Supercritical Carbon Dioxide System Research Articles

A greener bioreduction using baker’s yeast cells in supercritical carbon dioxide and glycerol system

This study reports results of an entire green methodology combining bioreduction by baker’s yeast supported cells and a medium formed by glycerol and scCO2 to a β-ketoester biotransformation. Fermented cells of Saccharomyces cerevisiae, immobilized in calcium alginate beads, were chosen to catalyze ethyl acetoacetate reduction in a biphasic system of scCO2 and glycerol 20% (vol/vol) (T = 45 °C and P = 100 bar). The bioreduction was also carried out at normal conditions (T = 45°C and P = 0.92 bar) in n-heptane and glycerol 20% (vol/vol). Using scCO2/glycerol the reaction reached 77% of conversion in 6 h, and the enantiopure (S)-ethyl-3-hydroxybutyrate (enantiomeric excess > 99%) was observed as the unique product. The same reaction under normal conditions led to only 12% conversion in 6 h. The approach evaluated in this study showed a great potential to be employed as a greener alternative to conventional bioreduction process.

Generation of Pd@Ni‐CNTs from Polyethylene Wastes and Their Application in the Electrochemical Hydrogen Evolution Reaction

AbstractMost polyethylene‐based plastics are used only few times, but the wastes resulted from them need hundreds of years to degrade completely in natural environment. Consequently, innovative treatment methods are highly desired to deal with these wastes thoroughly and convert them into more useful materials. Here in, carbon nanotubes with Ni particles encapsulation (marked as Ni‐CNTs) were synthesized in supercritical carbon dioxide system at 650 °C for 3 h firstly. The prepared Ni‐CNTs were tens of microns in length and 100 nm in diameter, and 20 wt% of Ni nanoparticles with a diameter of 100 nm were contained at the top of the carbon nanotubes. About 60.7 wt% carbon in the polyethylene wastes was converted to carbon nanotubes. Then Ni‐CNTs were modified by Pd (marked as Pd@Ni‐CNTs), and a plenty of Pd nanoparticles with a size of 10 nm were prepared on the surfaces of CNTs. The water splitting performance of the products was also obviously improved, and the overpotential can reach to 62 mV in N2‐saturated 0.5 M H2SO4 electrolyte with 7.5 wt.% of Pd. As the content of Pd increased, the performance of the products was also reinforced. At last, the performance of the catalyst can be comparable with commercial Pt/C catalyst.

Inactivation of the microbiota and effect on the quality attributes of pineapple juice using a continuous flow ultrasound-assisted supercritical carbon dioxide system.

Supercritical carbon dioxide inactivation technology represents a promising nonthermal processing method, as it causes minimum impact on the nutritional food properties. The aim of this study was to analyze the combined effect of supercritical carbon dioxide and high-power ultrasound on the inactivation of natural microbiota and the quality attributes of pineapple juice treated in a continuous flow system. Different juice residence times (3.06-4.6 min), at 100 bar and 31.5 ℃, were used. The results indicated that the microbiota inactivation was complete and the differences obtained in the quality attributes (2.2% for pH, 4.8% for °Brix, 2% for vitamin C) were minimal. During storage, microorganisms were not able to recover and the vitamin C decrease could be limited to 8.2% after four weeks. The results demonstrated that the supercritical carbon dioxide-high-power ultrasound technique could be an excellent alternative for the cold pasteurization of pineapple juice.

Solubility correlation of gall (Quercus infectoria) extract in supercritical CO2 using semi‐empirical equations

AbstractThe present work studied the solubilities of Quercus infectoria gall extract in supercritical carbon dioxide (SC‐CO2) system with the addition of methanol as polarity enhancer. Experimentally, the galls were extracted using SC‐CO2 at different operating pressures (20 to 30 MPa) and temperatures (50 to 70 °C). Six semi‐empirical equations (Chrastil, Adachi‐Lu, del Valle‐Aguilera, Sparks, Kumar‐Johnston and Bartle) were used to explain mathematically the solubility behaviour of the Q. infectoria gall extract. The results demonstrated that the extract solubility increases as pressure increases at fixed temperature, while at constant pressure, it increases with increasing temperature. Apparently, Bartle equation provides best correlation between experimental and calculated solubility data for gall extraction with high correlation coefficient, R2 (0.96), and small absolute average relative deviation (1.52%). © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.

Parameter and layout optimization of a high temperature solar combined cycle using low temperature thermal storage

A novel high temperature solar supercritical carbon dioxide (S‐CO2) and organic Rankine cycle (ORC) combined power system with low temperature thermal storage is introduced. The heat releasing of the S‐CO2 can be used as the heat source of the ORC. This system could keep high thermal efficiency, whereas thermal storage temperature is far lower than the maximum temperature of the system. Previous work has proved that the system efficiency can be kept at 38% when the thermal storage temperature is in the range of 220∼230°C. Basic relationship among system efficiency, power ratio and thermal storage temperature are analyzed. The key parameters of the system are optimized under certain constraints. Three possible improved layouts of this system are discussed in the end. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1234–1243, 2017

Application of aluminum-supported Pd, Rh, and Rh-Pd nanoparticles in supercritical carbon dioxide system for hydrodebromination of polybrominated diphenyl ethers

Al-powder-supported Pd, Rh, and Rh-Pd catalysts were synthesized through a spontaneous redox reaction in aqueous solutions. These catalysts hydrodebrominated 4- and 4,4′-bromodiphenyl ethers in supercritical carbon dioxide at 200 atm CO2 containing 10 atm H2 and 80 °C in 1 h. Diphenyl ether was the major product of Pd/Al. Rh/Al and Rh-Pd/Al further hydrogenated two benzene rings of diphenyl ether to form dicyclohexyl ether. The hydrogenolysis of CO bonds on diphenyl ether over Rh/Al and Rh-Pd/Al was observed to generate cyclohexanol and cyclohexane (<1%). With respect to hydrodebromination efficiency and catalyst stability, Rh-Pd/Al among three catalysts is suggested to be used for ex situ degradation of polybrominated diphenyl ethers in supercritical carbon dioxide.

Design Principles of Surfactants for Polymerization in Supercritical CO&lt;sub&gt;2&lt;/sub&gt;

In recent years, supercritical carbon dioxide, as a green chemical solvent, is widely used. The surfactants for polymerization in supercritical fluids have become one of the important issues. This paper mainly discusses the mechanism and influence of the surfactants in supercritical carbon dioxide system. The choice and design principle of surfactants and the recent development of surfactants were introduced in detail.

Study of the bubble nucleation and growth mechanisms in high-pressure foam injection molding through in-situ visualization

Although major efforts have been made to uncover the complex mechanisms of bubble nucleation and dynamics in foam injection molding, most theories and interpretations still require additional experimental verification. An innovative visualization mold was employed with which the mechanisms of bubble nucleation and growth in high-pressure foam injection molding were investigated. For the first time, the development of the cell structure in high-pressure foam injection molding was comprehensively explored and experimentally verified via in-situ visualization using polystyrene and supercritical carbon dioxide system. Two bubble-nucleation mechanisms were observed, namely, the nucleation due to a pressure drop at the gate during filling, and the nucleation due to melt shrinkage in the cavity after filling. It was the cavity pressure that determined which bubble-nucleation mechanism was dominated between these two in high-pressure foam injection molding. The final cellular structure and morphology of the foamed parts were, in turn, determined by the governing bubble-nucleation mechanism. It was concluded that a melt packing pressure is required to re-dissolve the bubbles nucleated at the gate back into the melt, and that a larger packing pressure was needed with a higher cell density by increasing the injection speed, the gate resistance, or the blowing-agent content. Because of the high resistance in the narrow cavity, the bubbles within the cavity were not pressurized uniformly, when the packing pressure was applied. A higher cell density increased the compressibility of the two-phase gas–melt mixture, aggravating the non-uniformity of the pressure in the cavity. Consequently, the bubbles far from the gate could not be pressurized immediately, and thereby could not dissolve into the polymer melt quickly. Additionally, the lower temperature of the melt far from the gate further delayed the permeation of gas into the polymer.

Partitioning of organics between ionic liquids and supercritical CO2: Limiting K-factors in [bmim][N(CN)2]–scCO2 system and generalized correlation with cation- and anion-specific LSERs

Infinite dilution partition coefficients (K-factors) of a selection of organic solutes in biphasic 1-n-butyl-3-methylimidazolium dicyanamide ([bmim][dca])–supercritical carbon dioxide (scCO2) system were obtained from retention measurements by open tubular capillary column supercritical fluid chromatography (SFC) with [bmim][dca] serving as the stationary liquid and scCO2 as the carrier fluid. Therefore, the SFC-based route to solute K-factors in ionic liquid (IL)–scCO2 systems is feasible even with low viscosity ILs such as [bmim][dca].The experimental K-factors in [bmim][dca]–scCO2 system were used to test an earlier generalized correlation of solute K-factors in IL–scCO2 systems. Further, another version of the generalized correlation was introduced and tested. In the linear solvation energy (LSER) part of the former correlation the IL has been treated as a single species whereas, in the new version, the IL cation- and anion-specific LSER part has been employed. The introduction of the ion-specific LSERs resulted in some performance improvement of the correlation.

One for two: conversion of waste chicken feathers to carbon microspheres and (NH4)HCO3.

Pyrolysis of 1 g of waste chicken feathers (quills and barbs) in supercritical carbon dioxide (sc-CO2) system at 600 °C for 3 h leads to the formation of 0.25 g well-shaped carbon microspheres with diameters of 1-5 μm and 0.26 g ammonium bicarbonate ((NH4)HCO3). The products were characterized by powder X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Raman spectroscopic, FT-IR spectrum, X-ray electron spectroscopy (XPS), and N2 adsorption/desorption measurements. The obtained carbon microspheres displayed great superhydrophobicity as fabric coatings materials, with the water contact angle of up to 165.2±2.5°. The strategy is simple, efficient, does not require any toxic chemicals or catalysts, and generates two valuable materials at the same time. Moreover, other nitrogen-containing materials (such as nylon and amino acids) can also be converted to carbon microspheres and (NH4)HCO3 in the sc-CO2 system. This provides a simple strategy to extract the nitrogen content from natural and man-made waste materials and generate (NH4)HCO3 as fertilizer.

Synthesis of 3C–SiC nanowires by reaction of poly(ethylene terephthalate) waste with SiO2 microspheres

3C–SiC nanowires have been synthesized by reaction of poly(ethylene terephthalate) (PET) waste with SiO2 microspheres in supercritical carbon dioxide system at 650°C for 3h, followed by vacuum annealing at 1500°C for 4h. The product was characterized by X-ray diffraction, Raman spectroscopic, Field Emission Scanning Electron Microscopy, and High-resolution Electron Microscopy. The 3C–SiC nanowires are tens of microns in length and 30–150nm in diameter. It is found that the reaction forming 3C–SiC nanowires take place in the inner of the carbon microspheres generated from PET. The formation mechanism of the 3C–SiC nanowires was discussed.

Supercritical carbon dioxide-soluble polyhedral oligomeric silsesquioxane (POSS) nanocages and polymer surface modification

In this work, a functionalized polyhedral oligomeric silsesquioxane (POSS) has been investigated for its solubility in supercritical carbon dioxide for the first time in literature. POSS nanocages, which can be functionalized with a wide variety of organic substituents, are most commonly studied as nanofillers in polymer nanocomposites and coatings. Solubility of trifluoropropyl POSS in supercritical carbon dioxide has been determined by cloud-point measurements performed in a high-pressure view cell. At temperature and pressure ranges of 308–323K and 8.3–14.8MPa, these fluorinated organic–inorganic hybrid nanocage structures exhibit solubility up to 4.4% by weight, which is promising for green material processing applications using the environmentally benign solvent. Solubility of CO2-philic POSS decreases with increasing temperature, while the solubility isotherms at two different temperatures converge. Choosing the processing conditions from the performed solubility studies, trifluoropropyl POSS–supercritical carbon dioxide system has been applied in high-pressure surface modification of a high-molecular weight, rigid poly(methyl methacrylate) (PMMA). Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analysis of the processed PMMA sheet show that the functionalized nanoparticles were deposited on the PMMA surface, forming a uniform coating of POSS aggregates. This work proves that functionalized POSS with CO2-philic groups can be solubilized in supercritical CO2, which might allow them to be applied in a plethora of materials modification processes using supercritical carbon dioxide.

Generalized linear solvation energy model applied to solute partition coefficients in ionic liquid–supercritical carbon dioxide systems

Biphasic solvent systems composed of an ionic liquid (IL) and supercritical carbon dioxide (scCO2) have become frequented in synthesis, extractions and electrochemistry. In the design of related applications, information on interphase partitioning of the target organics is essential, and the infinite-dilution partition coefficients of the organic solutes in IL–scCO2 systems can conveniently be obtained by supercritical fluid chromatography. The data base of experimental partition coefficients obtained previously in this laboratory has been employed to test a generalized predictive model for the solute partition coefficients. The model is an amended version of that described before by Hiraga et al. (J. Supercrit. Fluids, in press). Because of difficulty of the problem to be modeled, the model involves several different concepts – linear solvation energy relationships, density-dependent solvent power of scCO2, regular solution theory, and the Flory–Huggins theory of athermal solutions. The model shows a moderate success in correlating the infinite-dilution solute partition coefficients (K-factors) in individual IL–scCO2 systems at varying temperature and pressure. However, larger K-factor data sets involving multiple IL–scCO2 systems appear to be beyond reach of the model, especially when the ILs involved pertain to different cation classes.

Preservation of aged paper using borax in alcohols and the supercritical carbon dioxide system

Selecting an appropriate paper deacidification agent is very important for the deacidification of paper. The use of three deacidification agents (i.e., iso-butylamine, calcium propionate, and borax) is studied for the deacidification of paper using the immersion treatment by investigating the paper surface pH, alkaline residue, paper whiteness, strength, and other performance indicators. Results show the deacidification by borax solution not only results in the promotion of a proper pH range, high level of alkali reserves, and ignorable influence to paper appearance, but also to the enhancement of the mechanical intensities of paper even after artificial aging. Supercritical carbon dioxide (CO 2 SCF), as a solvent system, is used in the deacidification of acidic papers using the borax solution of water and alcohol. CO 2 SCF improved the deacidification process by significantly improving the pH value and the base residual value. The borax in supercritical fluids can be better combined with cellulose hydroxyl to improve the mechanical properties of paper substantially. The treatment of borax in CO 2 SCF could be an alternative for acidic papers. Aside from improving the pH and depositing a sufficient alkaline residual, CO 2 SCF also strengthens the mechanical properties of treated papers.

Solute Partitioning Between 1-n-Butyl-3-methylimidazolium Trifluoromethanesulfonate Ionic Liquid and Supercritical CO2

Limiting partition coefficients (K-factors) of a selection of low-to-medium volatility solutes in biphasic 1-n-butyl-3-methylimidazolium trifluoromethanesulfonate ([bmim][TfO]) ionic liquid–supercritical carbon dioxide (IL–scCO2) system were obtained by capillary column supercritical fluid chromatography (SFC) with [bmim][TfO] as the stationary liquid and scCO2 as the carrier fluid. Solute selection included 24 compounds of diverse volatilities and chemical functionalities and the retention factors were measured within (313.2 to 353.2) K and (7.3 to 23.2) MPa. At a constant temperature, some pressure-tunable selectivity can be obtained through changes in the operating pressure and the scCO2 density. At a fixed temperature and density of CO2, solute partition coefficients were correlated in terms of Abraham’s linear solvation energy relationships. Compared to our previous studies with other ILs ([hmim][Tf2N], [bmim][MeSO4], and [thtdp][Cl]), the loss of [bmim][TfO] from the column during the experimental run was markedly lower in the present work.

Diffusion coefficients of supercritical carbon dioxide and its mixtures using molecular dynamic simulations

Molecular dynamic simulations have been evaluated for systems containing supercritical carbon dioxide to predict high-pressure diffusion coefficients of binary mixtures. Diffusion coefficients of high boiling compounds in supercritical fluids are important for the design of supercritical extractors, separators and reactors. Since high-pressure experiments are time intensive and difficult to perform, molecular simulations could prove a useful framework to obtain thermodynamic properties; however, their reliability is still in question. In this work, an NVT ensemble single site model molecular dynamic simulation using gear predictor corrector algorithm has been applied to calculate diffusion coefficients of carbon dioxide, naphthalene, 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene in supercritical carbon dioxide system at 317.5 K. The Lennard-Jones (12–6) and the Coulomb potential function have been combined into an intermolecular potential function to measure the binary molecular interaction. The simulation results of the diffusion coefficients are being compared with similar experimental data near the critical points. The calculated diffusion coefficients for each system behaved as a monotonic decreasing function of the molar density and the molecular simulations results, and the selected experimental data are in good agreement.

Extraction Modelling and Characterization of Bioactive Components from Psoralea corylifolia L. Obtained by Supercritical Carbon Dioxide

The rapid development of nutraceuticals and functional foods which are more often prepared from the phytochemicals / plant extracts has created a new trend in food processing industries. Among the various plant materials available for extraction of bioactives, the present work focuses on Psoralea corylifolia L ., known commonly as bakuchi. It is widely used in Chinese medicine to treat a variety of diseases and possesses antitumor, antibacterial, cytotoxic and antihelmenthic properties. Thermally sensitive bakuchiol, psoralen and isosporalen, the major components present in the seed possess high biotechnological values. The extraction of bioactives from Psoralea corylifolia seeds was carried out using the high pressure supercritical carbon dioxide (SCCO 2 ) system at pressures 22, 26 and 30 MPa and at temperature of 313 K. Even though yield of extraction by SCCO 2 extraction process was slightly less than the yield by hexane extraction method, bakuchiol concentration in the extract was much higher than the hexane extraction. Experimental extraction data regressed well with diffusion model. LC-MS chromatogram of the extract identified presence of nine primary compounds. The results indicated that the extract having bakuchiol concentration of 51% was possible with SCCO 2 extraction.

Treatment of discarded oil in supercritical carbon dioxide for preparation of carbon microspheres

Carbon microspheres with diameter of 1–10 μm were prepared by treatment of waste oil in a supercritical carbon dioxide (scCO2) system. The structure and morphology of the products were characterized by X-ray diffraction, field-emission scanning electron microscopy, and Raman spectrometry. It is shown that the products consist of graphite microspheres with relatively low graphitization. The yield of solid products increased from 26.8 wt% to 42.2 wt% as the reaction temperature was raised from 530°C to 600°C. Spheres with multilayer structure could be obtained by means of subsequent vacuum annealing of the carbon microspheres at 1500°C. The formation mechanisms of carbon microspheres in the scCO2 system and the influence of vacuum annealing on the structure are discussed in detail.

An Economical, Green Pathway to Biaryls: Palladium Nanoparticles Catalyzed Ullmann Reaction in Ionic Liquid/ Supercritical Carbon Dioxide System

AbstractIn this paper, an economical, green pathway involving the palladium nanoparticles (Pd NPs) catalyzed reductive Ullmann reaction of an aryl chloride to afford a biaryl with high conversion and selectivity in an ionic liquid (IL)/supercritical carbon dioxide (ScCO2) system was developed. The combination of IL and ScCO2 provides superior advantages in product separation, catalyst recycling and reuse of reaction media over traditional organic solvents. Further investigations showed that the Brønsted‐acidic imidazolium IL {e.g., (1‐butyl‐3‐(sulfobutyl)‐imidazolium) hydrogen sulfate, [bmim(HSO3C4)][HSO4]}, can replace the traditional active hydrogen donor readily with much enhanced product separation efficiency, the use of IL also led to an obvious improved stability of the Pd NPs, which was very helpful for catalyst recycling. Carbon dioxide, a naturally abundant, non‐flammable, relatively non‐toxic, economical and recyclable “greenhouse” gas, was found to significantly promote the selectivity of the Pd NPs‐catalyzed aluminium‐induced reductive Ullmann reaction of aryl chlorides. Investigations showed that the Pd NPs catalyst and IL can be recycled for at least five runs, indicating the economic viability of this process.

Nonthermal inactivation and sublethal injury of Lactobacillus plantarum in apple cider by a pilot plant scale continuous supercritical carbon dioxide system

The objective of this study was to evaluate the efficacy of supercritical carbon dioxide (SCCO 2) for inactivating Lactobacillus plantarum in apple cider using a continuous system with a gas-liquid metal contactor. Pasteurized apple cider without preservatives was inoculated with L. plantarum and processed using a SCCO 2 system at a CO 2 concentration range of 0–12% (g CO 2/100 g product), outlet temperatures of 34, 38, and 42 °C, a system pressure of 7.6 MPa, and a flow rate of 1 L/min. Processing with SCCO 2 significantly ( P < 0.05) enhanced inactivation of L. plantarum in apple cider, resulting in a 5 log reduction with 8% CO 2 at 42 °C. The response surface model indicated that both CO 2 concentration and temperature contributed to the microbial inactivation. The extent of sublethal injury in surviving cells in processed apple cider increased as CO 2 concentration and processing temperature increased, however the percent injury dramatically decreased during SCCO 2 processing at 42 °C. Structural damage in cell membranes after SCCO 2 processing was observed by SEM. Refrigeration (4 °C) after SCCO 2 processing effectively inhibited the re-growth of surviving L. plantarum during storage for 28 days. Thus this study suggests that SCCO 2 processing is effective in eliminating L. plantarum and could be applicable for nonthermal pasteurization of apple cider.