JOURNAL OF FUEL CHEMISTRY AND TECHNOLOGY Volume 40, Issue 4, April 2012 Online English edition of the Chinese language journal Received: 08-Nov-2011; Revised: 18-Mar-2012 * Corresponding author. E-mail: ahmadpour@um.ac.ir Copyright  2012, Institute of Coal Chemistry, Chinese Academy of Sciences. Published by Elsevier Limited. All rights reserved. RESEARCH PAPER Cite this article as: J Fuel Chem Technol, 2012, 40(4), 385389 Improving methane storage on wet activated carbons at various amounts of water Mohammad Jaber Darabi Mahboub, Ali Ahmadpour*, Hamed Rashidi Department of Chemical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, 9177948944, Iran Abstract: Different mesoporous activated carbons were prepared by both chemical and physical activation processes and were examined for methane uptake in the presence of water. Methane isotherms were obtained at wet condition by wetting samples with water at mass ratio of water/carbon (R) close to 1.0. To compare, the amount of methane storage were also measured at dry situation. The maximum amount of methane stored was attained as 237 V/V at R=1.0 by hydrate formation at the methane critical pressure. In the next step, mass ratios of water/carbon were changed to investigate various amount of water for methane storage enhancement. Two other values of mass ratio of water/carbon (R=0.8 and 1.4) were selected and methane isotherms were obtained at the same conditions. Maximum values of 210 and 248 V/V were reached for methane storage, respectively. It was also observed that, in the pressure range lower than hydrate pressure, by increasing water ratio the hydrate formation pressure was decreased and methane uptake was much less than that of dry condition due to pore filling by water. Key words: methane storage; hydrate; isotherm; water; wetting In recent years, natural gas (with more than 80% methane) has noticed considerable regard as a clean fuel for vehicles and transportation because of various advantages such as abundant reserve, low price and clean fuel compared with the conventional fossil fuels [1,2] . Utilization of methane gas as a fuel produced less carbon dioxide and more water vapor per energy unit than burning gasoline or diesel [3] . Although methane is an appropriate fuel, it is difficult to store due to its low density, therefore suitable storage method is necessary to use NG as vehicular fuel [4] . Four different techniques known for methane (or natural gas) storage namely liquefied natural gas (LNG), compressed natural gas (CNG), adsorbed natural gas (ANG) and natural gas hydrate (NGH), have been considered to improve the energy density [5–9] . Among these methods, adsorbed natural gas on the porous materials have the advantage of operating at low pressure and room temperature, allowing methane consumption comparable to the other conventional petroleum based fuels [3,10–12] . Maximum storage pressure utilized in the ANG is normally in the range of 3.5–4.0 MPa and activated carbons with deliverable capacities ranging from 70 to 150 V/V at room temperature and pressure of around 3.5 MPa are appropriate adsorbents for this purpose [13–16] . The U.S. Department of Energy (DOE) has adjusted target of 180 V/V for methane storage at 3.5 MPa and ambient temperature [17] . Recently, one of the latest methods that has been investigated for storing methane onto wet activated carbons is the combined utilization of ANG and NGH techniques. In this method, hydrate formation plays major role to enhance methane storage and for this purpose a mesoporous structure is required for adsorbent. Methane molecules are trapped in cages made of water units that linked with each other through hydrogen bonding. However, the formation condition of NGH is rigorous and its formation rate is low [8,9] . Different research groups have conducted experiments with wet activated carbons to store methane. Perrin et al investigated the storage of methane proposed by two patents dealing with methane adsorption on wet activated carbons [18] . They applied commercial carbons for storing methane in the presence of water and isotherms for all samples in both wet and dry conditions were obtained. Methane storage of 227 V/V was attained for their best sample at wet condition. Zhou et al tried to achieve high gas adsorption by using moderate pressure and room temperature condition in microporous activated carbons produced from coconut shell. But, they found very little enhancement with wet activated carbons because pore size and pore size distribution of carbon samples used in their experiments were quite inappropriate and most of the micropores were filled by water [19] . Zhou et al studied the influence of pore size distribution on the adsorption