Pilot scale production of fermentable sugars from corn stover via distributed preprocessing

The logistics of supplying large (2,000+ ton/day) biorefineries with bulky, lightweight agricultural residues is a key challenge for the nascent cellulosic bioeconomy.  AFEX pretreatment of biomass at smaller depots (100-200 ton/day) followed by densification into pellets is an alternative model that can positively impact feedstock logistics.  These pellets can be handled in a manner similar to corn grain, and are directly hydrolyzed and fermented at a centralized biorefinery.  MBI is currently focused on derisking AFEX pretreatment, densification, and end-use application testing (cellulosic sugars and cattle feed). Fundraising efforts are also underway to support the construction and demonstration of the pioneer commercial-scale AFEX depot. 

In this presentation, we describe a simple, effective bale-to-sugar process that has been demonstrated at the pilot scale under commercially relevant conditions.  AFEX treatment and subsequent pelletization of corn stover resulted in a stable, storable, consistent feedstock for further processing.  Pelletization improved mixing, allowing up to 22% w/w solid loading during enzymatic hydrolysis.  This system results in rapid hydrolysis, releasing 90% of the total glucan in 30 hours.  As an example of end-use testing, fermentation of glucose and xylose to ethanol using Zymomonas mobilis 8b was complete within 30 hours, with an overall productivity of >2.5 g/L/h ethanol and a final titer of >60 g/L.  Despite using non-sterile pellets, no contamination issues were observed.  Sugars from AFEX-treated corn stover pellets were also observed to be highly fermentable for other organisms and final products as well.  Costs and sustainability criteria for these sugars will also be considered.