Elisabeth Oehl will represent EBIO with an oral presentation and a poster this year at the RRB conference, 31 May – 2 June 2023, Riga, Lativa. The two accepted abstracts can be read in full here:
Electrocatalytic kraft lignin conversion dissolved in industrial black liquorA
Today’s Kraft pulp mills have developed from energy consumers to modern biorefineries supplying pulp, green energy and valuable side products. Continuous optimisations enable to valorise lignin fractions from black liquor for chemicals and fuels production. This will not only generate additional income but also increase the pulp production rate, as the load of the recovery boiler is reduced.
In this work, performed within the framework of the EBIO H20202 project, we present the electrochemical conversion of kraft lignin into phenolic compounds for further production of basic chemicals and biofuels. Weak and intermediate black liquor was supplied from Stora Enso. Without modifications it represents an excellent electrolyte due to its high inorganic content. As electrode materials low-cost metals including nickel and copper were studied in batch using stirred tank batch reactors and flow through cells in multipath operation. Applying chrono-amperometry the optimal temperature window has been identified between 80 and 120 °C, resulting in current densities up to 500 A/m2 without deposit formation on the electrode surfaces, when working in the voltage range up to 2.2 V. Several process parameters, such as the black liquor flow rate and viscosity have been identified as crucial for stable operation both in chronoamperometric runs and in constant voltage runs of 12h and will be discussed in detail. Applying online-GC the formation rate and faradaic efficiencies have been calculated. It was found that the faradaic efficiencies towards lignin oxidation is close to 90%, while the efficiency towards hydrogenation is below 50%. Periodic sampling and analysis using GPC, C13-NMR and GCxGX-FID/MS enabled us to calculate apparent depolymerisation rates towards monomeric methoxy phenols, aldehydes and acids, such as vanillin, and guaiacol. The extent of undesired repolymerisation could be quantified and correlated both to the black liquor composition and the electrode materials. Implementation with further electrocatalytic reduction of produced monomers will be discussed. Further, the current progress towards scale- up of electrodes and cells, options for process intensification and integration into kraft pulp mills will be presented. Additional challenges, such as initial foaming of black liquor during electrochemical conversion and viscosity increase due to water consumption will be addressed.
Electrochemical upgrading of industrial bio liquids – Status update of the H2020 project EBIO (Poster)B
The dominant industrial processes for crude bio liquids production are Kraft pulping and fast pyrolysis. Several decades of optimisation have tuned those processes into producers of both green electricity and pumpable bio liquids. Within EBIO we explore routes to store this green electricity by electrochemical upgrading the bioliquids at the site of production. The fundamental studies are conducted using divided and undivided flow-through cells as part of electrochemical cell series applying industrially produced electrodes. This provides insight beyond batch cells and enables a rapid scale up to pilot scale. The targeted upgrading steps are 1) anodic decarboxylation of organic acids to alkanes and alcohols; 2) cathodic reduction of carbonyl groups in lignin and saccharide-based intermediates; and 3) the electrochemical depolymerisation of polymeric lignin. All three steps are technically feasible at mild conditions enabling an integration into the biorefineries. Effects of the electrode materials and process parameters, including temperature, applied voltage, liquid flow rate will be discussed, and optimised operation windows will be sketched.
Applying boron-doped diamond (BDD) and noble metal electrodes the decarboxylation reaction can be tuned towards either gaseous Kolbe products or non-Kolbe alcohols. The doping level of BDD as well as the liquid flow rates significantly impact the yields of methanol as non-Kolbe target product. BDD provides good performance and stability as compared to other carbon electrode materials.
Cathodic reduction of carbonyl functions to alcohols is achieved applying carbon, lead and copper-based electrode materials due to their high overpotential for hydrogen formation. The conversion of pyrolysis liquids requires additives to increase the electrolyte conductivity. Divided cell configurations limit the direct oxidation of reduced products.
Anodic depolymerisation is achieved both by applying electrochemically produced oxidants and direct electrochemical conversion. The second approach applies low-cost electrodes from copper and nickel as plates and open cell foams, depending on the cell design. Applying online gas product analysis and advanced liquid analyses kinetic mechanisms of depolymerisation, formation of oxygen and hydrogen as well as undesired repolymerisation will be presented.
AElisabeth Oehl1, Roman Tschentscher2, Audrey Minnard2, Francisco Pereira2, Niclas Schupp1, Carl-Johan Hjerpe3, Jonas Kihlman3, Bernd Wittgens2, Siegfried Waldvogel11 Department of Chemistry, Johannes Gutenberg-University, Mainz, Germany
2 Process Technology, SINTEF Industry, Oslo, Norway
3 ÅF-Industry AB, Karlstad, Sweden
B Elisabeth Oehl1, Roman Tschentscher2, Talal Ashraf3, Niclas Schupp1, Bastian Mei3, Tobias Grassl4, Guido Mul3, Robbie Venderbosch5, Siegfried Waldvogel1
1 Department of Chemistry, Johannes Gutenberg-University, Mainz, Germany
2 Process Technology, SINTEF Industry, Oslo, Norway
3 PhotoCatalytic Synthesis Group PCS -TNW, University of Twente, Enschede, The Netherlands
4 CONDIAS GmbH, Itzehoe, Germany
5 BTG – Biomass Technology group, Enschede, The Netherlands