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Oxidative dehydrogenation of ethane in short contact time reactors

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Chapter 1 Introduction 11 contact times. From other investigations (Beretta et al., 2001a and b) we have also seen that it seems quite established that ethylene formation occurs in the gas phase. Thus, a catalyst with good oxidation properties might be suitable to replace Pt, and can be a reliable alternative if such catalyst shows also high thermal stability and lower cost than Pt. In this work we propose the investigation of a non-noble metal-based catalysts for the oxidative dehydrogenation of ethane in short contact time reactors. In this field, we have recently developed novel structured catalytic systems, active in hydrocarbons deep oxidation processes and alternative to noble metals (Cimino et al., 2000). Specifically, the activity of the LaMnO 3 - based monolithic catalyst has been proven to be stable in the catalytic combustion of methane under 100 hours operation in ignited conditions at 1000°C (Cimino et al., 2001b). To test the applicability of such a catalyst in ethane ODH at short contact time, we intend to perform reaction tests in comparison with Pt with the aim of evaluating the applicability and reliability of a significantly cheaper catalyst (compared to Pt-based ones) in the development of a novel and more efficient process of olefin production. The investigation of a novel catalyst, such as the LaMnO 3 perovskite, can also be considered as a tool to assess the ultimate role of the catalyst, since changing the active phase undoubtedly affects the performance of the system. The direct comparison of a LaMnO 3 - based catalyst with a Pt-based one and with a blank reactor can help us to deepen the understanding on the subject. In particular, the assumption that the catalyst is not important in determining the performance of the ODH reaction in a short contact time reactor (Beretta et al., 2001b) requires more proof. We believe that it is true that any catalyst able to ignite and sustain the gas phase reactions can be in theory employed in the system, but looking at ethylene selectivity, it is better that more CO 2 than CO is formed on the catalyst surface. As intuitively understandable and shown in the stoichiometry of the reactions 1.3 and 1.4, less ethane is consumed and more heat is produced to react a given amount of oxygen when CO 2 is formed. 72 C 2 H 6 + O 2 → 74 CO 2 + 76 H 2 O ∆H r ° = - 408.2 kJ/mol 1.3 52 C 2 H 6 + O 2 → 54 CO + 56 H 2 O ∆H r ° = - 345.1 kJ/mol 1.4 Platinum is a highly active catalyst, very aggressive towards the oxidation of hydrocarbons. When O 2 is the limiting reactant, a larger amount of ethane is rather oxidized to CO than CO 2 . Catalysts other than noble metals, less active but more selective towards the oxidation of CO to CO 2 might be more effective in our process. Also in the gas phase, under conditions of short contact time reactors, larger amounts of CO are produced. A catalyst with

Anteprima della Tesi di Francesco Donsì

Anteprima della tesi: Oxidative dehydrogenation of ethane in short contact time reactors, Pagina 11

Tesi di Dottorato

Dipartimento: Ingegneria Chimica

Autore: Francesco Donsì Contatta »

Composta da 194 pagine.

 

Questa tesi ha raggiunto 1055 click dal 04/11/2004.

 

Consultata integralmente 5 volte.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.