A catalytically active membrane reactor for fast, exothermic, heterogeneously catalysed reactions

Abstract

ooo9-2509/92 s5.cIo+o.m Printed in Great Britain. 01992FWgMlOIlRessLM A catalytically active membrane reactor for fast, exothemic, heterogeneously catalysed reactions AbstractA membrane reactor with separated feed of reactants is demonstrated as a promising contactor type when dealing with heterogeneously catalysed, very fast and exothermic gas phase reactions. Due to the separation of reactants a good control of the system is obtained, because process variables can be varied independently from each other. Transport of reactants is the rate governing process and because this is only slightly temperature dependent a thermal runaway will not occur. When dealing with e.g. combustion processes no explosive mixtures will build up and safety is increased.Based on the dusty-gas model, the concentration profiles of zomponents inside the membrane can be calculated together with the fluxes. However this is a calculation time consuming process and not necessary in all cases. In absence of a pressure drop and no slip of reactants to the opposite side a linearisation is possible leading to a simplified expression for the interfacial flux of a reactant and a criterion to evaluate the possibility of slip of reactants. Using the oxidation of carbon monoxide cata.lysed by platinum as a model reaction this approximation was experimentally verified by comparison of measured fluxes with the calculated results. Apart hrn flux measurements exploratory overall conversion measurements were carried out with the membrane reactor module in order to demonstrate its operation performance. From these studies it was concluded that conversion levels up to 90% carbon monoxide could easily be achieved. I. IntroductionRecently in our laboratory a catalytically active membrane reactor with separated feed of reactants was studied by Sloot with an extremely fast reversible reaction (Sloot et al., 1990). In this reactor the reactants were separated by a catalytically active membrane and owing to transport in the pores inside the membrane reaction proceeds. On studying the well-known Claus reaction. this principle was demonstrated to be very useful when dealing with reactions requiring strict stoechiometric feed of reactants. From numerical simulations Sloot showed that applying a pressure difference over the membrane, favours the tluxes while the products can be directed preferentially to one side of the membrane. Zaspalis (199la, 1991b) also used a catalytically active membrane in the NOx-reduction and methanol dehydrogenation reactions. He discussed different types of operation (e.g. premixed and separated feed) with respect to the influence on selectivity. Separated feed of reactants to the reactor offers advantages with respect to safety in case mixing of reactants is restricted to explosion boundaries. A second advantage is an improved controllability, because all process variables can be varied independently from each other. As the rate governing process is the tranport of reactants, thermal runaway will not occur when dealing with exothermal re...

The catalytic combustion of natural gas in a membrane reactor with separate feed of reactants

“…In earlier papers concerning the operation and the modelling of membrane reactors with separate feed of reactants it was demonstrated that the use of a Stefan-Maxwell approach, particularly in the presence of a pressure difference over the membrane, has to be preferred to a merely Fickian approach [7,8,10]. In this context, the so-called Dusty-Gas Model approach [13] was successfully employed in models based on membrane isothermicity, an assumption supported by the comparatively high membrane conductivity and the limited conversions tested in the above studies.…”

“…The first studies with this type of reactor were reported in literature by Sloot et al [7] where it was demonstrated, using the Claus reaction as model reaction, that this concept has distinct advantages in the operation of reactions that normally require strict stoichiometric feed rates of reactants. Another application was worked out by Veldsink et al [8] and Saracco et al [9][10][11] for performing fast and exothermic reactions (in their studies: the catalytic combustion of CO and propane, respectively).…”

A Catalytically Active Membrane Reactor for Fast, Highly Exothermic, Heterogeneous Gas Reactions. A Pilot Plant Study

“…Concentrically inside the membrane a cooling pipe is placed to remove heat from the membrane surface. A general applicable flux model was developed (Veldsink, 1993), which describes the transport of reactants and products through the membrane accompanied with chemical reactions of arbitrary kinetic rate equations. For a catalytic membrane reactor with separated feed of reactants (CMRSR) slip of unconverted reactants through the membrane substantially reduces the attractive features of this type of reactor.…”

An experimental study of diffusion and convection of multicomponent gases through catalytic and non-catalytic membranes

“…Among others, it provides options to improve the reactor control and to avoid the build-up of explosive gas mixtures [2,3]. According to Veldsink et al [ 3 ] slip of unconverted reactants to the opposite side reduces substantially the aforementioned advantages.…”

“…Among others, it provides options to improve the reactor control and to avoid the build-up of explosive gas mixtures [2,3]. According to Veldsink et al [ 3 ] slip of unconverted reactants to the opposite side reduces substantially the aforementioned advantages. Therefore, the optimal performance of this type of membrane reactor is obtained for heterogeneous reactions with a high reaction rate compared with the transport rates of reactants through the membrane.…”