Scaled electrochemical adipic acid derivative production and the regeneration of periodate: electrifying technical organic synthesis
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Abstract
Chemical industrial processes accounted for 6% of all global greenhouse gas emissions in 2020. This account does not consider transport, fugitive emissions, unallocated fuel combustion, or waste emissions. Adipic acid and platform oxidizers like nitric acid are two of the most contributing chemicals, as both productions cause nitrous oxide (N₂O). Achieving a resilient and climate-neutral chemical industry requires rapid and drastic changes. Electrification appears to be one of the most promising approaches for achieving this goal. However, so far
only a scant few processes are electrified. The main challenges are constituted by the fragility of the active electrodes, trade-offs between activity and selectivity, and high electricity prices.
In my dissertation, I tackled these challenges with the example of the technical organic syntheses of 3-alkyladipic acid, as well as of the platform oxidizer para-periodate. I demonstrated the adaptable use of modular flow electrolyzers. To significantly increase the space-time yields, I also designed and successfully tested two electrochemical continuouslystirred tank reactors up to 13 L and electrolysis cells with an increased electrode surface.
For the production of 3-alkyladipic acid, we invented a robust anodic foam activation protocol together with industry partners. This includes multifold electrode cleaning and reusing for over 1000 working hours with unaltered performance. For 3-ethyladipic acid, the yield after scaleup was maximized to 59% by a targeted Design of Experiments (DoE) parameter screening. In this instance, the substrates 4-ethylcyclohexanol was chosen because it can be obtained from a massively available regenerative feedstock, namely lignin. Direct use of fluctuating photovoltaic electricity was demonstrated to retain an almost equal 3-propyladipic acid yield. This is realized by the reaction continuing solely during the timeframes when lots of green energy is available. No reactivation of the electrodes was required, despite several pauses of the reaction at nighttime. Such fluctuating usage can contribute to grid stability.
It has already been shown that para-periodate, a powerful platform oxidizer, can be successfully produced by electrooxidation. However, the robustness of the process against impurities, especially with the goal of product recycling, was still an open challenge. We resolved this issue by mineralizing the organic contaminants like active pharmaceutical ingredients, dyes, and iodine compounds. Thus, aqueous solutions, containing several critical organic compounds, can be self-cleaned during this periodate-production.
Overall, the approaches investigated in this study illustrate that a fast structural industrial transition toward the electrification of technical organic synthesis is possible.