Polymeric ionic liquid (PIL)-supported recyclable catalysts for biomass conversion into HMF

This contribution reports the first study of recyclable PIL-supported metal (Cr, Al) catalysts for effective biomass (glucose and cellulose) conversion into 5-hydroxymethylfurfural (HMF), a key biorefining building block and biomass platform chemical. Of the five different PILs investigated, poly(3-butyl-1-vinylimidazolium chloride), P[BVIM]Cl, has been found to be most effective; when combined with CrCl2 in situ or used as the preformed PIL-metalate P[BVIM]+[CrCl3]− in DMF, this PIL-supported catalyst converts glucose to HMF in 65.8% yield at 120 °C for 3 h. This yield is higher than those achieved by the catalysts based on the PIL monomer, [BVIM]Cl–CrCl2, as well as by the most commonly used molecular IL based catalyst, 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl)–CrCl2, under otherwise identical conditions. The P[BVIM]Cl–CrCl2 catalyst system also works well for the cellulose-to-HMF conversion via a two-step process. The analogous PIL–Al catalyst, P[BVIM]Cl–Et2AlCl, is less effective than the PIL–CrCl2 system, but recyclability tests indicate the PIL–Al system is more recyclable thus achieving a nearly constant HMF yield upon 6 cycles.