Estimating solubility of supercritical H2S in ionic liquids through a hybrid LSSVM chemical structure model

Development of a predictive tool for H₂S solubility estimation can be very helpful in gas sweetening industry. Experimental databases on H₂S solubility were rarely available, so as reliable predictive models. Thus, in this study the H₂S solubility database was established, and then a Least-Squares Support Vector Machine (LSSVM) approach based on the established database is proposed. Group contribution method was also applied to eliminate the model's dependence on experimental data. Accordingly, our proposed LSSVM model can predict H₂S solubility as a function of temperature, pressure, and 15 different chemical structures of Ionic liquids (ILs). Root Mean Square Error (RMSE) and coefficient of determination (R²) are 0.0122 and 0.9941, respectively. Moreover, comparison of our model with other existing models showed its reliability for H₂S solubility in ILs. This can be very useful for engineers dealing with gas sweetening process in different applications of analysis, simulation, and designation.     

Gas solubility in long‐chain imidazolium‐based ionic liquids

The gas solubility in 1‐dodecyl‐3‐methylimidazolium [C₁₂MIM] based ionic liquids (ILs) was measured at temperatures (333.2, 353.2, and 373.2) K and pressures up to 60 bar for the first time. The popular UNIFAC‐Lei model was successfully extended to long‐chain imidazolium‐based IL and gas (CO₂, CO, and H₂) systems. The free volume theory was used to explain the gas solubility and selectivity in imidazolium‐based ILs by calculating the fractional free volume and free volume by the COSMO‐RS model. Furthermore, the excess enthalpy of gas‐IL system was concerned to provide new insights into temperature dependency of gas (CO₂, CO, and H₂) solubility in ILs. The experimental data, calculation, and theoretical analysis presented in this work are important in gas separations with ILs or supported ionic liquid membranes. © 2017 American Institute of Chemical Engineers AIChE J, 63: 1792–1798, 2017     

Thermodynamic validation of 1‐alkyl‐3‐methylimidazolium carboxylates as task‐specific ionic liquids for H2S absorption

Solubilities of H₂S in five 1‐alkyl‐3‐methylimidazolium carboxylates ionic liquids (ILs) have been measured at temperatures from 293.15 to 333.15 K and pressures up to 350 kPa. It is shown that these ILs have significantly larger absorption capacities for H₂S than those common ILs reported in the literature. The solubility is found to increase dramatically with the increasing alkalinity of the anions and slightly with the increasing length of the alkyl chains on the cations. It is further demonstrated that the absorption isotherms are typically nonideal. With the assumption of complex formation between H₂S and ILs, a reaction equilibrium thermodynamic model is developed to correlate the experimental solubilities. The model favors a reaction mechanism of AB₂ type that two IL molecules interact with one H₂S molecule. Thermodynamic parameters such as Henry's law constants, reaction equilibrium constants, and heat of complex formation are also calculated to evaluate the absorption process of H₂S in these ILs. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2227–2235, 2013     

Screening ionic liquids as candidates for separation of acid gases: Solubility of hydrogen sulfide,methane, and ethane

The solubility of the major constituents of natural gas in ionic liquids (ILs) can be used to identify their potential for acid gas removal from a producing gas stream. We have developed models for the solubility of H₂S, CH₄, and C₂H₆ in ILs at typical conditions encountered in natural gas treatment. In this work, a conductor‐like screening model for realistic solvation was used to predict the activity coefficients for solutes in ILs and a cubic EOS was used for vapor‐phase corrections from ideality. Empirical correlations were developed to extrapolate solubilities where experimental data are not available at desired conditions; targeted in this study at 298.15 K and 2000 kPa. Over 400 possible ILs were ranked based on the higher selectivity of absorption of CO₂ and H₂S over CH₄ and C₂H₆. The best 15% (58) of promising ILs for sour gas treatment predominantly contain the anions BF₄, NO₃, and CH₃SO₄ and the cations N₄₁₁₁, pmg, and tmg. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2993–3005, 2013     

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.     

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.     

Hydrophobic protic ionic liquids tethered with tertiary amine group for highly efficient and selective absorption of H2S from CO2

Developing absorbents with both high absorption capacity of H₂S and large selectivity of H₂S/CO₂ is very important for natural gas sweetening process. To this end, a class of novel hydrophobic protic ionic liquids (ILs) containing free tertiary amine group as functional site for the absorption of H₂S were designed in this work. They were facilely synthesized through a simple neutralization‐metathesis methodology by utilizing diamine compounds and bis(trifluoromethylsulfonyl)imide as the building blocks for cation and anion, respectively. Impressively, the solubility of H₂S can reach 0.546 mol mol^?1 (1 bar) and 0.225 mol mol^?1 (0.1 bar), and the selectivity of H₂S/CO₂ can reach 37.2 (H₂S solubility at 1 bar vs. CO₂ solubility at 1 bar) and 15.4 (H₂S solubility at 0.1 bar vs. CO₂ solubility at 1 bar) in the hydrophobic protic ILs at 298.2 K. Comparing the hydrophobic protic ILs with other absorbents justifies their superior performance in the selective absorption of H₂S from CO₂. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4480–4490, 2016     

Protic ionic liquids for the selective absorption of H2S from CO2: Thermodynamic analysis

The solubilities of H₂S and CO₂ in four protic ionic liquids (PILs)—methyldiethanolammonium acetate, methyldiethanolammonium formate, dimethylethanolammonium acetate, and dimethylethanolammonium formate were determined at 303.2–333.2 K and 0–1.2 bar. It is shown PILs have higher absorption capacity for H₂S than normal ionic liquids (ILs) and the Henry's law constants of H₂S in PILs (3.5–11.5 bar at 303.2 K) are much lower than those in normal ILs. In contrast, the solubility of CO₂ in PILs is found to be a magnitude lower than that of H₂S, implying these PILs have both higher absorption capacity for H₂S and higher ideal selectivity of H₂S/CO₂ (8.9–19.5 at 303.2 K) in comparison with normal ILs. The behavior of H₂S and CO₂ absorption in PILs is further demonstrated based on thermodynamic analysis. The results illustrate that PILs are a kind of promising absorbents for the selective separation of H₂S/CO₂ and believed to have potential use in gas sweetening. © 2014 American Institute of Chemical Engineers AIChE J 60: 4232–4240, 2014     

Solubility of polystyrene with various molecular weights in subcritical 1,1,1,2‐tetrafluoroethane: experiment and modified model

The solubility of polystyrene with molecular weight of 100 000 and 260 000 g mol^?1 was measured at temperatures from 313 to 333 K and at pressures from 5.0 to 13.0 MPa in subcritical 1,1,1,2‐tetrafluoroethane (R134a). The effects of pressure, temperature and molecular weight on the solubility of polystyrene were investigated. Meanwhile, the solubility of polystyrene was correlated using six density‐based semi‐empirical models (Chrastil, A‐L, K‐J, S‐S, M‐S‐T and Bartle). The M‐S‐T model was used to verify the self‐consistency of the experimental data, and the enthalpy values of polystyrene, including ΔH_total, ΔH_sub and ΔH_sol, were estimated through the Chrastil and Bartle models. In addition, a modified M‐S‐T model was proposed through a detailed study of semi‐empirical model formulas and verified by the solubility of polystyrene in subcritical R134a and 38 other solid solutes in supercritical carbon dioxide and subcritical R134a. © 2018 Society of Chemical Industry     

Design and screening of ionic liquids for C2H2/C2H4 separation by COSMO‐RS and experiments

Ionic liquids (ILs) have been proposed as promising solvents for separating C₂H₂ and C₂H₄, but screening an industrially attractive IL with high capacity from numerous available ILs remains challenging. In this work, a rapid screening method based on COSMO‐RS was developed. We also present an efficient strategy to improve the C₂H₂ capacity in ILs together with adequate C₂H₂/C₂H₄ selectivity with the aid of COSMO‐RS. The essence of this strategy is to increase molecular free volume of ILs and simultaneously enhance hydrogen‐bond basicity of anions by introducing flexible and highly asymmetric structures, which is validated by a new class of tetraalkylphosphonium ILs featuring long‐chain carboxylate anions. At 298.1 K and 1 bar, the solubility of C₂H₂ in ILs reaches 0.476 mol/mol IL, very high for a physical absorption, with a selectivity of up to 21.4. The separation performance of tetraalkylphosphonium ILs to the mixture of C₂H₂/C₂H₄ was also evaluated. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2016–2027, 2015     

UNIFAC model for ionic liquid‐CO (H2) systems: An experimental and modeling study on gas solubility

The universal quasichemical functional‐group activity coefficients (UNIFAC) model for ionic liquids (ILs) has become notably popular because of its simplicity and availability via modern process simulation softwares. In this work, new group binary interaction parameters (α_mn and α_nm) between CO (H₂) and IL groups were obtained by correlating the solubility data in pure ILs at high temperatures (above 273.2 K) collected from the literature. the solubility of CO in [BMIM]⁺[BF₄]^?, [OMIM]⁺[BF₄]^?, [OMIM]⁺[Tf₂N]^?, and their mixtures, as well as that of H₂ in [EMIM]⁺[BF₄]^?, [BMIM]⁺[BF₄]^?, [OMIM]⁺[Tf₂N]^?, and their mixtures, at temperatures from 243.2 to 333.2 K and pressures up to 6.0 MPa were measured. The UNIFAC model was observed to well predict the solubility in pure and mixed ILs at both high (above 273.2 K) and low (below 273.2 K) temperatures. Moreover, the selectivity of CO (or H₂) to CO₂ in ILs increases with decreasing temperature, indicating that low temperatures favor for gas separation. © 2014 American Institute of Chemical Engineers AIChE J 60: 4222–4231, 2014     

Octanol/water partition coefficients of ionic liquids

BACKGROUND: Room temperature ionic liquids (ILs) are attractive alternatives to environmentally unfriendly volatile organic solvents. Partitioning is one of the most important and fundamental properties of a chemical, and the octanol/water partition coefficient is widely used to measure the tendency of a chemical to cross biological membranes. However, there is very limited information on the concentration dependence of the partition coefficients of ILs. This study investigated the octanol/water partitioning of 1‐butyl‐3‐methylimidazolium ([bmim]) ILs containing either hexafluorophosphate ([PF₆]) or bis[(trifluoromethyl)sulfonyl]amide ([Tf₂N]) over a wide range of IL concentrations of three to five orders of magnitude. RESULTS: It was found that the apparent partition coefficients of the ILs increased with increasing IL concentration. A model based on the ionic nature of ILs was proposed to explain this behaviour, and the results showed a good fit with the experimental data. The intrinsic partition coefficients and dissociation constants of the ILs were determined using the equations from the proposed model. The differences in the intrinsic partition parameter values between the two ILs showed a good correlation with other physicochemical properties. CONCLUSIONS: The present study clearly shows that the octanol/water partition coefficients of ILs increase with increasing IL concentration owing to the formation of ion pairs. By using the proposed partition model, it was possible to determine the intrinsic partition coefficients of ILs, and it was found that the apparent partition coefficients of ILs converge to the intrinsic partition coefficients of the ionic species and ion pairs of ILs with decreasing and increasing IL concentration respectively. Copyright © 2008 Society of Chemical Industry     

Thermodynamic modeling of CO2 solubility in ionic liquid ([C n -mim] [Tf2N]; n=2, 4, 6, 8) with using Wong-Sandler mixing rule, Peng-Rabinson equation of state (EOS) and differential evolution (DE) method

Environmental and safety regulations are creating increasing interest in ionic liquids which have been used as alternative solvents for a wide range of industrial applications. Knowing the phase equilibrium of these materials is very important. In this study, the solubility of CO₂ in ionic liquid 1-alkyl-3 methylimidazolium bis (trifluoromethylsulfonyl) imide ([C _n -mim][Tf₂N]; n=2, 4, 6, 8) was probed with the Peng-Robinson (PR) equation of state (EOS) and Wong-Sandler mixing rule and van Laar model for excess Gibbs free energy. The differential evolution (DE) optimization method was applied to optimize the binary interaction parameter and activity coefficients. Moreover, binary interaction parameters and activity coefficients were presented as mathematical correlations that for various materials have depended on temperature. Our results showed that average absolute derivations of our proposed model were less than other existing models, and by using the aforesaid method better prediction could be achieved.     

UNIFAC model for ionic liquid‐CO2 systems

The new group binary interaction parameters of UNIFAC model (a_nm and a_mn) between CO₂ and 22 ionic liquid (IL) groups were obtained by means of correlating the solubility data of CO₂ in pure ILs at different temperatures (>273.2 K). We measured the CO₂ solubility at low temperatures down to 243.2 K in pure ILs, i.e., [OMIM]⁺[BF₄]^? and [OMIM]⁺[Tf₂N]^?, and their equimolar amount of mixture, in order to fill the blank of solubility data at low temperatures and also to justify the applicability of UNIFAC model over a wider temperature range. It was verified that UNIFAC model can be used for predicting the CO₂ solubility in pure ILs and in the binary mixture of ILs both at high (>273.2 K) and low temperatures (<273.2 K) effectively, as well as identifying the new structure–property relation. This is the first work to extend the UNIFAC model to IL‐CO₂ systems. © 2013 American Institute of Chemical Engineers AIChE J 60: 716–729, 2014     

A mathematical model for equilibrium solubility of hydrogen sulfide and carbon dioxide in aqueous alkanolamine solutions

A thermodynamic model is proposed for the solubility of the acid gases (H₂S and CO₂) in alkanolamine solutions. The model is based on the exten Debye-Hückel theory of electrolyte solutions. Predicted partial pressures of the acid gases over monoethanolamine solutions are in good agreement wit experimental data over the temperature range 25—120°C.     

H2S–CO2 Separation Using Room Temperature Ionic Liquid [BMIM][Br]

Solubility and selective absorption of hydrogen sulfide (H₂S) over carbon dioxide (CO₂) in a room temperature ionic liquid, 1-butyl-3-methylimidazolium bromide ([BMIM][Br]) has been evaluated under ambient temperature and pressure. [BMIM][Br] demonstrated its potential as a solvent for selective removal of H₂S from CO₂/H₂S mixture. Our investigation indicated that H₂S solubility in [BMIM][Br] is comparable to or better than that in commercially available MDEA-based solvents. Meanwhile, CO₂ solubility in [BMIM][Br] is lower than that in the same amine resulting in H₂S/CO₂ absorption selectivity of within 3.5 to 3.75. The solubility behavior is relatively maintained after 4 times absorption-desorption cycles. A computational molecular study suggested that intramolecular hydrogen bonding interaction between anion Br and hydrogen atom of H₂S could stabilize the complex and resulted lower complexation energy than CO₂ interaction with [BMIM][Br]. Based on the experiment results, a separation process employing [BMIM][Br] is proposed to control the CO₂/H₂S ratio existing in a natural gas feed.     

Nano Cyclotetramethylene Tetranitramine Particles Prepared by a Green Recrystallization Process

The solubility of cyclotetramethylene tetranitramine (HMX) in four ionic liquids (ILs): 1,3‐dimethylimidazolium dimethylphosphate ([Memim]DMP), 1‐butyl‐3‐methylimidazolium chloride ([Bmim]Cl), 1‐hexyl‐3‐methylimidazolium bromide ([Hmim]Br), and 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ([Emim]BF₄) was investigated. Nano‐HMX were produced particles by spraying [Hmim]Br solution into purified ice water. Finally, the particle size, morphology, crystal phase, impact sensitivity, and thermal decomposition properties of nano‐HMX particles were tested and analyzed. All four ILs could dissolve HMX to a greater or lesser extent in the temperature range from 20 °C to 80 °C. The solubility of HMX in [Hmim]Br at 80 °C is up to 0.7 g mL⁻¹. Recrystallized HMX particles are of polyhedral or spherical shape and 40 to 130 nm in size. X‐ray diffraction indicated that nano‐HMX has a similar crystal structure as raw HMX (β‐form). Compared with raw HMX, the nano‐HMX particles have much lower impact sensitivity. However, they are easier to explode than raw HMX under thermal stimulus due to the lower peak temperature and activation energy.