Search

In the Hot Potassium Carbonate Process, carbon dioxide (CO2) is removed from gaseous streams by chemical absorption in an aqueous solution of potassium carbonate (K2CO3). It is common to activate the solvent by adding borates and vanadates as promoters. In the present investigation, we investigate the influence of borates and vanadates on the equilibrium solubility of CO2 in aqueous solutions of K2CO3. The solubility of CO2 in four activated aqueous solutions of K2CO3 was determined experimentally at two temperatures that are typical for CO2 absorption (343 K) and solvent regeneration (383 K) in the Hot Potassium Carbonate Process. The mass fraction of K2CO3 in the solvent was 0.26 g/g, and the mass fractions of boron (vanadium) was varied between 0.006 g/g and 0.013 g/g (0.01 g/g and 0.02 g/g). Two experimental setups were used: A headspace gas chromatography technique was applied to determine the solubility of CO2 at partial pressures of CO2 between 1 kPa and 140 kPa, and the synthetic gas solubility te...

The solubility of hydrogen sulfide in an aqueous mixture of 2,2'-methyliminodiethanol (N-methyldiethanolamine, [CAS 105-59-9], MDEA) and 1,4-diazacyclohexane (piperazine, [CAS 110-85-0], PIPH 2 ) was measured over a wide range of gas-loadings (stoichiometric molar ratios of hydrogen sulfide to (MDEA + PIPH 2 ) between about 0.014 and 1.67) at three temperatures (about 313 K, 353 K, and 393 K) by headspace gas chromatography as well as by a synthetic gas solubility method. The molality of MDEA in the aqueous mixture was about 4.5 mol·(kg water) ―1 and that of PIPH 2 about 1.6 mol·(kg water) ―1 . The headspace gas chromatography technique was applied in the low pressure range (partial pressure of H 2 S between 0.64 and 125.7 kPa, stoichiometric molar ratio of H 2 S to (MDEA + PIPH 2 ) between about 0.014 and 0.73). The synthetic method was applied in the high pressure range (total pressure between 0.2 and 5.5 MPa, stoichiometric molar ratio of H 2 S to (MDEA + PIPH 2 ) between about about 0.51 and 1.67). The new experimental results are compared to prediction results from a thermodynamic model that was parametrized using only experimental results for the solubility of H 2 S data in the aqueous solution of the single amines in the high pressure range.

The influence of the amino acid d,l-methionine on the solubility of carbon dioxide in pure water and in aqueous solutions of potassium carbonate was investigated. The solubility was measured with a high-pressure view-cell technique operating on the synthetic method. Temperature and total pressure ranged from about 353 to 393 K and 1 to 10 MPa, respectively. The molality of methionine was between about 0.42 mol·(kg H2O)−1 and 0.83 mol·(kg H2O)−1. The molality of potassium carbonate was about 1.25 and 2.5 mol·(kg H2O)−1. The solubility of carbon dioxide in aqueous solutions of potassium carbonate and methionine is influenced by chemical reactions: On one side, dissolving carbon dioxide in an aqueous solution of potassium carbonate shifts the chemical reaction equilibrium from carbonate to bicarbonate and, on the other side, methionine is a zwitterionic substance. The new experimental results are correlated using an extension of a previously published thermodynamic model for the solubility of carbon dioxide ...

Thermodynamic properties have always played essential roles in the engineering of chemical products and in the processes that manufacture them. Further, contemporary and future chemical technologies depend more than ever on property model formulation and application. This work explores how properties are utilized in process and product engineering, including opportunities and constraints of current property models, the current status of data availability and needs, and the interplay of data and models. Several case studies are given to illustrate underlying concepts, strategies for development, and methods of application to some industrial systems.

The correlation and prediction of the solubility of gases in (nonelectrolyte as well as in electrolyte) aqueous/organic solvent mixtures is an important topic in many areas of chemical engineering. Despite the importance of that field, comparatively little attention has been given to that area in both classical thermodynamics (i.e., correlation methods that are based on semiempirical expressions for the excess Gibbs energy) and molecular simulation (where gas solubility can be predicted from intermolecular pair potentials). In the work presented here, recently published experimental data for the solubility of carbon dioxide in aqueous solutions of acetone (covering temperatures from 313 to 395 K at pressures ranging up to about 9 MPa) are used for testing a semiempirical, classical method (for the correlation of such gas solubility phenomena) as well as the Gibbs ensemble Monte Carlo method (GEMC) (for predicting the solubility of carbon dioxide in aqueous solutions of acetone from published intermolecula...

New experimental results are reported for the influence of two single salts (sodium chloride and sodium sulfate) on the solubility of ammonia in liquid mixtures of water and methanol at 353 and 393 K. The mole fractions of methanol in the (gas-free and salt-free) solvent mixture of water and methanol were about 0.25, 0.5, and 0.75 in the experiments with sodium chloride and about 0.05 and 0.25 in the experiments with sodium sulfate. The molality of the salt varied between about 0.25 and 2 (0.15 and 1) mol/kg of the solvent mixture in the systems with sodium chloride (sodium sulfate). The maximum molality of ammonia was about 6.7 mol/kg of (water + methanol) for both temperatures and for both salts. The maximum total pressure above the liquid solutions was about 0.3 MPa (1 MPa) in the system containing sodium chloride at 353 K (393 K) and about 0.2 MPa (0.7 MPa) in the system with sodium sulfate at 353 K (393 K). The experimental results are used to test a thermodynamic framework which allows the influence...

This work reports new experimental results for the solubility of two single gases (methane and xenon) in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([hmim][Tf2N]). The solubility was measured with a high-pressure view-cell technique operating on the synthetic method. The temperature ranged from 293.3 to 413.3 K, and the maximum pressure (the maximum gas molality) was 9.3 MPa (0.51 mol·kg-1) for methane and 9.6 MPa (2.08 mol·kg-1) for xenon. Xenon shows a significantly higher solubility than methane at all conditions investigated. Both gases become less soluble in [hmim][Tf2N] with rising temperature. An extension of Henry's law is employed to correlate the solubility pressures. The final results for the Henry's constants (at zero pressure) of methane and xenon in [hmim][Tf2N] (on the molality scale) are represented within the experimental uncertainty (about 1.2% for methane and 1% for xenon) by ln( /MPa) = 6.4929 − 835.9/(T/K) − 0.003471(T/K) and ln( /MPa) = 6.3357 − 13...

A headspace gas chromatography technique was applied to determine the solubility of carbon dioxide in aqueous solutions of 2,2‘-methyliminodiethanol (N-methyldiethanolamine, MDEA) at low gas loadings (at stoichiometric molar ratios of carbon dioxide to MDEA between about 0.003 and 0.8). A temperature range T ≈ 313−393 K was covered. The stoichiometric molality of MDEA in water amounted to about 2, 4, and 8 mol/(kg of water) (mass fraction of MDEA ≈ 0.192, 0.323, and 0.488). The partial pressure of carbon dioxide was between about 0.1 and 70 kPa. A thermodynamic model for describing the vapor−liquid equilibrium (which applies Pitzer's molality-scale-based equation for describing the Gibbs excess energy of the aqueous phase) is revised and extended using the new data.

New experimental results are presented for the influence of sodium sulfate on the total pressure above liquid mixtures of (H2O + CH3OH + CO2) at temperatures of about 313.7, 354.4, and 395 K, total pressures up to about 10 MPa, mole fractions of methanol in the binary solvent mixture (water + methanol) of about 0.055 and 0.25, and salt molalities of about 0.92 and 0.15 mol/kilogram of water + methanol, respectively, always below the solubility limit of the salt in the gas-free solvent mixture. An extension of Pitzer's molality scale based model for the Gibbs excess energy of aqueous electrolyte solutions to mixed-solvent electrolyte solutions is successfully applied to predict/correlate the new gas solubility data.

Reactive extraction is a suitable process for the recovery/purification of ionic species (e.g., heavy metals) and electrolytes (e.g., carboxylic acids) from aqueous solutions. The computer-aided basic design of such processes requires a thermodynamic model for the liquid−liquid equilibrium of multicomponent systems, for example, of the system (water + carboxylic acids + organic solvent + reactive extractant). However, as even very small amounts of a strong electrolyte (e.g., sodium chloride) can considerably reduce the amount of carboxylic acid extracted from the aqueous into the organic phase, such models should also be able to account for such effects as was demonstrated in Part I of this series, which dealt with the influence of sodium nitrate, sodium chloride, sodium sulfate, sodium citrate, and hydrochloric acid on the partitioning of citric acid to the coexisting aqueous/organic liquid phases of the system (water + methyl isobutyl ketone (organic solvent) + tri-n-octylamine (chemical extractant)) at...

A thermodynamic model for liquid−liquid phase equilibrium and chemical equilibrium in the formaldehyde + water + 1-butanol system is presented. The model is an extension of the vapor−liquid phase equilibrium model for the formaldehyde + water + methanol system. Formaldehyde reacts with water and alcohols to form oligomers. New experimental results (from NMR spectroscopic investigations) are reported for the chemical equilibrium in liquid formaldehyde + 1-butanol and formaldehyde + water + 1-butanol systems at temperatures from 278 to 348 K. New liquid−liquid phase equilibrium data are reported for temperatures of 298, 313, and 333 K. The model is able to reliably describe the liquid−liquid phase equilibrium, as well as the specification in the liquid phases.

This investigation reports on a thermodynamic phenomenon that can be observed in aqueous solutions of hydrophilic organic solvents: A completely miscible binary liquid mixture of water and an organic solvent, e.g., 1-propanol, can reveal a liquid-phase split, when it is pressurized with a “near-critical” gas, i.e., a gas near its critical temperature. This phase split phenomenon is briefly explained and new experimental data are presented for the partitioning of some natural products (ethyl acetate, d-fructose, d-glucose, and maltol) on, at near-critical pressures, coexisting liquid phases of a three-phase vapor−liquid−liquid equilibrium in the ternary system carbon dioxide + water + 1-propanol. In addition to the experimental data, a semiempirical approach for the correlation of the partition coefficients is shortly outlined. As the partition coefficients significantly deviate from unity, this phase equilibrium phenomenon can be applied for a new mild high-pressure liquid−liquid extraction process for n...

New experimental results for the solubility of hydrogen sulfide in aqueous solutions of the single salts sodium sulfate, ammonium sulfate, sodium chloride, and ammonium chloride at temperatures from 313 to 393 K and total pressures up to 10 MPa are reported. As in the salt-free system, a secondhydrogen sulfide-richliquid phase is observed at high hydrogen sulfide concentrations. A model to describe the phase equilibrium is presented. Calculations are compared to the new experimental data.

Experimental results for the solubility of ammonia in 2−6 m aqueous solutions of four single electrolytes (NaCl, NaNO3, CH3COONa, and NaOH) at temperatures from 313 to 393 K and pressures up to about 0.7 MPa are reported. The experimental results are compared to correlations/predictions.

New experimental results for the solubility of sulfur dioxide in aqueous solutions of single solutes acetic acid, sodium acetate and ammonium acetate at temperatures from 313 to 393 K and total pressures up to 3.3 MPa are reported. Similar to the system sulfur dioxide−water, also in such systems with acetic acid and sodium or ammonium acetate a second (sulfur dioxide rich) liquid phase is observed at high sulfur dioxide concentrations. A model to describe the phase equilibrium is presented and calculated (i.e., predicted as well as correlated) phase equilibria are compared to the new experimental data.

The enthalpy changes upon partial evaporation of aqueous solutions containing ammonia and of aqueous solutions containing ammonia and carbon dioxide were measured at temperatures from 313 to 393 K with a thin film evaporator flow calorimeter. The molalities of ammonia and carbon dioxide entering the calorimeter ranged up to 12 and 6 mol/kg, respectively. The physicochemical model originally developed by Edwards et al. (1978) and further modified and extended by Kurz et al. (1995) to describe phase equilibria in aqueous systems containing ammonia and carbon dioxide is used to derive a predictive enthalpy model for this complex, chemical reactive system. Comparisons between the new experimental results for the enthalpy change upon partial evaporation and model predictions reveal deviations mostly within the experimental uncertainties.

The solubility of carbon dioxide in aqueous solutions containing acetic acid and in aqueous solutions containing sodium hydroxide was measured in the temperature range from 313 to 433 K and total pressures up to 10 MPa. The molalities of acetic acid or sodium hydroxide in the liquid phase were about 4 and 1 mol/kg, respectively. Experimental results are reported and compared to correlations and predictions.

A recently published model for the excess Gibbs energy of aqueous solutions containing mixed electrolytes (Lu and Maurer, 1993) is extended from 298 K to temperatures up to 573 K. The extension is achieved by introducing a universal relation for the influence of temperature on some model parameters. Although parameters are still ion specific, the influence of temperature on those parameters is universal. No additional parameters are required for describing aqueous solutions of mixed electrolytes. The model accurately predicts activity coefficients at high temperatures and at concentrations up to the solubility limit in electrolyte aqueous solutions containing, for example, K+, Na+, NH4+, SO42-, Cl- and NO3-.

The simultaneous solubility of ammonia and carbon dioxide in aqueous solutions of sodium chloride was measured in the temperature range from 313 to 393 K at total pressures up to 3 MPa. Experimental results are reported and compared to model predictions. Predicted results agree with measured data nearly within the experimental uncertainty.

The extraction of oxalic acid from an aqueous solution into solutions of tri-n-octylamine in single solvents toluene, chloroform, and methyl isobutyl ketone was investigated. In addition to batch extraction experiments and isopiestic measurements in the binary system oxalic acid/water, infrared spectroscopic measurements were performed. These spectroscopic investigations yield information about the stoichiometry of complex formation. All measurements were carried out at 298.15 K. A model for the liquid−liquid equilibrium is presented which was used to correlate the experimental data. The model takes into account chemical reactions as well as physical interactions in both phases. Many of the model parameters could be deduced from information about subsystems using also the new isopiestic measurements. However, as several complexes of oxalic acid and tri-n-octylamine with as well as without water have to be considered, some model parameters had to be adjusted using experimental data from batch extraction ex...

The solubility of weak electrolyte gases such as ammonia, carbon dioxide, sulfur dioxide, or hydrogen cyanide must be known for process design in many applications. Typical examples are applications in the chemical and oil-related industries, the production of fertilizers, and applications in environmental protection. Correlating and predicting the simultaneous solubility of ammonia and sour gases in aqueous phases are difficult tasks due to chemical reactions in the liquid phase resulting in the presence of ionic species. Furthermore, the liquid phase often contains other strong electrolytes, and solid phases might precipitate. The simultaneous solubility of ammonia and carbon dioxide in aqueous solutions of sodium sulfate was measured in the temperature range 313--393 K at total pressures up to 3 MPa. Experimental results are reported and compared to correlations and predictions. Predicted results generally agree well with experimental data.

In industrial processes, formaldehyde is mainly handled in aqueous solutions, which often contain methanol. In these solutions, formaldehyde forms predominantly adducts with the solvents. In aqueous solutions, methylene glycol and poly(oxymethylene) glycols are formed, in methanolic solutions hemiformal and poly(oxymethylene) hemiformals. As both the formation of poly(oxymethylene) glycol and of poly(oxymethylene) hemiformal are slow compared to typical residence times in separation equipment, reliable information on kinetics of these reactions is essential for process design. Two independent methods were applied to obtain this information: NMR spectroscopy and high-resolution densimetry. The experiments were carried out at temperatures between 273 and 334 K and pH between 2 and 9. Both for poly(oxymethylene) glycol formation and poly(oxymethylene) hemiformal formation, the minimal reaction rate occurs between pH 3 and 5. At 293 K, the inverse rate constant 1/k at this minimum is about 6 min for poly(oxymethylene) glycol formation and about 110 h for poly(oxymethylene) hemiformal formation. The rate constants determined with NMR spectroscopy and densimetry generally agree well. Previously reported discrepancies between results from both methods are explained by the fact that rate constants of poly(oxymethylene) glycol formation depend strongly on the solvent water or deuterium oxide. Reaction kinetics of poly(oxymethylene) glycol and poly(oxymethylene)more » hemiformal formation in the mixed-solvent system with water and methanol predicted from results obtained in the single-solvent systems are in good agreement with experimental data.« less

The linear solvation energy relationship (LSER) is extended to estimate partition coefficients of organic solutes in infinite dilution between water and organic solvents at 298 K. The LSER needs five parameters to characterize a solute as well as six parameters to characterize the organic solvent/water system. To extend the applicability of the LSER, estimation rules for all parameters are desirable. In the first part rules either given in the litterature or developed in the study are applied to determine the parameters of 101 organic substances. Predicted partition coefficients show that the estimation is reliable. Furthermore a generalized LSER equation, called LSER36, was developed, which allows estimating infinite dilution partition coefficients of organic solutes in organic solvent/water systems at 298 K, when no individual LSER equations are known. That generalized LSER contains 36 universal constants and for each organic solvent those 5 parameters which are used to characterize the same substance as solute. Partition coefficients predicted by LSER36 agree better with experimental data than results from other methods like UNIFAC or Marcus' recently published generalization of the LSER equation

Reliable information on chemical equilibria in formaldehyde solutions is needed for the design of separation process for formaldehyde containing mixtures. Chemical equilibria of the poly(oxymethylene) glycol formation in formaldehyde solutions in water (and deuterium oxide) and of the poly(oxymethylene) hemiformal formation in methanolic formaldehyde solutions were studied by [sup 1]H and [sup 13]C-NMR spectroscopy. Overall formaldehyde mole fraction and temperature range from 0.06--0.19 mol/mol, 275--357 K for solutions in water and 0.17--0.50 mol/mol, 274--317 K for methanolic solutions. Chemical equilibrium constants are determined assuming ideal solution behavior. Results from [sup 1]H and [sup 13]C-NMR spectroscopy agree well. Chemical equilibria of the poly(oxymethylene) glycol formation do not depend on whether water or deuterium oxide is used. The new experimental results confirm only some of the literature data.

Partition coefficients of organic solutes in infinite dilution between water and 30 organic solvents at 298.15 K have been correlated by applying the linear solvation energy relationship (LSER) developed by Kamlet et al. The LSER needs five parameters to characterize a solute. Four of those parameters are determined from experimental data (densitometry and spectroscopy) while one (describing the influence of polarizability) has to be estimated. By fitting that parameter to experimental results for the partition coefficient, an essential improvement of the correlation is achieved. Partition coefficients correlated with the LSER show considerably smaller deviations from experimental data than those either predicted by UNIFAC or correlated by a recently published modification of the LSER equations by Marcus. The average absolute deviation over about 600 partition coefficients correlated with the modified LSER is 0.11 compared with 0.76 predicted with UNIFAC; the average absolute deviation over about 550 data points is 0.12 with the modified LSER and 0.34 with the modification of Marcus

As part of an ongoing project dealing with experimental and theoretical work on phase equilibria in aqueous solutions containing weak electrolyte gases like ammonia, hydrogen cyanide, sulfur dioxide, or carbon dioxide, the solubility of ammonia in aqueous solutions of sodium sulfate and ammonium sulfate was measured by a synthetic method in the temperature range from 333.15 to 433.15 K at total pressures up to 3 MPa. The model proposed by Edwards et al. is used to correlate the data. That model is extended to include the formation of one or more solid phases. Experimental results and the correlations are reported and compared with literature data and other correlations

Methylal (also known as dimethoxymethane and formaldehyde dimethyl acetal) is a side product of the production of polyacetal plastics from formaldehyde, which has to be removed in downstream processing. The design of the separation equipment requires a verified model for the vapor−liquid-phase equilibrium. New experimental results are presented for the vapor−liquid and liquid−liquid equilibrium of the ternary system (formaldehyde + water + methylal) and for the vapor−liquid equilibrium of the ternary system (formaldehyde + methanol + methylal) and of the quaternary system (formaldehyde + water + methanol + methylal). New experimental results and the literature data are compared with prediction results.