Phase equilibria of poly(methyl methacrylate) in supercritical mixtures of carbon dioxide and chlorodifluoromethane

Phase behavior data are presented for poly(methyl methacrylate) (PMMA: M_w= 15,000, 120,000) in supercritical solvent mixtures of carbon dioxide (CO₂) and chlorodifluoromethane (HCFC-22). Experimental cloud point curves, which were the phase boundaries between single and liquid-liquid phases, were measured by using a high-pressure equilibrium apparatus equipped with a variable-volume view cell at various CO₂ compositions up to about 63 wt% (on a polymer-free basis) and at temperatures up to about 100 °C. The cloud point curves exhibited the characteristics of a lower critical solution temperature phase behavior. As the CO₂ content in the solvent mixture increased, the cloud point pressure at a fixed temperature increased significantly. Addition of CO₂ to HCFC-22 caused a lowering of the dissolving power of the mixed solvent due to the decrease of the solvent polarity. The cloud point pressure increased with increasing the molecular weight of PMMA.     

Solubility of astaxanthin in supercritical carbon dioxide

The solubility of astaxanthin in carbon dioxide was measured under supercritical conditions of a pressure range from 80 to 300 bar, and temperature range from 303 to 333 K, by using a dynamic flow-type. The solubility of astaxanthin increasing from 0.42×10⁻⁵ to 4.89×10⁻⁵ with higher temperature and pressure maintains certain density of supercritical carbon dioxide. The solubility data obtained were applied to the Chrastil model, based on the density of carbon dioxide. The data fitted well with the Chrastil model at most experimental conditions.     

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.     

Measurement of bubble point pressures and critical points of carbon dioxide and chlorodifluoromethane mixtures using the variable-volume view cell apparatus

The bubble point pressures and the critical points of carbon dioxide (CO₂) and chlorodifluoromethane (HCFC-22) mixtures were measured by using a high-pressure experimental apparatus equipped with a variable-volume view cell, at various CO₂ compositions in the range of temperatures above the critical temperature of CO₂ and below the critical temperature of HCFC-22. The experimental bubble point pressure data were correlated with the Peng-Robinson equation of state (PR-EOS) to estimate the corresponding dew point compositions at equilibrium with the bubble point compositions. The experimentally measured bubble point pressures and the mixture critical points gave good agreement with those calculated by the PR-EOS. The variable-volume view cell equipment was verified to be an easy and quick way to measure the bubble point pressures and the mixture critical points of high-pressure compressible fluid mixtures.     

Measurement and modeling solubility of bioactive coumarin and its derivatives in supercritical carbon dioxide

To design a supercritical fluid extraction process for the separation of bioactive substances from natural products, a quantitative knowledge of phase equilibria between target biosolutes and solvent is necessary. How-ever, mostly no such information is available in literature to date. Thus in the present study, illustratively the solubility of bioactive coumarin and its various derivatives (i.e., hydroxy-, methyl-, and methoxy-derivatives) in supercritical CO₂ were measured at 308.15–328.15 K and 10–30 MPa. Also, the pure physical properties such as normal boiling point, critical constants, acentric factor, molar volume and standard vapor pressure for coumarin and its derivatives were estimated. By these estimated information, the measured solubilities were quantitatively correlated by an approximate lattice equation of state proposed recently by the present authors.     

Extraction of lipids and cholesterol from squid oil with supercritical carbon dioxide

The oil obtained from waste squid viscera consists of multi-compounds such as EPA, DHA and other valuable polyunsaturated fatty acids. The refining of this squid oil, using supercritical carbon dioxide plus ethanol, was performed in a semi-continuous flow extractor at 8 to 17 MPa and 25 to 50 °C. When 1.5% w/w ethanol was added to the solvent, the solubility of lipids was increased by up to 50% over the neat CO₂ value. The extraction curves indicated mass transfer to be solubility limited. Cholesterol was co-extracted with the lipids but, with its lower solubility, less than 54% appeared in the refined oil. The results of the carbon dioxide/multi-compound squid oil system at applied to the extraction conditions were correlated with the mole fraction of the cholesterol and the density of the pure solvent.     

Frequency response of microcantilevers immersed in gaseous,liquid, and supercritical carbon dioxide

The frequency response of ferromagnetic nickel microcantilevers with lengths ranging between 200 μm and 400 μm immersed in gaseous, liquid and supercritical carbon dioxide (CO₂) was investigated. The resonant frequency and the quality factor of the cantilever oscillations in CO₂ were measured for each cantilever length in the temperature range between 298 K and 323 K and the pressure range between 0.1 MPa and 20.7 MPa. At a constant temperature, both the resonant frequency and the quality factor were found to decrease with increasing pressure as a result of the increasing CO₂ density and viscosity. Very good agreement was found between the measured cantilever resonant frequencies and predictions of a model based on simplified hydrodynamic function of a cantilever oscillating harmonically in a viscous fluid valid for Reynolds numbers in the range of [1;1000] (average deviation of 2.40%). At high pressures of CO₂, the experimental Q-factors agreed well with the predicted ones. At low CO₂ pressures, additional internal mechanisms of the cantilever oscillation damping caused lowering of the measured Q-factor with respect to the hydrodynamic model predictions.     

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.     

Solubility analysis of clozapine and lamotrigine in supercritical carbon dioxide using static system

The experimental techniques used to obtain the solubilities of clozapine and lamotrigine in supercritical carbon dioxide include a simple static technique. The solubility measurements were performed at temperatures between 318 and 348 K and pressures between 121.6 and 354.0 bar. These chemicals have solubilities with values ranging from 3.6 × 10⁻⁶ to 4.2 × 10⁻⁵ (clozapine) and 1 × 10⁻⁶ to 6 × 10⁻⁵ (lamotrigine) mole fraction. The solubility data were correlated using four semi-empirical density-based models (Chrastil, Bartle, K-J and M-T models). Correlation of the results shows good self-consistency of the data obtained with the Bartle model for clozapine with an overall average absolute relative deviation (AARD%) of 11.21. The calculated results with each four models show satisfactory agreement with the experimental data for lamotrigine with an overall AARD% 11.72, 8.99, 2.75, 3.86 for Chrastil, K-J, Bartle, M-T models, respectively. Using the correlation results, the heat of drug-CO₂ solvation and that of drug vaporization were approximated.     

Kinetics and rate of enzymatic hydrolysis of cellulose in supercritical carbon dioxide

Experiments were carried out on the application of supercritical fluid to the hydrolysis of cellulose by the enzyme, cellulase. The stability of cellulase was sustained at the pressures of up to 160 atm for 90 min at 50 ‡C in supercritical carbon dioxide. In the hydrolysis of cellulose the glucose yield was 100% at supercritical condition. Kinetic constants of hydrolysis at supercritical condition were increased as compared to those at atmospheric condition. The hydrolysis reaction was found competitively inhibited by glucose at supercritical condition.     

Phase equilibria of alcohols in supercritical fluids Part II. The effect of side branching on C8 alcohols in supercritical carbon dioxide

This paper is a continuation of a previous study and investigated the phase equilibria of six C₈ alcohols (2,2,4-trimethyl-1-pentanol, 2,4,4-trimethyl-1-pentanol, 2-ethyl-1-hexanol, 2-propyl-1-pentanol, 4-methyl-3-heptanol and 6-methyl-2-heptanol) in supercritical carbon dioxide. Data has been measured between 308 and 348 K for alcohol mass fractions between 0.660 and 0.0162. The results show that the position, size and quantity of side chains have a significant effect on the phase behaviour by changing the shape of the molecule and the effect of the hydroxyl group on the polarity of the molecule. The pressure required for total solubility increases in the following sequence: 4-methyl-3-heptanol < 2,2,4-trimethyl-1-pentanol < 6-methyl-2-heptanol < 2,4,4-trimethyl-1-pentanol < 2-propyl-1-pentanol < 2-ethyl-1-hexanol < 1-octanol. The difference in phase behaviour is believed to be a result of a difference in shielding of the hydroxyl group. Greater shielding of the hydroxyl group results in a less asymmetric system, and this, in turn, results in higher solubility of the molecule.     

Furfural production by acid hydrolysis and supercritical carbon dioxide extraction from rice husk

The aim of this research was to study the effect of furfural production from rice husk by hydrolysis accompanying supercritical CO₂ (SC-CO₂) extraction. The two-level fractional factorial design method was used to investigate the production process carried out with respect to furfural yield. The process variables are temperature range of 373–453 K, pressure 9.1–18.2 MPa, CO₂ flow rate 8.3 × 10⁻⁵–1.7 × 10⁻⁴ kg/s (5–10 g/min), sulfuric acid concentration 1 to 7 (%wt) and ratio of liquid to solid (L/S) 5 : 1 to 15 : 1 (vol/wt). The results obtained from the experimental design showed that increasing temperature, pressure, CO₂ flow rate and sulfuric acid concentration but decreasing ratio of liquid to solid would improve furfural yield. Moreover, furfural production by two-stage process (pre-hydrolysis and dehydration) can improve furfural yield further to be around 90% of theoretical maximum.     

Solubility of chlorpheniramine maleate in supercritical carbon dioxide

Solubility of chlorpheniramine maleate in supercritical carbon dioxide at different temperatures (308–338 K) and pressures (160–400 bar) is measured using static method coupled with gravimetric method. The measured solubility data demonstrated that the solubility of chlorpheniramine maleate was changed between 1.54 × 10⁻⁵ and 4.26 × 10⁻⁴ based on the mole fraction as the temperature and pressure are changed. The general trend of measured solubility data shows a direct effect of pressure and temperature on the solubility of chlorpheniramine maleate. Finally, the obtained solubilities correlated using four semi-empirical density-based correlations including Mendez Santiago–Teja (MST), Kumar and Johnston (KJ), Bartle et al., and Chrastil models. Although the results of modeling showed that the KJ model leads to the average absolute relative deviation percent (AARD %) of 8.1% which is the lowest AARD %, deviation of other utilized correlations are rather the same.     

A comparison between semiempirical equations to predict the solubility of pharmaceutical compounds in supercritical carbon dioxide

The aim of this work is to determine, depending on the operation conditions, which semiempirical equation provides the best fit to solubility data of pharmaceutical compounds in supercritical CO₂. Solubility data from 27 different pharmaceutical solutes were collected from literature and the different density-based models (Chrastil, Adachi-Lu, del Valle-Aguilera, Sparks, Kumar-Johnston, Bartle, Méndez Santiago-Teja) together with the Yu's model and Gordillo's model were employed. The results showed that, in general, Sparks’ equation provides the best fit to the solubility data for this kind of solids in supercritical CO₂. However, at certain specific conditions, the best correlation is obtained using Gordillo's equation. By means of a brief comparison with Peng-Robinson equation of state, semiempirical equations present a more accuracy prediction compared to cubic equations of state, and present no drawbacks such as properties estimation and computational difficulties.     

Ternary phase equilibria of the iso-propanol+water+carbon dioxide system at high pressure

Ternary phase diagrams are presented for the system: iso-propanol(IPA)+water+carbon dioxide at temperatures from 15 to 70 °C and pressures from 7 to 17 MPa. The distribution coefficients of IPA between the dense phase carbon dioxide and water changed dramatically with temperature and pressure. In the vicinity of the critical point, distribution coefficients was low, yet at liquid-like densities carbon dioxide had a high affinity for IPA. Selectivity reversal was observed at differing pressures. High selectivity of CO₂ for IPA was achieved in the near-critical liquid and in supercritical carbon dioxide at high pressure.     

Extrema of isochoric heat capacity of water and carbon dioxide

The experimental and predicted loci extrema behavior of the isochoric heat capacity C_v was examined for water and carbon dioxide along the subcritical and supercritical isotherms and along the liquid and vapor isochores. The studies were based on a nonanalytical Helmholtz energy-volume-temperature equation (AVT, fundamental equation of state), the IAPWS-95 formulation for water, and scaling-type crossover equations of state (CREOS). The measured isochoric heat capacity data for these fluids near the critical point were analyzed to study the behavior of loci of C_v maxima and to compare these with predictions by the equations of state. A CREOS was applied to study the behavior of the isochoric heat capacity maxima in the immediate vicinity of the critical point. Good agreement with the CREOS prediction and experimental isothermal C_v maxima loci was observed near the critical point. The basic characteristic points on the C_v extrema loci curves in the P-T and 𝜌-T planes were determined on the basis of detailed analysis of the experimental and prediction of C_v extrema loci behavior. Qualitative explanations are given for the nature of isochoric and isothermal C_v maxima-minima curves. The role of C_v extrema loci behavior in developing high-accuracy equations of state in the supercritical region and in the study of supercritical phase-transition phenomena are discussed.     

Correlation and estimation of solubilities of fatty acids in supercritical carbon dioxide using solution model approach

In this study, solid solubility data of five fatty acids in supercritical carbon dioxide (CO₂) at different temperatures and pressures are correlated using a two-parameter solution model developed from the regular solution model coupled with the Flory⿿Huggins equation. The developed solution model with fewer parameters yields correlated results comparable to those from commonly used semi-empirical equations. In addition, both parameters in the solution model can be further generalized with the chain length of fatty acids and a new predictive solution model is proposed for solubility prediction. The predictive solution model proposed in this study provides better predicted results and yields average deviation in predicted solubilities of 22.1%. To further apply this solution model to other compounds, solid solubility data of three triglycerides in supercritical CO₂ at 313 K are also correlated. After model simplification and generalization, a new predictive solution model for triglycerides is also proposed, which yields average deviation in predicted solubilities of 29.8%. These results demonstrate that the solution model used in this study is applicable for correlation and prediction of solid solubilities of structure-related compounds in supercritical CO₂.     

Crystallization of acetaminophen micro-particle using supercritical carbon dioxide

Fine particles of acetaminophen were produced by Aerosol Solvent Extraction System (ASES). The experiments were conducted to investigate the effects of various temperatures, pressures, solvents, solution concentrations and solution feed volume rates on particle size and morphology. The choice of solvent appears to be very important for getting specific particle shape and size. The result shows that when ethyl acetate is used as a solvent, the irregular and acicular morphology of raw material is recrystallized to be regular and monoclinic. The average particle size of recrystallized acetaminophen from ethyl acetate solution has been measured to be 3–4 Μm, which was about 1/20th of raw acetaminophen in size. The particle size distribution range also became narrow from 82 Μm to 4.9 Μm.     

Measurement and calculation of solubility of quinine in supercritical carbon dioxide

Solubility of quinine in supercritical carbon dioxide(SCCO_2) was experimentally measured in the pressure range of 8 to 24 MPa, at three constant temperatures: 308.15 K, 318.15 K and 328.15 K. Measurement was carried out in a semi-dynamic system. Experimental data were correlated by iso-fugacity model(based on cubic equations of state, CEOS), Modified Mendez–Santiago–Teja(MST) and Modified Bartle semi-empirical models. Two cubic equations of state: Peng–Robinson(PR) and Dashtizadeh–Pazuki–Ghotbi–Taghikhani(DPTG) were adopted for calculation of equilibrium parameters in CEOS modeling. Interaction coefficients(k_(ij) l_(ij)) of van der Waals(vdW) mixing rules were considered as the correlation parameters in CEOS-based modeling and their contribution to the accuracy of model was investigated. Average Absolute Relative Deviation(AARD) between correlated and experimental data was calculated and compared as the index of validity and accuracy for different modeling systems. In this basis it was realized that the semi-empirical equations especially Modified MST can accurately support the theoretical studies on phase equilibrium behavior of quinine–SCCO_2 media. Among the cubic equations of state DPGT within two-parametric vd W mixing rules provided the best data fitting and PR within one-parametric vd W mixing rules demonstrated the highest deviation respecting to the experimental data. Overall, in each individual modeling system the best fitting was observed on the data points attained at 318 K, which could be perhaps due to the moderate thermodynamic state of supercritical phase.     

Solubility of cyproheptadine in supercritical carbon dioxide; experimental and modeling approaches

Solubility of solute in supercritical fluids at different pressures and temperatures is one of the most important parameters necessary for design of any supercritical fluid-based processes. Among different supercritical fluids, carbon dioxide is one of the most widely used solvents due to its useful and green characteristics. In this work, with the assist of supercritical carbon dioxide as the solvent, solubility of cyproheptadine in different temperatures (308–338 K) and pressures (160–400 bar) are measured using static method. The obtained results demonstrated that solubility of cyproheptadine ranged between 3.35 × 10⁻⁵ and 3.09 × 10⁻³ based on mole fraction. A closer examination of measured solubility data show that not only solubility of cyproheptadine increases by increasing pressure but also experiences a cross over pressure about 200 bar. At last, the measured solubility data are correlated using four widely used density based correlations namely Mendez Santiago–Teja (MST), Kumar and Johnston (KJ), Bartle et al., and Chrastil models. The obtained results demonstrated that the best correlative capability was observed for KJ model leads to the average absolute relative deviation percent (AARD %) of 6.3%.