Reactions microreactor

APCI, ESI Mechanistic study of radical cation chain reactions, microreactor coupled on-line Meyer et al. [262]... 

Future Trends in Reactor Technology The technical reactors introduced here so far are those used today in common industrial processes. Of course, research and development activities in past decades have led to new reactor concepts that may have advantages with respect to process intensification, higher selectivities, and safety and environmental aspects. Such novel developments in catalytic reactor technology are, for example, monolithic reactors for multiphase reactions, microreactors to improve mass and heat transfer, membrane reactors to overcome thermodynamic and kinetic constraints, or multifunctional reactors combining a chemical reaction with heat transfer or with the separation in one instead of two units. It is beyond the scope of this textbook to cover all the details of these new fascinating reactor concepts, but for those who are interested in a brief outline we summarize important aspects in Section 4.10.8. 

Reproducible measurements of absolute activity for sulfur dioxide oxidation catalysts are very difficult to obtain for a number of reasons, including the fact that the reaction is extremely fast. In addition, there are differences in techniques and reporting methods used by the various workers. Pulse microreactors have been used to study quantities of these catalysts as small as 500 mg (83). 

Microwave technology has now matured into an established technique in laboratory-scale organic synthesis. In addition, the application of microwave heating in microreactors is currently being investigated in organic synthesis reactions [9-11] and heterogeneous catalysis [12, 13]. However, most examples of microwave-assisted chemistry published until now have been performed on a... 

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. 

Several reactions have been demonstrated using microreactors. One of the potentially more important is the direct synthesis of MIC from oxygen and methyl formamide over a silver catalyst. Dupont have demonstrated this process using a microreactor cell similar to that described above in which the two reactants are mixed, then heated to 300 °C in a separate layer and subsequently passed through another tube coated with the silver catalyst. The estimated capacity of a single cell with tube diameters of a few millimetres is 18 tpa. 

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). 

The authors developed a multi-layered microreactor system with a methanol reforma- to supply hydrogen for a small proton exchange membrane fiiel cell (PEMFC) to be used as a power source for portable electronic devices [6]. The microreactor consists of four units (a methanol reformer with catalytic combustor, a carbon monoxide remover, and two vaporizers), and was designed using thermal simulations to establish the rppropriate temperature distribution for each reaction, as shown in Fig. 3. 

A microreactor was also applied to this reaction. The slit interdigital micromixer was purchased from IMM (Mainz, Germany). The width of the interdigital channels is 25 pm. HPLC pumps were used to feed the two reaction solutions. One is a mixture of Boc-AMP and 1.2 molar equivalents of r-BocaO. The other is a 50% aqueous KOH solution. The microreactor was immersed in a temperature controlled cooling bath at 15 °C. The product was quenched with an acid, and samples were taken for HPLC analysis. 

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. 

In this experiment, the reaction temperature was isothermally controlled at 15 °C. The heat of reaction was completely removed using microreactor so that virtually no byproducts were produced during the reaction. It can be compared with other reactors described above, which should be operated at 0 °C or -20 °C to avoid side reactions. 

We have studied the steady-state kinetics and selectivity of this reaction on clean, well-characterized sinxle-crystal surfaces of silver by usinx a special apparatus which allows rapid ( 20 s) transfer between a hixh-pressure catalytic microreactor and an ultra-hixh vacuum surface analysis (AES, XPS, LEED, TDS) chamber. The results of some of our recent studies of this reaction will be reviewed. These sinxle-crystal studies have provided considerable new insixht into the reaction pathway throuxh molecularly adsorbed O2 and C2H4, the structural sensitivity of real silver catalysts, and the role of chlorine adatoms in pro-motinx catalyst selectivity via an ensemble effect. 

Reaction conditions 0.1 g of the zeolite Y modified catalyst, tested in a conventional glass microreactor with racemic butan-2-ol (7.35 x 10" mol h-1), prevaporized in a nitrogen diluent (6.2 -6.7 x 10" mol h-1). Products were analyzed using on-line GC with a 40m capillary y- cyclodextrin colimm with trifluoroacetyl stationary phase, temperature programmed from 25-70 "C with a split ratio of 120 1. 

This study presents kinetic data obtained with a microreactor set-up both at atmospheric pressure and at high pressures up to 50 bar as a function of temperature and of the partial pressures from which power-law expressions and apparent activation energies are derived. An additional microreactor set-up equipped with a calibrated mass spectrometer was used for the isotopic exchange reaction (DER) N2 + N2 = 2 N2 and the transient kinetic experiments. The transient experiments comprised the temperature-programmed desorption (TPD) of N2 and H2. Furthermore, the interaction of N2 with Ru surfaces was monitored by means of temperature-programmed adsorption (TPA) using a dilute mixture of N2 in He. The kinetic data set is intended to serve as basis for a detailed microkinetic analysis of NH3 synthesis kinetics [10] following the concepts by Dumesic et al. [11]. 

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]. ... 

Figures. Temperature-programmed reaction of methane with FeZSM-5 surface before a-oxygen loading (a) and after ot-oxygen loading (b). A - time moment of opening the microreactor B - time moment of switching on the programmed heating (6 K/s).

For this purpose we studied a temperature-programmed interaction of CH with a-oxygen. Experiments were carried out in a static setup with FeZSM-5 zeolite catalyst containing 0.80 wt % Fe203. The setup was equipped with an on-line mass-spectrometer and a microreactor which can be easily isolated from the rest part of the reaction volume. The sample pretreatment procedure was as follows. After heating in dioxygen at 823 K FeZSM-5 cooled down to 523 K. At this temperature, N2O decomposition was performed at 108 Pa to provide the a-oxygen deposition on the surface. After evacuation, the reactor was cooled down to the room temperature, and CH4 was fed into the reaction volume at 108 Pa. 

To determine its activity, the catalyst was placed in a quartz microreactor. Reactants were supplied through mass flow controllers and the product composition was determined by mass spectrometry. A typical reaction mixture contained 3.600 ppm NO, 1.06% CH4, and 6.0%... 

The very first investigations on this topic pointed out that a similar degree of optical purity is achievable for some reactions in microreactor as compared to conventional processing. Hence there is no reason not to investigate a chiral reaction in a micro reactor the feasibility has been proven. 

M., Zengerle, R., a modular microreactor design for high-temperature catalytic oxidation reactions, in Ehreeld,... 

Srinivasan, R., Schmidt, M.A., Harold, M. P., Lerou, J. J., Ryley, J. F., Reaction engineering for microreactor systems, in Ehreeld, W. (Ed.), Microreaction Technology - Proc. of the 1st International Conference on Microreaction Technology, IMRET 1, pp. 2-9, Springer-VerJag, Berlin (1997). 

Jahnisch, K., Baerns, M., Hessel, V, Haverkamp, V, Lowe, H., Wille, C., Selective reactions in microreactors -fluorination of toluene using elemental fluorine in a falling film microreactor, in Proceedings of tlie 37tli ESF/EUCHEM Conference on Stereocliemistry (13-19 April 2002), BUrgenstoclc, Switzerland. 

P., Warrington, B., Wong, S., A microreactor device for the Ugi four component condensation (4CC) reaction, in Ramsey,... 

Nielsen, C. A., Cheisman, R. W., LaPointe, E., Miller, T. E., Novel tubing microreactor for monitoring chemical reactions, Anal. Chem. 74, 13 (2002) 3112-3117. 

Groschel, L, Agar, D. W., Worz, O., Morgenschweis, K., The capillary-microreactor A new reactor concept for the intensification of heat and mass transfer in liquid-liquid reactions. Catalysis Today,... 

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