Continuous capillary microreactors

A two-step enantioselective synthesis of 2-amino-l,3.4-butanetriol 12 was performed in continuous mode using two serial capillary microreactors with HiSg-tagged transketolase (TK) /oo-transaminase (TAM) bound to the wall via immobihzed Ni-nitrilotriacetic add (Ni-NTA) complex [78]. The TK-catalyzed conversion of hydroxypyruvate 8 and glycolaldehyde 9 to L-erythrulose 10 followed by the TAM-catalyzed amination resulted in the formation of the product This work demonstrated the implementation of a dual enzyme microreactor system for the evaluation of a de novo pathway for an enzyme-catalyzed synthesis. 

Continuous flow capillary microreactors with embedded monometallic (Pd) or bimetallic (Pd25Zn75) catalysts have been tested in the selective hydrogenation of alkyne reagents, among which was 2-methyl-3-butyne-2-ol [155]. Under conventional reaction conditions a number of side products can be formed. 

Figure 6.29 Monoacylation of symmetric diamines in continuous droplet microreactor (a), capillary reactor (b), and batch reactor (c), respectively. (Reproduced from Ref [25j] with permission of the Royal Society of Chemistry.)...

Comer, E. and Organ, M.G. (2005). A Microreactor for Microwave-Assisted Capillary (Continuous Flow) Organic Synthesis. J. Am. Chem. Soc., 127, 8160-8167. 

The catalytic properties of the synthesised solids were determined during the partial oxidation of toluene (TO) to benzaldehyde (BA), p-methoxytoluene (MTO) to p-methoxybenzaldehyde (MBA, anisaldehyde) and p-chlorotoluene (CTO) to p-chlorobenzaldehyde (CBA). A microreactor set-up that contains a metering system for liquids and gases and a fixed bed quartz-glass reactor was used. The catalysts were introduced into the reactor as sieve fractions (1-1.25 mm) and mixed prior to oxidation runs with the equal portion of quartz glass (1 mm) to avoid local overheating. The product stream was analysed by on line-GC or it was trapped in aqueous ethanol and determined by off line-capillary GC. The formation of carbon oxides was continuously followed by non-dispersive IR photometry. 

The catalytic experiments were performed in a continuous flow tubular microreactor. The catalyst bed consisted of 0.8 cm of 0.3-0.5 mm pellets, prepared by compressing of the NH -T zeolite powder into flakes, crushing and sieving. The zeolite was activated in the reactor by deammoniation at 673 K. The vapors of the acids were diluted with helium. The reaction conditions are further specified in Table 1. The reaction products were analysed on-line with GC, using a capillary fused silica column, coated with CP Sil5 (Chrompack) and F.l.D. detector. CO2 and H2O were not analysed. 

He S, Kohira T, Uehara M, Kitamura T, Nakamura H, Miyazaki M, Maeda H (2005) Effects of interior wall on continuous synthesis of silver nanoparticles in micro-Capillary reactor. Chem Lett 34 748-749 10. Takagi M, Maki T, Miyahara M, Mae K (2004) Production of Titania nanoparticles by using a new microreactor assembled with same axle dual pipe. Chem Eng J 102 269-276... 

An interesting commercially available PEEK mixing tee (Alltech, Figure 5.1) can be seen as a useful microreactor [28, 29]. It can be directly coimected to the ESI spray capillary, allowing reaction times from 0.7 to 28 s in a continuous-flow mode to be... 

Another category of enzymatic transformations in multiphase systems is enzymes immobilized on the reactor wall as presented in Table 10.4. Enzymes are advantageously used in immobilized form because this strategy allows for increased volumetric productivity and improves stability. Continuous mode of operation is employed in these systems. The approaches commonly used for immobilization in conventional multiphase biocatalysis can also be employed in microreactors such as covalent methods, cross-linked enzyme aggregates (CLEA), and adsorption methods. The experimental setups can either be chip-type reactors with activated charmel surface walls where enzyme binds, or enzyme immobilized monolith reactors, where a support is packed inside a capillary tube. 

Biocatalytic reactions performed using immobilized enzyme microreactors under continuous flow mode have been found effective for hydrolysis reactions [121,158-161], with the enzyme either trapped in the matrix [159], covalently linked to modified surface wall [160,121], enzymes entrapped in hydrogels [162], or enzymes immobilized on monolith [179]. The experimental setup consists of either chip-type microreactors with activated chaimel walls where enzymes bind, enzymes that bind to beads, enzymes entrapped in the matrix, enzymes adsorbed in nanoporous materials, and most recently, nanosprings as supports for immobilized enzymes in chip-based reactors, or enzyme immobilized monolith reactors, where support is packed inside a capillary tube (Table 10.4). 

Figure 7.10 Schematic of a capillary-based droplet microreactor for the continuous synthesis of MOF hollow microsphere. (Reproduced from Ref. [78].)...

The limitation of a conventional batch process and the potential of continuous alkylation of 1-methylimidazole in microreactor rig with a micromixer followed by a capillary as residence time section were studied by Lob et al. (2007). A production rate of 0.2 1 h-i of... 

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