Selective hydrogenation of chloronitrobenzene to chloroaniline in supercritical carbon dioxide over Ni/TiO2: Significance of molecular interactions

The hydrogenation of chloronitrobenzene to chloroaniline was investigated over Ni/TiO₂ at 35 °C in supercritical CO₂ (scCO₂), ethanol, and n-hexane. The reaction rate followed the order of scCO₂ > n-hexane > ethanol. In scCO₂, the selectivity to chloroaniline and to aniline over Ni/TiO₂ were 97–99.5% and <1%, respectively, in the conversion range of 9–100%. The high chemoselectivity to chloroaniline cannot be achieved over Ni/TiO₂ in ethanol and n-hexane. In situ high-pressure Fourier transform infrared measurements were made to study the molecular interactions of CO₂ with the following reactant and reaction intermediates: chloronitrobenzene, chloronitrosobenzene, and N-chlorophenylhydroxylamine. The molecular interaction modifies the reactivity of each species and accordingly the reaction rate and the selectivity. The influence of Cl substituent on the interaction modes of CO₂ with these reacting species is discussed. Possible reaction pathways for the hydrogenation of chloronitrobenzene in scCO₂ over Ni/TiO₂ are also proposed.     

Sequential extraction of bioactive compounds from Melia azedarach L. in fixed bed extractor using CO2, ethanol and water

Melia azedarach L. is a plant with wide use in folk medicine since it contains many bioactive compounds of interest. The present study aimed to extract bioactive compounds from M. azedarach fruits by a sequential process in fixed bed using various solvent mixtures. Extractions were performed at 50 °C and 300 bar in four sequential steps using supercritical CO₂ (scCO₂), scCO₂/ethanol, pure ethanol, and ethanol/water mixture as solvents, respectively. The efficacy of the extraction process was evaluated by extraction yield and kinetics, and analysis of extracts by: (1) thin layer chromatography (TLC), (2) phenolics content, (3) reduction of surface tension of water, (4) gas chromatography (GC–MS), (5) electrospray ionization mass spectrometry (ESI–MS) and (6) antiviral activity. The overall extraction yield reached 45% and TLC analysis showed extracts with different composition. extract obtained from CO₂/ethanol mixture (SCEE) exhibited the greatest ability to reduce surface tension of water from 72.4 mN m⁻¹ [1] of pure water to 26.9 mN m⁻¹ of an aqueous solution of 40 g L⁻¹. The highest phenolics contents were observed in both the hydroalcoholic extract and scCO₂/ethanolic extract. Volatile oils were not detected in the supercritical extracts by GC–MS. MS analyses identified the fatty acids: linoleic, palmitic and myristic acid in the supercritical extract (SCE), and the phenolics: caffeic acid and malic acid in the other extracts. In addition, SCE and SCEE extracts showed significant inhibition percentage against Herpes Simplex Virus Type 1. The extraction process proposed in the present study produced extracts with significant potential for application in food and pharmaceutical industries.     

Fractionated extraction of saponins from Brazilian ginseng by sequential process using supercritical CO2, ethanol and water

Saponins are surfactants that reduce the surface tension of aqueous solutions, besides having pharmacological actions. In order to extract and fractionate saponins from Pfaffia glomerata roots and Hebanthe eriantha roots using supercritical technology, fractionated extracts were obtained from a sequential process in fixed bed using supercritical CO₂ (scCO₂), ethanol, and water as solvents. All extractions were carried out in four sequential steps, at 50 °C and 300 bar. In the first step, pure scCO₂ was used as solvent, while (a) scCO₂/etanol (70:30, w/w); (b) ethanol, and (c) ethanol/water (70:30, v/v) were used as solvents in the three subsequent steps. The extracts were analyzed by thin layer chromatography (TLC) and surface tension. The extraction yields of the four steps were 0.16, 0.55, 1.00, and 6.90% for P. glomerata roots, and 0.17, 0.58, 0.89, and 28% for H. eriantha roots, showing a predominance of high polarity compounds in these species. TLC analysis showed that the extraction process was selective according to the polarity of the solvent, and provided extracts containing different saponins, except for scCO₂ extraction. The extracts from the extraction using ethanol + scCO₂ (Step 2) showed the greatest ability to reduce the surface tension of water from 72 mN m⁻¹ (pure water) to 25 mN m⁻¹, suggesting that this step was the best for extraction of less polar saponins in the extracts. The critical micelle concentration (CMC) values were approximately 2 and 8 g L⁻¹ for P. glomerata and H. Eriantha, respectively. These results confirmed the efficacy of the extraction process under study.     

Supercritical CO2 generator using bubble collapse by water hammer

We have developed a new apparatus to dynamically generate supercritical CO₂ (scCO₂) bubbles in water using a water hammer facility by efficiently concentrating water energy. We measured the internal and external pressures of a CO₂ bubble covered with a rubber membrane using pressure transducers, and observed the bubble's oscillations by a high-speed video camera. We evaluated the maximum duration of the scCO₂ for conditions 60 μs in experiments. We performed numerical simulations using the Rayleigh–Plesset equation by substituting the experimental external pressure profiles of the bubble and confirmed that numerical results agreed with the experimental internal pressure. Moreover, in the minimum external pressure condition where we experimentally achieved the condition of scCO₂ in the bubble for 16 μs by water hammer, we obtained the maximum duration of scCO₂ conditions up to 55 μs by numerical simulations assuming isotropic compression.     

Supercritical fluid extracts from tamarillo (Solanum betaceum Sendtn) epicarp and its application as protectors against lipid oxidation of cooked beef meat

The possibility of using the tamarillo (Solanum betaceum (Cav.) Sendtn (syn. Cyphomandra betacea)) epicarp as source of compounds with antioxidant activity in cooked beef meat (CBM) was explored. Extracts from tamarillo by supercritical fluid extraction (SFE) and Soxhlet extraction (SE) were obtained. The SFE was performed using pure CO₂ at different temperatures and pressures (40 and 50 °C; 10, 20 and 30 MPa) and CO₂ added with ethanol (CO₂/EtOH) as co-solvent (2, 5 and 8%, w/w). The SFE kinetics and mathematical modeling of the overall extraction curves (OEC) were also investigated. EtOH and hexane were used in the SE. The antioxidant activity (AA) of extracts was evaluated in CBM as well as the protection against lipid oxidation was determined by measuring lipid hydroperoxides (LHP) and thiobarbituric acid reactive species (TBARS). The extract obtained by SFE with CO₂/EtOH (50 °C/30 MPa and 2% of EtOH) showed the highest AA. In SFE, the co-solvent addition improved considerably the AA and the extraction yield. The extracts obtained by SFE with CO₂/EtOH showed a better AA compared with the synthetic antioxidant TBHQ. The highest yield values were achieved by SE with ethanol (7.7 ± 0.4%) and by SFE with 5% EtOH (1.9 ± 0.1%). The results indicate that extracts of tamarillo epicarp are a potential source of antioxidant compounds.     

Phase equilibria of palm oil,palm kernel oil,and oleic acid + supercritical carbon dioxide and modeling using Peng–Robinson EOS

Vapor–liquid equilibria of the binary supercritical carbon dioxide (scCO₂) + oleic acid, scCO₂ + palm oil, and scCO₂ + palm kernel oil were measured at a wide range of temperatures from 333.2 to 373.2 K and pressures from 8.5 to 35 MPa in a circulation-type phase equilibrium apparatus. The samples from liquid and vapor phases were analyzed using UV–vis spectrometer and a liquid hold-up equipment. The phase equilibrium data were correlated with Peng–Robinson Equation of State (PR-EOS) using Wong–Sandler mixing rule and optimum values of binary interaction parameters were determined. The relative deviation between experimental data and predicted data was in the range of 6.9–8.7%, suggesting that the PR-EOS with Wong–Sandler mixing rule is capable of predicting the vapor–liquid equilibria of oleic acid + scCO₂, palm oil + scCO₂, and palm kernel oil + scCO₂.     

Extraction of phenolic compounds and anthocyanins from blueberry (Vaccinium myrtillus L.) residues using supercritical CO2 and pressurized liquids

This work explored the potential of subcritical liquids and supercritical carbon dioxide (CO₂) in the recovery of extracts containing phenolic compounds, antioxidants and anthocyanins from residues of blueberry (Vaccinium myrtillus L.) processing. Supercritical CO₂ and pressurized liquids are alternatives to the use of toxic organic solvents or extraction methods that apply high temperatures. Blueberry is the fruit with the highest antioxidant and polyphenol content, which is present in both peel and pulp. In the extraction with pressurized liquids (PLE), water, ethanol and acetone were used at different proportions, with temperature, pressure and solvent flow rate kept constant at 40 °C, 20 MPa and 10 ml/min, respectively. The extracts were analyzed and the highest antioxidant activities and phenolic contents were found in the extracts obtained with pure ethanol and ethanol + water. The highest concentrations of anthocyanins were recovered with acidified water as solvent. In supercritical fluid extraction (SFE) with CO₂, water, acidified water, and ethanol were used as modifiers, and the best condition for all functional components evaluated was SFE with 90% CO₂, 5% water, and 5% ethanol. Sixteen anthocyanins were identified and quantified by ultra performance liquid chromatography (UPLC).     

Integrated process of supercritical CO2-assisted melt polycondensation modification and foaming of poly(ethylene terephthalate)

An integrated process of melt polycondensation modification and foaming of poly(ethylene terephthalate) (PET) was performed in a high pressure vessel assisted by supercritical carbon dioxide (scCO₂). ScCO₂ was firstly employed to sweep PET melt, i.e., high pressure CO₂ continuously flows through the vessel at a fixed flow rate to remove small molecules for higher molecular weight PET, then this modified PET melt was directly foamed through a rapid depressurization process using scCO₂ as blowing agent. In this integrated process, PET with high melt strength after polycondensation modification could be foamed directly in molten state. Therefore, re-molten process of solid modified PET pellets was canceled to avoid its degradation and CO₂ saturation time could be saved in foaming process, thus processing time could be shortened and energy efficiency could be improved. The influences of scCO₂ sweeping treatment time, pressure and flow rate on properties of the modified PETs and cell morphologies of the foamed PETs were investigated respectively. The results showed that CO₂ sweeping treatment could effectively enhance PET melt polycondensation modification process, which was superior to that of N₂ treatment. PET foams with average cell diameter of 32–62 μm and cell density of 1 × 10⁷ to 4 × 10⁷ cells/cm³ have been obtained in the integrated process. Compared with the process of only foaming modified PET by scCO₂ or performing scCO₂ assisted modified PET further melt polycondensation process and scCO₂ foaming process separately, this integrated process produced better cell morphology.     

Kinetics of N-isopropylacrylamide polymerizations in supercritical carbon dioxide fluids

Free-radical polymerization kinetics of N-isopropylacrylamide (NIPAAm) using 2,2′-azobis(isobutyronitrile) (AIBN) as an initiator in supercritical carbon dioxide (scCO₂) was investigated. A high-pressure differential scanning calorimeter revealed that the melting temperatures of NIPAAm and AIBN were both decreased with increasing CO₂ pressure in a linear fashion and the polymerization could occur in CO₂ at 55 °C. The polymerization kinetics of NIPAAm in scCO₂ was compared with that in methanol (MeOH). At 55 °C, the induction periods of polymerizations in scCO₂ of 27.6 MPa were much longer (up to 6 h) than those in MeOH (about 30 min) for similar feed concentrations. The monomer conversions reached and molecular weights produced were much higher in scCO₂ than in MeOH. The reaction orders for initial monomer and initiator concentrations, [NIPAAm]₀ and [AIBN]₀, in initial stage of polymerizations were respectively 1.48 and 0.79 in scCO₂ and 1.27 and 0.51 in MeOH.     

Environmentally benign supercritical CO2 extraction of galanthamine from floricultural crop waste of Narcissus pseudonarcissus

The influence of diverse factors on the supercritical fluid extraction (SFE) with supercritical CO₂ (scCO₂) of galanthamine from bulbs of Narcissus pseudonarcissus cv. Carlton was investigated. The parameters that were studied were CO₂ density (temperature and pressure), flow rate and plant material particle size and pre-treatment. The highest yield (303 μg/g) was achieved by extracting 53–1000 μm particle-size powdered dried bulb material moistened with NH₄OH (25%, v/v) at 70 °C, 220 bar (690 kg/m³) for 3 h. Other N. pseudonarcissus alkaloids such as O-methyllycorenine and haemanthamine were also obtained. N. pseudonarcissus alkaloids as free bases are highly soluble in CO₂ at a high pH as opposed to the slightly soluble salt form in which they are generally found in plants. Therefore, plant material pre-treatment with a base is an essential step for galanthamine extraction. Scanning electron microscope (SEM) results also revealed that the desorption of N. pseudonarcissus alkaloids from the plant material rather than the solubility of the alkaloids in the scCO₂ plays a major role in this scCO₂ extraction. This extraction method has a good potential for industrial application.     

Extraction of bioactive enriched fractions from Eruca sativa leaves by supercritical CO2 technology using different co-solvents

Supercritical fluid extraction from freeze-dried Eruca sativa leaves is assessed with the aim of studying the feasibility to obtain bioactive enriched fractions containing different classes of valuable compounds. Total extraction yields and compositions using pure CO₂ and CO₂ + selected co-solvents are compared. Overall extraction curves, fitted by the model of broken and intact cells developed by Sovová, are reported and the influence of the main parameters that affect the extraction process is analysed. The extract with the highest content in glucosinolates and phenols was collected at 30 MPa and 75 °C using 8% (w/w) of water with respect to the CO₂ flow rate, whereas the fraction richest in lipids was obtained using 8% (w/w) of ethanol as co-solvent at 45 °C and 30 MPa. A process including a first step with supercritical CO₂ extraction using water as co-solvent followed by a second step, where a fraction rich in lipids is extracted using ethanol as co-solvent, is proposed. SCCO₂ results are compared with Soxhlet and other methods that combine organic solvents with ultrasounds.     

What is the state of aggregation of ethanol molecules in ethanol–supercritical carbon dioxide mixtures? An FTIR investigation in the full molar fraction range

The evolution of the degree of hydrogen bonding of ethanol molecules in scCO₂–ethanol mixtures for different molar fraction (from 0.5 to 100% in ethanol) in the temperature range 40–200 °C and at two different constant pressures P = 15 and 20 MPa is reported in this paper. For a given pressure, we observe a strong dependence of the degree of hydrogen bonding as a function of temperature and ethanol molar fraction. We emphasize that a detailed knowledge of the degree of hydrogen bonding of ethanol molecules in these binary systems is important for the understanding and the further development of the supercritical fluid technology.     

Dispersion polymerization of MMA in supercritical CO2 in the presence of poly(poly(ethylene glycol) methacrylate-co-1H,1H,2H,2H-perfluorooctylmethacrylate)

Various random copolymers of poly(poly(ethylene glycol) methacrylate-co-1H,1H,2H,2H-perfluorooctylmethacrylate) (p(PEGMA-co-FOMA)) with different poly(ethylene glycol) (PEG) chain length (M_n = 300, 475, and 1100) and different FOMA content have been synthesized in supercritical carbon dioxide (scCO₂) via free-radical polymerization. The copolymers containing above 50 wt% FOMA could be used as a stabilizer for the polymerization of methyl methacrylate (MMA) in scCO₂. For PEGMA (300) and PEGMA (475) copolymers, the copolymeric stabilizer with 67–69 wt% FOMA content was shown to be optimal to produce micrometer-size spherical PMMA powder. The size of pendant PEG group and the composition of copolymer as well as the concentration of MMA affected on the size of PMMA particles and the stability of PMMA latexes in CO₂.     

Tandem Staudinger-Aza-Wittig reaction in supercritical CO2: Synthesis of a pharmaceutical interest compound

The aim of this research was to investigate the capability of using supercritical CO₂ (scCO₂) as reagent and solvent in the synthesis of pharmaceutical cyclodextrinyl derivatives in smooth reaction conditions. In this way we have followed the kinetics of a synthesis which was previously realized in DMF, by using tandem Staudinger-Aza-Wittig (S.A.W.) reaction in scCO₂ at 200 bars pressure in a 100 mL reactor. The results show that the reaction in scCO₂ showed a second order kinetics with the yield of 92%.     

Reduction of gelatinization temperatures of starch blend suspensions with supercritical CO2 treatment

Modification of starch blend properties by contact with supercritical carbon dioxide (scCO₂) was studied. Potato starch (PS), sweet potato starch (SPS), and cassava starch (CS) were blended with wheat starch (WS) at 15, 25, 50, 75 and 85% (w/w) ratios. For WS, the maximum decrease in gelatinization temperature (T_P) was 13 °C. The WS–PS and WS–CS blends exhibited a decrease in T_P of 13 to 17 °C. Reduction in T_P by treatment was 10 to 18 °C for all blend ratios. Conditions for lowering the starch blend T_P were determined to be a minimum contact time of 1 h with scCO₂ at 60 °C and 20 MPa. Swelling of starch granules that leads to the lowering of T_P involves both kinetic and physicochemical factors. Gelatinization of wheat starch blends with scCO₂ pressure treatment provides a versatile and non-thermal method for modifying the properties of ingredients used in food processing applications.     

Measurement of entrainer effects of water and ethanol on solubility of caffeine in supercritical carbon dioxide by FT-IR spectroscopy

The solubilities of caffeine in supercritical CO₂, supercritical CO₂ + water, supercritical CO₂ + ethanol, and supercritical CO₂ + water + ethanol were measured with a circulation-type apparatus combined with an on-line Fourier transform infrared (FT-IR) spectrometer at 313.2 K and 15.0 MPa. The solubilities of caffeine were determined with the peak absorbances of caffeine at 1190 cm⁻¹. The solubilities of caffeine increase until water is saturated in supercritical CO₂. The maximum increase rate is 22%. In CO₂ + caffeine + ethanol system, the solubilities of caffeine increase with increasing the concentration of ethanol. The solubility of caffeine becomes five times when 1000 mol m⁻³ of ethanol is added. In CO₂ + caffeine + water + ethanol system, the solubilities of caffeine are smaller than those with single entrainer of water or ethanol. The shape of the peaks of two CO stretching bands for caffeine were changed by the addition of ethanol. It was confirmed that the interaction species of caffeine interacting with ethanol are produced by deconvolution of the CO stretching bands. The enhancement of solubility for caffeine in supercritical CO₂ by the addition of ethanol is due to the hydrogen bonding between caffeine and ethanol.     

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%.     

Laser analyses of mixture formation and the influence of solute on particle precipitation in the SAS process

Laser based Raman and elastic light scattering measurements were performed to study the process of mixture formation and the influence of the solute paracetamol onto the phase behaviour of the pseudo-binary system ethanol/CO₂ in the supercritical antisolvent process. From the Raman based technique, mole fraction and partial density distributions of CO₂ were obtained. The mole fraction distributions indicate a rapid mixture formation with fast supersaturation of the solute. At the same time, the increase of the CO₂ partial density at conditions considerably above the mixture critical point (MCP) indicate a change from a homogeneous supercritical to a multi-phase subcritical flow. This phase change goes along with particle precipitation. Thus, the results of our investigations proof, why past approaches failed to generate amorphous paracetamol nanoparticles with the system paracetamol/ethanol/CO₂ above the MCP. Process parameters like injection pressure (20.0–35.0 MPa), chamber pressure of CO₂ (7.5–17.5 MPa), temperature (313–333 K) and solute concentration (0–5 wt%) were varied.     

Hydrogenation of phenol in scCO2 over carbon nanofiber supported Rh catalyst

A catalyst of Rh nanoparticles supported on a carbon nanofiber, 5 wt.% Rh/CNF, with an average size of 2–3 nm has been prepared by a method of incipient wetness impregnation. The catalyst presented a high activity in the ring hydrogenation of phenol in a medium of supercritical CO₂ (scCO₂) at a low temperature of 323 K. The presence of compressed CO₂ retards hydrogenation of cyclohexanone to cyclohexanol under the reaction conditions used, and this is beneficial for the formation of cyclohexanone, increasing the selectivity to cyclohexanone. But the selectivity to cyclohexanone is very low at the completion of reaction in the absence of CO₂, at low CO₂ pressures, and in the presence of pressurized N₂ instead of CO₂. That is, high selectivity to cyclohexanone can be achieved with CO₂ species at higher pressures but not with the application of an inert hydrostatic pressure on the liquid substrate phase.     

Kinetic enzymatic resolution in scCO2 – Design of continuous reactor based on batch experiments

We developed an efficient method for the lipase-catalyzed consecutive kinetic resolution of trans-1,2-cyclohexanediol in scCO₂ with vinyl-acetate as acetyl donor catalyzed by a commercial immobilized Candida antarctica lipase B (CAL-B). The reaction was optimized in scCO₂ in a batch reactor. The first acylation step is moderately enantioselective, preferring the formation of (1R,2R)-2-acetoxycyclohexane-1-ol, while the second acylation step is fully enantioselective. Michaelis–Menten type reaction constants and turnover number values were calculated. A combined extractor–enzymatic packed-bed reactor unit was designed with a residence time of a few seconds (the time requirement of a batch reaction was several hours). The reactions were performed at 10 MPa and 45 °C. The mean residence time in the enzymatic reactor was varied from 2 to 13 s by changing the flow rate of the CO₂. The implemented continuous reactor was optimized to achieve maximum productivity and enantiopure products. The optimum residence time in the reactor entirely confirmed the calculated operational parameters (calculated necessary residence time: 9.6 s, measured mean residence time for full conversion: 9 s). No loss of enzyme activity was observed after 28 h at continuous operation.