Investigation of Synergistic Thermodynamic Inhibition Effect of MEG and Salt Solution on Gas Hydrate

This study examined the thermodynamic synergistic inhibition effects of MEG considering in case of produced water breakthrough, which includes high concentration of salts solution mixed with hydrocarbon fluids during natural gas production. First, we proposed the modified model based on Soave-Redlich-Kwong equation of state for expressing the vapor phase and van der Waals and Platteuw theory to predict the hydrate equilibrium conditions in the presence of both MEG and NaCl. The proposed model adopt the change of fugacity of gas component in aqueous MEG and NaCl solution using ENRTL-RK model in Aspen plus v8.6. The activity of water was determined by Margules equation for MEG, Pitzer equation for NaCl and temperature effect. The hydrate equilibrium conditions of solutions containing both MEG and NaCl with high salinity (∼ 20 wt%) was measured as well. The results showed that the hydrate formation condition was shifted toward lower temperature and higher pressure in accordance with the increased NaCl concentration. The proposed model was acceptably correspond with experimental data. For MEG and NaCl mixed solutions, the average deviation of hydrate formation pressures (AADP) of the proposed model had the lowest value of 5.37% compared to 17.52% of CSMGem and 13.77% of Multiflash.

Theory Research on Desalination of Brackish Water Using Gas Hydrate Method

In allusion to some methods on desalination of brackish water such as distillation, electrodialysis method and reverse osmosis, this paper introduced the mechanism, advantages and disadvantages of these methods. It is convinced that these methods have higher energy consumption. Temperature is much lower annually in alpine region of China, it provides a good condition for hydrate formation. It also provides the possibility for the desalinating process of brackish water using hydrate methods in alpine region. This paper proposed a new method of desalinating brackish water. Based on the model of van der Waals-Platteeuw, we calculated the phase equilibrium conditions of methane, ethane and propane hydrate in NaCl solution combined parameter equation which was used to calculate the Langmuir constant presented by DU Ya and GUO Tian-min and Pitzer equation used to water activity in the system of electrolyte solution. The result shows that it is possible to desalinate brackish water using environment cold quantity. It also shows that propane is more suitable for brackish water desalination among methane, ethane and propane. It is very significantly important to seek energy-saving and environment-friendly methods for the process of desalinating brackish water with energy shortage increasingly intensifying and with awareness of human being enthancing on energy conservation and emission reduction.

Thermodynamics of electrolytes in mixed solvent media — Application of the Pitzer ion interaction approach

Although for a long time considerable attention has been paid to the application of the Pitzer ion interaction approach to describe the thermodynamic properties of a variety of aqueous electrolyte solutions, such studies in mixed solvent media are still scarce. The present paper discusses the application of the Pitzer ion interaction approach in the case of electrolyte solutions in mixed solvent media. In particular, a comprehensive equation for the thermodynamic properties of hydrochloric acid in dioxane–water mixtures within the temperature range 273.15 to 323.15 K has been generated in the ion interaction (Pitzer) equation form on the basis of electrochemical cell measurements of the hydrochloric acid available in the literature. It was necessary to set varying values of the exponential coefficients α1 and α2 of the standard Pitzer model in different mixed solvent media to achieve a satisfactory fit. The present model quantitatively reproduces the experimental cell electromotive forces over the entire concentration and temperature range used for the experiments. The Pitzer ion interaction approach is, thus, proved to be a very valuable method for the correlation and prediction of thermodynamic properties of electrolytes in mixed solvent media. The implications of the Pitzer ion interaction parameters (β(0), β(1) β(2), and Cϕ) have also been discussed in terms of interionic forces. The present study also stresses the need for additional emf measurements to help interpolation through the dioxane composition. Key words: Pitzer's equations, Pitzer ion interaction parameter, activity coefficients, emf, hydrochloric acid.