Automation in Microreactor Systems

Silicon microreactors have been used in number of flow systems, such as gas-liquid [10], liquid-liquid [11], and gas-liquid-soHd [12] reactions, which are often used in conjunction with other unit operations, such as extraction [13] and distillation [14]. Furthermore, silicon microreactors have been shown to be able to operate at high temperatures and pressures [15]. In addition, the small volumes of microreactors allow potentially dangerous chemistry to be conducted more safely. For example, fluorination and chlorination of aromatics, nitration to form highly energetic compounds, and reactions carried out in the explosive regime have all been conducted safely in microreactors [2]. 

Microreactors in Organic Chemi ry and Catalysis, Second Edition. Edited by Thomas Wirth. 

The stepping trajectory-based algorithms, such as simplex [30] and steepest descent [31] methods, are designed as more directed searches than the other types 

Sj = ith search direction J — Objective function x = Experimental conditions  

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Moore, J.S. (2012) Kinetic Modeling and Automated Optimization in Microreactor Systems. Ph.D. thesis, Massachusetts Institute of Technology. 

Online monitoring of processes in microreactor systems has the potential to accelerate process development and continuous operation significantly. One of the main advantages of collecting information about the process, such as conversion, selectivity, side product formation, and so on, online is the option for subsequent automated operation. Since labor costs usually contribute a significant share to the overall total operational costs, automation provides a great opportunity for cost-efficient implementation of continuous-flow technologies. 

The application of solid catalysts in microreactors has been studied for different processes. Automated laboratory systems were applied for catalyst screenings [53,54]. Ag/Al and Ag/Al203 were applied in microflow-through reactors for the partial oxidation of ethylene [55]. For catalytic applications, a microflow-through arrangement with a static micromixer was used to prepare Au/Ag nanoparticles [56]. Microfluid segments are also of interest for catalytic reactions in microreactors [57]. 

In another example of application of the simplex method, McMullen et cd. [38] demonstrated the rapid optimization and scaling of a Heck reaction using an automated microreactor system with HPLC monitoring and feedback control. Optimal reaction conditions in the microreactor were determined after 19 automated experiments and required a relatively small amount of starting material. The reaction was then successfully scaled up 50-fold from a microreactor to a Coming meso-scale glass reactor using the optimal conditions determined by the microreactor system. 

One of the most successful applications of microsystem technology is the use of pTAS in diagnostics [332-335]. Microreactors have been integrated into automated analytical systems, which eliminate errors associated with manual protocols. Furthermore microreactors can be coupled with numerous detection techniques and pretreatment of samples can be carried out on the chip. In addition, analytical systems that comprise microreactors are expected to display outstanding reproducibility by replacing batch iterative steps and discrete sample treatment by flow injection systems. The possibility of performing similar analyses in parallel is an attractive feature for screening and routine use. 

Many speciahzed laboratory reactors and operating conditions have been used. Sinfelt has alternately passed reactants and inert materials through a tubular-flow reactor. This mode of operation is advantageous when the activity of the fixed bed of catalyst pellets changes with time. A system in which the reactants flow through a porous semiconductor catalyst, heated inductively, has been proposed for studying the kinetics of high-temperature (500 to 2000°C) reactions. An automated microreactor... 

For the laboratory prototype a Gilson fraction collector was used. The whole setup as depicted was named MICROTAUROS (Fig. 15.14) (microreactor for automated reaction optimisation) and worked fairly well with only a few drawbacks. The length of the tube necessary for reaching every position on the fraction collector rack precluded very short reaction times. Higher pump rates would compromise the advantage of a laboratory system with the rather small amoimts of materials and small syringes. A much more severe drawback is the fact that a three-way solenoid valve had to be used. In the equilibrium phase the material stream is switched to waste and only diverted for collection of analytical samples. 

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