Experimental and modeling studies on the asphaltene precipitation in degassed and gas-injected reservoir oils

The asphaltene precipitation in a Chinese crude oil has been studied experimentally under normal-pressure and high-pressure conditions. The onset of asphaltene precipitation was detected by using light transmission method. Normal pentane and hexane were used as precipitating agents for studying the onset of asphaltene deposition in (asphaltene+toluene) and (degassed crude oil+toluene) mixtures under normal pressure. A total of eighteen sets of normal pressure data have been measured. For high-pressure gas-injected reservoir oil systems, the effects of injection-gas concentration, temperature, pressure, and the presence of a coexisting aqueous electrolyte (brine) phase on the amount of asphaltene deposition were studied and a total of seven sets of data have been measured. In the modeling part, a modified Hirschberg solubility model and a new solubility parameter correlation were proposed. The model parameters determined from low-pressure precipitation data have been successfully extended to high-pressure systems. Extensive tests vs. the data measured in this work and literature data show that the proposed model is capable of giving reasonable calculation results for most cases.     

Solubility profiles of poly(ethylene glycol)/solvent systems, I: Qualitative comparison of solubility parameter approaches

Solubility of systems involving four different molecular weights of poly(ethylene glycol) (PEG) in tetrahydrofuran (THF), chloroform, dimethylsulfoxide (DMSO), methanol and water have been investigated by different algorithmic approaches as the mathematical application of the “like dissolves like” principle. In this study, the solubility parameters and their components for PEG and solvents have been evaluated by using of atomic group contribution methods; Small, van Krevelen-Hoftyzer (VKH), Hoy and Breitkreutz methods, respectively. Then their 2-dimensional graphs (Bagley, Henry and Hoernschemeyer diagrams) and 3-dimensional graph (Hansen diagram) have been drawn by creating the solubility profiles of the polymer in selected solvents. The dissolving capability of these solvents has been discussed. In addition the solubility parameters have been calculated by use of the van der Waals volume in the selected molecule or repeating unit of the polymer instead of the molar volume which is used in atomic group contribution methods (Askadskii approach). Surface tensions of the polymer and solvent systems have been calculated with this method and solubility criteria of PEG have been explained after a serial calculation steps. In addition, influence of molecular weight of PEG on solubility has been also analyzed. As a consequence of algorithmic calculations, THF has been determined as the best solvent whereas water is found to be the weakest solvent for polymer/solvent systems.     

Water Activity and Solubility Measurements and Pitzer Model Simulation of the MgCl<Subscript>2</Subscript>–RbCl–H<Subscript>2</Subscript>O Ternary System at 298.15 K

Water activities for the MgCl₂–RbCl–H₂O ternary system and its sub-binary MgCl₂–H₂O and RbCl–H₂O systems at 298.15 K have been measured using the isopiestic method. The measured results for the binary systems agree well with literature data. The measured equal water activity lines for the MgCl₂–RbCl–H₂O ternary system deviate from Zdanovskii’s rule. The solubilities for the MgCl₂–RbCl–H₂O ternary system also have been measured using a isothermal visual first/last crystal method, and the results are consistent with one reported set of solubility data. Pitzer’s model was selected to correlate the measured water activity and solubility data and the parameters reported in the literature are re-examined by comparing the model-calculated equal water activity lines and solubilities with experimental values measured in this work. New and reasonable parameters are obtained by fitting the water activity and solubility data measured in this work and those reported in the literature. The water activities and solubilities were simulated with the new parameters and the results show that the Pitzer model can successfully represent the thermodynamic properties and be used to calculate the solubility isotherms.     

Thermodynamics of phase equilibria of the K2SO4 +Rb2SO4+H2O system at 25°C

Activities of water in the K₂SO₄+Rb₂SO₄+H₂O system at 25°C have been measured isopiestically. On the basis of the experimental activities of water ternary parameters of the Pitzer equations have been calculated. According to our data and experimental solubility data from the literature, continous solid solutions between K₂SO₄ and Rb₂SO₄ are formed in this system. With the use of the Guggenheim polynomial for simulating excess functions of solid solutions on the basis of the original and literature solubility data, excess Gibbs energies of solid solution formation as well as a solubility diagram have been calculated. Results of the solubility calculation are in good agreement with experimental data.     

Determination of solubility parameter of poly(N-vinyl 2-pyrrolidon/ethylene glycol dimethacrylate) gels by swelling measurements

The solubility parameters of pure Poly(n-vinyl 2-pyrrolidone) (PVP) and Poly(n-vinyl 2-pyrrolidone/ethylene glycol dimethacrylate)P(VP/EGDMA) hydrogels have been evaluated via swelling experiments. Twenty solvents with various solubility parameters have been used in the swelling experiments. Considering the limitations of using the approach as developed by Gee, we have applied an asymmetric double sigmodial equation for locating the peak maxima in swelling curves. The solubility parameters are evaluated via this new approach. The solubility parameter of pure PVP is determined to be 11.38 ± 0.11 Hb. The incorporation of EGDMA into the gel system slightly reduced the solubility parameter. The influence of relative amount of EGDMA on the solubility parameter was investigated, and evaluated values compared with literature and theoretically determined solubility values by group contribution values of van Krevelen, Small, and Hoy. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 213–219, 1998     

Thermodynamics of binary mixtures containing organic carbonates Part XI. SLE measurements for systems of diethyl carbonate with long n-alkanes: comparison with DISQUAC and modified UNIFAC predictions

Using the available interaction parameters for organic carbonate+alkane mixtures the ability of the DISQUAC and modified UNIFAC group contribution model to predict solid–liquid equilibria (SLE) is investigated. Six sets of the SLE temperatures for diethyl carbonate+n-alkane (octadecane, eicosane, docosane, tetracosane, hexacosane, octacosane) systems have been measured by a dynamic method from 278.65 K to the melting point of the long chain n-alkane. The data have been correlated by three equations: Wilson, UNIQUAC and NRTL. The existence of a solid–solid first-order phase transition in n-alkanes has been taken into consideration in the solubility calculations. The relative standard deviations of the solubility temperature correlation for all measured data vary from 0.31 to 0.34 K and depend on the particular equation used.

The SLE curves are usually well predicted by DISQUAC and modified UNIFAC models with average standard deviation of <1.35 K.     

Interactions of organic halides with a polyurethane elastomer

Interactions of halogen-substituted organic penetrants have been studied with a polyurethane membrane over the temperature interval of 25-60°C. Transport parameters such as diffusivity, solubility, and permeability have been measured. A temperature dependence of these quantities has been used to predict activation parameters for the transport mechanism. Equilibrium sorption data were used to estimate the entropy and Gibbs energy for the sorption process by using the Van't Hoff relationship. Furthermore, a phenomenological treatment has been suggested to estimate the classical Flory-Huggins interaction parameter for polyurethane-solvent pairs. These data were used to calculate the molar mass between crosslinks of the polyurethane network. For all the penetrants, the transport mechanism was found to be anomalous.     

Experimental measurement and modelling of KBr solubility in water,methanol, ethanol,and its binary mixed solvents at different temperatures

A simple and accurate apparatus has been designed to measure the solubilities of potassium bromide by an analytical method. Salt solubility data have been measured in water, methanol, ethanol, (water  +  methanol), (water  +  ethanol), and (methanol  +  ethanol) solvents in the temperature range between 298.15 K and 353.15 K.A new formulation is presented for the calculation of salt solubility in pure and mixed solvents as a function of the temperature and solvent composition. This formulation is based on the symmetric convention for the normalization of the activity coefficients for all species in solution, and makes possible direct access to the solubility product of the salt in terms of its thermodynamic properties. The new solubility data measured in this work, as well as experimental information from the open literature, are used to estimate the interaction parameters of the two models proposed here. One model combines the original Universal Quasi Chemical (UNIQUAC) equation with a Pitzer–Debye–Hückel expression to take into account the long-range interaction forces; the other model only considers the short-range forces through the UNIQUAC equation with linear temperature dependent salt/solvent interaction parameters. Both models correlate satisfactorily the solubility data, although temperature and electrostatic effects are both very important in this type of equilibrium. Finally, some conclusions are drawn concerning the models versatility to represent other type of equilibrium data and prediction capabilities.     

Correlation for the variations with temperature of solute solubilities in high temperature water

Methods for estimating solute solubilities in high temperature water both below and above its boiling point (under pressure) are needed for applications of this medium in processing applications such as sub-critical water extraction, reaction chemistry in heated water, and in the material sciences. There is a paucity of data and correlative methods for estimating solute solubilities under these conditions; the limited existing methods are based on a limited solubility data base, and in some cases predicted solubility values are in quite serious disagreement with experimentally derived data. Here available solute solubility data both above and below the boiling point of water has been correlated for diverse solute types consisting of hydrocarbons, essential oil components, pesticides, polyphenolic compounds, as well as solutes exhibiting high solubility in water under the stated conditions. Utilizing solubility data from diverse sources, appropriate conversions and equations have been derived for converting all solubility data to a mole fraction basis, while the other required physicochemical parameters, such as melting point, boiling point, critical properties, have been estimated, when necessary, largely by group contribution-based methods. A solubility model based on such physicochemical parameters and critical properties of the solutes was derived. An excellent correlation is obtained for x_{c (estimated)}versus x_c using this approach and the prediction of solute solubility in water as a function of temperature was found to be excellent for 431 data points representing the solubility of 34 solutes in the temperature range between 298 and 573 K.     

Strategies to control the particle size distribution of poly-epsilon-caprolactone nanoparticles for pharmaceutical applications

In this work turbulent precipitation through solvent displacement for the production of poly-epsilon-caprolactone (PCL) nanoparticles is investigated; two different PCL molecular weights have been employed, using acetone and water as solvent and anti-solvent, respectively. The main important thermodynamic and kinetic parameters, such as solubility and interfacial tension of PCL in water-acetone mixtures, are determined and the effect of the process operating conditions on the final particle size distribution is also investigated. Particles produced under different conditions into a Confined Impinging Jets Reactor (CIJR) were characterized by Dynamic Light Scattering, Zeta potential measurements and Scanning Electronic Microscopy. Results clearly show the strong effect of mixing on the particle size distribution and how mixing must be controlled in order to obtain a product with particular characteristics. Eventually the measured thermodynamic and kinetic parameters are used to interpret the obtained experimental data.     

Solubility of antioxidant 1010 in pure alkanols

In an equilibrium vessel, the solubility of antioxidant 1010 in pure alkanols was measured in the temperature range from 283.15 K to 343.15 K using a method in which an excess amount of solute was equilibrated with the alkanol solution. The liquid concentrations of the investigated antioxidant 1010 in the saturated solution were analyzed by UV-spectrometry. The solubility data have been correlated as functions of the temperature. Activity coefficients for antioxidant 1010 have been calculated by means of the Wilson, NRTL and UNIQUAC equations and with them were correlated solubility data that were compared with the experimental ones. The best correlation of the solubility data has been obtained by the Wilson equation, by which the average root-mean-square deviation of temperature for the seven systems is 0.62 K.     

Machine learning simulation of pharmaceutical solubility in supercritical carbon dioxide: Prediction and experimental validation for busulfan drug

An artificial intelligence-based predictive model was developed using a support vector machine to investigate the solubility data of the drug Busulfan drug in supercritical carbon dioxide. The data for simulations were collected from literature. The model was trained and implemented in order to determine the correlation between the solubility values and the input parameters, namely, temperature and pressure. These parameters were used as the inputs as they are known to have a significant effect on the solubility of Busulfan in supercritical carbon dioxide. In the artificial intelligence model, a polynomial model with kernel function was applied to the data, and the model’s findings were compared with measured data for fitting. Good agreement was observed between the model’s outputs and the measured data with coefficient of determination greater than 0.99.     

A new approach in modelling phase equilibria and gas solubility in electrolyte solutions and its applications to gas hydrates

This paper presents a new predictive model for phase equilibria and gas solubility calculations in the presence of electrolyte solutions. It treats salts as pseudo-components in an equation of state (EoS) by defining the critical properties and acentric factor for each salt. The water–salt, gas–salt and salt–salt binary interaction parameters (BIP) have been determined by using available experimental data on freezing point depression and boiling point elevation as well as gas solubility and salt solubility data in saline solutions.The methodology has been applied in modelling sodium chloride, potassium chloride and their mixtures, as well as solubility of methane and carbon dioxide in aqueous single and mixed electrolyte solutions.The developed model is capable of accurately predicting the phase behaviour, gas hydrate stability zone and potential salt precipitation in single and mixed electrolyte solutions. The model predictions are compared with available independent experimental data, including hydrate inhibition characteristics of single and mixed electrolyte solutions, and good agreement is demonstrated.     

Solubility and rate of dissolution for Miscanthus in hydrophilic ionic liquids

Miscanthus is a potential feedstock for the production of biofuels. Lignocellulosic biomass is not soluble in conventional solvents, but Miscanthus and other lignocellulosic biomass have reasonable solubilities in some ionic liquids. The solubility of Miscanthus in a variety of hydrophilic ionic liquids was measured as a function of particle size, temperature and time for dissolution. In addition to temperature and time, the ionic liquid anion has a significant effect on solubility and rate of dissolution. The moisture content of Miscanthus lowers its solubility in certain ionic liquids. Chloride, acetate, and phosphate-based ionic liquids favor solubility. A tentative correlation for the solubility of Miscanthus is proposed in terms of Abraham solvation parameters obtained from quantum-chemical model COSMO-RS (Conductor like Screening Model-Real Solvents).     

The solubility of toluene in aqueous salt solutions

The solubility of toluene has been measured in distilled water, and in various inorganic salt solutions. Values of the Setschenow constant, K(S), which quantify toluene solubility versus salt concentration, have been determined for each salt. Values of K(S) are compared to the activity of water for the salt solutions. Data from this study, consistent with earlier data, suggests that the effects of salts upon toluene solubility are non-additive. This contrasts the additive behavior of inorganic salts upon the solubility of nonpolar organic compounds, such as benzene and naphthalene, reported in the literature. Specific interaction between slightly polar toluene and ions in solution is suggested as a possible explanation for the non-additive effect of salts on the solubility of toluene.     

Estimation of aqueous solubility of organic molecules by the group contribution approach. Application to the study of biodegradation.

A reliable and generally applicable aqueous solubility estimation method for organic compounds based on a group contribution approach has been developed. Two models have been established based on two different sets of parameters. One has a higher accuracy, while the other has a more general applicability. The prediction potentials of these two models have been evaluated through cross-validation experiments. For model I, the mean cross-validated r2 and SD for 10 such cross-validation experiments were 0.946 and 0.503 log units, respectively. While for model II, they were 0.953 and 0.546 log units, respectively. Applying our models to estimate the water solubility values for the compounds in an independent test set, we found that model I can be applied to 13 out of 21 compounds with a SD equal to 0.58 log unit and model II can be applied to all the 21 compounds with a SD equal to 1.25 log units. Our models compare favorably to all the current available water estimation methods. A program based on this approach has been written in FORTRAN77 and is currently running on a VAX/VMS system. The program can be applied to estimate the water solubility of the water solubility of any organic chemical with a good or fairly good accuracy except for except for electrolytes. Applying our aqueous solubility estimation models to biodegradation studies, we found that although the water solubility was not the sole factor controlling the rate of biodegradation, ring compounds with greater solubilities were more likely to biodegrade at a faster rate. The significance of the relationship between water solubility and biodegradation activity has been illustrated by predicting the biodegradation activity of 27 new chemicals based solely on their estimated solubility values.     

Comparative study on the thermodynamic retention models in HPLC

Summary A series of model substances with known solubility parameter were chromatographed and from the temperature dependence of the capacity factor, some of the thermodynamic parameters influencing solute retention were determined. A linear relationship was derived between the enthalpy density and the solute solubility parameter from which a graphical method was introduced for the determination of phase characteristics.Comparing the predicted and measured capacity factor values it has been found that the predicted values are very sensitive to the literature data selected for the computation; however, by using the van der Waals molecular volume in the calculation significantly lower deviation was found from the measured data. Two equations are given for the prediction of selectivity and as the mathematical criteria of the validity of the used thermodynamic models. The results show that the predicted selectivity values are similar to the measured data using given initial parameters in the computation. However, the unreliability of the literature data makes the application of the retention models difficult.Dedicated to Professor J. F. K. Huber on the occasion of his 60th birthday.     

Anomalous solubility parameter and probe dependency of polymer-polymer interaction parameter in inverse gas chromatography

Inverse gas chromatography (IGC) has been widely used to measure the Flory-Huggins interaction parameters, χ, between two polymers. For over two decades studies have shown the polymer-polymer interaction parameter to be probe dependent. This study found that the solubility parameters of miscible polymer blends measured by IGC were lower than the volume average values of the components. This led to the conclusion that when specific interactions occur between two polymers the probes have less probability to contact the functional groups of the polymers, leading to a lower apparent solubility parameter. Using the solubility parameter model this deviation was shown to cause the probe dependency. Two methods were proposed to test the miscibility. One was to examine the deviation of the specific retention volume from the weight average rule. The other was to plot ?₂?₃RT(χ₂₃/V₂) vs. the solubility parameters of probes. For miscible blends a linear trend with negative slope was observed. The slope was proportional to the deviation of solubility parameter of the polymer mixtures from the volume average, which could be used as a measurement for miscibility.