Review Cite This: J. Chem. Eng. Data XXXX, XXX, XXX-XXX
pubs.acs.org/jced
Solubility of Solids in Sub- and Supercritical Fluids: A Review 2010− 2017 Ž eljko Knez,*,†,‡ Darija Cör,† and Maša Knez Hrnčič† †
University of Maribor, Faculty of Chemistry and Chemical Engineering, Smetanova 17, SI-2000 Maribor, Slovenia University of Maribor, Faculty of Medicine, Taborska ulica 8, SI-2000 Maribor, Slovenia
‡
ABSTRACT: A review of the solubility data for solids in sub- and supercritical fluids published in the literature between 2010 and 2017 is presented, including the pressure and temperature ranges and correlation methods. Compounds are categorized into the following groups: pharmaceutical, biological, aromatic, nonaromatic, organometallic, and polymer. The most commonly used solvent is supercritical CO2; some data have also been published for other solvents, such as argon, propane, and fluorinated hydrocarbons.
1. INTRODUCTION Progress has been achieved in the past decade in the field of process intensification and development of scientific methods in chemical engineering. Boosting the industrial application of green chemistry and sustainable technologies, developing design tools, and the scale-up and implementation of emerging processes into industry are all goals that should be pursued in the near future. High-pressure technologies using sub- and supercritical fluids as processing tools have been considered as an attractive green alternative to the conventional chemicals used in several established and new industrial applications. Supercritical fluids have already been widely accepted as processing media in separation techniques such as extraction, sorption processes, chromatography, drying, and membrane separations; in mechanical processes, the most widely used applications are extrusion, homogenization, emulsification, micronization, crystallization, impregnation, and encapsulation, as well as chemical and biochemical reactions.1 Nevertheless, there are still several obstacles to SCF application. Data on phase equilibria and reaction kinetics, verification of process steps, and the design of process sequences to produce a product represent the main limitations in the wider application of advanced processing concepts (comprising supercritical fluid technologies) on an industrial scale. Detailed investigation of phase equilibria, along with thermodynamic and transport data must be carried out to understand the technical and natural processes occurring at elevated pressures. High-pressure phase behavior is often complex and difficult to predict. At high pressures, deviations from ideal behavior become much greater than at ambient or moderate pressure. Direct measurement remains an important and probably the most reliable source of information about the phase equilibria of different systems containing various compounds. Nevertheless, it is difficult and © XXXX American Chemical Society
expensive to obtain precise experimental data, especially for multicompound systems at elevated pressures.2 The number of publications in the field of high pressure phase equilibria is still increasing, although Schütz3 reports the highest number of patent applications on supercritical fluids in 2002. This is most probably a consequence of rising interest in new applications in emergent areas such as (i) best use of raw materials, (ii) use of clean solvents, (iii) use of energy, and (iv) minimal waste production. Because the quantity of experimental data for solid-supercritical fluid systems is relatively scarce, significant attention has been dedicated to the development of mathematical models used to precisely predict the phase behavior of such systems under conditions for which experimental results have not yet been attained.4 For evaluation of the solubility of solids in compressed gases, various thermodynamic models that utilize equations of state, lattice gas equations, or expanded liquid models have been suggested.4 An overview of the solubility data for solid compounds in sub- and supercritical fluids published in the literature between 2005 and 2010 was presented in our previous article,5 in which compounds were classified into different groups: inorganic compounds, organometallic compounds, biological and pharmaceutical compounds, other aromatic and other nonaromatic organic compounds, and polymers in pressurized fluids, while articles dealing with the solubility and diffusivity of gases in polymers were not included. The current review provides data Special Issue: In Honor of Cor Peters Received: August 31, 2017 Accepted: October 26, 2017
A
DOI: 10.1021/acs.jced.7b00778 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Review
on the solubility of solids in sub- and supercritical fluids published in the literature between 2010 and 2017, presented in tabular form with the pressure and temperature ranges and correlation methods. The method for solubility determination is defined as provided by the authors of the given manuscript. Compounds are categorized into the following groups: pharmaceutical, biological, aromatic, nonaromatic, organometallic, and polymer.
The solubility of gallium nitride (GaN) in supercritical ammonia and polyhedral oligomeric silsesquioxanes in CO2 was also measured. The influence of temperature, pressure, and mineralizer concentration on the solubility of gallium nitride was investigated. Tomida et al. reported that solubility increased with increasing temperature, while the pressure dependence was very small. The solubility increased linearly with the increase in mineralizer concentration.11 Leusbrock et al. have investigated the solubility of alkali chlorides MgCl2 and CaCl2, sulfate salts MgSO4 and CaSO4 in phosphate salts Na2HPO4 and NaH2PO4 in supercritical water. The results of the experiments were correlated with a semiempirical model.10,12 In these studies, different quantitative approaches to describe solubility in supercritical water were compared. The behavior of and a quantitative description for the solubility of monovalent chloride and nitrate salts and double-valent chloride salts were presented. Kany and Dilek investigated phase behavior of the binary systems containing CO2 and various hybrid polyhedral oligomeric silsesquioxanes with different functional groups. The impact of functional groups on system behavior was found to be significant. While methacryl, isooctyl and octaisobutyl POSS were observed to form homogeneous solutions with CO2, octamethyl POSS was found to be completely insoluble in the supercritical fluid.14 In addition, the influence of temperature was investigated. Increasing temperature under isobaric conditions lowers the solubility of both methacryl and isooctyl POSS in CO2 in its supercritical state, a decrease due to the decrease in its density.7 The interest in infiltrating supercritical fluids into the field of energy applications has been increasing in the past decade, particularly in the context of CO2 geological storage and enhanced oil or gas recovery operations. Phase behavior of ternary systems consisting of water, CO2 and mineral compounds has been investigated as a basis for the determination of interfacial tension, contact angle and diffusion in terms of the implications for CO2 geological storage.13 So far, the data is scarce, particularly for the conditions pertaining to the application. Undoubtedly, much research can still be expected on the phase behavior of these systems. 2.2. Organometallic Compounds. SC CO2, which is considered a green solvent, represents an alternative for the extraction of metal ions from waste. For the design of several industrial processes and also for the molecular design of precursors, the solubility data for metal complexes becomes extremely important.15 SC CO2 has lately been used to make polymer−metal nanocomposites and metal thin films on the high-aspect-ratio surfaces of semiconductors. For these kinds of processes, the solubility of metal complexes in SC CO2 constitutes the crucial data.15 The solubility of metal−organic compounds in supercritical fluids has already been reported in several publications and reviews, most recently in our previous review by Škerget et al.5 Solubility data for metal complexes published over the last 7 years is summarized in Table 3. The most recently studied systems include several β-diketonate metal complexes (including (acac) acetylacetonate, (thd) 2,2,6,6-tetramethyl-3,5heptanedionate, (thmd) 2,2,6,6-tetramethyl-3,5-heptanedionate, (hfac) hexafluoroacetylacetonate), and complexes with nickel and palladium. Mostly, the correlation proposed by the Chrastil model was used.16
2. SYSTEM INVESTIGATED The present literature review is the sequel to a review previously published by Knez et al. in 2010. The literature review for the years from 2010 to 2017 indicates that SC CO2 is still the most commonly used solvent for most applications. It is an effective solvent for nonpolar compounds, while polar compounds are slightly or practically insoluble in SC CO2. Its polarity can be changed by adding a cosolvent. Fluorinated hydrocarbons5 are known for their high solvation ability for polar compounds and have attracted a relatively high degree of interest, owing to their easily accessible critical conditions. Water is becoming a solvent of choice, based on its specific character, which changes considerably above its critical point. One of the most important properties is its dielectric constant, as a measure of polarity that rules the dissolution of organic and inorganic substances in water. Namely, under normal conditions, the dielectric constant of water is about 80 at 293 K and decreases along an isochore. At a temperature slightly higher than the critical temperature, it can be measured in tens. Along the isotherm, the value rapidly becomes small, along with decreasing density. However, its dielectrical constant decreases to about 5 in the supercritical state.6 The fluids investigated in the current review of the period 2010 to 2017 are summarized in Table 1, together with their critical conditions, acentric factor, and dipole moment. Table 1. Physicochemical Propertiesa of Fluids6 fluid
Tc/K
Pc/MPa
ω
1030·μ/C·m
ammonia (NH3) argon (Ar) carbon dioxide (CO2) dimethyl ether (DME) ethane (C2H6) isobutene (R600a) propane (C3H8) sulfur hexafluoride (SF6) 1,1,1,2-tetrafluoroethane (R134a) water (H2O)
405.4 150.8 304.1 400.0 305.3 407.8 369.8 318.7 374.2 647.1
11.3 4.87 7.38 5.24 4.87 3.64 4.25 3.75 4.06 22.06
0.001 0.250 0.244 0.200 0.099 0.185 0.152 0.210 0.327 0.344
1.42 0 0 1.30 0 0.440 0.280 0 6.865 6.188
Tc, critical temperature; Pc, critical pressure; ω, acentric factor; μ, dipole moment. a
2.1. Inorganic Compounds. The review of solubility of inorganic compounds is presented in Table 2. The solubility of CO2 in aqueous solutions of NaCl, KCl, CaCl2, and salt mixtures for binary and ternary systems has been determined at different temperatures and pressures.7 Binary systems including alkali chlorides, phosphate, and sulfate salts in H2O were investigated, since these are present in many waste streams. Monovalent salts (alkali nitrates and chlorides8,9) and bivalent salts (calcium and magnesium chloride10) were investigated. Here, a continuous flow method was used to investigate the solubility of these compounds. B
DOI: 10.1021/acs.jced.7b00778 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Review
Table 2. Solubility of Inorganic Compounds (X) in Pressurized Fluids (S) X
S
Tfus/Ka
Pmin/MPa to Pmax/MPa
Tmin/K to Tmax /K
solubility range mol·mol−1 0.037 to 0.085
measurement method
CaCl2
H2O
1045
18.5 to 23.5
660 to 690
CaCl2
CO2
1045
up to 16
308 to 328
GaN
NH3
5.5 to 14
673 to 873
4 × 10−5 to 5.47 × 10−2
Isooctyl polyhedral oligomeric silsesquioxane KCl
CO2
up to 30
308 to 323
1.5 × 10−4 to 6.8 × 10−4
up to 16
308 to 328
KCl + CaCl2 (1:1)
CO2
up to 16
308 to 328
Methacryl polyhedral oligomeric silsesquioxane MgCl2
CO2
Up to 30
308 to 323
3 × 10−5 to 4.1 × 10−4
H2O
987
18.5 to 23.5
660 to 690
0.047 to 0.163
analytical-dynamic/ gravimetric analytical-dynamic/ gravimetric analytical-dynamic/ gravimetric analytical-dynamic/ gravimetric analytical-dynamic/ gravimetric analytical-dynamic/ gravimetric analytical-others
MgSO4
H2O
1397
18.8 to 23.2
655 to 675
0.49 × 10−3 to 5.0 × 10−3
analytical-others
Na2HPO4
H2O
>523
20.5 to 24.2
665 to 690
0.0024 to 0.194
analytical-other
NaCl
CO2
1074
up to 16
308 to 328
NaCl + KCl + CaCl2 (1:1:1)
CO2
up to 16
308 to 328
NaCl + KCl/CaCl2 (1:1)
CO2
up to 16
308 to 328
NaH2PO4
H2O
20.5 to 24.2
665 to 690
0.0598 to 0.291
analytical-dynamic/ gravimetric analytical-dynamic/ gravimetric analytical-dynamic/ gravimetric analytical-other
a
CO2
1043
>443 (dec.b)
analytical-dynamic
correlation model semiempirical approach
ref 10 7 11 14 7 7 14
semiempirical approach semiempirical model semiempirical model
10 12 12 7 7 7
semiempirical model
12
Tfus: melting point of compound X. bdec.: decomposes.
dioxide. The high solubility of Pd(hfac)2 in supercritical CO2 is reported, while Ni(hfac)2·2H2O is barely soluble in supercritical CO2. The most likely explanation of this phenomenon is the presence of intermolecular H-bonding. The addition of EtOH involves breaking the hydrogen bonds between the Ni(hfac)2· 2H2O molecules and formation of new hydrogen bonds between the H2O ligands and EtOH.21 Antioxidants, such as sodium L-ascorbate and sodium erythorbate monohydrate, have found extensive application in the food industry in recent years, since they can be added to food for preservation in the place of conventional preservatives. Owing to the limited thermal stability of antioxidants, the supercritical fluid technique is a treatment safe enough for those compounds. Wang and Chang published a study on the solubility of sodium L-ascorbate and sodium erythorbate monohydrate in supercritical carbon dioxide. Solubility was obtained st three different temperature levels at 308.15, 313.15, and 318.15 K, over a range of pressures from 12 MPa up to 24 MPa.22 2.3. Pharmaceutical and Biological Compounds. The systems of pharmaceutical and biological compounds being investigated are summarized in Table 4. The solubility of pharmaceutical compounds includes antibiotics, anti-inflammatory drugs, anticancer drugs, hormones, steroids, vitamins, antipsychotics, and analgesics. The investigated system of biological compounds include fatty acids, carotenes, many antioxidants, and phenolic compounds. Precise experimental determination of a solid drug’s solubility in supercritical fluids and its correlation is extremely important to the development of high pressure technologies for the pharmaceutical industry.23 Phase equilibrium data are significant for the design of separation or formulation processes. Micronization techniques with supercritical fluids have been
Despite enhanced use of SCFs to process metal-based compounds, one limitation of the technology is a lack of fundamental data. Recent studies have aimed to quantify the ability of an SCF to act as a solvent and consequently, the feasibility of a particular process for a particular application.17 Kazemi and coauthors investigated the solubility of ferrocene and acetylferrocene in supercritical carbon dioxide by using an analytical method. A semiflow apparatus was applied to examine the effect of temperature and pressure on the solubility of ferrocene and acetylferrocene.18 Data on the solubility of the metal complexes that are precursors of metal compounds is relatively scarce, especially considering their solubility in supercritical CO2. Fluorine-free hydrocarbon basis β-diketonate complexes, such as metal acetylacetonate (metal(acac)n) and 2,2,6,6-tetramethyl-3,5heptanedionate (metal(thd)n), have been attracting specific interest, since their solubility can be controlled by adjusting the ligand structure. Recently, Haruki et al.19 investigated the influence of temperature on the solubility of copper(II) and cobalt(II) acetylacetonates (Cu(acac)2 and Co(acac)2), and 2,2,6,6-tetramethyl-3,5-heptanedionates (Cu(thd) 2 and Co(thd) 2 ) in supercritical carbon dioxide by using a circulation-type apparatus with in situ UV−vis spectrometry. At a pressure of 20 MPa, the solubility of Cu(thd)2 was about 50- to 65-fold higher than that of Cu(acac)2 at a constant temperature. When limited to both types of complexes, the solubility of Co(acac)2 was greater than that of Co(acac)3, and the solubility of Co(thd)2 was higher than that of Co(thd)3. The solubility of Cu(tmhd)2 in a pure supercritical CO2 system and binary mixtures of SC CO2 and H2 was measured by Momose and co-workers.20 The solubility of Ni(hfac)2·2H2O and Pd(hfac)2 was measured in pure and ethanol modified supercritical carbon C
DOI: 10.1021/acs.jced.7b00778 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Review
used in the polymer industry, in pharmaceuticals, cosmetics, and the food industry to produce ultrafine particles.24 For most pharmaceutical compounds, CO2 cannot be used as a good solvent because of its low polarity. To overcome this problem, many liquid cosolvents have been introduced to increase the solubility of pharmaceuticals in supercritical CO2.24 For this group of compounds, CO2 was the most common solvent. In the case of β-carotene, solubility and adsorption equilibria in propane were investigated, while Jin et al. reported the solubility of 4-aminosalicylic acid in 1,1,1,2-tetrafluoroethane (R134a).25,26 Generally, hydrophobic and polar substances are almost insoluble in SC CO2. To enhance the solubility of these substances, cosolvents like ethanol, ethyl acetate, and acetone can be used.27−33 Cör et al. experimentally determined the solubility of the ternary mixture β-carotene−glyceryl trioleate−CO2 (Figure 1). The experiments were performed in a pressure range from 25 to 60 MPa and temperatures (313, 323, and 333) K. Because of the poor solubility of carotenoids in pure SC−CO2, cosolvents such as triglycerides and/or alcohols can be used to increase the amount of dissolved compound. The solubility of glyceryl trioleate as well as the solubility of β-carotene in the gas-rich phase increase with increasing pressure at constant temperature. The solubility of pure vanillin and o-ethyl vanillin in argon was measured by Knez Hrnčič et al.34 at temperatures of 313.15 K, 333.15 K, and 363.15 K in a pressure range from 5.4 MPa to 50.7 MPa and is presented on Figure 2. Maximal solubility of vanillin in argon was obtained at a temperature of 313.15 K and a pressure of 43.8 MPa. Generally, in the case of lower temperature (333.15 K), greater solubility was observed. The highest solubility of o-ethyl vanillin in argon was obtained at a temperature of 363.15 K and at a pressure of 42.07 MPa. A comparison of results on the solubility data in argon and in CO2 was performed, and it can be concluded that the solubility of both vanillins in argon is higher in the entire pressure range investigated.34 The legal requirements of medical and pharmaceutical concerns are oriented toward the introduction of novel technologies that yield products of a high purity, without traces of solvents. In this sense, supercritical fluids have been widely employed in many processes for almost three decades. Supercritical micronization and extraction processes are common methods for processing bioactive compounds. Solvent density is easily tuned by varying processing conditions. This influences particle diameter and morphology. The difficulty of predicting phase equilibria is the main obstacle to proper design and operation of these processes to achieve the optimal outcome. A current study by Noroozi et al. evaluated the solubility of acetaminophen and ibuprofen in supercritical CO2 by using the thermodynamic integration method, which employs atomistic-free energy calculations in finding a solution to determine the solvation properties of complex molecular solids.35 Although acetaminophen, N-acetyl-p-aminophenol, is a widely used analgesic and antipyretic agent, its solubility data are very limited. Sabet24 investigated the solubility of acetaminophen in pure MeOH and modified supercritical carbon dioxide as a function of temperature (in the range from 313 to 343 K) and pressure (from 10 to 25 MPa). Apparently both parameters influence solubility, which increased with increasing pressure and temperature. Furthermore, solubility is enhanced by the addition of MeOH.24
to 30 to 30
to 24.4
308 to 348 313 333 to 413 313 to 343 313 to 343 373 to 433 313 to 343 313 to 343 313 to 343 313 to 413 308 to 348 313 to 333 313 to 333 313 308 to 318 to 24.4
EtOH
445
523 483 501 to 503 557 to 561 501 to 506
483 to 486
7.7 16 to 30 16 to 27.5 10 to 17 10 to19.8 16 to 25 10 to 16 14.3 11.9 11 to 20 7.7 5 to 20 5 to 20 5 to 20 12 to 24 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 Acetylferrocene Co(acac)2b Co(acac)3b Co(thd)2c Co(thd)3c Cr(acac)3b Cr(thd)3c Cu(acac)2b Cu(thd)2c Cu(tmhd)2d ferrocene Ni(hfac)2·2H2Oe Ni(hfac)2·2H2Oe Pd(hfac)2e sodium L-ascorbate
Tfus: melting point of compound X. bacac: acetylacetonate. cthd: 2,2,6,6-tetramethyl-3,5-heptanedionate. dthmd: 2,2,6,6-tetramethyl-3,5-heptanedionate. ehfac: hexafluoroacetylacetonate. a
Chrastil Chrastil Chrastil Chrastil, M-S-T
Chrastil Chrastil Chrastil
Chrastil
M-S-T
18 15 19 15 15 19 15 15 15 20 18 21 21 21 22 analytical-dynamic/HPLC analytical-dynamic/spectroscopic analytical-dynamic/spectroscopic analytical-dynamic/spectroscopic analytical-dynamic/spectroscopic analytical-dynamic/spectroscopic analytical-dynamic/spectroscopic analytical-dynamic/spectroscopic analytical-dynamic/spectroscopic analytical-dynamic/spectroscopic analytical-dynamic/HPLC analytical-other analytical-other analytical-other analytical-dynamic/spectroscopic 2.5 × 10 to 79.2 × 10 3.91 × 10−5 to 8.59 × 10−5 2.6 × 10−5 to 20.7 × 10−5 0.795 × 10−4 to 12.8 × 10−4 0.191 × 10−3 to 2.31 × 10−3 4.16 × 10−5 to 570.5 × 10−5 0.186 × 10−3 to 4.07 × 10−3 0.997 × 10−5 to 4.74 × 10−5 2.71 × 10−5 to 39.9 × 10−4 0.3 × 10−3 to 0.57 × 10−3 8.9 × 10−4 to 31.2 × 10−4 2.95 × 10−5 to 20.23 × 10−5 1.1 × 10−3 to 5.53 × 10−3
