Comparison of different equations of state in a model based on VdWeP for prediction of CO 2 hydrate formation pressure in Lw-H-V phase and a new correlation to degrade error of the model Seyed Ashkan Naghibzade a , Hamzeh Kahrizi a , Amin Soleimani Mehr b, * a National Iranian Oil Company, West Oil and Gas Production Company, Iran b Sh. Hasheminejad Gas Processing Co., National Iranian Gas. Co, Sarakhs, Iran article info Article history: Received 9 August 2014 Received in revised form 24 November 2014 Accepted 27 November 2014 Available online Keywords: VdWeP AADP Hydrate formation Empirical correlations abstract Carbon dioxide plays a significant role in global warming. Formation of carbon dioxide hydrate is one of the several ways to remove this gas from the atmosphere. In order to attain a proper process design, pressure and temperature of the hydrate formation should be estimated. The empirical correlations, charts and thermodynamic model scan be used to predict these conditions. In this work, a model based on van der WaalsePlatteeuw for prediction of hydrate formation condi- tions of CO 2 which uses four different equations of state, PR, RK, PT and ALS in L w -H-V phase and in temperature range of 271.6 Ke283.2 K is used and the results are brought out in order to compare with each other and with experimental data reported in the literature. Among PR, PT, RK and ALS equations of state, PR with total AADP of 2.52% shows better results than other equations of state. For the model based on VdWeP which uses PR as an equation of state a correlation is presented in order to reduce the amount of error which appears at high temperatures. This correlation reduces the amount of AADP for temperatures of hydrate formation higher than 280.44 K from 4.42 % to 1.04%. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The increasing demand of energy supply, as a result of industrial developments and elevation of standards of human life, has led to accelerate mining and combustion of fossil fuels. These worldwide activities cause a continuing increase in producing anthropogenic carbon dioxide (CO 2 ), resulting in increase of the level of atmo- spheric carbon dioxide (Sabil et al., 2011). According to Robinson et al. (Robinson et al., 2007), the atmospheric carbon dioxide level has increased 22% since 1958 and about 30% since 1880. CO 2 is considered to be the largest contributor to the global warming problem, and is thus the major target for reduction. In recent years idea of sequestrating global warming gases mainly CO 2 , in the form of CO 2 hydrate as a method to hold the CO 2 con- centration below a given level has been proposed. Gas hydrates or clathrate hydrates are ice-like crystalline com- pounds, which are formed through a combination of water and guest molecules under suitable conditions of low temperature and high pressures (Sloan and Koh, 2007). The majority of gas hydrates are known in three common crystal structures: structure I (sI), structure II (sII) and structure H (sH), where each structure is composed of a certain number of cavities formed by water molecules (Mohammadi and Richon, 2009). CO 2 has been known to be among a number of molecules that can form clathrate hydrate as a simple hydrate, carbon dioxide forms structure I hydrate under appropriate pressure and temper- ature conditions (Khalik, 2009). So far, several studies have been performed on the prediction of hydrate forming conditions for various gases. Generally, methods for prediction of hydrate phase equilibrium are empirical correla- tions, charts or thermodynamic models. A variety of thermody- namic models for the calculation of phase equilibrium properties of the hydrate system have been discussed, which some of these methods are based on a statistical thermodynamic approach developed by van der Waals and Platteeuw model. In this work, van der WaalsePlatteeuw model (Parrish and Prausnitz Development)is used for prediction of hydrate formation conditions of CO2 with application of four different equations of * Corresponding author. Gas Engineering Department, Petroleum University of Technology, 63431, Ahwaz, Iran. E-mail address: petro.amin@gmail.com (A. Soleimani Mehr). Contents lists available at ScienceDirect Journal of Natural Gas Science and Engineering journal homepage: www.elsevier.com/locate/jngse http://dx.doi.org/10.1016/j.jngse.2014.11.035 1875-5100/© 2014 Elsevier B.V. All rights reserved. Journal of Natural Gas Science and Engineering 22 (2015) 292e298