10-49: Optimization of the dilute-phosphoric-acid-pretreatment of Eucalyptus using design of experiments

Previous studies from our group have successfully used phosphoric acid for the pretreatment of sugarcane bagasse.  When we used the optimal conditions for the pretreatment of sugarcane bagasse to pretreat Eucalyptus benthamii, the xylose released from hemicellulose degradation was ~35%, confirming that pretreatment optimization was required for Eucalyptus.  Therefore, we decided to use a Box–Behnken design of experiments to optimize the pretreatment condition of Eucalyptus benthamii.  The range of the conditions chosen for the design was from 5 – 15 min retention time, 0.5 – 1.0% phosphoric acid soak, and 180 – 200°C.  Additional experiments were conducted using the pretreated material to do an enzymatic reaction (Novozyme Cellic CTec2; 50°C, pH 5.0).  Two separate models were developed, one using the pretreatment data and the other with the enzymatic hydrolysis results, in order to maximize sugar content while minimizing inhibitor concentrations.  The models resulted in two optimal conditions; 200°C, 0.5% acid soak, 10 min retention time (Condition A) for the model using the pretreatment data, and 200°C, 0.8% acid soak, 5 min retention time (Condition B) for the model using the enzyme hydrolysis data.  Using these conditions the xylose yield was increased to ~50% and ~60% for Condition A and Condition B respectively after pretreatment.  These conditions were then tested with four different genotypes of Eucalyptus grandis resulting in yields ranging from ~47% – 70% for Condition A, and from ~50% – 77% for Condition B.  Thanks to Florida Crystals for providing the Eucalyptus grandis used for this study.