If you missed the second episode of the EBIO webinar series, or you would like to watch it again, the full recording is available here:
https://youtu.be/x3zJ4eqPyj8?si=7Ne2aKKaQ2WhNhlm
The webinar welcomed 53 guests online and received about 7 questions.
A recap of all the questions and answers can be found here:
1 – Was only Cu electrode tested for aldehyde to alcohol conversion?
A: Yes we only tested Cu for two reasons – i) prior art has shown that Cu can be very selective in aldehyde hydrogenation (not producing large quantities of hydrogen) and ii) Cu surfaces are known to induce a socalled Surface Enhanced Raman Spectroscopy (SERS) effect – allowing detection of surface adsorbed species in (very) low quantities. Since Pt and BDD do not show this effect – analysis of surface processes by Raman is much more difficult for the oxidation reactions I discussed.
2 – Regarding decarboxylation reactions, we lose a carbon atom as CO2. In terms of carbon efficiency and LCA, is it worth doing these kinds of reactions to form the target products?
A: Yes, even though some CO2 is emitted from the acid decarboxylation treatment, the fact that the oil can now be converted in e.g. aviation fuel, without the need for energy intensive catalytic hydrogenation reactions (Hydrodeoxygenation) is still adding to the sustainability of producing transportation fuels. What the consortium is also considering is to convert this CO2 electrochemically into something useful, such as ethanol.
3 – Why there is absence of coupling reactions on a platinum surface for longer-chain (propionic) acid?
A: Indeed we hardly observe the coupling of ethyl radicals (formed in the decarboxylation step) to butane on Pt surfaces, but rather form ethylene and ethanol.
We do not have a solid explanation and can only speculate.
It might be that the rate constant of ethyl radicals to form butane is not as fast as the rate constant for recombination of two methyl radicals to ethane, and the formation of ethylene or ethanol from an ethyl radical is rapid.
Also there might be an important interplay between the composition of the liquid boundary film near the PT surface and the selectivity of the reaction – for example the pH and carbonate ions are known to have a dramatic effect on acid decarboxylation (see Olde Nordkamp et al., https://doi.org/10.1002/cctc.202200438)
4 – Are carboxylate radicals (not anions) absorbed on the platinum surface, or do they remain as free radicals?
A: Good question. We feel that the carboxylate radicals are formed after adsorption of carboxylate anions on the Pt surface by electron transfer.
We have no experimental evidence to prove or disprove what happens next : desorption and decarboxylation, or surface mediated decarboxylation (and desorption of CO2).
5 – Were there any experiments conducted on pyrolysis oil deoxygenation?
We are running electrochemical flow reactors for hydrogenation of oxygen containing species (aldehydes to alcohols) and to produce high quality pyrolysis oil – we are not yet treating large quantities of oil for acid decarboxylation.
6 – In the presented solution (for a larger, final scale) the aquous phase of bio-oil needs to be oxidised and the dense phase needs to be reduced, right?
A: Yes, this is correct. We intend to separate the oil in an aqueous phase – which also contains a useful quantity of hydrocarbons – which need to be converted to obtain upgraded solutions.
7 – In that way, the quality of the dense phase increases, and the aqueous phase gets poorer (no need to waste water treatment). And a small side question – Do the inorganics (ash-related) interfere in the process?
A: We discussed at length the effect of ‘promotors’ to electrocatalytic surfaces. While in heterogeneous catalysis promotors are added to the catalytic formulation, in electrocatalysis promotors can be used to manipulate the electrode – liquid interface. We have demonstrated that cations do have an effect on the (acid decarboxylation) chemistry occurring in the vicinity of BDD electrodes – so cations already present in the pyrolysis oil might indeed be involved acting as promotors (or inhibitors) of acid decarboxylation reactions.