Coplanar interdigitated band electrodes for electrosynthesis

Abstract

The behaviour of coplanar cathodic and anodic band electrodes was investigated and their use for standard syntheses was proven to be considerably advantageous, when compared to other techniques. Electrode arrays were fabricated by screen printing platinum, silver or carbon inks. The inter-electrode distances were in the range 1 mm to 250 pm for a constant band width of 1 mm.The mass transport was characterised for different inter-electrode distances and flow conditions. Figures compared positively with other cells. Two acceptable mathematical models were derived for the estimation of the resistance between coplanar band electrodes and were compared with results Obtained experimentally or by simulation Due to their excellent physical and chemical properties, platinum electrodes were found to be particularly well suited for the three syntheses investigated.The furan methoxylation, being carried out in a resistive solvent, was chosen to highlight the advantage of minimising the ohmic drop. It was also shown that the formation of by-product could be limited by acid neutralisation on the adjacent band. Vigorous mixing conditions were not crucial. With the 250 tm inter-electrode array, DHDMF could be produced with a current efficiency of 87 %. This compared extremely well with other cells and furthermore the energy consumption could be reduced to 1.4 kWh.kg , which represented a saving of at least 50 %.The importance of having small ohmic losses was also encountered for the Kolbe reaction, where the applied voltage was set at high values. However the printed platinum film was too porous and a passivation of the electrode was noticed.The advantage of having small inter-electrode distances was stressed by investigating the propylene epoxidation, which is a coupled reaction. Propylene oxide was produced at a rate of 0.12 mol.h 4 .dm 2 for an energy consumption of 2.0 kWh.kg 1 . This technique was thus found to be very competitive.Finally the possibility of using this method for the production of hypochlorite by electrolysis of sea water was investigated.(ii) 2-2 Electrical equipment 2-2-1 Characterisation of the electrode surface 2-2-2 Resistance determination 2-2-3 Electrosynthesis 40 CHAPTER 3 -Physical properties 42 3-1 Investigation of the effect of flow on the limiting current 42 3-1-1 Determination of the mass transfer coefficient in a parallel plate cell 42 3-1-2 Determination of the mass transfer coefficient with band arrays 46 3-2 Characterisation of the printed platinum electrode 53 3-2-1 Determination of the electrode thickness 53 3-2-2 Evolution of the printed electrode surface 53 3-2-2-1 Surface characterisation by Scanning Electron Microscopy 54 3-2-2-2 Surface characterisation by electrochemical means 54 3-3 Determination of the inter-electrode resistance 61 3-3-1 Analytical method 61 3-3-2 Numerical method 66 3-3-3 Experimental results 67 3-3-4 Comparison and interpretation of the results 71 CHAPTER 4 -Methoxylation of furan 78 4-1 Bibliography 78 4-2 Calibration and preliminary experiments 80 4-2-1 Invest...

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Microstructured reactor for electroorganic synthesis

“…In the first part of the investigation, a theoretical analysis showed that a reduction of the cell voltage could be obtained by this approach [3]. In the next step, a theoretical description was verified by furan methoxylation as a model reaction [4], followed by propylene epoxidation as a second example of an electroorganic reaction [5]. Both systems provided results comparable to, or even better than, most efficient industrial cells.…”

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