Techno-economic analysis of the deacetylation and disk refining process: characterizing the effect of refining energy and enzyme usage on minimum sugar selling price and minimum ethanol selling price

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.

Improving Sugar Yields and Reducing Enzyme Loadings in the Deacetylation and Mechanical Refining (DMR) Process through Multistage Disk and Szego Refining and Corresponding Techno-Economic Analysis

“…In our previous work, the TEA analysis showed refining energies over 200 kWh/ODMT will require a bioethanol plant to purchase electricity from the grid due to the high energy demand. 13 External energy input not only increases the sugar and final product costs, but also increases the greenhouse gas emissions. In addition, refining energy could also affect the biomass digestibility.…”

“…Previous TEA work revealed that enzyme loading at 20 mg total protein per gram of cellulose (14 FPU or 0.074 mL CTec3 product/g of cellulose) may not be economic because of the large tank volume needed and the associated high cost for air. 13 Therefore, we investigated the multistage SM-DRDCS process for potential reductions in enzyme loading. Figure 5 shows the enzymatic sugar yields using the SM-DRDCS-1 substrate at cellulase/hemicellulase enzyme loadings of 5, 10, 15, and 20 mg of total protein per gram of cellulose in the refined residues.…”

“…11 Sugar yields of approximately 80% are cost-effective enough in biofuels production according to the techno-economic analysis (TEA). 13 A recent paper showed that the minimum sugar selling price (MSSP) of the DMR process increases linearly with increasing refining energy and enzyme usage, indicating the 2−4% sugar yield increase (79% to 83% for increasing disk refiner input energy from 128 to 468 kWh/ ODMT) will be offset against the increased cost of electricity (2−4 times) and enzymes (1.5−2 times). 13 Therefore, to reduce further the MSSP, additional improvements in sugar yields are needed, while keeping the same or reducing the refining energy applied and reducing the enzyme loadings.…”

“…13 A recent paper showed that the minimum sugar selling price (MSSP) of the DMR process increases linearly with increasing refining energy and enzyme usage, indicating the 2−4% sugar yield increase (79% to 83% for increasing disk refiner input energy from 128 to 468 kWh/ ODMT) will be offset against the increased cost of electricity (2−4 times) and enzymes (1.5−2 times). 13 Therefore, to reduce further the MSSP, additional improvements in sugar yields are needed, while keeping the same or reducing the refining energy applied and reducing the enzyme loadings. To accomplish this goal, a better refining and enzymatic yield outcome at lower refining energy consumptions is key to the success of this process.…”

The costs of sugar production from different feedstocks and processing technologies

“…Pretreatment and hydrolysis expenditure accounts for 20% of the total capital and operating costs of biorefining and is only eclipsed by material and feedstock costs . Low‐cost sugar production is regarded as the primary driver for the use of biomass feedstocks to produce biofuels and other biobased chemicals, such as furfural, 5‐HMF, and levulinic acid, in the biorefining industry …”