium of methane on silica gel [11]. They found that the change in silica gel pore size and structure over different time intervals influences the storage capacity. The for- mation of hydrates in the pore space as well as in the space between solid particles on water-loaded carbon nanotubes could result in the storage of five times more gas than in dry porous media [14]. Kumar et al. described the kinetics of hydrate crystallization using glass beads [15]. Depending on the extent of water satu- ration of the porous media, the tendency to form hydrates in pores or on the grain surfaces is different. They concluded that water dispersion in glass beads increased the gas uptake compared with the hydrate formation in a bulk of water. Per- rin et al. improved the methane storage capacity in the hydrate form using wet activated carbon nanotubes [16]. The weight ratio of the porous media to water was proved to be an effec- tive parameter for the storage capacity [16, 17]. Because the temperatures of most sources of gas hydrates in nature are below the melting point of ice, researchers are inter- ested in studying hydrate formation and dissociation in this temperature range [18–22]. Intensive researches have been done to investigate the kinetics of hydrate formation and dis- sociation phenomena of natural gas components at tempera- tures below the freezing point of ice and in the presence of ad- Chem. Eng. Technol. 2012, 35, No. 11, 1973–1980 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cet-journal.com Nooshin Gholipour Zanjani 1 Abdolsamad Zarringhalam Moghaddam 1 Khodadad Nazari 2 Mahboobeh Mohammad- Taheri 1 1 Tarbiat Modares University, Chemical Engineering Department, Tehran, Iran. 2 Research Institute of Petroleum Industry, Chemistry and Petrochemical Research Division, Tehran, Iran. – Correspondence: Dr. A. Z. Moghaddam (zarrin@modares.ac.ir), Tarbiat Modares University, Chemical Engineering Department, P.O. Box 14115-143, Tehran, Iran. Gas hydrate 1973