(189f) Modeling a Fixed-Bed Reactor for the Oxidative Dehydrogenation of Ethane On a Multimetallic Mixed Oxide Catalyst

Authors: 
Che-Galicia, G., Universidad Autónoma Metropolitana-Iztapalapa
Quintana-Solórzano, R., Instituto Mexicano del Petróleo



Catalytic oxidative
dehydrogenation of ethane (ODH-Et) has become an attractive alternative to
replace the current processes for ethylene production, i.e., pyrolysis, steam
cracking, catalytic dehydrogenation and fluid catalytic cracking [1,2]. In the
context of catalysts, several formulations have been evaluated for ODH-Et, the
multimetallic mixed oxide system Mo-V-Nb-Te-O being one of the most promising
materials in view of its high efficiency for ethylene production [3,4]. In the
process scenario, however, the most convenient reactor configuration is still
under investigation from a potential industrial point of view due to the high
exothermicity of the main and, mostly, the secondary reactions associated to
the ODH-Et. In this regard, the aim of this work is to simulate the catalytic
behavior of a Mo-V-Nb-Te-O catalyst in a single-tube wall-cooled fixed-bed
reactor for the ODH-Et.

A 2D pseudo-homogeneous
fixed-bed reactor model that couples heat and mass transport phenomena to
kinetics was proposed to describe the ODH-Et on a Mo-V-Nb-Te-O catalyst. The
effective heat and mass transport parameters were obtained from a previous
study wherein the role of hydrodynamics was assessed with some detail [5]. The
reactor model was given in terms of a set of parabolic partial differential
equations, which were solved numerically by the method of orthogonal
collocation using 30 and 50 interior collocation points at the radial and axial
coordinates, respectively, employing shifted Legendre polynomials [6]. The
resulting set of ordinary differential equations was then solved by the
Runge–Kutta–Fehlberg method [7]. A kinetic model based on a
Langmuir-Hinshelwood-Hougen-Watson mechanism considering a single type of
active sites over the catalyst surface was developed. It considered that
surface reactions are RDS while adsorption/desorption steps were in quasi-equilibrium.
The corresponding kinetic parameters estimation was carried out using the
multi-response and multi-parameter optimization method of Levenberg-Marquardt [8].

For a 10 m length and 2.5 cm
ID reactor and the following operating conditions, viz., coolant inlet
temperature: 400-480 °C; reaction mixture inlet temperature: 100-200 °C, inlet
molar concentration of 9/7/84 for C2H6/O2/Inert
and Reynolds particle number of 630, predicted dimensionless concentration and
temperature profiles along the reactor indicate that ethane conversion varies
from 15%-75% and ethylene selectivity from 80%-95%, with a slightly temperature
increment in the range 5-70 °C indicating the presence of a slightly hot spot, see
Figures  1-3. These results suggest,
in principle, that the wall-cooled fixed-bed reactor represents a promising
alternative to carry out the ODH-Et over the mentioned catalyst formulation.


Figure 1. Simulated
dimensionless concentration and temperature profiles of ethane in the reactor
length. Operating conditions as follows: coolant temperature of 400 °C,
an inlet temperature of 200 °C, an inlet molar concentrations of 9/7/84 for C2H6/O2/Inert
and a Reynolds particle number of 630.


Figure 2. Simulated
dimensionless concentration and temperature profiles of ethane in the reactor
length. Operating conditions as follows: coolant temperature of 440 °C,
an inlet temperature of 200 °C, an inlet molar concentrations of 9/7/84 for C2H6/O2/Inert
and a Reynolds particle number of 630.


Figure 3. Simulated
dimensionless concentration and temperature profiles of ethane in the reactor
length. Operating conditions as follows: coolant temperature of 480 ¼C,
an inlet temperature of 200 ¼C, an inlet molar concentrations
of 9/7/84 for C2H6/O2/Inert and a Reynolds
particle number of 630.

[1] F. Cavani,
N. Ballarini and A. Cericola,
Catal. Today 127, 113-131, 2007.

[2] X. Liu, H. Zhu, Q. Ge, W. Li and H. Xu, Prog. Chem. 16, 900-910, 2004.

[3] J. M. L?pez
Nieto, P. Botella, M. I. V?zquez
and A. Dejoz, Chem. Commun.
1906-1907, 2002.

[4] P. Botella,
E. Garc'a-Gonz?lez, A. Dejoz,
J.M. L?pez Nieto, M.I. V?zquez
and J. Gonz?lez-Calbet, J. Catal.
225, 428-438, 2004.

[5] C.O. Castillo-Araiza, H. Jim?nez-Islas and F. L?pez-Isunza.
Ind. Eng. Chem. Res. 46, 7426-7435, 2007.

[6] B. Finlayson. Nonlinear
Analysis in Chemical 
Engineering. 
McGraw-Hill, 
New York, 1980.

[7] L. Lapidus
and J. Seinfeld. Numerical Solution of Ordinary Differential  Equations.  Academic Press, New York, 1971.

[8] W. E. Stewart, M. Caracotsios and J. P. Szrensen, AIChE Journal. 38, 641-650, 1995.

Checkout

This paper has an Extended Abstract file available; you must purchase the conference proceedings to access it.

Checkout

Do you already own this?

Pricing


Individuals

AIChE Members $150.00
AIChE Graduate Student Members Free
AIChE Undergraduate Student Members Free
Non-Members $225.00