Continuous capillary reactors

Lob P, Hessel V, Krtschil U, Lowe H (2006a) Continuous micro-reactor rigs with capillary sections in organic synthesis—generic process flow sheets, practical experience, and novel chemistry . Chimica Oggi Chem Today 24 46-50... 

Shore and coworkers [64] used a capillary reactor with a Pd thin film and microwave-assisted continuous-flow conditions for Suzttki-Miyara and Heck coupling reactions. The Pd film was prepared by passing Pd(OAc)2 solution into the 1150 pm eapillary at 150°C resulting in a highly porous catalyst composed of nanometer-size grains. 

He, P. and Heswell, S.J. and Fletcher, P.D.I. (2004). Microwave-assisted Suzuki reactions in a continuous flow capillary reactor. Applied Catalysis A General, 274, 111-114. 

Figure 11.1 Continuous cyanation using a laboratory capillary reactor.

In 2005, very similar reactions were shown to proceed smoothly in continuous flow reactors (Scheme 45). The yield of couplings with aryl bromides and iodides were overall high, although the authors noted that it was not clear exactly how long a sample was irradiated due to uncertainties regarding the focus of the irradiation over the capillary column [119]. 

Catalytic activity. Methylcyclopentane (Aldrich, 98 % purity) conversion was carried out at atmospheric pressure and 623 K of temperature in a fixed bed continuous flow reactor. The conversion was kept lower than 15 %. The saturation temperature of the reactant was 273 K. The reaction products were analyzed on-line using a Perkin-Elmer 8410 gas chromatograph, equipped with a FID detector and a 50 m fused silica capillary column with methyl-5%-phenyl-silicon coating. 

Suzuki-Miyaura coupling has also been conducted in a capillary reactor (400 i.m inner diameter).A commercial-scale continuous flow system consisting of a 14.5 cm x 25.4 mm column packed with Pd catalyst has also been developed. In this case, supercritical carbon dioxide is used as... 

Another example illustrating the safe operation of micro reactors at elevated temperatures and pressures was reported by Hessel et al. [25], for the industrially relevant Kolbe-Schmidt reaction (Scheme 6.8). Potassium hydrogencarbonate (31) was selected as a raw material as it is cheap and readily available, making it suitable for the industrial-scale preparation of 2,4-dihydroxybenzoic acid (32) water was selected as the reaction solvent as it is inexpensive (100-1000 lh-1). To optimize the continuous flow conditions, the authors employed a stainless-steel capillary reactor and evaluated the effect of pressure for a fixed reaction time of 6.5 min at 120 °C. 

A microwave continuous-flow capillary reactor was capable of local heating of Pd-Si02 and Pd-Al203 catalysts enhancing the rate of the Suzuki reaction to give 70% product yield in 60 s contact time [62]. A thin layer of gold metal on the outside surface enabled effective heating of the reaction mixture. 

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... 

P. Lob, V. Hessel, U. Krtschd, H. Lowe, Continuous micro-reactor rigs with capillary sections in organic synthesis. Chim. Oggi - Chem. Today, 2006, 24 (2), 46-50. 

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.)...

Initially, the synthesis steps were studied separately. After optimization experiments, the fully integrated continuous-flow synthesis was established. The experimental setup for the overall process is shown in Figure 6.52. In comparison to Figure 6.49, the setup was enlarged by two further capillary reactors that allow the adjustment of different temperature levels and a second mixer that allows the feeding of further reactants. 

The mass spectrometer sampling capillary or the dispersive infra-red analyzers used for continuous analysis and monitoring of the gas phase composition are situated between the reactor and the sampling valve, as close to the reactor as possible, in order to avoid any delay in the recording of changes in the composition of reactants or products. This delay should be taken into account when plotting simultaneously the time dependence of catalyst potential or current and gas phase concentration of the reactants or products. 

The catalytic degradation of PS was carried out in a semi-batch reactor where nitrogen is continuously passed with a flow rate of 30 mL/min. A mixture of 3.0 g of PS and 0.3 g of the catalyst was loaded inside a Pyrex vessel of 30 mL and heated at a rate of 30 C/min up to the desired temperature. The distillate from the reactor was collected in a cold trap(-10 °C) over a period of 2 h. The degradation of the plastic gave off gases, liquids and residues. The residue means the carbonaceous compounds remaining in the reactor and deposited on the wall of the reactor. The condensed liquid samples were analyzed by a GC (HP6890) with a capillary column (HP-IMS). 

The cracking of diphenylmethane (DPM) was carried out in a continuous-flow tubular reactor. The liquid feed contained 29.5 wt.% of DPM (Fluka, >99%), 70% of n-dodecane (Aldrich, >99% solvent) and 0.5% of benzothiophene (Aldrich, 95% source of H2S, to keep the catalyst sulfided during the reaction). The temperature was 673 K and the total pressure 50 bar. The liquid feed flow rate was 16.5 ml.h and the H2 flow rate 24 l.h (STP). The catalytic bed consisted of 1.0 g of catalyst diluted with enough carborundum (Prolabo, 0.34 mm) to reach a final volume of 4 cm. The effluent of the reactor was condensed at high pressure. Liquid samples were taken at regular intervals and analyzed by gas chromatography, using an Intersmat IGC 120 FL, equipped with a flame ionization detector and a capillary column (Alltech CP-Sil-SCB). 

Fig. 4 Setup for continuous-flow asymmetric hydrovinylation using an IL/SCCO2 biphasic system. Liquid and gaseous substrates are mixed with the SCCO2 stream before entering the tubular reactor unit and bubbled through the catalyst-containing IL using a capillary. The CO2 flow leaves the reactor on top and the product is collected in a cold trap after controlled expansion to ambient pressure...

The effect of reaction conditions (temperature, pressure, H2 flow, C02 and/or propane flow, LHSV) and catalyst design on reaction rates and selectivites were determined. Comparative studies were performed either continuously with precious-metal fixed-bed catalysts in a trickle-bed reactor, or batchwise in stirred-tank reactors with supported nickel or precious metal on activated carbon catalysts. Reaction products were analyzed by capillary gas chromatography with regard to product composition, by titration to determine iodine and acid value, and by elemental analysis. 

The stainless steel micro reactor (figure 2) is constructed for catalyst pellet sizes of 0.175 to 0.20 mm. The reactor exit is connected via 0.9 m stainless steel capillary (i.d. 0.2 mm) to the analysing unit. The reactor and part of the capillary is mounted in an electric oven. A continuous stream of carrier gas passes the four way valve, then the catalyst bed, and flows via a stainless steel capillary into the detector. The carrier gas can be switched to pulse gas with the four way valve. The pressure in the reactor is determined by the resistance of flow in the capillary. The pressure difference between the carrier gas and the pulse gas is measured with a differential pressure detector. During the experiment the gas velocities of the carrier and the pulse gas are equal. The gasses are regulated by mass flow controllers. The gases used in the experiments were of a high purity. 

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