NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Ex-Situ Catalytic Fast 

Pyrolysis Technology 

Pathway

Mary Biddy and Abhijit Dutta

National Renewable Energy Laboratory

Susanne Jones and Aye Meyer

Pacific Northwest National Laboratory

NREL is a national laboratory of the U.S. Department of Energy, 

Office of Energy Efficiency & Renewable Energy, operated by the 

Alliance for Sustainable Energy, LLC, under contract 

DE-AC36-08GO28308.

Pacific Northwest National Laboratory is operated by Battelle for the 

United States Department of Energy under contract 

DE-AC05-76RL01830.

Technical Report

NREL/TP-5100-58050

PNNL-22317

March 2013

Prepared for the U.S. Department of Energy Bioenergy Technologies Office
National Renewable Energy Laboratory

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Pacific Northwest National Laboratory

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Ex-Situ Catalytic Fast 

Pyrolysis Technology 

Pathway 

Mary Biddy and Abhijit Dutta

National Renewable Energy Laboratory

Susanne Jones and Aye Meyer

Pacific Northwest National Laboratory

NREL is a national laboratory of the U.S. Department of Energy, 

Office of Energy Efficiency & Renewable Energy, operated by the 

Alliance for Sustainable Energy, LLC, under contract 

DE-AC36-08GO28308.

Pacific Northwest National Laboratory is operated by Battelle for the 

United States Department of Energy under contract 

DE-AC05-76RL01830.

Technical Report 

NREL/TP-5100-58050

PNNL-22317

March 2013

Prepared for the U.S. Department of Energy Bioenergy Technologies Office
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1 

Ex-Situ Catalytic Fast Pyrolysis

Developing Technology Pathway Cases to Understand the Cost of 

Converting Biomass to Hydrocarbon Fuels

In support of the Bioenergy Technologies Office, the National Renewable Energy Laboratory 

(NREL) and the Pacific Northwest National Laboratory (PNNL) are undertaking studies of 

biomass conversion technologies to hydrocarbon fuels to identify barriers and target research 

toward reducing conversion costs. 

Process designs and preliminary economic estimates for each of these pathway cases were 

developed using rigorous modeling tools (Aspen Plus and Chemcad). These analyses 

incorporated the best information available at the time of development, including data from 

recent pilot- and bench-scale demonstrations, collaborative industrial and academic partners, and 

published literature and patents. The economic results of these analyses are in the process of 

further refinement and will be published in FY13 and FY14 design reports. This report 

summarizes the preliminary technical data used for the models and identified data gaps.

This technology pathway case investigates converting woody biomass using ex-situ catalytic fast 

pyrolysis followed by upgrading to gasoline-, diesel-, and jet-range hydrocarbon blendstocks. 

Technical barriers and key research needs that should be pursued for this pathway to be 

competitive with petroleum-derived blendstocks have been identified. 

Process Block Diagram

Key Highlights

• Catalytic vapor phase upgrading (VPU) of fast pyrolysis vapors has the potential to 

reduce costs associated with upgrading conventional fast pyrolysis oil to a hydrocarbon 

by producing a lower-oxygen-content intermediate with lower associated water. 

Hydrogen consumption during final upgrading to a hydrocarbon will also be reduced. 

-

Flue Gas

Vap Liq. .

Off-gas

Heat Integration and Power Generation

Hydrogen 

Plant

Uncatalyzed 

Fast 

Pyrolysis

Wastewater 

Treatment

Feed 

Handling & 

Preparation

Catalytic 

Vapor Phase 

Upgrading 

and Quench

Catalytic 

Hydrotreating & 

Product 

Fractionation

Woody

Biomass

Process Heat 

and Power 

Integration

Off-gas

H2

Hydrocarbon 

Biofuels (i.e., 

Gasoline, 

Diesel, Jet) 
2 

• The use of a vapor phase reactor separate from the pyrolyzer allows more control over 

the vapor phase reactions than if biomass pyrolysis and vapor phase upgrading occur in 

the same vessel (in-situ pyrolysis). This also allows the unreacted char and mineral 

components to be removed prior to exposing pyrolysis vapors to the upgrading catalyst. 

• The upgraded vapor’s lower reactivity may allow use of extended surface heat 

exchangers to recuperate heat and reduce the cooling water load when the vapors are 

condensed. 

• Important research needs for this pathway include the development of catalysts with 

improved yields, stability, and lifetimes, maximizing overall conversion to the desired 

hydrocarbon product, optimizing VPU oil hydrotreating, and developing economic 

wastewater treatments. 

Process Design Details

Feed handling: Woody biomass is dried to approximately 10 wt% moisture and finely ground to 

2–6 mm. Waste heat streams from the pyrolysis section are used to dry the biomass. Drying and 

grinding costs are included in the feedstock costs (Jones and Male 2012). 

Fast pyrolysis: The model is based on a circulating fluidized bed consisting of a pyrolysis 

reactor, cyclones, and combustor. Biomass is contacted with hot sand and fluidizing gas in a 

short residence time (<2 seconds) pyrolysis reactor at ~500°C and atmospheric pressure in the 

absence of air. Biomass is converted to predominately condensable vapors, non-condensable gas, 

and some char. Char and sand are separated from the vapor in cyclones and subsequently sent to 

a combustor to burn the char and reheat the sand, which is returned to the pyrolysis reactor. The 

pyrolysis vapors leaving the cyclone are passed to the vapor phase upgrading reactor. 

Conventional non-catalyzed fast pyrolysis is already commercialized (Envergent 2009–2011). 

The nth plant model assumes two parallel pyrolyzers processing 1,000 dry metric tonnes per day 

(tpd) of dry biomass. 

Vapor phase upgrading: Pyrolysis vapors that have been separated in a cyclone from sand and 

char are fed to a reactor where the vapors are catalytically upgraded to less reactive compounds. 

Coke deposits on the catalyst can be significant, and the catalyst is regenerated by burning off 

accumulated coke. The resultant oxygen content is dependent upon catalyst type, residence time, 

and temperature, and can range from very low (~4 wt%) to quite high (35 wt% or more on a wet 

basis). Very low oxygen content typically means very low yields. Reported yields range from 0.1 

to 0.2 mass dry oil/mass dry biomass (Dayton 2011; Mante and Agblevor 2011; Zacher et al.

2011; Czernik 2011; Diebold et al. 1994; Stefanidis et al. 2011). The primary objective is to 

retain as much carbon in the liquid product as possible while removing the highly reactive 

oxygen species. 

Unlike uncatalyzed fast pyrolysis, where use of extended surface heat exchangers is not possible 

because of excessive fouling, heat recovery from condensing the vapors may be possible, which 

will in turn decrease the cooling water demand. Upon cooling, non-condensable gases are 

removed and two liquid phases are formed. The predominately organic phase is sent to 

hydrodeoxygenation and the predominately aqueous phase goes to water treatment. The carbon 

content of each liquid phase is dependent upon the oxygen content of the vapors leaving the VPU 

reactor. The VPU reactor is likely to be a circulating fluidized bed with external catalyst 
3 

regeneration, similar to a petroleum refining fluidized catalytic cracking unit. Two base cases 

were modeled. The first case used a complete dataset (Mante and Agblevor 2011) with detailed 

reporting for pyrolysis and VPU. The second case used typical fast pyrolysis yields, followed by 

VPU results from various sources and with varying oxygen contents (Dayton 2011; Mante and 

Agblevor 2011; Zacher et al. 2011; Czernik 2011; Diebold et al. 1994; Stefanidis et al. 2011). 

Catalytic hydrodeoxygenation: VPU oil is combined with hydrogen at 255°–410°C and ~2,000 

psig and is converted to hydrocarbons, water, and gases over a fixed bed reactor. Depending 

upon the reactivity of the VPU oil, two beds may be needed. The first bed is operated at the 

lower end of the temperature range to further reduce any remaining highly reactive compounds. 

The second bed is operated at the higher end of the temperature range, and possibly at a lower 

space velocity to allow complete deoxygenation. The ideal goal is that the VPU oil is of high 

enough quality so that only a single hydrotreater is needed. After cooling, the products are 

separated and the hydrocarbon product is distilled into C4 minus, gasoline range, diesel range, 

and heavy oil (if any) range material. Experimental results suggest that there may be little or no 

heavy oil produced, thus the distillate fraction may not need a final boiling point correction 

(Zacher et al. 2011). The cost model assumes that the product quality of the gasoline- and dieselrange streams is sufficiently suitable for use as blendstocks. The targeted oxygen content of the 

upgraded product is <1 wt%. Wastewater is assumed to have <1 wt% carbon. The process model 

is based on experimental conditions and hydrodeoxygenation conversion for catalytic pyrolysis 

oil (Dayton 2011; Zacher et al. 2011) and conventional pyrolysis oil (Elliott et al. 2009). The 

flow scheme is based on Jones et al. 2009. 

Hydrogen plant: Off-gases from the VPU section, and from the hydrodeoxygenation section are 

sent to a conventional hydrogen plant consisting of a steam reformer, water gas shift reactor, 

pressure swing adsorption unit, and heat recovery. Supplemental natural gas to satisfy the 

hydrogen demand is not needed based on the modeled results at the assumed level of VPU 

deoxygenation. No processing penalty is assumed for using off-gas in place of natural gas as feed 

to the reformer; this may be optimistic. The hydrogen plant size is within typical commercial 

scale. Design conditions are based on commercial-type systems using natural gas (SRI 

Consulting 2007). Alternately, the fluidized bed reformer system developed for steam reforming 

of biomass syngas for the 2012 ethanol demonstration (Dutta et al. 2011) can be used as the 

reformer for this process. 

Wastewater treatment: The VPU aqueous phase contains acids, aldehydes, and phenolics and is 

assumed to be digestible in a process similar to the one described in NREL’s biochemical 

ethanol design report (Humbird et al. 2011). Off-gas from the digester is routed to the hydrogen 

plant. As no data yet exist for this treatment, the model was based on the biochemical ethanol 

design case. The process was modeled as a stoichiometric reactor with complete conversion to 

CO2 and CH4. 

Steam and power: Off-gases that are not needed for hydrogen generation are sent to a boiler for 

combustion to generate superheated steam for a turbine. The turbine design is based on the 

power generation system in the NREL thermochemical mixed alcohols design report (Dutta et al. 

2011). 
4 

Data Gaps, Uncertainties, and Research Needs

The majority of the model is literature based. Experimental results from FY13 and FY14 tasks 

will be used to update the VPU and hydrotreating portions of the model. The goal of this 

pathway is to reach a minimum fuel selling price of $3/gallon of gasoline equivalent (in 2011 

U.S. dollars). To reach this targeted product price, the key bottlenecks, uncertainties, and areas 

for further development are summarized as follows: 

• Demonstrate and optimize VPU yield. There is a wide range of literature data for yield 

and product quality (oxygen content) without a clear understanding of the effects on 

processing costs, organic losses to the aqueous phase, and severity of upgrading. The 

primary objective for optimization of this process is to retain as much carbon in the liquid 

product as possible while removing the highly reactive oxygen species.

• Develop VPU reactor design data. Careful design of the product recovery scheme is 

needed to ensure product stability and mitigate fouling. Handling of large amounts of 

solids will also need attention. Effective removal of solids prior to the VPU step may help 

improve VPU catalyst life and stability. Removal of solids after the VPU is necessary to 

ensure no negative effects on downstream integration. Design of the VPU catalyst 

regeneration system will be important to maximize catalyst life and productivity.

• Develop and optimize VPU catalysts. VPU catalyst maintenance and stability are 

unknown, as are regeneration protocols and lifetime. Testing with bio-oils and detailed 

characterization of catalyst performance and deactivation modes are needed. Catalysts 

developed for this process need to be both mechanically and thermally stable and robust 

to improve overall lifetimes. These catalysts must produce a VPU oil product that is an 

improvement over conventional pyrolysis oil, and that oil must be produced in good 

yield. A fundamental understanding of the detailed reaction mechanisms and kinetics can 

enable the design of catalysts with optimal productivity rates and yields toward desired 

product slates. Investigating the solid/vapor interface chemistry and increasing the 

catalytic conversion are key areas for realizing VPU catalysts improvements. Rational 

design and development of catalysts could be accomplished using a combination of 

computational and experimental techniques. 

• Optimize hydrotreating. Hydrodeoxygenation upgrading may be performed in a single 

bed if the catalytic pyrolysis oil is of sufficiently low oxygen content or if the oxygen 

content is contained within unreactive species that do not readily polymerize. Parameter 

testing and development of compounds’ structure-reactivity relationships are needed.

Hydrodeoxygenation catalyst maintenance issues are unknown but should be better than 

processing raw fast pyrolysis oil. A preliminary short term test suggested few problems 

(Zacher et al. 2011); however, this test used two catalyst beds. Ideally, a single upgrading 

reactor is needed in order to reduce costs, as is reduced hydrogen consumption. Long 

term catalyst testing, upgraded bio-oil speciation, and fuel quality tests are needed. 

Understanding the speciation of olefins, aromatics, and oxygenates will assist in 

optimizing hydrogen usage.

• Characterize fuels and intermediates. The final hydrocarbon product may not be of 

sufficient quality to use as a blendstock, which was assumed in the economics. Key 

properties such as cetane and octane, as well as flash points, smoke points, cloud or pour 
5 

points, and distillation curves must be verified against gasoline and diesel specifications. 

Consideration should be given to production of refinery intermediates instead of finished 

fuels, and as such, better characterization of the VPU oil is needed. The off-gas 

composition should also be better understood to verify its suitability as a hydrogen plant 

feedstock.

• Establish optimum VPU oil properties. A key element to the process design will be 

developing an understanding of effective process integration—specifically, the trade-offs 

between the amount and quality of oil produced via VPU and the impact this has on 

downstream hydrodeoxygenation. Higher quality oil requires less hydrodeoxygenation 

but the yield may be reduced from the VPU step. Lower quality oil will require higher 

severity hydrodeoxygenation but also may have higher yields. 

• Determine optimum wastewater treatment. Wastewater treatment is largely 

unexplored, and anaerobic digestion may not be appropriate for the types of species 

present. There is a need to understand the impact of organic compounds on wastewater 

treatment, to understand the toxicity of trace compounds, and to minimize carbon loss to 

wastewater treatment. Research is needed to understand the conversion of organics in the 

aqueous phase to hydrogen, bio-products, and species that can rejoin the predominately 

organic phase. Consideration should also be given to alternate wastewater treatment 

methods such as catalytic hydrothermal gasification. 

Summary and Next Steps

This study assessed the processing of woody biomass conversion via ex-situ catalytic fast 

pyrolysis followed by upgrading and finishing to gasoline-, diesel-, and jet-range hydrocarbon 

blendstocks. A mainly literature-based techno-economic analysis was performed to identify 

technology gaps, uncertainties, and research needed to achieve a minimum fuel selling price of 

$3/gallon of gasoline equivalent. A design case detailing this pathway will be developed in 

FY14. 

References

Czernik, S. (2011). “Catalytic Pyrolysis of Biomass at NREL.” Presented at TC Biomass 2011, 

Chicago, Illinois. 

Dayton, David. (February 2011). “Catalytic Deoxygenation of Biomass Pyrolysis Vapors to 

Improve Bio-Oil Stability.” Presented at the 2011 DOE/OBP Thermochemical Platform Review. 

Diebold, J.; Phillips, S.; Tyndall, D.; Scahill, J.; Feik, C.; Czernik, S. (August 1994). “Catalytic 

Upgrading of Biocrude Oil Vapors to Produce Hydrocarbons for Oil Refinery Applications.” 

Preprint from the 1994 Fall American Chemical Society Energy & Fuels Division Conference. 

Washington, DC: American Chemical Society. 

http://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/39_4_WASHINGTON%20DC_08-

94_1043.pdf.

Dutta, A.; Talmadge, M.; Hensley, J.; Worley, M.; Dudgeon, D.; Barton, D.; Groendijk, P.; 

Ferrari, D.; Stears, B.; Searcy, E. M.; Wright, C. T.; Hess, J. R. (2011). Process Design and 

Economics for Conversion of Lignocellulosic Biomass to Ethanol: Thermochemical Pathway by 
6 

Indirect Gasification and Mixed Alcohol Synthesis. NREL/TP-5100-51400. Golden, CO: 

National Renewable Energy Laboratory. 

Elliott, D.; Hart, T.; Neuenschwander, G.; Rotness, L.; Zacher, A. (2009). “Catalytic 

Hydroprocessing of Biomass Fast Pyrolysis Bio-Oil to Produce Hydrocarbon Products.” 

Environmental Progress & Sustainable Energy (28:3); pp. 441-449. 

Envergent. (2011). “Technology – Frequently Asked Questions.” Des Plaines, IL: Envergent 

Technologies. http://www.envergenttech.com. 

Humbird, D.; Davis, R.; Tao, L.; Kinchin, C.; Hsu, D.; Aden, A.; Schoen, P.; Lukas, J.; Olthof, 

B.; Worley, M.; Sexton, D.; Dudgeon, D. (May 2011). Process Design and Economics for 

Biochemical Conversion of Lignocellulosic Biomass to Ethanol: Dilute-Acid Pretreatment and 

Enzymatic Hydrolysis of Corn Stover. NREL/TP-5100-47764. Golden, CO: National Renewable 

Energy Laboratory. 

Jones, S.; Valkenburg, C.; Walton, C.; Elliott, D.; Holladay, J.; Stevens, D.; Kinchin, C.; Czernik, 

S. (February 2009). Production of Gasoline and Diesel from Biomass via Fast Pyrolysis, 

Hydrotreating and Hydrocracking: A Design Case. PNNL-18284. Richland, WA: Pacific 

Northwest National Laboratory.

Jones, S.; Male, J. (2012). Production of Gasoline and Diesel from Biomass via Fast Pyrolysis, 

Hydrotreating and Hydrocracking: 2011 State of Technology and Projections to 2017. PNNL 

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Biomass Conversion and Biorefinery (1); pp. 203-215. 

SRI Consulting. (2007). PEP Yearbook. Menlo Park, CA: SRI Consulting. 

http://www.sriconsulting.com/. 

Stefanidis, S.; Kalogiannis, K.; Iliopouulou, E.; Lappas, A.; Pilavachi, P. (2011). “In-situ 

Upgrading of Biomass Pyrolysis Vapors: Catalyst Screening on a Fixed Bed Reactor.” 

Bioresource Technology (102); pp. 8261-8267. 

Zacher, A.; Santosa, D.; Elliott, D. Brown, C.; Beckman D. (2011). “Mild Catalytic Fast 

Pyrolysis of Biomass and Catalytic Hydrotreating to Liquid Transportation Fuels.” PNNL-SA82908. Presented at TC Biomass 2011, Chicago Illinois.