Scale miniaturized reactors

Figure 3 shows a schematic view of a flow reactor. It is similar to the photochemical reactor previously described in [5] but the UV photolysis cell has been replaced by a 1 m. stainless steel coil in a heated oil bath. As before, FTIR is used to monitor the conversion and optimise the conversion of reactant to product. Using such a system (C5Me5)Mn(CO)2(C2H4) can be obtained in a high yield as in Scheme 1. We are now scaling up this miniature reactor to a technical scale, ultimately with the aim of carrying out solvent-free reactions on a kilogramme scale.

Miniaturized bioreactors can be divided into two categories based on scale microreactors and nanoreactors. These bioreactors present several fundamental advantages and open new venues. Miniaturized reactors allow for bench-scale chemical and biochemical production, which can be used by researchers. They also allow for cost-effective production when smaller quantities of a chemical are required. Other larger bioreactors are often not feasible because the production is not cost effective if the product is not very valuable or if the production is not consistent or pure enough for higher value chemicals. Miniaturized bioreactors, however, provide a great deal of conpol over reaction kinetics and hydrodynamics. 

Novel mechanical or bubble-induced flow designs are not trendsetters nor do they solve many of the and gas-liquid mass transfer problems. Miniaturized reactors, however, could decrease process design and implementation signiflcantly. The numbering-up method for these reactors reduces the time and amount of work necessary for scale-up the process is determined for one experimental unit and then the unit is copied multiple times. The rest of the work is spent on the industrial and economic problems rather than hydrodynamic and gas-liquid mass transfer issues commonly found in scale-up issues for other bioreactors. 

Transport phenomena are crudal in the scale-up of conventional, large-scale chemical reactors because many processes are heat and/or mass transfer controlled. Since transport coeflEcients are typically inversely proportional to the characteristic dimension of the system, miniaturization of chemical systems leads to a substantial increase in transport rates. This increase in turn enhances the overall rate of processes that are transport limited, leading to considerable process intensification, i.e. the same throughput can be achieved with a much smaller device and thus with much lower capital. Alternatively, much higher throughput can be achieved using a system of the same size as a conventional one, but made up of many small components (scaling out). 

Many other, less obvious physical consequences of miniaturization are a result of the scaling behavior of the governing physical laws, which are usually assumed to be the common macroscopic descriptions of flow, heat and mass transfer [3,107]. There are, however, a few cases where the usual continuum descriptions cease to be valid, which are discussed in Chapter 2. When the size of reaction channels or other generic micro-reactor components decreases, the surface-to-volume ratio increases and the mean distance of the specific fluid volume to the reactor walls or to the domain of a second fluid is reduced. As a consequence, the exchange of heat and matter either with the channel walls or with a second fluid is enhanced. 

More favorable for miniaturization are processes with an operation time-scale proportional to or (d f. For a linear dependence on the channel diameter, the product N L df is conserved under the conditions described above. This means that with shrinking df and for fixed efficiency, the reactor volume decreases proportionally with the channel diameter. For a quadratic dependence of the operation time-scale with channel diameter, the product N L is conserved and the reactor volume decreases as the channel diameter squared. 

Worz et al. give a numerical example to illustrate the much better heat transfer in micro reactors [110-112]. Their treatment referred to the increase in surface area per unit volume, i.e. the specific surface area, which was accompanied by miniaturization. The specific surface area drops by a factor of 30 on changing from a 11 laboratory reactor to a 30 m stirred vessel (Table 1.7). In contrast, this quantity increases by a factor of 3000 if a 30 pm micro channel is used instead. The change in specific surface area is 100 times higher compared with the first example, which refers to a typical change of scale from laboratory to production. 

Rinard dedicated his research to a detailed analysis of methodological aspects of a micro-reactor plant concept which he also termed mini-plant production [85] (see also [4, 9, 10] for a commented, short description). Important criteria in this concept are JIT (Just-in-time) production, zero holdup, inherent safety, modularity and the KISS (keep it simple, stupid) principle. Based on this conceptual definition, Rinard describes different phases in plant development. Essential for his entire work is the pragmatic way of finding process solutions, truly of hybrid character ]149] (miniaturization only where really needed). Recent investigations are concerned with the scalability of hybrid micro-reactor plants and the limits thereof ]149], Expliddy he recommends jointly using micro- and meso-scale components. 

Another advantage of the micro-LC approach is that the required sample size is minimal, so the sample can be drawn from a 1-1 laboratory scale reactor without influencing the reactor composition. The ISCO pLC-500 microflow syringe pump has proven to be reliable and reproducible in evaluations in our laboratory. Capillary liquid columns have been fabricated on planar devices such as silicon to form a miniaturized separation device.19... 

Miniaturizing a conventional-flow screening system (macro-scale system) to a chip-based system comprises a number of changes, such as flow rates, reagent supply, and the material. While the conventional system with the open tubular reactors is restricted to polymer reactors, the choice of materials for the chip is... 

A measure that has been the subject of extensive publication is that of microreactors with catalytically coated walls (7,8). A microreactor has been defined as a miniaturized reaction vessel with characteristic dimensions in the range 10-300 pm which has been fabricated using state-of-the-art high-precision engineering (7). Such reactors exhibit well-defined laminar-flow patterns and permit facile scale-up by simple numbering up of the number of channels and flexible... 

Many potential applications are under study. Miniature chemical reactors could be used for portable applications in which they provide advantages of rapid startup and shutdown and of increased safety (intensification by requiring only small quantities of hazardous materials). The development of chip-scale chemical and biological analysis systems has the potential to reduce the time and cost associated with conventional laboratory methods. These devices could be used as portable analysis systems for detection of hazardous chemicals in air and water. There is considerable interest in using a microreactor to provide in situ production of hydrogen for small-scale fuel-cell power applications by conducting a reformation reaction from some liquid hydrocarbon raw material (e.g., methanol). 

With conventional protocols requiring low reaction temperatures, typically —78 °C, to prevent side reactions from occurring, scaling the reaction for industrial production of such compounds has proved difficult. As such, the authors evaluated the process under continuous flow, proposing that the effective temperature control and accurate residence times attainable within miniaturized flow reactors would enable the synthesis of diarylethenes at temperatures above — 78 °C and thus facilitate the large-scale synthesis of such compounds. 

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