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Activity coefficient

About: Activity coefficient is a(n) research topic. Over the lifetime, 6020 publication(s) have been published within this topic receiving 132928 citation(s).
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Journal ArticleDOI
Hesam Najibi1, Arezoo Azimi2, Jafar Javanmardi2, Reza Roozbahani1  +1 moreInstitutions (3)
Abstract: Gas hydrates can form under specific thermodynamic conditions when water and dissolved salt mixtures exist in the gas and oil reservoirs. One of the best ways to prevent gas hydrate formation is to inject hydrate inhibitors like mono ethylene glycol or methanol aqueous solutions in the pipelines. To design productive facilities and overcome operation faults, studying the stability conditions of natural gas hydrates in the presence of aqueous solutions of salt(s) and/or inhibitors is necessary. However, a few studies have been conducted on stability conditions of natural gas hydrates while salt mixtures and MEG are present. Here, the hydrate stability conditions of synthetic natural gas in aqueous mixtures of 20 and 30 wt% of MEG, and 2.5 wt% NaCl + 2.5 wt% KCl were experimentally measured under 272-293 K and 3.30-12.70 MPa. An isochoric pressure-search method was employed to conduct the measurements. Then, a thermodynamic model was developed to estimate hydrate stability conditions in the presence of the aforementioned inhibitors. In this developed model, the aqueous phase fugacity is estimated using a combined form of Cubic-Plus-Association Equation of State with the modified Debye-Huckel electrostatic term and the hydrate phase is modeled using van der Waals and Platteeuw solid solution theory. To improve model accuracy, the aqueous phase activity was measured in various concentrations at atmospheric pressure and 298.15 K using a standard activity meter called Novasina LabMaster-aw neo AS, Switzerland. These measured data were used to correlate the activity coefficient parameters in the thermodynamic model. Finally, it is noted that the modeling results and the experimental data are in satisfactory agreement.

Journal ArticleDOI
Mai Han1, Yuanyuan Han1, Houchun Yan1, Huanhuan Gui1  +2 moreInstitutions (1)
Abstract: 2,2,2-trifluoroethanol (TFE) is used more and more widely in industry, but there are few reports on its separation at present. The purpose of this work is to explore the feasibility of separating 2,2,2-trifluoroethanol from aqueous solution using different extractants, as isopentanol, 2-Ethyl-1-hexanol, n-Propyl acetate, and dichloromethane. The liquid–liquid equilibrium data of TFE + water +{isopentanol or 2-ethyl-1-hexanol or n-propyl acetate or dichloromethane} at standard pressure and 303.2 K were measured. The estimated partition coefficient (D) and separation factor (S) of TFE are higher than 1. Meanwhile, Othmer-Tobias and Hand's empirical equations verified the experimental data's consistency, and the squares of its linear correlation are all greater than 0.99. The NRTL and UNIQUAC activity coefficient models were used to correlate the experimental data, and different model parameters were obtained by regression. After comparing the calculated values of the model with the experimental data, it was found that the root means square deviation (RMSD%) was less than 0.34%, which indicate that both models have a reasonable correlation with the experimental data of the ternary system and can accurately predict the experimental data.

Journal ArticleDOI
Huiyuan Li1, Yanli Zhang1, Yuanyuan Shen1, Zhengrun Chen1  +3 moreInstitutions (1)
Abstract: The development of green and clean solvents has always been an important research area in the separation industry. Ionic liquids have been widely used in the extraction processes because of their designability and nonvolatility. In this study, ionic liquids were used to separate n-heptane and DMC. According to COSMO-SAC model, the activity coefficients of 280 ionic liquids composed of 20 cations and 14 anions were determined using quantum chemical calculations. Then, the separation coefficient (S) and distribution coefficient (D) of the n-heptane–DMC system were calculated when ionic liquids were used as extractants, and the extractant with a better extraction effect was selected. The mechanism of the extraction process was analyzed using the bond energies, charge densities, and bond lengths of molecular interactions. The hydrogen-bonding interactions between the ionic liquids and DMC were confirmed, which provided a theoretical basis for separation mechanism of DMC and n-heptane. The experimental data corresponding to the liquid–liquid equilibrium of ternary system were measured, and D and S values were calculated. The NRTL model was used to regress the experimental data and calculate the corresponding binary interaction parameters. This study lays a foundation for the large-scale application of ionic liquids and provides theoretical guidance for computer-aided selection of green solvents with good separation effect.

Journal ArticleDOI
Seung-Mo Kim1, Kyung-Min Kim2, Bong-Keun Choi1, Ji-Hun Mun1  +8 moreInstitutions (5)
Abstract: The absorption mechanism of CO2 in an aqueous solution containing three alkanolamines was analyzed experimentally and theoretically. The vapor–liquid equilibrium of a CO2–monoethanolamine (MEA)–diisopropanolamine (DIPA)–2-amino-2-methyl-propanol (AMP)–H2O system was evaluated experimentally over a wide temperature range (323.15–393.15 K) at several MEA:DIPA:AMP:H2O blending ratios (15:10:5:70, 10:10:10:70, 7.5:7.5:15:70, and 5:15:10:70 wt%). The successive substitution method was used to calculate the concentrations of five molecules (CO2, MEA, DIPA, AMP, and H2O) and nine electrolytes (four cations and five anions) in the liquid phase by solving eight equilibrium equations, four mass balance equations, and one charge balance equation. The Deshmukh–Mather model, which is based on an activity coefficient approach, and the fugacity coefficient model were used to evaluate the nonideality of the liquid and vapor phases, respectively. Thereafter, the effect of the MEA:DIPA:AMP blending ratio was evaluated using the triangular diagrams of the carbamate, bicarbonate and carbonate molar fractions in liquid phase, CO2 loading ratio, CO2 cyclic capacity, and heat of CO2 absorption.

Journal ArticleDOI
Abstract: Nicotinamide is an active pharmaceutical ingredient (API) with high structural complexity and one form of vitamin B3 still poorly understood. For the pharmaceutical industry, the solubility knowledge of APIs is truly relevant for their production, bioavailability, and to be careful with polymorphs formation. In this context, it was determined nicotinamide solid–liquid equilibrium in temperatures from 20 to 50 °C for two solvent systems: water–ethanol and water-propylene glycol (PG), by a refractometric method. The experimental results were compared with a correlative thermodynamic model (Apelblat), three activity coefficient models (Wilson, UNIQUAC, NRTL) with (Δcp = 0, Δcp = ΔS, Δcp = f(t)) and with literature data. The Apelblat model showed a good correlation in both solvent systems, the best predictive fit model. For the water–ethanol system was NRTL (Δcp = 0), and for the water-PG was UNIQUAC (Δcp = 0). Maximum solubility values were observed in a 25 % m/m water-PG composition at 50 °C. The results of this work were compared with the literature and indicated to be in good agreement for the water-nicotinamide and ethanol-nicotinamide data. X-ray diffraction measurements of the solids in equilibrium with the liquid indicated that the behavior of solubility curves is not associated with a change in the crystalline structure of solids, probably due to the formation of oligomers in solution.

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