| 1. |
- Andersson, Martin, et al.
(författare)
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Dynamic pH determination at high pressure of aqueous additive mixtures in contact with dense CO2
- 2018
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446 .- 1872-8162. ; 136, s. 95-101
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Tidskriftsartikel (refereegranskat)abstract
- A system consisting of a high-pressure tolerant microfluidic glass chip, high-speed absorbance imaging, and image processing has been developed to study rapid dynamic events like pH change in a multiphase flow. The system gives both kinetic and quantitative equilibrated information. By tracking the interactions of aqueous additive mixtures and liquid CO2, at 80 bar and 24 °C, under flow, measurement at a given P, T condition is done in 0.25 s. The acidification rate to steady state was found to be mass transport limited, occurring in less than 1 s. For 30 mM of the additives ammonium acetate and ammonium formate, equilibrium pH of 4.5 and 4.1, respectively, was seen. These additives are of key importance in common mobile phases used in SFC.
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| 2. |
- Cui, Jingwen, et al.
(författare)
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Measurement of relative static permittivity and solvatochromic parameters of binary and ternary CO2-expanded green solvents
- 2021
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446 .- 1872-8162. ; 171
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Tidskriftsartikel (refereegranskat)abstract
- CO2-expanded liquids (CXLs) is a class of solvent systems giving relatively low viscosity in comparison to neat organic solvents. The challenge is to achieve a high overall polarity of the CXL, despite the presence of compressed liquid CO2. In this study, the relative static permittivity (εr) was measured for binary and ternary one-phase mixtures of CO2 + green solvent using an in-line microfluidic device. In addition, Kamlet-Taft solvatochromic parameters were experimentally determined, allowing the characterization of the polarizability, acidity, and basicity. Novel data is shown for binary and ternary systems of CO2 expanded ethanol and ethyl lactate, with or without glycerol or water added, at moderate conditions of pressure and temperature (8 MPa and 35 °C). One-phase CXLs systems of a wide relative permittivity range (7.7–75.3) at lowered viscosity were enabled, by mixing different green solvents with CO2.
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| 3. |
- Gustinelli, Graziele, et al.
(författare)
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Supercritical extraction of bilberry (Vaccinum myrtillus L.) seed oil: Fatty acid composition and antioxidant actvitiy
- 2018
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446 .- 1872-8162. ; 135, s. 91-97
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Tidskriftsartikel (refereegranskat)abstract
- Bilberry seed oils extracted with supercritical carbon dioxide (SC-CO2) for 80 min at 20, 35, and 50 MPa and at 40°, 50° and 60 °C were evaluated to compare the yield, composition, and antioxidant recovery. Analyses of fatty acids, free radical scavenging activity (DPPH), vitamin E and peroxide contents revealed that yield, vitamin E, efficient concentration (EC50), and Peroxide value (PV) varied significantly among the obtained bilberry seed oils, whereas the fatty acid compositions were similar. The oil extracted at 20 MPa and 60 °C had the best recovery of vitamin E and the lowest EC50 and PV.The high levels of vitamin E and polyunsaturated fatty acids, as well as the low ω6/ω3 ratios (
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| 4. |
- Knaust, Stefan, 1985-, et al.
(författare)
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Influence of surface modifications and channel structure for microflows of supercritical carbon dioxide and water
- 2016
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446 .- 1872-8162. ; 107, s. 649-656
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Tidskriftsartikel (refereegranskat)abstract
- Miniaturization offers a possibility to increase the performance and decrease the time scales of systems. Existing microsystems using supercritical CO2 mainly utilizes multiphase segmented flows. To allow for a broader toolbox for future systems, also parallel flows are useful which eases the separation of the different phases. Here, the effect of different surface coatings are studied for multiphase flows of scCO2 and H2O in flat microchannels, with and without a 4 μm high ridge guide, which allows for pinning of the fluid interface inside the 190 μm wide and 35 μm high channel. Three different surfaces with different wettings towards scCO2 and H2O are studied, where a surface terminated with a hydrocarbon-based silane was observed to be neutral in the H2O/scCO2 system, a surface terminated with a fluorocarbon-based silane was hydrophobic, and an uncoated glass surface was hydrophilic.Using two flow rates of 5:5 μl/min (CO2:H2O) and 6.5:3.5 μl/min (CO2:H2O), a parallel flow between scCO2 and H2O was observed for uncoated and flat channels where the H2O flow pushed the CO2 to the side, before the flows eventually breaks up into segments. With a ridge guide in the middle of the channel, the interface was pinned at half the channel width, although still breaking up into segments. The neutral hydrocarbon-based surface coating with approximately 90° contact angles resulted in evenly created segments without a ridge guide. Including a guide in the middle of the channel, a parallel flow was observed throughout the channel, although occasionally small CO2 segments entered the H2O outlet. Using the fluorocarbon-based silane resulted in an unstable segmented system with pressure fluctuations.Using surface modifications, an increased control can be achieved for either segmentation or parallel flow where a neutral surface is favored for a stable flow behavior. Together with a ridge guide, the fluid interface was pinned at the center.
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| 5. |
- Liu, Jiewei, et al.
(författare)
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Numerical simulation of particle formation in the rapid expansion of supercritical solution process
- 2014
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446 .- 1872-8162. ; 95, s. 572-587
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we numerically study particle formation in the rapid expansion of supercritical solution (RESS) process in a two dimensional, axisymmetric geometry, for a benzoic acid + CO2 system. The fluid is described by the classical Navier-Stokes equation, with the thermodynamic pressure being replaced by a generalized pressure tensor. Homogenous particle nucleation, transport, condensation and coagulation are described by a general dynamic equation, which is solved using the method of moments. The results show that the maximal nucleation rate and number density occurs near the nozzle exit, and particle precipitation inside the nozzle might not be ignored. Particles grow mainly across the shocks. Fluid in the shear layer of the jet shows a relatively low temperature, high nucleation rate, and carries particles with small sizes. On the plate, particles within the jet have smaller average size and higher geometric mean, while particles outside the jet shows a larger average size and a lower geometric mean. Increasing the preexpansion temperature will increase both the average particle size and standard deviation. The preexpansion pressure does not show a monotonic dependency with the average particle size. Increasing the distance between the plate and the nozzle exit might decrease the particle size. For all the cases in this paper, the average particle size on the plate is on the order of tens of nanometers.
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| 6. |
- Orhan, Mehmet, et al.
(författare)
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Supercritical carbon dioxide application using hydantoin acrylamide for biocidal functionalization of polyester
- 2020
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Ingår i: Journal of Supercritical Fluids. - : Elsevier. - 0896-8446 .- 1872-8162. ; 165
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Tidskriftsartikel (refereegranskat)abstract
- Biocidal functionalization in polyester fibers is a really tough challenge because of the lack of tethering groups. This study indicated supercritical carbon dioxide application using N-halamine would be an alternative solution for obtaining antibacterial function on the polyester surface. Firstly, N-(2-methyl 1-(4 methyl-2,5-dioxo-imidazolidin-4 yl)propan-2-yl)acrylamide was synthesized and applied to the polyester in supercritical carbon dioxide medium, at 120 degrees C, 30 MPa for different processing times. The addition of N-halamine on the surface significantly brought antibacterial activity against E. coli. The chlorine loadings showed that 6-h exposure time was critical to obtain sufficient antibacterial activity. This treatment caused a reasonable and tolerable loss in color and mechanical properties. But, the durability to abrasion, stability, and rechargeability of oxidative chlorine, and the durability of N-halamine on the surface were remarkably good. Conclusively, it can be available to work on polyester surfaces with resource-efficient and eco-friendly supercritical carbon dioxide technique for getting more functionalization and modification. (C) 2020 Elsevier B.V. All rights reserved.
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| 7. |
- Ovaskainen, Louise, et al.
(författare)
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Superhydrophobic polymeric coatings produced by rapid expansion of supercritical solutions combined with electrostatic depostion (RESS-ED)
- 2014
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446 .- 1872-8162. ; 95, s. 610-617
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a method to produce superhydrophobic polymeric coatings by combining the rapid expansion of supercritical solutions (RESS) with electrostatic deposition (ED). A copolymer, poly(vinyl acetate)-poly(vinyl pivalate) was dissolved in a mixture of supercritical carbon dioxide and acetone and sprayed through a nozzle with an applied voltage of 8 kV onto a surface placed on a earthed collector. Spray distance and polymer concentration were altered to find the most suitable spraying conditions. Superhydrophobic surfaces were produced when spraying both with and without a voltage, although the water repellent surfaces could be produced at a larger variety of processing parameters using the RESS-ED technique. The greatest improvement of using the RESS-ED process was that larger and thinner coatings were produced with a more even surface coverage of the created polymer particles compared to spraying without the applied voltage.
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| 8. |
- Ovaskainen, Louise, et al.
(författare)
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Towards superhydrophobic coatings made by non-fluorinated polymers sprayed from a supercritical solution
- 2013
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446 .- 1872-8162. ; 77, s. 134-141
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to create a superhydrophobic surface using polymers that are non-fluorinated and applying them to a surface via rapid expansion of a supercritical solution (RESS). Solubility studies of poly(epsilon-caprolactone) (PCL) and a statistical copolymer of vinyl acetate and vinyl pivalate (P(VAc-VPi))in supercritical carbon dioxide (scCO(2)) were carried out using an extraction procedure. It was found that the most suitable process parameters for spraying these polymers using the RESS technique were 30 MPa, 40 degrees C and 10% (v/v) acetone as a co-solvent. The surfaces produced were characterized in terms of their morphology and hydrophobic properties by scanning electron microscopy and contact angle measurements, respectively. The most hydrophobic surfaces were obtained by spraying the P(VAc-VPi) copolymers, giving advancing water contact angles in the range of 120-155 degrees due to the hydrophobic character of the polymer and the microstructure formed with the RESS technique. These results show great promise for the creation of superhydrophobic surfaces using non-fluorinated polymers applied to surfaces via RESS technique.
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| 9. |
- Padrela, Luis, et al.
(författare)
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Screening for pharmaceutical cocrystals using the supercritical fluid enhanced atomization process
- 2010
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446 .- 1872-8162. ; 53:1-3, s. 156-164
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Tidskriftsartikel (refereegranskat)abstract
- The supercritical fluid enhanced atomization (SEA) process was used to produce cocrystals of six different active pharmaceutical ingredients (APIs): indomethacin, theophylline, caffeine, sulfamethazine, aspirin and carbamazepine. Micrometric cocrystals using the FDA-approved sweetener saccharin (SAC) as a cocrystal former were produced from ethanol solutions using supercritical CO2 as the atomization enhancing fluid. The corresponding cocrystalline phases were characterized by differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). Particle morphologies and size distributions were analyzed by scanning electron microscopy (SEM) and by aerosizer.The results presented here show the formation of cocrystals of all the APIs selected, evidencing the ability and the potentiality of the SEA technique to generate different pharmaceutical cocrystals. Cocrystal particles produced by SEA had similar mean particle size than those produced by classical grinding methods. Interestingly, a new cocrystal form of theophylline-saccharin (likely with a 1:2 stoichiometry) was obtained by the SEA method that has not been previously reported by traditional screening methods.
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| 10. |
- Padrela, Luis, et al.
(författare)
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Tuning physicochemical properties of theophylline by cocrystallization using the supercritical fluid enhanced atomization technique
- 2014
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446 .- 1872-8162. ; 86, s. 129-136
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Tidskriftsartikel (refereegranskat)abstract
- Formation of different micro- to nanosized cocrystals of theophylline is addressed by using the supercritical enhanced atomization (SEA) process. The experimental results presented here help to highlight how to prepare cocrystals of theophylline (TPL), using a supercritical fluid-based technique to accomplish the required physicochemical properties of that active pharmaceutical ingredient (API). The SEA process shows a strong versatility and feasibility towards the formation of highly pure theophylline cocrystals, using tetrahydrofuran as a solvent. The formation of TPL cocrystals with different types of morphology and dissolution behaviour/properties is induced by using different coformers, such as urea, saccharin, gentisic acid, salicylic acid, glutaric acid, sorbic acid, 1-hydroxy-2-naphthoic acid, oxalic acid, maleic acid and nicotinamide. The solubility of each coformer in the dissolution medium of phosphate-buffered saline (pH 7.4 at 25 °C), could determine the dissolving rate behaviour of the produced cocrystals. Consequently, the low-soluble coformers generate TPL cocrystals with a slow-dissolving rate, while the use of highly-soluble coformers produces faster-dissolving TPL cocrystals. Albeit the SEA process operating temperature influences the mean cocrystal particle size, this technique shows a high potential as an effective cocrystal screening tool.
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