ALOHA

Problem: 

Key monomers like acrylic acid or methacrylic acid are currently produced in high temperature oxidation reactions of alkenes (propylene, isobutene) on multimetal oxide catalysts. It is however difficult to control the selectivity in these reactions; even if the reaction is conducted in 2 separate steps (propene ® acrolein; acrolein ® acrylic acid), still up to 10% of the feedstock may be lost by deep oxidation to CO₂. Chemicals like (meth)acrylic acid are currently produced at large scale in Flanders’ petrochemical cluster; there is a strong need to pioneer alternative technologies that emit less CO₂.

Idea:

Aloha targets electrochemical allylic activation of alkenes for oxidation at much lower temperatures. The central idea is that at lower temperatures, it will be possible to exert better control over selectivity and to avoid aselective oxidation to CO₂. An anodic process implies that the initial activation of the alkene is driven by electricity, at a specifically selected electrode; next dioxygen is used as oxidant to fully convert the intermediates to the unsaturated acid. The anodic activation of the olefin fits with the need to use renewable electric power in large scale chemical processes. Ideally, the electron can be envisioned as a catalyst: we only need to invest the initially necessary activation energy via renewable electricity for an otherwise exothermic reaction. This operation minimizes voltage and power consumption as much as possible.

Approach: 

To bring these ideas via the proof-of-concept to credible upscalability, a stepwise strategy is followed: 

• We will fabricate effective electrodes for the electrocatalytic allylic oxidation, e.g. by anchoring redox mediators onto the backbone of graphite (see Figure 1). Understanding the electrode surface and controlling its properties (e.g. hydrophobicity) are the handles to steer the reaction selectivity and rate;

• With these electrodes, we bring the oxidation of propylene to industrially relevant values, by selecting appropriate voltage, solvent, O₂ partial pressure etc. Reaction improvement is intertwined with mechanistic electrochemical experiments and electrode monitoring;

• The new reaction concept will be demonstrated in an electrochemical flow cell, which will be designed and constructed. Depending on whether sufficient yield is obtained in one step, one or more consecutive cells are envisioned, allowing optimal conditions for each oxidation step, coupled with cathodic hydrogen evolution;

• We aim at obtaining reactor effluents that can be directly purified in the current downstream trains (i. e. distillation of aqueous mixtures), ideally using reaction enthalpy as energy source in the workup.