Microreactors column reactor

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... 

Within the field of radical polymerization, special attention was recently drawn to the use of microreactors for controlled radical polymerization techniques, namely, ATRP, NMRP and RAFT. Shen and Zhu [126] have devised a column reactor packed with silica-gel-supported copper bromide-hexamethyltriethylenetetramine (HMTETA) for the continuous ATRP of homo- and block copolymers of MMA. Wu et al. [127] report the use of microfluidic chips made from thiolene polymer for continuous ATRP of... 

CLEA capillary column reactor and monolith microreactor... 

Catalytic activity tests have been performed in a quartz microreactor (I.D.=0.8 cm) filled with 0.45 g of fine catalyst powders (dp=0 1 micron). The reactor has been fed with lean fiiel/air mixtures (1.3% of CO, 1.3% of H2 and 1% of CH4 in air resp ively) and has been operated at atmospheric pressure and with GHSV= 54000 Ncc/gcath The inlet and outlet gas compositions were determined by on-line Gas Chromatography. A 4 m column (I D. =5mm) filled with Porapak QS was used to separate CH4, CO2 and H2O with He as carrier gas. Two molecular sieves (5 A) columns (I D.=5 mm) 3m length, with He and Ar as carrier gases, were used for the separation and analysis of CO, N2, O2, CH4, and H2, N2, O2 respectively... 

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... 

Apparatus and Procedure. The conventional microreactor was used to determine catalytic activities. The reactor was a 4 mm id borosilicate glass tubing, directly connected to the dual column gas chromatograph... 

The reaction system consisted of a flow stainless steel microreactor operated at 5 MPa and 523-623 K. Hydrogen and carbon monoxide were supplied to the reactor through mass flow controllers (Brooks). Products were sampled through heated lines into an on-line gas chromatograph equipped with TCD and FID detectors, with a Porapak Q + R column for Ci products and a Tenax column for hydrocarbons (C,-C13) or alcohols (Cj-Cfi), respectively. Reaction products were identified with a gas chromatograph-mass spectrometer (Hewlett-Packard Model 5971), using a 60 m DB-1 capillary column (J W Scientific). 

With the use of falling-film microreactor or a microbubble column, yields of up to 28% were obtained with acetonitrile as solvent at conversions ranging from 7 to 76% and selectivities from 31 to 43% with regard to the monofluorinated product [308]. With the use of dual-channel reactor, conversions from 17 to 95% and selectivities from 37 to 10% were achieved using methanol as solvent [274]. The conversion of a laboratory bubble column, taken for comparison, ranged from 6 to 34% with selectivities of 17-50%, which is equivalent to yields of 2-8% [308],... 

The mass transfer efficiency of the falling-film microreactor and the microbubble column was compared quantitatively according to the literature reports on conventional packed columns (see Table 4.3) [318]. The process conditions were chosen as similar as possible for the different devices. The conversion of the packed columns was 87-93% the microdevices had conversions of 45-100%. Furthermore, the space-time yield was compared. Flere, the microdevices resulted in larger values by orders of magnitude. The best results for falling-film microreactors and the microbubble columns were 84 and 816 mol/(m3 s), respectively, and are higher than conventional packed-bed reactors by about 0.8 mol/(m3 s). 

Several reactors are presently used for studying gas-solid reactions. These reactors should, in principle, be useful for studying gas-liquid-solid catalytic reactions. The reactors are the ball-mill reactor (Fig. 5-10), a fluidized-bed reactor with an agitator (Fig. 5-11), a stirred reactor with catalyst impregnated on the reactor walls or placed in an annular basket (Fig. 5-12), a reactor with catalyst placed in a stationary cylindrical basket (Fig. 5-13), an internal recirculation reactor (Fig. 5-14), microreactors (Fig. 5-16), a single-pellet pulse reactor (Fig. 5-17), and a chromatographic-column pulse reactor (Fig. 5-18). The key features of these reactors are listed in Tables 5-3 through 5-9. The pertinent references for these reactors are listed at the end of the chapter. 

A conventional pulse catalytic microreactor was used with 15-65 mg of the catalyst for the cumene runs and 65 mg for the 2,3-dimethylbutane runs. The catalyst was held between 2 small plugs of borosilicate glass wool in a 5-mm ID diameter borosilicate reactor. In some experiments, the catalyst was diluted with 96% silica porous glass powder. The helium gas was purified by passage through alumina kept at liquid nitrogen temperature. The reaction temperature was measured by a thermocouple located adjacent to the reactor. The catalyst was pretreated at the desired temperature for 16 hours in a stream of helium. The products were analyzed with a dioctyl phthalate gas chromatography column at llO C. 

The activity of the catalysts in N2O decomposition was tested in the same flow microreactor at 320 - 520°C and space velocity 2 10 h using the gas mixture [93 vol.% of He + 6.88 vol.% of N2O]. Samples of the reactor effluents were periodically analyzed by GC, with catarometer, using a Polisorb column. 

Alkylation of isobutane with 1-butene was carried out in a fixed bed down flow stainless steel tubular microreactor. The experiments were carried out in the gas phase at 1 atm total pressure, isobutane/l-butene molar ratio of 14 and 1-butene space velocity 1.0 h". Premixed isobutane and 1-butene (>99% purity, Matheson) was fed from a gas cylinder. A high paraffin to olefin ratio was choosen to reduce the chance of olefin dimerization. The catalysts (300 mg, 60-80 pm particle size) were activated in the reactor by calcining in air at 450°C for 4 hours. Air flow was then replaced by nitrogen and the catalyst temperature was lowered to the desired reaction temperature. The feed gas and the products were analyzed by a on-line gas chromatograph equipped with a CP-Sil PONA capillary column (length 50 m, film thickness 0.25 pm). 

One way of process simplification is to make molecular complex compounds out of much simpler building blocks (e.g., by multi-component one-pot syntheses like the Ugi reaction), at best directly out of the elements. Especially in the latter case, this is often quoted as a dream reaction [14]. Typically, such routes have been realized so far with hazardous elements, easily undergoing reaction, but lacking selectivity. One example is direct fluorination starting with elemental fluorine, which has been performed both with aromatics and aliphatics. Since the heat release cannot be controlled with conventional reactors, the process is deliberately slowed down. While, for this reason, direct fluorination needs hours in a laboratory bubble column it is completed within seconds or even milliseconds when using a miniature bubble column operating close to the kinetic limit. Also, conversions with the volatile and explosive diazomethane, commonly used for methylation, have been conducted safely with microreactors in a continuous mode [14]. 

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