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Adsorption/desorption studies of 224-trimethylpentane in β-Zeolite and mesoporous materials using a tapered element oscillating microbalance (TEOM) / Kening Gong in Industrial & engineering chemistry research, Vol. 48 N° 21 (Novembre 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 21 (Novembre 2009) . - pp. 9490–9497 Titre : Adsorption/desorption studies of 224-trimethylpentane in β-Zeolite and mesoporous materials using a tapered element oscillating microbalance (TEOM) Type de document : texte imprimé Auteurs : Kening Gong, Auteur ; Tiepan Shi, Auteur ; Palghat A. Ramachandran, Auteur Année de publication : 2010 Article en page(s) : pp. 9490–9497 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : 224-Trimethylpentane  β-Zeolite  Mesoporous  materials Résumé : The facile desorption of C8 and heavier products from solid acid alkylation catalysts is essential to thwart catalyst deactivation by fouling. To better understand this phenomenon, a tapered element oscillating microbalance (TEOM) was employed to investigate the adsorption/desorption characteristics of 224-trimethylpentane (224-TMP), a proxy C8 alkylate product, on β-zeolite and mesoporous materials (T = 298−473 K, P224-TMP = 0−0.3 bar). It is found that the 224-TMP desorption rates from saturated β-zeolite (by helium purging) are characterized by a rapid initial “burst” of 224-TMP followed by a rather long desorption phase. Complementary experimental and modeling investigations using pelletized β-zeolites of known sizes indicate that the adsorption rate and initial desorption (during the burst phase) rate of 224-TMP are controlled by meso-/macropore diffusion resistance external to the β-zeolite crystals and that the long transient could be due to pore diffusion resistance within the β-zeolite crystals. In contrast, mesoporous silica materials provide facile pore accessibility for large alkylate molecules such as 224-TMP, as evidenced by complete desorption of 224-TMP even at mild temperatures. These insights provide guidance for rational engineering of stable solid acid alkylation catalysts. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie900334g [article] Adsorption/desorption studies of 224-trimethylpentane in β-Zeolite and mesoporous materials using a tapered element oscillating microbalance (TEOM) [texte imprimé] / Kening Gong, Auteur ; Tiepan Shi, Auteur ; Palghat A. Ramachandran, Auteur . - 2010 . - pp. 9490–9497. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 21 (Novembre 2009) . - pp. 9490–9497 Mots-clés : 224-Trimethylpentane  β-Zeolite  Mesoporous  materials Résumé : The facile desorption of C8 and heavier products from solid acid alkylation catalysts is essential to thwart catalyst deactivation by fouling. To better understand this phenomenon, a tapered element oscillating microbalance (TEOM) was employed to investigate the adsorption/desorption characteristics of 224-trimethylpentane (224-TMP), a proxy C8 alkylate product, on β-zeolite and mesoporous materials (T = 298−473 K, P224-TMP = 0−0.3 bar). It is found that the 224-TMP desorption rates from saturated β-zeolite (by helium purging) are characterized by a rapid initial “burst” of 224-TMP followed by a rather long desorption phase. Complementary experimental and modeling investigations using pelletized β-zeolites of known sizes indicate that the adsorption rate and initial desorption (during the burst phase) rate of 224-TMP are controlled by meso-/macropore diffusion resistance external to the β-zeolite crystals and that the long transient could be due to pore diffusion resistance within the β-zeolite crystals. In contrast, mesoporous silica materials provide facile pore accessibility for large alkylate molecules such as 224-TMP, as evidenced by complete desorption of 224-TMP even at mild temperatures. These insights provide guidance for rational engineering of stable solid acid alkylation catalysts. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie900334g

On the gradient diffusion hypothesis and passive scalar transport in turbulent flows / Daniel P. Combest in Industrial & engineering chemistry research, Vol. 50 N° 15 (Août 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 15 (Août 2011) . - pp. 8817–8823 Titre : On the gradient diffusion hypothesis and passive scalar transport in turbulent flows Type de document : texte imprimé Auteurs : Daniel P. Combest, Auteur ; Palghat A. Ramachandran, Auteur ; Milorad P. Dudukovic, Auteur Année de publication : 2011 Article en page(s) : pp. 8817–8823 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Turbulent  flow  Transport  process  Diffusion Résumé : A discussion of modeling passive scalar transport in turbulent flows is given. Several methods employed to dose the scalar-flux term 〈u'φ'〉 that arises during Reynolds averaging are provided. Alternatives and improvements to the gradient diffusion hypotheses are addressed, most notably, the need for an alternative to the global constant turbulent Schmidt and Prandtl numbers. The reader is given a brief history covering methods used to predict turbulent Schmidt and Prandtl numbers, along with recommendations for future research, based partially on studies by Professor Stuart Churchill. More detailed formulations of turbulent Schmidt or Prandtl numbers will enable better approximations of the influence of turbulence in models of passive scalar flows using the gradient diffusion hypothesis. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24395827 [article] On the gradient diffusion hypothesis and passive scalar transport in turbulent flows [texte imprimé] / Daniel P. Combest, Auteur ; Palghat A. Ramachandran, Auteur ; Milorad P. Dudukovic, Auteur . - 2011 . - pp. 8817–8823. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 15 (Août 2011) . - pp. 8817–8823 Mots-clés : Turbulent  flow  Transport  process  Diffusion Résumé : A discussion of modeling passive scalar transport in turbulent flows is given. Several methods employed to dose the scalar-flux term 〈u'φ'〉 that arises during Reynolds averaging are provided. Alternatives and improvements to the gradient diffusion hypotheses are addressed, most notably, the need for an alternative to the global constant turbulent Schmidt and Prandtl numbers. The reader is given a brief history covering methods used to predict turbulent Schmidt and Prandtl numbers, along with recommendations for future research, based partially on studies by Professor Stuart Churchill. More detailed formulations of turbulent Schmidt or Prandtl numbers will enable better approximations of the influence of turbulence in models of passive scalar flows using the gradient diffusion hypothesis. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24395827