18-06: Biorefining at Borregaard: development of a sulfite based pretreatment for lignocellulosic biomass

Founded as a sulfite paper mill more than 120 years ago, the Borregaard biorefinery has over the last 50 years evolved into one of the world's most advanced biorefineries in operation. About 90% of the spruce feedstock is converted to specialty cellulose, lignosulfonate, bioethanol and vanillin. Inspired by the current sulfite digestion of wood chips, Borregaard has directed substantial resources into developing a pretreatment process for lignocellulosics that addresses 3 of the main challenges of other pretreatment technologies: 1) Lignin binds to enzymes, requiring higher dosing and preventing recycling, 2) Impure and strongly condensed lignins are unattractive for most lignin applications and 3) Low yields of value added products and high yields of products valued only by their energy content result in an unfavorable mass balance and process economy. The development work done at Borregaard has resulted in a sulfite based pretreatment process that yields a water soluble lignin with identified applications and a cellulose pulp that can be hydrolyzed with enzymes under industrially relevant conditions. The resulting hydrolyzates are easily fermented due to the absence of fermentation inhibitors. Details on the preatreatment and hydrolysis will be presented as well as an update on the planned 50 kg/h pilot plant for the process.