Electrochemical production of methyltetrahydrofuran, a biofuel for diesel engines

Methyltetrahydrofuran (MTHF) can be derived from non-edible biomass and used to replace diesel fuel. MTHF can be produced through the hydrogenation of furfural using hydrogen sourced from methane. Electrochemical hydrogenation (ECH) offers a method to source hydrogen from water, while bypassing the challenges associated with H_2(g) handling and storage. Thus, if furfural were converted into MTHF through ECH, clean liquid fuels could be formed for internal combustion engines. The challenge is that ECH has not been proven to produce MTHF in meaningful yields due to solubility and thermodynamic constraints. We report here the successful electrochemically-driven hydrogenation of furfural to MTHF using a membrane reactor. This membrane reactor is able to produce MTHF because the site of water electrolysis is separated from the site of hydrogenation so that hydrogenation can occur in organic media at high current densities. We show how the membrane reactor favors MTHF production at a selectivity of >75% at 200 mA cm⁻², compared to conventional ECH using a single cell that operates at lower selectivities (<35%) and current densities (50 mA cm⁻²). We mapped out the reaction pathway to show that in the membrane reactor MTHF is produced from the deoxygenation of a furfuryl alcohol intermediate, a pathway that does not occur in single-cell ECH. This work shows the power of using the membrane reactor for producing a liquid fuel from a biomass-derived chemical, water, and electricity.