Pure scCO2 Research Articles

Recent Advances of Supercritical CO2 in Green Synthesis and Activation of Metal–Organic Frameworks

This review considers the recent advancements of using supercritical carbon dioxide (scCO2) in the synthesis and activation of metal-organic frameworks (MOFs). The first section outlines MOF synthesis by scCO2-based methods; pure scCO2 system, and also in conjunction with a co-solvent, auxiliary ligand, expandable solvent or an ionic liquid. This is followed by elaborating on MOF activation techniques that employed scCO2, be it independently or together with thermal activation. The third section considers the effects of scCO2 on MOF and polymer structures. To conclude, projections are made for current researchers in this area to better exploit scCO2 utilization.

Added-value porous materials for controlled thymol release obtained by supercritical CO2 impregnation process

This study explores utilization of biodegradable and biocompatible polymers for controlled release of natural bioactive substance. For that purpose, poly(ε-caprolactone) (PCL) beads, cellulose acetate (CA) film, and poly lactic- co-glycolic acid (PLGA) flakes were impregnated with thymol by employing environmentally friendly process of supercritical carbon dioxide (scCO2) impregnation. At selected pressure and temperature, prolongation of operating time increased thymol loading. Pure scCO2 did not affect CA film with average pore diameter of approximately 3 µm, while it enabled change of PCL beads and PLGA flakes into foams with average pore diameter approximately 175 µm and 87 µm, respectively. Additionally to scCO2, thymol acted as a plasticizer increasing pore size of polymers up to three times. Kinetic of thymol release from selected samples was tested using phosphate buffer saline at 37°C and successfully described with Korsmeyer–Peppas, zero-order, first-order, and Higuchi models. The suggested method of PCL, CA, and PLGA supercritical impregnation led to development of porous, solvent free, added-value materials that release thymol in a controlled manner from 5 h to several days.

Analysis of the antitumor activity of bioactive compounds of Cannabis flowers extracted by green solvents

The inhibitory effects of Cannabis flower extracts, obtained by supercritical carbon dioxide (scCO2) with and without modifier, on various human tumour cells and non-tumour cells were evaluated. Different techniques were used to optimize the polarity interaction between solute and solvent before extraction. An increase in the cannabinoid content of interest (CBD/THC) was evaluated by decarboxylation of the flowers at 110 and 140 °C. Extractions with pure scCO2 were conducted in a single step at temperatures of 50 and 70 °C and pressures of 22 and 40 MPa, varying the time of prior decarboxylation by 0.5 or 2.0 h. Sequential extractions were conducted in a first step at 35 °C and 10 MPa and then in a second step at 70 °C and 40 MPa, with and without modifier. Contents of the cannabinoids were evaluated using HPLC. Antitumor activity of the extracts was evaluated using the MTT assay. The highest yields and highest cannabinoid contents in the extracts were obtained with high solvent density values. Extracts with high concentrations of neutral cannabinoids showed high antitumor activity for cervical cancer cell lines.

The Hansen theory to choose the best cosolvent for supercritical CO2 extraction of β-carotene from Dunaliella salina

The Hansen solubility theory was used to predict the best cosolvent for supercritical carbon dioxide (sc-CO2) to achieve the selective extraction of β-carotene from Dunaliella salina. Among four organic cosolvents, ethanol was predicted to be the best based on minima Ra values. The predictions were validated through equilibrium data and extraction curves from the microalgae. The addition of ethanol reduced the bubble pressures, and therefore increased the solubility of the β-carotene. With 5% mass fraction, at 318.15 K and 20 MPa, the extraction yield was 25 g carotenoids kg microalgae−1, much more than in pure sc-CO2 (6 g).

Solubility of caffeic acid in CO2 + ethanol: Experimental and predicted data using Cubic Plus Association Equation of State

This work evaluated the solubility of caffeic acid (CA) in mixtures of supercritical carbon dioxide (scCO2) and ethanol at different temperatures (313, 323 and 333 K), pressures (20, 30 and 40 MPa) and concentrations of ethanol (2.2, 5.4 and 10.2 mol%). The Soave-Redlich-Kwong and Cubic Plus Association (CPA) equations of state were used to correlate the binary mixture data and to predict the ternary system data. CA solubility in ethanol is approximately 106 times higher than its solubility in pure scCO2. By using 10.2 mol% ethanol in scCO2, CA solubility increased 30,000 times at 313 K and 20 MPa. Both models provided reasonable descriptions of the experimental data for the binary systems. However, CPA-EoS can better describe the strong interactions between acid molecules and ethanol, and can predict that the addition of small amounts of ethanol to scCO2 provides a large increase in CA solubility.

Laboratory experiment on a toluene-polydimethyl silicone thickened supercritical carbon dioxide fracturing fluid

Supercritical carbon dioxide (SCCO2) fracturing fluid is an excellent application in CO2 re-use. It has many advantages than water-based fracturing fluids. However, the low viscosity hinders its application in unconventional oil and gas reservoirs. Therefore, we tried to improve the property of SCCO2 fracturing fluid by increasing the viscosity. A thickened SCCO2 fracturing fluid was constructed and the fracturing property of the fracturing fluid was investigated. The fracturing fluid consisted of toluene (cosolvent), polydimethyl silicone (thickener) and SCCO2. In SCCO2, toluene and polydimethyl silicone obtain low miscible pressure at 42 °C. In addition, the constructed fracturing fluid system obtains higher viscosity value (as high as 1.5 mPa·s), which can be 40 times high than the viscosity of pure SCCO2 at 42 °C and 20 MPa. These features match the viscosity requirement as a fracturing fluid. Molecular dynamics (MD) simulations were carried out to study the solubility parameter of the fracturing fluid system in molecular level. These MD simulation results show that, as a cosolvent, toluene helps polydimethyl silicon dissolve in SCCO2, which is consistent with laboratory experiment results. Moreover, the studied fracturing fluid obtains good properties as a fracturing fluid in terms of high proppant carrying capability, low fluid leakoff coefficient, and low formation damage rate.

Copper(II)/Palladium(II) catalysed highly selective cross-coupling of terminal alkynes in supercritical carbon dioxide

An efficient protocol for the synthesis of unsymmetrical 1,3-diynes was developed using supercritical carbon dioxide (ScCO2) as the solvent. The direct coupling of two different terminal alkynes is catalysed by a bimetallic catalyst, CuCl2·2H2O/Pd(NH3)4Cl2·H2O, in the presence of the base tetramethylethylenediamine (TMEDA) and O2. In pure ScCO2, our bimetallic catalytic system maintains high activity over a wide substrate scope to provide unsymmetrical 1,3-diynes in good to excellent yields. In the proposed reaction mechanism, the synergistic cooperation between copper(II) and palladium(II) centres is responsible for the superior selectivity of the cross-coupling.

Supercritical CO2 extraction in chia oils production: impact of process duration and co-solvent addition

This study was conducted to show impact of supercritical fluid extraction using pure SC-CO2 or SC-CO2 enriched by 2, 6, and 10% of acetone, simultaneously varied by the extraction time (1 vs. 5 h), on the quality of chia seed oils. Obtained oils were relatively similar in the fatty acid composition, but they differed in total content of phytochemicals (from 4956 to 6391 mg/kg of oil). Among them, three oils were the most different: oil extracted 1 h with pure SC-CO2 (the most abundant in squalene, sterols, and tocopherols), oil extracted 5 h with pure SC-CO2 (the poorest in squalene, polyphenols, and carotenoids, with medium level of sterols and tocopherols) and oil extracted 1 h with SC-CO2 enriched by 10% acetone (the most abundant in polyphenols and carotenoids). Such unique chia oils can be valuable for special market needs, such as cosmetics, pharmaceuticals, functional food or diet supplement production.

Separation of major and minor lipid components using supercritical CO2 coupled with cross-flow reverse osmosis membrane filtration

A reverse osmosis polyamide membrane was used to test the feasibility of concentrating triacylglycerol (TAG) and α-tocopherol/β-sitosterol from model mixtures (Oleic Acid (OA)/TAG and OA/α-tocopherol/β-sitosterol, respectively) solubilized in SC-CO2 using cross-flow filtration regime. SG membrane was used for up to 26 h at pressures of 120 and 280 bar and temperature of 40 °C and its performance was measured in terms of CO2 flux and separation factor at a transmembrane pressure of 10 bar. Increasing the pressure to 280 bar resulted in a higher reduction in CO2 flux in comparison to that at 120 bar, which was attributed to fouling. CO2 flux was reestablished after cleaning with pure SC-CO2. Feed pressure of 120 bar showed the best separation factors, where the OA separation factor was higher than 1 and those for TAG and α-tocopherol/β-sitosterol were less than 1. The preferential permeation of OA through the reverse osmosis membranes in comparison to TAG and α-tocopherol/β-sitosterol could be attributed to the higher diffusivity of this smaller molecular weight compound and the effect of plasticization and swelling of the membrane upon exposure to SC-CO2. The cross-flow regime efficiently reduced the extent of fouling and subsequent decline of permeate flux. The findings demonstrate the potential to separate bioactive components present in vegetable oil deodorizer distillate and/or to deacidify vegetable oils using coupled supercritical and membrane technologies.

Utilization of the integrated process of supercritical extraction and impregnation for incorporation of Helichrysum italicum extract into corn starch xerogel

Supercritical CO2 extraction of Helichrysum italicum and impregnation of starch xerogels with the extract by using an integrated scCO2 extraction and impregnation process were performed at 350 bar and 40?C in order to produce biomaterials for possible oral intake of the extract. Xerogels produced by air-drying of acetogels and alcogels were used as carriers in the supercritical impregnation process. The effect of ethanol as a co-solvent, contact time, plant material/carrier mass ratio and xerogel preparation on the impregnation loading was studied. The highest impregnation loading (1.26?0.22%) was achieved after 5 h impregnation of the xerogel obtained from alcogel using pure scCO2 and plant material/ /carrier mass ratio of 10. Chemical analysis of the extracts showed that the addition of ethanol as co-solvent had a positive effect on scCO2 selectivity to terpene fraction and total flavonoids, while it lowered the total phenolic content. Despite the difference in chemical composition, both extracts expressed similar antioxidant activity according to the DPPH and FRAP methods. The integrated process was shown to be a feasible method for isolation and incorporation of bioactive components of H. italicum into starch xerogels.

Challenges in the production of pharmaceutical and food related compounds by SC-CO2 processing of vegetable matter

The recovery of active ingredients from vegetable matter is one of the most attractive research fields in the literature. The perspective that moves this large interest, is the possibility to selectively solubilize the compounds of interest in SC-CO2 and to avoid the use of organic solvents that pollute the environment, the products and the processed material. Nevertheless, care must be devoted in selecting process arrangement and extraction conditions, minimizing co-extracted compounds. Fractional extraction and/or fractional separation should be a possible solution. The addition of a co-solvent has been proposed in the case of less soluble compounds in pure SC-CO2; but, the so-called supercritical antisolvent extraction could represent a valuable solution for these compounds.

Study on the solubility parameter of supercritical carbon dioxide system by molecular dynamics simulation

The enhancement of the solubility parameter of supercritical carbon dioxide plays pivotal role in the application of extraction operation. The solubility parameter of supercritical CO2 solvent (SC-CO2) and supercritical CO2 with cosolvent (SC-CO2-cosolvent) system have been studied using the molecular dynamics simulations (MD). The calculated results reveal that the solubility parameters of pure SC-CO2 solvent and SC-CO2-cosolvent both reduce with the raising of temperature, enhance with the raising of pressure, and boost linearly with the raising of their density. The adding of the cosolvent (methanol, ethanol, acetone and cyclohexane) into the SC-CO2 system can enhance the solubility parameter of SC-CO2 solvent significantly, and the solubility parameter boosts with the raising of the cosolvent concentration. The cosolvent effect on solubility parameter of SC-CO2 solvent decreases in the order: methanol, ethanol, acetone, cyclohexane. The hydrogen bonding ability of the cosolvent has significant effect on solubility parameter of SC-CO2 solvent via the strengthening of the interactions among the CO2 and cosolvent molecules.

Measurement and correlation study of silymarin solubility in supercritical carbon dioxide with and without a cosolvent using semi-empirical models and back-propagation artificial neural networks

The solubility data of compounds in supercritical fluids and the correlation between the experimental solubility data and predicted solubility data are crucial to the development of supercritical technologies. In the present work, the solubility data of silymarin (SM) in both pure supercritical carbon dioxide (SCCO2) and SCCO2 with added cosolvent was measured at temperatures ranging from 308 to 338 K and pressures from 8 to 22 MPa. The experimental data were fit with three semi-empirical density-based models (Chrastil, Bartle and Mendez-Santiago and Teja models) and a back-propagation artificial neural networks (BPANN) model. Interaction parameters for the models were obtained and the percentage of average absolute relative deviation (AARD%) in each calculation was determined. The correlation results were in good agreement with the experimental data. A comparison among the four models revealed that the experimental solubility data were more fit with the BPANN model with AARDs ranging from 1.14% to 2.15% for silymarin in pure SCCO2 and with added cosolvent. The results provide fundamental data for designing the extraction of SM or the preparation of its particle using SCCO2 techniques.

Effects of a Nano-Silica Additive on the Rock Erosion Characteristics of a SC-CO2 Jet under Various Operating Conditions

In order to improve the erosion capacity of a supercritical carbon dioxide (SC-CO2) jet, the influence of a nano-silica additive on the rock erosion characteristics was experimentally investigated. By impinging the SC-CO2 jets with nano-silica mass fractions of 0 wt % (pure SC-CO2 jet), 3 wt %, 6 wt %, 9 wt %, 12 wt %, 15 wt %, and 18 wt % on specimens of red sandstone, the erosion volumes under various operating conditions were measured and analyzed. Results show that an appropriate amount of nano-silica additive can greatly enhance the erosion ability of a SC-CO2 jet. The effect on the erosion ability largely depends on the operating conditions. For instance, when the other conditions are fixed, 6 wt %, 9 wt %, 12 wt %, and 15 wt % were the optimum mass fractions, successively, with the inlet pressure increasing from 30 MPa to 60 MPa. With the increase in ambient pressure, the optimum mass fraction is unchanged under the constant inlet pressure, while it increases under the constant pressure drop. Additionally, the optimum mass fraction decreases when the fluid temperature increases. In addition, the optimal standoff distances are about five times the nozzle diameter of the nano-silica SC-CO2 jet, and three times for the pure jet. This research provides a new method for effectively enhancing the rock erosion performance of a SC-CO2 jet.

Prediction of solid solute solubility in supercritical carbon dioxide with organic cosolvents from the PR+COSMOSAC equation of state

Supercritical carbon dioxide (ScCO2) plays an important role in industries, such as in the purification/crystallization processes in the pharmaceutical industry, in the extraction of natural flavors and nutrients in the food/pharmaceutical industry, and in wafer cleaning in the semiconductor industry. Therefore, the solubility of solid solutes in ScCO2, with and without organic solvents, is essential information for the design and optimization of such processes. It has been shown that PR+COSMOSAC EOS is able to provide a reasonable prediction accuracy for drug solubility in organic solvents and in ScCO2. In this study, PR+COSMOSAC EOS is applied to predict the solubility of solid solutes in mixtures of ScCO2 + organic solvents (e.g., acetone and ethanol). The solubility of 23 solid solutes in different mixtures of ScCO2 + organic solvents with pressures up to 40 MPa and temperatures ranging from 298.15 K to 353.15 K are used to evaluate the accuracy of PR+COSMOSAC EOS. The overall average logarithmic deviation (ALD-x) in the prediction of drug solubility in binary ScCO2 + organic solvent mixtures is 0.76. The accuracy is slightly better than that of the drug solubility in pure ScCO2 and similar to that in pure organic solvents. This study shows that PR+COSMOSAC EOS may be a useful tool in predicting the solubility of solid solutes when no experimental data are available.

Metallization on Silk Utilizing Supercritical Carbon Dioxide Assisted Electroless Plating for Wearable Device

According to the International Data Corporation (IDC) report [1], the worldwide wearable devices market will swell to 111.9 million networked devices sold in 2018 projecting the trend and blossom of this potential technology. To fulfill both conductivity and flexibility for wearable device, combining the conductive materials and the flexible fabrics, such as metal and polymer, becomes the greatest challenge. There are many techniques to achieve the combination, such as sputtering and evaporation. Among these, electroless plating is the most potential method owing to its eminent advantages, e.g. low processing temperature, low cost, and simple operation procedures [2]. Electroless plating consists of a pretreatment step to clean and roughen the substrate, a catalyzation step to inlay the catalyst seeds, and a plating step to carry out the metallization on the substrate. A novel catalyzation step with the assist of supercritical carbon dioxide (sc-CO2) was conducted in this study. Distinct from the conventional catalyzation, catalyzing the polymer in sc-CO2 allows exclusion of the pretreatment step and further results a defect-free and smoother surface [3]. With the outstanding self-diffusivity, high compatibility with non-polar materials, and low surface tension characteristics of sc-CO2, organo-metallic catalysts can be embedded into the polymer without damaging the structure. Furthermore, with sc-CO2, the chemical solution used in the catalyzation step can also be withdrawn, which is friendlier to the environment. In previous studies, we have proposed an electroless plating method involving Ni-P plating step on polyimide followed by catalyzation in pure sc-CO2 containing Pd (II) acetylacetonate (Pd(acac)2) [3,4]. Ni-P solution is a common electrolyte for the plating due to the advantages, such as relatively high deposition rate and high corrosion resistivity. To obtain higher mobility and the application of wearable devices, softer silk is chosen as the substrate in this study. Moreover, silk is a common material in clothes. The combination of Ni-P and silk is thus considered to be a potential candidate for the wearable devices. This work, therefore, executed the electroless plating between Ni-P and silk. A piece of the silk textile was immersed in the sc-CO2 fluid containing Pd(acac)2 at 80 oC and 15 MPa. Appropriate amount of the Pd(acac)2 catalyst was used to maintain the concentration at the saturation concentration throughout the catalyzation step. No pretreatment was conducted in this study. The plating step was thereupon being carried out on the catalyzed silks at 70 oC and atmospheric pressure in the acidic Ni-P solution. Various lengths of plating times were performed to inspect the relationship between the plating time and the properties. The surface morphology, cross-section and composition were examined by an optical microscope (OM), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDX). The phase and crystal structure were identified by an X-ray diffractometer (XRD). The electrical resistance was measured by the four-point probe method. By conducting the catalyzation in sc-CO2, smooth and uniform coverage of Ni-P coatings were successfully plated on the silk textiles under various plating times. The composition, thickness, and coverage trend increase with plating time. The composites turn out to be conductive as the plating time is extended to 2 mins. Lowest electrical resistance at 1.23 ohm can be achieved with plating time at 4 min.

Ferulic acid solubility in supercritical carbon dioxide, ethanol and water mixtures

Ferulic acid (FA) is a phenolic compound present in many natural extracts. To obtain high FA extraction yields using supercritical carbon dioxide (scCO2), the extraction should be performed in the presence of co-solvents. This work reports FA solubility in scCO2/ethanol/water mixtures and its thermodynamic modelling using the Peng-Robinson equation of state. FA solubility in scCO2/ethanol was measured by a dynamic method at different temperatures (313, 323 and 333)K, pressures (20, 30 and 40)MPa and mole ratios of the scCO2/ethanol mixture (95:5 and 90:10). FA solubility in scCO2 with ethanol and water was evaluated at 323K and 30MPa, at three different mole ratios of the scCO2/ethanol/water mixture (97.4:2:0.6, 93.5:5:1.5 and 88:9.3:2.7). Also measured was the solubility of FA in water and in ethanol at ambient pressure. By using 10% ethanol, the FA solubility in (scCO2+ethanol) attained values 120 times higher than FA solubility in pure scCO2 and about 50 times lower than solubility in ethanol. The lowest value was obtained at 313K and 20MPa and the highest at 333K and 40MPa (1.9×10−3); however, the co-solvent effect decreased when increasing pressure. Finally, the presence of the co-solvent is very important to obtain natural extracts rich in ferulic acid. The prediction of FA solubility in ternary and quaternary systems using the binary interaction parameters did not produce good results. Calculated values were smaller than the experimental values, probably due to the strong interactions between acid molecules and alcohol.

The study of microalgae Nannochloropsis salina fatty acid composition of the extracts using different techniques. SCF vs conventional extraction

The extraction of lipids and other valuable components from microalgae (Nannochloropsis salina) has been performed using various conditions: pure SC-CO2; SC-CO2+acetone (at 32MPa and 40°C); Soxhlet apparatus with n-hexane; and Soxhlet apparatus with chloroform. Small amounts of co-solvents (3.2wt.% of acetone) were added to modify the polarity and solvent strength of the supercritical CO2 to increase the solute solubility and to minimize operating costs of the extraction process. The extractions of lipids from algae were performed using a laboratory scale SCF extraction experimental apparatus. High pressure supercritical reactor with volume of 993cm3, which made from stainless steel, was used. The flow rate of SCF was maintained constant (1.5±0.05kg/h). The extraction time was within 1.5h. Four extracted lipid fractions were collected separately for each extraction conditions (for pure CO2 and CO2+co-solvents) and analyzed using GC–MS. The experimental results showed that extraction technique is negligible small affecting on total extract yields and fatty acids content.

Regeneration of Aluminopalladium Catalyst for Hydrogenation Using Supercritical Fluid CO2-Extraction Process

An experimental setup was designed for studying the solubility of a catalyst-deactivating compound – polyisoprene – in pure supercritical carbon dioxide (SC-CO2) and in SC-CO2 with a co-solvent (3,5 wt % chloroform). In pure SC-CO2, the crossover-type variations in the solubility was observed in isotherms t = 70, 100 and 120 °C at the pressure region between 15 and 34 MPa, and the pressure of ca. 19 MPA determined in the top crossover point. Addition of chloroform to SC-CO2 was shown to result in an average 2 to 2,5 times increase in the solubility. The process of supercritical fluid CO2-extraction regeneration of the aluminopalladium catalyst LD-265 for hydrogenation was studied. Dimethylsulfoxide and ethanol were used as co-solvents for SC-CO2. The maximal efficiency of the regeneration was observed at the co-solvent concentration of 5,5–6,5 wt %, dimethylsulfoxide being more effective co-solvent than ethanol. With the catalysts subjected to the SC-CO2 regeneration, the resulting diene and bromine numbers, as well as conversions of styrene and methylcyclopentadiene, meet the standards on catalytic systems for selective hydrogenation of diene hydrocarbons to benzene-toluene-xylene fractions.

Swelling kinetics and impregnation of PLA with thymol under supercritical CO2 conditions

The present work was aimed to study swelling kinetics of polylactic acid (PLA) and its impregnation with thymol in supercritical carbon dioxide (scCO2) medium. The influences of temperature and soaking time on the swelling kinetics and impregnation yield of PLA cylindrical disc and film were investigated. Swelling experiments were performed in a high pressure view cell at 10 MPa and temperatures of 40°C, 60°C and 75°C for 2 to 24 h. On the basis of swelling kinetics, pressure of 10 MPa and temperature of 40°C were chosen for supercritical solvent impregnation (SSI) of the PLA samples during 2 to24 h. The highest swelling extent was observed for the PLA monolith after 24 h treatment with pure scCO2 (7.5%) and scCO2 with thymol (118.3%). It was shown that sufficiently high amount of thymol can be loaded into both PLA monolith and film using SSI after only 2 h (10.0% and 6.6%, respectively). Monolith and film of PLA impregnated with thymol could be suitable for active food packaging and sterile medical disposables.