Phase behavior measurement for poly(isobornyl acrylate) + cosolvent systems in supercritical solvents at high pressure

We have conducted experiments to obtain cloud-point data of binary and ternary mixtures for poly(isobornyl acrylate) [P(IBnA)] (Mw = 100,000) + isobornyl acrylate(IBnA) in supercritical carbon dioxide (CO₂), P(IBnA) (Mw = 100,000) + dimethyl ether (DME) in CO₂, P(IBnA) (Mw = 100,000) in propane and butane, and P(IBnA) (Mw = 1,000,000) in propane, propylene, butane and 1-butene at high pressure conditions. Phase behaviors for these systems were measured at a temperature range from 323.4 K to 474.1 K and pressure up to 296.7 MPa. The cloud-point curves of P(IBnA) (Mw = 100,000) + IBnA and DME in CO₂ change from upper critical solution temperature (UCST) behavior to lower critical solution temperature (LCST) behavior as IBnA and DME concentration increases, and liquid–liquid–vapor phase behavior appears for the P(IBnA) (Mw = 100,000) + CO₂ + 80.3 wt.% IBnA system. Phase behaviors of P(IBnA) and 50 wt.% IBnA in CO₂ and P(IBnA) in propane and butane show the pressure difference in accordance with Mw = 1,000,000 and Mw = 100,000 of P(IBnA). Also, the solubility curves for IBnA in supercritical CO₂ were measured at a temperature range of (313.2–393.2) K and pressure up to 22.86 MPa. The experimental results were modeled with the Peng–Robinson equation of state (PR-EOS) using a mixing rule including two adjustable parameters. The critical property of IBnA is estimated with the Joback–Lyderson method.     

Phase behavior for the poly[2-(2-ethoxyethoxy)ethyl acrylate] and 2-(2-ethoxyethoxy)ethyl acrylate in supercritical solvents

Pressure-composition (p, x) isotherms were obtained for the carbon dioxide + 2-(2-ethoxyethoxy)ethyl acrylate [2-(2-EE)EA] system at five temperatures (313.2 K, 333.2 K, 353.2 K, 373.2 K, and 393.2 K) and pressure up to 22.86 MPa. The carbon dioxide + 2-(2-EE)EA system exhibits type-I phase behavior with a continuous mixture critical curve. The experimental results for carbon dioxide + 2-(2-EE)EA mixtures are correlated using the Peng–Robinson equation of state (PR-EOS) using mixing rule including two adjustable parameters. The critical property of 2-(2-EE)EA is estimated with the Joback–Lyderson method.Experimental data up to 485 K and 206.6 MPa are reported for binary and ternary mixtures of poly(2-(2-ethoxyethoxy)ethyl acrylate) [P(2-(2-EE)EA)] + carbon dioxide + 2-(2-EE)EA, P(2-(2-EE)EA) + carbon dioxide + dimethyl ether (DME), P(2-(2-EE)EA) + carbon dioxide + propylene and P(2-(2-EE)EA) + carbon dioxide + 1-butene systems. High-pressure cloud-point data are also reported for P(2-(2-EE)EA) in supercritical carbon dioxide, propane, propylene, butane, 1-butene, and DME at temperature to 474 K and a pressure range of (8.45–206.6) MPa. Cloud-point behavior for the P(2-(2-EE)EA) + carbon dioxide + 2-(2-EE)EA system were measured in changes of the pressure–temperature (p, T) slope and with 2-(2-EE)EA mass fraction of 0.0 wt%, 5.9 wt%, 14.9 wt%, 30.3 wt% and 60.2 wt%. With 0.650 2-(2-EE)EA to the P(2-(2-EE)EA) + carbon dioxide solution, the cloud point curves take on the appearance of a typical lower critical solution temperature boundary. The P(2-(2-EE)EA) + carbon dioxide + (0.0–46.6) wt% DME systems change the (p, T) curve from upper critical solution temperature region to lower critical solution temperature region as the DME mass fraction increases. Also, the impact by propylene and 1-butene mass fraction for the P(2-(2-EE)EA) + carbon dioxide + propylene and 1-butene system is measured at temperatures to 454 K and a pressure range of (75.7 to 119.6) MPa.     

Cosolvent effect on the phase behavior for the poly(benzyl acrylate) and poly(benzyl methacrylate) in supercritical carbon dioxide and dimethyl ether

Experimental cloud-point data up to 433.2 K and 193.0 MPa are reported for binary and ternary mixtures of poly(benzyl methacrylate) [poly(BzMA)] + carbon dioxide + benzyl methacrylate (BzMA) and poly(benzyl acrylate) [Poly(BzA)] + carbon dioxide + benzyl acrylate (BzA) systems. High-pressure cloud-point data are also reported for Poly(BzMA) + carbon dioxide and Poly(BzA) + carbon dioxide in supercritical dimethyl ether (DME). Cloud-point behavior for the Poly(BzMA) + carbon dioxide + BzMA system was measured in changes of the pressure–temperature (p–T) slope, and with BzMA weight fraction of 50.6, 61.0, 67.2 and 95.0 wt.%. The Poly(BzA) + carbon dioxide + 30.4, 40.7 and 49.4 wt.% BzA systems change the (p–T) curve from upper critical solution temperature region (UCST) to lower critical solution temperature (LCST) region as the BzA concentration increases. With 52.3 wt.% BzA to the Poly(BzA) + carbon dioxide solution, the cloud-point curves are taken on the appearance of a typical lower critical solution temperature boundary. Also, the impact by cosolvent (BzMA and BzA) concentrations for the Poly(BzMA) + DME and Poly(BzA) + DME systems is measured at temperature to 453.2 K and pressure range of 24.6–61.3 MPa.     

Phase behavior for the poly(dimethylsiloxane) in supercritical fluid solvents

In this work, cloud-point and bubble-point phase behavior data are reported for the poly(dimethylsiloxane) [PDMSA] in supercritical carbon dioxide, propane, propylene, butane, 1-butene and dimethyl ether (DME). The static-type method, using a variable-volume view cell, was employed to obtain the experimental data at the temperature range for (315.2–454.9) K and pressure up to 55.52 MPa. PDMS (M_w = 38,900) + C₄ cloud-point curves are ～10 MPa lower than the PDMS + C₃ curves at constant temperature of 423 K. Cloud-point curves for the PDMS + solvents system show the lower critical solution temperature (LCST) region.     

Supercritical CO2 assisted formation of poly(vinylidenefluoride) aerogels containing amoxicillin,used as controlled release device

In this work, a supercritical CO₂ (SC-CO₂) drying process for the formation of poly(vinylidenefluoride) (PVDF) aerogels containing amoxicillin has been tested. Experiments at pressures ranging between 150 and 250 bar and at temperatures ranging between 35 and 55 °C have been performed; then, the PVDF – isopropyl alcohol – N-methylpirrolidone solution at 10% (w/w) polymer has been selected for the addition of amoxicillin at concentrations between 10 and 30% (w/w) with respect to PVDF. Since amoxicillin is soluble in isopropyl alcohol, a quaternary solution has been obtained that produced PVDF aerogels characterized by drug coated nanometric fibers. A two step formation mechanism has been hypothesized that puts in evidence the non-interference of amoxicillin on PVDF gelation process and the heterogeneous amoxicillin precipitation on PVDF nanofibers. The coverage of nanofibers by amoxicillin turned the structure from hydrophobic to quasi-hydrophilic. A homogeneous drug distribution was obtained; a quasi-constant release rate and no burst effect were observed.     

Superior carbon-based CO2 adsorbents prepared from poplar anthers

A series of renewable nitrogen-containing granular porous carbons with developed porosities and controlled surface chemical properties were prepared from poplar anthers. The preparation conditions such as pre-carbonization and activation temperatures and KOH amount significantly influence the structures and chemical compositions of the porous carbons, the CO₂ adsorption capacities of which are highly dependent on their pore structures, surface areas, nitrogen contents and adsorption conditions. The sample with developed microporosity, especially with the pores between 0.43 and 1 nm and high nitrogen content shows high CO₂ adsorption capacity at 1 bar and 25 °C. In contrast, when the adsorption pressure is higher than 5 bar, its CO₂ adsorption capacity is dominated by its surface area, and more accurately by its pore volume. Irrespective of this, if the pressure was decreased to 0.1 bar, its CO₂ capture ability is closely correlated to its nitrogen content but not to its porosity. By optimizing the preparation conditions, a porous carbon with a surface area of 3322 m² g⁻¹ and a CO₂ adsorption capacity as high as 51.3 mmol g⁻¹ at 50 bar and 25 °C was prepared.     

MLCT interaction in [Rh(II)2(CO3)4]4 −( x L)

Complexes of the type [Rh^II₂(CO₃)₄(H₂O)L]^n − with L = N-methylpyrazinium⁺ and 1-heptyl-4-(4-pyridinyl)pyridinium⁺ cations display intense long-wavelength (Rh(II) to L) MLCT absorptions. With L = H₂O, MLCT absorptions are not identified, but the photoreactivity of the complex in aqueous solution supports the assumption that (Rh(II) to CO₃^2 −) MLCT excited states are accessible. Upon irradiation with white light, Rh(II) is photooxidized while carbonate is reduced to CO. The efficiency of this photolysis is very low. However, the occurrence of this photoredox reaction is, nevertheless, of general interest with regard to the photochemical reduction of CO₂.     

Preparation in supercritical CO2 of porous poly(methyl methacrylate)–poly(l-lactic acid) (PMMA–PLA) scaffolds incorporating ibuprofen

Partially biodegradable porous scaffolds incorporating bioactive molecules prepared by clean techniques posses an enormous interest in tissue engineering applications. Poly(methyl methacrylate)–poly(l-lactic acid) (PMMA–PLA) blends were submitted to CO₂ supercritical conditions (P = 160–260 bar, T = 60 °C) after certain time and then rapidly depressurized to obtain porous structures that have been related with the supercritical parameters and to the polymer blend composition. In some cases ibuprofen was also incorporated to the formulations previously to the CO₂ treatment and studied the appropriate conditions for avoiding its extraction in SCCO₂. Scaffolds purity, thermal transitions, swelling and degradation behaviour, and the ibuprofen release were also studied to determine the appropriate scaffolds with a desired porosity for cell seeding. Cell culture was performed on the selected porous scaffolds using human fibroblast examined by scanning electron microscopy (SEM).     

Decaffeinated black tea: Process optimization and phenolic profiles

The low-quality black tea was extracted at 27 different conditions using a lab-scale supercritical fluid extraction system according to four factor, three level Box–Behnken design [pressure (150–450 bar), temperature (40–80 °C), modifier flow rate (0.5–1.0 ml/min), and ethanol concentration in aqueous solution (75–100%)] at constant CO₂ flow rate (2 l/min). Response surface methodology was used in order to optimize the extraction conditions for obtaining minimum caffeine and maximum phenolic profiles of the decaffeinated black tea. The R² values for caffeine and phenolics were 99.5 and 96.6%, respectively. The lowest caffeine and the highest phenolics were obtained at following conditions [pressure (300 bar), temperature (53 °C), modifier flow rate (0.70 ml/min), and ethanol concentration (87.5%)] for 1 h. Using these conditions, the average loss of caffeine and phenolics in the decaffeinated tea were 99.8 and 3.3%, respectively. The present work suggests that optimum extraction conditions found can be applied for a pilot or large-scale production of decaffeinated black tea.     

Extraction of bioactive compounds from peach palm pulp (Bactris gasipaes) using supercritical CO2

Natural compounds with biological activity have recently attracted special interest in the agro-industry as sources of additives in nutraceutical food production and pharmaceutical industries. Herein, we evaluated extracts obtained from peach palm fruit (Bactris gasipaes) using supercritical carbon dioxide, in terms of yield, total phenolic content, total flavonoids, total carotenoids, and antioxidant activity by β-carotene bleaching method. Extractions were performed at 40, 50, and 60 °C and 100, 200, and 300 bar; additionally, Soxhlet (with petroleum ether) and methanol extraction were conducted. The results showed that supercritical CO₂ allows obtaining extracts rich in carotenoids and, although it presents lower yield than conventional extraction (SOX), supercritical CO₂ represents a technique with greater advantages. The best operation condition for supercritical extraction was 300 bar–40 °C, given that the highest concentration of carotenoids was obtained, without the yield being significantly different from that obtained with 300 bar–60 °C, this extract had antioxidant activity comparable to that of commercial caffeic acid.     

Mechanism of NO reduction by CO over Pt/SBA-15

The mechanism of the CO + NO reaction catalyzed by Pt/SBA-15 was studied via independent investigations of CO oxidation and NO disproportionation. Below 400 °C, both CO + O₂ and CO + NO reactions approach 100 % conversion, while the catalyst shows negligible activity for NO disproportionation. These results suggest that CO oxidation by atomic oxygen arising from NO dissociation is not a major route for CO₂ formation in the CO + NO reaction. In situ IR spectra reveal the formation of isocyanates (NCO⁻) adsorbed on silica. Their surface concentration changes with the extent of the CO + NO reaction. A mechanism is proposed in which isocyanates are reaction intermediates.     

Controllable synthesis of α-MoC1-x and β-Mo2C nanowires for highly selective CO2 reduction to CO

Transition metal carbides are attractive catalysts because of their similar properties to precious metals. Here, we report the controllable synthesis of α-MoC_1-x and β-Mo₂C nanowires as highly active and selective catalysts for CO₂ reduction to CO (CO₂ + H₂ → CO + H₂O, reverse water-gas shift reaction, RWGS). CO₂ conversion of > 60% together with nearly 100% CO selectivity was achieved at 600 °C, H₂:CO₂ molar ratio of 4:1, and space velocity of 36,000 mL g^− 1 h^− 1. A formate decomposition mechanism for the RWGS reaction was proposed based on the in-situ DRIFTS results.     

Hydrogen formation from a real biogas using electrochemical cell with gadolinium-doped ceria porous electrolyte

The electrochemical cell consisting of a gadolinium-doped ceria (GDC, Ce_0.9Gd_0.1O_1.95) porous electrolyte, Ni–GDC cathode and Ru–GDC anode was applied for the dry-reforming (CH₄+CO₂→2H₂+2CO) of a real biogas (CH₄ 60.0%, CO₂ 37.5%, N₂ 2.5%) produced from waste sweet potato. The composition of the supplied gas was adjusted to CH₄/CO₂=1/1 volume ratio. The supplied gas changed continuously into a H₂–CO mixed fuel with H₂/CO=1/0.949–1/1.312 vol ratios at 800 °C for 24 h under the applied voltage of 1–2 V. The yield of the mixed fuel was higher than 80%. This dry-reforming reaction was thermodynamically controlled at 800 °C. The application of external voltage assisted the reduction of NiO and the elimination of solid carbon deposited slightly in the cathode. The decrease of heating temperature to 700 °C reduced gradually the fraction of the H₂–CO fuel (61.3–18.6%) within 24 h. Because the Gibbs free energy change was calculated to be negative values at 700–600 °C, the above result at 700–600 °C originated from the gradual deposition of carbon over Ni catalyst through the competitive parallel reactions (CH₄→C+2H₂, 2CO→C+CO₂). The application of external voltage decreased the formation temperature of carbon by the disproportionation of CO gas. At 600 °C, the H₂–CO fuel based on the Faraday's law was produced continuously by the electrochemical reforming of the biogas.     

Phase equilibrium data of guaçatonga (Casearia sylvestris) extract + ethanol + CO2 system and encapsulation using a supercritical anti-solvent process

The aim of this research was to investigate the phase equilibrium behavior of a system containing guaçatonga extract + ethanol + CO₂ in order to help define the adequate conditions of temperature and pressure for the co-precipitation process, performed by means of supercritical anti-solvent (SAS) technique. Guaçatonga (Casearia sylvestris) is a native medicinal plant from Brazil, rich in valuable components such as β-caryophyllene, α-humulene and bicyclogermacrene. Phase equilibrium data were obtained by the static method using guaçatonga extract dissolved in ethanol (1:100, wt/wt), at temperatures ranging from 35 to 75 °C and CO₂ mass content from 60 to 90 wt%. It was noticed that the system exhibited solid–vapor–liquid, solid–liquid–liquid and solid–vapor–liquid–liquid transition types and a lower critical solution temperature behavior. Phase behavior study was considered for the definition of the SAS conditions applied for the encapsulation of guaçatonga extract in the biopolymer Pluronic F127. The conditions tested ranged from 80 to 140 bar at 45 °C. At 80 bar only segregated particles of extract and the biopolymer were detected, while at 110 and 140 bar an extract encapsulation was achieved.     

Characteristics of integrated micro packed bed reactor-heat exchanger configurations in the direct synthesis of dimethyl ether

The performance of three integrated micro packed bed reactor-heat exchangers (IMPBRHEs) for direct DME synthesis over physical mixtures of CuO–ZnO–Al₂O₃ and γ-Al₂O₃ catalysts was experimentally investigated. Systematic variations in reactor and slit dimensions and configuration were analyzed in terms of thermal behaviour, mass transfer, pressure drop and residence time distribution (RTD). The pressure drop was always small (<0.12 bar) relative to the total pressure (50 bar), and linear dependence with GHSV confirms the predicted laminar flow for Re = 0.1–2. A narrow RTD was estimated by the dispersion analysis. Careful temperature measurements confirmed that the reaction temperature is mainly controlled by the oil heat exchange to give a practically uniform temperature profile for set inlet oil temperatures of 220–320 °C. The micro packed beds were found free of the internal as well as external mass transfer limitations, as showed by no significant change in the CO conversion and DME yield for different catalyst particle sizes, no effect of varying the linear gas velocity, and no effect of manipulating reactant diffusion coefficient. Packed bed microstructured reactors hence provide an isobaric and isothermal environment free from transport limitations for the direct DME synthesis, in the kinetic regime as well as at equilibrium conversion.     

Phase equilibria for the 2-ethoxyethyl acetate and 2-(2-ethoxyethoxy)ethyl acetate in supercritical CO2 at various temperatures and pressures up to 20 MPa

The (CO₂ + 2-ethoxyethyl acetate) and (CO₂ + 2-(2-ethoxyethoxy)ethyl acetate) systems at 313.2, 333.2, 353.2, 373.2 and 393.2 K as well as pressures up to 20.59 MPa have been investigated using variable-volume high pressure view cell by static-type. The solubility curve of 2-ethoxyethyl acetate and 2-(2-ethoxyethoxy)ethyl acetate in the (CO₂ + 2-ethoxyethyl acetate) and (CO₂ + 2-(2-ethoxyethoxy)ethyl acetate) systems increases as the temperature increases at a constant pressure. The (CO₂ + 2-ethoxyethyl acetate) and (CO₂ + 2-(2-ethoxyethoxy)ethyl acetate) systems exhibit type-I phase behavior. The experimental results for the (CO₂ + 2-ethoxyethyl acetate) and (CO₂ + 2-(2-ethoxyethoxy)ethyl acetate) systems correlate with the Peng–Robinson equation of state using a van der Waals one-fluid mixing rule including two adjustable parameters. The critical properties of 2-ethoxyethyl acetate and 2-(2-ethoxyethoxy)ethyl acetate are predicted with the Joback–Lyderson group contribution and Lee–Kesler method.     

New catalytic system for oxidation of isopropyl alcohol with thin film catalysts

This paper describes a new catalytic system developed to study catalysts deposited as thin films on a metallic support. This device uses the electromagnetic induction for heating the metallic support. Therefore, it enables homogeneous sample heating, up to 400 °C·min^− 1 with a good regulation and a very low thermal inertia allowing fast cooling and accurate hold on temperature plateau. Catalysts SnO₂, 0.3 and 1 wt.% Pt on SnO₂ were deposited on stainless steel by an electrophoretic technique and evaluated in the abatement of isopropyl alcohol in air, a common model for VOCs.     

Supercritical carbon dioxide immobilization of glucose oxidase on polyurethane/polypyrrole composite

Glucose oxidase (GOX) was immobilized on polyurethane/polypyrrole (PU/PPY) composite foam via supercritical fluid immobilization (SFI) towards the preparation of biosensors. Buffer solution was used as the immobilization medium along with scCO₂. To provide insight into the relation between the scCO₂ and the GOX-buffer solution, the GOX-buffer solutions were subjected to scCO₂ and the protein amounts of the GOX-buffer solutions before and after scCO₂ exposure were determined at 80, 100 and 150 bar and 30, 40 and 50 °C for an exposure time of 24 h. The protein amount in GOX-buffer solution decreased in all cases after exposure to scCO₂. The lowest and highest loss in GOX amounts observed were 2.9 and 36.4 μg at 80 bar, 30 °C and 100 bar, 50 °C, respectively. The effects of immobilization pressure (80, 100 and 150 bar), temperature (30, 40 and 50 °C) and time (4, 24 and 72 h) on the activities of the GOX-immobilized PU/PPY composites were investigated. At 30 °C immobilization temperature, the activity values of the GOX-immobilized PU/PPY composites were slightly increased as the pressure was increased from 80 to 100 bar. Further increase in immobilization pressure from 100 to 150 bar at 30 °C caused a decrease in the activity values. At 40 °C immobilization temperature, increasing the immobilization pressure from 80 to 100 bar did not provide an increase in activity values, but further increase to 150 bar caused a decrease in the activity values. At 100 bar immobilization pressure, decrease in temperature enhanced the activity values of the samples. When immobilization was performed via SFI, the activity values were doubled compared to the immobilization at atmospheric conditions. Among all the immobilization pressures and temperatures investigated, both the highest activity (U/cm²) and the highest specific activity (U/mg) were obtained for the samples processed at 100 bar, 30 °C.     

Development of electrochemical cell with layered composite of the Gd-doped ceria/electronic conductor system for generation of H2–CO fuel through oxidation–reduction of CH4–CO2 mixed gases

This paper shows the recent results on the development of layered composite promoting two types of electrochemical reactions (oxidation and reduction) in one cell. This cell consisted of porous Ni–Gd-doped (GDC) ceria cathode/thin porous GDC electrolyte (50 μm)/porous SrRuO₃–GDC anode. The external electric current was flowed in this cell at the electric field strength of 1.25 and 6.25 V/cm. The mixed gases of CH₄ (30–70%) and CO₂ (70–30%) were fed at the rate of 50 ml/min to the cell heated at 400–800 °C under the electric field. In the cathode, CO₂ was reduced to CO (CO₂ + 2e^? → CO + O^2?) and the formed CO and O^2? ions were transported to the anode through the pores and surface and interior of grains of GDC film. On the other hand, CH₄ was oxidized in the anode to form CO and H₂ through the reaction with diffusing O^2? ions (CH₄ + O^2? → CO + 2H₂ + 2e^?). As a result, H₂–CO mixed fuel was produced from the CH₄–CO₂ mixed gases (CH₄ + CO₂ → 2H₂ + 2CO). This electrochemical reaction proceeded completely at 800 °C and no blockage of gases was measured for long time (>10 h). Only H₂–CO fuel was generated in the wide gas compositions of starting CH₄–CO₂ gases.     

Modelling of the inactivation kinetics of Escherichia coli,Saccharomyces cerevisiae and pectin methylesterase in orange juice treated with ultrasonic-assisted supercritical carbon dioxide

The combined effect of supercritical carbon dioxide (SC-CO₂) and high power ultrasound (HPU) on the inactivation kinetics of Escherichia coli, Saccharomyces cerevisiae and pectin-methyl esterase (PME) in orange juice was studied in order to select models that can predict their inactivation behaviour based on process parameters. Experiments were performed at different temperatures (31–41 °C, 225 bar) and pressures (100–350 bar, 36 °C). The inactivation rate of E. coli, S. cerevisiae and PME increased with pressure and temperature during SC-CO₂ + HPU treatments. The SC-CO₂ + HPU inactivation kinetics of E. coli, S. cerevisiae and PME were represented by models that included temperature, pressure and treatment time as variables, based on the Biphasic, the Peleg Type B, and the fractional models, respectively. The HPU-assisted SC-CO₂ batch system permits the use of mild process conditions and treatment times that can be even shorter than those of continuous SC-CO₂ systems.