Reactor designs for ethylene production via ethane ODH: comparison of performance

M. L. RODRIGUEZ; D.E. ARDISSONE; E. LÓPEZ; M. N. PEDERNERA; D.O. BORIO

Ixtapa - Zihuatanejo, México.

Congreso; International - Mexican Congress on Chemical Reaction Engineering 2010; 2010

The ethane oxidative dehydrogenation (ODH), in the presence of a suitable catalyst [1,2], appears as the most promising alternative to the industrial ethylene production processes of thermal steam cracking and FCC, which are energy intensive. In the ODH process the reactions are irreversible and exothermic; therefore, no external heating is required and no equilibrium limitations are observed. The reactions proceed via a triangular series/parallel scheme with the undesired complete combustions of both ethane and ethylene. Ethane ODH has been studied over a wide range of catalytic materials [1,3]. Recently, Heracleous and Lemonidou [4,5] reported the development of bulk Ni-Nb-O mixed oxides as both highly active and selective catalytic materials for the desired reaction. Multitubular reactors are commonly used in industry to carry out exothermic processes to control the reaction temperature and maintain adequate selectivity levels [6]. Membrane reactors are recently proposed to axially distribute the oxygen feed as lower oxygen partial pressures increase the selectivity, decreasing the generated heat and increasing the ethylene yield [4,5].   In the present contribution, a performance comparison of two different designs of multitubular reactors for the ODH of ethane to ethylene is presented. A Conventional Reactor (CR) with oxygen injection only at the tube mouth, and a Membrane Reactor (MR) with oxygen injection at both the tube mouth and the tube wall (membrane) are studied. The MR is assumed to be cooled not only by convective heat exchange between reactants and coolant (as in the case of CR), but also by cold-shot of the permeated oxygen. In both cases (CR and MR) co-current flow is selected. The reactor´s steady-state performance is analyzed by means of a pseudo-homogeneous 1-D model. The heat generation rate is considerably lower for MR that for CR (the combustion reactions of ethane and ethylene are much more exothermic than the ODH). For a constant ethylene production, the MR could lead to considerable saving of ethane. The ethane conversion, however, can be lower for the MR design, which implies higher recycle streams. The main challenge for a multitubular MR is the prevention of failures in the tubes, to avoid temperature runaway and explosive mixtures. REFERENCES [1] G. Centi, F. Cavani, F. Trifiró, “Selective Oxidation by Heterogeneous Catalysis”, Kluwer Academic Publishers / Plenum Press, New York, USA, 2001. [2] F. Cavani, N. Ballarini, A. Cericola, Catal. Today 127 (2007) 113. [3] M.A. Bañares, Catal. Today 51 (1999) 319. [4] E. Heracleous, A.A. Lemonidou, J. Catal., 237 (2006) 162. [5] E. Heracleous, A.A. Lemonidou, J. Catal., 237 (2006) 175. [6] P. Arpentinier, F. Cavani, F. Trifiró “The Technol. of Catalytic Oxidations”, Technip, Paris, 2001. [7] M. Pedernera, R. Mallada, M. Menéndez, J. Santamaría, AIChE J. 46 (12) (2000) 2489. [8] E. López, E. Heracleous, A.A. Lemonidou, D.O. Borio, Chem. Eng. J. 145 (2008) 308.