Initial Comparative Process Economics of Leading Biomass Pretreatment Technologies Richard T. Elander, National Renewable Energy Laboratory Charles E

Initial Comparative Process Economics of Leading Biomass Pretreatment Technologies

Richard T. Elander, National Renewable Energy LaboratoryCharles E. Wyman, Dartmouth College

Bruce E. Dale, Michigan State UniversityMark Holtzapple, Texas A&M UniversityMichael R. Ladisch, Purdue University

Y.Y. Lee, Auburn UniversityTim Eggeman, Neoterics International

The International Symposia on Alcohol Fuels and Other Renewables XVSan Diego, CA

September 28, 2005Biomass Refining CAFI

Pretreatment in a Biomass Conversion Process Context

Biomass Refining CAFI

Cellulosic Biomass Pretreatment Needs• High cellulose accessibility to enzymes • High sugar yields from hemicellulose• Low capital cost – low pressure, inexpensive

materials of construction• Low energy cost• Low degradation• Low cost and/or recoverable chemicals• A large number of pretreatment technologies

have been studied, but only a few show promise


• Biomass Refining Consortium for Applied Fundamentals and Innovation organized in late 1999

• Included top researchers in biomass hydrolysis from Auburn, Dartmouth, Michigan State, Purdue, NREL, Texas A&M, UBC, Univ. Sherbrooke

• Mission: – Develop information and a fundamental understanding of

biomass hydrolysis that will facilitate commercialization,– Accelerate the development of next generation

technologies that dramatically reduce the cost of sugars from cellulosic biomass

– Train future engineers, scientists, and managers


Project Background: CAFI

• Developing data on leading pretreatments using:– Common feedstocks– Shared enzymes– Identical analytical methods– The same material and energy balance methods– The same costing methods

• Goal is to provide information that helps industry select technologies for their applications

• Also seek to understand mechanisms that influence performance and differentiate pretreatments– Provide technology base to facilitate commercial use– Identify promising paths to advance pretreatment

technologies


CAFI Approach

CAFI USDA IFAFS Project Overview• Multi-institutional effort funded by USDA Initiative for Future

Agriculture and Food Systems Program for $1.2 million to develop comparative information on cellulosic biomass pretreatment by leading pretreatment options with common source of cellulosic biomass (corn stover) and identical analytical methods– Aqueous ammonia recycle pretreatment - YY Lee, Auburn University– Water only and dilute acid hydrolysis by co-current and flowthrough

systems - Charles Wyman, Dartmouth College– Ammonia fiber explosion (AFEX) - Bruce Dale, Michigan State University– Controlled pH pretreatment - Mike Ladisch, Purdue University– Lime pretreatment - Mark Holtzapple, Texas A&M University– Logistical support and economic analysis - Rick Elander/Tim Eggeman,

NREL through DOE Biomass Program funding• Completed in 2004


CAFI USDA Project Corn Stover• NREL supplied corn stover to all project participants

(source: BioMass AgriProducts, Harlan IA)• Stover washed and dried in small commercial operation,

knife milled to pass ¼ inch round screen

Component Composition (wt %)

Glucan 36.1 %

Xylan 21.4 %

Arabinan 3.5 %

Mannan 1.8 %

Galactan 2.5 %

Lignin 17.2 %

Protein 4.0 %

Acetyl 3.2 %

Ash 7.1 %

Uronic Acid 3.6 %

Non-structural Sugars 1.2 %Biomass Refining CAFI

Hydrolysis Stages


Stage 2Enzymatichydrolysis

Dissolved sugars, oligomers

Solids: cellulose, hemicellulose,

lignin

Chemicals

Biomass Stage 1 Pretreatment

Dissolved sugars, oligomers, lignin

Residual solids: cellulose,

hemicellulose,lignin

Cellulase enzyme

Stage 3Sugar

fermentation

Dilute Acid Pretreatment

• Mineral acid gives good hemicellulose sugar yields and high cellulose digestibility

• Sulfuric acid usual choice because of low cost

• Requires downstream neutralization and conditioning

• Typical conditions: 120-200oC, 50 to 85% moisture, 0-1%

H2SO4

• Some degradation of liberated hemicellulose sugars

Mineral acid

Biomass Stage 1. Pretreatment

Stage 2.Enzymatichydrolysis

Glucoseand ligninCellulose

and lignin

Hemicellulose sugars and oligomers

Schematic of Flowthrough Pretreatment System

Back Regulator

Sand Bath

Valve-1

P

Cold Water

Rea

ctor

T1

HPLC

Pump

Wateror

DiluteAcid

TC

Valve-2

Sample

Controlled pH Liquid Hot Water Pretreatment

• pH control through buffer capacity of liquid

• No fermentation inhibitors, no wash stream

• Minimize hydrolysis to monosaccharides thereby minimizing degradation

Water

Steam Stover Heat Recovery

Saccharification

Trim Heat Plug Flow

Reactor Coil

The AFEX/FIBEX Process

• Liquid “anhydrous” ammonia treats and explodes biomass

• Ammonia is recovered and reused• Ammonia can serve as N source downstream• Batch process is AFEX; FIBEX is continuous version• Conditions: 60-110oC, moisture 20-80%, ammonia:biomass ratio 0.5-1.3 to 1.0 (dry basis)

• No fermentation inhibitors, no wash stream required, no overliming

• Only sugar oligomers formed, no detectable sugar monomers• Few visible physical effects

Reactor Explosion

AmmoniaRecovery

BiomassTreatedBiomass

LiquidAmmonia

GaseousAmmonia

Reactor Explosion

AmmoniaRecovery

BiomassTreatedBiomass

LiquidAmmonia

GaseousAmmonia

• Moderate temperatures, pH prevent/minimize sugar & protein loss

N2 Gas

PG TG

TG

Vent

Oven

(Preheating Coil and Reactor)

Holding TankPumpPG : Press. Gauge

TG : Temp. Gauge

C.W.: Cooling Water

Aq

ueo

us A

mm

on

ia

Wa

ter

PG

C.W.

Ammonia Recycle Percolation (ARP)

Temp. monitoring

system (DAS)

Lime Pretreatment

Biomass + Lime

Gravel

Air

Typical Conditions: Temperature = 25 – 55oC Time = 1 – 2 months Lime Loading = 0.1 – 0.2 g Ca(OH)2/g biomass

Process Modeling in CAFI 1 Project

Pretreatment ModelAspen Plus

Bioethanol Plant Model2001 NREL Design Case

2000 Metric Ton (dry)/Day StoverStover Cost: $35/ton

Enzyme Cost: ~$0.15/gal ethanol

Thermodynamics ProcessAnalogies

Design Methods

Chemistry

CAFIResearcher


General Process Flow Diagram


Boiler +

Generator

Hydrolysis +

Fermentation

Feed Handling Recovery Pretreatment

Stover

Syrup + Solids

Chemicals Water

Enzymes CO2 Water

EtOH

Steam

Power

Hydrolysis Stages


Stage 2Enzymatichydrolysis

Dissolved sugars, oligomers

Solids: cellulose, hemicellulose,

lignin

Chemicals

Biomass Stage 1 Pretreatment

Dissolved sugars, oligomers, lignin

Residual solids: cellulose,

hemicellulose,lignin

Cellulase enzyme

Stage 3Sugar

fermentation

Pretreatment Yield Comparisons at 15 FPU/g Glucan

PretreatmentSystem

Xylose yields* Glucose yields* Total sugars*

Stage 1 Stage 2 Totalxylose

Stage 1 Stage 2 Totalglucose

Stage 1 Stage 2 Combinedtotal

Maximum possible

37.7 37.7 37.7 62.3 62.3 62.3 100.0 100.0 100.0

Dilute acid 32.1/31.2 3.2 35.3 3.9 53.2 57.1 36.0/35.1 56.4 92.4/91.5

Flowthrough 36.3/1.7 0.6/0.5 36.9/2.2 4.5/4.4 55.2 59.7/59.6 40.8/6.1 55.8/55.7 96.6/61.8

Controlled pH 21.8/0.9 9.0 30.8 3.5/0.2 52.9 56.4 25.3/1.1 61.9 87.2

AFEX 34.6/29.3 34.6/29.3 59.8 59.8 94.4/89.1 94.4/89.1

ARP 17.8/0 15.5 33.3/15.5 56.1 56.1 17.8/0 71.6 89.4/71.6

Lime 9.2/0.3 19.6 28.8/19.9 1.0/0.3 57.0 58.0/57.3 10.2/0.6 76.6 86.8/77.2

*Cumulative soluble sugars as total/monomers. Single number = just monomers.

Incr

easi

ng p

H


0

25

50

75

100

Suga

r yi

elds

, % o

f max

tota

l -

Oligoxylose

Monoxylose

Oligoglucose

Monoglucose

Dil

ute

aci

d

Flo

wth

rou

gh

Con

trol

led

pH

Max

imu

m p

ossi

ble

AR

P

AF

EX

Lim

e

Pretreatment Yields at 15 FPU/g Glucan

0

25

50

75

100

Suga

r yi

elds

, % o

f max

tota

l -

Oligoxylose S1

Monoxylose S1

Monoxylose S2

Oligoglucose S1

Monoglucose S1

Monoglucose S2

Pretreatment Yields at 15 FPU/g Glucan

Pretreatment Yield Comparisons at 15 FPU/g Glucan—Alternative Basis


PretreatmentSystem

Xylose Yields,

% of Theoretical*

Glucose Yields,

% of Theoretical*

After Pretreatment

After Enzymatic Hydrolysis

After Pretreatment

After Enzymatic Hydrolysis

Dilute Acid 90.2 / 89.7 95.6 / 95.1 8.0 / 7.5 85.1 / 84.6

Controlled pH 50.8 / 7.3 81.8 / 38.3 4.5 / 2.0 90.5 / 88.0

AFEX 0 / 0 92.7 / 77.6 0 / 0 95.9

ARP 47.2 / 0 88.3 / 41.1 1.4 90.1

Lime 24.3 / 0.8 75.3 / 51.8 1.6 / 0.5 92.4 / 91.3

No Pretreatment 0 8.5 0 15.7

Ideal Pretreatment

- 100 - 100

*Cumulative soluble sugars as (oligomers+monomers) / monomers. Single number = just monomers.

Capital Cost Estimates


PretreatmentSystem

Pretreatment Direct Fixed

Capital ($MM)

Pretreatment Breakdown,

(% Reactor/% Other)

Total Fixed Capital ($MM)

Ethanol Production

(MM gal/yr)

Total Fixed Capital ($/gal

Annual Capacity)

Dilute Acid 25.0 64/36 208.6 56.1 3.72

Hot Water 4.5 100/0 200.9 44.0 4.57

AFEX 25.7 26/74 211.5 56.8 3.72

ARP 28.3 25/75 210.9 46.3 4.56

Lime 22.3 19/81 163.6 48.9 3.35

No Pretreatment

0 - 200.3 9.0 22.26

Ideal Pretreatment

0 - 162.5 64.7 2.51

Minimum Ethanol Selling Price (MESP)


0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

Dilute Acid Hot Water AFEX ARP Lime Ideal

Net Stover Other Variable Fixed w/o Depreciation Depreciation Income Tax Return on Capital

Proof Year: 4th Year of Operation$/gal EtOH

CashCostPlantLevel

MESP

Effect of Oligomer Conversion


1.00

1.25

1.50

1.75

Dilute Acid Hot Water AFEX ARP Lime

ME

SP

, $/

gal

EtO

H

w/o Oligomer Credit w/ Oligomer Credit

Solids Loading and Ethanol Concentration—Energy Impacts


PretreatmentSystem

Pretreatment Effluent (wt %

Liquid)

Fermentation Titer (wt % Ethanol in

Liquid)

Process Steam Usage Electrical Power

HP Steam (kg/hr)

LP Steam (kg/hr)

VLP Steam (kg/hr)

Total Generated

(Mwe)

Process Needs (Mwe)

Dilute Acid 66.8 5.07 14,663 83,377 16,426 42.1 14.0

Hot Water 83.7 3.09 34,281 146,580 48,374 42.2 13.5

AFEX 61.2 4.62 0 154,980 31,932 35.6 17.4

ARP 74.5 5.06 112,330 56,972 11,469 38.0 11.9

Lime 80.0 3.16 0 160,540 42,265 0 14.4

No Pretreatment

80.0 0.92 0 59,697 51,477 88.8 13.9

Ideal Pretreatment

80.0 5.86 0 71,230 20,160 45.2 32.4

Key Findings from USDA CAFI Project• Initial set of comparative pretreatment data has been developed

– 1st generation economic models developed

• Significant differences in pretreatment and enzymatic hydrolysis yields observed– Especially, when and to what extent xylan is converted

• Pretreatment capital costs more similar than anticipated– High costs for catalyst recovery or regeneration

• Findings to be published in a special issue of Bioresource Technology (December, 2005)

• Data gaps remain (addressed in current CAFI DOE Project)– Optimal enzyme types for each pretreatment– Hydrolyzate fermentability at relevant sugar concentrations– Rigor of economic models (esp. pretreatment area capital costs)


DOE Office of the Biomass Program Project: April 2004 Start

• Funded by DOE Office of the Biomass Program for $1.88 million through a joint competitive solicitation with USDA

• Using identical analytical methods and feedstock sources to develop comparative data for corn stover and poplar

• Determining more in-depth information on:– Enzymatic hydrolysis of cellulose and hemicellulose in solids– Conditioning and fermentation of pretreatment hydrolyzate liquids– Predictive models

• Added University of British Columbia to team through funding from Natural Resources Canada to– Capitalize on their expertise with xylanases for better

hemicellulose utilization– Evaluate sulfur dioxide pretreatment along with those previously

examined: dilute acid, controlled pH, AFEX, ARP, lime• Augmented by Genencor Int’l to supply enzymes


Objectives of CAFI DOE Project1. Cellulosic biomass will be pretreated by leading technologies to improve

cellulose accessibility to enzymes.

2. Conditioning methods will be developed as needed to maximize fermentation yields by a recombinant yeast, the cause of inhibition will be determined, and fermentations will be modeled.

3. Cellulose and hemicellulose in pretreated biomass will be enzymatically hydrolyzed, as appropriate, and models will be developed to understand the relationship between pretreated biomass features, advanced enzyme characteristics, and enzymatic digestion results.

4. Capital and operating costs will be estimated for each integrated pretreatment, hydrolysis, and fermentation system and used to direct research.

5. The proposal team will work with an Industrial and Agricultural Advisory Board and others to evaluate these findings; identify opportunities to utilize the pretreatment technologies; define opportunities to improve coupled pretreatment, fermentation, and enzymatic hydrolysis; and disseminate the results widely.


Acknowledgements US Department of Agriculture Initiative for Future

Agricultural and Food Systems Program, Contract 00-52104-9663

US Department of Energy Office of the Biomass Program, Contract DE-FG36-04GO14017

Natural Resources Canada Genencor International Our team from Dartmouth College; Auburn, Michigan State,

Purdue, and Texas A&M Universities; the University of British Columbia; and the National Renewable Energy Laboratory


Documents

Initial Comparative Process Economics of Leading Biomass Pretreatment Technologies Richard T. Elander, National Renewable Energy Laboratory Charles E