Search results for "Supercritical fluid"
showing 10 items of 166 documents
Modelling small angle neutron scattering data from polymers in supercritical fluids
2000
In this paper we report a SANS investigation of micelle formation by fluorocarbon-hydrocarbon block copolymers in supercritical CO2(scCO2) at 313K. A sharp unimer-micelle transition is obtained due to the tuning of the solvating ability of scCO2 by profiling pressure. At high pressure the copolymer is in a monomeric state with a random coil structure. By lowering the pressure aggregates are formed with the hydrocarbon segments forming the core and the fluorocarbon segments forming the corona of spherical aggregates. This aggregate-unimer transition is driven by the gradual penetration of CO2 molecules toward the core of the aggregate and is critically related to the density of the solvent, …
Hydrothermal liquefaction of waste biomass in stirred reactors: One step forward to the integral valorization of municipal sludge
2020
Abstract Hydrothermal liquefaction (HTL) of municipal sludge (MS) was performed at 350 °C for 30 min (subcritical water) and at 400 °C for 0 min (supercritical water) at fixed kinetic severity (LogR0 = 8.9) in static and stirred batch reactors to study the effect of the flow regime on the energy recovery (ER) of the process and on the quality of the products. With adopted experimental procedures it was possible to reduce to less than 10% the yield of lost organic compounds, termed volatiles (VT), and to collect and quantify a liquid hydrocarbon fraction (HC) separated from the biocrude (BC). The highest value of the HC yield, 25% w/w, was obtained in supercritical conditions. The C content …
A Novel Gas Chromatographic Method to Measure Sorption of Dense Gases into Polymers
2006
A novel experimental approach to determine the solubility of gaseous compounds inside polymers is here described. The method is based on the gas chromatographic determination of the composition of the fluid phase at equilibrium with the polymer. To take into account the effect of the volume swelling on the measurement a suitable probe, nonabsorbable by the polymer, was added to the fluid phase. Under the adopted configuration the apparatus can operate up to 35 MPa and 80°C. This experimental technique has been used to determine the solubility of carbon dioxide in poly(vinylidene fluoride) using argon as a probe. The latter was chosen because it is negligibly absorbed by the polymer and does…
High Pressure Solubility Data of the System Limonene + Linalool + CO2
2001
The feasibility of deterpenating orange peel oil with supercritical CO2 depends on relevant vapor−liquid equilibrium data because the selectivity of this solvent for limonene and linalool (the two key components of the oil) is of crucial importance. In this work the solubility data for the CO2 + limonene + linalool ternary system were measured at (318.2 and 328.2) K. The range of pressures covered was from (70 to 110) bar. Two different mixtures of limonene + linalool were used: a 40 mass % limonene + 60 mass % linalool mixture and a 60 mass % limonene + 40 mass % linalool mixture. To correlate the obtained results, two equations of state were successfully used (Peng−Robinson (PR) and Soav…
Fast and continuous synthesis of nanostructured iron spinel in supercritical water: influence of cations and citrates
2014
International audience; Spinel iron oxide nanoparticles were obtained under supercritical water conditions in a continuous and fast (less than 10s) way by modifying the initial stoichiometric Fe II /Fe III molar ratio from (1/2) to (3/0), without base solution, and using citrates directly with iron precursors. This result opens the way of an economical and environmentally benign approach to synthesize superparamagnetic iron oxide nanoparticles (SPIONs) in important yields.
Expanded micro-particles by supercritical antisolvent precipitation: Interpretation of results
2008
Abstract Supercritical antisolvent (SAS) micronization has been used to obtain nanoparticles and micro-particles of several kinds of materials. Sometimes hollow expanded micro-particles have also been obtained. This work is focused on the analysis of this last morphology. We organized literature data and our previous experiments and we added new experiments on previously tested compounds and on compounds never tested before. As a result, expanded micro-particles using several compounds belonging to different categories and precipitated from different solvents in laboratory and pilot scale plants were obtained with diameters between about 10 and 180 μm. They also showed different sub-structu…
Pressure-induced formation of diblock copolymer "micelles" in supercritical fluids. A combined study by small angle scattering experiments and mean-f…
2004
We developed a simple time-dependent mean-field theory to describe the phase separation kinetics of either homopolymers or AB-diblock copolymers in supercritical (SC) fluids. The model, previously used to describe the phase behavior of AB-block copolymers under the assumption of strong solvent selectivity for just one copolymer chain, has been extended to study the kinetics of the phase separation process. Time resolved small angle x-ray scattering (TR-SAXS) measurements have been performed on different AB-diblock copolymers containing a perfluorinated chain and dissolved in SC-CO2. The data obtained over a wide range of pressure and temperature confirm our theoretical predictions. Particul…
QENS from polymer aggregates in supercritical CO2
2000
Abstract We report QENS measurements from PS-b-PFOA aggregates in supercritical CO2. Line shapes are dominated by localized diffusive modes and segmental dynamics of the anchored, finite-length PFOA chains. For Q⩽0.6 A−1, we obtain effective diffusion coefficients of ≅0.8 10−6 cm2/s. At higher Q, a single component is not sufficient as shown by excess intensity on the flanks. For Q⩾1.5 A−1, the wings reflect contributions due to a distribution of faster, more localized chain modes.
The morphology of block copolymer micelles in supercritical carbon dioxide by small-angle neutron and x-ray scattering
1997
Above its critical point, carbon dioxide forms a super-critical fluid, which promises to be an environmentally responsible replacement for the organic solvents traditionally used in polymerizations. Many lipophilic polymers such as polystyrene (PS) are insoluble in CO2, though polymerizations may be accomplished via the use of PS-fluoropolymer stabilizers, which act as emulsifying agents. Small-angle neutron and X-ray scattering have been used to show that these molecules form micelles with a CO2-phobic PS core and a CO2-philic fluoropolymer corona. When the PS block was fixed in length and the fluorinated corona block was varied, the number of block copolymer molecules per micelle (six to …
Supercritical-fluid extraction of chlorofluoroalkanes from rigid polyurethane foams
1996
Abstract Preliminary results about a process for recovering expanding agents chlorofluoroalkanes (CFCs) both trapped in the cavities and dissolved in the polymer from rigid polyurethane foams are reported. The performances of liquid and supercritical carbon dioxide, and of CO2-propane supercritical mixtures were compared. Better results in terms of extraction time and amount of extracted CFCs were obtained with finely ground materials and supercritical propane-carbon dioxide fluids.