Steam Explosion Pretreatment with 2-Naphthol for High Softwood Recalcitrance

Steam explosion pretreatment is the most common pretreatment method in commercial biorefineries. However, it is not effective for the extremely high recalcitrance of softwood to chemical conversion. Recent studies, though, show that addition of a carbocation scavenger, like 2-naphthol, can enhance the enzymatic digestibility of softwood. ETH Zurich researchers studied the potential of this approach in a larger steam explosion pilot plant.

The addition of 2-naphthol to the steam explosion pretreatment of spruce wood chips significantly enhanced the enzymatic cellulose digestibility. Different ways of adding the solid 2-naphthol to steam pretreatment were also tested. Researchers found that mixing 2-naphthol with the biomass before pretreatment could enhance digestibility by up to 55%.

Impregnation of the biomass with 2-naphthol was found to be more effective. Acetone and ethanol were tested to dissolve 2-naphthol and impregnate the biomass. The solvents were then removed by evaporation before the pretreatment. The impregnation with both solvents enhanced digestibility by more than 100%.

This is the first study that shows that a carbocation scavenger in steam pretreatment can enhance the enzymatic digestibility of lignocellulosic biomass. This opens up new possibilities for overcoming the high softwood recalcitrance.