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Serious issues regarding the scarcity of freshwater encouraged researchers to work on various methods for seawater desalination. Hydrate-based desalination (HBD) is a novel method that has received investigators’ attention due to its outstanding properties. According to the literature, refrigerant hydrates have great potential to be employed in the HBD process because of their highly moderate phase equilibrium. The main purpose of the current study is to investigate the influence of different concentrations of NaCl (0, 1, 3.5, 5, and 8 wt %) on the major kinetic parameters of R410a refrigerant hydrate formation in the presence and absence of cyclopentane with the concentration of 0.5 mol % as a coformer. The experiments were performed in a stirred laboratory reactor at an initial temperature of 278.15 K and initial pressures of 0.9 and 1 MPa. The measurements of induction time and mole of gas consumption show that NaCl increases the induction time and decreases the amount of gas consumption. However, the addition of 0.5 mol % cyclopentane decreases the induction time slightly and increases the final amount of gas consumed. Besides, despite the fact that cyclopentane decreases the initial rate of gas uptake, it could promote the amount of gas consumption during hydrate formation. The results of the water-to-hydrate conversion ratio illustrated that NaCl with concentrations up to 5 wt % exhibits an insignificant decrease of water-to-hydrate conversion, while 8 wt % NaCl decreases this parameter down to 51.48%. Moreover, the positive effect of cyclopentane on the growth stage was revealed by determination of the apparent rate constant of hydrate growth. This study provides useful data for designing and understanding the HBD process via R410a hydrate formation.

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The effects of addition of an ionic liquid to pure water as a physical absorbent and monoethanolamine (MEA) solutions as a chemical absorbent on carbon dioxide (CO2) absorption through hollow fiber membrane contactors were investigated using a 2D axisymmetric model. A numerical simulation was developed based on finite element method using computational fluid dynamics techniques. Liquid phase flowed in the tube side and gas mixture containing CO2 passed in the shell side of the membrane contactor in co-current and countercurrent modes. The simulation results are consistent with experimental data, and the root-mean-square error was calculated as 9 and 13% for pure water and 25 wt % for ionic liquid solution. The results showed that addition of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]­[BF4]) to the base fluids increases CO2 absorption in both physical and chemical absorbents. However, the effects of an ionic liquid in physical absorption is higher than that in chemical absorption. Addition of 10 wt % [Bmim]­[BF4] to 3.5 wt % MEA solution could increase the absorption rate by 12% in countercurrent flow compared to a 6 wt % MEA solution without [Bmim]­[BF4] despite lower MEA concentration. Also, the results indicate that reaction term in a chemical absorbent is more important in low liquid flow rates. It can also be found that addition of 25 and 50 wt % of [Bmim]­[BF4] to pure water can enhance absorption performance up to 30 and 75%.

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Much attention has been made to solidified natural gas (SNG) technology via clathrate hydrates in recent years. Tetra-n-butyl ammonium bromide (TBAB) is known as a promising promoter to tackle hydrate technology limitations. This research focuses on investigating the effect of NaCl, MgCl2, and the mixture of NaCl + MgCl2 (two major soluble salts in naturally occurring water are NaCl and MgCl2) on hydrate stability conditions of methane in the presence of TBAB aqueous solution. An isochoric pressure search method was employed to generate the dissociation/equilibrium data in the temperature, pressure, and TBAB composition ranges of 275–291 K, 0.5–5.5 MPa, and 5–20 wt %, respectively. The experimental results reveal that in the case of wTBAB = 5%, NaCl and MgCl2 with the low concentration of 5% have a promotion effect for the systems of CH4 + TBAB + NaCl + H2O, CH4 + TBAB + MgCl2 + H2O, and CH4 + TBAB + NaCl + MgCl2 + H2O and shift the dissociation curve toward milder region (higher temperature and lower pressure). However, in the case of wTBAB = 20%, NaCl and MgCl2 play an inhibition role in all of the aforementioned systems. A thermodynamic model was developed based on the van der Waals–Platteeuw (vdWP) solid solution theory, to predict the behavior of methane in the presence of the promoter in saline water. The Peng–Robinson equation of the state (PR EOS) is used to describe the thermodynamic properties of the gas phase, and the electrolyte non-random two-liquid (e-NRTL) activity coefficient model is employed to determine the activity coefficient of water and promoter in the electrolyte solution. The presented model results are in satisfactory agreement with the experimental data generated in this work. The discrepancy of the model results with experimental is 10.78%.

In this communication, the promoting effects of two additive mixtures (cyclopentane + TBANO3) on CH4 hydrate phase equilibrium were experimentally investigated using the isochoric method. The mass fractions of TBANO3 employed in this paper were 5, 10, 15, and 20. The results showed that cyclopentane is a good promoter in comparison with pure water + CH4 systems, and TBANO3 has a promoting effect but not like cyclopentane in compassion with pure water + CH4 systems. Additionally, the mixture of cyclopentane + TBANO3 has an important promoting effect in comparison with pure water and TBANO3 + water + CH4 systems, but it has a less promoting effect in comparison with cyclopentane + water + CH4 systems. Furthermore, a new thermodynamic model was investigated to predict the equilibrium conditions of hydrate dissociation (pressure and temperature). The hydrate phase was described by the van der Waals–Platteeuw model, and the aqueous phase was predicted with the E-NRTL model. In addition, the NRTL model was used to predict the organic phase, and the gas phase was described with SRK EOS. The results revealed that the experimental hydrate dissociation data’s agreement with the proposed model is acceptable and possesses an average of 2.43%. Finally, an analogy was generated with the literature data. This study gives a better comparison of hydrate phase equilibrium combined with CH4 capture.

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