Reactive extraction of citric acid from dilute aqueous solutions was studied using three different extractants, namely tri-n-butylphosphate (TBP), tri-n-octylamine (TOA), and Aliquat 336 (A336), dissolved in three different diluents: butyl acetate, decanol, and benzene. The isothermal batch equilibrium experiments were carried out at T = 300.15 ± 1 K. The extraction was interpreted in terms of the distribution coefficient (K D ). Maximum extraction efficiency (E = 95.5%) was obtained at 20% (v/v) TOA in butyl acetate with complexation constant K E2 = 1039.7 (kg mol −1 ) 2 for the (2:1) complex. In addition to having a higher loading ratio (Z > 0.5), the overloading of amine(TOA) in the case of the citric acid + TOA + decanol system was also confirmed by spectroscopic (FTIR) analysis. The linear solvation energy relationship model was successfully applied to predict the distribution coefficient. The complex stoichiometry was also optimized using differential evolution. A close resemblance was observed between experimental and model values.

To develop the crucial concepts of clathrate hydrates toward the hydrate-based technological implications, it is indispensable to comprehend their formation and growth mechanisms and stability in pure and saline water environments. In this view, we provide fundamental insights into the gas hydrate dynamics by carefully conducting a molecular dynamics simulation in an extensive range of carbon dioxide (CO 2 ) gas (CO 2 /H 2 O from 1:5 to 1:18) and sodium chloride (NaCl) salt (from 0.0 to 18.0 wt %) concentrations. Using the F 4φ order parameter and the radial distribution function, we assess the important information about the time evolution of the visualization states and the formation and growth of small (5 12 ) and large (5 12 6 2 and 5 12 6 4 ) cages of hydrates along with their crystalline nature. We found that (1) CO 2 forms the pure S−I type of hydrate structure irrespective of guest gas and salt concentrations; (2) lower CO 2 gas concentration (CO 2 /H 2 O from 1:8 to 1:18) leads to fast but incomplete conversion of water to hydrate, while the higher CO 2 gas concentration (1:6) causes the phase separation and consequent sluggish hydrate growth; (3) 1:7 is an optimum CO 2 /H 2 O ratio for the rapid, complete, and properly ordered hydrate growth; (4) at the optimum amount of CO 2 and H 2 O, the lower range of salt concentrations (0.0−5.0 wt %) has a slight inhibition effect on the hydrate growth, while there is a notable inhibition effect for the higher salt concentrations (7.0−18.0 wt %); (5) the number of oxygen atoms of water present in the first coordination sphere remains constant for the lower salt concentrations (0.0−5.0 wt %), and they get reduced with the higher salt concentrations (7.0−18.0 wt %); (6) the inhibition effect is due to the reduction of CO 2 solubility in the aqueous phase in the presence of salt ions. These novel findings provide useful assistance for choosing an appropriate combination of the imperative elements of gas hydrate systems toward carbon dioxide separation, sequestration, storage, and transportation.

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Either concerning to the energy production from natural gas hydrates or employing the hydrate technology to gas handling and seawater desalination purposes, various pure and mixture clathrate hydrates need to be understood in terms of their phase behavior and stability. The ab initio methods have compelling implications in quantifying the anisotropic guest−water interactions that are responsible for the guest-specific nature of the hydrates. Howbeit, the accurate cavity interactions for large guests are obscure due to computational infeasibility. With this research gap, we devise the Møller−Plesset theory with Dunning's basis sets that are suitably advanced to the complete basis limit using the Pauling point counterpoise weight. The viability of the proposed scheme is attested with the Raman spectroscopy, second virial coefficient, and viscosity data of methane and its binary hydrates with tetrahydrofuran and cyclopentane. These two promoters are chosen because they are perhaps the most useful and efficient compounds in their class, for which the experimental cage occupancy data with methane are available to validate our new scheme of estimating the hydrate cavity potential.

The growth dynamics of natural gas hydrates in saline water has been studied using copious experiments and spectroscopic observations; however, the microscopic evidences to the structural and molecular transformations that they have provided are poorly understood. In this view, we perform extensive molecular dynamics simulations to gain physical insights into the formation and growth mechanism of naturally occurring gas hydrates with a wide variation in the amount of methane (1:5 to 1:18 methane/water ratio) in pure and salt (0–5 wt %) water environments at 50 MPa and 260 K. A couple of new findings analyzed from the number of cages and F 4φ order parameter are as follows: (a) 1:6 (methane/water ratio) is an optimum ratio for the rapid growth of a properly ordered hydrate in pure water at which the hydrate growth retards with increasing salt concentration, (b) there is an inconsequential difference between methane hydrate dynamics in pure water and 0.8 and 1.5 wt % salt water at a ratio of 1:12 (methane/water), and (c) lower methane (1:18) and salt (0.8 wt %) concentrations promote hydrate growth. Besides, this study observes the structural coexistence of S-I and S-II methane hydrates as the large 51264 cages appear along with the small 512 and large 51262 cages, in which the low methane concentration favors the S-II structure.