Multifunctional Reactor Concepts

The above considerations indicate that, independent of implementation details, the space-time yield of endothermic reactions could be significantly enhanced by shifting the reaction site to the heat-exchanging surfaces. This intention has led to the production of a large variety of multifunctional reactor concepts for coupling endothermic and exothermic reactions. In the following section the state of the art in this area will be discussed for selected examples. 

Multifunctional Reactors Reaction may be coupled with other unit operations to reduce capital and/or operating costs, increase selectivity, and improve safety. Examples are reaction and distillation and reaction with heat transfer. Concepts that combine reaction with membrane separation, extraction, and crystallization are also being explored. In each case, while possibly reducing cost, the need to accommodate both reaction and the additional operation constrains process flexibility by reducing the operating envelope. 

In addition to the well-established fixed-bed reactor configurations mentioned above, new concepts are being discussed where specific features like educt addition and selective product removal are integrated in the fixed bed. From these multifunctional reactors , autothermal reactor concepts where the heat exchange between the cold feed and the hot effluent is integrated in the fixed-bed have already been established in industrial practice. 

Apparently, it is not difficult to imagine coupling a chemical reaction with separation or heat transfer to obtain a concept of multifunctional reactors which frequently result in higher productivity. 

The concept of nanofluids to further intensify microreactors has been discussed by Fan et al. [17]. The nano-fluids are suspensions of solid nano-partides with sizes typically of 1-100 nm in traditional liquids such as water, glycol and oils. These solid-liquid composites are very stable and show higher thermal conductivity and higher convective heat transfer performance than traditional liquids. They can thus be used to enhance the heat transfer in nanofluids in compact multifunctional reactors. A nanofluid based on Ti02 material dispersed in ethylene glycol showed an up to 35% increase in the overall heat transfer coefficient and a... 

Future Trends in Reactor Technology The technical reactors introduced here so far are those used today in common industrial processes. Of course, research and development activities in past decades have led to new reactor concepts that may have advantages with respect to process intensification, higher selectivities, and safety and environmental aspects. Such novel developments in catalytic reactor technology are, for example, monolithic reactors for multiphase reactions, microreactors to improve mass and heat transfer, membrane reactors to overcome thermodynamic and kinetic constraints, or multifunctional reactors combining a chemical reaction with heat transfer or with the separation in one instead of two units. It is beyond the scope of this textbook to cover all the details of these new fascinating reactor concepts, but for those who are interested in a brief outline we summarize important aspects in Section 4.10.8. 

Research activities in past decades have produced new reactor concepts. For example, hybrid (multifunctional) reactors combining reaction and heat or mass transfer are an interesting new option. Progress has also been achieved with monolithic reactors, which are already used commercially in emission control systems. An overview of these developments is given by Moulijn, Makkee, and Van Diepen (2004). Details are given by Westerterp (1992) and Cybyulski and MouUjn (1997). 

Coupling Reaction and Adsorption A multifunctional reactor may also combine reaction and adsorption. At the laboratory scale, this concept has been apphed for a few reactions, for example, for ammonia and methanol synthesis. Although these processes have been optimized to a high degree of sophistication, improvements... 

Nowadays, the most common small-scale application of hydrogen is the use in residential or mobile fuel cell systems. Special requirements of this application are compact design, integrated CO-removal, high energetic efficiency, quick start-up and fast transient behavior. The proposed solutions comprise unit-operation-based concepts as well as multifunctional, micro-structured reactors. 

The concept of process intensification aims to achieve enhancement in transport rates by orders of magnitude to develop multifunctional modules with a view to provide manufacturing flexibility in process plants. In recent years, advancement in the field of reactor technology has seen the development of catalytic plate reactors, oscillatory baffled reactors, microreactors, membrane reactors, and trickle-bed reactors. One such reactor that is truly multifunctional in characteristics is the spinning disk reactor (SDR). This reactor has the potential to provide reactions, separations, and good heat transfer characteristics. 

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