Abstract
BackgroundA novel, highly efficient deacetylation and disk refining (DDR) process to liberate fermentable sugars from biomass was recently developed at the National Renewable Energy Laboratory (NREL). The DDR process consists of a mild, dilute alkaline deacetylation step followed by low-energy-consumption disk refining. The DDR corn stover substrates achieved high process sugar conversion yields, at low to modest enzyme loadings, and also produced high sugar concentration syrups at high initial insoluble solid loadings. The sugar syrups derived from corn stover are highly fermentable due to low concentrations of fermentation inhibitors. The objective of this work is to evaluate the economic feasibility of the DDR process through a techno-economic analysis (TEA).ResultsA large array of experiments designed using a response surface methodology was carried out to investigate the two major cost-driven operational parameters of the novel DDR process: refining energy and enzyme loadings. The boundary conditions for refining energy (128–468 kWh/ODMT), cellulase (Novozyme’s CTec3) loading (11.6–28.4 mg total protein/g of cellulose), and hemicellulase (Novozyme’s HTec3) loading (0–5 mg total protein/g of cellulose) were chosen to cover the most commercially practical operating conditions. The sugar and ethanol yields were modeled with good adequacy, showing a positive linear correlation between those yields and refining energy and enzyme loadings. The ethanol yields ranged from 77 to 89 gallons/ODMT of corn stover. The minimum sugar selling price (MSSP) ranged from $0.191 to $0.212 per lb of 50 % concentrated monomeric sugars, while the minimum ethanol selling price (MESP) ranged from $2.24 to $2.54 per gallon of ethanol.ConclusionsThe DDR process concept is evaluated for economic feasibility through TEA. The MSSP and MESP of the DDR process falls within a range similar to that found with the deacetylation/dilute acid pretreatment process modeled in NREL’s 2011 design report. The DDR process is a much simpler process that requires less capital and maintenance costs when compared to conventional chemical pretreatments with pressure vessels. As a result, we feel the DDR process should be considered as an option for future biorefineries with great potential to be more cost-effective.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0358-0) contains supplementary material, which is available to authorized users.
Highlights
A novel, highly efficient deacetylation and disk refining (DDR) process to liberate fermentable sugars from biomass was recently developed at the National Renewable Energy Laboratory (NREL)
The minimum sugar selling price (MSSP) and minimum ethanol selling price (MESP) of the DDR process falls within a range similar to that found with the deacetylation/dilute acid pretreatment process modeled in NREL’s 2011 design report
The DDR process is a much simpler process that requires less capital and maintenance costs when compared to conventional chemical pretreatments with pressure vessels
Summary
A novel, highly efficient deacetylation and disk refining (DDR) process to liberate fermentable sugars from biomass was recently developed at the National Renewable Energy Laboratory (NREL). The DDR corn stover substrates achieved high process sugar conversion yields, at low to modest enzyme loadings, and produced high sugar concentration syrups at high initial insoluble solid loadings. While the cost of renewable biofuels is heavily impacted by the market price and availability of biomass feedstocks, the primary drivers for sugar production costs from lignocellulosic biomass are the processes and efficiencies of biomass pretreatment and enzymatic hydrolysis. In 2011, NREL generated a TEA model for estimating intermediate sugar production costs that reported a MSSP (i.e., $/lb) for a process that utilized dilute acid pretreatment, solid/liquid separation, and the concentration of the sugar syrups up to 50 wt% without further purification [1]. The model is helpful for the biofuels industry (mainly for non-ethanol producers) as a tool to compare feedstocks and pretreatment process costs [1]
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