Estimation of H2S solubility in ionic liquids using a rigorous method

Prediction of acid gases solubilities in ionic liquids (ILs), have recently emerged as promising mediums for refining of natural gas, using powerful paradigms is of great importance from technical and economical point of view. In this respect, this study aims at appraising the effectiveness of one of the new generation soft computing methodologies called gene-expression programming (GEP) for estimating the hydrogen sulfide (H₂S) solubility in ionic liquids (ILs). A total data set of 465 experimental data belonging to 11 ionic liquids, which gathered from literatures, were used to develop a general correlation. The temperature and pressure accompanied with acentric factors and critical temperature and pressure of ILs were used as independent input variables, while H₂S solubility as dependent output variables. The modeling results showed the coefficient of determination (R²) of 0.9902 and 0.0438% mean absolute relative error (MARE) for the predicted solubilities from the corresponding experimental values. Therefore, the model is comprehensive and accurate enough to be used to predict the H₂S solubility in various ILs. In addition, the GEP-model predictions were compared with the outputs of two well-known engineering approaches named Soave–Redlich–Kwong (SRK) and Peng–Robinson (PR). Results showed that the proposed evolutionary-based method was more accurate than the widely used aforementioned thermodynamic models.     

Modeling of aqueous amino acid and polypeptide solutions with PC-SAFT

Vapor pressures, liquid densities and solubilities of aqueous amino acid and oligopeptide solutions were modeled with an equation of state based on PC-SAFT. The amino acids glycine (Gly), alanine (Ala), serine (Ser), proline (Pro), and valine (Val) as well as the oligopeptides (Gly)_n=1−5, and Ala(Gly)_n=1−4 were considered. Five pure-component model parameters for each amino acid were fitted using experimental densities, vapor pressures, and solubility data. The oligopeptides were treated as co-polymers built up by the respective amino acids. Thus, no additional parameters had to be fitted for the prediction of densities and vapor–liquid behavior of their aqueous solutions besides the segment number. The model is able to excellently reproduce the experimental densities, vapor pressures and solubility data of aqueous amino acid and oligopeptide solutions.     

Mutual solubility study for 94.2:5.8 of ethanol to octane with supercritical carbon dioxide solvent

Solubility data of a mixture containing 94.2% ethanol and 5.8% octane was measured in carbon dioxide solvent using a high-pressure type phase equilibrium apparatus at pressures up to 103.5 bar and at temperature of 75 °C. The results showed that considerable separation was not achieved in this ethanol and octane ratio. However, the experimental data were then compared with the theoretical data which were obtained from two models which are regular solution theory and Redlich-Kwong equation of state. Regular solution theory is employed to each phase by applying activity coefficient expressions. Redlich-Kwong equation of state is employed to the vapor phase and then with applying fugacity coefficient, liquid phase data is obtained. The regular solution theory as a novel model approach has been found to be encouraging for the prediction of phase equilibria solubilities. It concluded that the regular solution theory model could predict two phases equilibrium data better than Redlich-Kwong equation of state.     

Hydrogen recovery from cyclohexane as a chemical hydrogen carrier using a palladium membrane reactor

A palladium membrane reactor was applied to recover the hydrogen from cyclohexane as one of the promising chemical hydrogen carriers. The operation conditions of the palladium membrane reactor to obtain a higher hydrogen recovery were predicted by computer simulation. As a result, it was shown that the hydrogen recovery rate becomes higher as the pressure on the hydrogen permeation side is lowered below atmospheric pressure or as the reaction pressure increases. This was confirmed experimentally. As the perm-side pressure was lowered, the conversion as well as the hydrogen recovery rate at 573 K was found to increase. About 80% of the hydrogen contained in cyclohexane, depending on the operation condition was successfully recovered.     

Density correlation of solubility of C. I. disperse orange 30 dye in supercritical carbon dioxide

The solubility of C. I. Disperse Orange 30 (O30) dye in CO₂ has been measured by using a closed-loop (batch) solid-fluid equilibrium apparatus at temperatures between 313 and 393 K and at pressures between 11 and 33 MPa. Kumar and Johnston’s equation based on Chrastil’s concept has been used to describe the experimental solubility data. The solubility versus density plot appears much simpler than the solubility versus pressure plot. The isotherms are nearly straight and parallel to each other, as seen in the previous studies. Peng-Robinson equation of state (PR EOS) has also been used successfully in modeling the dye solubility in supercritical carbon dioxide as a function of pressure or density of the fluid phase. The validity of this method has been verified by the vapor pressure calculation. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Dye solubility in supercritical carbon dioxide. Effect of hydrogen bonding with cosolvents

The use of supercritical carbon dioxide is emerging as a potential method for achieving pollution-free dyeing. An important factor in supercritical fluid dyeing is the solubility of the dye in supercritical carbon dioxide. Our measurements show that the solubility of C. I. Disperse Red-60 dye in supercritical carbon dioxide is significantly enhanced upon addition of polar csolvents : ethanol and acetone. The solubility enhancement is attributed to the formation of hydrogen bonds between cosolvent and dye molecules. Observed solubility behavior is correlated using dilute-solution theory with lattice-fluid-hydrogen-bonding model. Needed physical and hydrogen-bonding molecular parameters are estimated using the experimental data.     

A new model for predicting solute solubility in supercritical fluids based on the Wilson equation

In this work, a new model based on the Wilson solution theory was proposed for predicting the solubility of solids in supercritical fluid (SCF) with and without cosolvent(s) of binary and ternary systems via computation of activity coefficients. For binary systems the model contains two adjustable parameters, while for ternary systems there are four adjustable parameters. The calculated results of the proposed model were compared with that of the literature models, and it is shown that the proposed model is a more accurate one.     

混合物MH-81状态方程的研究——从无限稀释活度系数预测混合物汽液平衡

本文由无限稀释活度系数求取混合物MH-81状态方程的二元相互作用参数,预测了二元混合物的汽液平衡,获得了较满意的结果。     

Solubility of chemical warfare agent simulants in supercritical carbon dioxide: experiments and modeling

Solubility data are reported for ethyl phenyl sulfide (EPS) and 2-chloroethyl ethyl sulfide (CEES) in CO₂ at temperatures from 25 to 100 °C. These two sulfide-based compounds are homomorphs for chemical warfare agents (CWAs). Both sulfide–CO₂ mixtures exhibit type-I phase behavior. The maximum in the 100 °C isotherm is approximately 2600 psia for the CEES–CO₂ system and approximately 3400 psia for the EPS–CO₂ system. The Peng–Robinson equation of state (PREOS) is used to model both sulfide–CO₂ mixtures as well as the phase behavior of the 2-chloroethyl methyl sulfide (CEMS)–CO₂ system previously reported in the literature. The Joback–Lydersen group contribution method is used to estimate the critical temperature, critical pressure, and acentric factor for the sulfides. Semi-quantitative estimates of the phase behavior are obtained for the CEES–CO₂ and EPS–CO₂ systems with a constant value of k_ij, the binary interaction parameter, fit to the 75 °C isotherms. However, very poor fits are obtained for the 2-chloroethyl methyl sulfide–CO₂ system regardless of the value of k_ij. On the basis of the high solubility of EPS and CEES in CO₂, supercritical fluid (SCF)-based technology could be used to recycle or recover chemical warfare materials.     

由修正的SRK方程推算HF饱和蒸汽压

对ＳＲＫ方程吸力项温度依变参数作了修正，使之能精确的推算了ＨＦ体系的饱和蒸汽压。     

Solubility, swelling degree and crystallinity of carbon dioxide–polypropylene system

Solubilities are reported for carbon dioxide (CO₂) in polypropylene (PP) at temperatures from 313.2 to 483.7 K and at pressures up to 25 MPa. Buoyancy corrections required in the data reduction were estimated with the Sanchez and Lacombe equation of state (S-L EOS). Solubilities of CO₂ in molten state PP could be correlated to within 5% for both the S-L EOS and the group-contribution lattice-fluid equation of state (GCLF EOS). The change in crystallinity of rubbery state PP with CO₂ dissolution into the polymer was predicted with the GCLF EOS and the solubility data under the assumption that CO₂ could dissolve only in the amorphous regions. The trend of the estimated crystallinity with CO₂ dissolution into the polymer was consistent with results in the literature.     

Measurement and modeling of solubility of H2S in aqueous diisopropanolamine solution

Modeling of solubility of acid gases in aqueous alkanolamine solutions is essential for design of an absorber for natural gas sweetening. In this work an apparatus similar to the device of Hayduk and Chen (1970), which was improved by Pahlavanzadeh and Motahhari (1997), for the measurement of gas solubility data by the synthetic method was used. The solubility of hydrogen sulfide in aqueous diisopropanolamine (DIPA) solution in mass concentration range of 30–40% for 101,325 Pa pressure and for temperature ranging from 313–343 K was reported. The obtained experimental solubility data of H₂S in aqueous solutions of DIPA was used to predict the different interaction parameters of modified UNIQUAC-NRF model for calculating the activity coefficients. For nonideality of species in liquid phase, the UNIQUAC-NRF equation with ion-pair approach was applied. For long range interaction, the Pitzer-Debye-Huckel term was used.     

厌氧发酵产氢反应器研究进展3

随着生物制氢技术的迅速发展,各种新型厌氧反应器不断出现。为了更好更快实现生物产氢的产业化,许多学者及工程技术员对生物制氢反应器进行研究和设计。本文综述了产氢反应器的发展及生物制氢反应器连续流稳定运行的工程控制参数,比较了这些系统的启动特点及存在的问题,最后展望了生物产氢研究领域反应器发展及这些系统的应用前景。     

Calculation of pure saturation properties using cubic equations of state

A robust algorithm is outlined for the solution of the classical non-linear isofugacity problem by using equations of state (EOS). The procedure suggested is free of numerical pitfalls from the triple point to the critical point. The combination of differential stability (spinodal curve) and zero pressure reference concepts yields an automatic initialization of the calculations inside a region of convergence where the EOS can always predict pure compound vapor pressures at a given temperature.     

A predictive method for the solubility of drug in supercritical carbon dioxide

We present a predictive approach for the solubility of drug in supercritical CO₂. The fugacity of drug in the solid phase is estimated from its melting temperature and heat of fusion, and the fugacity of the drug in its hypothetical liquid state. The fugacity of the drug is calculated from the Peng–Robinson (PR) EOS. Temperature and composition dependence of the interaction parameters a(T,x) and b(x) of the PR EOS are obtained from the quantum mechanics-based, COSMO-SAC solvation model. As a consequence, the method does not require input of experimental data of the mixture. The average logarithmic deviation (ALD-x) in predicted solubility of 46 drugs in subcritical and supercritical carbon dioxide (T = 293.15–473 K, P = 8.5–50 MPa, and 1160 solubility data ranging from 10⁻⁷ to 10⁻²) was found to be 0.81 (a factor of 5.3). The same method was also examined for solid solubility in a variety of solvents (60 solids including 34 different solvents (with different polarities) and 190 drug-solvent pairs) at ambient pressure. The ALD-x was found to be slightly better (0.58 or a factor of 2.89). The proposed method, the PR + COSMOSAC EOS, is thus a useful tool for a priori prediction of solid solubility in scCO₂, as well as for other solvents.     

平均吸引势模型状态方程用于固体在超临界流体中溶解度的计算

基于膨胀液体概念，把超临界流体看作是被气体膨胀了的液体，并假设体系的分子吸引势为范德华气体和凝聚液体吸引势的体积平均值、导出了一个平均吸引势模型状态方程。该方程较好地关联了纯溶剂蒸汽压及超临界二氧化碳的Ｐ－Ｖ－Ｔ关系；并关联了１４种固体溶质在超临界二氧化碳中的溶解度数据，结果优于ＲＫ、ＳＲＫ及ＰＲ方程。     

Multiphase equilibria calculation by direct minimization of Gibbs free energy with a global optimization method

This paper presents a new method for multiphase equilibria calculation by direct minimization of the Gibbs free energy of multicomponent systems. The methods for multiphase equilibria calculation based on the equality of chemical potentials cannot guarantee the convergence to the correct solution since the problem is non-convex (with several local minima), and they can find only one for a given initial guess. The global optimization methods currently available are generally very expensive. A global optimization method called Tunneling, able to escape from local minima and saddle points is used here, and has shown to be able to find efficiently the global solution for all the hypothetical and real problems tested. The Tunneling method has two phases. In phase one, a local bounded optimization method is used to minimize the objective function. In phase two (tunnelization), either global optimality is ascertained, or a feasible initial estimate for a new minimization is generated. For the minimization step, a limited-memory quasi-Newton method is used. The calculation of multiphase equilibria is organized in a stepwise manner, combining phase stability analysis by minimization of the tangent plane distance function with phase splitting calculations. The problems addressed here are the vapor–liquid and liquid–liquid two-phase equilibria, three-phase vapor–liquid–liquid equilibria, and three-phase vapor–liquid–solid equilibria, for a variety of representative systems. The examples show the robustness of the proposed method even in the most difficult situations. The Tunneling method is found to be more efficient than other global optimization methods. The results showed the efficiency and reliability of the novel method for solving the multiphase equilibria and the global stability problems. Although we have used here a cubic equation of state model for Gibbs free energy, any other approach can be used, as the method is model independent.     

Estimating hydrogen sulfide solubility in ionic liquids using a machine learning approach

For the design and development of new processes of gas sweetening using ionic liquids (ILs), as promising candidates for amine solutions, an amazing model to predict the solubility of acid gases is of great importance. In this direction, in the current study, the capability of artificial neural networks (ANNs) trained with back propagation (BP) and particle swarm optimization (PSO), to correlate the solubility of H₂S in 11different ILs have been investigated. Different structures of three-layer feed forward neural network using acentric factor (ω), critical temperature (T_c), critical pressure (P_c) of ILs accompanied by pressure (P) and temperature (T), as input parameters, were examined and an optimized architecture has been proposed as 5–9–1.Implementation of these models for 465 experimental data points collected from the literature shows coefficient of determination (R²) of 0.99218 and mean squared error (MSE) of 0.00025 from experimental values for PSO-ANN predicted solubilities while the values of R² = 0.95151 and MSE = 0.00335 were obtained for BP-ANN model. Therefore, through PSO training algorithm we are able to attain significantly better results than with BP training procedure based on the statistical criteria.