Documents disponibles écrits par cet auteur

Controlling homogeneous chemistry in homogeneous-heterogeneous reactors / Georgios D. Stefanidis in Industrial & engineering chemistry research, Vol. 48 N° 13 (Juillet 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 13 (Juillet 2009) . - pp. 5962–5968 Titre : Controlling homogeneous chemistry in homogeneous-heterogeneous reactors : application to propane combustion Type de document : texte imprimé Auteurs : Georgios D. Stefanidis, Auteur ; Dionisios G. Vlachos, Auteur Année de publication : 2009 Article en page(s) : pp. 5962–5968 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Homogeneous  chemistry  Homogeneous-heterogeneous  reactors  Two-dimensional  computational  fluid  dynamics  model Résumé : Operation strategies for controlling the extent of homogeneous chemistry in homogeneous−heterogeneous (HH) reactors were developed for a catalytic plate microreactor using a two-dimensional computational fluid dynamics model for propane combustion on Pt as our prototype system. The effect of the reactor gap size (distance between plates) was analyzed. We found that homogeneous chemistry is sustained for gaps well below the quenching diameter as a result of enhanced catalyst-induced heating. This finding has important ramifications for catalyst lifetime and safety and could be used to produce chemicals, for example, in oxidative dehydrogenation and oxidative coupling reactions. The homogeneous chemistry contribution decreases with decreasing gap size. Catalytic chemistry alone can occur under suitable flow rates, compositions, and heat loss/heat exchange rates. The synergism or competition between homogeneous and catalytic chemistries is delineated. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801480m [article] Controlling homogeneous chemistry in homogeneous-heterogeneous reactors : application to propane combustion [texte imprimé] / Georgios D. Stefanidis, Auteur ; Dionisios G. Vlachos, Auteur . - 2009 . - pp. 5962–5968. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 13 (Juillet 2009) . - pp. 5962–5968 Mots-clés : Homogeneous  chemistry  Homogeneous-heterogeneous  reactors  Two-dimensional  computational  fluid  dynamics  model Résumé : Operation strategies for controlling the extent of homogeneous chemistry in homogeneous−heterogeneous (HH) reactors were developed for a catalytic plate microreactor using a two-dimensional computational fluid dynamics model for propane combustion on Pt as our prototype system. The effect of the reactor gap size (distance between plates) was analyzed. We found that homogeneous chemistry is sustained for gaps well below the quenching diameter as a result of enhanced catalyst-induced heating. This finding has important ramifications for catalyst lifetime and safety and could be used to produce chemicals, for example, in oxidative dehydrogenation and oxidative coupling reactions. The homogeneous chemistry contribution decreases with decreasing gap size. Catalytic chemistry alone can occur under suitable flow rates, compositions, and heat loss/heat exchange rates. The synergism or competition between homogeneous and catalytic chemistries is delineated. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801480m

Microwave swing regeneration vs temperature swing regeneration comparison of desorption kinetics / Robert Cherbański in Industrial & engineering chemistry research, Vol. 50 N° 14 (Juillet 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 14 (Juillet 2011) . - pp. 8632-8644 Titre : Microwave swing regeneration vs temperature swing regeneration comparison of desorption kinetics Type de document : texte imprimé Auteurs : Robert Cherbański, Auteur ; Magdalena Komorowska-Durka, Auteur ; Georgios D. Stefanidis, Auteur Année de publication : 2011 Article en page(s) : pp. 8632-8644 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Microwave  Desorption  kinetics Résumé : This paper presents a comparison of microwave swing regeneration (MSR) and temperature swing regeneration (TSR) of acetone and toluene from 13X molecular sieves in terms of desorption kinetics and desorption efficiencies. The experiments were performed for two forms of the adsorbent: adsorbent bed consisting of spherical beads and adsorbent pressed in the shape of pastilles to allow for precise temperature measurement of the solid adsorbent. In TSR the adsorbent is heated by means of a hot inert gas stream whereas in MSR the adsorbent dissipates microwave energy into heat. It was found that MSR runs faster even when the adsorbent temperature is much lower than the gas temperature in TSR. This implies more efficient desorption due to less energy waste in the form of heat losses and less sensible enthalpy of purge gas stream since the total gas consumption is considerably decreased. The observed enhancement of microwave-driven desorption is more pronounced for the polar adsorbate (acetone) or high heat transfer resistances (pastilles). Finally, it was verified that microwaves do not affect the adsorption capacity of the molecular sieves after several consecutive adsorption–desorption cycles. DEWEY : 660 ISSN : 0888-5885 En ligne : http://journals1.scholarsportal.info/details.xqy?uri=/08885885/v50i0014/8632_msr [...] [article] Microwave swing regeneration vs temperature swing regeneration comparison of desorption kinetics [texte imprimé] / Robert Cherbański, Auteur ; Magdalena Komorowska-Durka, Auteur ; Georgios D. Stefanidis, Auteur . - 2011 . - pp. 8632-8644. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 14 (Juillet 2011) . - pp. 8632-8644 Mots-clés : Microwave  Desorption  kinetics Résumé : This paper presents a comparison of microwave swing regeneration (MSR) and temperature swing regeneration (TSR) of acetone and toluene from 13X molecular sieves in terms of desorption kinetics and desorption efficiencies. The experiments were performed for two forms of the adsorbent: adsorbent bed consisting of spherical beads and adsorbent pressed in the shape of pastilles to allow for precise temperature measurement of the solid adsorbent. In TSR the adsorbent is heated by means of a hot inert gas stream whereas in MSR the adsorbent dissipates microwave energy into heat. It was found that MSR runs faster even when the adsorbent temperature is much lower than the gas temperature in TSR. This implies more efficient desorption due to less energy waste in the form of heat losses and less sensible enthalpy of purge gas stream since the total gas consumption is considerably decreased. The observed enhancement of microwave-driven desorption is more pronounced for the polar adsorbate (acetone) or high heat transfer resistances (pastilles). Finally, it was verified that microwaves do not affect the adsorption capacity of the molecular sieves after several consecutive adsorption–desorption cycles. DEWEY : 660 ISSN : 0888-5885 En ligne : http://journals1.scholarsportal.info/details.xqy?uri=/08885885/v50i0014/8632_msr [...]

Millisecond production of hydrogen from alternative, high hydrogen density fuels in a cocurrent multifunctional microreactor / Niket S. Kaisare in Industrial & engineering chemistry research, Vol. 48 N°4 (Février 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N°4 (Février 2009) . - pp. 1749–1760 Titre : Millisecond production of hydrogen from alternative, high hydrogen density fuels in a cocurrent multifunctional microreactor Type de document : texte imprimé Auteurs : Niket S. Kaisare, Auteur ; Georgios D. Stefanidis, Auteur ; Dionisios G. Vlachos, Auteur Année de publication : 2009 Article en page(s) : pp. 1749–1760 Note générale : Chemical enginnering Langues : Anglais (eng) Mots-clés : Pseudo-2-dimensional  model  Hydrogen  Catalytic  ammonia  Platinum Résumé : A pseudo-2-dimensional model is used for modeling a multifunctional microreactor for hydrogen generation by coupling catalytic ammonia decomposition on ruthenium with catalytic propane combustion on platinum. The two reactions are carried out in adjacent parallel plate channels in a cocurrent flow mode. Operating lines defining the attainable region are computed. The high temperatures and fast heat transfer ensure that both reactions go to completion in as low as submillisecond contact times and enable compact hydrogen production for portable and distributed power generation. The ammonia decomposition reaction tends to be limited by the intrinsic rate of reaction, whereas catalytic combustion is also affected by mass and heat diffusion. We have found that moderate and high conductivity materials are preferable because they support a rather wide attainable region. We show that one such device could enable variable hydrogen supply for variable power needs. A simple operating strategy to dial in the desirable power is proposed, which ensures high thermal efficiency (∼75% once-through efficiency of the integrated device and ∼85% reformer efficiency, both without any heat recuperation), wall isothermicity, and high conversions. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800392z [article] Millisecond production of hydrogen from alternative, high hydrogen density fuels in a cocurrent multifunctional microreactor [texte imprimé] / Niket S. Kaisare, Auteur ; Georgios D. Stefanidis, Auteur ; Dionisios G. Vlachos, Auteur . - 2009 . - pp. 1749–1760. Chemical enginnering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N°4 (Février 2009) . - pp. 1749–1760 Mots-clés : Pseudo-2-dimensional  model  Hydrogen  Catalytic  ammonia  Platinum Résumé : A pseudo-2-dimensional model is used for modeling a multifunctional microreactor for hydrogen generation by coupling catalytic ammonia decomposition on ruthenium with catalytic propane combustion on platinum. The two reactions are carried out in adjacent parallel plate channels in a cocurrent flow mode. Operating lines defining the attainable region are computed. The high temperatures and fast heat transfer ensure that both reactions go to completion in as low as submillisecond contact times and enable compact hydrogen production for portable and distributed power generation. The ammonia decomposition reaction tends to be limited by the intrinsic rate of reaction, whereas catalytic combustion is also affected by mass and heat diffusion. We have found that moderate and high conductivity materials are preferable because they support a rather wide attainable region. We show that one such device could enable variable hydrogen supply for variable power needs. A simple operating strategy to dial in the desirable power is proposed, which ensures high thermal efficiency (∼75% once-through efficiency of the integrated device and ∼85% reformer efficiency, both without any heat recuperation), wall isothermicity, and high conversions. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800392z

Process intensification of reactive distillation for the synthesis of n - propyl propionate / Ernesto Altman in Industrial & engineering chemistry research, Vol. 49 N° 21 (Novembre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 10287–10296 Titre : Process intensification of reactive distillation for the synthesis of n - propyl propionate : The effects of microwave radiation on molecular separation and esterification reaction Type de document : texte imprimé Auteurs : Ernesto Altman, Auteur ; Georgios D. Stefanidis, Auteur ; Thomas Van Gerven, Auteur Année de publication : 2011 Article en page(s) : pp. 10287–10296 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Esterification  Microwave  Distillation  with  reaction Résumé : An envisioned reactive distillation (RD) process for the esterification reaction of n-propyl propionate (ProPro) from I-propanol (ProOH) and propionic acid (ProAc) using microwave irradiation (MW) (f = 2.45 GHz) is studied. In this frame, the fundamental research performed is divided in two parts comparing reaction conditions and equilibrium curves under MW and conventional heating, looking for possible improvement in process efficiency. For the test system, the use of microwaves docs not improve the conversion of the esterification reaction catalyzed by selected zeolite catalysts possibly because microwaves are dissipated in the liquid phase before they interact with the zeolites. Concerning molecular separation, however, it was found that when the vapor-liquid interface is exposed to microwaves, the system can be disturbed from conventional equilibrium conditions and a positive deviation in phase composition can be achieved, as the vapor phase becomes richer in the component with the lower boiling temperature; the extent of separation improvement depends on the boiling points and the dielectric properties of the mixture components. This finding may have significant practical impact as it implies smaller columns with a lower number trays for a given separation efficiency, compared to conventional designs involving heat exchange in the reboiler and the condenser only. It is stressed, though, that the effect is present only when the vapor—liquid interface is exposed to microwaves; no effect is observed when solely the bulk liquid volume is irradiated. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23447919 [article] Process intensification of reactive distillation for the synthesis of n - propyl propionate : The effects of microwave radiation on molecular separation and esterification reaction [texte imprimé] / Ernesto Altman, Auteur ; Georgios D. Stefanidis, Auteur ; Thomas Van Gerven, Auteur . - 2011 . - pp. 10287–10296. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 10287–10296 Mots-clés : Esterification  Microwave  Distillation  with  reaction Résumé : An envisioned reactive distillation (RD) process for the esterification reaction of n-propyl propionate (ProPro) from I-propanol (ProOH) and propionic acid (ProAc) using microwave irradiation (MW) (f = 2.45 GHz) is studied. In this frame, the fundamental research performed is divided in two parts comparing reaction conditions and equilibrium curves under MW and conventional heating, looking for possible improvement in process efficiency. For the test system, the use of microwaves docs not improve the conversion of the esterification reaction catalyzed by selected zeolite catalysts possibly because microwaves are dissipated in the liquid phase before they interact with the zeolites. Concerning molecular separation, however, it was found that when the vapor-liquid interface is exposed to microwaves, the system can be disturbed from conventional equilibrium conditions and a positive deviation in phase composition can be achieved, as the vapor phase becomes richer in the component with the lower boiling temperature; the extent of separation improvement depends on the boiling points and the dielectric properties of the mixture components. This finding may have significant practical impact as it implies smaller columns with a lower number trays for a given separation efficiency, compared to conventional designs involving heat exchange in the reboiler and the condenser only. It is stressed, though, that the effect is present only when the vapor—liquid interface is exposed to microwaves; no effect is observed when solely the bulk liquid volume is irradiated. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23447919

Scale - out of microreactor stacks for portable and distributed processing / Matthew S. Mettler in Industrial & engineering chemistry research, Vol. 49 N° 21 (Novembre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 10942-10955 Titre : Scale - out of microreactor stacks for portable and distributed processing : Coupling of exothermic and endothermic processes for syngas production Type de document : texte imprimé Auteurs : Matthew S. Mettler, Auteur ; Georgios D. Stefanidis, Auteur ; Dionisios G. Vlachos, Auteur Année de publication : 2011 Article en page(s) : pp. 10942-10955 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Production  Synthesis  gas  Microreactor Résumé : Computational fluid dynamics (CFD) simulations are used to simulate stacks of different sizes, to understand nonlinear effects that arise in scaleout of microchemical systems. As an example process, syngas production from methane is studied using a multifunctional, parallel-plate reactor with alternating combustion and steam reforming channels. A scale-out strategy is proposed that creates larger stacks from a base unit. Stacks are evaluated in terms of efficiency, maximum wall temperature, and stability under external heat loss for both high and moderate wall thermal conductivities. We find that smaller stacks are unstable under laboratory heat-loss conditions. Stacks with high wall thermal conductivities are more stable than those with moderate wall conductivities under our conditions. At high heat-loss coefficients, significant transverse thermal gradients exist between interior and edge channels of the stacks that result in a significant loss of efficiency. A transition from all ignited to some ignited and extinguished and finally to all extinguished channels is discovered as criticality is approached in moderate size stacks. Microsystems provide 1-3 orders of magnitude larger volumetric and gravimetric throughputs than conventional technology, irrespective of model uncertainty, and such intensification is central to portable and distributed processing. They exhibit energy efficiency that is a strong function of size and heat loss but can outperform conventional processing under many conditions. However, they result in higher cost per unit syngas volume unless system optimization is performed. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23447988 [article] Scale - out of microreactor stacks for portable and distributed processing : Coupling of exothermic and endothermic processes for syngas production [texte imprimé] / Matthew S. Mettler, Auteur ; Georgios D. Stefanidis, Auteur ; Dionisios G. Vlachos, Auteur . - 2011 . - pp. 10942-10955. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 10942-10955 Mots-clés : Production  Synthesis  gas  Microreactor Résumé : Computational fluid dynamics (CFD) simulations are used to simulate stacks of different sizes, to understand nonlinear effects that arise in scaleout of microchemical systems. As an example process, syngas production from methane is studied using a multifunctional, parallel-plate reactor with alternating combustion and steam reforming channels. A scale-out strategy is proposed that creates larger stacks from a base unit. Stacks are evaluated in terms of efficiency, maximum wall temperature, and stability under external heat loss for both high and moderate wall thermal conductivities. We find that smaller stacks are unstable under laboratory heat-loss conditions. Stacks with high wall thermal conductivities are more stable than those with moderate wall conductivities under our conditions. At high heat-loss coefficients, significant transverse thermal gradients exist between interior and edge channels of the stacks that result in a significant loss of efficiency. A transition from all ignited to some ignited and extinguished and finally to all extinguished channels is discovered as criticality is approached in moderate size stacks. Microsystems provide 1-3 orders of magnitude larger volumetric and gravimetric throughputs than conventional technology, irrespective of model uncertainty, and such intensification is central to portable and distributed processing. They exhibit energy efficiency that is a strong function of size and heat loss but can outperform conventional processing under many conditions. However, they result in higher cost per unit syngas volume unless system optimization is performed. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23447988