solubility in sub- and supercritical ethanol
“Nitric acid 70 percent” by W. Oelen via Wikipedia licensed under CC-BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0/deed.en

Extraction by subcritical and supercritical ethanol has been applied to many materials for the recovery of useful products from them. The treatment of coals and oil shales with these solvents may yield liquid fuels and many plant biomass materials are sources of bio-active products when subjected to extraction with ethanol at the named conditions. The solubility of the prospective solutes is, therefore, of importance, and the solubility parameter of the ethanol solvent is useful for its estimation.

Ethanol at ambient conditions has a highly hydrogen-bonded structure, which is destroyed to an appreciable extent as the temperature is increased. This phenomenon reduces its permittivity and makes it less polar and tight, and facilitates the dissolution of non-polar substances in it. But the increased temperatures do not detract from the dipolarity and hydrogen bond donation and acceptance abilities of this solvent so that it also dissolves polar solutes.

The total (Hildebrand) solubility parameters, δH, has often been used for the estimation of solubilities. The difference between the solubility parameter of the solvent, δHE, and that of the solute, δHS, should not exceed 4 MPa1/2 for appreciable solubility to ensue. A more detailed estimation of the solubility is the use of the partial (Hansen) solubility parameters: δd for dispersion interactions, δp for dipolar interactions, and δhb for hydrogen bonding. Such quantities are known for many potential solutes.

solubility in sub- and supercritical ethanol

Republished with permission from Elsevier from https://doi.org/10.1016/j.jct.2018.06.023

Subcritical liquid ethanol extends along the liquid-vapor equilibrium line from the normal boiling point 351.4 K to the critical point 514.1 K. Over this range its Hildebrand solubility parameter is derived from the usual expression: δH = [(ΔVH(T) − RT)/V(T)]1/2, where ΔVH(T) is the molar enthalpy of vaporization and V(T) is the molar volume, all being temperature-dependent. The molar enthalpy of vaporization and the density ρ of liquid ethanol are well known as functions of the temperature, yielding the total (Hildebrand) solubility parameters of liquid ethanol. It follows the quadratic expression: δH/MPa1/2  = 28.39 + 6.815×10−3(T/K) – 5.2385×10−5(T/K)2, diminishing with increasing temperatures, from 26.14 at 298.15 K to 24.25 at the normal boiling point Tb (351.4 K) to 17.55 just below the critical point Tc (513 K).

Above the critical temperature Tcthe enthalpy of vaporization is meaningless, and the solubility parameter must be estimated from the configurational internal energy: δH = [−U(T,P)/V(T,P)]1/2.  The Soave-Redlich-Kwong equation of state provides the configurational internal energy and U and V depend on both the temperature T and the pressure P. In terms of the reduced temperature Tr = T/Tc and reduced density ρr = ρ/ρc the total solubility parameter of supercritical ethanol is: δH/MPa1/2 = 7.31[1 + 1.410(1 − Tr1/2)] Tr−1/4 ρr. The main dependency of δH is a proportionality to the reduced density ρr, the effects of the temperature-dependent quantities being small. At three supercritical temperatures, 548 K (●), 623 K (▲), and 673 K (◼) the values of δH increase as a function of the pressure, but are much smaller than those for subcritical ethanol.

solubility in sub- and supercritical ethanol

Republished with permission from Elsevier from https://doi.org/10.1016/j.jct.2018.06.023

The total (Hildebrand) solubility parameter is related to the partial (Hansen) parameters as: δH2 = δd2 + δp2 + δhb2. At elevated temperatures and pressures the partial solubility parameters vary with the molar volume according to expressions that involve those for the reference conditions (ambient temperature and pressure): for dispersion δd ref = 15.81 MPa1/2, for polarity δp ref = 8.80 MPa1/2, and for hydrogen bonding δhb ref= 19.43 MPa1/2 and the reference molar volumeis Vref = 58.7 cm3 mol−1. The relative sizes of the partial solubility parameters are δhb (squares) > δd (triangles) > δp (circles) and they diminish as the temperature is raised, but for supercritical conditions (at 20 MPa, black symbols) they increase with the pressure.

solubility in sub- and supercritical ethanol

Republished with permission from Elsevier from https://doi.org/10.1016/j.jct.2018.06.023

According to Hansen, the solubility sphere in three dimensions with a radius Ra describes whether the solubility of a solute (subscript S) in ethanol (subscript E) is good or not: (Ra)2 = 4(δdS– δdE)2 + (δpS– δpE)2 + (δhbS– δhbE)2. Values of the parameters for the solute that provide squares of the differences that reside inside the sphere denote good solubility and outside it denote poor solubility.

Desulfurization is one aspect of the application of supercritical fluids to coals. Chinese coals are rich in sulfur, and a high ranking coal with 4.0 wt% sulfur was treated with supercritical ethanol at 673 K and 12 MPa. Desulfurization of Thai low-ranking coal requires the addition of potassium hydroxide to the supercritical ethanol  and up to 48% of the sulfur could be removed at 623 K and 8.3 MPa of supercritical ethanol. The creation of liquid fuels from coal is another aspect: the conversion of South African coals to liquid and gaseous products by extraction with ethanol at 723 K and 20 MPa resulted in 25.5 % conversion. Supercritical extraction at 673 K with ethanol at 11.9 MPa of Illinois No. 6 bituminous coal converted 17.5 % to liquid products. Brazilian coals were extracted by supercritical ethanol with a recovery of >40% of liquid and gaseous products.

Bio-active products are apt to decompose at very high temperatures, hence supercritical extraction is replaced by pressurized liquid extraction (PLE) or accelerated solvent extraction (ASE) with subcritical hot ethanol at elevated pressures. Anti-oxidants, such as carotenoids and polyphenols from microalgae, have been obtained by the PLE technique: at 383 and 443 K from spirulina platensis, at 313, 373 and 433 K from dunaliella salina, and at 323, 373, 423, and 473 K from haematococcus fluvialis. An increase in the temperature enhanced the yield but was deleterious to the antioxidant activity. Application of pressurized ethanol to olive leaves at 423 K and to spent coffee grounds at 468 K produced polyphenolic antioxidants and extraction of anthocyanin antioxidants from Brazilian jabuticaba skins required pressurized ethanol at 5 to 15 MPa and 313 to 393 K. Ketones of polycyclic aromatic hydrocarbons were obtained from contaminated soil by PLE with ethanol at 373 K and 15 MPa.

All these examples reflect the desirability to know the (partial or even only the total) solubility parameters of ethanol, whether sub- or supercritical, for the prior estimation of its suitability for the planned extraction. The corresponding values for the potential solutes are generally available in the literature.

These findings are described in the article entitled Total and partial solubility parameters of sub- and supercritical ethanol, recently published in the Journal of Chemical Thermodynamics. This work was conducted by Yizhak Marcus from The Hebrew University of Jerusalem.

TECH NEWS RELATED

NASA JPL Says Voyager 1 Spacecraft Seem to Be Mysteriously Confused With Data

NASA experts are investigating a mystery with Voyager 1 spacecraft’s telemetry data. In a statement, the space agency said that the Voyager 1 probe, which is presently 14.5 billion miles beyond Earth, is receiving and executing orders from a NASA team on Earth and transmitting back science data. However, data from ...

View more: NASA JPL Says Voyager 1 Spacecraft Seem to Be Mysteriously Confused With Data

China will soon launch a huge space telescope with a 2.5 billion-pixel camera

China’s first large space telescope could launch as soon as 2023. The new telescope will be called the Chinese Space Station Telescope. It will be roughly comparable to NASA’s long-standing Hubble Space Telescope, though its field of view will be somewhat larger. China’s first large space telescope could launch ...

View more: China will soon launch a huge space telescope with a 2.5 billion-pixel camera

Physicists Control Reactions With Laser Light at the Nanoscale

A nanoparticle in the field of a femtosecond laser pulse with tailored waveform and polarization. The controlled enhancement of the field in specific nanoscopic regions of the nanoparticle (yellow spots) induces site-selective photochemical reactions of the molecules adsorbed on the surface. Imaging of the molecular fragments emitted from these ...

View more: Physicists Control Reactions With Laser Light at the Nanoscale

Solar Orbiter Captures New Before Seen Footage of the Sun

The new videos that were captured by the ESA and NASA’s Solar Orbiter show the Sun in a brand-new light. The said videos were captured during the probe’s first close perihelion passages. This is the first time that the space probe will zoom in on the Sun’s details. New ...

View more: Solar Orbiter Captures New Before Seen Footage of the Sun

What Is Monkeypox? A Microbiologist Explains What’s Known About This Disease

The first human case of monkeypox was recorded in 1970 in the Democratic Republic of the Congo (DRC) during a period of intensified effort to eliminate smallpox. Credit: CDC On May 18, 2022, Massachusetts health officials and the Centers for Disease Control and Prevention (CDC) confirmed a single case ...

View more: What Is Monkeypox? A Microbiologist Explains What’s Known About This Disease

Novel Preclinical Drug Could Have Potential to Combat Depression, Brain Injury, and Cognitive Disorders

Summary: A preclinical drug that inhibits the kinase enzyme Cdk5 may have the potential to treat depression, brain injuries, and disorders associated with cognitive impairment. Source: University of Alabama Birmingham James Bibb, Ph.D., and colleagues have described a novel preclinical drug that could have the potential to combat depression, brain ...

View more: Novel Preclinical Drug Could Have Potential to Combat Depression, Brain Injury, and Cognitive Disorders

Ruminating on Our Ruminations Causes More Depression

Summary: Negative metacognitions and rumination can exacerbate symptoms of depression, researchers say. Source: NTNU Once you have depressive symptoms, it’s easy to fall into a pattern where you aggravate the disorder by ruminative thinking. One of the key issues is what is called negative metacognitions, a phrase that needs an ...

View more: Ruminating on Our Ruminations Causes More Depression

Sixth child in US dies of unexplained hepatitis as global cases top 600

There are now over 600 cases worldwide and 15 deaths, but still no firm answers.

View more: Sixth child in US dies of unexplained hepatitis as global cases top 600

Serious spacesuit problem forces NASA to pause ISS spacewalks

Analysis of prehistoric feces shows Stonehenge people had parasites

Climate Crisis Is Driving Cousins of Zazu, From the Lion King, to Local Extinction

Brain Mechanism Tied to Age-Related Memory Loss Discovered

In Defense of Bread – The “Staff of Life” Throughout History

Unique quantum material could enable ultra-powerful, compact computers

Unraveling a perplexing explosive process that occurs throughout the universe

Geothermal drilling successes offer potential gain for petroleum industry

Where do "Hawaiian box jellies" come from?

All-optical phase recovery and quantitative phase imaging performed instantly without a computer

Researchers demonstrate organic crystals can serve as energy converters for emerging technologies

New Research Challenges Established Ideas About Infant Crying

OTHER TECH NEWS

Top Car News Car News