High production of levulinic acid from cellulosic feedstocks being catalyzed by temperature-responsive transition metal substituted heteropolyacids

Heteropolyacids (HPAs), super strong Bronsted acid solids, were recently reported to achieve cellulose conversion with high efficiency. To achieve higher levulinic acid (LA) yield, a series of Lewis metal- substituent phosphotungstic acids HnPW11LO39 (HPWL, L = Cu-II, Sn-IV, Cr-III, Zn-II, Fe-III; L = Ti-IV, Zr-IV, oxygen is 40) were used as catalysts in polysaccharides conversion. Identification of the reaction intermediates and products provided some information for cellulose conversion pathway. H5PW11TiO40 (Brensted/Lewis acid = 2.84:1) was found to be most active with highest cellulose conversion giving highest glucose yield in water and highest LA yield in methyl isobutyl ketone (MIBK)/water. In addition, for overcome the drawbacks in mass transferring and separation, the temperature-responsive catalyst of HOCH2CH2N(CH3)(3)H4PW11TiO40 (ChH(4)PWTi) was prepared giving as high as 76.1% LA yield at 93.8% cellulose conversion more than those by HPWTi (65.6%, 90.5%). Also, ChH(4)PWTi was obtained 93.7% conversion and 70.9% yield at microwave. ChH(4)PWTi also presented higher feedstocks - tolerance to mono-, di- or polysaccharides and even lignocellulose (corn straw, pinewood, husk of xanthoceras, coconut shell) to LA. As highest as 33.0% LA yield at 68.0% conversion was obtained by ChH(4)PWTi from husk of xanthoceras under mild conditions. ChH(4)PWTi could be recycled 12 times without significant loss of activity, which showed longer duration. (C) 2019 Elsevier Ltd. All rights reserved.