Ash-forming elements of poplar and hybrid pennisetum negatively affect selective delignification ability of hydrogen peroxide-acetic acid pretreatment.

Hydrogen peroxide-acetic acid (HPAA) is widely used in bio-refinery by delignification but exhibits different delignification ability and xylan loss toward different biomass materials. This work discovered that the synergistic cyclic catalysis of ash-forming elements (Fe, Cu, and Mn) in biomass was responsible for the differences in lignin and xylan removal in HPAA pretreatment. After the addition of 10 mg/mL ash in HPAA at 60 °C for 2 h, the concentrations of H2O2 and peracetic acid were reduced to 50.2 and 12.8 mg/mL, respectively. The corresponding reduction in the redox potential of HPAA from 605.0 to 553.5 mV ultimately weakened the delignification capacity of HPAA. Moreover, the addition of ash-forming elements in HPAA pretreatment greatly reduced the xylan retention of poplar from 67.4 % to 12.3 %. Water and acidic H2O2 removed more than 55.0 % and 51.0 % biomass ash content. After the removal of ash-forming elements, hybrid pennisetum showed reduced xylan loss from 42.4 % to 29.9 % and enhanced lignin removal from 74.2 % to 90.5 % in HPAA pretreatment. Subsequently, the glucose and ethanol yields of hybrid pennisetum were reached to 92.8 % and 81.1 % in saccharification and fermentation, respectively. The removal of ash-forming elements prior to HPAA pretreatment could facilitate the conversion of biomass into valuable products and energy in a more efficient and sustainable manner. This advancement holds particular significance for lignocellulosic biorefineries seeking to optimize feedstock utilization while minimizing carbohydrate losses during pretreatment.