Reaction process intensification

Micro-processing will be another paradigm. Micro-reactors, micro-heaters, microexchangers and the lab-on-a-chip will be developed to provide industrial scale production, especially for liquid and gaseous phase reactions. Process intensification will also offer new opportunities for industrial safety and pollution control [3],... 

Mbodji, M., Commenge, J. M., Falk, L., Di Marco, D., Rossigno, F., Prost, L., et al. (2012). Steam methane reforming reaction process intensification by using a milistructured reactor experimental setup and model validation for global kinetic rate estimation. Chemical Engineering Journal, 207, 871—884. 

The term process intensification is used synonymously with minimization. Process intensification is also often used more specifically to describe new technologies which reduce the size of unit operations equipment, particularly reactors. Innovative process intensification techniques are receiving more and more attention. Interesting possibilities for a range of unit operations, including reaction, gas-liq-... 

An interesting way to retard catalyst deactivation is to expose the reaction mixture to ultrasound. Ultrasound treatment of the mixture creates local hot spots, which lead to the formation of cavitation bubbles. These cavitation bubbles bombard the solid, dirty surface leading to the removal of carbonaceous deposits [38]. The ultrasound source can be inside the reactor vessel (ultrasound stick) or ultrasound generators can be placed in contact with the wall of the reactor. Both designs work in practice, and the catalyst lifetime can be essentially prolonged, leading to process intensification. The effects of ultrasound are discussed in detail in a review article [39]. 

Integration of the separation and reaction step has several advantages, but an inherent downside of such a process intensification step is the loss of degrees of freedom for process design and process control (Figure 10.9). 

Micro-reaction technology can be one of the tools that process intensification may use [5]. Hence chemical micro processing and process intensification have a share, where the former supplies devices for the latter concept or purpose. However, both chemical micro processing and process intensification also cover imique aspects that the other field does not comprise. 

As examples of micro-channel process intensification and the respective equipment, in particular gas/liquid micro reactors and their application to toluene and various other fluorinations and also to carbon dioxide absorption can be mentioned [5]. Generally, reactions may be amenable to process intensification, when performed via high-temperature, high-pressure, and high-concentration routes and also when using aggressive reactants [5]. 

Note that the tasks defined by Worz et al, when matched perfectly to the reaction requirements, exactly correspond to the criteria introduced by the BHR Group for defining process intensification (see Section 1.1.6.2). CPC give a similar selection of basic (micro-) reactor tasks [113]. 

In practice, the process regime will often be less transparent than suggested by Table 1.4. As an example, a process may neither be diffusion nor reaction-rate limited, rather some intermediate regime may prevail. In addition, solid heat transfer, entrance flow or axial dispersion effects, which were neglected in the present study, may be superposed. In the analysis presented here only the leading-order effects were taken into account. As a result, the dependence of the characteristic quantities listed in Table 1.5 on the channel diameter will be more complex. For a detailed study of such more complex scenarios, computational fluid dynamics, to be discussed in Section 2.3, offers powerful tools and methods. However, the present analysis serves the purpose to differentiate the potential inherent in decreasing the characteristic dimensions of process equipment and to identify some cornerstones to be considered when attempting process intensification via size reduction. 

A detailed characterization of micro mixing and reaction performance (combined mixing and heat transfer) for various small-scale compact heat exchanger chemical reactors has been reported [27]. The superior performance, i.e. the process intensification, of these devices is evidenced and the devices themselves are benchmarked to each other. 

Jahnisch, K., Ehrich, H., Linke, D., Baerns, M., Hessel, V, Morgen-scHWEis, K., Selective gas/liquid-reactions in microreactors, in Proceedings of tfie Inten. Conference on Process Intensification for tfie Cfiemical Industry (13-15 October 2002), Maastricht, The Netherlands. 

This class is the simplest of all micro reactors and certainly the most convenient one to purchase, but not necessarily one with compromises or reduced fimction. HPLC or other tubing of small internal dimensions is used for performing reactions. There are many proofs in the literature for process intensification by this simple concept. As a micro mixer is missing, mixing either has to be carried out externally by conventional mini-equipment or may not be needed at all. The latter holds for reactions with one reactant only or with a pre-mixed reactant solution, which does not react before entering the tube. 

Reactive distillation is one of the classic techniques of process intensification. This combination of reaction and distillation was first developed by Eastman Kodak under the 1984 patent in which methyl acetate was produced from methanol and acetic acid. One of the key elements of the design is to use the acetic acid as both a reactant and an extraction solvent within the system, thereby breaking the azeotrope that exists within the system. Likewise, the addition of the catalyst to the system allowed sufficient residence time such that high yields could be obtained, making the process commercially viable. Other examples in which reactive distillation may enhance selectivity include those of serial reactions, in which the intermediate is the desired product, and the reaction and separation rates can be systematically controlled to optimize the yield of the desired intermediate. ... 

Process Intensification. Continnous Two-Phase Catalytic Reactions in a Table-Top Centrifngal... 

With this understanding of cascade reactions for the purpose of process intensification, we now turn out attention to the relatively few literature examples that exhibit these features. 

They observed the complete deactivation of the rhodium catalyst whether immobilized or not in the presence of free amines. When no amine was present, styrene formation was not observed. After 17 h of a reaction in which both catalysts were immobilized, the yield of the product, ethylbenzene, was 52%, again demonstrating the principle of enabling two otherwise incompatible catalysts to work concomitantly in order to achieve process intensification. 

The use of multiple otherwise incompatible catalysts allows multistep reactions to proceed in one reaction vessel, providing many potential benefits. In this chapter, literature examples of nanoencapsulation for the purpose of process intensification have been discussed comprehensively. Current efforts in the literature are mostly concentrated in the areas of LbL template-based nanoencapsulation and sol-gel immobilization. Other cascade reactions (without the use of nanoencapsulation) that allow the use of incompatible catalysts were also examined and showcased as potential targets for nanoencapsulation approaches. Finally, different methods for nanoencapsulation were investigated, thereby suggesting potential ways forward for cascade reactions that use incompatible catalysts, solvent systems, or simply incompatible reaction conditions. 

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