Multi-injection reactor

Figure 5.26 Scheme of a multi-injection reactor with N injection points. 

Table 5.6 Temperature rise at different injection point in multi-injection reactor.

The influence of the transformation rate, respectively the characteristic reaction time on the temperature profile in multi-injection reactors, is shown in Figure 5.28 for a second order reaction. For nearly all instantaneous reactions, the... 

Figure 5.28 Temperature profile in a multi-injection reactor with N = 4 injection points. Influence of the effective characteristic reaction time. Tq = T j = T. ...

Number of Injection Points The hot spot within a multi-injection reactor is controlled mainly by the amount of injection points (Af). For a first approximation of the temperature rise at each injection point, a simplified system can be considered [34]. For the case of instantaneous mixing and reaction with an equally distributed flow among the injection points (1 2i = 22 = = = 2o/ )>... 

Compared to an equally distributed multi-injection reactor with Af = 4 a 20% reduced temperature rise at the first injection point is obtained. Especially in cases with high F, this kind of channel design can be beneficial (see Example 5.7). 

Three examples of new designs of single-injection MSR and one example of multi-injection reactor applied for fast and exothermic liquid phase reactions are presented. Finally, it is demonstrated that the process intensification has been achieved using these microreactors. 

Figure 5.34 Scheme of a modular multi-injection reactor [34]. (Adapted with permission from Wiley.)... 

In order to work safely with multi-injection reactor, an accumulation of the limiting reactant and of heat in the main channel has to be thoroughly prevented. As the considered reactions are mostly Umited by mixing, the time required to mix can be estimated by using the correlation between specific energy dissipation and mixing time. Sufficient residence time should be provided between two injection points to minimize the hot spot. 

Bieler, N., and Zimmermarm, B. (2008) Continuous multi-injection reactor for multipurpose production — part I. Chem. 

For endothermic reactions the problem can be solved by dividing the reactor into multiple stages, with intermediate heat exchangers, defining a multi-bed reactor. In exothermic processes, the intermediate cooling may be achieved by mean of heat exchangers or by injection of cold feed. A schematic illustration of a multi-bed reactor is shown in Fig 11.2. 

In view of these temperature rises, a fixed-bed reactor would be feasible only if the oxygen could be added in stages in a multi-bed reactor so that the temperature rise across each bed were limited. Interstage cooling could be accomplished by injection of recycle methane and indirect heat exchange. For example, if the performance in each reactor bea is as shown in Fig. 2a, the temperature rise across each bed will be 46°C. Laboratory experiments [ref.4] have shown that selectivity is not significantly affected by a temperature rise of this magnitude. 

Murakami Y, Takeuchi T, Yokoyama K, Tamiya E, Karube I and Suda M 1993 Integration of enzyme-immobilized column with electrochemical flow cell using micromachining techniques for a glucose detection system Anal. Chem. 65 2731-5 Olson B, Stalbom B and Johansson G 1986 Determination of sucrose in the presence of glucose in a flow Injection system with immobilized multi-enzyme reactors Anal. Chim. Acta 179 203-8... 

B. Olsson, B. Stalbom, and G. Johansson, Determination of Sucrose in the Presence of Glucose in a Flow-Injection System with Immobilized Multi-Enzyme Reactors. Anal. Chim. Acta, 179 (1986) 203. 

For the described limits, one possible solution to combine high-throughput with good thermal management is a multi-injection microchannel reactor, where one reactant is injected along the reactor. This concept is used as one of the approaches for scale-up [34, 35]. Distributed feeding of one reactant in multiple locations reduces the local heat power released depending on the number of injection points. The concept corresponds to the semibatch operation of conventional reactor vessels. 

Mass and Energy Balance in Multi-injection Microstructured Reactors... 

For a multi-injection MSR with a total of N injection points (Figure 5.26), the mass balance can be derived in a similar approach as for a plug flow reactor with only one inlet (Equation 5.27) [35]. 

Example 5.6 Characteristics of a multi-injection microchannel reactor... 

Example 5.7 Multi-injection microtubular reactor with identical... 

Haber, J., Kashid, M.N, Renken, A., and Kiwi-Minsker, L. (2011) Heat management in single and multi-injection microstructured reactors scaling effects, stability analysis, and role of mixing. Ind. 

Nova Chemicals/200P SURPASS Advanced Sclairtech Solution Process (either single- or multi-solution reactors) Film, Injection and Rotomolding Grades... 

Although phthalic anhydride first was made commercially from the oxidation of naphthalene, by 1980 more than 75 percent of the production had been converted to o-xylene as the feedstock. This is now essentially the only major use for the o-xylene. The flowsheet in Fig. 22.46 shows a typical process for making phthalic anhydride. The o-xylene is vaporized by injection into the hot gas stream and then passes through a catalyst-filled multi-tube reactor. The crude phthalic anhydride is desublimated, and any acid present is dehydrated in the pre-decomposer vessel. The crude is finally purified in two distillations. Although the fixed-bed process currently is important, there are a number of plants in which a fluidized-bed reactor is used. 

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