(655a) Optimization of a Biomass Fractionation Process and Evaluation of Its Economic Feasibility

PureVision Technology, Inc.'s two-stage process fractionates biomass into three streams: a solid cellulose stream and two liquid streams containing mostly hemicellulosic sugars and lignin, respectively. Process optimization was initiated for both stages using corn stover as feedstock in a continuous process development unit (PDU) with the goals of efficient hemicellulosic and lignin hydrolysis for the first and second stage, respectively. Both autohydrolysis and acid-catalyzed prehydrolysis were evaluated for the first stage, and autohydrolysis was selected as the preferred mode for the first stage. Although autohydrolysis achieves lower xylose recovery (about 65% at 210C) compared to acid-catalyzed pretreatment, it also offers benefits including: 1) no cost of acid, 2) cheaper materials of construction, 3) no gypsum formation and related disposal and handling costs, and 4) no need for L/S separation after liquor conditioning. For the second stage, 220C was determined to be optimal with NaOH charge being 0.06 g/g biomass, which is half of that in the kraft process. Using the level of performance currently possible using the PDU, economic feasibility of the PureVision process for ethanol production was compared to that of the NREL process. Major differences between the two scenarios are that the PureVision process generates lignin as a sellable output but needs to replace the lost fuel value of the lignin with additional stover. An average lignin selling price of $330/mt is used based on lower end applications such as concrete binder ($250/short ton) and feed binder ($350?425/short ton). The minimum ethanol selling price (MESP), calculated following the NREL protocol, is projected to be lower for the PureVision process than that for the NREL process, the differential depending on lignin selling price. Potential for further lowering the MESP exists by reducing NaOH usage by tweaking the second stage parameters, and by reducing corn stover consumption for fuel by fully optimizing the turbogenerator operation. As these changes are within practical realm, PureVision's process is economically attractive and has excellent commercial potential.