Flow microreactor

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]. ... 

The NSR capability of the catalysts was investigated under transient conditions in a flow microreactor system with samples in the powder form. 

In each run, 120 mg of catalyst (75-100 xm) were used and a total flow rate by 200 cm3/min STP was maintained in the different phases. The flow microreactor system... 

Carbon dioxide chemisorptions were carried out on a pulse-flow microreactor system with on-line gas chromatography using a thermal conductivity detector. The catalyst (0.4 g) was heated in flowing helium (40 cm3min ) to 723 K at 10 Kmin"1. The samples were held at this temperature for 2 hours before being cooled to room temperature and maintained in a helium flow. Pulses of gas (—1.53 x 10"5 moles) were introduced to the carrier gas from the sample loop. After passage through the catalyst bed the total contents of the pulse were analysed by GC and mass spectroscopy (ESS MS). 

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. 

Overall, the microreactor provides greater safety for individuals and equipment and reduces the likelihood of loss of process and the consequent disruption and even loss of sales that can follow. In common with other fine chemical manufacturers, most pharmaceutical companies have programs to capture the benefits of flow microreactors as adjuncts to or even replacements for their current batch methods for scaling up production of candidate molecules to satisfy clinical and manufacturing needs. This paper attempts to demonstrate that microreactors can be deployed more widely in pharmaceutical R D than as a tool for enhanced production and that they have the potential to underpin significant paradigm shifts in both early- and late-phase R D. 

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. 

Baxendale IR, Ley SV, Smith CD et al (2008) A bifurcated pathway to thiazoles and imidazoles using a modular flow microreactor. J Comb Chem 10(6) 851-857... 

The adsorption of NO, under lean conditions was studied by imposing a step change of NO and NO2 feed concentrations in the presence and absence of excess oxygen over the reference catalysts in a fixed-bed flow microreactor operated at 350 ° C and analyzing the transient response in the outlet concentrations of reactants and products [transient response method (TRM)[. The adsorption/desorption sequence was repeated several times in order to condition the catalytic systems fully due to the regeneration procedure adopted (either reduction with 2000 ppm H2 + He or TPD in flowing He), BaO was the most Ba-abundant species present on the catalyst surface. FT-IR spectroscopy was used as a complementary technique to investigate the nature of the stored NO species. 

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... 

The catalysts were tested in the dehydrogenation of tetrahydrothiophene (DHN of THT), the hydrodesulphurization of thiophene (HDS of thiophene) and the hydrogenation of biphenyl (HN of BP). The reactions were carried out in the vapor phase using dynamic flow microreactors equipped with an automatic online analysis. Reaction conditions are given in Table 1. 

The N-alkylation of 2-methyl-6-ethylaniline (MEA) with methoxy-2-propanol (MOIP) was investigated in the same flow microreactor under atmospheric pressure. Feed MEA MOIP = 0.5 (3 ml/h) and hydrogen (4,7 ml/min). The reaction product was condensed in a cooling trap. Each catalyst was tested for 24 h and 7 samples were collected and analyzed separately by GLC on a fused silica capillary column with methylsilicon fluid (Hewlett Packard) as stationary phase. 

They were performed in a flow microreactor operated at atmospheric pressure between 548 K and 673 K. Prior to any measurement, the catalyst was dehydrated in situ, under flowing N2 at 723 K overnight. 

A differential flow microreactor was used for the preparation of the nitrided catalyst and the TPD, TPR, and NH3-TPD measurements. Nitriding of the molybdena-alumina and alumina was carried out by temperature-programed reaction with NH3 (NH3-TPR).1719 The MoCV A1203 precursor was oxidized at 723 K for 24 h, cooled to 573 K, reacted with NH3 at 49.6 (xmols-1 from 573 to 773, 973 or 1173 K at a rate of 0.0167 Ks-1, held at the nitriding temperature for 3 h, and then cooled to room temperature (RT) in flowing NH3. The catalysts were characterized by TPD, TPR, and NH3-TPD under in situ conditions, while BET and diffuse reflectance FTIR measurements were carried out after passivation. For the diffuse reflectance FTIR study, the catalysts after NH3 treatment... 

Fig. 3. Kinetics of n-butyl alcohol consumption (a) and dehydration (b) in HZSM-5 (flow microreactor, sample I, 399 K) (A) Water ( ) di-n-butyl ether, n-butene (X) unreacted n-butyl alcohol.

Dehydration kinetics of the four alochols were followed using two distinct types of catalytic reactors a static FTIR spectrometer cell, in which the concentration of alcohol adsorbed by the catalyst was adjusted to be less than or equal to the concentration of the active sites and a flow microreactor, which allowed the escaping products (and reactant) to be identified by gas chromatography. Kinetic measurements conducted with the FTIR cell refer to the... 

Note that the rate coefficients k determined by our kinetic studies with the static FTIR reactor for all four butyl alcohols are the true rate coefficients for the forward step of stage II of Scheme 1, i. e., k = k+//. But under the steady-state conditions of the flow microreactor, the observed reation rate, Wbuoh, of butyl alcohol dehydration is less than or equal to the product (k+//N) of the rate... 

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. 

Figure4.36 Design ofaTaylor-flow microreactor also given below and the reaction channel with feeds and mixing zone (left), and reaction is 100 tm wide and 50 tm deep at a length channel and outlet (right). Please note that in of 2.2 cm. The outer dimensions of this the image T-type mixer design is given, which chip are 45 mm x 8 mm x 1.5 mm (by courtesy differs somewhat from the one shown in of M. Warmer, Eindhoven University of...

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