Heterodoxy in fast pyrolysis:Air-blown reactors and sugar production
Robert C. BrownDirector, Bioeconomy Institute
tcbiomassplus2019Rosemont, IL
October 7-9, 2019
Orthodoxy in fast pyrolysis• Definition of pyrolysis: “Thermal decomposition of organic
compounds in the absence of oxygen.” – Biorenewable Resources: Engineering New Products from Agriculture
• Products of pyrolysis: “Bio-oil, biochar, non-condensable gases.” – Biorenewable Resources: Engineering New Products from Agriculture
• Bio-oil: “Bio-oil is an emulsion of lignin-derived oligomers in an aqueous phase composed primarily of carbohydrate-derived compounds.”
– Biorenewable Resources: Engineering New Products from Agriculture
2
Heterodoxy in fast pyrolysis• Definition of pyrolysis: “Thermal
decomposition of organic compounds – and a little oxygen is just fine.”
• Products of pyrolysis: “Let’s add sugar among the major products.”
• Bio-oil: “Why would you even want to produce an unstable emulsion?”
3
A scientist and engineer walk into a bar…
• Scientist: Asks questions.
4
• Engineer: Solves problems.
Why do we exclude oxygen from pyrolysis?
• Combustion happens: C6H10O5 + 6O2 6CO2 + 5H2O
• Mitigating factors:‒ Operation at low equivalence
ratios‒ Operation at temperatures
lower than traditional combustion
‒ Variations in reaction rates among pyrolysis products
5
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E+02
450 500 550 600 650 700 750 800
Pred
icte
d Ig
nitio
n De
lay
(sec
onds
)
Temperature (ºC)
LevoglucosanGlyoxal
What is the upside of adding oxygen (as air)?• Eliminates tail gas recycle • Exothermic energy release of
oxidation can provide enthalpy for pyrolysis
• Heat transfer bottleneck to process intensification can be removed!
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φ = 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆
Autothermal Pyrolysis0.06 ≤ φ ≤ 0.12
Gasification0.20 ≤ φ ≤ 0.35
Pyrolysisφ = 0.00
Combustionφ > 1.0
• Simulate adiabatic operation‒ Use of guard heaters to overcome
parasitic heat losses at small scale
• Mitigate hot spots that promote undesired oxidation reactions‒ Use of fluidized bed for good
internal heat and mass transfer• Operate at minimum equivalence
ratio that provides enthalpy for pyrolysis
7
Design considerations for a lab-scale autothermal pyrolyzer
Polin et al., Applied Energy 249 (2019) 276-285
Process intensification through autothermal pyrolysis
8
Both nitrogen-blown, conventional pyrolysis and air-blown (φ=0.11), autothermal pyrolysis were performed in the same 8.9 cm diameter fluidized bed reactor.
Polin et al., Applied Energy 249 (2019) 276-285
9
“hairless”
furry
0
50
100
150
200
0 10 20 30 40Th
roug
htut
(TPD
)
Diameter (in.)
Throughput vs Pyrolyzer Size
ConventionalAutothermal
0.0
20.0
40.0
60.0
80.0
100.0
0 10 20 30 40 50
Reac
tor C
ost (
Rela
tive)
Reactor Throughput (TPD)
Relative Cost of Pyrolyzer
Conventional
Autothermal
What is the impact of heat transfer on scaling up processes?
𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 =𝐼𝐼𝑎𝑎𝐼𝐼𝐼𝐼𝐼𝐼𝑎𝐼𝐼𝑎𝑎𝑎𝑎𝐼𝐼𝑎𝑎 𝑝𝑝𝑎𝑎𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝑝𝑝 𝑎𝑎𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝑐𝑐𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝑎𝑎 𝑝𝑝𝑎𝑎𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝑝𝑝 𝑎𝑎𝐼𝐼𝐼𝐼𝐼𝐼
How much sugar can be produced via fast pyrolysis?
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Compound Glucose(wt%)
Cellobiose(wt%)
Maltose(wt%)
Malto-hexaose
(wt%)
Cellulose(wt%)
Curdlan(wt%)
Waxy maize starch(wt%)
Levoglucosan 7.00 24.4 20.5 33.1 58.8 44.2 48.5
Unidentified* 40.8 23.6 32.4 20.5 7.1 18.1 13.2
*Includes gases, water and some unidentified organic compounds
Patwardhan et al., J. Anal. Appl. Pyrolysis 86 (2009) 323-330
Why don’t we find much sugar in bio-oil?
11Patwardhan et al., Bioresource Technology 101 (2010) 4646-4655
Alkali and alkaline earth metals (AAEM) catalyze pyranose (and furanose) ring fragmentation during pyrolysis
Overcoming the deleterious effect of AAEM on sugar yields
12
0.002.004.006.008.00
10.0012.0014.0016.0018.0020.00
Light Oxygenates Anhydrosugars Furans Phenols
wt.%
of b
iom
ass
(wet
bas
is) Switchgrass Control
Acetic AcidFormic AcidNitric AcidHydrochloric AcidPhosphoric AcidSulfuric Acid
Mineral acid pretreatments convert AAEM into thermally stable salts that passivate catalytic activity of the metals
Kuzhiyil et al, ChemSusChem 5 (2012) 2228-2236
Process intensification through py sugar production
13
Sugar production for pyrolysis and solvent liquefaction based on sugar yields and processing rates experimentally observed at ISU. Enzymatic hydrolysis data from Nguyen et al., 2015.
0.1
1
10
100
1000
10000
0 20 40 60 80 100
Volu
met
ric P
rodu
ctiv
ity o
f Sug
ar fr
om
Cellu
lose
(g/h
/L)
Reaction Time (h)
Pyrolysis
Solventliquefaction
2 mg/g
5 mg/g
15 mg/g
30 mg/g
Enzyme Loading
How can we separate organic components of pyrolysis vapors?
14Pollard et al., Journal of Analytical and Applied Pyrolysis 93 (2012) 129-138
Selective condensation of pyrolysis vaporsmethanol methanol
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Fractionating Bio-oil Recovery
Feeder
ReactorCyclones
Heavy Ends
Quench Reactor
Heavy Ends ESP
Water injection
Biochar
Sugars & phenolic oil
Light oxygenates & water
Pollard et al., Journal of Analytical and Applied Pyrolysis 93 (2012) 129-138
Polin et al., Journal of Analytical and Applied Pyrolysis 143 (2019) 104679
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Separating heavy ends into sugars and phenolic oil
Heavy ends
Water Pyrolytic Sugars
PhenolicOil
Component Heavy ends
(wt% d.b.)
Extracted sugar
fraction(wt% d.b.)
Sugars 29.2 61.1
Phenols 61.9 22.4
Acids 3.0 3.8
Other 5.87 12.7
Extraction of corn stover-derived heavy ends
Rover et al., ChemSusChem 7 (2014) 1662-1668
Cleaning py sugars
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Pyrolytic Syrup
Contaminant Removal (phenolic compounds)
Pyrolytic Sugars (99.5% pure)
Levoglucosan (99.4% pure)
Phenolic Monomers
Rover et al., Green Chemistry (2019) DOI: 10.1039/C9GC02461A
Stanford et al., Separation & Purification Technology 194 (2018) 170-180
Why does acid pretreated biomass agglomerate?
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AAEM
H+ SO42-
Biomass Lignin
H+
• Alkali and alkaline earth metals in biomass catalyze both pyranose/ furanose ring fragmentation and lignin depolymerization
• Lignin melts and agglomerates rather than depolymerizes and volatilizes in the absence of suitable metal catalyst
Why does acid pretreated biomass agglomerate?
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AAEM
H+
SO42-
Stable salt
Biomass Lignin
H+
• Alkali and alkaline earth metals in biomass catalyze both pyranose/ furanose ring fragmentation and lignin depolymerization
• Lignin melts and agglomerates rather than depolymerizes and volatilizes in the absence of suitable metal catalyst
Agglomerated char from acid pretreated biomass
Lignin catalyst lost!
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• Find an ionic compound for which:‒ Anion passivates AAEM‒ Cation selectively catalyzes lignin depolymerization
• Compound must be water soluble to assure its diffusion into the plant cell walls
• Ferrous sulfate provides these functions
AAEM
Fe2+ SO42-
Biomass Lignin
Preventing char agglomeration
Rollag et al., manuscript in preparation (2019)
Lignin catalyst replaced!
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• Find an ionic compound for which:‒ Anion passivates AAEM‒ Cation selectively catalyzes lignin depolymerization
• Compound must be water soluble to assure its diffusion into the plant cell walls
• Ferrous sulfate provides these functions
AAEM
Fe2+
SO42-
Stable salt
Biomass Lignin
Preventing char agglomeration
Powdered char from ferrous sulfate
pretreated biomass
Rollag et al., manuscript in preparation (2019)
Lignin catalyst replaced!
Preventing char agglomeration
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Ferrous sulfate pretreatment eliminated char agglomeration for most kinds of biomass tested
0%
2%
4%
6%
8%
10%
12%
14%
16%
Ash
Con
tent
[wt%
]
Not Melted Melted
Agglomerated char deposits
No deposits after removing loose char
Rollag et al., manuscript in preparation (2019)
Why don’t we get more than 60% yield of sugars from cellulose?
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OHO
O
OH
OH
OO
OH
HO
OH
n
100 wt% yields not observed O
OH2COH
OH
HO
Cellulose
O
OH2COH
OH
HO
Levoglucosan
Anhydro-oligosaccharides
Cracking into anhydro-oligosaccharides
Unzipping
Vapor phase decomposition
HOO
Glycoaldehyde
O
HO
AcetolO
O OH
5-Hydroxymethyl furfural
H2O
Light Oxygenates
Non-condensable gases (eg: CO, CO2, CH4)
Char
OHO
O
OH
OH
OO
O
HOOH
m
OO
OH
HOOH
OHO
HO
OH
OH
+ OHO
O
OH
OH
OO
OHHOOH
m
OO
OH
HOOH
OHO
HO
OH
OH
OH
Levoglucosan
Competition between ring fragmentation and chain unzipping limits monosaccharide yields
Lindstrom et al., Green Chemistry 21 (2019) 178-186
Lignocellulosic Biomass
Product Recovery
Unrefined Sugars from Polysaccharide
Unrefined Acetate from Hemicellulose
Autothermal Pyrolysis
Phenolic Oil from Lignin Biochar
First GenerationProducts
Ethanol Bio-asphalt and marine fuel
Soil Amendment
Potential Future Products
-Pharmaceuticals-Polymers
-Octane enhancers-Drop-in Fuels-Biobased Chemicals
-Acetone-Acetic Acid-Bio-cement-Alcohols
-Activated Carbon
Putting it all together: Py refinery
In-plant thermal energy
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Economics of Py Refinery
$84
-$81
-$214
$245
$80
-$53
$441
$275
$142
-$300-$200-$100 $0 $100 $200 $300 $400 $500
ISU ($-33/MT Red Oak, $50/MT PO)
ISU ($-33/MT Red Oak, $300/MT PO)
ISU ($-33/MT Red Oak, $500/MT PO)
ISU ($0/MT Red Oak, $50/MT PO)
ISU ($0/MT Red Oak, $300/MT PO)
ISU ($0/MT Red Oak, $500/MT PO)
ISU ($40/MT Red Oak, $50/MT PO)
ISU ($40/MT Red Oak, $300/MT PO)
ISU ($40/MT Red Oak, $500/MT PO)
Sugar Production Cost ($/MT)
• Low cost cellulosic sugars from woody biomass across a wide range of assumptions
• Feedstock cost and phenolic oil (PO) value are key cost drivers
Price range for enzymatic hydrolysis
of cellulosic biomass
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• Iowa project (Redfield, IA)‒ Privately financed by Stine Seed
Farms‒ Engineering, Procurement and
Construction provided by Frontline Bioenergy
‒ Conversion of corn stover into sugars, phenolic oil and biochar
• California project (El Dorado Hills)‒ Funded by CA Energy Commission‒ Partnership with Lawrence
Livermore National Laboratory and Frontline Bioenergy
‒ Feasibility of converting wood waste into drop-in biofuels
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Next Step: Demonstrate autothermal pyrolysis at 50 tons per day scale
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Acknowledgments
I appreciate the creativity and dedicated efforts of a long line of graduate students and staff scientists and engineers who made possible the discoveries and innovations described in my talk.
Heterodoxy in pyrolysis has been made possible through funding from several sources in the last decade including the U.S. DOE, the USDA, the NSF, Conoco-Phillips, Phillips 66, and ExxonMobil. Our work is currently being supported by the U.S. DOE AMO sponsored RAPID Institute as part of an effort to develop modular chemical process intensification (MCPI) in pyrolysis. We are indebted to Stine Seed Company for financing the construction of the first demonstration-scale autothermal pyrolysis plant.
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Questions?
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