Continuous-flow microreactor

Multiphase catalytic reactions, such as catalytic hydrogenations and oxidations are important in academic research laboratories and chemical and pharmaceutical industries alike. The reaction times are often long because of poor mixing and interactions between the different phases. The use of gaseous reagents itself may cause various additional problems (see above). As mentioned previously, continuous-flow microreactors ensure higher reaction rates due to an increased surface-to-volume ratio and allow for the careful control of temperature and residence time. 

Lewis acids are usually used as catalysts for the Pudovik reaction [97]. On the contrary, the Stevens group [98] performed the reaction in a microreactor and proved that it can be successfully performed in the absence of any catalyst. The authors were guided by the reaction as reported by Fields in 1952 (performed in the absence of catalysts and also solvents), but certain modifications had to be applied to make the process suitable for continuous flow microreactor conditions, that is the use of methanol as a reaction promoting solvent. 

The aldol condensation/hydrogenation reaction was carried out in a continuous flow microreactor. The catalysts (0.5 g) were reduced in situ in a flow of H2 at atmospheric pressure at 723 K for 1 h for the palladium systems and 2 h for the nickel systems. The liquid reactant, acetone (Fisher Scientific HPLC grade >99.99%), was pumped via a Gilson HPLC 307 pump at 5 mL hr into the carrier gas stream of H2 (50 cm min ) (BOC high purity) where it entered a heated chamber and was volatilised. The carrier gas and reactant then entered the reactor containing the catalyst. The reactor was run at 6 bar pressure and at reaction temperatures between 373 and 673 K. Samples were collected in a cooled drop out tank and analyzed by a Thermoquest GC-MS fitted with a CP-Sil 5CB column... 

Novel microreactors with immobilized enzymes were fabricated using both silicon and polymer-based microfabrication techniques. The effectiveness of these reactors was examined along with their behavior over time. Urease enzyme was successfully incorporated into microchannels of a polymeric matrix of polydimethylsiloxane and through layer-bylayer self-assembly techniques onto silicon. The fabricated microchannels had cross-sectional dimensions ranging from tens to hundreds of micrometers in width and height. The experimental results for continuous-flow microreactors are reported for the conversion of urea to ammonia by urease enzyme. Urea conversions of >90% were observed. 

Continuous-flow microreactors were successfully fabricated from PDMS and entrapped urease. Conversions increased almost proportion-... 

Continuous-flow microreactors were successfully fabricated by etching channels in silicon and immobilizing urease onto channel surfaces by a layer-by-layer self-assembly technique. Preliminary results show urea conversion. The potential advantages of this surface-coating technique in microreactors warrant continued investigation. 

Performing plasma processes in a continuous-flow microreactor leads to precise control of residence time and to extreme quenching conditions, therewith enabling control over the composition of the reaction mixture and product selectivity. In a nonequilibrium microplasma reactor, low-temperature activation of hydrocarbons and fuels, which is difficult to obtain in conventional thermochemical processes, can be achieved at ambient conditions. 

Kinetic studies of dehydroisomerisation of n-butane were performed at 530°C. The reaction was carried out at atmospheric pressure in a continuous flow microreactor with 100% n-butane as feed. Reaction products were analysed by on-line GC equipped with... 

Conversion of n-butane into isobutene over theta-1 and ferrierite zeolites was studied in a continuous flow microreactor at 530°C and 100% n-butane as a feed. The zeolites were used as catalysts in the H- and Ga-forms. Insertion of Ga into the zeolites resulted in improved isobutene selectivities due (i) to an increase in the dehydrogenation activities and (ii) to a decrease in the cracking activities of the catalysts. The highest selectivities to isobutene (-27%) and butenes (-70%) were obtained with the Ga-theta-1 catalyst at n-butane conversions around 10%. These selectivities decreased with increasing conversion due to olefin aromatisation, which was enhanced considerably by the Ga species present in the catalysts. 

Binary copper-based catalysts were prepared by coprecipitation method and some components were added as promoters into the binary catalysts. The methanol synthesis reaction was carried out in a continuous flow microreactor operated at 22 atm and at various temperatures. Reaction pathway of the methanol synthesis was investigated through FT-IR spectroscopy. For the catalyst with a copper content over 15wt%, the diffuse reflectance method (DRIFT) was applied, but for fee catalyst wife a copper content of 7wt%, the transmission teclmique was used. For more information about intermediates, TPD of adsorbed methanol was carried out and the products were analyzed using mass spectrometer. 

Isomerization of n-butane was carried out in a continuous-flow microreactor operated at atmospheric pressure. The catalyst (0.5 g, 0.2-0.315 mm fraction)) was activated at 450 °C in flowing dry air for 1.5 h and then cooled at 250°C (reaction temperature). The reactor was purged with helium prior to admission of the feed mixture, which consisted of 1 ml min ... 

Catalytic activity data for both CO and propane oxidation were obtained using a conventional continuous flow microreactor. The catalyst sample (0.5g) is situated in a pyrex glass tube located within a stainless steel heated block. Catalyst samples were activated by in situ preheating in the reactor for 2 hours under a flow of air. The catalysts were then allowed to cool to ambient temperature still under the air flow before acquiring %conversion versus temperature data. Input gas mixture compositions, which were controlled by mass flow controllers, and flow rates are shown in Table 10. 

Catalyst Evaluation. The powdered molecular sieves were evaluated following the treatment described above, without further activation. The 1-hexene isomerization and Cg aromatic isomerization tests were conducted in tubular, fixed bed, continuous flow microreactors. The catalyst bed contained one gram molecular sieve powder and one to three grams of similarly sized quartz chips used as diluent. The reactor was heated to the chosen reaction temperatures in a fluidized sand bath, and the reaction temperature was monitored by a thermocouple located m the catalyst bed. Typical runs lasted 3 to 5 hours during which samples were collected every 30 minutes. 

Catalytic activity measurements in CH steam reforming were carried out at T - 625°C (PR - 1.1 bar) in a continuous flow microreactor operating at GH5Y = 150.000 h"1 with P = Z-54. Before test, catalysts were reduced... 

Catalysts used in this work had a composition of 3 wt% nickel, 8 wt% molybdenum and 0 or 2 wt% phosphorus. They were prepared by incipient wetness impregnation, followed by drying at 393 K and calcination at 773 K. Details of the catalyst preparation can be found elsewhere [2], The HDN reactions were carried out in a continuous-flow microreactor. A sample of 0.1 g catalyst diluted with 9.5 g SiC was used for each reaction. The catalyst was sulfided in situ with a mixture of 10% (mol) H2S and H2 at 643 K and 1.5 MPa for 4 h. After sulfidation, the pressure was increased to 3.0 MPa and liquid reactant was fed to the reactor by means of a high pressure pump, with n-octane as the solvent. The catalyst was stabilised at 643 K and 3.0 MPa for 100 h before samples were taken. The initial reactant partial pressure (P°) of Q, THQ5 and OPA was usually 4.76 kPa, and that of H2S was 6.5 kPa by adding dimethyldisulfide to the liquid reactant. n-Nonane as well as n-dodecane were used as internal standards. 

The two types of continuous flow microreactors used are depicted in Figure 9.15. All isocyanate reactions were studied in two inlet chips (Figure 9.15a). A list of channel lengths (L), channel volumes (F) and respective residence times at flow rates ranging from 20 to 100 nLmin-1 is given in Table 9.3. 

Fig. 6.14 Flow sheet of a fine chemical continuous-flow microreactor plant of table-top size for throughputs from 1 to 100 Lh . (Source IMM.)...

Catalytic properties were examined in a fixed bed continuous flow microreactor at atmospheric pressure with Hg resp. N2 as carrier gases (flow rate 10 1 h applying the conversion of ethylbenzene and the isomerization of m-xylene as probe reactions on one gram of the binder-free zeolite (0.35 - 1.0 mm). The shape selectivity was tested as described elsewhere [7]. ... 

The surface silylated zeolites were prepared by suspending the H-ZSM-5 or FeH-ZSM-5 zeolite in n-hexane into which a calculated amount of tetraethyl orthosilicate was added to obtain addition of 1.5 wt. % of Si in the final product (abbrev. SiH-ZSM-5 or SiFeH-ZSM-5). n-Hexane was evaporated and the zeolites were dried and calcined in an oxygen stream at 770 K for 5 hours. To add some Fe cations to the surface of silylated zeolites, the SiH-ZSM-5 was introduced into a FeCl solution, filtered and dried (abbrev. FeSiH-ZSM-5). The characteristics of the parent and modified zeolites are given in the Table. The alkylation of toluene with ethylene was carried out in a vapour phase continuous flow microreactor at atmospheric pressure. Nitrogen as a carrier gas was saturated with toluene to 18.5 vol. %, the toluene to ethylene molar ratio was 3.8. The reaction products were analyzed by an "on-line" gas chromatograph (Hewlett-Packard 5890) with MS and FID detection. 

Continuous flow reaction studies were performed in a 0.101 MPa, continuous flow microreactor with the gas stream exit the reactor being sampled by on-line GC. Using this system the catalysts (typically 0.25 g) could be reduced in situ in flowing 6% hydrogen in nitrogen (30 cm min ) by heating to 573 K at 5 K min and then holding at this temperature for 3 h. Whilst still at temperature the flow was switched to helium and held for 2 h. The temperature of the catalyst bed was then altered to that required in the experiment. Once at temperature the flow was switched to butane and samples of the exit gas were analysed by on-line GC. 

The use of microreactor technology for polymer chemistry presents an interesting alternative to conventional processing methods, in both batch and macroscale continuous flow. Microreactors offer a better process control of many exothermic polymerization processes, leading to increased product quality such as narrower polydispersity, and they allow for the synthesis of novel polymeric materials for a range of new applications. 

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