Experimental Measurement and Modeling of R22 (CHClF 2 ) Hydrates in Mixtures of Acetone + Water Jafar Javanmardi,* Shahabedin Ayatollahi, Razieh Motealleh, and Mahmood Moshfeghian † Department of Chemical and Petroleum Engineering, Shiraz University, Shiraz, Iran The effect of acetone on R22 (CHClF 2 ) hydrate equilibrium conditions was investigated. A full view equilibrium cell and associated equipment were designed, fabricated, and used for this purpose. Adding acetone caused an increase in the equilibrium pressure. The investigated mole fractions of acetone in water were 0.02, 0.04, and 0.06. The equilibrium conditions were measured in the pressure range 0.223 to 0.704 MPa. In contrast to methane hydrate in the presence of acetone, the system of R22 + water + acetone showed an inhibition effect for all of the above concentrations of acetone. The existing model for structure II hydrates in the ternary mixtures of methane + water + acetone was applied to the system R22 + water + acetone. The measured dissociation temperatures were compared with the model prediction. Introduction Gas hydrates (or clathrate hydrates) are icelike crystal- line compounds formed from water and small gas molecules such as methane and nitrogen. Within the hydrate lattice, water molecules form a network of hydrogen bonded cagelike cavities that host the small “guest” gas molecules which are required to stabilized the structure. The result- ing crystalline structures thermodynamically are solid solutions. Some aqueous solutions containing organic solutes such as 1,4-dioxane and acetone act as a methane hydrate promoter at concentrations not exceeding 0.06 mole fraction of acetone. At higher concentrations, this effect gradually changes and the organic eventually becomes a hydrate inhibitor. 1-4 The promotion effect of these water-solute hydrate formers has been investigated because it is sug- gested that these compounds can be used to store natural gas in a stabilized gas hydrate under more feasible condi- tions. 2 In this work, the effect of acetone on the R22 hydrate equilibrium is investigated. The objective of this study is to determine the three phase equilibrium, hydrate-aque- ous solution-vapor, of R22 hydrate in the presence of water + acetone. The model developed by Javanmardi et al. 4 for structure II hydrates in the ternary mixtures of methane + water + acetone has been extended to the system R22 + water + acetone. The chemical potential of the hydrate phase and the water activity have been represented using the van der Waals and Platteeuw theory 5 and the van Laar free energy model, respectively. Experimental Section Materials. The R22 gas was supplied by Rhodia Chemi- cal Co, with purity equal to 99.8 mol % (at least). Double distilled water was used for preparing the required solu- tions. Acetone with a minimum purity equal to 99.0% was supplied by Merck Chemical Co. Apparatus. A full view of the equilibrium cell and associated equipment is shown schematically in Figure 1. The equilibrium cell primarily consists of a constant- volume glass tube (1.2 cm i.d. × 1.8 cm o.d. × 34 cm), as shown in Figure 2. The glass tube is sealed at either end with conical O-rings. The total internal volume of the equilibrium cell is about 80 cm 3 . The maximum safe pressure of the cell is 1.400 MPa. The equilibrium cell is immersed in a cooling bath of about 40 L of refrigerated water-ethanol solution. As shown in Figure 1, the hydrate former stored in a gas cylinder is injected into the equilibrium cell after passing through a 0.5 mm i.d. helical tube immersed in the cooling bath. The length of the tube is about 1.5 m, and at the flow rates used, thermal equilibrium is achieved. The stirring system of the bath consists of an ac motor equipped with an impeller. Because of the small internal diameter of the glass tube, the hydrate former bubbles provide the stirring in the cell and ensure the uniform temperature distribution inside the cell. For measuring the system pressure, two Bourdon-type pressure gauges as shown in Figure 1 are used. The first pressure gauge indicates the regulated pressure of the gas * Corresponding author. Current address: Department of Petroleum Engineering, Shiraz University of Technology, Shiraz, Iran. E-mail: javanj@shirazu.ac.ir. Fax: +98-711-6287294. † Present address: Kuwait Institute for Scientific Research, Petroleum Research & Studies Center. Figure 1. Schematic of the experimental apparatus. 886 J. Chem. Eng. Data 2004, 49, 886-889 10.1021/je034198p CCC: $27.50 © 2004 American Chemical Society Published on Web 06/23/2004