Dual-channel reactor

Figure 5.6 Flow pattern map for a gas/liquid flow regime in micro channels. Annular flow wavy annular flow (WA) wavy annular-dry flow (WAD) slug flow bubbly flow annular-dry flow (AD). Transition lines for nitrogen/acetonitrile flows in a triangular channel (224 pm) (solid line). Transition lines for air/water flows in triangular channels (1.097 mm) (dashed lines). Region 2 presents flow conditions in the dual-channel reactor ( ), with the acetonitrile/nitrogen system between the limits of channeling (I) and partially dried walls (III). Flow conditions in rectangular channels for a 32-channel reactor (150 pm) (T) and singlechannel reactor (500 pm) (A) [13].

Another annular-flow concept was provided by the so-called dual-channel reactor with two parallel microchannels separated by a wall. In this way, four thin liquid layers in annular flow were created at once (see Figure 4.34, bottom) [274]. In front of this section, the liquid feed enters through a hole directed to the wall, whereas the two gas feeds point to the two reaction channels. Consequently, the liquid flow splits and a larger interface is created than given for single-channel guidance. 

The dual-channel reactor is a silicon chip device and was manufactured by photolithography and potassium hydroxide etching [274]. Silicon oxide was thermally grown on silicon and thin films of nickel were evaporated for passivation because direct fluorination was carried out in this device. Pyrex was bonded anodically to the modified microstructured silicon wafer (see Figure 4.34, top). 

With the use of falling-film microreactor or a microbubble column, yields of up to 28% were obtained with acetonitrile as solvent at conversions ranging from 7 to 76% and selectivities from 31 to 43% with regard to the monofluorinated product [308]. With the use of dual-channel reactor, conversions from 17 to 95% and selectivities from 37 to 10% were achieved using methanol as solvent [274]. The conversion of a laboratory bubble column, taken for comparison, ranged from 6 to 34% with selectivities of 17-50%, which is equivalent to yields of 2-8% [308],... 

Table 6.7 summarizes results obtained in four different reactor types at two different citronellol concentrations. Yields and ratios were determined by H NMR analysis with internal standard after treatment of the crude reaction mixture with NaBH4. Entry 7 represents results achieved in a scaled-up dualchannel reactor, which has a total volume of 285 pi. Hence, the reactor volume is increased by a factor of 7 compared to the dual-channel reactor applied for entries 1 and 4. 

Compared to batch and single-channel microreactors, the results clearly demonstrate that the daily output can considerably be increased by application of the scaled-up dual-channel microreactor. In the next step, the dual-channel reactor was applied for the photosensitized oxidation of aDyUc alcohols 99 (Figure 6.48). The corresponding products, aUyl hydroperoxide alcohols 100, can be employed for the synthesis of artemisinin-derived antimalarial 1,2,4-trioxanes. The... 

Figure 6.48 Photosensitized oxygenation of allylic alcohols 99 in the dual-channel reactor. (Reproduced from Ref [44] with permission of the Royal Society of Chemistry.)...

Reactor type Dual-channel micro reactor Base plate material of interfacing chip housing Silicon stainless steel... 

GL 1] [R 4][P 2] For the dual-channel micro reactor, the highest yield of 14% was found using acetonitrile (58% conversion 24% selectivity) [13]. Slightly lower yields were obtained for methanol. The selectivities were as high as for acetonitrile, the conversion being lower. Still lower yields (7%) were achieved in octafluorotoluene for the same reason as for methanol, selectivity decreasing considerably. 

GL 1] [R 4] [P 2] Variation of solvent affects also the substitution pattern to a certain extent [13], A ratio of ortho-, meta- and para-isomers for mono-fluorinated toluene amounting on average to 3.5 1 2 was found in the dual-channel micro reactor at room temperature, using acetonitrile as solvent [13]. Using methanol as solvent, the ratio was on average 5.5 1 2.4. Hence more products referring to an electrophilic substitution were formed [13]. 

GL 1] [R 4] [P 2] A temperature rise of 0.4 K was estimated for a typical experiment in a dual-channel micro reactor based on assuming reaction rates and heat conductivity of the medium [13]. However, there are experimental indications that the real value is higher. 

A flow-pattern map was derived for nitrogen/acetonitrile flows in the dual-channel micro reactor [274]. Bubbly, slug, churn and annular flows as well as wavy annular and wavy annular-dry flows with smaller region of stability were found (see Figure 4.35). 

MCR, multiple-channel reactor (dual channel, triple channel,...)... 

As a result of the increased illumination as well as the increased gas-liquid contact area per unit volume, the triple-channel microreactor exhibited better performance compared to the batch reactor, or even compared to a typical dual-channel microreactor [138,139]. Moreover, the scaleup process using the microreactor revealed higher productivity than the batch reactor, which would be valuable for the practical applications in a broad range of gas-liquid chemical reactions. 

The photooxygenation of citronellol (93) was also studied by Park et al. [44]. In this work, different types of reactors were compared regarding the gas-hquid contact area and their performance in photooxygenation reactions. In this context, the authors developed a transparent dual-channel microreactor. The potential of dual-channel microreactors designed by Kim et al. has already been described in Section 6.2.2. 

Reactor 4 [R 4] Dual-Micro Channel Chip Reactor... 

Besser et al. [86] studied the reaction in a silicon reactor fabricated by applying MEMS technology, namely photolithography and DRIE by inductively coupled plasma. Each reactor incorporated dual gas inlets, a pre-mixer, a single reaction channel and an outlet zone where the product flow was cooled (see Figure 2.54). The single channel was 500 pm wide, 470 pm deep and 45 mm long. 

The heart of the system is a microreactor packaging scheme that is based upon a commercially available microchip socket. This approach allows the silicon-based reactor die, which contains dual parallel reaction channels with more than 100 electrical contacts, to be installed and removed in a straightforward fashion without removing any fluidic and electronic connections. Various supporting microreactor functions, such as gas feed flow control, gas feed mixing, and various temperature control systems, are mounted on standard CompactPCI electronic boards. The boards are subsequently installed in a commercially available computer chassis. Electrical connections between the boards are achieved through a standard backplane and custom-built input-output PC boards. A National Instruments embedded real-time processor is used to provide closed-loop process control and... 

Dual-microchannel chip reactor [42, 43] This consists of two parallel microchaimels which are separated by a wall. I n front of the channel section a hole is located for the liquid feed which is followed by two holes for the gas feed... 

On-power refuelling provides the principal means for controlling reactivity in the CANDU 6. Additional reactivity control, independent of the safety shutdown systems, is achieved through use of reactivity control mechanisms. These include light-water zone compartments, absorber rods, and adjuster rods all are located between fiiel channels within the low pressure heavy water moderator and do not penetrate the heat transport system pressure boundary. The reactor is controlled by the dual redundant computer control system. The overall station control system is described in Section 5.7.2.3. 

Ajou University developed AMBIDEXTER-NEC (Advanced Molten-salt Breakeven Inherently-safe Dual-function EXcellenTly-Ecological Reactor Nuclear Energy Complex). The objective of the reactor is to bum DUPlC fuel, minimize minor actinides production, and of course, generate electric power. To achieve the objectives, the AMBIDEXTER reactor core consists of two parts, a blanket and a seed. The blanket consists of only molten salt fuel (LeF-BeF2-(Th,U,Pu)F4), and the seed consists of the molten salt fuel and graphite moderator channel. The blanket area has very hard neutron spectrum, almost looks like fast reactor neutron spectium, and the seed area has a soft neutron spectium almost looks like PWR. Therefore, AMBIDEXTER can achieve low conversion ratio, about 0.298, ie, it is a burner reactor. The code developed to analyze AMBIDEXTER is called AMBIKIN2D. The code system consists of HELIOS, AMDEC, and AMBIKIN2D. 

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