Pilot-Scale Pretreatment of Forest Residue by SPORL: Process Scale-up Design and Inhibitor Reduction for High Solids Fermentation without Detoxification

Sulfite Pretreatment to Overcome the Recalcitrance of Lignocelluloses (SPORL) has demonstrated robust performance for effective bioconversion of forest biomass.  We will present SPORL pretreatment forest residue at pilot scale.  Laboratory scale pretreatments of 150 g residue were first conducted in a range of temperatures, sulfite and acid loadings, and times.  Optimal pretreatment for sugar yield at 180°C for 30 min using 12%  sulfite on wood and pH=2 was identified.  A combined hydrolysis factor (CHF) was developed as a severity factor to scale-up pretreatment of 50 kg Douglas-fir forest residue using a pilot scale wood pulping digester of 375 L. The same CHF = 22.5 based on the optimal lab scale pretreatment was used to design pilot scale pretreatment at a low temperature of 165°C for 75 min to balance inhibitor formation and sugar yield.  The same chemical loading and liquor to wood ratio of 3 as those for the optimal pretreatment was used.  The pretreated solids was blown into a tank and disk-milled. Noncondensable such as SO₂ were wet scrubbed.  HMF and furfural concentration were only 0.84 and 0.96 g/L, respectively, significantly lower than 2.12 and 2.23 g/L for the lab scale optimal run.  Excellent total glucose yield of 87% was achieved with mannose recovery of 71%.  The unwashed milled-solids and liquor (whole slurry) were combined for direct simultaneous saccharification and combined fermentation without detoxification using CTec3 at 0.7 g/g glucan using YRH400.  Excellent ethanol yield of over 291 L/ton wood at high titer of 49 g/L were achieved.