Experimental and Modeling of Carbon Dioxide Hydrate Phase Equilibrium in the Presence of Thermodynamic Inhibitors
Paolo F. Ferrari1; Amanda Z. Guembaroski1; Moisés A. Marcelino Neto1; Rigoberto E. M. Morales1; Luciano F. dos Santos Rossi1; Amadeu K. Sum2
1 NUEM / PPGEM / UTFPR; 2 Chemical & Biological Engineering Department, Colorado School of Mines, Golden, CO, USA
doi:10.20906/CPS/COB-2015-0914
Resumo
Gas hydrates are crystalline structures composed by molecules of water and gas that requires formation conditions of high pressure and/or low temperatures. The formation and agglomeration of hydrates can cause blockage of oil and gas lines in the petroleum industry, reducing process efficiency, damaging equipments and risking safety operation. It is well-know that carbon dioxide (CO2) is one of the most common non-hydrocarbon gases found in petroleum reservoirs. In addition to this, most of the pre-salt fields in Brazil hold a significant rate of CO2. Therefore understanding the phase equilibrium behavior of CO2 hydrates is fundamental. In this work the phase equilibrium of CO2 hydrates in the presence of thermodynamic inhibitors was determined over a wide range of temperatures and pressures. The parameter of main interest was the equilibrium pressure, at which the hydrates formed at a given temperature and inhibitor concentration. Experimental measurements were performed using the isochoric method by monitoring the pressure response of the system with changes in the temperature. The evaluated systems were composed of carbon dioxide, water and thermodynamic inhibitors (methanol and sodium chloride). Two thermodynamic models capable of describing dissociation pressure of gas clathrate hydrates formed from the mixtures of CO2 and water were presented. One of the models utilized the Cubic-Plus-Association (CPA) equation of state (Eos) for the thermodynamic description of the non-solid phases (vapor and liquid), the other one used the Soave-Redlich-Kwong (SRK) EoS for this task. The solid hydrate phase was described by the van der Waals-Plateeuw model. A MATLAB computational routine that combines the EoS with the van der Waals-Plateeuw model was implemented. The two models were validated against experimental hydrate equilibrium data. The predictions with the CPA EoS were more accurate than with SRK.
Palavras-chave: Hydrates; Inhibitor; Prediction; Experimental; Modeling