Coupling dehydrogenation of ethylbenzene with hydrogenation of nitrobenzene in an autothermal catalytic membrane reactor

• Main Author: Abo-Ghander, Nabeel Salim M.
• Language: English
• Published: University of British Columbia 2011
• Online Access: http://hdl.handle.net/2429/31105

Dehydrogenation of ethylbenzene and hydrogenation of nitrobenzene form an interesting pair of reactions to be coupled in a catalytic membrane reactor. The former is reversible and thermodynamically limited, supplying hydrogen with a net endothermality, while the latter is irreversible and exothermic, consuming hydrogen to produce aniline. In this work, coupling of these two reactions is simulated in a catalytic fixed bed membrane reactor where hydrogen produced on the dehydrogenation side is transferred through hydrogen membranes to the hydrogenation side where it reacts to produce aniline. Heat generated on the hydrogenation side is transferred to the dehydrogenation side, where it is utilized by the endothermic dehydrogenation reaction to improve the styrene yield. A pseudo-homogeneous model for the coupled reactor based on the concept of fixed bed reactors accounting for both the diffusion of hydrogen and transfer of heat is first developed. The effects of the operating and design parameters considered on the production of styrene and aniline show conflicting behaviour, i.e. improving the yield of styrene results in decreased production of aniline. Consequently, the cocurrent configuration of the coupled reactor was optimized within constraints so that it can be operated effectively to produce ~98% styrene as a one limiting option or ~80% aniline at the other extreme. The intraparticle diffusion resistance, a major limitation in fixed bed reactors, is evaluated by developing a heterogeneous reactor model based on Fickian diffusion and the dusty gas model for both isothermal and non-isothermal catalyst pellets. Both heterogeneous models predict a significant reduction in yield and conversion relative to the pseudo-homogeneous model, indicating the importance of heterogeneity. This reduction is generally less severe for the dusty gas model than for Fickian diffusion. The mean square deviation and absolute deviation along the reactor are calculated for all models relative to the heterogeneous reactor model with dusty gas for non-isothermal catalyst pellets, considered to be the most rigorous model tested. Assuming isothermality causes larger deviations than assuming Fickian diffusion. The deviations in the predictions of the homogenous model and the heterogeneous models from those of the dusty gas model for non-isothermal pellets are ~6% and ~11%, respectively.