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, C. ; Watts, P. Micro Reaction Technology in Organic Synthesis ; CRC Press Inc. : Boca Raton Florida , 2011 . 13. Ehrfeld , W. ; Hessel. , V. ; Lowe. , H. Microreactors: New

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. Modak , S. Y. ; Juvekar , V. A. Ind. Eng. Chem. Res. Dev. 1995 , 34 , 4297 – 4309. 13. Microreactors: New Technology for Modern Chemistry ; Ehrfield, W

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Abstract

A novel microreactor with a structured catalyst was proposed. The structured catalyst has micro partition (MP), which functions as a catalyst support. The MP has fins on the plate with holes and consists of aluminum, and it was loaded into the tube. To demonstrate the influence of MP on reactivity, the methanol conversion for steam reforming was measured. First, the methanol conversion of the MP and MP with flatten fins on the surface (i.e., plate-like structure) catalysts were compared. The MP-structured catalyst demonstrated higher reactivity for methanol than the conventional plate-like catalyst. It was also shown that direction of fins must be taken into account for improving the reactivity. The influence of MP on reaction rate constant was analyzed and compared with the plate-type catalyst. Moreover, a simulation was carried out to determine the steady-state flow behavior. It was found that the streamlines went through the holes only when the holes were aligned behind the fins against the stream. This behavior corresponded with the experimental result that directions of fins are important for improving the reactivity.

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Abstract

The inner walls of a glass microreactor were functionalized in a one-step procedure with a single layer of a strong perfluoroalkylsulfonic acid. The applicability of the catalytic device was demonstrated in the successful hydrolysis of benzaldehyde dimethyl acetal in acetonitrile, achieving quantitative conversion within a residence time of only 60 s. Furthermore, the catalytic system showed high conversion for the Friedlander quinoline synthesis between 2-aminobenzophenone and ethyl acetoacetate. The cyclization of pseudoionone in methylcyclohexane proved the wide applicability of the acid-functionalized microreactor also for reactions carried out in apolar media. The platform showed activity for 6 h to 2 days, depending on the solvent, and was reactivated by simple treatment with the catalyst precursor.

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Based on previous work studying complex microreactors, it was desired to further improve the mixing efficiency by varying the mixing unit design for fast liquid—liquid reactions. Different flow regimes were studied, including slug flow, parallel flow, and drop flow. The two-phase hydrolysis of 4-nitrophenyl acetate in sodium hydroxide solution was used to evaluate the overall volumetric mass transfer coefficients (K org a) as a function of the average rate of energy dissipation (ε) for each microreactor design and all flow regimes. The liquid—liquid systems investigated used n-butanol or toluene as the organic phase solvent and a 0.5-M NaOH aqueous solution. The use of surfactant was also investigated with the toluene—water system. All microreactor geometry designs were based on contraction—expansion repeating units with asymmetric obstacles to aid the breakup of slugs and desynchronize the recombination of split streams. The investigated designs were chosen to avoid the formation of the parallel flow regime, contrary to curvature-based mixing-unit designs. The microreactor design can then be optimized to reduce the ε required to reach drop flow, since K org a has been found to be constant at equal ε for a given solvent system in this flow regime, regardless of the reactor selection. Additionally, the “3/7th” scaleup rule was applied and confirmed with the LL-Triangle mixer. It was found that, for low interfacial-tension systems (i.e., n-butanol—water), the onset of drop flow occurred at a lower ε for the LL-Triangle mixer when compared with the Sickle or LL-Rhombus mixers.

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The secondary high explosive 2,6-diamino-3,5-dinitropyrazine-1-oxide, or LLM-105, has been synthesized using a commercially available flow microreactor system. Investigations focused on optimizing flow nitration conditions of the cost effective 2,6-diaminopyrazine-1-oxide (DAPO) in order to test the feasibility and viability of flow nitration as a means for the continuous synthesis of LLM-105. The typical benefits of microreactor flow synthesis including safety, tight temperature control, decreased reaction time, and improved product purity all appear to be highly relevant in the synthesis of LLM-105. However, the process does not provide any gains in yield, as the typical 50—60% yields are equivalent to the batch process. A key factor in producing pure LLM-105 lies in the ability to eliminate any acid inclusions in the final crystalline material through both a controlled quench and recrystallization. The optimized flow nitration conditions, multigram scale-up results, analyses of sample purity, and quenching conditions for purity and crystal morphology are reported.

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Abstract

The covalent attachment of piperazine onto the inner walls of a microreactor using glycidyl methacrylate polymer brushes has been demonstrated. The piperazine-containing polymer brushes were first grown on a flat silicon oxide surface and were characterized by contact angle, Fourier transform infrared (FT-IR), ellipsometry, and X-ray photoelectron spectroscopy (XPS). The applicability of the catalytic polymer brushes in a microreactor was demonstrated for the Knoevenagel and nitroaldol condensation reactions, and the synthesis of coumarin derivatives. The catalytic activity of the microreactor was still intact even after 2 months.

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Journal of Flow Chemistry
Authors: Rajesh Munirathinam, Andrea Leoncini, Jurriaan Huskens, Herbert Wormeester and Willem Verboom

Cinchona alkaloid and proline derivatives as enantioselective catalysts were covalently attached onto the inner walls of a microreactor using glycidyl methacrylate polymer brushes. The successful formation of the organocatalyst-functionalized brush layers on flat silicon oxide surfaces was confirmed by several techniques such as Fourier transform infrared (FT-IR), ellipsometry, and X-ray photoelectron spectroscopy (XPS). The applicability of the cinchona alkaloid (cinchonidine or quinidine)- and proline-containing polymer brushes in a microreactor was demonstrated for the Diels–Alder reaction between anthrone and N-substituted maleimides, and the aldol reaction between 4-nitrobenzaldehyde and cyclohexanone, respectively, which showed moderate conversions (up to 55% and 23%, respectively) and moderate to good enantioselectivities (up to 55% and 93%, respectively). The pristine catalytic activity of the microreactor was intact even after 1 month.

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Journal of Flow Chemistry
Authors: Anita Šalić, Katarina Pindrić, Gordana Hojnik Podrepšek, Nikolina Novosel, Maja Leitgeb and Bruno Zelić

. ; Hessel , V. ; Löwe , H. Microreactors: New Technology for Modern Chemistry ; Wiley-VCH: Weinheim, 2000 , 1 – 12 . 3. Doku , G. N

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Different electrochemical microreactors for continuous flow synthesis are described in this review. Advantages of flow over batch type chemistry are highlighted as well as novel developments in construction of such devices.

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