Supercritical CO2 extraction of essential oil from yarrow

Essential oil was extracted from yarrow flowers (Achillea millefolium) with supercritical CO₂ at pressure of 10 MPa and temperatures of 40–60 °C, and its composition and yield were compared with those of hydrodistillate. The yield of total extract, measured in dependence on extraction time, was affected by extraction temperature but not by particle size of ground flowers. CO₂-extraction of cuticular waxes was lowest at 60 °C. Major essential oil components were camphor (26.4% in extract, 38.4% in distillate), 1,8-cineole (9.6% in extract, 16.2% in distillate), bornyl acetate (16.7% in extract, 4.3% in distillate), γ-terpinene (9.0% in extract, 9.4% in distillate), and terpinolene (7.6% in extract, 3.9% in distillate). Compared to hydrodistillation, the yield of monoterpenes was lower due to their incomplete separation from gaseous CO₂ in trap but the yield of less volatile components like monoterpene acetates and sesquiterpenes was higher. Hydrolysis of γ-terpinene and terpinolene, occuring in hydrodistillation, was suppressed in supercritical extraction, particularly at extraction temperature of 40 °C.     

Supercritical CO2 extraction of Plumula nelumbinis oil: Experiments and modeling

Supercritical CO₂ extraction of Plumula nelumbinis oil was investigated at temperatures of 308–338 K and pressures of 15–45 MPa. The yield of the extracted oil was 0.128 g/g material at optimal conditions, in which gamma-sitosterol, unsaturated fatty acids and gamma-tocopherol had higher relative concentrations as determined by GC–MS. The broken and intact cell (BIC) model, with reduced adjustable parameters, was utilized to simulate the SFE process. The values of average absolute relative deviation (AARD) were in the range 2.34–10.9%, indicating that the improved method had a similar effect to the BIC model when three parameters were adjusted. The parameters obtained during the modeling had clear physical meanings and were used to gain an in-depth understanding of the SFE process theoretically.     

Supercritical CO2 extraction of lipids and astaxanthin from Brazilian redspotted shrimp waste (Farfantepenaeus paulensis)

Brazilian redspotted shrimp (Farfantepenaeus paulensis) waste is an important source of carotenoids such as astaxanthin and lipids with a high ω−3 fatty acids content, mainly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). In order to establish an efficient and environmental friendly recovery process, the lipids and astaxanthin were extracted from the freeze-dried redspotted shrimp waste (including head, tail and shell) using supercritical carbon dioxide. The effects of the extraction conditions of pressure (200-400 bar) and temperature (40-60 °C) on the global yield (X₀), astaxanthin extraction yield and astaxanthin concentration in the extract were evaluated. It was found that the pressure and temperature showed a very low significant effect on the lipid extraction yield using supercritical CO₂. In comparison with lipid extraction by solvents, maximum efficiency of supercritical fluid extraction achieved 64% of hexane extraction yield. On the other hand, temperature and pressure had significant effects on astaxanthin extraction yield. Thegreatest amount of extract was obtained at 43 °C and 370 bar, with 39% of recovery.     

CO2 supercritical fluid extraction of Jordanian oil shale utilizing different co-solvents

In this study, extracting shale oil from Jordanian oil shale using supercritical fluid extraction has been investigated. Experimental data indicates that by using supercritical extraction with carbon dioxide, using co-solvents can be viable. A relatively high yield can be obtained at relatively moderate pressure. At the highest temperature and pressure of 450 °C and 3200 psi, respectively, and with hexane as a co-solvent, the highest yield obtained was 100 kg/ton of oil shale, which was at the highest temperature and pressure of 450 °C and 3200 psi, respectively, and with hexane as a co-solvent. Increasing both the operating pressure and temperature increases the oil yield. In the supercritical state, carbon dioxide along with other co-solvents, such as hexane and acetone, interact with the kerogen leading to the dissolution of fragments due to an increase in solubility and mass transfer.Increasing the particle size of oil shale for extraction decreases the oil yield. Most of the extracted oil obtained is saturated hydrocarbons, olefinic and a portion of aromatic hydrocarbons. As the extraction temperature increases, the production of low-molecular weight compounds increases.     

Supercritical CO2 sterilization of ultra-high molecular weight polyethylene

The aim of this study was to use a benign technique for the sterilization of ultra-high molecular weight polyethylene (UHMWPE), which is broadly used in artificial joints. The feasibility of using supercritical (SC) CO₂ modified with additives such as ethanol, water and hydrogen peroxide was assessed for the sterilization of UHMWPE. The operating conditions and the amount of modifiers were changed to achieve a complete inactivation of bacteria such as spores and fungi. Complete inactivation of all microorganisms including spores was achieved within 2 h at 37 °C and 170 bar CO₂, when at least 25 μL hydrogen peroxide was mixed with equal volume of other modifiers. The physio-chemical properties of the polymer were tested for untreated, as well as treated samples. Mechanical strength and elongation of the polymer were measured using an Instron and the oxidation of the polymer was measured using FTIR. Both the physical and chemical properties of the polymer were unchanged after the SC CO₂ sterilization technique.     

Effect of solvent (CO2/ethanol/H2O) on the fractionated enhanced solvent extraction of anthocyanins from elderberry pomace

The management of agro-industrial residues is an important issue for environmental reasons and the reuse of byproducts represents a good alternative, especially if it is conjugated with green technologies and the production of valuable products. Portuguese elderberry pomace is rich in anthocyanins with therapeutic properties that confer to this byproduct potential to be applied in the food and pharmaceutical industries. Fractionated high pressure extractions from elderberry pomace were performed using supercritical CO₂ extraction, followed by enhanced solvent extraction (ESE) with diverse CO₂/ethanol/H₂O solvent mixtures (0-90%, 0.5-100%, 0-95%, v/v/v), at 313 K and 21 MPa, in order to obtain anthocyanin-rich fractions. The ESE solvent mixtures had a substantial effect on extracts yield and composition. The maximum extraction yield (24.2%), total phenolic compounds (15.8% gallic acid equivalents), total flavonoids (8.9% epicatechin equivalents), total anthocyanins (15.0% cyanidin-3-glucoside equivalents) and antioxidant activity (IC₅₀ of 21 μg) achieved highlight the great potential of elderberry pomace for valuable applications.     

Supercritical CO2 processing and annealing of polytetrafluoroethylene (PTFE) and modified PTFE for enhancement of crystallinity and creep resistance

A method is reported to improve creep resistance in tension for polytetrafluoroethylene (PTFE) and modified PTFE (M-PTFE). PTFE and M-PTFE from different sources were annealed in air, N₂ or supercritical CO₂ (scCO₂) at a range of temperatures, pressures and time intervals. Annealing PTFE in scCO₂ increases crystallinity from 9 to 53%, depending on the material and annealing conditions. No corresponding increase occurs for samples annealed in air or N₂. In comparison to as-received PTFE, significant improvements in tensile creep resistance (18-60%) are observed also dependent upon the material and annealing conditions. For a given temperature and duration, the increase in PTFE tensile creep resistance after annealing in air or N₂ is greater than after annealing in scCO₂ despite the higher crystallinity for post-scCO₂ processed PTFE. Density measurements indicate that the effect of increased crystallinity is counterbalanced by scCO₂-generated microvoids, particularly at higher pressures, leading to smaller creep resistance. In contrast, thermal annealing in air or N₂, which does not significantly change the density or enhance the crystallinity of PTFE or M-PTFE, yields better tensile creep resistance. The detailed morphological origin of improved resistance to tensile creep is unknown, but stress relief by thermal annealing is evident.     

Supercritical carbon dioxide extraction of oil from Mexican chia seed (Salvia hispanica L.): Characterization and process optimization

Supercritical carbon dioxide (SC-CO₂) was employed to extract oil rich in omega-3 fatty acids (FAs) from chia seeds, and the physicochemical properties of the oil were determined. A central composite rotatable design was used to analyze the impact of temperature (40 °C, 60 °C and 80 °C), pressure (250 bar, 350 bar and 450 bar) and time (60 min, 150 min and 240 min) on oil extraction yield, and a response surface methodology (RSM) was applied. The extraction time and pressure had the greatest effects on oil. The highest oil yield was 92.8% after 300 min of extraction time at 450 bar. The FA composition varied depending on operating conditions but had a high content of α-linolenic acid (44.4-63.4%) and linoleic acid (19.6-35.0%). The rheological evaluation of the oils indicated a Newtonian behavior. The viscosity of the oil decreased with the increase in temperature following an Arrhenius-type relationship.     

Kinetics and specificity of Lipozyme-catalysed oil hydrolysis in supercritical CO2

Blackcurrant seed oil is rich in linoleic and linolenic acids. Selective enzyme-catalysed oil hydrolysis was studied with aim to obtain different levels of α- and/or γ-linolenic acid in the mixture of liberated fatty acids and in the fraction of di- and monoacylglycerols, making them suitable for special dietary needs. The oil was dissolved in supercritical carbon dioxide flowing through a packed bed reactor (temperature 40 °C, pressure 15–28 MPa, and superficial velocity 0.1–0.7 mm s⁻¹) with Lipozyme^®, a 1,3-specific lipase from Mucor miehei immobilised on a macroporous ion-exchange resin. The enzyme activity was stable as long as water precipitation in the reactor was prevented. The reaction was found to be controlled by both Michaelis–Menten kinetics and mass transfer. The maximum rate of fatty acids liberation per unit amount of enzyme, 2.6 × 10⁻³ mol s⁻¹ kg⁻¹, was achieved at the maximum flow velocity and pressure. Compared to oil, the liberated fatty acids contained more α-linolenic, palmitic and stearic acids, while di- and monoacylglycerols contained increased levels of γ-linolenic and stearidonic acids.     

Mathematical model of supercritical extraction applied to oil seed extraction by CO2+saturated alcohol — I. Desorption model

Supercritical fluid extraction of solutes from solid matrix is represented by the extraction curve, where cumulated extracted oil is plotted versus time. Experimental data obtained in laboratory scale and pilot plant is adjusted with different extraction models; in order to predict extraction curves for full-scale extractors. Sometimes, a shortcut method is useful to adjust experimental data; these correlations are typical in most of engineering processes. In this paper, three shortcut methods are reviewed. First, a model based on flux models considering residence time distribution curves for serially interconnected perfectly mixed tanks and plug flow in series or in parallel with them. It could be used to analyze extractor behavior taking into account bed distribution (preferential ways, dispersion). Second, fast adjusting or ‘t^n’ model considers a differential mass balance where mass transfer coefficient is an ‘nth^’ potential function of time; analytical solution gives an explicit equation. Third, it is presented a linear shortcut method by intervals based on Sovovà model; it predicts considering four extraction periods: delay, rapid extraction, slow extraction and depletion; delay time and solubility are evaluated using the ‘t^n’ model. This model gives a process transfer function (Laplace domain). Supercritical fluid extraction of sunflower seed oil with carbon dioxide was performed in a pilot plant at 30.0 MPa and 40°C, using different amounts of methanol, ethanol, butanol and hexanol as cosolvents. Experimental data are fitted with proposed shortcut methods. Fitting error is less than 5% except in linear shortcut method by intervals which is higher.     

Extraction of nimbin from neem seeds using supercritical CO2 and a supercritical CO2–methanol mixture

Nimbin, a component found in neem seeds, which is reported to have several valuable medicinal properties including: anti-inflammatory, anti-pyretic, anti-fugal, antihistamine and antiseptic was extracted from neem seeds using supercritical CO₂ and CO₂ with a methanol modifier.Nimbin extraction yields using supercritical carbon dioxide were found to be approximately 85% at 308 K, 23 MPa and a CO₂ flow rate of 0.62 cm³/min for a 2-g sample of neem. An optimum extraction pressure appears to exist at ≈23 MPa and 328 K. Although extraction using a methanol modifier did improve the extraction somewhat, methanol was not found to be an effective modifier for extracting nimbin.Dynamic extraction curves were predicted using three empirical models and a theoretical model. The three empirical models were: a Langmuir gas adsorption model, a first order plus dead time (FOPDT) model and a so-called tⁿ cyclone model used to incorporate sigmoidal curves. The parameters in the empirical models were fitted to the experimental data. The Goto et al. [J. Chem. Eng. Jpn. 31 (1998) 171] theoretical model was compared to the experimental results and was found to fit the data well. The theoretical model shows that the extraction yield depends strongly on the solvent flow rate, that is, external mass transfer or equilibrium is the controlling step of this process.     

Impact of SO2 concentration on the corrosion rate of X70 steel and iron in water-saturated supercritical CO2 mixed with SO2

The corrosion behavior of X70 steel and iron in water-saturated supercritical CO₂ mixed with SO₂ was investigated using weight-loss measurements. As a comparison, the instantaneous corrosion rate in the early stages for iron in the same corrosion environment was measured by resistance relaxation method. Surface analyzes using SEM/EDS, XRD and XPS were applied to study the morphology and chemical composition of the corroded sample surface. Weight-loss method results showed that the corrosion rate of X70 steel samples increased with SO₂ concentration, while the corrosion rate increased before decreasing with SO₂ concentration for iron sample. Comparing resistance relaxation method results with weight-loss method results, it is found that the instantaneous corrosion rate of iron is much higher than the uniform corrosion rate of the iron tablet specimens which are covered with thick corrosion product films after a long period of corrosion. The corrosion product films were mainly composed of FeSO₄ and FeSO₃ hydrates. The possible reaction mechanism under such environment was also analyzed, and the electrochemical reaction between the dissolved SO₂ in the condensed water film with iron is the critical reaction step.     

Cetirizine solubility in supercritical CO2 at different pressures and temperatures

A simple static technique was used to obtain the solubility of cetirizine in supercritical carbon dioxide. The solubility measurements were performed at temperatures and pressures ranging from 308.15 to 338.15 K and 160 to 400 bar, respectively; resulting in mole fractions in the 1.05 × 10⁻⁵ to 4.92 × 10⁻³ range. The Chrastil, Bartle, Kumar & Johnston and the Mendez-Santiago and Teja (MST) models were used to correlate the experimental data. The calculated solubilities showed good agreement with the experimental data in the temperature and pressure ranges studied.     

High-pressure sorption isotherms and sorption kinetics of CH4 and CO2 on coals

Using a manometric experimental setup, high-pressure sorption measurements with CH₄ and CO₂ were performed on three Chinese coal samples of different rank (VR_r = 0.53%, 1.20%, and 3.86%). The experiments were conducted at 35, 45, and 55 °C with pressures up to 25 MPa on the 0.354-1 mm particle fraction in the dry state. The objective of this study was to explore the accuracy and reproducibility of the manometric method in the pressure and temperature range relevant for potential coalbed methane (CBM) and CO₂-enhanced CBM (CO₂-ECBM) activities (P > 8 MPa, T > 35 °C). Maximum experimental errors were estimated using the Gauss error propagation theorem, and reproducibility tests of the high-pressure sorption measurements for CH₄ and CO₂ were performed. Further, the experimental data presented here was used to explicitly study the CO₂ sorption behaviour of Chinese coal samples in the elevated pressure range (up to 25 MPa) and the effects of temperature on supercritical CO₂ sorption isotherms.The experiments provided characteristic excess sorption isotherms which, in the case of CO₂ exhibit a maximum around the critical pressure and then decline and level out towards a constant value. The results of these manometric tests are consistent with those of previous gravimetric sorption studies and corroborate a crossover of the 35, 45, and 55 °C CO₂ excess sorption isotherms in the high-pressure range. The measurement range could be extended, however, to significantly higher pressures. The excess sorption isotherms tend to converge, indicating that the temperature dependence of CO₂ excess sorption on coals at high-pressures (>20 MPa) becomes marginal. Further, all CO₂ high-pressure isotherms measured in this study were approximated by a three-parameter excess sorption function with special consideration of the density ratio of the “free” phase and the sorbed phase. This function provided a good representation of the experimental data.The maximum excess sorption capacity of the three coal samples for methane ranged from 0.8 to 1.6 mmol/g (dry, ash-free) and increased from medium volatile bituminous to subbituminous to anthracite. The medium volatile bituminous coal also exhibited the lowest overall excess sorption capacity for CO₂. However, the subbituminous coal was found to have the highest CO₂ sorption capacity of the three samples. The mass fraction of adsorbed substance as a function of time recorded during the first pressure step was used to analyze the kinetics of CH₄ and CO₂ sorption on the coal samples. CO₂ sorption proceeds more rapidly than CH₄ sorption on the anthracite and the medium volatile bituminous coal. For the subbituminous coal, methane sorption is initially faster, but during the final stage of the measurement CO₂ sorption approaches the equilibrium value more rapidly than methane.     

Reducing heavy oil carbon footprint and enhancing production through CO2 injection

The world's dependence on heavy oil production is on the rise as the existing conventional oil reservoirs mature and their production decline. Compared to conventional oil, heavy oil is much more viscous and hence its production is much more difficult. Various thermal methods and particularly steam injection are applied in the field to heat up the oil and to help with its flow and production. However, the thermal recovery methods are very energy intensive with significant negative environmental impact including the production of large quantities of CO₂. Alternative non-thermal recovery methods are therefore needed to allow heavy oil production by more environmentally acceptable methods. Injection of CO₂ in heavy oil reservoirs increases oil recovery while eliminating negative impacts of thermal methods.In this paper we present the results of a series of micromodel and coreflood experiments carried out to investigate the performance of CO₂ injection in an extra-heavy crude oil as a method for enhancing heavy oil recovery and at the same time storing CO₂. We reveal the pore-scale interactions of CO₂-heavy oil-water and quantify the volume of CO₂ which can be stored in these reservoirs.The results demonstrate that CO₂ injection can provide an effective and environmentally friendly alternative method for heavy oil recovery. CO₂ injection can be used independently or in conjunction with thermal recovery methods to reduce their carbon footprint by injecting the CO₂ generated during steam generation in the reservoirs rather than releasing it in the atmosphere.     

CO2 pressure effects on melting, crystallization, and morphology of poly(vinylidene fluoride)

Supercritical CO₂ fluids (SCF CO₂) assisting melting of poly(vinylidene fluoride) (PVDF) and the SCF CO₂ pressure affecting surface and bulk morphology, melting and crystallization of PVDF were investigated by means of SEM, AFM, FTIR, WAXD, DSC and SAXS. Three SCF CO₂ conditions at 84, 283, and 476 atm all at 140 °C for 30 min were studied. Morphological changes, induced by melting of PVDF under SCF CO₂ and recrystallization during depressurization of CO₂, were found. The level of the CO₂-assisted melting of PVDF was found to increase with increasing pressure. SEM and AFM images showed that the 84 atm of CO₂ assisted melting on the surface of PVDF film while both 283 and 476 atm of CO₂ gave rise to melting of the whole film. FTIR spectra and WAXD patterns found that the hot-pressed PVDF film exhibited predominant α-crystalline form, which is one of the reported four crystalline forms including α, β, γ, and δ forms, and did not transform to other crystalline form(s) upon the SCF CO₂ treatments although they lowered the bulk crystallinities of PVDF. SEM images showed that the SCF CO₂ treatments at 283 and 476 atm resulted in foam formations in PVDF, with smaller foam cells resulting from the lower pressure treatment. SAXS data found that the thickness of crystalline layer in the lamellar stacks increased while that of amorphous layers insignificantly changed after SCF CO₂ treatments at 283 and 476 atm, as compared with untreated PVDF. SAXS and DSC data suggested the presence of a bimodal distribution of crystal size of PVDF after SCF CO₂ treatments.     

Supercritical fluid extraction of jojoba oil

Supercritical fluid extraction of jojoba oil from Simmondsia chinensis seeds using CO₂ as the solvent is presented in this study. The effects of process parameters such as pressure and temperature of extraction, particle size of jojoba seeds, flow rate of CO₂, and concentration of entrainer (hexane) on the extraction yield were examined. Increases in the supercritical CO₂ flow rate, temperature, and pressure generally improved the performance. The extraction yield increased as the particle size decreased, indicating the importance of decreasing intraparticle diffusional resistance. The maximum extraction yield obtained was 50.6 wt% with a 0.23-mm particle size and a 2 mL/min CO₂ flow rate at 90°C and 600 bar. Use of an entrainer at a concentration of 5 vol% improved the yield to 52.2 wt% for the same particle size and also enabled the use of relatively lower pressure and temperature, i.e., 300 bar and 70°C.     

Supercritical CO2 extraction of dittany oil: Experiments and modelling

The extraction of oil from dittany (Origanum dictamnus) using supercritical carbon dioxide was investigated. The experiments were performed in a bench scale apparatus at the pressures of 100 and 150 bar and at the temperatures of 40 and 60 °C. The effect of the solvent flow rate and the mean particle diameter of dittany on the extraction yield was also investigated at 100 bar and 40 °C. It is shown that the extraction yield increases with pressure, while the increase of temperature and mean particle diameter leads to the opposite effect. Different flow rates of SCCO₂ lead to similar extraction yields. Finally, the overall extraction curves are well correlated by a mass balance model of plug flow, in which the intraparticle diffusion resistance has the controlling role.     

Grafting of polypropylene with N-cyclohexylmaleimide and styrene simultaneously using supercritical CO2

Monomer mixture of styrene (St) and N-cyclohexylmaleimide (ChMI) and initiator benzoyl peroxide (BPO) were first impregnated into isotactic polypropylene (iPP) films simultaneously using supercritical carbon dioxide (SC CO₂) as a solvent and swelling agent at 35.0 °C. The composites were obtained after the monomers were grafted onto the iPP matrix at 70 °C. The effects of various conditions, such as pressure, monomer concentration, and the molar ratio of the two monomers in the soaking process, on the composition of the composites were determined. The molar ratios of St to ChMI in the composites were estimated by Fourier transform infrared spectroscopy. The thermal properties, the morphology, and the mechanical properties of the composites were characterized by different techniques. The results demonstrated that the phase size of the grafted St-ChMI was very small and the phase boundary was very ambiguous. The composites had better thermal stability than the original iPP film. The Young's modulus and tensile strength of the film increased continuously with increasing grafting percentage. The two grafted monomers in the composites had good synergetic effect.     

In situ study of ionic conductivity for polyether-LiCF3SO3 electrolytes with subcritical and supercritical CO2

In situ measurements of the ionic conductivity were performed on polyethers, poly(ethylene oxide) (PEO) and poly(oligo oxyethylene methacrylate) (PMEO), with lithium triflate (LiCF₃SO₃) as crystalline and amorphous electrolytes, and at CO₂ pressures up to 20 MPa. Both PEO and PMEO systems in subcritical and supercritical CO₂ increased more than five fold in ionic conductivity at 40 °C composed to atmospheric pressure. The pressure dependence of the ionic conductivity for PEO electrolytes was positive under CO₂, and increased by two orders of magnitude under pressurization from 0 to 20 MPa, whereas it decreases with increasing pressure of N₂. The enhancement is caused by the plasticizing effect of CO₂ molecules that penetrate into the electrolytes.