Membrane microreactors selectivity

A feed gas mixture of 1-butene, N2 and Ar was passed through the membrane microreactor to observe the dependence of conversion and selectivity on the 1-butene flow rate. It was observed that at higher flow rates (or lower residence times), the conversion of 1-butene and selectivity to n-butane was suppressed. 

Another example for microreactor-controlled selectivity in the reaction of olefin with x02 can be found in the photosensitized oxidation of DPB in ZSM zeolite [160], Nafion membranes [161], and vesicles [163], In homogeneous solution, ZSM zeolite, and Nafion membranes, the oxidation of DPB with 02 yielded the [2 + 4] reaction product, endoperoxide 6, as the unique product (Figs. 15 and 18). In sharp contrast, in vesicle medium, the oxidation produced the aldehydes 1 and 2 ([2 + 2] reaction) in quantitative yield as described in Section III.B.l (Fig. 

The field of chemical process miniaturization is growing at a rapid pace with promising improvements in process control, product quality, and safety, (1,2). Microreactors typically have fluidic conduits or channels on the order of tens to hundreds of micrometers. With large surface area-to-volume ratios, rapid heat and mass transfer can be accomplished with accompanying improvements in yield and selectivity in reactive systems. Microscale devices are also being examined as a platform for traditional unit operations such as membrane reactors in which a rapid removal of reaction-inhibiting products can significantly boost product yields (3-6). 

The benefits of the use of micromembranes for the selective removal of one or more products during reaction have been demonstrated for equdibrium-limited reactions [289]. For example, the performance of hydrophilic ZSM-5 and NaA membranes over multichannel microreactors prepared from electro-discharge micromachining of commercial porous stainless steel plates was studied by Yeung et al. in the Knoevenagel condensation [290,291] and andine oxidation to azoxybenzene [292]. For such kind of reactions, the zeolite micromembrane role consists of the selective removal of water, which indeed yields higher conversions, better product purity, and a reduction in catalyst deactivation in comparison to the traditional packed bed reactor. 

A Rh supported catalyst was chosen because Rh has been shown to be one of the most active and selective catalysts for methane partial oxidation [6-8]. A 3% Rh/Ti02 was the most active catalyst, which ignited at 320°C in a fixed bed microreactor when using methane and oxygen feed rates of 500 and 250 cc/min respectively. It yielded a methane conversion of 70% and a CO selectivity of 85%[10]. It was also found that 100% oxygen conversion is achieved in all cases and that the ignition temperature could be even lower for lower methane/oxygen feed ratios. Experiments were performed initially in the fixed bed reactor so that results obtained in the membrane reactor could be compared to those obtained in the fixed bed reactor. 

Oxidation of Aliphatic Compounds. - A general review of the use of supra-molecular systems as microreactors for photochemical reactions contains a section dealing with the photosensitized oxidation of alkenes included in zeolites, nation membranes and vesicles. Particular consideration is given to the possibility of controlling the form and environment of the sensitizer and substrate so that the reaction selectively follows an energy-transfer or an ET pathway. The same authors have also provided a more substantial review on the same theme. Recent developments in relation to the stereochemistry and mechanism of the ene photooxygenation of alkenes by O2 have also been reviewed. ... 

The optimal contact between two immiscible solvents (MTBE/H2O) in the microreactor set-up resulted in a high initial reaction rate and enantio-selectivity, comparable to the batch process in which optimized conditions were only obtained under vigorous stirring (2008CEJS89). In-line work-up of the cyanohydrin 6 was achieved via a membrane-based phase separation, allowing the continuation of the two-step reaction approach toward the protected mandelonitrile 7, while both steps have incompatible reaction conditions (2015OBC1634). 

As stated above, the focus of recent investigations of microreactor applications in the field of emulsification was on the use of micromixers, and different types of micromixers have been employed. However, it is difficult to compare them with regard to liquid-liquid dispersion performance since the mixers are most often investigated for different specific applications. However, a suitable comparison is the basis for future targeted equipment selection. Furthermore, micrombcers are in competition with conventional and other innovative equipment such as static mixers, membranes and homogenizers. Therefore, benchmarking with such equipment is also required. 

Interesting KRs of ibuprofen were performed in single chaimel three-phase continuous-flow microreactors [108, 109]. Laminar streams of two phases were separated by an interposed third stream of an IL. Selective esterification of (S)-ibuprofen by CrL in the ethanoUc stream was followed by transportation of the (S)-ester through the IL serving as a pseudo-membrane and finally the (S)-acid was recovered by hydrolysis catalyzed by porcine pancreas lipase (PPL) in the aqueous stream. 

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. 

Knoevenagel condensation between carbonyl compounds and methylene malo-nic esters on a CsNaX zeolitic coating in a microreactor demonstrated an order of magnitude higher productivity as compared with a traditional packed-bed reactor while the selectivity remained the same in both reactors [107,108]. A nearly fourfold increase in reaction conversion was obtained for the microreactor when NH2 modified CsNaX zeolitic coatings were apphed [109]. The conversion was further improved when zeolitic coatings were grown onto a stainless steel membrane (0.2 pm pores) inserted in a microreactor [110]. 

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