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Abstract
Hydrogen sulfide is toxic by-product of many petroleum, petrochemical and mineral treatment operations. Due to the increasing stringent environment regulations, toxic H2S must be completely removed from industrial waste gases before venting to the atmosphere. The H2S decomposition reaction is a well known thermodynamically limited reaction. Alumina membrane fixed bed catalytic reactors offer the potential for improved conversions at reduced operating temperature due to product separation and catalyst activity. A theoretical and experimental work dealing with a packed bed membrane reactor is the subject of this thesis.
A tubular alumina membrane reactor possessing thermal and corrosion resistance has been developed. A multicomponent permeation study indicated that the fluxes of gases could be quantitatively described as a combination of Knudsen diffusion and viscous flow through the porous alumina membrane. The catalytic decomposition of hydrogen sulfide to hydrogen and sulfur was conducted in membrane reactor incorporating a commercial porous alumina membrane in combination with catalytic function of bimetallic RuMo sulfide catalyst. The obtained results demonstrate the possibility of achieving conversion above the equilibrium conversion. The reaction rate is equal to the intrinsic rate since both internal/external mass transfer and heat transfer resistance are negligible for the size of catalyst particles considered. Results obtained with this system have shown a maximum of 2.3 times the equilibrium conversion at the operating temperature 983K, which was equivalent to the conversion at operating temperature 1200K in a conventional fixed bed reactor. The conversion enhancement was significant for the operation with high sweep to feed molar ratio. The reactor configuration of membrane reactor appeared to have an influence on its performance. Comparative experimental and simulation study showed that the cocurrent mode gave slightly higher conversion over counter-current mode.
Mathematical models were developed for the reactor, based on plug flow behavior. Simulation had been performed in order to validate the model against experimental data. Reactor optimization was carried out using the validated model. The simulation results from the non-isothermal model were in reasonable agreement with the experimental data. On the other hand, the isothermal model which neglected heat effects that took place in the reactor, has leaded to over-predicted conversion. This study also illustrated that predictive simulations could be used to explore the effects of recycle operation; the optimization study showed that the alumina membrane reactor permitting retentate recycle, could achieve up to 48.6% conversion, corresponding to 6 folded of the equilibrium conversion. The simulations provide a logical methodology for experimental planning and design.
To further elucidate the effect of reactor configuration, operation conditions and permeation parameters on the performance of membrane reactors, a high permselective Pt-composite MR model was developed. Comparison of alumina MR and Pt-composite MR was carried out via computer simulation. Porous membrane reactor with higher permeability but lower Permselectivity can attain comparable conversion as the composite membrane reactor with higher permselectivity but lower permeability. Ptcomposite MR was more superior to alumina MR without recycle. Retentate recycle in alumina MR is shown to outperform the Pt-composite MR. Alumina MR was therefore considered as potential candidate for industrial H2S treatment.