Technical Memorandum 

To: National Bioenergy Center 

Title: Technoeconomic Modeling to Support the EPA Notice of Proposed 

Rulemaking (NOPR) 

Author: Ling Tao and Andy Aden 

Platform: Process Analysis 

Date: November 3rd, 2008 

Abstract: Under the Interagency Agreement between the Environmental 

Protection Agency (EPA) and U.S. Department of Energy (DOE), a 

statement of work (SOW) was established to generate “Cellulosic 

Process and Cost Analysis”. Three biochemical technoeconomic 

scenarios have been developed for this work to date, corresponding to 

years 2010, 2015 and 2022. The material and energy balances 

contained in the report were generated using Aspen Plus models. 

Economic calculations are done by in house databank and tools in a 

spreadsheet framework. Using a discounted cash flow rate of return 

analysis, the minimum ethanol selling prices (MESP) are $2.43, $1.33 

and $1.21 per gal ethanol with respect to model 2010, 2015 and 2022. 

Keywords: State of Technology, Emission, Cost, Design Report, Ethanol, 

Biochemical, EPA, MESP 

Background:

Under the Interagency Agreement between the Environmental Protection Agency 

(EPA) and U.S. Department of Energy (DOE), a statement of work (SOW) was 

established to generate “Cellulosic Process and Cost Analysis”. Task 1 under this 

SOW pertains to the development of the preferred scenarios that NREL engineers 

will develop technoeconomic models for. Discussions between NREL and EPA have 

led to agreement on the set of scenarios to be modeled as part of this project. This 

memo is a summarization of those scenarios per the deliverable under Task 1. 

A total of 6 technoeconomic models will be developed as part of this effort. This is 

shown in Table 1. Three of the models use a biochemical platform to produce fuel 

ethanol from corn stover, and three of the models use a thermochemical platform 

- 1 - 
to produce Fischer-Tropsch fuels from woody feedstocks. These models cover 3 

specific timeframes: 2010, 2015, and 2022. Economics will be reported using 

year-$2007 estimated. 

Each of these 6 models will assume a 2000 dry metric tonnes-per-day feedrate of 

biomass. The process configurations for the respective biochemical and 

thermochemical processes have been generally documented in two design reports. 

The primary difference is that the thermochemical design report targets mixed 

alcohols production high ethanol concentration instead of Fischer-Tropsch (FT) 

fuels. 

Process Feedstock 2010 2015 2022 

Biochemical Corn Stover Model 1 – 

Ethanol 

Model 2 – 

Ethanol 

Model 3 – 

Ethanol 

Thermochemical Wood Model 4 – FT Model 5 – FT Model 6 – FT 

Table 1 – Summary of Modeled Scenarios 

Biochemical – http://www.nrel.gov/docs/fy02osti/32438.pdf 1 

Thermochemical – http://www.nrel.gov/docs/fy07osti/41168.pdf 2 

The Biochemical Scenarios were listed as the highest priority. These will be 

completed first. The thermochemical models will entail a higher degree of modeling 

development since the mixed alcohol designs must be converted to FischerTropsch. The reasoning behind the decision to target FT fuels instead of mixed 

alcohols needs to be summarized if this indeed becomes the final decision. 

Standard economic assumptions in these models include: 

♦ 10% IRR 

♦ 100% equity financing 

♦ 20-year plant life 

♦ IRS MACRS depreciation accounting system (not straight-line) 

♦ Depreciation period = 7 years general plant, 20 years steam & utilities 

♦ Income Tax Rate 39% 

♦ Construction and startup period = 3.0 years 

♦ Nth plant assumption – no extra costs included for first-of-a-kind pioneer 

plant “over-engineering”. 

In addition to delivering the actual models to EPA, the following results will also be 

delivered for each model: 

♦ Yield (gallon per dry ton) 

♦ Minimum Ethanol Selling Price (MESP, $/gallon ethanol) 

♦ Annual Production (MM gal/yr) 

♦ Total Project Investment and Total Installed Cost ($MM) 

♦ Assumed Feedstock Cost ($/dry ton) delivered 

In order to quantify progress towards programmatic cost targets, analysts at NREL 

have developed what are known as State of Technology (SOT) assessments. These 

- 2 - 
- 3 - 

could also be thought of as “experimentally verified” cases since the data supplying 

these models is generated from actual bench- and pilot-scale experiments. In this 

fashion, the actual data is input into the technoeconomic models to assess what the 

plant economics might be if research results were scaled to commercial scale. As 

the SOT costs reduce over time, progress can easily be quantified as can the level 

of challenge remaining. The 2007 Biochemical State of Technology Assessment 

was recently published as an NREL report and can be found at 

http://www.nrel.gov/docs/fy08osti/43205.pdf 3

. The MESP was calculated to be 

$2.43/gallon (year 2007 estimated dollar). This model and data will serve as Model 

1 under the biochemical 2010 scenario. This makes sense because of the assumed 

construction and startup period of 3 years. Similarly, NREL will also use its market 

target model, which contains process parameters and targets for 2012, to serve as 

the 2015 scenario models. The 2022 models will need to be developed. 

The relationship of these SOT values are shown with respect to DOE Budget and 

Cost Targets in Figure 1 and 2. The cost target for year 2010 is consistent with the 

value proposed for the 2007 SOT3

 and the value for year 2015 is consistent with the 

Market Target case from the Aden, et. al. design report1

.

Methodology and approach:

Process economics requires a wide range of detailed studies, including conceptual 

level of process design to develop process flow diagram (based on research data 

from NREL and other data sources), rigorous materials and energy balance 

calculations (via commercial simulation tools, Aspen Plus), Capital and project cost 

estimation (via in house model using spreadsheets), discounted cash flow economic 

model (via in house model using spreadsheets) and then a final calculation of 

minimum ethanol selling price. 

Conceptual design refers to the engineering decision-making that is required to 

conceive a process from information on the products, feeds, and chemical and 

physical steps proposed as a basis (Douglas 19894

). The effective use of conceptual 

design methods in the early stages of process design can have a large impact on 

overall process design and development. There are frequently many processes 

alternatives that can be chosen and many design variables to specify. Conceptual 

design approaches practically always include both assumptions and heuristics along 

with numerical modeling and optimization techniques. Overall process design basis 

has been determined based on years of NREL research. The process design 

presented here for model 2010, has reflected the best available estimates for 

performance of an enzyme based process with the current status of our research 

efforts. Basis of the process includes four steps: 

I. Conversion of feedstocks to sugar. We have used corn stover as the feedstock 

exclusively in this study. Small variations to the process simulation and overall 

process conceptual level design are required if different feedstocks are 

introduced, such as switchgrass, miscanthus. The approach used to accomplish 

this step normally distinguishes different process technologies (or 

configurations) for the overall process design, since it is the most critical and 

challenging step. 
II. Fermentation sugar to ethanol. The fermenting organism Zymomonas mobilis

is used in our research and is well studied organism for sugar fermentation. 

III. Ethanol recovery area. High purity of ethanol is produced with 99.5 wt% in the 

recovery area, using distillation columns, molecular sieve unit and water 

evaporation units. Although it is an energy intensive operation, the 

temperature gradient from the first distillation column (or called beer column) 

can be used as a driving force for energy intensification in the area. Recycled 

water streams with reasonable levels of impurities are introduced into different 

areas such as pretreatment of feedstocks, in order to optimize the water 

and/or steam usage. 

IV. Residue utilization. The solids from distillation, the concentrated syrup from the 

evaporator, and the biogas from anaerobic digestion are combusted in a 

fluidized bed combustor to produce high pressure steam for electricity 

production and provide process steam or heat. Excess electricity credits are 

collected in the cost analysis. 

Overall design flow diagram is simplified in the following Figure: 

Feedstock Handling

Corn Stover Steam & 

Acid

Pretreatment

Conditioning

Steam

Electricity

Burner/Boiler

Turbogenerator

Ethanol

Distillation &

Ethanol Purification

Steam

Lime

Gypsum

CO2 Enzyme

Saccharification

&

Fermentation

Lignin

Residue

Wastewater

Treatment

Dewatering

Recycle

Feedstock Handling

Corn Stover Steam & 

Acid

Pretreatment

Conditioning

Steam

Electricity

Burner/Boiler

Turbogenerator

Ethanol

Distillation &

Ethanol Purification

Steam

Lime

Gypsum

CO2 Enzyme

Saccharification

&

Fermentation

CO2 Enzyme

Saccharification

&

Fermentation

Lignin

Residue

Wastewater

Treatment

Dewatering

Recycle

Lignin

Residue

Wastewater

Treatment

Dewatering

Recycle

Figure 1 – Schematic process flow diagram from corn stover to ethanol 1 

Brief Process Description: This design uses dilute acid pretreatment followed by 

enzymatic hydrolysis and co-fermentation with recombinant Zymomonas mobilis. 

The corn stover (or biomass) is first treated with dilute sulfuric acid catalyst at a 

high temperature (190  ̊C) for a short time (average at 2 minutes), liberating the 

hemicelluloses sugars and other compounds. Before going into enzymatic 

hydrolysis, proper conditioning is required to detoxification to the enzyme and 

fermenting organisms. If overliming is used for conditioning, then a solid and liquid 

- 4 - 
separation step would follow to remove gypsum from the process. If ammonia is 

used, the neutralized salt remains in the liquor and would be forwarded to the next 

step without solid and liquid separation. Although the solid removal and liquid 

separation step for overlimed gypsum is beneficial to the overall capital cost, 

ammonia is much more expensive than lime; therefore, the overall cost in terms of 

MESP does not change much in either case. Detoxification is only applied to the 

liquor from pretreatment before charging into enzymatic hydrolysis. Solids from 

pretreatment will be internally washed before remixed with the detoxified liquor for 

simultaneous saccharification and fermentation. A purchased enzyme is added to 

the hydrolyzate at an optimized temperature for enzyme activity. In cases with 

higher temperature for saccharification than for fermentation, a cooling step is 

required to ensure growth of fermenting organism Zymomonas mobilis at anaerobic 

condition. Several days (total 3 to 7 days depending on the models or SOTs) are 

required to convert most of the cellulose and xylose to ethanol. The “beer” liquor 

with ~4-8wt% of ethanol is then sent to recovery unit to purify ethanol to the 

desired purity. The solids after fermentation are combusted in a fluidized bed 

combustor to produce high pressure steam for electricity credits and process heat. 

We chose to use the Aspen Plus simulation environment for our process simulator, 

which includes all the management and convergence of hundreds of steams and 

blocks. A detailed process diagram from conceptual design is provided. 

Combined process flow diagram and rigorous materials and energy data generated 

from Aspen Plus simulator are used to define detailed equipment sizes and costs 

using an in house spreadsheet model for capital cost. Please note that proper 

choices of equipment design and configurations are also critical, which internal 

processing technology research combined with outside engineering firm consulting 

were applied. Some purchased and installed costs for equipments are obtained from 

vendor quotes (and also inflated to 2007 dollar if the quote was obtained before 

year 2007). This exercise has been done for most of highly specialized units, such 

as fermentors. Other standard equipment unit costs are from the ICARUS cost 

estimation software. These units are normally pumps, heat exchangers, etc. The 

summary of the capital costs of each major operation area for all three models is 

listed in the following Table: 

Capital Costs 2010 2015 2022

 Pretreatment $23,000,000 $22,700,000 $19,000,000

 Neutralization/Conditioning $8,400,000 $9,400,000 $7,600,000

 Saccharification & Fermentation $20,500,000 $11,200,000 $10,100,000

 Distillation and Solids Recovery $23,400,000 $26,100,000 $23,300,000

 Wastewater Treatment $3,400,000 $3,700,000 $3,100,000

 Storage $3,800,000 $2,400,000 $2,500,000

 Boiler/Turbogenerator $45,500,000 $46,000,000 $43,200,000

 Utilities $5,600,000 $5,500,000 $5,300,000

Total Installed Equipment Cost $133,500,000 $127,000,000 $114,000,000

- 5 - 
Table 2 – Summary of capital cost for all three models

Operation cost (fixed and variable costs) is summarized in the following table for all 

three models: 

 ($/yr) ($/gal Ethanol) ($/yr) ($/gal Ethanol) ($/yr) ($/gal Ethanol)

Feedstock $46,400,000 0.84 $35,400,000 0.51 $35,400,000 0.50

CSL $7,700,000 0.14 $2,100,000 0.03 $1,700,000 0.02

Cellulase $17,900,000 0.32 $6,800,000 0.10 $5,400,000 0.08

Other Raw Matl. Costs $17,200,000 0.31 $3,700,000 0.05 $10,900,000 0.15

Waste Disposal $1,000,000 0.02 $2,700,000 0.04 $1,000,000 0.01

Electricity -$5,800,000 -0.10 -$6,500,000 -0.09 -$11,300,000 -0.16

Fixed Costs $8,900,000 0.16 $8,700,000 0.13 $8,200,000 0.12

Capital Depreciation $11,600,000 0.21 $11,000,000 0.16 $9,900,000 0.14

Average Income Tax $8,700,000 0.16 $8,300,000 0.12 $7,500,000 0.11

Average Return on Investment $21,300,000 0.38 $19,700,000 0.28 $17,800,000 0.25

Total $134,900,000 $2.43 $91,900,000 $1.33 $86,500,000 $1.21

2010 2015 2022

Operating Costs

Table 3 – Summary of operating cost for all three models

Once the capital and operational costs have been established, a discounted cash 

flow analysis can be used to determine the minimum selling price per gallon of 

ethanol produced. The discounted cash flow model calculates in iterations on the 

selling cost of ethanol until the net value of the overall design project is approaching 

zero. In Table 3, the minimum selling price per gallon of ethanol was calculated for 

each model studied in this report. 

General comparison among all three models: 

The 2015 scenario adapts the market target model used in 2002 design report, in 

which an overliming step was used to condition the pretreated biomass prior to 

enzymatic hydrolysis. Lime is added at greater than stoichiometric amounts to 

both neutralize the sulfuric acid present, as well as to further detoxify the material 

through mechanisms that are not fully understood. The benefit is that lime is 

cheap in comparison against other potential conditioning agents. Overliming 

conditioning has a potential of high sugar degradation resulting in yield loss. 

Overliming also has mixing challenges due to the insoluble nature of the lime. 

Gypsum precipitates out of solution. This can be a potentially large solid waste 

emission point. Since that time, NREL has researched alternate conditioning 

technologies, particularly ammonium hydroxide. While ammonium hydroxide as a 

conditioning agent is more expensive than lime, it is able to be used on the entire 

slurry. Not only it does not have mixing issue, but also the solid liquid separation 

unit can be removed because ammonium salts are soluble. The main benefit is that 

it greatly minimizes the sugar degradation losses seen in overliming, and has 

potential nutritive benefits downstream in fermentation. However, the fate of the 

ammoniated species downstream in the process has not been thoroughly explored. 

The potential for increased NOx, SOx emissions in the flue gas or for higher loading 

to wastewater treatment are both possibilities. The 2010 and 2022 scenarios both 

assume ammonium hydroxide conditioning, while the 2015 scenario assumes 

overliming conditioning. As a result of this variation, NREL data shows that the 

"other raw materials" category drops from 31.1 cents-per-gallon in 2010 to 5.4 

cents in 2015 and rises back to 16.2 cents in 2022. Much of this is due to the 

- 6 - 
difference in costs between lime and ammonia assumed in the models. Also, note 

that the waste disposal costs rise from 1.9 cents per gallon to 4 cents and drops 

back down to 1.5 cents. Again, much of this is due to the increased cost of gypsum 

disposal in the 2012 scenario where overliming is used. 

Detailed discussion:

1. Model 2010 

This model uses 2007 State of Technology SOT assumptions, assuming three years 

of construction and start-up in 2007. 

Figure 2 - “Back Cast” State of Technology Cases 2007 3 

- 7 - 
2005

Post EnzymeSubcontract

2007 2008 2009 2010 2011

2012 

Market 

Target

Minimum Ethanol Selling Price $2.52 $2.43 $1.33

TPI/Annual Gallon $4.79 $4.17 $3.17 

Yield (Gallon/dry ton) 65 72 90

Feedstock

Feedstock Cost ($/dry ton) $60 $60 $60 $46

Pretreatment

 Solids Loading (wt%) 30% 30% 30% 30% 30% 30% 30%

 Xylan to Xylose 63% 75% 75% 75% 85% 90% 90%

 Xylan to Degradation Products 0% 13% 8% 6% 6% 6% 0%

Conditioning

 Xylose Sugar Loss 13% 2% 2% 2% 2% 1% 1%

 Glucose Sugar Loss 12% 1% 1% 1% 1% 1% 0%

Enzymes

Enzyme Contribution ($/gal EtOH) $0.32 $0.32 $0.32 $0.32 $0.16 $0.10 $0.10

Saccharification & Fermentation 

 Total Solids Loading (wt%) 20% 20% 20% 20% 20% 20% 20%

 Combined Saccharification & 

Fermentation Time (d) 7 77753 3

 Overall Cellulose to Ethanol 0% 85% 85% 85% 85% 85% 85%

 Xylose to Ethanol 76% 76% 80% 80% 80% 85% 85%

 Minor Sugars to Ethanol 0% 0% 40% 40% 80% 85% 85%

Table 4 - State of Technology Cases 2007 Summary 3 

2. Model 2015 

This model uses 2012 market goal of “Cost effective cellulosic ethanol, $1.33/gal, as 

primary market goal of DOE programs, shown in Figure 1 and Table 2. Similar to 

2010 model, it is assumed three years of construction and start-up in 2012. Main 

cost reduction is from feedstock, enzyme pricing, as well as improvements on xylan, 

sugar yields. 

3. Model 2022 

Research beyond 2012 could be focused on the following area: Feedstocks, 

pretreatment processing technologies, advanced enzyme systems, advanced fuels, 

and advanced process system. For feedstock, more sustainable crops beyond corn 

stover (switchgrass, miscanthus, and many more) are needed, since there is a 

potential of cost increase due to increasing demand and larger distances for 

transportation. Research on transgenic crops could also provide further 

improvement in the area of feedstocks. In pretreatment, a lower cost in processing, 

less severe operational conditions are needed. This could be coupled with advanced 

enzymes, so combined yield in pretreatment, saccharification and fermentation 

- 8 - 
could be improved drastically. For advanced enzyme systems, research should be 

focused on advanced cellulase, hemicellulase and accessory enzymes. Other 

advanced fuels, such as butanol, hydrocarbon fuels, advanced ethanologens, can 

release the burden of the overall biofuel dependence solely on cellulosic ethanol. 

This would provide alternatives for future research. Higher solid loading to all the 

major reaction steps is always an exciting but challenging topic for process 

improvement in this biological conversion process for cellulosic ethanol. Additionally, 

the biochemical conversion process can be integrated with thermochemical 

conversion process using process intensification techniques, or using combined 

bioprocessing techniques. Therefore, with all the above ongoing research topics, we 

can assume the base design model of 2022 can be a dramatic process improvement 

on a variety of changes, such as enzyme cost, ethanol yield, sugar loss, minor sugar 

yield, etc. 

A summary of the base condition studied in model 2010, model 2015 and model 

2022 (assuming three years of construction and start-up in 2019 as well) are shown 

in Appendix A. 

4. Process concept comparison: 

Comparison of the previously reported SOT values (2010 model) and market goal 

values (2015 model) can be sensitive because underlying assumptions may be 

updated and improved from year to year. For example: 

• Total yield of ethanol per dry ton of biomass 

Theoretical yield of ethanol is 112.7 gal/ton dry basis of corn stover. The 

yield (and ethanol production) calculated based on the overall conversion is 

gradually increased over the years with R&D effects, as shown in the 

following table: 

MODEL YEAR 2010 2015 2022

Ethanol Production (MM Gal. / Year) 55.5 69.3 71.3

Ethanol Yield (Gal / Dry US Ton Feedstock) 71.9 89.8 92.3

Table 5 – Comparison of ethanol yield and production 

• Feedstock price 

The price of feedstock in FY 2005 SOT model was $53 per dry ton to the plant 

gate and was $60 per dry ton in FY 2007 SOT of overall delivered cost. The 

$46 per dry ton was based on President’s AEI goal in 2007 dollar. In this 

study, 2015 and 2022 models used $46 per dry ton, while 2010 model used 

$60 per dry ton feedstock delivered. 

MODEL YEAR 2010 2015 2022

Feedstock price ($/dry ton) 60 46 46

Table 6 – Comparison of feedstock pricing 

• The yield in pretreatment has been assumed to increase gradually over years 

of research efforts worldwide. The summary of yields of all three models are 

listed as following including all the basis operating conditions in the 

pretreatment area: 

- 9 - 
Pretreatment 2010 2015 2022

Acid Conc (wt%) 1.64% 1.64% 1.64%

Acid Loading (g acid/g dry biomass) 0.038 0.038 0.024

Total Solids (wt%) 29.8% 30.0% 40.0%

Temperature (°C) 190 190 190

Pressure (atm) 12 12 12

Conversions:

 Cellulose to Glucose 0.099 0.09 0.099

 Xylan to Xylose 0.75 0.9 0.9

 Xylan to Furfural 0.048 0.05 0.048

Minor surgar to monomer 0.75 0.9 0.9

Table 7 – Comparison of pretreatment operational conditions 

• The contamination ratio 

MODEL YEAR 2010 2015 2022

Contamination 7% 3% 1%

Table 8 – Comparison of contamination rate 

• The sugar loss due to severity of pretreatment condition 

In addition to contamination loss, sugar loss due to severity of pretreatment 

condition cannot be neglected. 

Conditioning 2010 2015 2022

Ca(OH)2 to Gypsum 5634 0 0

Sugar Conversion to TAR:

 Xylose 0.018 0.018 0

 Glucose 0.006 0.006 0

 Minor Sugars 0.006 0.006 0

Table 9 – Comparison of conditionings 

• Enzyme cost 

The cost of enzyme was used to be equivalent to 32, 10 and 8 cents per 

gallon ethanol produced, in model 2010, 2015 and 2022 respectively; 

assuming cutting edge technologies would be matured by then without any 

availability issues. 

MODEL YEAR 2010 2015 2022

Enzyme cost ($/gal Ethanol) 0.32 0.10 0.08

Table 10 – Comparison of enzyme costs 

• Saccharification conditions 

In addition to small changes in reaction conversion, the total solids have 

assumed to change dramatically to the out year model in 2022 to improve 

process intensification as well as to improve capital investment. 

Consequently, the total solids are different in model 2022 from models 2010 

and 2015 in fermentation. 

- 10 - 
Saccharification 2010 2015 2022

Enzyme Loading (mg/g cell) 5.5 20.0 20.0

Total Solids (wt%) 20.0% 20.0% 25.0%

Insoluble Solids (wt%) 11.4% 11.1% 13.2%

Temperature (°C) 32 65 35

Pressure (atm) 1 1 1

Residence Time (days) 5 1.5

Conversions:

 Cellulose to Glucolig 0.024 0.04 0.024

 Cellulose to Cellobiose 0 0.012 0

 Cellulose to Glucose 0.9 0.9 0.9

1.5

Table 11 – Comparison of Saccharification conditions 

• Fermentation conditions 

With higher solids level and improved yield in fermentation, the final ethanol 

concentration in the liquor out of the fermentors increased significantly. This 

results in improved energy efficiency in ethanol purification step. 

Fermentation 2010 2015 2022

Total Solids (wt%) 0.20 0.20 0.25

Insoluble Solids (wt%) 0.06 0.05 0.06

Temperature (°C) 32 32 32

Pressure (atm) 1 1 1

Residence Time (days) 2 1.5 1.5

Conversions:

 Glucose to Ethanol 0.95 0.95 0.95

 Glucose to Zymo 0.02 0.02 0.02

 Glucose to Glycerol 0.004 0.004 0.004

 Glucose to Succinic Acid 0.006 0.006 0.006

 Glucose to Acetic Acid 0.015 0.015 0.015

 Glucose to Lactic Acid 0.002 0.002 0.002

 Xylose to Ethanol 0.756 0.85 0.886

 Xylose to Zymo 0.019 0.019 0.019

 Xylose to Glycerol 0.003 0.003 0.003

 Xylose to Xylitol 0.046 0.046 0.046

 Xylose to Succinic Acid 0.009 0.009 0.009

 Xylose to Acetic Acid 0.014 0.014 0.014

 Xylose to Lactic Acid 0.002 0.002 0.002

 Minor Sugar to Ethanol 0 0.85 0.9

 Minor Sugar to Zymo 0 0.019 0.019

 Minor Sugar to Glycerol 0 0.003 0.003

 Minor Sugar to Succinic Acid 0 0.015 0.015

 Minor Sugar to Acetic Acid 0 0.014 0.014

 Arabinose to Lactic Acid 0 0.002 0.002

Contamination Loss 7% 3% 1%

Ethanol Out of Fermenters (wt%) 4.88% 6.21% 8.13%

Table 12 – Comparison of fermentation conditions 

• Emission data 

- 11 - 
 Boiler ash Fermentation off gas Flue gas 

Gypsum

waste Boiler ash 

Fermentation 

off gas Flue gas Boiler ash 

 Fermentation 

off gas Flue gas 

Mass Flow kg/hr 

Biomass 205.0 - 89.2 266.1 177.2 - 81.2 171.1 - 89.2

aldehydes - 0.0 2.1 3.4 - 0.0 1.3 - 0.0 2.1

Organic acid - 0.0 44.7 23.1 - 0.0 43.2 - 0.0 17.7

Nutrients - 0.0 4,660.0 1.1 - 0.0 1,406.5 - 0.0 1,146.4

Sugars - - 77.6 135.8 - - 33.3 - - 30.6

 ASH 4,308.9 - - 21.697 4,287.4 - 4,308.9 - - -

 H2O - 338.9 124,850.3 1261.205 - 432.3 68,749.3 - 433.0 74,660.5

 N2 - 265,393.6 0.3 0 - 0.3 206,378.0 - 0.3 220,115.0

 CO2 - 18,750.7 80,723.3 0 - 23,381.3 65,694.7 24,017.8 - 65,204.0

 O2 - 153.2 13,079.1 0 - 196.4 10,277.8 - 196.9 10,539.8

 CH4 - - 2.4 0 - - 2.8 - - 2.1

 NO - - - 0 - - - - - -

 NO2 - - 74.8 0 - - 60.9 - - 59.4

 SO2 - 0.0 9,424.0 0 - 0.0 100.3 - - 2,812.9

 CO - - 74.8 0 - - 60.9 - - 59.4

Others - 0.0 0.3 2.755 - 0.0 0.1 - 0.0 0.2

 H2SO4 - 4.3 0.1 0.217 - 4.3 0.0 - 4.3 0.1

 ETHANOL - - 0.6 12.027 - - 0.6 - - 0.6

Emission Data

2010 2015 2022

Table 13 – Comparison of emission data 

• Overall condition comparison 

2007

2012 

Market 

Target

2019 

Outyear 

Target

Minimum Ethanol Selling Price $2.43 $1.33 $1.21

TPI/Annual Gallon $4.17 $3.17 $2.79 

Yield (Gallon/dry ton) 72 90 92

Feedstock

Feedstock Cost ($/dry ton) $60 $46 $46

Pretreatment

 Solids Loading (wt%) 30% 30% 40%

 Xylan to Xylose 75% 90% 90%

 Xylan to Degradation Products 13% 5% 5%

Conditioning

 Xylose Sugar Loss 2% 1% 0%

 Glucose Sugar Loss 1% 0% 0%

Enzymes

Enzyme Contribution ($/gal EtOH) $0.32 $0.10 $0.08

Saccharification & Fermentation

 Total Solids Loading (wt%) 20% 20% 25%

 Combined Saccharification & 7 3 3

 Overall Cellulose to Ethanol 85% 85% 85%

 Xylose to Ethanol 76% 85% 90%

 Minor Sugars to Ethanol 0% 85% 90%

Table 14 – Comparison of overall conditions 

• Process economics overview 

Units 2010-BC 2015-BC 2022-BC

Minimum Ethanol Selling Price ($/gallon) ($/gallon) $2.43 $1.33 $1.21

Annual Production (MM gal/yr) (MM gallon/yr) 55.5 69.3 71.3

Yield (gallon ethanol / ton biomass) (gallon ethanol / dry ton biomass) 71.9 89.8 92.3

Total Installed Cost ($MM) $133.5 $127.0 $124.5

Total Project Investment ($MM) $231.7 $220.1 $202.9

Feedstock Cost ($ / dry ton) $60.10 $45.90 $45.90

Reference Model:

A0802A, 

T0808D

A0806H, 

T0808E T0809C

Table 16 – Comparison of overall process economics 

- 12 - 
An analysis was performed to “back cast” current knowledge to the previous years’ 

State of Technology cases so that the economic effects of improved technology 

demonstrations can more easily identified. The following are important features of 

the back-casting exercise: 

• All costs were put on a 2007 year estimated basis. 

• The feedstock composition used was that reported in the 2007 SOT3

. 

Feedstock costs were $60 per dry ton corn stover for model 2010 referenced 

to 2007 SOT, and they were maintained at $46 per dry ton corn stover for 

years in 2012 and beyond. More data would be available soon from feedstock 

design report by Idaho National Laboratory. 

• Cellulase costs were chosen to make cost equivalent to $0.32 to $0.08 per 

gal of ethanol depending on the model year. 

• Sugar losses from overliming was applied only to 2010 model and ammonia 

conditioning for models of 2015 and 2022, which leads to less sugar loss. 

• The solid separation step to remove gypsum is then removed for model 2015 

and 2022, resulting in slight reduction in equipment cost in pretreatment 

area. However, the ammonia is considerably more expensive than lime. 

5. Sensitivity study on the main effects for model 2022: 

Beyond year 2012, although the research targets are stated clearly, the uncertainty 

remains. It makes sense to research on how sensitive each main parameter on the 

final cost structure, therefore a sensitivity study using design of experiment 

statistical analysis is used. 

Seven main effects are selected for this study: 

I. Feedstock cost, from $45.9 to $60.1 per dry ton corn stover. 

II. Enzyme cost, adjusted to be equivalent to 5-10 cents per gal ethanol 

produced. 

III. Contamination ratio from 1 to 3%. 

IV. Sugar loss due to pretreatment condition from 25% to 50% of the values in 

2007 SOT. 

V. Xylan yield to xylose, mannan yield to mannose, galactan yield to galactose, 

arabinan yield to arabinose, from 80% to 90%. 

VI. Xylose yield to ethanol, from 80% to 90%. 

VII. Minor sugar yield to ethanol, from 80% to 90%. 

Feedstock 

price $/ton

Enzyme 

cost c/gal 

ETOH

contamination 

%

Sugar loss % 

of 2007SOT 

data

Xylan to 

Xylose 

yield %

Xylose to 

ethanol 

yield %

Minor 

sugar 

yield %

- 45.9 5 1 25 80 80 80

+ 60.1 10 3 50 90 90 90

Table 17 – Parameters (or Main effects) for full factorial design of 

experiments 

- 13 - 
The total sensitivity cases are 128 (27

) if each main effect is two-fold under full 

factorial design of experiment. Detailed statistical analysis refers to the Appendix A. 

The conclusions are listed as following: 

For MESP ($/gal ethanol): 

• All seven parameters are statistically significant main effects, and feedstock 

price is the strongest main effect among all in the studied data range. 

Figure 3 – Pareto chart for MESP $/gal 

• A number of binary effects are also statistically significant. An interaction plot 

shows the impact that changing the settlings of one factor has on another 

factor. Because an interaction can magnify or diminish main effects, 

evaluating interactions is extremely important. Whether an interaction effect 

is statistically important can also be judged by the P value in the Design of 

Experiment analysis (shown in Appendix B, interaction plot). For instance, 

there is no interaction effect between feedstock and enzyme costs, as shown 

in P value of 0.944, or shown in the interaction plot as almost perfect parallel 

lines of both. 

AB

CE

BD

BF

BG

BC

BE

AD

DG

EF

DE

CD

FG

CG

DF

CF

EG

AG

AC

AF

D

AE

G

C

F

B

E

A

0 200 400 600 800 1000 1200 1400 1600

Term

Standardized Effect

2

A F eedstock price $ /ton

B Enzy me cost c/gal ETO H

C contamination %

D Sugar loss % SO T

E Xy lan to Xy lose y ield %

F Xy lose to ethanol y ield %

G Minor sugar y ield %

Factor Name

Pareto Chart of the Standardized Effects

(response is ETOH cost $/gal, Alpha = 0.05)

Effect on MESP: 

A>>E>B>F>C>G>D

- 14 - 
45.9 60.1

152

144

136

5 10 1 3

25 50

152

144

136

80 90 80 90

80 90

152

144

136

Feedstock price $/ton

Mean

Enzy me cost c/gal ETO H contamination %

Sugar loss %SO T Xy lan to Xylose y ield % Xy lose to ethanol yield %

Minor sugar y ield %

Main Effects Plot for ETOH cost $/gal

Data Means

Figure 4 – Main effect chart for MESP $/gal. Leverage of individual main 

effect can be studied using this chart. 

• Please note that although main effects of contamination%, sugar loss 

percentage of values in 2007 SOT, and minor sugar yield% are relatively less 

significant to MESP ($/gal ethanol), it is due to the studied data range of 

these parameters is quite narrow. The statistical properties of all the main 

effect parameters are dependent strongly on the data range studied. In 

another word, if minor sugar yields are from 0 to 90%, it could be more 

statistically important than what is in this study. 

For percentage actual ethanol yield to theoretical yield: 

Feedstock and enzyme costs are not impacting the ethanol yield at all. Therefore, 

there are five parameters as main effects, as following: 

I. Contamination ratio from 1 to 3%. 

II. Sugar loss due to pretreatment condition from 25% to 50% of the values in 

2007 SOT. 

III. Xylan yield to xylose, mannan yield to mannose, galactan yield to galactose, 

arabinan yield to arabinose, from 80% to 90%. 

IV. Xylose yield to ethanol, from 80% to 90%. 

V. Minor sugar yield to ethanol, from 80% to 90%. 

The conclusions are listed as following: 

• All seven parameters are statistically significant main effects, and feedstock 

price is the strongest main effect among all in the studied data range. 

- 15 - 
CG

DF

CD

DG

FG

CF

DE

CE

EG

EF

D

G

C

F

E

0 100 200 300 400 500

Term

Standardized Effect

2.0

C contamination %

D Sugar loss %SO T

E Xylan to Xylose y ield %

F Xylose to ethanol y ield %

G Minor sugar y ield %

Factor Name

Pareto Chart of the Standardized Effects

response is Current Yield (Actual/Theoretical), Alpha = 0.05

Figure 5 – Pareto chart for ethanol yield 

1 3

0.79

0.78

0.77

0.76

25 50 80 90

80 90

0.79

0.78

0.77

0.76

80 90

contamination %

Mean

Sugar loss %SOT Xylan to Xylose yield %

Xylose to ethanol yield % Minor sugar yield %

Main Effects Plot for Current Yield (Actual/Theoretical)

Data Means

Figure 6 – Main effect chart for ethanol yield 

• A number of binary effects are also statistically significant. Binary effect chart 

is attached in Appendix B for reference. 

Please note that although main effects of contamination%, sugar loss percentage of 

values in 2007 SOT, and minor sugar yield% are relatively insignificant to MESP 

($/gal ethanol), it is due to the truly narrowed studied data range of these 

parameters. The statistical property of the each main effect is strongly influenced by 

the data range studied. 

- 16 - 
- 17 - 

Conclusion:

Three biochemical conversion models, model 2010, model 2015 and model 2022, 

from corn stover to ethanol were studied in this report. Each model has been 

studied from conceptual level of design, rigorous calculations of mass and energy 

balances using Aspen Plus simulation tools, detailed and logical capital cost to the 

final calculation of minimum selling price per gallon ethanol. Using a discounted 

cash flow rate of return analysis, the minimum ethanol selling prices (MESP) are 

$2.43, $1.33 and $1.21 per gal ethanol with respect to model 2010, 2015 and 

2022. Detailed comparison of process condition, operational condition and cost 

structures are discussed in the report. Particularly in model 2022, since there are 

too many known main effects on the final minimum selling price per gallon ethanol, 

a sensitivity study using full factorial Design of Experiments is applied to understand 

which main effect has the most significant impact, as well as to understand any 

existing binary effects. This sensitivity study result can help to lead future study. 

For instance, it is logical that feedstock price is the dominant main effect on 

minimum selling price per gallon ethanol, while the xylan yield is the dominant for 

overall ethanol yield in the cellulosic process. Binary effects based on this sensitivity 

study of data range are also statistically significant to both minimum selling price 

per gallon ethanol and overall ethanol yield. 

A similar study will be done for all three thermochemical conversion models 4, 5 and 

6 in Table 1. 

References:

1. Aden, A.; Ruth, M.; Ibsen, K.; Jechura, J.; Neeves, K.; Sheehan, J.; Wallace, R. 

Lignocellulosic Biomass to Ethanol Process Design and Economics Utilizing CoCurrent Dilute Acid Prehydrolysis and Enzymatic Hydrolysis For Corn Stover. NREL 

Report NREL/TP-510-32438, June 2002. 

http://www.nrel.gov/docs/fy02osti/32438.pdf 

2. Phillips, S.; Aden, A.; Jechura, J; Dayton, D. (2007). “Thermochemical Ethanol 

via Indirect Gasification and Mixed Alcohol Synthesis of Lignocellulosic Biomass.” 

National Renewable Energy Laboratory, Golden, CO. NREL Report No. TP-510-

41168. Http://www.nrel.gov/docs/fy07osti/41168.pdf

3. Aden, A. “FY07 State of Technology Update” (2007), 

http://devafdc.nrel.gov/bcfcdoc/10025.pdf 

4. Douglas, J. M., Conceptual Design of ChemicalProcesses, McGraw-Hill (1989 

 
Appendix A 

Pretreatment Saccharification Fermentation

Acid Conc (wt%) 0.0164 Enzyme Loading (mg/g cell) 5.5 Total Solids (wt%) 20.1%

Acid Loading (g acid/g dry biomass) 0.0381 Total Solids (wt%) 20.0% Insoluble Solids (wt%) 5.6%

Total Solids (wt%) 0.2976 Insoluble Solids (wt%) 11.4% Temperature (°C) 32

Temperature (°C) 190 Temperature (°C) 32 Pressure (atm) 1.0

Pressure (atm) 12.1 Pressure (atm) 1.0 Residence Time (days) 2

Residence Time (min.) Residence Time (days) 5 Conversions:

Conversions: Conversions: Glucose to Ethanol 0.95

 Cellulose to Glucolig 0.003 Cellulose to Glucolig 0.024 Glucose to Zymo 0.02

 Cellulose to Cellobiose 0 Cellulose to Cellobiose 0 Glucose to Glycerol 0.004

 Cellulose to Glucose 0.099 Cellulose to Glucose 0.9 Glucose to Succinic Acid 0.006

 Cellulose to HMF 0.003 Glucolig to Cellobiose 0 Glucose to Acetic Acid 0.015

 Xylan to Oligomer 0.06 Glucolig to Glucose 0 Glucose to Lactic Acid 0.002

 Xylan to Xylose 0.75 Cellobiose to Glucose 1 Xylose to Ethanol 0.756

 Xylan to Furfural 0.048 Xylan to Oligomer 0 Xylose to Zymo 0.019

 Xylan to Tar 0.085 Xylan to Xylose 0 Xylose to Glycerol 0.003

 Mannan to Oligomer 0.06 Xylose Oligomer to Xylose 0 Xylose to Xylitol 0.046

 Mannan to Mannose 0.75 Xylan to Tar 0 Xylose to Succinic Acid 0.009

 Mannan to HMF 0.048 Arabinan to Oligomer 0 Xylose to Acetic Acid 0.014

 Galactan to Oligomer 0.06 Arabinan to Arabinose 0 Xylose to Lactic Acid 0.002

 Galactan to Galactose 0.75 Galactan to Oligomer 0 Arabinose to Ethanol 0

 Galactan to HMF 0.048 Galactan to Galactose 0 Arabinose to Zymo 0

 Arabinan to Oligomer 0.06 Galactose Oligomer to Galactose 0 Arabinose to Glycerol 0

 Arabinan to Arabinose 0.75 Mannan to Oligomer 0 Arabinose to Succinic Acid 0

 Arabinan to Furfural 0.048 Mannan to Mannose 0 Arabinose to Acetic Acid 0

 Arabinan to Tar 0.085 Mannose Oligomer to Mannose 0 Arabinose to Lactic Acid 0

 Acetate to Oligomer 0 Galactose to Ethanol 0

 Acetate to Acetic Acid 1 Galactose to Zymo 0

 Furfural to Tar 1 Sugar & Solids Flow Rates (kg/hr) Galactose to Glycerol 0

 HMF to Tar 1 Soluble Sugars From PT 26,248 Galactose to Succinic Acid 0

 Lignin to Soluble Lignin 0.1 Other Soluble Solids From PT 11,446 Galactose to Acetic Acid 0

Soluble Sugars in Purchased Cellulase 0 Galactose to Lactic Acid 0

Other Sol Solids in Purchased Cellulase 0 Mannose to Ethanol 0

S/L Separation Soluble Sugars in Produced Cellulase 0 Mannose to Zymo 0

Water/Hydrolyzate Ratio (kg/kg) 0.58 Other Sol Solids in Produced Cellulase 0 Mannose to Glycerol 0

Water to S/L Separator (kg/hr) 136,268 Mannose to Succinic Acid 0

Dilution Water (kg/hr) 43,391 Soluble Sugars From Sacc 49,357 Mannose to Acetic Acid 0

Other Soluble Solids From Sacc 10,301 Mannose to Lactic Acid 0

Soluble Sugars From Seed Train 1,068

Other Soluble Solids From Seed Train 1,251 Contamination Loss 7.0%

Conditioning Soluble Sugars From DAP 0

Ca(OH)2 to Gypsum #N/A Other Soluble Solids From DAP 0 Ethanol Out of Fermenters (wt%) 4.9%

Sugar Conversion to TAR: Soluble Sugars From CSL 0

 Xylose 0.018 Other Soluble Solids From CSL 2,215

 Arabinose 0.018

 Glucose 0.006

 Galactose 0.006

 Mannose 0.006

 Cellobiose 0.006

Table A1 - Operation Condition in Model 2010

Reference: Aspen Model A0802A 

Tao and Aden 18
Pretreatment Saccharification Fermentation

Acid Conc (wt%) 0.0164 Enzyme Loading (mg/g cell) 20.0 Total Solids (wt%) 19.7%

Acid Loading (g acid/g dry biomass) 0.0377 Total Solids (wt%) 20.0% Insoluble Solids (wt%) 5.1%

Total Solids (wt%) 0.2996 Insoluble Solids (wt%) 11.1% Temperature (°C) 32

Temperature (°C) 190 Temperature (°C) 65 Pressure (atm) 1.0

Pressure (atm) 12.0 Pressure (atm) 1.0 Residence Time (days) 1.5

Residence Time (min.) Residence Time (days) 1.5 Conversions:

Conversions: Conversions: Glucose to Ethanol 0.95

 Cellulose to Glucolig 0.007 Cellulose to Glucolig 0.04 Glucose to Zymo 0.02

 Cellulose to Cellobiose 0.007 Cellulose to Cellobiose 0.012 Glucose to Glycerol 0.004

 Cellulose to Glucose 0.09 Cellulose to Glucose 0.9 Glucose to Succinic Acid 0.006

 Cellulose to HMF 0 Glucolig to Cellobiose 0 Glucose to Acetic Acid 0.015

 Xylan to Oligomer 0.025 Glucolig to Glucose 0 Glucose to Lactic Acid 0.002

 Xylan to Xylose 0.9 Cellobiose to Glucose 1 Xylose to Ethanol 0.85

 Xylan to Furfural 0.05 Xylan to Oligomer 0 Xylose to Zymo 0.019

 Xylan to Tar 0 Xylan to Xylose 0 Xylose to Glycerol 0.003

 Mannan to Oligomer 0.025 Xylose Oligomer to Xylose 0 Xylose to Xylitol 0.046

 Mannan to Mannose 0.9 Xylan to Tar 0 Xylose to Succinic Acid 0.009

 Mannan to HMF 0.05 Arabinan to Oligomer 0 Xylose to Acetic Acid 0.014

 Galactan to Oligomer 0.025 Arabinan to Arabinose 0 Xylose to Lactic Acid 0.002

 Galactan to Galactose 0.9 Galactan to Oligomer 0 Arabinose to Ethanol 0.85

 Galactan to HMF 0.05 Galactan to Galactose 0 Arabinose to Zymo 0.019

 Arabinan to Oligomer 0.025 Galactose Oligomer to Galactose 0 Arabinose to Glycerol 0.003

 Arabinan to Arabinose 0.9 Mannan to Oligomer 0 Arabinose to Succinic Acid 0.015

 Arabinan to Furfural 0.05 Mannan to Mannose 0 Arabinose to Acetic Acid 0.014

 Arabinan to Tar 0 Mannose Oligomer to Mannose 0 Arabinose to Lactic Acid 0.002

 Acetate to Oligomer 0 Galactose to Ethanol 0.85

 Acetate to Acetic Acid 1 Galactose to Zymo 0.019

 Furfural to Tar 1 Sugar & Solids Flow Rates (kg/hr) Galactose to Glycerol 0.003

 HMF to Tar 1 Soluble Sugars From PT 28,093 Galactose to Succinic Acid 0.015

 Lignin to Soluble Lignin 0.05 Other Soluble Solids From PT 10,529 Galactose to Acetic Acid 0.014

Soluble Sugars in Purchased Cellulase 0 Galactose to Lactic Acid 0.002

Other Sol Solids in Purchased Cellulase 0 Mannose to Ethanol 0.85

S/L Separation Soluble Sugars in Produced Cellulase 0 Mannose to Zymo 0.019

Water/Hydrolyzate Ratio (kg/kg) 0.58 Other Sol Solids in Produced Cellulase 0 Mannose to Glycerol 0.003

Water to S/L Separator (kg/hr) 135,470 Mannose to Succinic Acid 0.015

Dilution Water (kg/hr) 58,060 Soluble Sugars From Sacc 51,778 Mannose to Acetic Acid 0.014

Other Soluble Solids From Sacc 9,476 Mannose to Lactic Acid 0.002

Soluble Sugars From Seed Train 612

Other Soluble Solids From Seed Train 1,158 Contamination Loss 3.0%

Conditioning Soluble Sugars From DAP 0

Ca(OH)2 to Gypsum 0.000 Other Soluble Solids From DAP 0 Ethanol Out of Fermenters (wt%) 6.2%

Sugar Conversion to TAR: Soluble Sugars From CSL 0

 Xylose 0.018 Other Soluble Solids From CSL 545

 Arabinose 0.018

 Glucose 0.006

 Galactose 0.006

 Mannose 0.006

 Cellobiose 0.006

Table A 2 - Operation Condition in Model 2015

Reference: Aspen Model T0808E 

Tao and Aden 19
Table A3 - Operation Condition in Model 2022

Reference: Aspen Model T0809C 

Tao and Aden 20
Appendix B 

Minitab Project Report 

73.0% 74.0% 75.0% 76.0% 77.0% 78.0% 79.0% 80.0% 81.0% 82.0%

165

160

155

150

145

140

135

130

125

Current Yield (Actual/Theoretic

ETOH cost $/gal

Scatterplot of ETOH cost $/gal vs Current Yield (Actual/Theoretic

Factorial Fit: ETOH cost $/ versus Feedstock pr, Enzyme cost , ... 

Estimated Effects and Coefficients for ETOH cost $/gal (coded units) 

Term Effect Coef SE Coef T P 

Constant 144.119 0.005699 25289.68 0.000 

Feedstock price $/ton 16.515 8.257 0.005699 1448.97 0.000 

Enzyme cost c/gal ETOH 5.067 2.534 0.005699 444.60 0.000 

contamination % 2.431 1.216 0.005699 213.33 0.000 

Sugar loss %SOT 0.260 0.130 0.005699 22.78 0.000 

Xylan to Xylose yield % -6.217 -3.108 0.005699 -545.46 0.000 

Xylose to ethanol yield % -3.439 -1.719 0.005699 -301.71 0.000 

Minor sugar yield % -1.071 -0.536 0.005699 -94.01 0.000 

Feedstock price $/ton* 0.001 0.001 0.005699 0.11 0.914 

 Enzyme cost c/gal ETOH 

Feedstock price $/ton* 0.154 0.077 0.005699 13.51 0.000 

 contamination % 

Feedstock price $/ton* 0.017 0.008 0.005699 1.49 0.139 

 Sugar loss %SOT 

Feedstock price $/ton* -0.386 -0.193 0.005699 -33.91 0.000 

 Xylan to Xylose yield % 

Feedstock price $/ton* -0.220 -0.110 0.005699 -19.32 0.000 

 Xylose to ethanol yield % 

Tao and Aden 21
Feedstock price $/ton* -0.069 -0.035 0.005699 -6.06 0.000 

 Minor sugar yield % 

Enzyme cost c/gal ETOH* 0.005 0.003 0.005699 0.47 0.642 

 contamination % 

Enzyme cost c/gal ETOH* 0.002 0.001 0.005699 0.16 0.874 

 Sugar loss %SOT 

Enzyme cost c/gal ETOH* -0.008 -0.004 0.005699 -0.66 0.509 

 Xylan to Xylose yield % 

Enzyme cost c/gal ETOH* -0.002 -0.001 0.005699 -0.19 0.852 

 Xylose to ethanol yield % 

Enzyme cost c/gal ETOH* 0.003 0.001 0.005699 0.26 0.798 

 Minor sugar yield % 

contamination %*Sugar loss %SOT 0.035 0.017 0.005699 3.04 0.003 

contamination %* 0.002 0.001 0.005699 0.15 0.880 

 Xylan to Xylose yield % 

contamination %* 0.042 0.021 0.005699 3.68 0.000 

 Xylose to ethanol yield % 

contamination %*Minor sugar yield % -0.036 -0.018 0.005699 -3.13 0.002 

Sugar loss %SOT* 0.033 0.016 0.005699 2.86 0.005 

 Xylan to Xylose yield % 

Sugar loss %SOT* 0.036 0.018 0.005699 3.20 0.002 

 Xylose to ethanol yield % 

Sugar loss %SOT*Minor sugar yield % -0.022 -0.011 0.005699 -1.97 0.052 

Xylan to Xylose yield %* -0.030 -0.015 0.005699 -2.66 0.009 

 Xylose to ethanol yield % 

Xylan to Xylose yield %* -0.062 -0.031 0.005699 -5.48 0.000 

 Minor sugar yield % 

Xylose to ethanol yield %* -0.035 -0.018 0.005699 -3.08 0.003 

 Minor sugar yield % 

S = 0.0644737 PRESS = 0.687939 

R-Sq = 100.00% R-Sq(pred) = 99.99% R-Sq(adj) = 100.00% 

Analysis of Variance for ETOH cost $/gal (coded units) 

Source DF Seq SS Adj SS Adj MS F P 

Main Effects 7 11392.2 11392.2 1627.46 391513.15 0.000 

2-Way Interactions 21 7.7 7.7 0.37 87.93 0.000 

Residual Error 99 0.4 0.4 0.00 

Total 127 11400.3 

Estimated Coefficients for ETOH cost $/gal using data in uncoded units 

Term Coef 

Constant 104.520 

Feedstock price $/ton 1.94636 

Enzyme cost c/gal ETOH 1.03137 

contamination % 0.513596 

Sugar loss %SOT -0.0294059 

Xylan to Xylose yield % -0.183356 

Xylose to ethanol yield % -0.0869187 

Minor sugar yield % 0.123201 

Feedstock price $/ton* 0.000034794 

 Enzyme cost c/gal ETOH 

Feedstock price $/ton* 0.0108429 

 contamination % 

Feedstock price $/ton* 9.57699E-05 

 Sugar loss %SOT 

Feedstock price $/ton* -0.00544346 

Tao and Aden 22
 Xylan to Xylose yield % 

Feedstock price $/ton* -0.00310065 

 Xylose to ethanol yield % 

Feedstock price $/ton* -9.72426E-04 

 Minor sugar yield % 

Enzyme cost c/gal ETOH* 0.00106179 

 contamination % 

Enzyme cost c/gal ETOH* 0.000028986 

 Sugar loss %SOT 

Enzyme cost c/gal ETOH* -3.01962E-04 

 Xylan to Xylose yield % 

Enzyme cost c/gal ETOH* -8.53226E-05 

 Xylose to ethanol yield % 

Enzyme cost c/gal ETOH* 0.000117032 

 Minor sugar yield % 

contamination %*Sugar loss %SOT 0.00138582 

contamination %* 0.00017280 

 Xylan to Xylose yield % 

contamination %* 0.00418919 

 Xylose to ethanol yield % 

contamination %*Minor sugar yield % -0.00356814 

Sugar loss %SOT* 0.000261026 

 Xylan to Xylose yield % 

Sugar loss %SOT* 0.000291600 

 Xylose to ethanol yield % 

Sugar loss %SOT*Minor sugar yield % -1.79394E-04 

Xylan to Xylose yield %* -6.06842E-04 

 Xylose to ethanol yield % 

Xylan to Xylose yield %* -0.00124833 

 Minor sugar yield % 

Xylose to ethanol yield %* -7.02483E-04 

 Minor sugar yield % 

Least Squares Means for ETOH cost $/gal 

 Mean SE Mean 

Feedstock price $/ton 

 45.90 135.9 0.008059 

 60.10 152.4 0.008059 

Enzyme cost c/gal ETOH 

 5 141.6 0.008059 

 10 146.7 0.008059 

contamination % 

 1 142.9 0.008059 

 3 145.3 0.008059 

Sugar loss %SOT 

 25 144.0 0.008059 

 50 144.2 0.008059 

Xylan to Xylose yield % 

 80 147.2 0.008059 

 90 141.0 0.008059 

Xylose to ethanol yield % 

 80 145.8 0.008059 

 90 142.4 0.008059 

Minor sugar yield % 

 80 144.7 0.008059 

 90 143.6 0.008059 

 

Effects Pareto for ETOH cost $/gal 

Tao and Aden 23
AB

CE

BD

BF

BG

BC

BE

AD

DG

EF

DE

CD

FG

CG

DF

CF

EG

AG

AC

AF

D

AE

G

C

F

B

E

A

0 200 400 600 800 1000 1200 1400

Term

Standardized Effect

2

A Feedstock price $/ton

B Enzy me cost c/gal ETO H

C contamination %

D Sugar loss %SO T

E Xy lan to Xy lose y ield %

F Xy lose to ethanol y ield %

G Minor sugar y ield %

Factor Name

Pareto Chart of the Standardized Effects

(response is ETOH MESP $/gal, Alpha = 0.05)

Alias Structure (up to order 3) 

I 

Feedstock price $/ton 

Enzyme cost c/gal ETOH 

contamination % 

Sugar loss %SOT 

Xylan to Xylose yield % 

Xylose to ethanol yield % 

Minor sugar yield % 

Feedstock price $/ton*Enzyme cost c/gal ETOH 

Feedstock price $/ton*contamination % 

Feedstock price $/ton*Sugar loss %SOT 

Feedstock price $/ton*Xylan to Xylose yield % 

Feedstock price $/ton*Xylose to ethanol yield % 

Feedstock price $/ton*Minor sugar yield % 

Enzyme cost c/gal ETOH*contamination % 

Enzyme cost c/gal ETOH*Sugar loss %SOT 

Enzyme cost c/gal ETOH*Xylan to Xylose yield % 

Enzyme cost c/gal ETOH*Xylose to ethanol yield % 

Enzyme cost c/gal ETOH*Minor sugar yield % 

contamination %*Sugar loss %SOT 

contamination %*Xylan to Xylose yield % 

contamination %*Xylose to ethanol yield % 

contamination %*Minor sugar yield % 

Sugar loss %SOT*Xylan to Xylose yield % 

Sugar loss %SOT*Xylose to ethanol yield % 

Sugar loss %SOT*Minor sugar yield % 

Xylan to Xylose yield %*Xylose to ethanol yield % 

Xylan to Xylose yield %*Minor sugar yield % 

Xylose to ethanol yield %*Minor sugar yield % 

 

Tao and Aden 24
Residual Plots for ETOH cost $/gal 

-0.2 -0.1 0.0 0.1 0.2

99.9

99

90

50

10

1

0.1

Residual

Percent

130 140 150 160

0.2

0.1

0.0

-0.1

-0.2

Fitted Value

Residual

-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20

40

30

20

10

0

Residual

Frequency

120

110

100

90

80

70

60

50

40

30

20

1

1

0

0.2

0.1

0.0

-0.1

-0.2

Observation Order

Residual

Normal Probability Plot Versus Fits

Histogram Versus Order

Residual Plots for ETOH cost $/gal

 

Main Effects Plot for ETOH cost $/gal 

45.9 60.1

152

144

136

5 10 1 3

25 50

152

144

136

80 90 80 90

80 90

152

144

136

Feedstock price $/ton

Mean

Enzy me cost c/gal ETO H contamination %

Sugar loss %SO T Xy lan to Xy lose y ield % Xy lose to ethanol y ield %

Minor sugar y ield %

Main Effects Plot for ETOH cost $/gal

Data Means

Interaction Plot for ETOH cost $/gal 

Tao and Aden 25
5 10 31 25 50 80 90 80 90 80 90

150

140

130

150

140

130

150

140

130

150

140

130

150

140

130

150

140

130

Feedstock price $/ton

Enzyme cost c/gal ETOH

contamination %

Sugar loss %SOT

Xylan to Xylose yield %

Xylose to ethanol yield %

Minor sugar yield %

45.9

60.1

price $/ton

Feedstock

5

10

ETOH

c/gal

cost

Enzyme

1

3

contamination %

25

50

%SOT

loss

Sugar

80

90

yield %

Xylose

Xylan to

80

90

yield %

ethanol

Xylose to

Interaction Plot for ETOH cost $/gal

Data Means

 

Cube Plot (data means) for ETOH cost $/gal 

80 90

90

80

90

80

25 50

3

1

10

5

45.9 60.1

Minor sugar yield %

Xylose to ethanol yield %

Xylan to Xylose yield %

Sugar loss %SOT

contamination % Enzyme cost c/gal ETOH

Feedstock price $/ton

150.564

129.469 145.467

134.566

148.013

127.262 142.967

132.308

150.219

129.205 145.175

134.249

147.760

127.046 142.723

132.083

157.255

135.400 152.185

140.470 154.679

133.134 149.575

138.202 157.007

135.186 151.944

140.249 154.434

132.925 149.375

137.984

154.258

132.753 149.200

137.812 151.715

130.519 146.661

135.573 154.005

132.536 148.955

137.586 151.466

130.306 146.421

135.351

160.934

138.603 155.826

143.711

158.350

136.338 153.243

141.445

160.699

138.402 155.599

143.503

158.107

136.130 153.008

141.228

152.136

130.875 147.067

135.944

149.107

128.227 144.063

133.272

151.428

130.282 146.298

135.324

148.855

128.011 143.819

133.047

158.429

136.402 153.319

141.512 155.735

134.068 150.719

139.130 158.178

136.187 153.076

141.289 155.488

133.856 150.435

138.910

155.427

133.783 150.371

138.840 152.864

131.532 147.812

136.584 155.171

133.564 150.123

138.612 152.702

131.316 147.569

136.449

161.916

139.501 156.863

144.555

159.399

137.304 154.345

142.358

161.677

139.297 156.631

144.343

159.154

137.094 154.108

142.140

Cube Plot (data means) for ETOH cost $/gal

 

 

Tao and Aden 26
Factorial Fit: Current Yield versus contamination, Sugar loss %, ... 

Estimated Effects and Coefficients for Current Yield (Actual/Theoretic (coded 

 units) 

Term Effect Coef SE Coef T 

Constant 0.775719 0.000032 23981.30 

contamination % -0.014438 -0.007219 0.000032 -223.17 

Sugar loss %SOT -0.001562 -0.000781 0.000032 -24.15 

Xylan to Xylose yield % 0.036312 0.018156 0.000032 561.30 

Xylose to ethanol yield % 0.020813 0.010406 0.000032 321.71 

Minor sugar yield % 0.006437 0.003219 0.000032 99.51 

contamination %*Sugar loss %SOT -0.000188 -0.000094 0.000032 -2.90 

contamination %* -0.000562 -0.000281 0.000032 -8.69 

 Xylan to Xylose yield % 

contamination %* -0.000313 -0.000156 0.000032 -4.83 

 Xylose to ethanol yield % 

contamination %*Minor sugar yield % 0.000062 0.000031 0.000032 0.97 

Sugar loss %SOT* -0.000437 -0.000219 0.000032 -6.76 

 Xylan to Xylose yield % 

Sugar loss %SOT* -0.000187 -0.000094 0.000032 -2.90 

 Xylose to ethanol yield % 

Sugar loss %SOT*Minor sugar yield % 0.000188 0.000094 0.000032 2.90 

Xylan to Xylose yield %* 0.000938 0.000469 0.000032 14.49 

 Xylose to ethanol yield % 

Xylan to Xylose yield %* 0.000563 0.000281 0.000032 8.69 

 Minor sugar yield % 

Xylose to ethanol yield %* 0.000312 0.000156 0.000032 4.83 

 Minor sugar yield % 

Term P 

Constant 0.000 

contamination % 0.000 

Sugar loss %SOT 0.000 

Xylan to Xylose yield % 0.000 

Xylose to ethanol yield % 0.000 

Minor sugar yield % 0.000 

contamination %*Sugar loss %SOT 0.005 

contamination %* 0.000 

 Xylan to Xylose yield % 

contamination %* 0.000 

 Xylose to ethanol yield % 

contamination %*Minor sugar yield % 0.336 

Sugar loss %SOT* 0.000 

 Xylan to Xylose yield % 

Sugar loss %SOT* 0.005 

 Xylose to ethanol yield % 

Sugar loss %SOT*Minor sugar yield % 0.005 

Xylan to Xylose yield %* 0.000 

 Xylose to ethanol yield % 

Xylan to Xylose yield %* 0.000 

 Minor sugar yield % 

Xylose to ethanol yield %* 0.000 

 Minor sugar yield % 

S = 0.000365963 PRESS = 0.0000195918 

R-Sq = 99.98% R-Sq(pred) = 99.97% R-Sq(adj) = 99.97% 

Analysis of Variance for Current Yield (Actual/Theoretical) (coded units) 

Source DF Seq SS Adj SS Adj MS F P 

Tao and Aden 27
Main Effects 5 0.0641306 0.0641306 0.0128261 95768.40 0.000 

2-Way Interactions 10 0.0000643 0.0000643 0.0000064 47.97 0.000 

Residual Error 112 0.0000150 0.0000150 0.0000001 

 Lack of Fit 16 0.0000150 0.0000150 0.0000009 

 Pure Error 96 0.0000000 0.0000000 0.0000000 

Total 127 0.0642099 

Estimated Coefficients for Current Yield (Actual/Theoretical) using data in 

 uncoded units 

Term Coef 

Constant 0.488594 

contamination % -3.12500E-05 

Sugar loss %SOT 0.000250000 

Xylan to Xylose yield % 0.00132500 

Xylose to ethanol yield % 0.000075000 

Minor sugar yield % -9.12500E-04 

contamination %*Sugar loss %SOT -7.50000E-06 

contamination %* -5.62500E-05 

 Xylan to Xylose yield % 

contamination %* -3.12500E-05 

 Xylose to ethanol yield % 

contamination %*Minor sugar yield % 6.25000E-06 

Sugar loss %SOT* -3.50000E-06 

 Xylan to Xylose yield % 

Sugar loss %SOT* -1.50000E-06 

 Xylose to ethanol yield % 

Sugar loss %SOT*Minor sugar yield % 1.50000E-06 

Xylan to Xylose yield %* 1.87500E-05 

 Xylose to ethanol yield % 

Xylan to Xylose yield %* 1.12500E-05 

 Minor sugar yield % 

Xylose to ethanol yield %* 6.25000E-06 

 Minor sugar yield % 

Least Squares Means for Current Yield (Actual/Theoretic 

 Mean SE Mean 

contamination % 

 1 0.7829 0.000046 

 3 0.7685 0.000046 

Sugar loss %SOT 

 25 0.7765 0.000046 

 50 0.7749 0.000046 

Xylan to Xylose yield % 

 80 0.7576 0.000046 

 90 0.7939 0.000046 

Xylose to ethanol yield % 

 80 0.7653 0.000046 

 90 0.7861 0.000046 

Minor sugar yield % 

 80 0.7725 0.000046 

 90 0.7789 0.000046 

 

Effects Pareto for Current Yield (Actual/Theoretical) 

Tao and Aden 28
CG

DF

CD

DG

FG

CF

DE

CE

EG

EF

D

G

C

F

E

0 100 200 300 400 500

Term

Standardized Effect

2.0

C contamination %

D Sugar loss %SO T

E Xy lan to Xy lose y ield %

F Xy lose to ethanol y ield %

G Minor sugar y ield %

Factor Name

Pareto Chart of the Standardized Effects

response is Current Yield (Actual/Theoretical), Alpha = 0.05

Alias Structure 

I 

contamination % 

Sugar loss %SOT 

Xylan to Xylose yield % 

Xylose to ethanol yield % 

Minor sugar yield % 

contamination %*Sugar loss %SOT 

contamination %*Xylan to Xylose yield % 

contamination %*Xylose to ethanol yield % 

contamination %*Minor sugar yield % 

Sugar loss %SOT*Xylan to Xylose yield % 

Sugar loss %SOT*Xylose to ethanol yield % 

Sugar loss %SOT*Minor sugar yield % 

Xylan to Xylose yield %*Xylose to ethanol yield % 

Xylan to Xylose yield %*Minor sugar yield % 

Xylose to ethanol yield %*Minor sugar yield % 

 

Residual Plots for Current Yield (Actual/Theoretical) 

Tao and Aden 29
-0.0010 -0.0005 0.0000 0.0005 0.0010

99.9

99

90

50

10

1

0.1

Residual

Percent

0.74 0.76 0.78 0.80 0.82

0.0010

0.0005

0.0000

-0.0005

-0.0010

Fitted Value

Residual

-0.0012 -0.0008 -0.0004 0.0000 0.0004 0.0008

48

36

24

12

0

Residual

Frequency

120

110

100

90

80

70

60

50

40

30

20

1

1

0

0.0010

0.0005

0.0000

-0.0005

-0.0010

Observation Order

Residual

Normal Probability Plot Versus Fits

Histogram Versus Order

Residual Plots for Current Yield (Actual/Theoretic

 

Main Effects Plot for Current Yield (Actual/Theoretical) 

1 3

0.79

0.78

0.77

0.76

25 50 80 90

80 90

0.79

0.78

0.77

0.76

80 90

contamination %

Mean

Sugar loss %SOT Xylan to Xylose yield %

Xylose to ethanol yield % Minor sugar yield %

Main Effects Plot for Current Yield (Actual/Theoretical)

Data Means

 

Interaction Plot for Current Yield (Actual/Theoretic 

Tao and Aden 30
25 50 80 90 80 90 80 90

0.800

0.775

0.750

0.800

0.775

0.750

0.800

0.775

0.750

0.800

0.775

0.750

contamination %

Sugar loss %SOT

Xylan to Xylose yield %

Xylose to ethanol yield %

Minor sugar yield %

1

3

contamination %

25

50

%SOT

Sugarloss

80

90

yield %

Xylose

Xylan to

80

90

yield %

ethanol

Xylose to

Interaction Plot for Current Yield (Actual/Theoretical)

Data Means

 

Cube Plot (data means) for Current Yield (Actual/Theoretical) 

90

80

80 90

90

80

50

25

1 3

Minor sugar yield %

Xylose to ethanol yield %

Xylan to Xylose yield %

Sugar loss %SOT

contamination %

0.800

0.817 0.802

0.815

0.763

0.778 0.764

0.777

0.778

0.794 0.780

0.793

0.743

0.758 0.744

0.757

0.791

0.810 0.795

0.808

0.757

0.772 0.758

0.771

0.772

0.788 0.773

0.786

0.737

0.752 0.739

0.751

Cube Plot (data means) for Current Yield (Actual/Theoretical)

 

Tao and Aden 31