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Electrochemical Polyvanillin Production: A valorization route from lignin to biobased polymers

Poster presented at 3. Internationaler Bioökonomiekongress Baden-Württemberg, 21.-22. September 2020, Online
: Kunkel, Robin; Schmidt, Volkmar M.; Cremers, Carsten; Müller, Dominik; Schmiedl, Detlef; Tübke, Jens

2020, 1 Folie
Internationaler Bioökonomiekongress Baden-Württemberg <3, 2020, Online>
Fraunhofer ICT ()
Polyvanillin; biobased polymers; Lignin
Anfrage beim Institut / Available on request from the institute

The development of sustainable processes for polymer synthesis from renewable resources is of urgent matter, as conventional petroleum-based routes exhibit ecologic concerns as well as rely on limited resources. Lignin, which is obtained on a million ton scale from the paper and pulp industry, is mostly used energetically to provide process heat and is the least utilized lignocellulosic biopolymer. One promising valorization route is to produce vanillin from lignin, which can be produced with appropriate yields and highselectivity via classical thermal catalytic or more recently by electrochemical oxidation. Electrochemical conversion of vanillin to biobased polymers would be an attractive route enabling an overall green process, since electrochemistry is intrinsically fulfilling several SDGs. A feasibility study of polyvanillin was published in 2012 [1]. Polyvanillin was produced by electrochemical pinacolization of divanillin, which can be easily obtained enzymatically by oxidative phenol coupling of vanillin. However, to further establish a reliable electrochemical process for divanillin polymerization, a more detailed understanding of the reaction mechanism and electrochemical parameters such as current density, applied charge or electrode material on polyvanillin formation is required.
Methods: To obtain information about the reaction mechanism of aldehyde pinacolization in aqueous alkaline media, the electrochemical pinacolization of vanillin was studied in a batch cell as a first step. Alternative cathode materials to the currently used toxic lead electrodes were screened for aldehyde pinacolization.As a second the electrochemical polymerization of divanillin was investigated. Influence parameters such as current density and applied charge on the molecular weight distribution (MWD) were studied.
Results: Cathode materials Zn and glassy carbon (GC) were found as stable, non-toxic and cheap alternatives for the electroreduction of vanillin and divanillin with comparable activity beside the currently used toxic and unstable Pb cathodes. Pinacolization product was found as the main reaction pathway for all three electrode materials. However, a significant amount of side product formation (alcohol) was observed at high current densities for Pb and GC. Molecular weights up to 2650 g mol-1 were achieved until a final state of polymerization set in. MWD was independent on current density for Zn up to 60 mA cm-2, whereas a decrease of MWD was found for Pb and GC at these high currents.
Conclusion: A deeper insight into the sustainable and green synthesis of polyvanillin by electrochemical reductive pinacolization of divanillin was presented in this study. Shown results of electrochemical polyvanillin synthesis further pave the way towards the development of a reliable overall green electrochemical process and providing information of a further transformation into an flow reactor.