Enhancing enzymatic saccharification of spruce by 2-naphthol impregnation during pre-treatment

Today, the production of fuels, chemicals and materials is highly dependent on unsustainable fossil reserves. Usage of fossil energy is the key contributor to emissions of greenhouse gasses (GHG). Buildup of GHG such as CO2 in the atmosphere causes the temperature on earth to increase at an alarming rate, causing environmental problems around the globe. To prevent or slow down anthropogenic climate change it is time to look for other, more sustainable sources of energy. Woody biomass is a renewable and abundant resource that is rich in lignocellulose that can be used for production of fuels and chemicals. Lignocellulose is a recalcitrant matrix rich in cellulose, hemicellulose and lignin. To access the large amounts of sugars the recalcitrant nature of the biomass needs to be overcome using pre-treatment techniques. There are many possible methods used to pre-treat lignocellulosic biomass. One efficient method is steam explosion which disrupts the lignocellulosic matrix by applying steam under high pressure followed by a rapid drop in pressure. To enhance the efficacy of the pre-treatment it is possible to impregnate the substrate or add a catalyst. Dilute sulfuric acid is frequently used. Dilute acid pre-treatment may cause both economic and environmental problems in downstream processing steps, such as the extra cost of neutralizing the pre-treated material. Carbocation scavengers, such as 2-naphthol has been used as an additive during steam explosion. Steam explosion causes lignin to de-polymerise and form carbocations which are highly reactive and will repolymerise to form a lignin that is more inhibitory for enzymes. The carbocation 2-naphthol prevents this reaction and thus make enzymatic hydrolysis of the pre-treated material more efficient. In this study, 2-naphthol impregnation of Norwegian spruce was tested together with steam explosions at different severities to find out how it affected glucose release. The different pre-treatments were assessed by enzymatic hydrolysis using the commercial cellulase cocktail Cellic® CTec 2 under several oxidative conditions to investigate the importance of the lytic polysaccharide monooxygenases (LPMOs) present in the cocktail. This study shows that positive effects of 2-naphthol is related to increased LPMO activity which again is positive for saccharification yield