“Three” major challenges in production of lignocellulosic fuels

Chris SomervilleEnergy Biosciences Institute

Distillation EthanolDrying

Co-Product Recovery

Animal FeedChemicalsBoiler fuel

Sugar Cane Process

Cellulose Conversion

Hydrolysis

Corn Process

Cellulose Process

Cellulose PretreatmentCellulose

• Miscanthus• Switchgrass• Forest Residues• Ag Residues• Wood Chips

Ferment-ationSugarSugar

Cane

CornKernels

Starch Conversion

(Cook or Enzymatic Hydrolysis)

Ethanol Production Schemes

Slide Courtesy of Bruce Dale

Dilute acid schematics 1-6

Feed handling Prehydrolysis

Solid-liquid separation Lime addition

Seed production Saccharification and fermentation

Aden et al (2002) NREL/TP-510-32438

Dilute acid schematics 7-12

Beer distillation Rectification distillation

Ethanol dehydration Evaporation

Lignin separation and recycle Anaerobic digestion

Aden et al (2002) NREL/TP-510-32438

Dilute acid schematics 13-18Aerobic digestion Storage

Boiler feed drying Combustion and turbogenerator

Boiler feed water preparation Boiler feed water adjuvants

Aden et al (2002) NREL/TP-510-32438

Dilute acid schematics 19-21

Cooling water

Process water

Sterile water

Aden et al (2002) NREL/TP-510-32438

7

Breakdown of Capital Costs for NREL Biorefinery

Source : Paul Willems from NREL design, May 2011

Detailed Split by SectionPretreatment

Sacharification &FermentationEnzyme Production

Distillation

Waste treatment

Boiler & Utilities

Storage

Process costs

Humbird et al (2011) NREL/TP-5100-47764

Total $2.15

$0.828

Batch processes have many inefficiencies

9

Time

Suga

r co

ncen

trat

ion Fuel accum

ulation

Unused capital

Catalyst Loss

Cell Loss

Wastewater

SolidsBoiler

Sugar inhibition

Fuel,lignin

inhibition

An ideal process

10

Time

Suga

r co

ncen

trat

ion

Fuel accumulation

optima

Fuel Removal

Strategies for reducing costs

• Reduction in capex– Minimize number of unit processes, minimize residence

time, minimize down time, eliminate solids boiler, minimize wastewater

• Reduction in opex– Operate under optimal conditions (sugar, fuel, nutrients,

temperature…), minimize enzyme inactivation, recycle enzyme, maximize longevity, control contaminaion

Plugged reactor conceptbased on continuous removal of fuel

Fuel producingorganism

ConcentratedSugar solution membrane

Water+

Fuel

Hypothetical continuous process

Biomassgrinding

Ligninremoval

Solvent recovery

Ligninuse

Polysaccharidedepolymerization

Catalyst production

Catalystrecovery fermentation

Fuel separation and volume adjustment

Wastemanagement

Fueluse

Major challenge

• Remove all lignin without “losing” polysaccharides

• Lignin solvent must be inexpensive or recycled at very high efficiency

Structure and organization of lignin

Harris & Stone in Biomass Recalcitrance, pp 75 ed M Himmel, Blackwell (2008)Ralph, Ralph & Landucchi

http://ars.usda.gov/Services/docs.htm?docid=10491

Side view of secondary cell wall

Cellulose Hemicellulose

Lignin

3 nm

Acid pretreatment removes hemicellulose

Cellulose Hemicellulose

Lignin

50 kdenzyme

3 nm

Dissolution of cellulose in an ionic liquid(Also ueful for polysaccharide-lignin separation)

Swatloski, Spear, Holbrey, Rogers J. Am. Chem. Soc., 124 (18), 4974 -4975, 2002

Untreated

Treated

All of these C-O bonds can be cleavaged by Ni-NHC complexes. Selectivity contrasts that of the heterogeneous catalysts

Relative rates:

Ar-OAr > RO-Bn > ArOR

The important bonds to cleave are most reactive toward Ni-NHC

Depolymerization of lignin

A G Sergeev, J F Hartwig Science 2011;332:439-443

Example:Analysis of effects of catalyst action

Courtesy of D. Wemmer & D Toste, UC Berkeley

Pretreatment technologies

• Weak acid, high temperature• Strong acid, low temperature• Aqueous base

– Ammonia (rapid or slow decompression)– Base plus oxidant

• Ionic Liquid• Organosolve, hot water, …• Supercritical water,…

Carvalheiro et al J Sci Indust Res 67,849

What might a breakthrough look like?

• Biomass chipped• 30 min in 40% HCL (continuous

process)• HCL extracted into water-

immiscible solvent• Lignin and sugars separated by

solids/liquid separation– Sugars clean (no acetic

acid, no furans…)• HCL recovered from

extractant and reused• Extractant cleaned up and

reused

Virdia pilot plant

Technology Review, march 6 2012

Wood chips

40% HCL

Free sugars + Lignin +HCL

Fuel synthesis Combustion(trade)

Potential +/-

Positives• Short process = reduced

capital• No inhibitors in fermenter• Concentrated sugars• Sterile sugars• No enzymes• Enables continuous

process• No wastewater• Low temperature• No distillation• No boiler?

Negatives• Hazardous reagent• Special materials of

construction• Chlorine emissions?

Major Challenges

• How can we produce optimized catalysts for depolymerization?

Many enzymes are required for some pretreatments

Courtesy of Isaac Caan, U Illinois

Recently discovered polysaccharide monoxygenases catalyze a novel reaction

Beeson et al J. Am. Chem. Soc., Article ASAP DOI:10.1021/ja210657t

Karkehabadi S, et al. J. Mol. Biol (2008).

27,755 candidate genes

Discovery of new enzymes

Hess et al

Other challenges• Recycle enzymes• Extend enzyme longevity• Eliminate feedback inhibition• Maintain hygiene

Major challenge

• Unsubsidized diesel & jet from sugars

Major types of components of FACE9A diesel

CRC Report FACE-1

Conversion of sugar to alkanes

Huber et al., (2005) Science 308,1446

Routes to potential fuels

Fortman et al, Trends Biotechnology 26,375

Many additional fuels can be made from biomolecules by simple chemistry

(eg. Guerbet reactions)

Some observations about process development

• The problems span many disciplines– eg, Verdia’s problem is in material science not biofuels

• The good news:The problems have a factorial character

• The bad news:The problems have a factorial character

• It should be hard to displace a mature trillion dollar industry