Coated Wall Reactor

Various reactor types have been used as the foundation for microreactor designs, including coated wall reactors, packed-bed reactors, structured catalyst reactors, and membrane reactors. 

Coated Wall Reactors. Techniques for depositing catalyst onto the reactor walls include... 

The catalyst bed was a coated wall reactor using commercial CuZnAl catalyst. An alumina sol was used to enhance the adhesion of the catalyst to the channel walls. After the shims were washed thoroughly, the alumina adhesion layer was deposited using an alumina sol (NYACOL AL20DW colloidal alumina, PQ Corporation) and then dried at 60 °C. To decrease the surface tension of the wash-coat solvent, small amounts of 2-propanol were added to a catalyst slurry of ICI Synetix 33—5 catalyst, with 20 wt % alumina sol and water. The catalyst was calcined at 350—400 °C for 2 h after air-drying. Before testing, the catalyst was reduced by flowing H2/N2 over it at 280 °C. 

A measure that has been the subject of extensive publication is that of microreactors with catalytically coated walls (7,8). A microreactor has been defined as a miniaturized reaction vessel with characteristic dimensions in the range 10-300 pm which has been fabricated using state-of-the-art high-precision engineering (7). Such reactors exhibit well-defined laminar-flow patterns and permit facile scale-up by simple numbering up of the number of channels and flexible... 

The fluidized bed reactor can also handle fast, complex reactions, with mixing and temperature control being especially good when stirring is provided. Unfortunately, the extent of back mixing is difficult to assess so that the residence time distribution of the reactants in the reactor is uncertain. In addition, only small catalyst particles can be used, and attrition, with the consequent breakdown and loss of catalyst, is a problem. Finally, a catalyst bed is adequately fluidized over only a comparatively narrow range of flow rates. More information about kinetic reactors can be found in reviews [33,34,50], Applications of the basket-type mixed reactor to liquid-solid systems are discussed by Suzuki and Kawazo [62] and by Teshima and Ohashi [63], and the development of a laminar flow, liquid-solid reactor by Schmalzer et al. [64], In the latter reactor the wall is coated with a catalyst layer. 

Photoreactors for dissolved pollutants operate by bubbling a carrier gas (usually air) through a reservoir of liquids (usually water). The pollutant-loaded gas is then passed though the photocatalytic reactor and released. Several t)q)es of reactors have been connected with this application, including PBRs and coated wall reactors. 

Figure 8 A coated wall tubular reactor in a spiral configuration (based on Arana et al., 2008 Vorontsov and Dubovitskaya, 2004).

Coated wall annular reactors (Figure 12) are characterized by a thin film of photocatalyst located either on the outer side of inner tube or on the inner side of the outer tube. There are many reasons for preferring the inner side of the outer tube for the coating. The first reason has to do with the flux if is known that at high flux of lighf (>l-2 mW cm ) fhe quantum efficiency is proportional to 1 divided by the square root of fhe intensity. Hence, it is... 

Consider diffusion with convection in a coated wall reactor, where the reaction takes place at the wall. [9] The governing equation and boundary conditions for concentration are ... 

Figure 10.6. Schematic diagram of methanation reactor showing catalyst coating on the inside of the reactor tube wall.

For calculating the concentration profile as function of channel length and radius the model of the isothermic tube reactor with catalytically coated wall and laminar flow (ref. 5) was used with the following simplifications ... 

Figure 10.3 Schematic diagram of a coated wall reactor.

This appears to be a formidable task. To accomplish it, we shall need some new tools. Under certain conditions, it may be possible to compute C without a trial-and-error basis. To do this, we shall need to study a class of ODE with homogeneous boundary conditions called the Sturm-Liouville equation. We shall return to the coated-wall reactor after we gamer knowledge of the properties of orthogonal functions. 

The new tool we needed in the previous coated-wall reactor problem can be stated very simply as... 

In the gas-liquid-solid MSR, catalyst is incorporated either as a packed bed or as a coating. In the packed bed reactors, standard porous catalysts are incorporated and the fluid streams are brought into contact. In the falling film MSR, the catalyst is incorporated as thin nonporous films or as particles in alumina-coated walls [4]. 

However, in other cases internal diffusion limitation can be significant even with very thin washcoat thicknesses [127], when temperature is high (> 700°C). This refers, for example, to catalytic combustions, which are extremely fast. Hayes et al. [135] evaluated the extent of intraphase and interphase resistances to the catalytic conversion of low concentrations of carbon monoxide in air in a tube wall reactor (coated with a platinum-alumina deposit). Above 610 K there was strong evidence of both intraphase and interphase resistances to catalytic conversion. In Sections 8.3.2, 8.3.3, and 8.3.4, we provide a systematic analysis for prediction of the extension of external and internal diffusion limitations. 

Berger RJ, Kapteijn F. Coated-wall reactor modeling-criteria for neglecting radial concentration gradients. 2. Reactor tubes filled with inert particles. Industrial and Engineering Chemistry Research 2007 46 3871-3876. 

Figure 6.7 Conventional heat exchanger (top), cooled catalytic burner (middle) and coupling of exothermic and endothermic reaction at the wall of a heat-exchanger reactor coated with...

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