Transient Redox Activity of Vanadyl Pyrophosphate at Ambient and Elevated Pressure
Notice bibliographique
Résumé
Abstract The transient catalytic activity of vanadyl pyrophosphate (VPP) catalyst was studied at ambient and elevated pressure (4.1 bar) and a wide range of operating conditions. The range included the commercial operating conditions typical of fixed bed, fluidized bed and circulating fluidized beds (CFB) for the partial oxidation of n-butane to maleic anhydride (MA). The maleic anhydride yield improved by increasing the feed oxygen molar fraction, temperature and pressure. When the catalyst was cycled between an oxidizing (synthetic air) and a reducing environment; yield increased with an increase in the catalyst residence time in the oxidizing environment. This effect was more pronounced at higher pressure. At ambient pressure, MA selectivity varied between 50-73 % while it decreased to about 48-54 % at a pressure of 4.1 bar. A strong MA selectivity dependency on feed composition was observed when the oxidation time was in the range of actual industrial reactors (< 1 minute). Selectivity data suggested that different oxygen species might be responsible for CO formation compared to other products such as CO2 and MA. Under oxidizing feed conditions (oxygen/n-butane ≥ than 3.7), an increase in n butane conversion was the main contributor to improved MA yield: n-butane conversion increased by about 70 % when the catalyst oxidation time extended from 0.3 to 10 minute. While, under fuel rich feed conditions, typical of industrial CFB operations, both MA selectivity and n-butane conversion contributed to enhancement in MA yield. Depending on the feed composition, MA selectivity increases by about 16-30 % and n butane conversion increases by about 32-55 % by extending the catalyst oxidation time. These results show the critical importance of catalyst oxidation time on reaction yield improvement especially when operating under fuel rich feed conditions. The surface adsorbed or surface lattice oxygen species were suggested to be the main responsible for n butane activation. While, the contribution of catalyst’s sub-surface lattice oxygen was believed to be very limited at fuel rich feed conditions. Under these conditions, catalyst over-reduction cannot be effectively compensated even after excessive catalyst regeneration and presence of gas phase oxygen is critical to maintain a high catalytic activity. As the reactor pressure increased to 4.1 bar, up to 60 % increase in n butane conversion accompanied by 100 % increase in oxygen conversion was observed. MA selectivity decreased by about 20 % on average but the increase in n-butane conversion resulted in an overall yield improvement of up to 30 %. Data show that the catalytic performance could be enhanced at certain combination of reactor pressure and temperature.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».