An effective process for the enzymatic conversion of softwood into a sugar syrup and a functional lignin

Plantation forests of radiata pine are the most promising biomass feedstock for processing into biofuels and other biomaterials in New Zealand by either biochemical or thermochemical routes.  However, the well-known recalcitrance of softwoods towards cellulase enzymes is a formidable barrier to efficient biochemical conversion which needs to be overcome for an enzymatic process to become viable.  This paper will outline our LBI (Lignocellulosic Biofuel Initiative) process which is a high-yield, cost-effective and environmentally benign process for the enzymatic conversion of radiata pine into a sugar syrup plus a functional lignin. 

The process which has been tested at pilot scale, involves a relatively mild initial thermomechanical treatment of radiata pine wood chips to produce a glucan-rich solid substrate plus a hemicellulose-rich liquid stream which are then converted to monomeric sugars in separate process lines. Saccharification of the pretreated glucan-rich substrate using a low (for softwoods) enzymes dose after two-stage attrition affords a syrup containing monomeric sugars and a lignin-rich solid residue.  The hemicellulose-rich steam is converted without enzymes to sugars which may be added to the final sugar syrup to provide a high overall sugar yield.  The mild pretreatment conditions used during the process result is a sugar syrup containing only low levels of fermentation inhibitors and a lignin product that analysis suggests has undergone only limited modification during pretreatment.  Another attractive feature of the process is that it uses only standard equipment that is largely proven at commercial scale, which reduces risks during commercialisation.