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Chitin microstructure formation by rapid expansion techniques with supercritical carbon dioxide / Ricardo Salinas-Hernández in Industrial & engineering chemistry research, Vol. 48 N°2 (Janvier 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N°2 (Janvier 2009) . - p. 769–778 Titre : Chitin microstructure formation by rapid expansion techniques with supercritical carbon dioxide Type de document : texte imprimé Auteurs : Ricardo Salinas-Hernández, Auteur ; F. Alberto Ruiz-Trevino, Auteur ; Ciro H. Ortiz-Estrada, Auteur Année de publication : 2009 Article en page(s) : p. 769–778 Note générale : chemical engenireeng Langues : Anglais (eng) Mots-clés : Carbon  Dioxide Résumé : Rapid expansion techniques (of supercritical solution (RESS) and into a liquid solvent (RESOLV)) with supercritical carbon dioxide are used to form chitin microstructures. The effect of the pre-expansion conditions, temperature (40−60 °C), pressure (104−208 bar), chitin concentration (1−6 mg/mL), and nozzle diameter (100−500 μm), on the morphology and the size of the chitin microstructures formed with both RESS and RESOLV are studied. Depending on the experimental conditions, it is found that spherical microparticles, with average diameters of 1.7−5.3 μm, are obtained with RESS, while continuous microfibers, with average diameters of 11.5−19.3 μm, are obtained with RESOLV. For both RESS and RESOLV it was observed that the pre-expansion temperature−pressure conditions studied here have practically no effect on the average diameters of the formed material. On the contrary, it is shown that concentration and nozzle diameter directly influence the morphology and size obtaining that lower concentrations and smaller diameter nozzles lead to the production of smaller diameter microstructures and closed-size distributions. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800084x [article] Chitin microstructure formation by rapid expansion techniques with supercritical carbon dioxide [texte imprimé] / Ricardo Salinas-Hernández, Auteur ; F. Alberto Ruiz-Trevino, Auteur ; Ciro H. Ortiz-Estrada, Auteur . - 2009 . - p. 769–778. chemical engenireeng Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N°2 (Janvier 2009) . - p. 769–778 Mots-clés : Carbon  Dioxide Résumé : Rapid expansion techniques (of supercritical solution (RESS) and into a liquid solvent (RESOLV)) with supercritical carbon dioxide are used to form chitin microstructures. The effect of the pre-expansion conditions, temperature (40−60 °C), pressure (104−208 bar), chitin concentration (1−6 mg/mL), and nozzle diameter (100−500 μm), on the morphology and the size of the chitin microstructures formed with both RESS and RESOLV are studied. Depending on the experimental conditions, it is found that spherical microparticles, with average diameters of 1.7−5.3 μm, are obtained with RESS, while continuous microfibers, with average diameters of 11.5−19.3 μm, are obtained with RESOLV. For both RESS and RESOLV it was observed that the pre-expansion temperature−pressure conditions studied here have practically no effect on the average diameters of the formed material. On the contrary, it is shown that concentration and nozzle diameter directly influence the morphology and size obtaining that lower concentrations and smaller diameter nozzles lead to the production of smaller diameter microstructures and closed-size distributions. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800084x

Gas transport properties of some fluorine - containing polyethers / J. C. Ignacio Lara-Estevez in Industrial & engineering chemistry research, Vol. 49 N° 23 (Décembre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 23 (Décembre 2010) . - pp. 11948–11953 Titre : Gas transport properties of some fluorine - containing polyethers Type de document : texte imprimé Auteurs : J. C. Ignacio Lara-Estevez, Auteur ; Claudia Camacho-Zuniga, Auteur ; F. Alberto Ruiz-Trevino, Auteur Année de publication : 2011 Article en page(s) : pp. 11948–11953 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Gas  Polyethers Résumé : A set of five polyethers containing the highly fluorinated monomer, 1,3-bis(1,1,1,3,3,3-hexafluoro-2-pentafluorophenylmethoxy-2-propyl)benzene (12F-FBE), were obtained by polycondensation with the monomers: biphenol, bisphenol F, bisphenol A, bisphenol AF, and a biphenol-substituted spirodilactam. Significant physical properties to characterize their application as membranes for gas separations processes were measured. They exhibit little crystalline domains (below 8%), very similar cohesive energy densities (CED) (with differences smaller than 1.8 (cal/cm3)1/2), glass transition temperatures (Tg) above 94 °C, good thermal resistance (Td > 350 °C), low specific volumes (V ≤ 0.6516 cm3/g), and fractional free volumes (FFV) above 0.170. Their permeabilities, at 35 °C and 2 atm, to He, H2, O2, N2, CH4, and CO2 exceed those of commercial polysulfone (PSF) membranes. 12F-BISAF, the most permeable polyether with permeability coefficients (in Barrers) of 51 for He, 28 for H2, 3.8 for O2, and 12 for CO2, is also the material with the highest FFV. However, the observed relation between permeability and FFV confirms that besides FFV other features need to be taken into consideration to determine permeability—especially for the smaller permeants He and H2. Concerning the ideal selectivity factors of these materials, they are in the same order of magnitude as those of PSF. The material identified as 12F-SDL is the most selective member of this series with selectivity factors to H2/CH4, O2/N2, and CO2/CH4 of 84, 4.8, and 28, respectively. Such superior selectivity of 12F-SDL could be related mainly to inhibited segmental movements. These results are interpreted in terms of CED, FFV, and Tg together with their respective contribution of gas solubility and diffusivity to the overall selectivity coefficients. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie100249j [article] Gas transport properties of some fluorine - containing polyethers [texte imprimé] / J. C. Ignacio Lara-Estevez, Auteur ; Claudia Camacho-Zuniga, Auteur ; F. Alberto Ruiz-Trevino, Auteur . - 2011 . - pp. 11948–11953. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 23 (Décembre 2010) . - pp. 11948–11953 Mots-clés : Gas  Polyethers Résumé : A set of five polyethers containing the highly fluorinated monomer, 1,3-bis(1,1,1,3,3,3-hexafluoro-2-pentafluorophenylmethoxy-2-propyl)benzene (12F-FBE), were obtained by polycondensation with the monomers: biphenol, bisphenol F, bisphenol A, bisphenol AF, and a biphenol-substituted spirodilactam. Significant physical properties to characterize their application as membranes for gas separations processes were measured. They exhibit little crystalline domains (below 8%), very similar cohesive energy densities (CED) (with differences smaller than 1.8 (cal/cm3)1/2), glass transition temperatures (Tg) above 94 °C, good thermal resistance (Td > 350 °C), low specific volumes (V ≤ 0.6516 cm3/g), and fractional free volumes (FFV) above 0.170. Their permeabilities, at 35 °C and 2 atm, to He, H2, O2, N2, CH4, and CO2 exceed those of commercial polysulfone (PSF) membranes. 12F-BISAF, the most permeable polyether with permeability coefficients (in Barrers) of 51 for He, 28 for H2, 3.8 for O2, and 12 for CO2, is also the material with the highest FFV. However, the observed relation between permeability and FFV confirms that besides FFV other features need to be taken into consideration to determine permeability—especially for the smaller permeants He and H2. Concerning the ideal selectivity factors of these materials, they are in the same order of magnitude as those of PSF. The material identified as 12F-SDL is the most selective member of this series with selectivity factors to H2/CH4, O2/N2, and CO2/CH4 of 84, 4.8, and 28, respectively. Such superior selectivity of 12F-SDL could be related mainly to inhibited segmental movements. These results are interpreted in terms of CED, FFV, and Tg together with their respective contribution of gas solubility and diffusivity to the overall selectivity coefficients. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie100249j