Electrochemical microstructured reactors: design and application in organic synthesis

Abstract

The use of micro structured reactors is an accepted technology in fundamental chemical research as well as in industrial applications. The application of electrochemical microreactors (ECMR) has not attracted as much attention as continuously performed reactions in a confined space. Nevertheless ECMRs are in use to perform electro-organic reactions. In this review, different aspects of ECMRs with structured electrodes and interelectrode distances of mainly B100 lm are investigated and discussed, together with various manufacturing techniques and prototypes described therein. Based on representative examples described in various publications for electrolysis (for direct and indirect electrolysis) advantages and disadvantages of electrochemical microreactors are presented and compared with those of conventional electrochemical reactors. List of symbolsA e Electrode surface A e = Lw (m 2 ) a e Volume specific electrode area (m -1 ) a inv Specific investment costs (€/m 2 h) A, B, C, D Reagent or product of the electrochemical reaction b A Kinetic constant of the reaction involving reagent A (V -1 ) b inv Current costs (€/kW h) C A Concentration of reagent A (mol m -3 or mol L -1 ) D Inter-electrode gap (m) d e Electrode thickness (m) d eq Equivalent or hydraulic diameter D Diffusion coefficient (m 2 s -1 ) E c , E a Cathodic, anodic potential (V) E c e ; E a e Cathodic, anodic equilibrium potential (V) E cell Cell voltage (V) E tn Thermoneutral cell voltage F Faraday constant (96,486 A s mol -1 ) i Current density (A m -2 )

Optimal design of multi-channel microreactor for uniform residence time distribution

“…To overcome this drawback, the use of several parallel microchannels is necessary but this solution could exhibit a poor uniformity in the fluid distribution between them. Recently, Ziogas et al (2009) have summarized the advantages and disadvantages of the use of microreactors compared with conventional reactors applied to electrochemistry.…”

Miniaturization of electrochemical cells for mass spectrometry

“…Several platforms can be distinguished for fabricating microfluidic chips, based on the substrate material used [9,40]. Here, we focus mainly on the materials that are more suitable for EC-MS applications.…”

“…These types of system generally employ small volumes (nL range) and provide enhanced control over reaction and analysis conditions. Both miniaturized electrochemical reactors [9] and the coupling of microfluidic devices to ESI-MS have been reviewed [65]. Table 3 gives an overview of microfluidic electrochemical cells used for different analytical applications.…”

“…Electrochemical detection and electrokinetic systems are excluded from this review, since a more general review on electrochemical microsystems is published by Zimmerman [7]. Moreover, many papers on electrochemical detectors for column or electrophoretic separations, or microreactors for electrosynthesis have been published since the end of the 1960s, and these have already been reviewed by Ewing et al [8], and Ziogas et al [9], respectively.…”

Microstructured reactor for electroorganic synthesis

“…Gas, in this particular case hydrogen, dissolved in the electrolyte solution may be oxidized at the working electrode, thus reducing process efficiency. The list of the most important contributions to this field is rounded off by the recent review of microstructured reactors in organic synthesis published by Ziogas et al [22]. The authors selected methoxylation of 4-MA to demonstrate the advantages of this approach over the classical capillary-gap cell.…”