Edward Gobina

Ethane dehydrogenation using a high-temperature catalytic membrane reactor

Abstract Experiments have been conducted for the dehydrogenation of ethane to ethylene using a high-temperature catalytic membrane reactor under isothermal conditions. Typically, conversions of up to 7 times (cocurrent mode) and 8 times (countercurrent mode) higher than the equilibrium value achievable in conventional fixed-bed reactors have been attained at high sweep flow rates. The membrane used in this study was a thin layer of Pd-23 wt% Ag on porous Vycor glass. The significant improvement in the ethane conversion is attributed to the exclusive and continuous permeation of hydrogen through the membrane.

Ethane dehydrogenation in a catalytic membrane reactor coupled with a reactive sweep gas

Abstract An experimental and simulation study has been carried out for the dehydrogenation of ethane to ethylene in a catalytic membrane reactor, with and without reaction on the permeate side. The membrane comprised a palladium-silver alloy deposited as a thin film on a Vycor glass support and palladium catalyst pellets were packed inside the membrane tube. Permeation data for the model were determined separately. The differential equations for transport and reaction within the membrane module were solved using orthogonal collocation to give concentration profiles as a function of contact time, reactor length and radius. The simulation was validated with experimental data and was observed to correctly predict the increase in conversion with contact time for the range of experimental conditions investigated.

An experimental evaluation of high-temperature composite membrane systems for propane dehydrogenation

Abstract Experiments have been performed using a high-temperature membrane reactor to evaluate the relative performance of various composite membranes. Two membrane categories (porous and dense) and three types of composite membrane systems (Pd/Ag, silica and Pd-dispersed porous) have been studied and their performance compared. Also considered is the special case of the PdAg composite system having imperfections. The industrially important reaction of propane dehydrogenation over noble metal catalysts to produce propylene was selected for study. Results have been obtained which indicate that the dense PdAg composite system does possess higher performance levels in the temperature range studied. However, metal-dispersed porous systems have advantages due to their significantly higher contact surface-to-volume ratio. High hydrogen permselectivity is confirmed as a key factor in determining reactor performance in terms of conversion enhancement.

Mathematical analysis of ethylbenzene dehydrogenation: Comparison of microporous and dense membrane systems

Abstract A comprehensive mathematical model has been developed and used to simulate the catalytic dehydrogenation of ethylbenzene to styrene using two types of membrane reactor system, i.e. a composite membrane consisting of a thin but continuous metal membrane film of PdAg alloy deposited on the outside surface of a porous ceramic substrate and a microporous membrane tube with the thin permselective layer on the outside of the tube. Various operating parameters have been considered including the separation layer thickness, porosity, reactor length and contact time. Feed stream compositions were also varied. Superior performance in terms of conversion enhancement far above the equilibrium value was observed for the PdAg composite membrane system and was attributed to its exclusive hydrogen permeability characteristics.

Equilibrium-shift in alkane dehydrogenation using a high-temperature catalytic membrane reactor

Abstract This study involves the application of a tubular fixed-bed catalytic membrane reactor to effect equilibrium-shift during the catalytic dehydrogenation of ethane to ethylene and hydrogen. The specific characteristic behaviour of the reactor to shift the equilibrium was analysed using a two-dimensional mathematical model which was solved using the orthogonal collocation method. An important extrinsic variable, the time factor (W/F Ao ) was manipulated to yield results which were then used to explain reactor performance. Experimental results showed that under optimal conditions an eight-fold shift in the equilibrium conversion could be attained. Generally, good agreement was obtained between model and experimental predictions for reactor operation using pure nitrogen as sweep gas. When air was employed as sweep, the agreement was not as expected; possibly due to oxidation of the Pd surface.

Reaction coupling in catalytic membrane reactors

Abstract An experimental and modelling study of the catalytic dehydrogenation of n-butane has been made in a membrane reactor. Use of nitrogen, carbon monoxide/nitrogen and oxygen/nitrogen sweep gases produced conversions up to 5 to 8 times the equilibrium conversion, the largest values occuring due to reaction coupling of the permeated hydrogen with O 2 or CO.

Reaction assisted hydrogen transport during catalytic dehydrogenation in a membrane reactor

Abstract Composite Pd/Ag alloy membranes have been prepared and used to study the catalytic dehydrogenation of n-butane in a high-temperature membrane reactor. Conversions obtained by using oxygen and carbon monoxide as sweep gases have been compared to results obtained using nitrogen as a sweep gas and with the equilibrium value for the dehydrogenation reaction. Increases of conversion at 670 K of 4 and 6 fold respectively above the equilibrium value were observed when using CO and O2 as sweep gases. The potential formation of metallic oxide on the membrane surface was eliminated by a high temperature reduction with H2 prior to the reaction experiments.

Performance of pure and mixed gas transport in reconfigured hybrid inorganic membranes Pt. 1

This two-part article considers the application of reconfigured hybrid membranes for stripping CO 2 from natural gas mixtures in order to meet various specifications, including pipeline transportation. The first part, which appears here, provides the background to this research, including key benefits of this technology. It also describes the apparatus used in this study and discusses the experimental results. Part two will be published in the July issue.

Ultra-thin palladium technologies enable future commercial deployment of PEM fuel cell systems

Hydrogen is widely used in various process industries. It is used in petroleum refining, the manufacture of chemicals and fertilisers, metallurgy, and by the electronics sector. Concern worldwide about the effect that carbon dioxide is having on the global climate is also a major driving force behind the use of hydrogen in the future as an important source of energy. In this feature article we present results of an unconventional electroless plating technique, using a partial vacuum, for the deposition of thin palladium dense films on porous ceramic supports.

Hybrid inorganic membrane technology shows promise in gas processing

Abstract This paper examines how the use of novel hybrid inorganic membrane technology is enabling natural gas processing and the production of high density hydrogen without any impurities.