Corn stover what do we know about what makes a good feedstock

1
Corn stoverwhat do we know about what makes a
good feedstock?

• John Sheehan
• Steve Thomas
• Jim McMillan
• Bonnie Hames
• David Templeton
• National Renewable Energy Laboratory
• November 8, 2001

2
Outline

• Key issue
• Key questions
• Corn stover and the Biofuels Program
• Corn stover processing
• Corn stover composition
• What we have observed
• Rapid biomass analysis
• Quality variables and their impacts
• Ash
• Moisture
• Carbohydrate and lignin

3
Key Issue

• Feedstock composition influences process
  economicspossibly at several levels.
• Yield effects
• Equipment compatibility and operability
• Safety
• Though this may be obvious, it is important to
  recognize that the bottom line issue for corn
  stover specifications is economics.
• Its the economy, stupid

4
Key Questions

• What is the span of variability in corn stover
  composition?
• Near term Corn Belt hybrid lines
• Other commercial hybrids, inbred lines, primitive
  species
• Are the factors that control stover composition
  mainly genetic or environmental?
• Can we control the variability
• Do harvesting and storage affect stover
  composition ?
• Does stover variability influence process
  strategy?
• Is there a best corn stover composition?

5
Corn stover and BiofuelsThe biorefinery based on
corn stover

• The building blocks of a biorefinery
• The program is focused on the enabling pieces for
  sugars and for ethanol
• Industry will focus on the application of this
  technology for new products from sugars and lignin

6
Processing corn stover
7
Processing corn stover
(22x micrographs)
8
Processing corn stover its not wood
9
Processing corn stover
EXT Extractives AC Acetyl/formyl
Following components through the process
10
Corn stover composition what do we know?
Research requiring thousands of samples is now
possible

• Stover composition as a function of
• Location
• Soil types
• Irrigation/ drainage
• Weather
• Commercial variety
• Storage time and methods
• Harvesting and handling methods
• Harvest years

• Information obtained
• Average composition
• Heterogeneity within a feedstock
• Variance between feedstocks
• Sampling protocol
• Harvesting protocol
• Storage protocol
• Definition of ideal feedstock

11
Corn stover compositionon average

• Ranges (17 feedstocks)
• Glucan 35.1-39.5
• Xylan 20.1-24.6
• Lignin 11.0-19.1
• Ash 2.2-15.9

12
Corn stover composition heterogeneity within
the feedstock
13
Corn stover compositionRapid biomass analysis

• Faster
• Minutes instead of days
• Minimal sample preparation
• Real time feedback in the field and the process
• Cheaper
• About 10 per sample
• Compared to 800-1,000 for wet analysis
• Better
• Calibrated using best methods
• Less operator dependent
• Suitable for large volume screening

14
NIR/PLS Rapid Method forCorn Stover Feedstock
Composition
15
Rapid biomass analysisin the field

• Field analysis methods being developed
• Instrument manufacturers developing tools
  specific to biomass analysis
• Farm equipment manufacturers developing
  combine-mounted spectrometers for total harvest
  analysis.
• Feedstock prices could be based on quality
  instead of weight

16
Rapid biomass analysis Industrial applications
Slide courtesy of B. Meglen
17
Corn stover composition Summing up what we know

• Stover has a lower carbohydrate content relative
  to wood.
• Different anatomical parts of the plant have
  distinctly different chemical composition.
• Wide variation observed in ash content of
  as-received samples.

18
Corn stover composition Summing up what we know

• Whole stover composition is variable (NIR
  results).
• Component Range (Wt max-min)
• GlucoseXylose 8.4
• Total sugars 10.0
• Lignin 8.1

19
Corn Stover Composition Summing up rapid
biomass analysis

• NIR and wet chemical results are in pretty good
  agreement on average but both are being improved.
  
• The NIR calibration set is being expanded to
  cover a wider range of stover materials and
  composition.
• NIR and other rapid analysis techniques could
  bring a new level of sophistication to setting of
  biomass specifications

20
Quality variables for corn stoverCauses of
variability

• Seed variety - genetics
• Location, harvest year environment
• Collection and storage methods
• Quantity of entrained dirt.
• May affect the ratio of leaves/stalks/cobs.
• May affect the amount of non-structural
  (extractable) carbohydrates present.
• Analytical method used and data reported
• Different test methods
• Extracted vs whole stover vs ash free stover

21
Quality variables for corn stoverImpacts of ash
content

• Two sources
• Structural Inorganics minerals in plant cells
• Entrained soil (when soil becomes dirt)
• Issues
• Erosion damage to machinery and equipment
• Buffering capacity (more acid to reach target pH)
• Undesirable reactions catalyzed by inorganics
  (e.g., Fe, Mn) that could explain observed losses
• Targets
• Structural Inorganics 5 expected average
• Entrained Soil 5 max.

22
Quality variables for corn stoverImpacts of
Moisture

• Two sources
• In stover at time of collection
• Added (or lost) during handling and storage
• Issues
• Storage stability
• Safety
• Ease of processing
• Decreased reactivity (too dry) vs. increased
  energy requirements (too wet)
• Targets
• At collection determined by grain harvest ?
• At delivery to conversion facility 10

23
Quality variables for corn stoverImpacts of
carbohydrates and lignin

• Source
• In plant cells, carbohydrates are both structural
  (SC) and non-structural (NSC)
• Losses occur during storage, NSC are first to go.
• Issues
• Carbohydratesugar potentialproduct potential
• Ligninenergy and other product potential
• Targets
• Conventional wisdom is more sugar, less lignin
• Minimize losses during storage and processing

24
Quality variables for corn stoverNRELs B/MAP
Stover Specifications

• Less than 10 ash.
• Washed stover but includes some dirt.
• Structural inorganics range is 5-10.
• Less than 20 moisture.
• Aids in storage stability.
• Three particle sizes.
• Testing size effect on pretreatment yields.
• Maximum fiber length 0.5 to 3 inches.

25
Concluding remarks

• Stover composition affects process economics and
  may influence process design.
• We have a very crude understanding of the range
  of variability in corn stover composition.
• Classical breeding and selection, and genetic
  engineering could be used to manipulate stover
  composition.
• Effects of environmental factors on composition
  is poorly understood.
• Harvesting, handling, and storage affect the ash
  and moisture content as well as organic
  composition of the stover.

26
Next Steps

• Coordinate stover collection and conversion
  activities
• Understand system tradeoffs, variable impacts,
  capabilities, and overall optimization
• Suggestions ?