Electrolyte Nonrandom Two-liquid Model Research Articles

Synergistic effect of blended amines on carbon dioxide absorption: Thermodynamic modeling and analysis of regeneration energy

Chemical absorption using amine-based aqueous solutions is a promising approach for limiting CO2 emissions. This study evaluated the performance of commercial amines, including monoethanolamine (MEA), diethanolamine (DEA), diisopropanolamine (DIPA), N-methyldiethanolamine (MDEA), triethanolamine (TEA), and 2-amino-2-methyl-1-propanol (AMP), along with their binary mixtures, with a focus on their synergistic effect in reducing the regeneration energy. The thermodynamic behavior of these aqueous amine systems for CO2 capture was analyzed using the electrolyte nonrandom two-liquid model; the shortcut method was used to estimate the regeneration energy. The CO2 loading ratio, concentrations of the molecules and ions in the liquid phase, heat of absorption, pH, and regeneration energy were included in the analysis. Amine blending was found to synergistically lower the regeneration energy in the following two cases. First, blending carbamate-forming and non-carbamate-forming amines enhanced carbamate formation, thereby increasing the CO2 cyclic capacity and reducing the regeneration energy in the DIPA-MDEA and DEA-AMP systems. Second, the MEA-MDEA system revealed an optimal blending ratio for balancing different heat components (sensible, reaction, and latent heat). These findings offer a guide for selecting and blending amines to optimize the CO2 capture performance.

New Process for Na2CO3 Production from Na2SO4 Based on Modeling the Na2SO4-(NH4)2SO4-MEA-MEG-H2O System.

Alternative means for soda ash (Na2CO3) production from sodium sulfate (Na2SO4) are needed due to the intensive consumption of energy in the conventional Mirabilite-Solvay process (MSP). We demonstrate a new process to produce soda ash using sodium sulfate as a feed material. The new process relies on the antisolvent crystallization of unreacted Na2SO4 to separate it from soluble (NH4)2SO4 in a mixed monoethanolamine (MEA) and monoethylene glycol (MEG) solution. To develop the process, the solubilities of Na2SO4 and (NH4)2SO4 solids in aqueous mixed MEA-MEG solutions were first measured and then modeled using regressed paired-ion interactions from the electrolyte nonrandom two-liquid (E-NRTL) model. Anhydrous dense soda ash with a bulk density of up to 1146 kg/m3 was obtained when the concentrated Na2SO4 brines reacted with CO2 and NH3.

Thermodynamic study of imidazolium halide ionic liquid–water binary systems using excess Gibbs free energy models

In this work, the excess Gibbs free energy models, i.e., non-random two-liquid (NRTL) model and electrolyte NRTL model, including the original one and those with new strategies (association or hydration), were used to describe the macroscopic properties and interpret the microstructure of ionic liquid (IL) - H2O binary systems, clarifying the role of IL association and ion hydration in model development. To provide systematic data for model development, the enthalpy of mixing of three imidazolium-based IL-H2O systems containing the same cation but different sizes of anions, i.e., Cl−, Br−, and I−, were measured. The models were developed and evaluated based on the newly measured data and the osmotic coefficient from the literature. The results reveal that the model reflecting the intrinsic mechanism of dissociation and hydration gives the best modeling results; and the ionic strength and the degree of IL dissociation as a function of water content can be predicted using the newly established model. The study clarifies the significance of IL association and anion hydration in model development and quantitatively demonstrates how water content influences the microstructure and real species in IL-H2O systems.

Liquid–Liquid Equilibria of the System Nitric Acid + Phosphoric Acid + Calcium Nitrate + Water + Tri-n-Octylamine at 298.15 K

Liquid–liquid equilibrium (LLE) data of the system nitric acid + phosphoric acid + calcium nitrate + water + tri-n-octylamine (TOA) were measured at 298.15 K and atmospheric pressure. The distribution coefficients of nitric acid, phosphoric acid, calcium nitrate, and water and the separation factors of nitric acid against phosphoric acid, nitric acid against calcium nitrate, and nitric acid against the water were calculated. Based on these data, the capability and selectivity of TOA for extracting nitric acid in this system were evaluated. The experimental results were used to obtain binary interaction parameters and pair parameters as correlated by the electrolyte non-random two-liquid (eNRTL) model. The eNRTL model was shown to be suitable for predicting the LLE data of this system, with a root-mean-square deviation of just 1.17%.

Thermodynamic modeling of aqueous lithium salt solutions with association electrolyte nonrandom two-liquid activity coefficient model

The high charge density of lithium ion and the resulting strong association phenomena make thermodynamic modeling of aqueous lithium electrolyte solutions extremely challenging. In this study, the association electrolyte nonrandom two-liquid activity coefficient model of Lin et al. (AIChE J. 2022, 68(2), e17422) is utilized to correlate and predict thermodynamic properties and solubility behavior of aqueous single electrolyte solutions of LiCl, LiBr, LiI, and LiNO3, and their mixed electrolyte solutions. Capturing self-association of water, cross-association of ion and water for hydration, and cross-association of cation and anion for ion-pairing, the association model accurately represents the literature experimental data up to saturation concentrations and at the temperature ranging from 263 K to 523 K. This study further investigated the effect of anions of the lithium salts, and re-confirmed that the order of solution non-ideality as LiI > LiBr > LiCl > LiNO3 because the anions with stronger association strengths are more likely to form ion pairs and thus lower the mean ionic activity coefficients.

Rate-Based Modeling and Assessment of an Amine-Based Acid Gas Removal Process through a Comprehensive Solvent Selection Procedure

In this study, an industrial acid gas removal (AGR) process which uses amine-based solvents was designed and simulated. The selection of suitable absorbents is crucial for an effective AGR process. Therefore, various single and blended amine-based solvents for capturing acid gases were evaluated through a comprehensive procedure, including solvent screening and process design steps. First, various solvents were screened for their CO2 and H2S absorption efficiencies. Promising solvents were then selected for the process design step, in which all process alternatives were simulated and rigorously designed using Aspen Plus. The non-equilibrium rate-based method with an electrolyte non-random two-liquid thermodynamic model was employed for modeling the absorption column. All processes were evaluated in terms of energy requirements, costs, and carbon emissions. The results show that a blend of methyldiethanolamine and piperazine solutions are the most promising solvents for the AGR process, as they can save up to 29.1% and 30.3% of the total annual costs and carbon emissions, respectively, compared to the methyldiethanolamine + diethanolamine solvent process.

Thermodynamic analysis of H2O − 3-aminopropyl tributyl phosphonium glycinate as a working pair for absorption refrigeration system

In this paper, A hydrophilic dual amino-functionalized ionic liquid 3-aminopropyl tributyl phosphonium glycinate ([aP4443][Gly]) with high thermal stability was used as absorbent and the refrigerant was water for the absorption refrigeration system (ARS). The heat capacities of the system were estimated by the differential scanning calorimetry (DSC) with various water mass fractions (w1) (0.004 to 0.6993) and temperatures (285 K to 365 K), and a polynomial equation on temperature and mass fraction of ionic liquid (w2) was associated. Between the experimental and estimated values, the average relative deviation (ARD) was 0.66%. The vapor–liquid equilibrium (VLE) data of the H2O–[aP4443][Gly] binary mixture was correlated using the electrolyte nonrandom two-liquid (eNRTL) model, and the binary mixture's excess thermodynamic properties were simulated. The first and second laws of thermodynamics were used to simulate the performance of a single-effect ARS with a solution heat exchanger (SHE). The ARS simulation results show that the coefficient of performance (COP) of the system with H2O–[aP4443][Gly] as the working pair is higher than that of the conventional working pair NH3-H2O but slightly lower than that of H2O-LiBr. Furthermore, the effect of generator temperature (Tg) on ARS is investigated; simulation results show that the ARS of the novel working pair has a higher COP value at higher generator temperature, indicating that H2O–[aP4443][Gly] has the potential to be a new type of absorption refrigeration working pair.

Linear relationships for modeling CO2 absorption in aqueous alkanolamine solutions in a thermodynamically consistent way

AbstractA thermodynamically consistent model for the carbon dioxide (CO2) absorption in aqueous alkanolamine system is of great importance in the research and development of a CO2 capture process. To facilitate the development of thermodynamic models, linear Gibbs free energy, enthalpy, and heat capacity relationships using well‐known amines as reference are used to correlate the standard reference state properties of ionic species with those of molecular species in the electrolyte system, which has been approved to provide a reliable and consistent way to estimate required parameters when there is minimal or no appropriate experimental data available. The proposed relationships have been applied to the development of an electrolyte nonrandom two liquid (NRTL) activity coefficient model for CO2 absorption in aqueous 1‐amino‐2‐propanol (A2P) solution, as an example to demonstration the methodology. With limited vapor–liquid equilibrium data and other thermodynamic properties, the parameters in the electrolyte NRTL model are identified with good accuracy.

Assessment of carbon dioxide separation by amine solutions using electrolyte non-random two-liquid and Peng-Robinson models: Carbon dioxide absorption efficiency

A high pressure carbon dioxide (CO2) absorption from a specific gas in a conventional column has been evaluated by the Aspen HYSYS simulator using a wide range of single absorbents and blended solutions to estimate the outlet CO2 concentration, absorption efficiency and CO2 loading to choose the most proper solution in terms of CO2 capture for environmental concerns. The property package (Acid Gas-Chemical Solvent) which is compatible with all applied solutions for the simulation in this study, estimates the properties based on an electrolyte non-random two-liquid (E- NRTL) model for electrolyte thermodynamics and Peng-Robinson equation of state for the vapor and liquid hydrocarbon phases. Among all the investigated single amines as well as blended solutions, piperazine (PZ) and the mixture of piperazine and monoethanolamine (MEA) have been found as the most effective absorbents respectively for CO2 absorption with high reactivity based on the simulated operational conditions.

Effect of CaCl2 and ZnCl2 salts on isobaric vapor-liquid equilibrium in separation of the azeotropic mixture of ethanol + water

Present work analyzes potential of calcium chloride (CaCl2) and zinc chloride (ZaCl2) salts as entrainer for breaking the minimum boiling azeotrope of ethanol and water. Isobaric vapor-liquid equilibrium (VLE) data for the binary systems of water + ethanol and ternary system of water + ethanol + calcium chloride, and water + ethanol + zinc chloride were measured at a constant pressure of 94.5 kPa. The effect of salts on the relative volatility of ethanol to water as well as on the vapor phase mole fractions of ethanol were also studied experimentally. From the experimental results, it is observed that with addition of salts, the azeotropic point of the ethanol and water system can be eliminated. Salting out effects in case of calcium chloride was more than that zinc chloride salt. The results obtained in this work showed that calcium chloride could be a better choice for separation of the water + ethanol azeotrope. Electrolyte nonrandom two-liquid (eNRTL) model was used to correlate the experimental VLE data. The model prediction with the regressed parameters was found in well agreement with the experimental data. The experimental data obtained in this work was found thermodynamically consistent using van Ness test.

Operational Limits in Processes with Water, Salt, and Short-Chain Alcohol Mixtures as Aqueous Two-Phase Systems and Problems in Its Simulation

The low critical solution temperature (LCST) and minimum salt concentration that cause phase splitting in water and short-chain alcohol mixtures were determined experimentally. The short-chain alcohols, which are completely miscible with water (methanol, ethanol, 1-propanol, 2-propanol, and tert-butanol) and most of the common salts (those with Na+, K+, Ca2+, and NH4+ cations and Cl–, SO42–, CO32–, and NO3– anions), were studied. Experimentally determined data increased future development opportunities of column sequences and process design using aqueous two-phase systems (ATPSs) by establishing alcohols, some salts, and their operational limits. An example using these systems in phase transition extraction (PTE) separation processes was proposed and discussed. Finally, the use of different thermodynamic models, such as the extended UNIQUAC for electrolytes and the electrolyte nonrandom two-liquid (NRTL) model, for equilibrium calculations and the LCSTs necessary for simulation of these extraction processes with ATPS systems were analyzed.

Thermodynamic Modeling of Aqueous LiCl, LiBr, LiI, and LiNO3 Solutions

Thermodynamic models are essential to facilitate the advancement of process design, optimization, and operation of electrolyte systems. In this work, a comprehensive thermodynamic framework based on the Electrolyte Nonrandom Two-Liquid model is developed to calculate phase equilibria behavior and salt solubility of aqueous LiCl, LiBr, LiI, and LiNO3 solutions. The model describes the non-ideality of the electrolyte solutions by using two binary interaction parameters for each molecule-electrolyte pair in the system. Each binary interaction parameter is further expressed with up to three temperature coefficients which are regressed from experimental data. To take into account the hydration of lithium ion, two separate chemistries for the dissociation of lithium salts are investigated. In the first case, the lithium ion is considered as a bare ion, Li+, while in the second case hydration of the lithium ion from Li+ to Li(H2O)+ is considered. The calculated thermodynamic properties compare adequately with the experimental data for both sets of chemistries for concentrations up to saturation and temperatures from 273.15 K up to 623.15 K. Moderate to significant improvements are observed with the incorporation of the hydration chemistry for aqueous LiCl, LiBr, and LiI solutions when compared to the non-hydrated lithium ion model results.

Experimental and an electrolyte non-random two-liquid model to predict the vapor–liquid equilibrium of CO2 in aqueous solutions of diethylenetriamine

The absorption and desorption data of CO2 in aqueous solutions with a mass fraction of 10% and 20% of diethylenetriamine are measured at 313.15, 343.15, 373.15, and 393.15 K. The electrolyte non-random two-liquid theory is developed using Aspen V9.0 to correlate and predict the vapor–liquid equilibrium of CO2 in aqueous diethylenetriamine solutions. The model predicted the heat capacity and saturated vapor pressure data of diethylenetriamine, the mixed heat of a diethylenetriamine–H2O binary system, and the vapor–liquid equilibrium data of a diethylenetriamine–H2O–CO2 ternary system. The physical parameters and the interaction parameters of the model system are calculated. The model predicted CO2 solubility showing a 10% average absolute deviation from experimental data. The calculated values of the model are basically consistent with the experimental values.

Effect of Blending Ratio and Temperature on CO2 Solubility in Blended Aqueous Solution of Monoethanolamine and 2-Amino-2-methyl-propanol: Experimental and Modeling Study Using the Electrolyte Nonrandom Two-Liquid Model.

This paper reports the newly measured experimental data for CO2 solubility in a blended aqueous solution of monoethanolamine (MEA) and 2-amino-2-methyl-propanol (AMP) at different amine mixing ratios (MEA/AMP/H2O = 9:21:70, 15:15:70, and 21:9:70 wt %) and working temperatures (323.15, 373.15, and 383.15 K). The successive substitution method was used for calculating the mole fractions of all molecules (four molecules) and electrolytes (three cations and four anions) from the equilibrium along with the material and charge balance equations (11 equations). The electrolyte nonrandom two-liquid (e-NRTL) model was used to investigate nonideality in the liquid phase. Using the abovementioned thermodynamic models, the partial pressures of CO2 in the gas phase, mole fractions of all components in the liquid phase, pH variations, heats of absorption, and cyclic capacities of CO2 according to the absorption/desorption temperature and the blending ratio of MEA/AMP were estimated.

Modeling and validation of carbon dioxide absorption in aqueous solution of piperazine + methyldiethanolamine by PC-SAFT and E-NRTL models in a packed bed pilot plant: Study of kinetics and thermodynamics

A pilot plant with a closed cycle of the absorption/desorption process has been taken into account for the simulation of carbon dioxide (CO2) capture by piperazine (PZ) + methyldiethanolamine (MDEA) solution using Aspen Plus rate-based model with all design and operational parameters such as the hydraulic specifications of absorber and stripper as well as inlet flue gas conditions which are present in a commercial gas-fired burner for heating houses. Metal FLEXIPAC 250Y has been considered as the packing type to apply the model to the proposed correlations on Aspen Plus for calculation of flooding and pressure drop. In order to simulate the process, a new property package has been developed by electrolyte non-random two-liquid (E-NRTL) model and perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state which are used for the calculation of activity and fugacity coefficients respectively. The model has been compared with some experimental data e.g. CO2 absorption efficiency and CO2 loading and demonstrated good agreement with them.

An ion-specific electrolyte non-random two-liquid segment activity coefficient model with improved predictive capabilities for aqueous electrolyte solutions

The accurate prediction of activity coefficients of electrolyte solutions is of great importance for many engineering applications. The electrolyte non-random two-liquid (eNRTL) model is a commonly used semi-empirical activity coefficient model for electrolyte solutions. This work presents a modified version of the eNRTL model, which aims to extend its predictive capabilities. An ion-specific parameterization scheme is developed to replace the conventionally used salt-specific parameterization scheme. Consequently, this new method allows for the prediction of the properties of electrolytes consisting of ions for which optimal ion-specific parameter values have been determined, which is inherently not possible when using salt-specific parameters. In order to capture the features of solvent-ion interactions, a segment-based local composition term is used and experimental activity data of both the salt and the solvent are utilized for parameter fitting. The modified eNRTL model with optimal ion-specific parameters is applied to aqueous electrolyte solutions and shows satisfying prediction performance.

Thermodynamic modeling and experimental measurement of semi-clathrate hydrate phase equilibria for CH4 in the presence of cyclohexane (CH) and tetra-n-butyl ammonium bromide (TBAB) mixture

In the current study, the effect of tetra-n-butyl ammonium bromide (TBAB) and cyclohexane mixture on CH4 semi-clathrate hydrate formation was studied. Semi-clathrate dissociation conditions for CH4 + TBAB + cyclohexane + water were investigated at different concentrations of TBAB (0.05, 0.10, and 0.15) mass fraction in the presence of cyclohexane at the pressure and temperature ranges of 1–8 MPa and 275.1–295 K, respectively. In addition, a thermodynamic model was suggested to predict the phase equilibria of our system, which is divided into four phases, where the van der Waals–Platteeuw Solid Solution Theory has been used to predict the hydrate phase. For gas phase, The SRK equation of state was applied. For oil phase, the cyclohexane activity coefficient in the organic phase was calculated by the non-random two-liquid model (NRTL). Finally, to determine the activity coefficient of the electrolyte species in the aqueous phase, the semi-empirical electrolyte NRTL (eNRTL) activity model was used. The results showed that the proposed model has an acceptable agreement with the experimental semi-clathrate hydrate dissociation data with an approximately average absolute relative deviation of 5.4%.

Experimental and e-NRTL model predicted VLE of CO2 in aqueous solutions of 2-((2-aminoethyl)-amino)-ethanol and speciation study

Recently, 2-((2-Aminoethyl) amino) ethanol (AEEA), containing a primary and a secondary amino group, is focused as a new solvent for post-combustion CO2 absorption. In this work, vapour-liquid equilibrium (VLE) of CO2 absorption in the aqueous AEEA is studied over a wide temperature range of 303.15–343.15 K and pressure up to 243 kPa in the amine concentration range of 0.51–4.11 mol AEEA.kg−1 water using a stirred cell thermostatic setup. A rigorous thermodynamically consistent model based on Electrolyte Non-Random Two-Liquid (ENRTL) theory is developed using Aspen V9.0 to correlate and predict the vapour liquid equilibrium of CO2 in aqueous AEEA solutions. The model predicted CO2 solubility showing 28% of average absolute deviation (AAD) from experimental data. The model predicted pair parameters, binary interaction parameters, equilibrium constant, dielectric constant, pure component physical properties and coefficients of extended Antoine vapour pressure correlation are presented in this study. Equilibrium liquid phase speciation for all solvents is predicted using ENRTL-model. The ENRTL model is also used to predict the heat of reactions for the individual equilibrium reactions as function of temperature and the heat of absorption of CO2 in aqueous AEEA solutions as a function of CO2 loading.

Process Modeling and Techno-Economic Analysis of a CO2 Capture Process Using Fixed Bed Reactors with a Microencapsulated Solvent

A detailed model of a capsule containing sodium carbonate solution is developed here to study the microencapsulated carbon capture solvents (MECS). A rigorous vapor–liquid equilibrium model is developed for the Na2CO3–CO2–H2O system, where liquid-phase nonideality is modeled by the electrolyte nonrandom two-liquid model. The data from the experiments conducted at the Lawrence Livermore National Laboratory is used to obtain a maximum likelihood estimate of the initial solvent concentration inside the capsules and the parameters for the capsule model. A nonisothermal, dynamic model of a fixed bed contactor filled with these capsules is then developed. In addition to direct steam injection, indirect heating using an embedded heat exchanger is modeled for desorption. Finally, the model is used to simulate temperature swing absorption and desorption cycles. The results of these studies indicate that there is an optimal residence time or superficial flue gas velocity to minimize the bed volume. However, the tot...

Isobaric vapor-liquid equilibria for the extractive distillation of tert-butyl alcohol + water mixtures using 1-ethyl-3-methylimidazolium dicyanamide ionic liquid

Isobaric vapor-liquid equilibria for the binary systems tert-butyl alcohol + water, and tert-butyl alcohol + 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]), as well as the vapor-liquid equilibria for the tert-butyl alcohol + water + [emim][DCA] ternary system, have been obtained at 100 kPa using a recirculating still. The electrolyte nonrandom two-liquid (e-NRTL) model was successfully used for fitting the experimental data. The effect of [emim][DCA] on the tert-butyl alcohol + water system has been compared with that produced by other ionic liquids reported in the literature. From the results, [emim][DCA] appears as a good entrainer for the extractive distillation of this solvent mixture, causing the azeotrope to disappear at 100 kPa when the ionic liquid mole fraction is >0.095.