Comparison of Models for Calculation of the Thermodynamic Properties of NH3-CO2-H2O Mixture

Couple of models have been developed to calculate thermodynamic properties of NH3-CO2-H2O systems. These models are typically an equation of state for the vapor phase and an activity coefficient model for the liquid phase (Que & Chen, 2011). The activity coefficient models can be divided into three groups based on previous studies, Pitzer model, electrolyte Non Random Two Liquid (e-NRTL) model and extended UNIQUAC model. Que & Chen (2011) deem the e-NRTL model the model the most suitable for process modelling and simulations since it requires only binary interaction parameters and makes use of mole fraction concentration scale consistently for both the short range local compositions interactions and the long range Debey-Huckel expression. Darde (2011) compared the built in e-NRTL model from Aspen Plus to an upgraded version of the extended UNIQUAC model developed by Thomsen et al. (1996). His findings were that the extended UNIQUAC model is significantly more accurate than the e-NRTL model from Aspen. He does mention that if the binary interaction parameters were better fitted to experimental data for NH3-CO2-H2O mixture, the e-NRTL model might become more competitive with the extended UNIQUAC model. Since then the e-NRTL model has been modified in this way by couple of authors, included Que & Chen (2011) and Niu et al. (2013). Both of their adjusted models have then been used by other authors for process modelling, for example Zhang & Guo (2014) used the model with adjusted parameters from Niu et al. (2013) and Liu et al. (2015) used the modified model from Que & Chen (2011). In this paper the extended UNIQUAC model is compared with the e-NRTL thermodynamic model that is built into the most recent version of Aspen Plus, and two modified e-NRTL models; the one developed by Que and Chen (2011) and a new fit. This is done to confirm if the modified models can reach similar accuracy as the extended UNIQUAC model and how much more accurate they are compared to the built in model in Aspen Plus

Flash-point prediction for binary partially miscible mixtures of flammable solvents

Flash point is the most important variable used to characterize fire and explosion hazard of liquids. Herein, partially miscible mixtures are presented within the context of liquid-liquid extraction processes. This paper describes development of a model for predicting the flash point of binary partially miscible mixtures of flammable solvents. To confirm the predictive efficacy of the derived flash points, the model was verified by comparing the predicted values with the experimental data for the studied mixtures: methanol + octane; methanol + decane; acetone + decane; methanol + 2,2,4-trimethylpentane; and, ethanol + tetradecane. Our results reveal that immiscibility in the two liquid phases should not be ignored in the prediction of flash point. Overall, the predictive results of this proposed model describe the experimental data well. Based on this evidence, therefore, it appears reasonable to suggest potential application for our model in assessment of fire and explosion hazards, and development of inherently safer designs for chemical processes containing binary partially miscible mixtures of flammable solvents

Prediction of Miscible Mixtures Flash-point from UNIFAC group contribution methods

Flash point is one of the most important variables used to characterize fire and explosion hazard of liquids. This paper predicts the flash point of miscible mixtures by using the flash point prediction model of Liaw and Chiu (J. Hazard. Mater. 137 (2006) 38-46) handling non-ideal behavior through liquid phase activity coefficients evaluated with UNIFAC-type models, which do not need experimentally regressed binary parameters. Validation of this entirely predictive model is conclusive with the experimental data over the entire flammable composition range for twenty four flammable solvents and aqueousorganic binary and ternary mixtures, ideal mixtures as well as Raoult’s law negative or positive deviation mixtures. All the binary-mixture types, which are known to date, have been included in the validated samples. It is also noticed that the greater the deviation from Raoult’s law, the higher the probability for a mixture to exhibit extreme (minimum or maximum) flash point behavior, provided that the pure compound flash point difference is not too large. Overall, the modified UNIFAC-Dortmund 93 is recommended, due to its good predictive capability and more completed database of binary interaction parameters. Potential application for this approach concerns the classification of flammable liquid mixtures in the implementation of GHS

An evaluation of thermodynamic models for the prediction of drug and drug-like molecule solubility in organic solvents

Prediction of solubility of active pharmaceutical ingredients (API) in different solvents is one of the main issue for crystallization process design. Experimental determination is not always possible because of the small amount of product available in the early stages of a drug development. Thus, one interesting perspective is the use of thermodynamic models, which are usually employed for predicting the activity coefficients in case of Vapour–Liquid equilibria or Liquid–Liquid equilibria (VLE or LLE). The choice of the best thermodynamic model for Solid–Liquid equilibria (SLE) is not an easy task as most of them are not meant particularly for this. In this paper, several models are tested for the solubility prediction of five drugs or drug-like molecules: Ibuprofen, Acetaminophen, Benzoic acid, Salicylic acid and 4-aminobenzoic acid, and another molecule, anthracene, a rather simple molecule. The performance of predictive (UNIFAC, UNIFAC mod., COSMO-SAC) and semi-predictive (NRTL-SAC) models are compared and discussed according to the functional groups of the molecules and the selected solvents. Moreover, the model errors caused by solid state property uncertainties are taken into account. These errors are indeed not negligible when accurate quantitative predictions want to be performed. It was found that UNIFAC models give the best results and could be an useful method for rapid solubility estimations of an API in various solvents. This model achieves the order of magnitude of the experimental solubility and can predict in which solvents the drug will be very soluble, soluble or not soluble. In addition, predictions obtained with NRTL-SAC model are also in good agreement with the experiments, but in that case the relevance of the results is strongly dependent on the model parameters regressed from solubility data in single and mixed solvents. However, this is a very interesting model for quick estimations like UNIFAC models. Finally, COSMO-SAC needs more developments to increase its accuracy especially when hydrogen bonding is involved. In that case, the predicted solubility is always overestimated from two to three orders of magnitude. Considering the use of the most accurate equilibrium equation involving the ΔCp term, no benefits were found for drug predictions as the models are still too inaccurate. However, in function of the molecules and their solid thermodynamic properties, the ΔCp term can be neglected and will not have a great impact on the results

HIx system thermodynamic model for hydrogen production by the sulfur-iodine cycle

The HIx ternary system (H2O – HI – I2) is the latent source of hydrogen for the Sulfur – Iodine thermo-chemical cycle. After analysis of the literature data and models, a homogeneous approach with the Peng-Robinson equation of state used for both the vapor and liquid phase fugacity calculations is proposed for the first time to describe the phase equilibrium of this system. The MHV2 mixing rule is used, with UNIQUAC activity coefficient model combined with of hydrogen iodide solvation by water. This approach is theoretically consistent for HIx separation processes operating above HI critical temperature. Model estimation is done on selected literature vapor – liquid, liquid – liquid, vapor – liquid – liquid and solid – liquid equilibrium data for the ternary system and the three binaries subsystems. Validation is done on the remaining literature data. Results agree well with the published data, but more experimental effort is needed to improve modeling of the HIx system

Flash-Point prediction for binary partially miscible aqueous-organic mixtures

Flash point is the most important variable used to characterize fire and explosion hazard of liquids. Herein, partially miscible mixtures are presented within the context of liquid-liquid extraction processes and heterogeneous distillation processes. This paper describes development of a model for predicting the flash point of binary partially miscible mixtures of aqueous-organic system. To confirm the predictive efficiency of the derived flash points, the model was verified by comparing the predicted values with the experimental data for the studied mixtures: water + 1-butanol; water + 2-butanol; water + isobutanol; water + 1-pentanol; and, water + octane. Results reveal that immiscibility in the two liquid phases should not be ignored in the prediction of flash point. Overall, the predictive results of this proposed model describe the experimental data well when using the LLE and VLE parameters to estimate sequentially the span of two liquid phases and the flash point, respectively. Potential application for the model concerns the assessment of fire and explosion hazards, and the development of inherently safer designs for chemical processes containing binary partially miscible mixtures of aqueous-organic system

Flash Point Measurements and Modeling for Ternary Partially Miscible Aqueous­Organic Mixtures

Flash point is the most important variable used to characterize the fire and explosion hazard of liquids. This paper presents the first partially miscible aqueousorganic mixtures flash point measurements and modeling for the ternary type-I mixtures, water + ethanol + 1-butanol, water + ethanol + 2-butanol, and the type-II mixture, water + 1-butanol + 2-butanol. Results reveal that the flash points are constant in each tie line. Handling the non-ideality of the liquid phase through the use of activity coefficient models, the general flash-point model of Liaw et al. extended to partially miscible mixtures predicts the experimental data well when using literature LLE and the VLE activity coefficient model binary parameters to estimate sequentially the span and flash point in each tie line and the flash point in the mutual solubility region, respectively. The constant flash-point behavior in a tie line is also observed and predicted, in agreement with the VLLE tie line property that a single vapor is in equilibrium with all liquid composition on a tie line. For the aqueousorganic mixtures here studied, a deviation between prediction and measurements is observed, arising from the failure of the constant lower flammable limit assumption in the mutual solubility inert-rich region. Potential application for the model concerns the assessment of fire and explosion hazards and the development of inherently safer designs for chemical processes containing partially miscible aqueousorganic mixtures

Vapor-Liquid Equilibria for R-32 and R-410A Mixed With a Polyol Ester: Non-Ideality and Local Composition Modeling

Vapor-liquid equilibria (VLE) data were obtained over a wide range of mixture composition and saturation conditions for difluoromethane (R-32) mixed with a polyol ester oil (POE). These data were correlated using the following local composition models from the literature: Wilson, Heil, Wang and Chao, Tsuboka and Katayama, NRTL, and UNIQUAC. The results were used to evaluate the suitability of these models in predicting the saturation behavior of the R-32/POE mixture. The Heil model had the best performance, with a 2-a error of 4.81 % in predicted saturation pressure; UNIQUAC was the worst, with a 2-a pressure error of more than 12%. Using VLE results from the literature for pentafluoroethane (R-125) mixed with the same oil and model parameters for that mixture, and attempt was undertaken to make a priori predictions of the P-T-x behavior of a blend containing R-32, R-125 and the oil (R-410A/POE). Data were obtained for this blend, and the results indicate that the Heil model can make such predictions with a 2:' a pressure error of about 11 %.Air Conditioning and Refrigeration Project 5

Effect of stirring on the safety of flammable liquid mixtures

Flash point is the most important variable employed to characterize fire and explosion hazard of liquids. The models developed for predicting the flash point of partially miscible mixtures in the literature to date are all based on the assumption of liquid-liquid equilibrium. In real-world environments, however, the liquid-liquid equilibrium assumption does not always hold, such as the collection or accumulation of waste solvents without stirring, where complete stirring for a period of time is usually used to ensure the liquid phases being in equilibrium. This study investigated the effect of stirring on the flash point behavior of binary partially miscible mixtures. Two series of partially miscible binary mixtures were employed to elucidate the effect of stirring. The first series was aqueous-organic mixtures, including water + 1-butanol, water + 2-butanol, water + isobutanol, water + 1-pentanol, and water + octane ; the second series was the mixtures of two flammable solvents, which included methanol + decane, methanol + 2,2,4-trimethylpentane, and methanol + octane. Results reveal that for binary aqueous-organic solutions the flash-point values of unstirred mixtures were located between those of the completely stirred mixtures and those of the flammable component. Therefore, risk assessment could be done based on the flammable component flash point value. However, for the assurance of safety, it is suggested to completely stir those mixtures before handling to reduce the risk