Microreactor monolith

In particular, two main streams of PI applications have been identified (i) PI innovations for reactors (e.g., microreactors, monolith reactors, spinning disc reactors, reactive separations) and (ii) PI technologies for more efficient energy transfer (e.g., ultrasound, pulse, plasma, microwave). Several PI technologies offer important potential, but require important fundamental/strategic research to reach proof-ofconcept on the laboratory scale. These PI technologies are ... 

To highlight the benefits from microstructuring in reducing dispersion, equivalent fixed bed and microreactor/monolith were compared in terms of a dispersion ratio (ratio of the widths of initially delta-like concentration tracers at the reactor exit) [88, 89]. In terms of the Peclet number (with Dax as the axial dispersion), an expression for fixed bed reactor of the type... 

Several kinetic studies in microreactors/monoliths are available in the literature over a wide range of conditions. In particular, measurements under severe conditions are attractive for a number of reasons. We mention some examples in the following. 

Static mixing catalysts Operation Monolithic reactors Microreactors Heat exchange reactors Supersonic gas/liquid reactor Jet-impingement reactor Rotating packed-bed reactor... 

In the first stage of the investigation the catalyst can be considered in the form of powder in order to derive intrinsic transient kinetics of all the relevant reactive processes. To this purpose, dynamic reactive experiments can be performed in a simple tubular fixed-bed microreactor over small quantities (50-200 mg) of finely powdered catalyst in principle, this guarantees negligible transport limitations and more controlled conditions (e.g. isothermal catalyst bed), hence enabling a direct estimation of intrinsic rate parameters by kinetic fit. Internal diffusion limitations are particularly relevant to the case of bulk (extruded) monolith catalysts, such as vanadium-based systems for NH3/urea SCR however, they... 

In a second and possibly alternative stage of the kinetic investigation, laboratory experiments are performed over the same catalyst as for the microreactor tests, but now in the form of small monolith samples with volumes of few cubic centimeter. Flow rates, as well as catalyst size, are thus typically increased about by a factor of 100 with respect to the microreactor kinetic runs. This experimental scale provides data either for intermediate validation of the intrinsic kinetics from stage one, or directly for kinetic parameter estimation if runs over catalyst powders are omitted. 

The up-scaling from microreactor to small monoliths principally deals with the change of geometry (from powdered to honeycomb catalyst) and fluid dynamics (from turbulent flow in packed-bed to laminar flow in monolith channels). In this respect, it involves therefore moving closer to the conditions prevailing in the real full-scale monolithic converter, while still operating, however, under well controlled laboratory conditions, involving, e.g. the use of synthetic gas mixtures. 

This intermediate scale affords a preliminary validation of the intrinsic kinetics determined on the basis of microreactor runs. For this purpose, the rate expressions must be incorporated into a transient two-phase mathematical model of monolith reactors, such as those described in Section III. In case a 2D (1D+ ID) model is adopted, predictive account is possible in principle also for internal diffusion of the reacting species within the porous washcoat or the catalytic walls of the honeycomb matrix. 

The transient experiments herein described were carried out over powdered catalyst in a microreactor a portion consisting of several grams from the original extruded monolith was crushed and sieved to a powder (140-200 mesh). One hundred and sixty milligrams of this powder, diluted with 80 mg of quartz were eventually loaded in the microreactor. Intraparticle gradients and gas-solid mass transfer limitations were ruled out by theoretical criteria (Mears, 1971). 

Altogether, the data reported in this section indicate a very good predictive quality of the model simulations this implies in the first place that the SCR kinetics estimated over powdered catalyst were successfully validated at this bigger scale. However, the excellent agreement between monolith data and model predictions based on intrinsic kinetics also confirms the accurate model description of physical phenomena, specifically external and intraporous mass transfer, which were not significant in the microreactor runs over the powdered catalyst, but played an important role in the monolith runs, as pointed out by the direct comparison in Fig. 44. 

Wiessmeier G, Schubert K, Honicke D. Monolithic microreactors possessing regular mesopore systems for the successful performance of heterogeneously catalysed reactions. In Ehrfeld W, ed. Proceedings of the 1st International Conference on Microreaction Technology., Berlin Springer, 1998 20-26. 

Microfluidic concepts can be used to develop an integrated total chemical analysis system (TAS) [40], which include sample preparation, separation, and detection. The microminiaturization of a TAS onto a monolithic structure produces a //-TAS that resembles a small sensor. The first /(-TAS was a micro-gas chromatograph (GC) fabricated on a 5-in. silicon wafer in 1979 by a group at Stanford University [41]. Since then, developments in micromachining has led to the development of microsensors, microreactors,... 

Peterson, D.S., Rohr, T., Svec, F., Frechet, J. M.J., Enzymatic microreactor-on-a-chip Protein mapping using trypsin immobilized on porous polymer monoliths molded in channels of microfluidic devices. Anal. Chem. 2002, 74(16), 4081M088. 

In structured reactors, the structural units are repeated. In monoliths, the units are usually simple channels with a square cross section, though many variations are encountered. In Sulzer-t)q)e packings, the units are combinations of corrugated sheets. In microreactors, the basic unit can have any of several shapes. What structured reactors have in common is that a precise design is made, starting from a description of one single unit. 

Digestion can also be achieved using a trypsin IMER, where trypsin is immobilized to a solid support, e.g, macroporous silica [38], on POROS material (Porozyme IMER) [39-40], a PVDF membrane in a microreactor [41], or silica-based [42] or porous polymer monoliths [43-45]. 

A.K. Palm, M.V. Novotny, Analytical characterization of a facile porous polymer monolithic trypsin microreactor enabling peptide mass mapping using MS, Rapid Commun. Mass Spectrom., 18 (2004) 1374. 

J. Kfenkova, Z. Bilkova, F. Foret, Characterization of a monolithic immobilized trypsin microreactor with on-line coupling to ESI-MS, J. Sep. Sci., 28 (2005) 1675. 

Microfabrication technology used to manufacture microreactors also introduces many advantages, most notably the ability to rapidly and cheaply mass-produce devices. The low cost of microfabricated devices makes it possible for these devices to be disposable, a characteristic desirable for many medical applications. Rapid scale-up of production by operating many microreactors in parallel can also be accomplished. Microfabrication also presents the opportunity for complete systems in a single monolithic device or systems on a chip as microreactors are incorporated with chemical sensors and analysis devices, microseparation systems, microfluidic components, and/or microelectronics. 

The relatively high surface of microreactors can be taken advantage of to enhance surface-catalyzed reactions. For example, Langer et al. have utilized reactive polymer coatings in microreactors to produce various biomolecules and to perform bioassays, as illustrated in Fig. The addition of monoliths or posts to... 

Spinning disk reactor Static mixer reactor Monolithic reactors Microreactors HEX reactors... 

All three types of reactors mentioned in Table 8 are used for the quaUty control during the preparation and the use of monolithic systems. Additionally, microreactors are used for the development of new catalysts, whereas bench-scale reactors are used for reactor design. Pilot-scale systems have been used for the determination of the activity during the lifetime of the monolith. 

A pepsin microreactor was developed using a sol-gel monolithic column photo-polymerized within a fused silica capillary [6]. The column was used for on-line ESI CE/MS. Although monolithic microreactors are fast and efficient, the process of their preparation may require more than 24 h and can be difficult to reproduce. 

Fig. 11 Top SU-8 based microfluidic system, which includes an enzymatic microreactor, a chromatographic device, and an integrated ionization emitter tip. Bottom SEM photograph of a section of a monolithic phase prepared from LMA/EDMA. Reproduced from [133]...

Samples of the three calcined monoliths, after completing the campaign of DeNOx tests and being unloaded from the reactor, were reduced into fine powders and subject to TPD analysis (temperature programmed desorption) in a microreactor. Under a flow of He, the temperature of the catalyst bed was progressively increased up to 800°C and a mass spectrometer registered the nature and concentration of desorbed species. Sulfate... 

Scheme 12 Immobilization of palladium(O) particles onto the monolithic phase inside the microreactor...

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