Microreactor conversion

Conversion rises with the increasing temperature, as expected [308]. For the falling-film microreactor, conversion is increased from 15 to 30% when heating up from —40 to —15 °C. The selectivity varies largely and exhibits no clear trend. 

The catalytic tests were carried out using a single pass microreactor. Conversions and products yields were determined by capillary gas chromatography. 

With the use of microreactor processing, 70% conversion was achieved that gave only product and no side product [4]. Actually, the microreactor conversion is lower than the conversion for batch, but the former is now the preferred route as the separation of the product from the reactant can be accomplished, whereas product, as mentioned, can be hardly purified from the side product. A throughput of 300 g/h was achieved. 

The advantages of microreactors, for example, well-defined control of the gas-liquid distributions, also hold for photocatalytic conversions. Furthermore, the distance between the light source and the catalyst is small, with the catalyst immobilized on the walls of the microchannels. It was demonstrated for the photodegradation of 4-chlorophenol in a microreactor that the reaction was truly kinetically controlled, and performed with high efficiency [32]. The latter was explained by the illuminated area, which exceeds conventional reactor types by a factor of 4-400, depending on the reactor type. Even further reduction of the distance between the light source and the catalytically active site might be possible by the use of electroluminescent materials [19]. The benefits of this concept have still to be proven. 

In this way, the operational range of the Kolbe-Schmitt synthesis using resorcinol with water as solvent to give 2,4-dihydroxy benzoic acid was extended by about 120°C to 220°C, as compared to a standard batch protocol under reflux conditions (100°C) [18], The yields were at best close to 40% (160°C 40 bar 500 ml h 56 s) at full conversion, which approaches good practice in a laboratory-scale flask. Compared to the latter, the 120°C-higher microreactor operation results in a 130-fold decrease in reaction time and a 440-fold increase in space-time yield. The use of still higher temperatures, however, is limited by the increasing decarboxylation of the product, which was monitored at various residence times (t). 

When the reaction was performed in the microreactor, the maximum conversion of 97.0 % was attained when the flow rate of Boc-AMP solution was 9 ml/min and the molar equivalents of KOH to Boc-AMP was 13 as shown in Fig. 1. Optimum operating conditions were obtained from a statistical method by using factorial design [6]. The yield decreased over the KOH equivalency of 13 in Fig. 1, since the phase separation between the t-Boc20 and the aqueous phase was observed due to the increased water content with increasing KOH equivalency. As the heat transfer performance of the microreactor was greatly improved compared with conventional reactors, higher reaction temperature could be admissible. 

The catalytic experiments were performed at the stationnary state and at atmospheric pressure, in a gas flow microreactor. The gas composition (NO, CO, O2, C3H, CO2 and H2O diluted with He) is representative of the composition of exhaust gases. The analysis, performed by gas chromatography (TCD detector for CO2, N2O, O2, N2, CO and flame ionisation detector for C3H6) and by on line IR spectrometry (NO and NO2) has been previously described (1). A small amount of the sample (10 mg diluted with 40 mg of inactive a AI2O3 ) was used in order to prevent mass and heat transfer limitations, at least at low conversion. The hourly space velocity varied between 120 000 and 220 000 h T The reaction was studied at increasing and decreasing temperatures (2 K/min) between 423 and 773 K. The redox character of the feedstream is defined by the number "s" equal to 2[02]+[N0] / [C0]+9[C3H6]. ... 

R. S., Carbon dioxide conversions in microreactors, in Proceedings of the 4th International Conference on Microreaction Technology, IMRET 4, pp. 187-193 (5-9 March 2000), AIChE Topical Conf. Proc., Atlanta, USA. 

Microreactors Low conversion, catalytic reactions Simple design, transport rates can be increased by external recycling Limited ease of variation of parameters, maldistribution of flow can be prohibitive... 

However, the detailed description of the FT product distribution together with the reactant conversion is a very important task for the industrial practice, being an essential prerequisite for the industrialization of the process. In this work, a detailed kinetic model developed for the FTS over a cobalt-based catalyst is presented that represents an evolution of the model published previously by some of us.10 Such a model has been obtained on the basis of experimental data collected in a fixed bed microreactor under conditions relevant to industrial operations (temperature, 210-235°C pressure, 8-25 bar H2/CO feed molar ratio, 1.8-2.7 gas hourly space velocity, (GHSV) 2,000-7,000 cm3 (STP)/h/gcatalyst), and it is able to predict at the same time both the CO and H2 conversions and the hydrocarbon distribution up to a carbon number of 49. The model does not presently include the formation of alcohols and C02, whose selectivity is very low in the FTS on cobalt-based catalysts. 

Apparatus and Procedure. The kinetic studies of the catalysts were carried out by means of the transient response method (7) and the apparatus and the procedure were the same as had been used previously (8). A flow system was employed in all the experiments and the total flow rate of the gas stream was always kept constant at 160 ml STP/min. In applying the transient response method, the concentration of a component in the inlet gas stream was changed stepwise by using helium as a balancing gas. A Pyrex glass tube microreactor having 5 mm i.d. was used in a differential mode, i.e. in no case the conversion of N2O exceeded 7 X. The reactor was immersed in a fluidized bed of sand and the reaction temperature was controlled within + 1°C. 

Metal-catalyzed cross-couplings are key transformations for carbon-carbon bond formation. The applicability of continuous-flow systems to this important reaction type has been shown by a Heck reaction carried out in a stainless steel microreactor system (Snyder et al. 2005). A solution of phenyliodide 5 and ethyl acrylate 6 was passed through a solid-phase cartridge reactor loaded with 10% palladium on charcoal (Scheme 2). The process was conducted with a residence time of 30 min at 130°C, giving the desired ethyl cinnamate 7 in 95% isolated yield. The batch process resulted in 100% conversion after 30 min at 140°C using a preconditioned catalyst. 

Palm oil has been cracked at atmospheric pressure and a reaction temperature of 723 K to produce biofuel in a fixed-bed microreactor. The reaction was carried out over microporous HZSM-5 zeolite, mesoporous MCM-41, and composite micromesoporous zeolite as catalysts. The products obtained were gas, organic liquid product, water, and coke. The organic liquid product was composed of hydrocarbons corresponding to gasoline, kerosene, and diesel boiling point range. The maximiun conversion of palm oil, 99 wt.%, and gasoUne yield of 48 wt.% was... 

VPO catalyst selectivity is tested by both fixed-bed microreactor measurements and by pulsed microreactor measurements. In the former, the rate constants are measured in a microreactor on about 1 g of catalyst at temperature between 360 and 390 °C in a 1.5% butane/air environment. The pulsed microreactor evaluations are carried out by injecting 0.05 ml pulses of butane using a gas-sampling valve over about 0.5 g of catalyst in a microreactor heated to about 380 °C. /i-butane conversion and selectivity to maleic anhydride (MA)... 

Fig. 35. Overall NOx conversion during lean/rich cycling microreactor experiments over a range of temperatures for an LNT (50k/h, 500 ppm NOx inlet).

Catalytic Combustion Properties of M-substituted Hexaaluminates - Most of the catalytic studies performed over hexaaluminate materials deal with the combustion of CH4 as the main component of natural gas, i.e., the typical fuel of gas turbines. Arai and co-workers were the first to investigate the CH4 combustion activity of BaMAlnOjg with M=Cr, Mn, Fe, Co, Ni prepared via the alkoxide route.5 Activity tests were performed over powder catalysts using a conventional quartz microreactor fed with a diluted CH4-air mixture (1% CH4) at high-space velocity (GHSV=48000 h 1). The results are summarized in Table 3 in terms of T10% (i.e., the temperature required to achieve 10% conversion). 

The cracking reactions of normal alkanes such as n-C7°, n-Cio°, n-Ci2° and n-Ci6° were performed in a pulse microreactor at 500 °C with N2 flow rate of 15 ml/min and pulse amount of 0.5 ul. 100 mg of catalysts were put into a quartz tube with diameter of 4 mm. For n-Ci6° cracking, similar conversions were obtained by varying the amount of the catalysts used. 

Charged interphases may also be exploited to create high local concentrations of electron acceptors which affect the rate of electron transfer reactions confined within these restricted reaction volumes and diminish considerably the efficiency of the corresponding back-transfer [24], These results have been primarily applied in photochemical conversion projects [22,25], but technically more interesting applications may be found in their use for the development of new specific analytical procedures (e.g., optical or photoelectrochemical probes). High local concentrations are also of considerable interest in the optimization of photochemical dimerization reactions [22], as the rate of bimolecular reactions between excited and ground state molecules confined in an extremely restricted reaction volume (microreactor) will be considerably enhanced. In addition, spatial gradients of polarity may lead to preferential structures of the solvated substrate and, hence, to the synthesis of specific isomers [24, 22, 26], Similar selectivities have been found when monomolecular photochemical or photoinduced reactions [2,3] are made via inclusion complexes [27,28]. 

Fig. 4. Conversion after 2 hours of vigorous stirring of C5 to CIO n-alkanes to alcohols and ketones, carried out at 298 K and 0.1 MPa in a microreactor of 3 ml with 2.4 mmol t.BHP, and 6 mmol paraffin. 8.10 mmol FePc was used in 1.5 ml dichloromethane and 0.1 g FePcY in 1.5 ml acetone.

That such conversions are indeed reversible under steady state conditions follows from the fact that the steady-state rates of butene formation over both HZSM-5 and AAS catalysts remain the same when n-butyl alcohol is substituted for di-n-butyl ether in the flow that feeds the microreactor (8j). 

Methyloxirane showed a complex pattern of transformations over various solid acids in a pulse microreactor study.728 Nafion-H was found to exhibit the highest activity (30% conversion at 90°C) to produce propanal (about 22% selectivity) and cyclic dimers (substituted 1,3-dioxacycloalkanes, 60% selectivity). 

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