Supercritical Carbon Dioxide Solvent Research Articles

Novel reaction systems for catalytic synthesis of structured phospholipids.

Phospholipids are distinctive, adaptable molecules that are crucial to numerous biological systems. Additionally, their various architectures and amphiphilic characteristics support their unrivaled crucial functions in scientific and industrial applications. Due to their enormous potential for use in the fields of medicine, food, cosmetics, and health, structured phospholipids, which are modified phospholipids, have garnered increased attention. Traditional extraction methods, however, are pricy, resource-intensive, and low-yielding. The process of enzyme-catalyzed conversion is effective for producing several types of structured phospholipase. However, most frequently employed catalytic procedures involve biphasic systems with organic solvents, which have a relatively large mass transfer resistance and are susceptible to solvent residues and environmental effects due to the hydrophobic nature of phospholipids. Therefore, the adoption of innovative, successful, and environmentally friendly enzyme-catalyzed conversion systems provides a new development route in the field of structured phospholipids processing. Several innovative catalytic reaction systems are discussed in this mini-review, including aqueous-solid system, mixed micelle system, water-in-oil microemulsion system, Pickering emulsion system, novel solvent system, three-liquid-phase system, and supercritical carbon dioxide solvent system. However, there is still a glaring need for a thorough examination of these systems for the enzymatic synthesis of structural phospholipids. In terms of the materials utilized, applicability, benefits and drawbacks, and comparative effectiveness of each system, this research establishes further conditions for the system's selection. To create more effective biocatalytic processes, it is still important to build green biocatalytic processes with improved performance. KEY POINTS: • The latest catalytic systems of phospholipase D are thoroughly summarized. • The various systems are contrasted, and their traits are enumerated. • Different catalytic systems' areas of applicability and limitations are discussed.

Solubility Modeling of Some Chlorophenols in Supercritical Carbon Dioxide

The basic information required to implement any supercritical processes is solubility. The solubility data is correlated with various models. For binary systems (solute-solvent), solubility data is limited in the literature, which makes it’s modelling essential. Equation of state (EoS) method is one of the best techniques to model solubility data. For EoS modelling to be implemented, critical properties of the solute and the solvent are essential but, the exact realistic properties are sparse for solutes. The present work deals with the modelling of the solubility of solid solutes in supercritical carbon dioxide solvent with and without critical properties of the solute. Redlich-Kwong (RK) EoS along with Kwak-Mansoori (KM) mixing rules is used for the solubility data modelling. In this work, three substituted phenols and supercritical carbon dioxide systems are considered for modelling. Finally, the correlating abilities of RK EoS along with KM mixing rules with and without critical properties of the solute are indicated in terms of the average absolute relative deviation percentage (AARD%) and Akaike information criterion (AIC).

Two-dimensional ruthenium nanoparticles between graphite layers: The effect of reduction temperature

A mixture of graphite powder and ruthenium chloride (III) anhydrous was treated at 723 K under 0.3 MPa chlorine for 3 days, followed by reduction under 40 kPa of hydrogen for 1 h to produce ruthenium metal particles intercalated between graphite layers (Ru-GIC). The structures of ruthenium particles depended on the reduction temperatures. Sheet-like ruthenium particles with 1–3 nm thickness and 10 to several hundred nm width containing numerous irregularly shaped holes with round edge, were formed by reduction at 573 K. A Ru-GIC sample treated at 653 K possessed two-dimensional ruthenium nanosheets with hexagonal holes (straight lines intersect at an angle of 120°) in a similar range of thickness and width. On the other hand, Ru-GIC samples reduced at 773 and 823 K showed two-dimensional plate morphology with a thickness of 1–4 nm. In addition, ruthenium nanoparticles supported on the graphite surface (Ru/Gmix) were also prepared from a slurry of ruthenium chloride (III) hydrate and graphite powder by impregnation and hydrogen reduction. The ruthenium particles in Ru/Gmix were spherical at about 3.6 nm, and the reduction temperature did not affect their particles size. Both Ru-GIC and Ru/Gmix samples were evaluated for cinnamaldehyde (CAL) hydrogenation in supercritical carbon dioxide solvent at 323 K, and they were active to produce cinnamyl alcohol (COL) and hydrocinnamaldehyde (HAL). However, Ru-GIC samples showed higher COL selectivity than Ru/Gmix prepared at the same reduction temperature, and COL selectivity over Ru-GIC increased with the reduction treatments at 773 and 823 K.

The Role of Hidden Conformers in Determination of Conformational Preferences of Mefenamic Acid by NOESY Spectroscopy.

Mefenamic acid has been used as a non-steroidal anti-inflammatory drug for a long time. However, its practical use is quite limited due to a number of side effects on the intestinal organs. Conformational polymorphism provides mefenamic acid with unique properties regarding possible modifications obtained during the micronization process, which can improve pharmacokinetics and minimize side effects. Micronization can be performed by decompression of supercritical fluids; methods such as rapid expansion of the supercritical solution have proven their efficiency. However, this group of methods is poorly applicable for compounds with low solubility, and the modification of the method using a pharmaceutically suitable co-solvent may be useful. In our case, addition of only 2 mol% dimethyl sulfoxide increased the solubility remarkably. Information on the conformational state may be critically important for carrying out micronization. In this work, structural analysis and estimate of conformational preferences of mefenamic acid in dimethyl sulfoxide-d6 (at 25 °C and 0.1 MPa) and in a mixed solvent supercritical carbon dioxide + dimethyl sulfoxide-d6 (45 °C, 9 MPa) were performed based on nuclear Overhauser effect spectroscopy. Results show changes in the conformation fractions depending on the medium used. The importance of allowing for hidden conformers in estimating the conformational state was demonstrated in the analysis. Obtained results may be useful for improving micronization parameters.

Supercritical fluid extraction with cosolvent of alkaloids from Lupinus mutabilis Sweet and comparison with conventional method

AbstractThe purpose of this study was to evaluate the use of supercritical fluid extraction with cosolvent (SFE‐co) as an alternative process in the extraction of lupin alkaloids. A sample of crushed Lupinus mutabilis Sweet seeds, with a high content of alkaloids, was treated using aqueous extraction (AQE) and SFE‐co, where the effect of the operating conditions and the solvent in the SFE‐co were evaluated applying a factorial design. Results showed that both methods reduced the content of total alkaloids in the lupin seed, ensuring its safe consumption. SFE‐co got an extraction yield (39.19 ± 0.14 mg/g) comparable with AQE (39.22 ± 0.16 mg/g) at a temperature of 323 K, a pressure of 27 MPa, using as a solvent supercritical carbon dioxide (scCO2) and dilute ethanol solution, but limited to a fraction of the treated sample. SFE‐co, unlike AQE, was able to keep the nutritional value of the lupin seeds, reducing the time process from 235 hr (AQE) to 2.5 hr, assuring the non‐use of an excessive amount of water and hazardous solvents. Moreover, the fractions formed in the extraction vessel by SFE‐co allowed the understanding of the extraction mechanism of different components from a complex matrix related to their chemical polarity.Practical ApplicationsThis study shows that it is possible to remove lupin alkaloids with green technology as supercritical fluid extraction with cosolvents, reaching extraction yields comparable with the conventional method (aqueous extraction), keeping the nutritional value of the sample, saving time and resources. However, working with a larger quantity of material than the usual used in a laboratory showed an inhomogeneous extraction of alkaloids from the sample, limiting the optimal extraction yield to one of the fractions formed. This reveals a future problem in the use of this technology at an industrial level, where the characteristics of the extracts are not only important but also the material treated since, in the lupin industry, the debittered seed and the released alkaloids are useful in the food and pharmaceutical industries, respectively.

Response Surface Methodology Towards Optimization of Calotropis Procera Essential Oil Extraction by Using Supercritical CO2

Aim: In this research, we aim to investigation on the extraction of essential oil from Calotropis Procera with the family name of Asclepiadaceae, by supercritical carbon dioxide (CO2) solvent. Objective: The comparison of the yield and chemical profile of the extracts achieved by this method with those resulted by the conventional Hydro distillation method. Methods: The extraction experiments were carried out in a bench-scale SC-CO2 unit. The effects of temperature, pressure, and extraction time on the oil yield are considered for investigation. The Response Surface Methodology (RSM) with Central Composite Design (CCD) was employed to optimize the process parameters of CO2 supercritical extraction (SCE) of the Calotropis Procera. In this experimental design, the design was required 19 experiments with eight (23) factorial points and five replications of the center. Results: Results showed that the data were sufficiently fitted into the second-order polynomial model. The extraction conditions, including pressure, temperature, and extraction time, were studied between 150-200 bar, 40-50 ºC, and 50-100 min, respectively. Conclusion: The optimal conditions are achieved as the temperature of 47.19ºC, the pressure of 172.2 bar, and time of 86 minutes with the retrieval rate of 31.39%.

Review on green solvent supercritical carbon dioxide and its chemical reactions

Review on green solvent supercritical carbon dioxide and its chemical reactions

Preparation and Structural Characterization of Platinum Nanosheets Intercalated between Graphite Powder with High Surface Area

Synthesis of platinum nanoparticles intercalated between layers of commercially available graphite powder samples possessing surface area values ranging from 20 to 750 m2 g-1 was attempted by the insertion of platinum chloride between the layers followed by hydrogen reduction. Platinum nanosheets with 1-4 nm thickness and 5-300 nm width and hexagonal holes were obtained for the graphite powder with 20 m2 g-1 independent of the platinum loadings (5, 10, and 15 wt%). Platinum nanosheets with the similar size (1-4 nm thickness and 5-300 nm width) and hexagonal holes were formed for graphite powder with 120 and 300 m2 g-1 with only 15 wt% platinum loading, but not for 5 and 10 wt% platinum loadings. Interestingly, for the graphite powder with higher surface area of 500 and 750 m2 g-1, platinum nanosheets were not formed. Platinum nanosheets intercalated between graphite samples were evaluated for cinnamaldehyde hydrogenation in supercritical carbon dioxide solvent. High cinnamyl alcohol selectivity was obtained for the platinum nanosheets intercalated between graphite layers having surface area of 20 m2 g-1; however, hydrocinnamaldehyde selectivity was high for the platinum nanosheets intercalated between graphite samples having surface area of 120 m2 g-1.

Cryogenic drilling of aluminum-based printed circuit boards: a review and analysis

An aluminum-based printed circuit board (Al-PCB) is a composite material comprising a copper layer, an insulating layer, and an aluminum base layer. In the drilling of Al-PCBs, exit burrs are formed because of the plastic deformation of the remnant aluminum under high drilling temperatures. In this work, a new method using cryogenic media is suggested to prevent exit burrs in Al-PCB drilling. The effects of cryogenic media, such as cold air, supercritical carbon dioxide solvent (scCO2), and liquid nitrogen (LN2), on the drilling temperature, chip removal, tool wear and exit burr formation were observed and analyzed. The Al-PCB drilling temperature could be effectively reduced when drilling with cold air, scCO2 or LN2. The chip removal and tool wear could be improved when drilling with cold air or LN2. The exit burr formation when drilling with scCO2 or LN2 was greater than that when drilling under cooling and cold air conditions. A cold air matching composite wood backup board (MW-0.5) could effectively control the exit burr formation within 20 μm. This is the first study on the effects of three different cryogenic media on PCB drilling and is expected to provide a good reference for the cryogenic drilling of PCBs.

Graphite Intercalated Iridium Nanodisks for Cinnamaldehyde Hydrogenation

Disk-shaped metal particles having 1–3 nm thickness and 1–14 nm diameter were prepared by the reduction of iridium chloride intercalated between graphite layers. These iridium nanodisks between graphite layers showed higher activity for cinnamaldehyde hydrogenation and higher selectivity towards cinnamyl alcohol compared with those of iridium particles on graphite surface in supercritical carbon dioxide solvent.

Cover Feature: Stereoselective Aromatic Ring Hydrogenation over Supported Rhodium Catalysts in Supercritical Carbon Dioxide Solvent (9/2019)

Cover Feature: Stereoselective Aromatic Ring Hydrogenation over Supported Rhodium Catalysts in Supercritical Carbon Dioxide Solvent (9/2019)

Engineered microbial biofuel production and recovery under supercritical carbon dioxide

Culture contamination, end-product toxicity, and energy efficient product recovery are long-standing bioprocess challenges. To solve these problems, we propose a high-pressure fermentation strategy, coupled with in situ extraction using the abundant and renewable solvent supercritical carbon dioxide (scCO2), which is also known for its broad microbial lethality. Towards this goal, we report the domestication and engineering of a scCO2-tolerant strain of Bacillus megaterium, previously isolated from formation waters from the McElmo Dome CO2 field, to produce branched alcohols that have potential use as biofuels. After establishing induced-expression under scCO2, isobutanol production from 2-ketoisovalerate is observed with greater than 40% yield with co-produced isopentanol. Finally, we present a process model to compare the energy required for our process to other in situ extraction methods, such as gas stripping, finding scCO2 extraction to be potentially competitive, if not superior.

Stereoselective Aromatic Ring Hydrogenation over Supported Rhodium Catalysts in Supercritical Carbon Dioxide Solvent.

The combination of supported rhodium metal catalysts and supercritical carbon dioxide solvent was effective for the stereoselective ring hydrogenations of aromatic compounds at low temperature. Higher solubility of hydrogen in supercritical carbon dioxide provides higher concentration of hydrogen on the rhodium surface, but lower that of the intermediate on rhodium surface, which suppresses the flipping of surface intermediate, leading to higher catalyst activities and cis selectivities to the corresponding ring-hydrogenated products as compared with those in organic solvents.

Highly effective impregnation and modification of spruce wood with epoxy-functional siloxane using supercritical carbon dioxide solvent

Chemical modification of wood is an established approach to improve its biological durability, water repellence, dimensional stability, and UV resistance. Norway spruce wood (Picea abies) in dry state, however, has an extraordinarily high recalcitrance towards impregnation with liquid modification reagents as drying triggers the irreversible closure of pits, i.e. the cell-to-cell valves in softwood. In the present study, it is shown that supercritical carbon dioxide is a highly suitable impregnation medium to overcome the recalcitrance of dry spruce wood. This has been exemplarily demonstrated for deca(dimethylsiloxane)-α,ω-diglycidylether (D8M 2 OG ), a linear oligosiloxane with terminal epoxy-functionalities, which could be loaded into respective wood samples affording a weight gain of up to 63%. The thermally assisted reaction of the epoxy-functional siloxane with the wood polymers was catalysed with ring-opening Tin (II) octoate. The effort resulted in a remarkably reduced wettability with water, as evident from contact angle measurements (~ 140°), and in a significant decrease (≤ 20%) of the sample’s sensitivity towards moisture-induced dimensional changes.

Cinnamaldehyde Hydrogenation over Platinum Nanosheet Intercalated Graphite Layers in Supercritical Carbon Dioxide Solvent

Abstract Cinnamaldehyde hydrogenation behaviors of platinum nanosheets intercalated between graphite layers (Pt-GIC) were studied and compared with those of platinum particles on graphite surface (Pt/Gmix) in supercritical carbon dioxide solvent at 323 K. The conversions of cinnamaldehyde of Pt-GIC were lower than those of Pt/Gmix; however, the cinnamyl alcohol yields were higher than those of Pt/Gmix at similar conversions. Carbon dioxide solvent would carry hydrogen and cinnamaldehyde molecules to the edge sites of platinum nanosheets located between graphite layers, which are selective sites for the cinnamyl alcohol production.

Hollow Microcrystals of Copper Hexafluoroacetylacetonate-Pyridine Derivative Adducts via Supercritical CO2 Recrystallization

An innovative crystallization process, based on the use of the ecofriendly supercritical carbon dioxide (scCO2) solvent, is presented for the production of coordination compound macrocrystals of general formula [Cu(hfacac)2(dPy)2], with intriguing prismatic hollow structures and single polymorphic forms. In contrast, conventional solvents yielded compact microstructures. The studied pyridine derivatives (dPy) were 4-phenylpyridine, PhPy; 4-benzylylpyridine, BzPy; and 4-acetylpyridine, AcPy. In the specific case of the [Cu(hfacac)2(AcPy)2] adduct, the use of scCO2 as a solvent allowed obtaining a pure polymorph, while the conventional solvent trials yielded a mixture of two polymorphs. Four new crystalline structures have been resolved from single crystal X-ray diffraction. All the structures consist of mononuclear complexes connected through intermolecular interactions, including H···H, H···O, F···F, C–F···Caromatic, and/or C–F···π interactions, generating bi-dimensional networks that determine their crystallization mode in scCO2.

Driving Forces Controlling Host-Guest Recognition in Supercritical Carbon Dioxide Solvent.

The formation of supramolecular host-guest complexes is a very useful and widely employed tool in chemistry. However, supramolecular chemistry in non-conventional solvents such as supercritical carbon dioxide (scCO2 ), one of the most promising sustainable solvents, is still in its infancy. In this work, we explored a successful route to the development of green processes in supercritical CO2 by combining a theoretical approach with experiments. We were able to synthesize and characterize an inclusion complex between a polar aromatic molecule (benzoic acid) and peracetylated-β-cyclodextrin, which is soluble in the supercritical medium. This finding opens the way to wide, environmental friendly, applications of scCO2 in many areas of chemistry, including supramolecular synthesis, reactivity and catalysis, micro and nano-particle formation, molecular recognition, as well as enhanced extraction processes with increased selectivity.

Adsorption of Bitumen Model Compounds on Kaolinite in Liquid and Supercritical Carbon Dioxide Solvents: A Study by Periodic Density Functional Theory and Molecular Theory of Solvation

The geometry of phenanthridine, benzothiophene, tetralin, and naphthalene representative of the heterocyclic, naphthenic, and aromatic components of bitumen adsorbed on kaolinite is optimized using density functional theory and periodic boundary conditions in gas phase. These bitumen model compounds preferentially adsorb on the aluminum hydroxide surface of kaolinite with energy decreasing in the order phenanthridine > naphthalene > tetralin ∼ benzothiophene. The adsorption of phenanthridine is strengthened by hydrogen bonding between the pyridinic N atom and an axial hydroxyl group of kaolinite, while the rest of the molecules adsorb through van der Waals interactions. The mechanism of solvation in CO2 and the effect of liquid and supercritical CO2 on the adsorption thermodynamics are studied using the three-dimensional reference interaction site model theory with the closure approximation of Kovalenko and Hirata (3D-RISM-KH) molecular theory of solvation at 293–333 K and 10–30 MPa. The CO2 solvent inter...

Enzymatic synthesis of poly(ɛ-caprolactone) in supercritical carbon dioxide medium by means of a variable-volume view reactor

Poly (ɛ-caprolactone) (PCL) is a biodegradable polyester approved for applications in the human body such as drug delivery devices and sutures. Conventional synthesis of PCL involves metal catalysts and organic solvents that may leave toxic residues in the products and contribute to environmental pollution. Polymerization processes catalyzed by enzymes are becoming more attractive due to the importance of clean processes, which produces substances free of residues, ideal for pharmaceutical and food applications. The aim of this work was to investigate the enzymatic ring-opening polymerization (e-ROP) of PCL in supercritical carbon dioxide (scCO2) solvent medium through a set of experiments assessing the influence of pressure (120–280bar), solvent/monomer ratio (2:1–1:2 mass ratio) and enzyme percentage related to monomer (5–15wt%) on the reaction yield, number-average molecular weight (Mn), weight-average molecular weight (Mw) and polydispersity index (P.I.). The results of these first experiments were used in the selection of the conditions for the kinetic experiments evaluating the influence of catalyst content and temperature on reaction yield, Mn, Mw, P.I. and on the characteristics of the polymer produced. This study also evaluates the enzyme reuse in order to reduce the impact of the enzyme cost on the process. Results for ANOVA statistical analysis for the first set of experiments show that the pressure or the solvent density has no significant influence over the parameters evaluated, while the solvent/monomer mass ratio presented significant effect on Mn and on Mw, with the best results obtained for the solvent/monomer mass ratio of 1:2. As expected, the enzyme content affects significantly all parameters evaluated. Polymerization results for the kinetic experiments indicate reaction yields up to 90wt%, Mn up to 13,700Da and Mw up to 22,200Da, with P.I. ranging from 1.2 to 1.7. Taking into account the reaction productivity, the conditions for the reuse assays were chosen: 120bar, 1:2 solvent/monomer ratio, 3wt% of enzyme, 65°C and 12h of reaction. The enzyme recycling experiments suggested viability up to the second cycle as an alternative to improve the enzyme use. The variable-volume view reactor was adequate to provide simultaneous control of the process variables.

Hydrogenation of Anthracene in Supercritical Carbon Dioxide Solvent Using Ni Supported on Hβ-Zeolite Catalyst

Catalytic hydrogenation of anthracene was studied over Ni supported on Hβ-zeolite catalyst under supercritical carbon dioxide (sc-CO2) solvent. Hydrogenation of anthracene in sc-CO2 yielded 100% conversion at 100 °C, which is attributed to the reduced mass transfer limitations, and increased solubility of H2 and substrate in the reaction medium. The total pressure of 7 MPa was found to be optimum for high selectivity of octahydroanthracene (OHA). The conversion and selectivity for OHA increased with an increase in H2 partial pressure, which is attributed to higher concentration of hydrogen atoms at higher H2 pressures. The selectivity reduced the pressure below 7 MPa because of enhanced desorption of the tetrahydro-molecules and intermediates from Ni active sites, due to higher solubility of the surface species in sc-CO2. The selectivity of OHA increased with the increase in catalyst weight and reaction time. The rate of hydrogenation of anthracene was compared with that found for napthalene and phenanthrene. The use of acetonitrile as co-solvent or expanded liquid with CO2 decreased the catalytic activity.