Continuous catalyst-free production of fatty acid ethyl esters from soybean oil in microtube reactor using supercritical carbon dioxide as co-solvent

This work reports the transesterification of soybean oil in supercritical ethanol in a continuous catalyst-free process in microtube reactor using carbon dioxide as co-solvent. For this purpose it was employed two microtube reactors with different internal diameter, 0.775 and 0.571 mm. The experiments were performed in the temperature range of 523-598 K, pressure of 10 MPa and 20 MPa, oil to ethanol molar ratio of 1:20 and 1:40, and co-solvent to substrates mass ratio from 0.05:1 to 0.2:1. Results demonstrated that temperature, pressure and co-solvent to substrate mass ratio had a positive effect on fatty acid ethyl esters (FAEE) production, with appreciable yields achieved at 598 K, 20 MPa, oil to ethanol molar ratio of 1:20, using a CO₂ to substrate mass ratio of 0.2:1. The micro-reactor with the smallest inner diameter led to slightly higher FAEE yields at the specified reactions conditions compared to the micro-reactor with greater internal diameter. A semi-empirical kinetic model was proposed in attempt to represent the experimental data with satisfactory fitting results found.     

Continuous enzymatic production of biodiesel from virgin and waste sunflower oil in supercritical carbon dioxide

A continuous process for biodiesel production in supercritical carbon dioxide was implemented. In the transesterification of virgin sunflower oil with methanol, Lipozyme TL IM led to fatty acid methyl esters yields (FAME) that exceeded 98% at 20 MPa and 40 °C, for a residence time of 20 s and an oil to methanol molar ratio of 1:24. Even for moderate reaction conversions, a fractionation stage based on two separators afforded FAME with >96% purity. Lipozyme TL IM was less efficient with waste cooking sunflower oil. In this case, a combination of Lipozyme TL IM and Novozym 435 afforded FAME yields nearing 99%.     

Transesterification of rapeseed oil over acid resins promoted by supercritical carbon dioxide

The methanolysis of rapeseed oil catalyzed by commercial styrene-divinylbenzene macroporous acid resins was performed in a batch reactor at 100-140 °C and 10-46 MPa to study the effect of supercritical carbon dioxide (scCO₂) on the performances of the process. Reaction temperatures of 120-140 °C were necessary to obtain high enough yields of fatty acid methyl esters. Upon addition of scCO₂ faster transesterification kinetics was obtained also at the lowest investigated operating pressure (10-11 MPa), working in two fluid phase systems. Experiments performed changing the reaction time indicated that most of the esters were formed during the first 3 h. When the pressure was increased at 38-46 MPa, the fluid phases merged in a single one without significant modification of the performances of the process.The enhancement effect of scCO₂ on the transesterification kinetics is tentatively discussed in terms of modification of the phase behaviour of the reaction system and swelling of the polymeric acid resin.     

Experimental optimization and mathematical modeling of supercritical carbon dioxide extraction of essential oil from Pogostemon cablin

The supercritical carbon dioxide extraction was applied to obtain essential oil from Pogostemon cablin in this work. Effect of extraction parameters including temperature, pressure, extraction time and particle size on extraction yield was investigated, and the response surface methodology with a Box-Behnken Design was used to achieve the optimized extraction conditions. The maximum yield of essential oil was 2.4356% under the conditions of extraction temperature 47℃, pressure 24.5 MPa and extraction time 119 min. Moreover, based on the Brunauer-Emmett-Teller theory of adsorption, a mathematical modeling was performed to correlate the measured data. The model shows a function relationship between extraction yield and time by a simple equation with three significantly adjustable parameters. These model parameters have been optimized through simulated annealing algorithm. The predicted data from the mathematical model show a good agreement with the experimental data of the different extraction parameters.     

Separation of squalene from olive oil deodorizer distillate using supercritical fluids

In this study, an integrated strategy using supercritical fluids for extraction of squalene from olive oil deodorizer distillate (OODD), one of the most important by‐products of the olive oil refining process is presented. First, OODD was esterified in supercritical methanol, and then squalene was extracted from the sample consisting of 66% methyl ester using supercritical CO₂. The extraction conditions, i.e., pressure (88.2–121.8 bar), temperature (41.6–58.4°C) and extraction time (129.6–230.4 min), were optimized via RSM to achieve the highest squalene content. The optimal results were obtained at a temperature of 52.05°C, pressure of 104.8 bar and extraction time of 180 min. Consequently, two kinds of value‐added products such as biodiesel (up to 96% FAME, in extract) and olive squalene (up to 75%, in raffinate) were produced in shorter processing times when compared with distillation results of 70 h. Practical applications: Traditionally, squalene is extracted from liver oil of rare deep‐sea sharks. Here we present the recovery of vegetal squalene in high purity from OODD. Our approach also presents a simple, reliable, and mobile solution. Squalene is widely used in cosmetics as a protective agent and natural moisturizer and as an adjuvant in influenza vaccines.     

Lipase-catalyzed glycerolysis of soybean oil in supercritical carbon dioxide

The transesterification of soybean oil with glycerol, 1,2-propanediol, and methanol by an immobilized lipase in flowing supercritical carbon dioxide for the synthesis of monoglycerides is described. A lipase from Candida antarctica was used to catalyze the reaction of soybean oil with glycerol, 1,2-propanediol, ethylene glycol, and methanol. Reactions were performed in supercritical carbon dioxide at a density of 0.72 g/L and at a flow rate of 6 μL/min (expanded gas). The substrates were added at flows ranging from 2.5 to 100 μL/min. Monoglycerides were obtained at up to 87 wt%, and fatty acid methyl esters at nearly 100 wt%. The reactivity of the alcohols paralleled the solubility of the substrate in liquid carbon dioxide. Glycerol has the slowest reaction rate, only 2% of that of methanol.     

Diffusion coefficients of C18 unsaturated fatty acid methyl esters in supercritical carbon dioxide containing 10% mole fraction ethanol as modifier

To determine the molecular diffusion coefficients of C18 unsaturated fatty acid methyl esters in supercritical carbon dioxide (scCO₂) containing 10 mol% ethanol as a modifier, four methyl esters of C18 fatty acids, i.e., methyl oleate, methyl ricinoleate, methyl linoleate and methyl linolenate were selected as the typical solutes. The diffusion coefficients were measured at temperatures from 313.15 to 333.15 K and pressures from 15 to 27 MPa using the Taylor–Aris chromatographic peak broadening (CPB) technique. The influences of temperature, pressure, density and viscosity of the solvent mixture on the diffusion coefficients were examined. The results show that methyl oleate always diffuses faster than methyl ricinoleate at the same operating condition. Moreover, the D₁₂ values in ethanol-modified scCO₂ decrease with the increase of the number of C-C double bonds in C18-methyl ester, which is consistent with the trend reported in pure scCO₂. The diffusivity data are compared with the estimation of eleven predictive models. The modified Wilke–Chang equation is the best purely predictive model and the free volume model of Dymond with two adjustable parameter gives the least errors with average absolute deviations lower than 2.5%.     

Biodiesel production from supercritical carbon dioxide extracted Jatropha oil using subcritical hydrolysis and supercritical methylation

This study investigates supercritical carbon dioxide (SC-CO₂) extraction of triglycerides from powdered Jatropha curcas kernels followed by subcritical hydrolysis and supercritical methylation of the extracted SC-CO₂ oil to obtain a 98.5% purity level of biodiesel. Effects of the reaction temperature, the reaction time and the solvent to feed ratio on free fatty acids in the hydrolyzed oil and fatty acid esters in the methylated oil via two experimental designs were also examined. Supercritical methylation of the hydrolyzed oil following subcritical hydrolysis of the SC-CO₂ extract yielded a methylation reaction conversion of 99%. The activation energy of hydrolysis and trans-esterified reactions were 68.5 and 45.2 kJ/mole, respectively. This study demonstrates that supercritical methylation preceded by subcritical hydrolysis of the SC-CO₂ oil is a feasible two-step process in producing biodiesel from powdered Jatropha kernels.     

Continuous production of biodiesel with supercritical methanol: Optimization of a scale-up plug flow reactor by response surface methodology

A scale-up plug flow reactor was evaluated for the continuous production of biodiesel from refined palm kernel oil (PKO) with supercritical methanol and optimized by response surface methodology. The effects of the operating temperature (270–350 °C), pressure (15.0–20.0 MPa) and methanol:PKO molar ratio (20:1–42:1) were evaluated at a constant residence time of 20 ± 2 min by using a central composite design. Analysis of variance demonstrated that a modified quadratic regression model gave the best coefficient of determination (R² = 0.9615) and adjusted coefficient of determination (Adj. R² = 0.9273). The interaction terms in the regression model illustrated small synergistic effects of both temperature–pressure and temperature–methanol:PKO molar ratio. The optimal conditions were 325 ± 5 °C, 18.0 ± 0.5 MPa and a methanol:PKO molar ratio of 42 ± 2:1, attaining a maximum production rate of 18.0 ± 1.5 g biodiesel/min with a fatty acid methyl ester content of 93.7 ± 2.1%. The product obtained from the optimal conditions had high cetane number, and could be considered as a fuel additive for cetane number enhancement.     

Cross-linking polymerization of acrylic acid in supercritical carbon dioxide

Cross-linking polymerization of acrylic acid in supercritical carbon dioxide (scCO₂) was studied in a batch reactor at 50 °C and 207 bar with either triallyl pentaerythritol ether or tetraallyl pentaerythritol ether as the cross-linker and with 2,2′-azobis(2,4-dimethyl-valeronitrile) as the free radical initiator. All polymers were white, dry, fine powders. Scanning electron microscopy showed that the morphology of the polymer particles was not affected by cross-linking. As the cross-linker concentration was increased, the polymer glass transition temperature first decreased, then increased. Water-soluble and water-insoluble polymers were synthesized by adjusting the cross-linker concentration. Viscosity measurements showed that the polymer thickening effect strongly depended on the degree of cross-linking. Finally, cross-linking polymerization of acrylic acid in scCO₂ was carried out in a continuous stirred tank reactor. The use of cross-linker decreased the monomer conversion in this system.     

Continuous extraction of glycerol acetates from their mixture using supercritical carbon dioxide

Supercritical carbon dioxide was used for partially selective extraction of triacetin from a mixture of triacetin, diacetin, and monoacetin with a molar ratio of 1:2:1. The extraction was carried out in two stages. In the first stage, a central composite design was used to optimize the four variables of pressure, temperature, liquid CO₂ flow rate, and extraction time at three levels using a semi-continuous, supercritical carbon dioxide extraction setup. The composition of the extract under the predicted optimum conditions (i.e., 109 bar, 56 °C, 0.86 mL min⁻¹, and 61 min) was about 69% triacetin accompanied by only 30% diacetin and no detectable monoacetin. In the second stage, the effect of the two factors, pressure (100, 109, and 140 bar) and liquid CO₂ flow rates of 0.86 and 1.5 mL min⁻¹ measured at average laboratory temperature (27 °C) and pressure (0.89 bar), were studied using a continuous, supercritical carbon dioxide fractionation setup equipped with a glass-bead packed column kept under a thermal gradient of 56-70 °C. The experimental design was organized as a 3 × 2 general factorial design. Under the best conditions (i.e., 140 bar and 1.5 mL min⁻¹), the extraction yield of triacetin and diacetin were 41.8 and 3.0%, respectively, without any detectable monoacetin as verified by GC-FID.     

Optimization of supercritical CO2 extraction of different anatomical parts of lovage (Levisticum officinale Koch.) using response surface methodology and evaluation of extracts composition

Supercritical carbon dioxide extraction (SFE-CO₂) parameters were optimized using response surface methodology and central composite design for lovage (Levisticum officinale Koch.) roots and leaves containing valuable phytoconstituents. Mathematical model predicted the highest yields of extracts from roots and leaves 2.26 and 2.29%, respectively, at 45 MPa pressure, 60 °C temperature, 90 min (roots) and 30 min (leaves) extraction time, whereas the yield of hydrodistilled essential oil was 0.24 and 0.74%, respectively. The highest relative content of the most valuable constituent Z-ligustilide in roots and leaves extracts was 77 and 50% at 10 MPa; however, the highest yields of this compound from 100 g of dry material were obtained at the highest applied pressure and constituted 1188 mg (roots) and 540 mg (leaves). This study showed that lovage is a good source of Z-ligustilide and SFE-CO₂ is a preferable technique for its isolation.     

Polymerization of acrylonitrile in supercritical carbon dioxide

A series of fluorinated diblock copolymers, consisting of styrene (St)-acrylonitrile (AN) copolymer [poly(St-co-AN)] and poly-2-[(perfluorononenyl)oxy]ethyl methacrylate, with various compositions as well as with different molecular weights were synthesized by atom transfer radical polymerization and characterized. Dispersion polymerization of acrylonitrile in supercritical carbon dioxide (scCO₂) at 30 MPa and at 65 °C with this kind of amphiphilic block copolymer as a stabilizer and 2,2′-azobisisobutyronitrile as an initiator was investigated. The experimental results indicated that, in the presence of a small amount of poly(St-co-AN) (5 wt% to AN), spherical particles of polyacrylonitrile (PAN) were prepared with small diameter and narrow polydispersity (d_n = 153 nm, d_w/d_n = 1.12), resulting from the high stabilizing efficiency of this fluorinated block copolymer. Furthermore, the polymerization of AN in scCO₂ under different initial pressures especially under low pressure (<14 MPa) was studied. When the polymerization was carried out around the critical pressure of CO₂ (7.7-7.8 MPa), the PANs with high molecular weight (M_ν ≈ 130,000-194,000) were synthesized at high monomer conversion (>90%) no matter whether the stabilizer was added, compared to those synthesized by dispersion polymerization at 30 MPa. It was also found that the crystallinity of PAN synthesized at 7.7-7.8 MPa was somewhat higher than that synthesized at 30 MPa, while its crystallite size did not change.     

Lipase-catalysed hydrolysis of blackcurrant oil in supercritical carbon dioxide

The effect of reaction conditions on the extent of conversion in hydrolysis of blackcurrant oil was investigated. The enzyme used was Lipozyme, a lipase from Mucor miehei immobilised on macroporous anionic resin. The reaction was carried out in a continuous flow reactor at 10- and 30-50°C with carbon dioxide saturated with oil and water (55-100%) flowing up through the enzyme bed. Analysis of product composition indicated unfavourable hydrodynamics with significant mixing in the reactor when solvent interstitial velocity was lower than , while above this velocity value the flow pattern was near to plug flow. Lipase stability was very good with no activity reduction observed during a long-term experiment. The reaction rate was a function of the ratio of enzyme load to solvent volumetric flow rate. A complete hydrolysis of oil was achieved in the experiments carried out with the enzyme load of and CO₂ flow rate of 0.4-. The effects of pressure (10-) and temperature (30-40°C) on the reaction rate were small, and the effects of CO₂ saturation with water and of enzyme distribution in the reactor were negligible. Lipozyme displayed specificity towards linolenic acids; the release of α-linolenic acid was faster and that of γ-linolenic acid slower than the release of other constituent acids present in blackcurrant oil.     

Kinetic resolution of 4-phenyl-2-azetidinone in supercritical carbon dioxide

The lipase-catalysed kinetic resolution of rac-4-phenyl-2-azetidinone was investigated in supercritical carbon dioxide (scCO₂). Water (0.5 mol equivalent) was used as nucleophilic donor. The effects of pressure and temperature were studied in a batch reactor (internal volume: 30 mL). The optimum pressure and temperature of the β-lactam ring-opening reaction proved to be 14 MPa and 70 °C. Under optimum conditions, full conversion was achieved in 120 h. The resulting (R)-β-phenylalanine (ee ≥ 98%) and (S)-4-phenyl-2-azetidinone (ee ≥ 99%) could be easily separated by scCO₂ extraction of the (S)-β-lactam and subsequent washing of the enzyme with hot water to recover the amino acid.     

Reactive extraction of succinic acid using supercritical carbon dioxide

Reactive extraction using supercritical carbon dioxide (scCO₂) and tri-n-octylamine (TOA) was evaluated as a separation method of succinic acid from an aqueous solution. The reactive extraction of succinic acid was performed at varying initial acid concentrations in aqueous solution (0.07–0.45 mol?dm^?3), temperature (35–65°C) and pressure (8–16 MPa). The succinic acid separation was conducted in both batch mode and semi-continuous mode. The highest reactive extraction efficiency of approx. 62% was obtained for the process conducted in semi-continuous mode at 35°C and 16 MPa for the initial acid concentrations in aqueous phase of 0.39 mol?dm^?3.     

Solubility of fish oil fatty acid ethyl esters in suband supercritical carbon dioxide

Mutual solubilities and K-values of fish oil fatty acid ethyl esters, prepared from sand launce oil, and sub- and supercritical carbon dioxide have been measured in an apparatus originally designed for phase equilibrium, density and gasoil ratio measurements of reservoir fluids. The measurements were performed at pressures from 2 to 22 MPa at temperatures of 283.2, 313.2 and 343.2°K. Experimental temperatures, pressures, solubilities, K-values and densities are reported. The K-values of ethyl myristate, palmitate, oleate, eicosapentaenoate and docosahexaenoate are compared with published experimental binary and/or multicomponent data. Because both vapor and liquid solubilities are reported, such data are applicable in the design of supercritical extraction plants.     

Acetylation of plant cellulose fiber in supercritical carbon dioxide

Natural cellulosic ramie fiber was acetylated using supercritical carbon dioxide (sc-CO₂) as a reaction medium. The structure and properties of the acetylated fibers were investigated using infrared spectroscopy, scanning electron microscopy, X-ray diffraction (including synchrotron microbeam X-ray diffraction), nano-Raman scattering, and a tensile test. The acetylation reaction proceeded without using an organic solvent, and it reached to the core part of the fiber within a short period while maintaining the fiber morphology. The crystallites of cellulose triacetate II and cellulose coexist in the fiber. The acetylated fiber with an average degree of substitution of 1.9 showed high modulus (34.5 GPa) and high strength (763 MPa), which are the highest values for cellulose diacetate so far reported to date.     

pH Sensitive polypropylene porous membrane prepared by grafting acrylic acid in supercritical carbon dioxide

pH sensitive membrane was prepared by grafting acrylic acid (AA) on the porous polypropylene (PP) membrane using supercritical (SC) CO₂ as a solvent. The monomer (AA) and the initiator (benzyl peroxide, BPO) were impregnated into the PP substrate with the aid of SC CO₂, and were grafted onto the microporous PP substrate. The grafted membranes were characterized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), and the water permeability of the virgin and grafted membranes were determined at different pH values. It was demonstrated that the grafting degree (Dg) could be easily controlled by varying operating conditions, such as the monomer concentration, pressure, and temperature during the soaking process. The water permeation of the virgin membrane is nearly independent of pH. However, the water permeation of grafted membranes decreases dramatically with pH as the pH varies from 3 to 6 because the conformation of the PAA changes significantly with the pH of the contacting solution.