Pumping systems, microreactor

The combination of fluoride ions and enol silyl ethers provides a useful method for the generation of enolate anions [9]. Watts, Haswell and coworkers applied a borosilicate glass microreactor, having channel dimensions of 100 pm x 50 pm and equipped with an electrosmotic flow (EOF) pumping system, to the C-acylation of enolate anions, which leads to 1,3-diketones [10,11]. A THF solution of tetrabutyl-ammonium fluoride (TBAF) was placed in reservoir A, a THF solution of benzoyl... 

Fig. I a The FIA IV-I and II integrated biosensor systems I concentrated sample solution, 2 diluted sample solution, 3 reagent solution, 4 eightK hannel distribution valve, 5 peristaltic pump, 6 microreactors, 7 eightway injection valve, 8 temperature chamber control, 9 colorimeter, 10 micro computer, II waste, 12 coil, 13 peristaltic pump for sample dilution, 14 phosphate buffer, b The SIA integrated biosensor system I, 2 and 3 phosphate buffer solution 4 ethanol diluted sample 5 reagent solution 6 waste 7 1,000-pl micro-buiette 8 500-pl micro-burette P peristaltic pump 10 two three-way valves II six-channel distribution valve 12 colorimeter, 13 serpentine 14 AOD-immobilized microieactor 15 HRP-immobilized microreactor, 16 computer 17 Interface RS-232/RS-485...

The microreactor system used was the commercial CYTOS College System [18]. The reactor is made of stainless steel, has 100 ptm channels and 2 ml volume. It has two inlets operated by two piston pumps. An additional 45 ml residence time unit (RTU) is coimected to the system after the reactor itself to increase the reaction time. The parts of the device are comiected by polytetrafluoroethylene (PTFE) tubings. 

Ruy et al. have performed a similar reaction under microreactor conditions in a multiphase solvent system containing an ionic liquid as the catalyst carrier and reaction promoter [35]. Their system consisted of two T-shaped micromixers (i.d. 1,000 and 400 pm) and a capillary stainless steel tube as an RTU (1,000 pm i.d. and 18 m length, giving a 14.1 ml volume), equipped with pumps and control valves. Under the optimized conditions, Pd-catalysed carbonylation of aromatic iodides in the presence of a secondary amine provided only the double carbonylated product, ot-ketoamide, while the amide obtained by the single carbonylation was observed in high quantities only when the reaction was performed in batch (Scheme 13). 

The microreactor system consists of a pumping module (R2+) and a four-channel heated component (R4). Two independently conducted flow streams are mixed in a T-piece and driven through a convection-flow coil (CFC, volume 10 ml) made of poly(fluoroacetate) (PFA). After the CFC, the flow is guided through Omnifit glass columns [41] packed with immobilized scavengers. 

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... 

Specimens of catalysts (0.125 gram) were deactivated at 360° C for desorption experiments by using continuous (rather than pulsed) operation. Purified liquid benzene or cumene was pumped to the injection port of the microreactor system with a syringe pump at the rate of 0.00241 moles/hour. Propylene was fed from a gas lecture bottle through a rotameter at a rate of 0.00245 moles/hour. Parent H-mordenite catalyst samples were de-... 

Fig. 3. Proposed integrated FIA system, with microreactor packed with immobilized AOD 1, buffer solution 2, sample solution 3, horseradish peroxidase and reagents solution 4, eight-channel distribution valve 5, coil 6, peristaltic pump 7, colorimeter 8, computer 9, micro reactor 10, eight-channel injection valve 11, waste.

For the urease enzyme system, a reactant solution ofO.lmol/Lofurea was fed to the microreactors by Cole Parmer Series 74900 Syringe pumps. 

In general, microreactors are systems consisting of tiny channels in which a number of fluidizable substances are combined under specific physical conditions. The temperature, pressure and dwell time are the most important parameters, which are either set or altered by peripheral equipment such as pumps, heaters/coolers and control systems. 

The very term microreactor has been grossly misused or even abused because it has been used to encompass everything from a trickle column reactor, T-piece mixer, a simple syringe pump-driven device and circulating systems, to elaborate pumping and separation equipment. More often than not there is an ineffective and inadequate... 

Figure 7.26 Assembly of a microreactor system empty tubing (a) filled with AO resin (b) with filter caps (c), and attached to syringe pumps (d). Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission...

When the reactor is operated at vacuum pressures the slide valve is retracted, and the microreactor vents directly into the vacuum system. In this case transient response data are collected one mass peak at time in a mass intensity versus time format. The high pumping speed of the vacuum system, and the near proximity of the quadrupole to the microreactor insure that pulses measured by the quadrupole reflect the true microreactor transient response. 

For the laboratory prototype a Gilson fraction collector was used. The whole setup as depicted was named MICROTAUROS (Fig. 15.14) (microreactor for automated reaction optimisation) and worked fairly well with only a few drawbacks. The length of the tube necessary for reaching every position on the fraction collector rack precluded very short reaction times. Higher pump rates would compromise the advantage of a laboratory system with the rather small amoimts of materials and small syringes. A much more severe drawback is the fact that a three-way solenoid valve had to be used. In the equilibrium phase the material stream is switched to waste and only diverted for collection of analytical samples. 

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