Continuous microreactors

Grant D, Dahl R, Cosford NDP (2008) Rapid multistep synthesis of 1, 2, 4-oxadiazoles in a single continuous microreactor sequence. J Org Chem 73(18) 7219-7223... 

Apparatus, procedure and analysis. The fixed-bed, continuous, microreactor assembly employed, the procedure and the GC analysis of the reactor effluent are described in detail elsewhere [1,7]. The main species detected by GC have been identified by GC-M3 and through a comparison with preformed mixtures of known composition. 

Figure4.54 Arrhenius plotforthe Pd/Al203 (open circles) and Pt/ Al203 (filled rhombs) catalysts. Continuous microreactor operation 2—3 bar 1 M reactant solution in methylcyclohexane 0.1 ml/min liquid flow rate (by courtesy of Royal Society of Chemistry) [271],...

Fig. 15 CYTOS benchtop continuous microreactor system. (From Ref. l) (View this art in color at www.dekker.com.)...

Kim, J., Park, J.-K. and Kwak, B.-S.(12-15 June, 2005), Development of pharmaceutical fine chemicals using continuous microreactor technology (MRT). Proceedings of the 4th Asia-Pacific Chemical Reaction Engineering Symposium, APCRE05, Gyeongju,... 

Application of On-line Raman Spectroscopy to Characterize and Optimize a Continuous Microreactor... 

Catalyst Screenins All catalyst screening studies were performed in continuous microreactor units operated in the downflow configuration. For experiments conducted using a two-bed catalyst design, each bed comprised 4 cc of catalyst having the same composition, separated by 4 cc of inert material. Internal... 

The Zn-Cr-O/Pd catalyst was prepared as described In previous work [11]. The principal characteristics a -e Zn/Cr atomic ratio 3/1, Pd concentration 1 wt X, BET surface area 52.9 m /g, pore volume 0.4 cmvg, bulk density 1.12 g/cm, particle size 0.15 to 0.18 mm. Details of the fixed-bed, continuous, microreactor assembly and of the GC analysis of the reactor effluent are given elsewhere [6]. The Identification of the various species was done by GC-MS. The overall mass balance around the reactor was ca. 10054 (99 3, Including the experimental error). The principal products, covering more than 9854 of the organic matter, with respect to the reactants transformed, were MP, dlhydro-2-methylpyrazlne (DHMP), acetone (A), pyrazlne (P) and dimethylpyrazlne (DMP). Due to the practical purpose of the present study, all of the analytical data take Into account only these species, besides reactants, neglecting minor byproducts. 

Continuous microreactor systems have gained a lot of interest in the field of organic synthesis as these possess enhanced mass and heat transfer properties. Microreactor technology also offers a contemporary way of conducting chemical reactions In a more sustainable fashion due to the miniaturization and increased safety, and also In a technically improved manner due to intensified process efficiency. Recent developments in this area related to the synthesis of heterocyclic compounds are recorded in this chapter. Also, telescoping, in which several subsequent reaction steps (with or without purification) can be achieved by connecting different reactors to each other, is covered. 

There are already many examples of advances ofPSE embedding sustainabihty aspects as part of the process development cycle. Continuous microreactors from Coming utilized for fine chemicals and pharmaceuticals [97], continuous formulation processes, process intensification demonstrated in several processes [98], and life cycle assessment evaluations integrated into process development [99], to mention a few. However, a more widespread uptake is needed, so they are used routinely. 

Raman spectroscopy has been used to monitor a variety of industrial processes to improve product quality and process understanding [18,19]. The same features that make Raman spectroscopy a useftd technique for traditional process monitoring, such as the short analysis time and ease of optical sampling, mean that it can also be a useful tool for analyzing and understanding chemical reactions performed in continuous microreactors. 

Due to short residence times inside the micromixer almost no heat was released there. In the residence time tube, temperatures up to 150 °C have been observed. In these experiments, we were able to show that it is possible to finish the first reaction step on the continuous microreactor laboratory-scale plant in less than 60 s. The same reaction step in the cooled batch vessel of the production plant took about 4 h. With these results, we came to the conclusion that it should be possible to realize the first exothermic step of the process in a microreactor. After finishing this step continuously in a closed system, the reaction solution could be transferred into the existing batch vessel and be heated there to finish the second reaction step. As the time for the first step is reduced from several hours to a few minutes for the same amount of product, it should be possible nearly to double the capacity just by installing a microreactor right before the existing batch vessel to mix the first two educts. 

The impact category AP (Figure 14.5b) includes the environmental impact of acidifying pollutants. This may be, for example, fish mortality, forest decline or crumbling of building materials [16]. Nearly the same reduction in the AP (32%) was determined if the synthesis of m-anisaldehyde was conducted in the continuous microreactor mode rather than the batch mode. Here, on the one hand the supply of m-bromoanisole [42% (batch) and 62% (microreactor)] and on the other hand the supply of liquid nitrogen [34% (batch)] play the major roles. In contrast, the electric current demand (3% and 8%, respectively) and the other chemicals (except m-bromoanisole) have no outstanding effect. 

Focus of R D patent increasing interest in continuous microreactor technologies Product improvement Process... 

However, for commercial production, the use of continuous microreactor technology should be justified by a dear cost advantage in comparison to presenfly applied technologies. The use of microfluidic bioreactors opens up possibilities for new production concepts, particularly continuous processing and flexible scale-up on demand via parallelization. There is, however, a need for a modular networks consisting of upstream steps (reaction) and downstream step (separation and purification), that is, the development of whole biocatalytic processes for real implementation in industrial setting. 

A Canadian firm, SBI Fine Chemicals, is out to prove that continuous microreactor techniques can also be used on a larger scale. For that purpose, SBI is building a biodiesel demonstration plant in Edmonton, Alberta, that can make 201 of the fuel per minute from a variety of vegetable oils [9]. 

One of the main aspects of modem chemistry is the safety of the chemical processes. It is easy to see that the volume of a batch reactor must be some orders of magnitude higher than that of the continuous-flow microreactor to reach the identical quantity of final products (using equal amounts of reactants). The small quantity of reactants in the reactor minimizes the potential of thermal explosion by dangerous reactions. Indeed, explosion or depressurization of reaction systems with hazardous substances in the continuous microreactors leads only to insignificant technical problems or to a minimum leakage of chemicals, as opposed to the scales of explosions or leaks in standard reactor volumes. Microreactors, with their narrow channel dimensions, hold such a small quantity of reaction fluid that a mechanical failure in one reactor requires merely a temporary shutdown and subsequent replacement. 

Life-cycle assessment of multistep mfinamide synthesis from isolated reactions in a batch to a continuous microreactor network is reported [148]. A continuous solvent- and catalyst-free flow process utilizing relatively inexpensive and green dipolarophile, ( )-methyl 3-methoxyacrylate, was shown. Here, benzyl chloride, instead of very reactive benzyl bromide, was employed for azide formation, which was produced utilizing benzyl alcohol and hydrogen chloride. 

---