Single-mode continuous-flow reactors

Catalytic transformation of 1-butene over acidic (low polarity) zeolites resulted in somewhat higher yield and selectivity toward isobutene. A single mode continuous-flow reactor was used and the results were explained by formation of hot spots [119]. 

Current single-mode continuous-flow microwave reactors allow the processing of comparatively small volumes. Much larger volumes can be processed in continuous-flow reactors that are housed inside a multimode microwave system. In a 2001 publication, Shieh and coworkers described the methylation of phenols, indoles, and benzimidazoles with dimethyl carbonate under continuous-flow microwave conditions using a Milestone ETHOS-CFR reactor (see Fig. 3.11) [104]. In a typical procedure, a solution containing the substrate, dimethyl carbonate, 1,8-diazabicy-clo[5.4.0]undec-7-ene (DBU) base, tetrabutylammonium iodide (TBAI), and a solvent was circulated by a pump through the microwave reactor, which was preheated to 160 °C and 20 bar by microwave irradiation (Scheme 4.31). Under these condi-... 

For gas phase heterogeneous catalytic reactions, the continuous-flow integral catalytic reactors with packed catalyst bed have been exclusively used [61-91]. Continuous or short pulsed-radiation (milliseconds) was applied in catalytic studies (see Sect. 10.3.2). To avoid the creation of temperature gradients in the catalyst bed, a single-mode radiation system can be recommended. A typical example of the most advanced laboratory-scale microwave, continuous single-mode catalytic reactor has been described by Roussy et al. [79] and is shown in Figs. 10.4 and... 

In principle the use of a well-stirred bioreactor in a continuous flow mode offers significant advantages over operation in a batch or semibatch mode, but the majority of bioreactors in industrial use are operated in the latter modes. However, the actual performance of single CSTR or a cascade of such reactors often fails to meet the expectations... 

In this chapter the most important operation modes of reactors are considered. Models are developed by combining simple reaction kinetics for single-phase reactions with mass balances for five ideal model reactors the ideal batch reactor the semi-batch reactor the plug flow reactor the perfectly mixed continuous reactor and the cascade of perfectly mixed reactors. For isothermal conditions, conversions can be calculated on the basis of chemical kinetics only. 

Fig. 2.7 Definition sketch showing common modes of operation for reactors, (a) Simple-batch reactor, (b) Single-pass reactor, (c) Batch-recirculation reactor, (d) Cascade of n identical reactors. PFR, plug flow reactor CSTR, continuously stirred tank reactor.

On the other hand, an industrial process may be operated in a continuous mode, rather than in a batch mode. To achieve this, either a single or a series of interconnected vessels may be used. The required raw materials are continuously fed into this vessel or the first vessel and the reaction products continuously removed from the last so that the volume of material in the reactor(s) stays constant as the reaction proceeds. The concentrations of starting materials and products in the reactor eventually reach a steady state. One or more tanks in series may be used to conduct the continuous process. Another option for a continuous process is to use a pipe or tube reactor, in which the starting material(s) is fed into the tube at one end, and the product(s) is removed at the other. In this case, the reaction time is determined by the rate of flow of materials into the tube divided by the length of the tube. 

Solar photocatalytic reactors can be operated in either continuous single pass mode or discontinuous batch mode. In the continuous single pass mode, complete oxidation of the contaminant is achieved in a single pass with the water flow rate being adjusted for fixed solar flux densities. On the other hand, batch mode operation requires a set volume of water to be treated with varying solar flux densities (Alfano et al., 2000). Table 2.4 reports the main types of solar reactors reported in the technical literature. 

In continuous operation mode, both feed and effluent streams flow continuously. The main characteristic of a continuous stirred tank reactor (CSTR) is the broad residence time distribution (RTD), which is characterized by a decreasing exponential function. The same behavior describes the age of the particles in the reactor and hence the particle size distribution (PSD) at the exit. Therefore, it is not possible to obtain narrow monodisperse latexes using a single CSTR. In addition, CSTRs are hable to suffer intermittent nucleations [89, 90) that lead to multimodal PSDs. This may be alleviated by using a tubular reactor before the CSTR, in which polymer particles are formed in a smooth way [91]. On the other hand, the copolymer composition is quite constant, even though it is different from that of the feed. 

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