Bioreactor performance data and preliminary biorefinery techno-economics for the production of distillate fuels via bioconversion of pretreated corn stover by Lipomyces starkeyi.

The bioconversion of pretreated corn stover (PCS) to triglyceride lipids by the oleaginous yeast Lipomyces starkeyi, and the subsequent upgrading of the lipids to distillate hydrocarbons, were modeled within CHEMCAD to identify techno-economic factors that must be optimized to enable biorefinery production of diesel and jet fuels with a minimum fuel selling price (MFSP) of $3/gallon of gasoline equivalent (gge). Microbial growth and lipid synthesis parameters for the model were drawn from our own laboratory cultivations of L. starkeyi grown in 20-liter bioreactors on hydrolyzed PCS to simulate actual biorefinery operations, such as seed train inoculum scale-up and fed-batch cultivations.  The resulting data were integrated with lipid extraction and upgrading data from the literature to develop a Base Case biorefinery process model that estimated the current plant gate MFSP for a distillate-range hydrocarbon fuel to be $9/gge, with  assumptions of 2011 $US, 10% internal return on investment, and 2205 ton/day dry feed rate.  Maximum biochemically feasible yield predictions from a preliminary L. starkeyi metabolic model and sensitivity analysis of biorefinery financial and technical assumptions were used to develop an interim Target Case model with an MFSP of $5.5/gge. Increasing bioconversion lipid yields, reducing bioreactor residence times, and improving hydrogenation catalyst selectivity for lipid upgrading were among the most import factors for attaining the Target Case MFSP. Possible options for reducing the MFSP toward $3/gallon by finding higher value uses for lignin other than power generation will be discussed.