Reactions intensification

Do not use coatings, such as poly L-lysine or chrom-alum, since the charge will interfere with the silver intensification reaction. For paraffin sections, remove paraffin with xylene and rehydrate to water. Penetration of reagents into plastic-embedded sections may be improved by treating the sections for 15 min with xylene and rehydrating to water. Following rehydration, the sections should not be allowed to dry. 

Do not use coatings, such as poly-L-lysine or chrome-alum, since the charge will interfere with the silver intensification reaction. For paraffin sections, remove paraffin with xylene... 

Note Be sure to perform the intensification reaction first, as indicated above, otherwise the two reaction products may turn an identical dark-blue-black color. (For a sample preparation, see Mardon et al. 1994.)... 

The simplest method of reduciag stresses and reactions is to provide additional pipe ia the system ia the form of loops or offset-bonds. When physical limitations restrict the use of additional bends, a multiple arrangement of several small-size pipe mns may sometimes be used. Owiag to stress intensification, the maximum stress generally occurs at elbows, bends, and Ts. Thus, heavier-walled fittings may reduce the stress without significantly impairing flexibiUty. FiaaHy, effectively located restraints can reduce thermal effects on the equipment. 

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-... 

The chromatograms are freed from mobile phase in a stream of warm air, then immersed in the dipping solution for 2 s or homogeneously sprayed with the appropriate spray solution. Then, in the case of N-ethyl derivatives, the plate is heated to 105-110 °C for 2 min to accelerate the reaction [7]. Heating (e. g. to 80-105 °C for 15 min) can also lead to color intensification and color change in the case of other alkaloids [5, 6]. 

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]. 

The reactions are still most often carried out in batch and semi-batch reactors, which implies that time-dependent, dynamic models are required to obtain a realistic description of the process. Diffusion and reaction in porous catalyst layers play a central role. The ultimate goal of the modehng based on the principles of chemical reaction engineering is the intensification of the process by maximizing the yields and selectivities of the desired products and optimizing the conditions for mass transfer. 

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). 

A number of reactions presenting different characteristics have been carried out in HEX reactors [28]. In the following, some of those that exhibit different intensification opportunities are discussed ... 

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. 

Groschel, L, Agar, D. W., Worz, O., Morgenschweis, K., The capillary-microreactor A new reactor concept for the intensification of heat and mass transfer in liquid-liquid reactions. Catalysis Today,... 

Burns, J. R., Ramshaw, C., The intensification of rapid reactions in multiphase systems using slug flow in capillaries. Lab. Chip 1 (2001) 10-15. 

The high specific activity of enzymes and tfie tfieoretical possibility of using them to conduct electrochemical reactions are topics of great scientific interest. However, it is difficult to envisage prospects for a practical nse of enzymes for an acceleration and intensification of industrial electrode processes. The difficulty resides in the fact that enzymes are rather large molecnles, and on the surface of an enzyme electrode, fewer active sites are available than on other electrodes. Per unit snrface area, therefore, the effect expected from the nse of enzymes is somewhat rednced. 

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