CO2-expanded Ethanol Research Articles

Comparative analysis of biological potential of acerola by-product extracts obtained by hydrothermal and gas-expanded liquid extraction

The acerola non-pomace, a by-product from the juice clarification step and rich in phenolic compounds and ascorbic acid, was investigated for its biological potential through in vitro tests. Extracts were obtained using hydrothermal extraction (HT) at 121°C as well as CO2-expanded ethanol (GXL) at 40°C. The GXL extract contained 159 mg/g of ascorbic acid, while the HT extract showed 70 mg/g. Catechin was found only in the HT extract, and quercetin only in the GXL extract. Both extracts exhibited similar antiglycemic potential, but the GXL extract showed twice the neuroprotective potential against acetylcholinesterase (AChE, IC50=302 μg/mL) and lipoxygenase (LOX, IC50=227 μg/mL) activities. In human breast cancer cells (MDA-MB-231), the GXL extract demonstrated better antitumor potential with an IC50 of 100 μg/mL compared to 250 μg/mL for the HT extract.

Extraction of valuable compounds from granadilla (Passiflora ligularis Juss) peel using pressurized fluids technologies

Valuable products, including carotenoids, phenolic compounds, and pectin were obtained from granadilla peel using green technologies based on pressurized fluids. The processes of pressurized liquid extraction (PLE) and CO2-expanded ethanol (GXE) were evaluated to recover the carotenoids and phenolic compounds, while pressurized hot water extraction (PHWE) was evaluated to extract pectin from the granadilla peel. The results demonstrated that although PLE and GXE had no significant difference in the carotenoids yield and antioxidant activity of the extracts obtained, PLE was faster than GXE to achieve the highest extraction yield. The pectin yield obtained by PHWE was affected by the process temperature with the highest value obtained at 160 °C. Further studies are needed to characterize the chemical composition of the pectin obtained, but the present results enable establishing a biorefinery for the complete use of granadilla wastes (seeds and peel).

Sequential two-stage extraction of Xanthoceras sorbifolia seed oil using supercritical CO2 and CO2-expanded ethanol

A new method of seed oil extraction from X. Sorbifolia was developed using a two-stage process with supercritical CO2 (SC-CO2) and CO2-expanded ethanol (CXE). The BIC model was employed to optimize the extraction process. During the SC-CO2 extraction stage, the CLSM imaging showed rapid release of EAO from the broken cells at the edge of the particles with an oil yield of 74.11% after 4 h. The follow-up CXE extraction at 10 MPa, 333 K, and 1.5 kg/h, with a CO2 molar fraction of 0.5 resulted in 68% broken cells by SEM imaging, and obtained 18.42% of remaining HAO, with a total oil yield of 92.53%. The whole process was completed in 60% less time compared to the Soxhlet method. Lipid composition analysis found a small amount of fatty acid ethyl ester in CXE oil and a higher content of functional fatty acid nervonic acid at 4.12%.

Solubility and Thermal Degradation of Quercetin in CO2-Expanded Liquids.

The solubility of quercetin and its thermal degradation was studied in CO2-expanded ethanol and ethyl lactate. An equipment setup was constructed that enabled the separation of the products of degradation while quantifying the solubility of quercetin. Three different conditions of temperature were analyzed (308, 323, and 343 K) at 10 MPa. Higher solubility and thermal degradation of quercetin were observed for CO2-expanded ethyl lactate in comparison with CO2-expanded ethanol. At the same time, as the amount of CO2 was increased in the CO2-expanded liquids mixtures, the thermal degradation of quercetin decreased for almost all the conditions of temperature considered in this work. The importance of considering thermal degradation while performing solubility measurements of compounds that are thermally unstable such as quercetin was highlighted.

Extraction of oil from grape seeds (Vitis vinifera L.) using recyclable CO2-expanded ethanol

A novel green solvent, CO2-expanded ethanol (CXE), was employed to extract oil from grape seeds, which is one of the main by-products generated by the grape-processing industry. The optimum extraction conditions were obtained by response surface methodology (RSM) coupled with Box-Behnken design (BBD): a pressure of 7.4 MPa, a temperature of 314 K and a CO2 mole fraction of 0.3. The highest oil yield of 13.6 % by CXE extraction was equivalent to or even higher than that obtained with conventional methods, including organic solvent and supercritical CO2 extraction. In terms of reducing solvent consumption and extraction time, the CXE-based process was superior than the conventional methods. CXE oil contained 87.5 % total unsaturated fatty acids, especially linoleic acid was up to 75.5 %, presenting a higher antioxidant capacity.

Utilization of pressurized CO2, pressurized ethanol and CO2-expanded ethanol mixtures for de-oiling spent bleaching earths

Compressed fluids were used in a two-step scheme to extract oil from rapeseed and sunflower spent bleaching earths. The first extraction, performed with CO2 at 45 °C, 23 MPa, yielded matrices depleted in neutral lipids (contents of 1% and 3.5% compared to initial 22% and 28%) and of better flowing characteristics thanks to the downsizing of particle (83% of particles had sizes below 50 μm). The second step was assisted by ethanol used either as a compressed liquid, as a co-solvent or as a CO2-expanded mixture by changing temperature (35°, 60 °C) pressure (6, 18 MPa) and ethanol percentage (10–100 wt%). A statistical analysis concluded that extraction yield and oligomers percentage were dependent on pressure, ethanol percentage and their interaction, whilst temperature was a significant factor only for yield. The pigments content of oils produced by CO2 and extracts produced by pressurized ethanol was below 5 μg/goil and 32 mg/gextract.

Evaluation of lipid extraction from microalgae based on different phase regions of CO2-expanded ethanol

CO2-expanded ethanol (CXE) has been proposed as an ideal green medium for performing natural products extractions and chemical reactions. However, its systematic complexity concerning vapor-liquid equilibrium (VLE) in extractions is not favorable to the industrial application. In this study, the isothermal binary system was theoretically split into three phase regions in consideration of the state of CO2 as well as the phasic behaviors. In different phase regions, the lipid extractions from microalgae were investigated, showing that subcritical CO2-expanded ethanol in one phase region exhibited higher solubility of lipids, with the maximum recovery approaching 25.0%(w/w), basically equivalent to the complete extraction with organic solvent. Meanwhile, subcritical CXE extracted 15.6 mg of lipids per milliliter of ethanol, significantly higher than 3–6 mg lipids per milliliter of other organic solvent, suggesting more efficient process than other methods. Compared with the conventional products, CXE extracts presented the higher DHA content, 41.92%(w/w) as well as the larger antioxidant capacity (IC50 of 2.49 mg/mL). This study revealed the necessity of the consideration of key factors such as phase equilibrium during employing CXE for the extraction of oxidizable or thermolabile products.

Supercritical CO2 extraction of solids using aqueous ethanol as static modifier is a two-step mass transfer process

This study re-analyzes literature data on S. platensis’ chlorophyll (CHL) extraction using 5-25 cm3 of 20–80% v/v ethanol in water (static modifier) and 82.5–62.5 cm3 of CO2 at 50 °C and 40 MPa. Under these conditions, a CO2-expanded aqueous ethanol (liquid) phase coexists with an aqueous-ethanol-modified CO2 (SCF) phase in the extraction vessel. Authors hypothesize the resulting extraction is a two-step process consisting of slow transfer of CHL from the substrate to the liquid phase, followed by fast (equilibrium) transfer of CHL to the SCF phase. For analysis, we described the ternary (CO2 + ethanol + water) system at 50 °C and 40 MPa using Peng-Robinson Equation of State and Wong-Sandler mixing rules with binary interaction parameters describing phase equilibrium of binaries (CO2 + ethanol), (ethanol + water), and (CO2 + water). Authors propose a simple mathematical model of the extraction process, and identify research needs to validate/refine it.

Experimental measurements and modeling of curcumin solubility in CO2-expanded ethanol

Carbon dioxide expanded liquids (CXLs) is a relatively recent type of solvent used in separation processes such as extraction. It combines the benefits of high solubility in the organic liquid with enhanced mass transfer mediated by the compressed CO2. In this work, we investigate the solubility of curcumin in CO2-expanded ethanol and for this purpose an equipment setup was built and used for experimental measurements at the temperatures of 308 and 323K and the pressure range of 10–30MPa. The amount of CO2 added to ethanol was varied between 10 and 50mol%. Results show that the highest solubility of curcumin was obtained at the highest temperature and the lowest amounts of CO2 (10mol%) in the mixture. Moreover, the new-built equipment setup allows the determination of the solubility for compounds with high molar light absorptivity such as curcumin. The experimental data was correlated using PR-EOS and the modified Chrastil model.

Green downstream processing using supercritical carbon dioxide, CO2-expanded ethanol and pressurized hot water extractions for recovering bioactive compounds from Moringa oleifera leaves

A green platform based on a three-step downstream processing including the use of supercritical carbon dioxide (ScCO2), carbon dioxide-expanded ethanol (CXE) and pressurized hot water (PHWE) extractions has been developed to obtain different fractions from Moringa oleifera leaves. Each process was optimized based on the extraction yield. Optimal extracts were functionally characterized by measuring total phenolic (TPC) and total flavonoid contents (TF). The antioxidant activity by TEAC assay was also tested. Moreover, a chemical characterization of the extracts was performed by GC–MS and HPLC–ESI–QTOF–MS. The extraction yields of the optimized process were 3.1, 29.5 and 30.2% respectively. The extraction of total phenolics was higher in PHWE than in CXE extract (62.4 vs. 20.3mg GAE/g leaves) while TF showed the opposite (3.8 vs. 9.6mg quercetin/g leaves respectively). ScCO2 fraction was rich in fatty acids such as α-linoleic acid and alkanes. CXE fraction was richer in glycosylated flavonoids than PHWE while the latest fraction was richer in phenolic acids, which could explain the higher antioxidant activity of this fraction (13.4mmol Eq trolox/100g dry leaves) compared to CXE (6mmol Eq trolox/100g dry leaves).

CO2-expanded liquid assisted self-assembly between Disperse Red 1 and PS-b-P4VP

This work shows that CO2-expanded liquids facilitate the modulation of morphology and photoluminescence performance of the self assembled fluorescent composite formed between DR1 and PS-b-P4VP in CO2-expanded ethanol.

Optimization of continuous lipid extraction from Chlorella vulgaris by CO2-expanded methanol for biodiesel production

CO2-expanded methanol (CXM) was used to extract lipids from the microalgae Chlorella vulgaris (a total lipid content of 20.7% was determined by Soxhlet extraction with methanol at 373K for 96h) in a continuous mode. The CXM was found to be a superior solvent to methanol, ethanol, pressurized methanol and ethanol, and CO2-expanded ethanol for lipid extraction. The effects of operation variables including temperature, pressure and CO2 flow rate on extraction performance were examined using the response surface and contour plot methodologies. The optimal operating conditions were at a pressure of 5.5MPa, a temperature of 358K, a methanol flow rate of 1mL/min and a CO2 flow rate of 3.0mL/min, providing an extracted lipid yield of 84.8wt% over an extraction period of 30min. Compared with propane methanol mixture, CXM was safer and more energy efficient for lipid extraction from C. vulgaris.

Continuous extraction of lipids from Schizochytrium sp. by CO2-expanded ethanol

CO2-expanded ethanol (CXE) was used to extract DHA-containing lipids from Schizochytrium sp. with a 35.7wt% lipid content of dry biomass in a continuous mode. The effects of operation variables such as temperature, pressure, ethanol flow rate and CO2 flow rate on extraction performance were investigated. Based on a 24-central composite design and response surface methodology, the optimal operating conditions were determined to be a pressure of 6.9MPa, a temperature of 313K, an ethanol flow rate of 1mL/min and a CO2 flow rate of 6.0mL/min, providing an extracted lipid yield of 87wt% over an extraction period of 30min. Not only the lipid yield obtained using CXE was observed to be significantly greater than those using ethanol and pressurized ethanol as the solvents, but also a lower amount of ethanol and less time were required to achieve the same extraction yield by using CXE.

Use and limitations of a quartz crystal microbalance to measure viscosity of carbon dioxide-expanded fish oil fatty acid ethyl esters

The use of a quartz crystal microbalance (QCM) to determine the viscosity of CO2-expanded (CX) liquids was evaluated. This study presents a calibration method for QCM to be used for viscosity measurements at elevated hydrostatic pressures, taking into account the effects of hydrostatic pressure and surrounding fluid density on the resonant frequency of the QCM in an effort to isolate the effect of viscosity. The viscosity values obtained for CX fatty acid ethyl esters and CX ethanol with increasing pressure using the QCM were lower compared to literature data, indicating that the no-slip boundary condition between the QCM surface and the CX liquid was compromised. Thus, a QCM was found not to be suitable for measuring viscosity of CX liquids but could be used to determine the viscosities of gas-free liquids at ambient and elevated pressures.

CO2 assisted synthesis of highly dispersed Co3O4 nanoparticles on mesoporous carbon for lithium ion battery

Co3O4 nanoparticles were uniformly dispersed onto the mesoporous carbon support (Co3O4/mC) using a facile process in CO2–expanded ethanol (CE) solution. During the synthesis, CO2 played the dual roles, one is to provide a simple physical expansion to evenly disperse the precursors onto the mesoporous carbon support, and the other is to offer some chemical groups such as CO32− to facilitate the complete and uniform deposition through the coordination to the metallic cations with these anions. When used as anode material for lithium ion batteries (LIBs), the Co3O4/mC synthesized in CO2-expanded ethanol solution exhibited larger surface area and better cycle performance compared with the reference sample synthesized in pure ethanol. The enhanced cycle performance could be attributed to the synergistic effects between the superior structures of mesoporous C support and the highly dispersed Co3O4 nanoparticles. More importantly, the synthesis of Co3O4/mC composite in CE solution was green and highly efficient, avoiding the use of precipitant and the aggregation of Co3O4, which would definitely enrich the strategies for the fabrication of carbon-based transition-metal oxide composites with great applications.

CO2-assisted synthesis of mesoporous carbon/C-doped ZnO composites for enhanced photocatalytic performance under visible light.

Visible-light-responsive mesoporous carbon/C-doped ZnO (mC/C-ZnO) composites were fabricated using a facile, fast, one-step process in CO2-expanded ethanol solution. It is a green and sustainable process that does not need tedious pretreatment, surfactants or precipitants. CO2 played triple roles in the synthesis of mC/C-ZnO composites; the first was to provide a simple physical expansion to evenly dope the carbon in the ZnO; the second was to offer some chemical groups such as CO3(2-) and HCO3(-), facilitating the uniform and complete deposition through the coordination of a metallic cation with these anions; and the third was to offer CO3(2-) acting as a template for the formation of mesoporosity in the carbon. When used as a photocatalyst for the photodegradation of RhB and the organic pollutant phenol, the mC/C-ZnO composites with glucose content at 22 wt% (mC/C-ZnO-CE-2) synthesized in CO2-expanded ethanol exhibited better recycling stability and photodegradation rate than the corresponding sample synthesized in pure ethanol. Such improved photocatalytic performance was attributed to the well-mixing of the mesoporous carbon and the small sized C-doped ZnO particles in the mC/C-ZnO-CE-2 composites. The facile and fast synthesis method could be extended to other mesoporous carbon/C-doped metal oxide composites, which are expected to be good photocatalyst candidates, or in other application fields.

Astaxanthin extraction from Haematococcus pluvialis using CO2-expanded ethanol

Microalgae represent diverse branch of microorganism that can produce a wide range of unique functional ingredients that can be used in food, cosmetics, pharmaceuticals, and energy. Among them, Haematococcus pluvialis is known for accumulating the highest levels of a potent natural antioxidant, astaxanthin, which has demonstrated positive health effects. Therefore, the aim of numerous studies has been to develop novel and efficient extraction techniques to produce high-quality (purity and antioxidant activity) extracts, while complying with the Green Chemistry Principles. Supercritical CO2 (scCO2) emerges as an alternative to organic solvents because of its high selectivity and bioactivity-preserving qualities. Nevertheless, astaxanthin is a large molecule with low solubility in scCO2 that usually requires long extractions at high pressures. Ethanol has been used as co-solvent to increase astaxanthin solubility in scCO2. In this work, a Box–Behnken experimental design was used to study the effects of operating pressure (20–35MPa), temperature (40–70°C), and ethanol content in scCO2 (0–13%, w/w) on the yield, astaxanthin content, and antioxidant activity of H. pluvialis extract. Results showed that ethanol content in CO2 has a more significant effect on all responses than pressure and temperature. These results lead us to investigate the effect of a further increase in ethanol content, up to the region of gas-expanded liquids. We studied the effects of temperature (30–60°C) and ethanol content (50–70%, w/w) at a fixed pressure (7MPa) on the same response variables using CO2-expanded ethanol (CXE). Results showed that temperature and ethanol content had a significant influence on astaxanthin yield and antioxidant activity. Also, the overall responses of CXE surpassed scCO2 extractions to match conventional extraction with acetone, maintaining high quality extracts, thus validating the use of this new type of green technology for extraction of high-value compounds.

Instantaneous Solid–Liquid–Gas Carbonation of Ca(OH)2and Chameleonic Phase Transformation in CO2-Expanded Solution

In this study, a CO2-expanded ethanol–water solution system was applied for the solid–liquid–gas carbonation of Ca(OH)2 to CaCO3. The system revealed, for the first time, instantaneous (within 1 min) conversions of Ca(OH)2 (95.1–100.0%) with the volume ratios of ethanol between 10% and 80%, indicating that both the water content and the expansion of the system take effect in the carbonation process. The instantaneous carbonation with 80% ethanol ratio led to production of 12.8% aragonite polymorph. Further examination of this carbonation case under different reaction times found that, interestingly and importantly, pure calcite phase was stabilized within a short time (210 min) as compared to those reported in the literature; however, in this period, the system exhibited chameleonic phase transformation between calcite, aragonite, and vaterite, normal to abnormal and vice versa.

Dispersion polymerization of styrene in CO2-expanded ethanol

Dispersion polymerization of styrene has been performed in CO2-expanded ethanol at ≤9 MPa and 70 °C using PVP as stabilizer. The polymerizations proceeded with good colloidal stability, resulting in spherical particles of diameters of ∼2 μm. Pressurization with CO2 leads to an increase in particle size (∼1 μm in the corresponding CO2-free system), and a decrease in both polymerization rate and molecular weight. The main effect of CO2 is proposed to be its influence on the partitioning of monomer between the continuous and the particle phase–the results indicate that CO2-pressurization causes a reduction in monomer concentration in the particles. Overall, the results are consistent with literature data on the effects of the polarity of the continuous phase in dispersion polymerization of styrene in alcohols and alcohol/water mixtures.

Trace Amounts of Water-Induced Distinct Growth Behaviors of NiO Nanostructures on Graphene in CO2-Expanded Ethanol and Their Applications in Lithium-Ion Batteries

In this work, we have developed a new method to grow NiO nanomaterials on the surface of graphene nanosheets (GNSs). The morphologies of NiO nanomaterials grown on GNSs could be tailored by trace amounts of water introduced into the mixed solvents of CO2-expanded ethanol (CE). Small and uniform Ni-salt nanoparticles (Ni-salt-NPs) were grown on the surface of graphene oxide (GO) through the decomposition of nickel nitrate directly in CE. However, when trace amounts of water were introduced into the mixed solvents, Ni-salt nanoflakes arrays (Ni-salt-NFAs) were grown on the surface of GO with almost perpendicular direction. After thermal treatment in N2 atmosphere, these Ni-salt @GO composites were converted to NiO@GNSs composites. The forming mechanisms of the NiO-NPs@GNSs and NiO-NFAs@GNSs were discussed by series comparative experiments. The presence of the trace amounts of water affected the chemical composition and structure of the precursors formed in CE and the growth behaviors on the surface of GNSs. When used as anode materials for lithium-ion batteries, the NiO-NPs@GNSs composite exhibited better cycle and rate performance compared with the NiO-NFAs@GNSs.