On the oligomerization mechanism of Brønsted acid-catalyzed conversion of furans to diesel-range fuels

• Brønsted-acid catalyzed trimerization mechanism of furans is investigated.
• Furans self-trimerize via hydrolysis and two electrophilic substitutions.
• Microkinetic modeling reveals that hydrolysis limits oligomerization rate.
• Electron-donating substituents can accelerate the oligomerization.
• Addition of a non-self-condensing aldehyde can accelerate oligomerization.

The conversion of biomass to fuels and chemicals is considered to be a promising alternative to petroleum-based conventional routes. The oligomerization of biomass-derived furans can yield an important precursor toward diesel fuel; yet, the underlying mechanism is not well understood. This study investigates the furan oligomerization mechanism and kinetics via density functional theory and microkinetic modeling. The oligomerization proceeds in the presence of water and a Brønsted acid and requires an aldehyde and two furan molecules, each with at least one unprotected α-C. If only furans are present in the acidic, aqueous environment, the initial hydrolysis to produce the aldehyde limits the oligomerization rate. Two strategies to accelerate the oligomerization are proposed: furnishing the furans with electron-donating substituents or supplying a non-self-condensing aldehyde in the reaction mixture.

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