Electrochemical Valorization of Biomass-Derived Feedstocks: Levullinic Acid to 4-Hydroxyvaleric Acid

Abstract

Fossil fuel-based sources of energy are being gradually replaced by renewable electricity (such as solar, wind, etc), while there is a rising interest in biomass as a sustainable platform to produce fuels and other carbon-based chemicals.1,2 Electrochemistry is thus an attractive approach for the valorization of biomass-derived feedstocks. This approach has shown some advantages compared to traditional thermal- or bio-based chemical conversion such as the amenability to operate directly on aqueous biomass hydrolysate streams, and operability near ambient conditions, which also facilitates distributed scale production.2 This work discusses the electrochemical conversion of levulinic acid (LA) to 4-hydroxyvaleric acid (HVA). HVA is a versatile compound that can be used as a monomer for the production of biodegradable and biocompatible polyesters, in addition to diverse commodities and fine chemicals.3,4 It is projected that the biopolymers industry will reach a global market size of USD 27.9 billion by 2025.5 While prior work has demonstrated that LA can be electrochemically converted into valeric acid (VA) and γ-valerolactone (GVL), among other compounds,2, HVA has only previously been fund as a trace-level intermediate of LA electrochemical reduction into GVL.Here, we show a maximum HVA production rate higher than 40 g L-1 h-1 (i.e., 200 kg L-1 m-2 h-1) at 100% selectivity, and conversion and faradaic efficiency of 81%, while complete LA conversion could also be achieved under lower rates. Our characterization indicates this can further be optimized by reactor design (particularly the mass transport properties) and electrolyte engineering. Though evaluation of different pHs, aqueous supporting electrolytes, temperature, electrode potential, stirring rates, and initial concentration of LA we also elaborate on mechanistic underpinnings of the reaction selectivity, proposing that the formation of VA and GVL is through surface-mediated reactions, while HVA is formed via an outer sphere electron transfer (OSET) route (Fig.1). References (1) npj Clim. Atmos. Sci. 2019, 2 (1), 35.(2) ACS Energy Lett. 2021, 1205–1270. https://doi.org/10.1021/acsenergylett.0c02692.(3) . J. Biotechnol. 2015, 210, 38–43.(4) J. Agric. Food Chem. 2019, 67 (9), 2540–2546.(5) Global Bioplastics & Biopolymers Market Outlook 2020-2025 https://www.globenewswire.com/news-release/2020/04/17/2017839/0/en/Global-Bioplastics-Biopolymers-Market-Outlook-2020-2025.html (accessed April 22, 2021). Figure 1