Electrochemical flow microreactor electrolyte

A stack-type electrochemical flow microreactor having interdigitated band electrodes on a ceramic body was developed (Figure 9.2). The anodic oxidation of furans in methanol using H2SO4 as the supporting electrolyte was carried out, and the effect of the residence time was investigated by mass spectrometry analysis [13]. 

One of the most interesting features of electrochemical flow microreactor systems seems to be electrolysis without using an intentionally added supporting electrolyte by virtue of short distance between the electrodes. This field has attracted significant research interest, although various electrolyte-free electrochemical systems have been developed [17,18]. High electrode surface area to reactor volume ratios are also advantageous for conductivity and reaction efficiency. 

Marken and coworkers accomplished electrolysis without using intentionally added electrolyte using an electrochemical flow microreactor having a parallel plate-to-plate electrode configuration [19]. A substrate solution was introduced into the chamber, in which two electrodes were placed facing each other at a distance of micrometer order. In this system, the substrate solution flow and the current flow were perpendicular. 

Figure 9.4 Electrochemical flow microreactor system without using intentionally added supporting electrolyte. Electrochemical oxidation of furan.

Figure 9.5 Methoxylation of p-methoxytoluene using an electrochemical flow microreactor with a serial electrode configuration without using intentionally added electrolyte.

There is another type of electrochemical flow microreactors that can be used for electrolyte-free electrolysis (Figure 9.5) [24]. In this system, two carbon fiber electrodes are separated by a spacer (porous PTFE membrane, pore size 3 pm, thickness 75 pm) at a distance of micrometer order. A substrate solution is introduced into the anodic chamber. The anodic solution flows through the spacer membrane into the cathodic chamber. The product solution leaves the system from the cathodic chamber. In this system, the electric current flow and the liquid flow are parallel. Using this electrochemical flow microreactor having a serial electrode configuration, the anodic methoxylation of p-methoxytoluene was accomplished effectively without intentionally added electrolyte. Protons generated by the anodic oxidation acted as carriers of the electricity. This process will be discussed in detail in the practical part of this chapter. The device could also be used for the anodic methoxylation of N-methoxycarbonyl pyrrolidine and acenaphthylene. 

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