Forced flow through catalyst

Effect of Pressure Drop in Reactor (Forced Flow through Catalyst... 

In low RH conditions, the cathode MPL can force flow through the membrane into the anode by capillary pressure forces, reducing dryout and increasing performance. The backflow of water would occur primarily through the hydrophilic pore network in the catalyst layer, since complete pore saturation in the catalyst layer would result in nearly total performance loss, and high saturation in the hydrophobic pores of the CL would likely... 

The most reliable recycle reactors are those with a centrifugal pump, a fixed bed of catalyst, and a well-defined and forced flow path through the catalyst bed. Some of those shown on the two bottom rows in Jankowski s papers are of this type. From these, large diameter and/or high speed blowers are needed to generate high pressure increase and only small gaps can be tolerated between catalyst basket and blower, to minimize internal back flow. 

In this type of reactor, an agitator is used for mixing the fluid in the main body of the vessel, whereas the gas is rapidly circulated throughout the reactor and forced to flow through the catalyst bed. A low conversion per pass through the catalyst is required so that uniform composition in the reactor is achieved. 

A special case arises when the "skin" (membrane) layer of a normal composite membrane element is immobilized with a catalyst and not intended for separating reaction species. Consider the example of an enzyme, invertase, for the reaction of sucrose inversion. Enzyme is immobilized within a two<layer alumina membrane element by filtering an invertase solution from the porous support side. After enzyme immobilization, the sucrose solution is pumped to the skin or the support side of the membrane element in a crossflow fashion. By the action of an applied pressure difference across the element, the sucrose solution is forced to flow through the composite porous structure. Nakajima et al. [1988] found that the permeate direction of the sucrose solution has pronounced effects on the reaction rate and the degree of conversion. Higher reaction rates and conversions occur when the sucrose solution is supplied from the skin side. The effect on the reaction rate is consistently shown in Figure 11.6 for two different membrane elements membrane A is immobilized by filtering the enzyme solution from the support layer side while membrane B from the skin layer side. 

Pressure gradients in the gas channels are caused by friction to flow in the channels and by variations of gas velocity in the channels. Friction in the channels causes a reduction in pressure in the flow direction, in both the inlet and outlet channels. Since these channels generally have their openings at the opposite ends of a catalyst slab, the pressure gradients in the inlet and outlet channels are in the same direction, and therefore there is some compensating effect in the local driving force for lateral flow through the bed. 

The reaction or regeneration cross-flow gas in the moving bed is imposed by the phenomenon of pinning [14,16,17], which means that the drag exerted on the catalyst bed by the gas flowing through this bed forces the bed against the downstream wall. The consequence will be that the downward motion ceases and the bed is said to be pinned. 

The Tapered Element Oscillating Microbalance (TEOM) reactor has recently been applied to study deactivation of zeolite catalysts [7,8]. The main advantage of the TEOM reactor is that all gases in the reaction mixture are forced to flow through the catalyst bed as in a conventional fixed-bed reactor. Coupled with on-line gas chromatography, the catalyst activity, selectivity and coking rate can be measured simultaneously as a fimction of the amount of coke on the catalyst. Hence, the TEOM represents a unique way of studying the effect of coke deposition in detail. 

Control of Contact between Catalyst and Reactants - In this use of catalytic membranes, the membrane is porous and in the CMR configuration, and is either intrinsically active or has had a catalyst deposited within the pores. The membrane geometry allows for a degree of control of the contact time. It is operated in the cross-flow mode, in which all of the reactant is forced to flow through the membrane by feeding it to one side with a closed exit. This is illustrated schematically in Figure 19. 

In the next section we shall compare some experimental results on flow through porous catalysts with the mechanisms of diffusion and forced flow described above. 

It seems that application of this type of force to multiphase catalytic reactors is still poorly explored. In the proposed work, we will illustrate the application of strong inhomogeneous magnetic fields to a small-scale trickle-bed reactor that consists of two-phase gas-liquid cocurrent flow through a fixed bed of catalyst... 

H+) Produced by the dissociation of Hj at the anode to the cathode, (3) Prevention of the associated electron flow through the membranes forcing them to flow in the external circuit to the cathode to produce DC current, and (4) Support for the catalyst loaded on the electrodes. When Hj is replaced by methanol as a fuel in liquid form in direct methanol fuel cell (DMFC), the dissociation of methanol solution at the anode produces protons that are transported through the hydrated PEM to the cathode, where a reduction of O2 produces water in the presence of the protons. To qualify PEM for commercial application in PEMFC and DMFC, it should have a combination of properties including (Maiyalagan and Pasupathi 2010 Neburchilov et al. 2007 Nagarale et al. 2010) ... 

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