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Photo of Brennan Pecha

Brennan Pecha

Postdoctoral Researcher-Chemical Engineering

Michael.Pecha@nrel.gov | 303-275-4817

Research Interests

Biomass Pyrolysis

Pyrolysis is a process that uses heat to thermally degrade polymers such as cellulose, lignin, and plastics, into a carbonaceous residue (char), condensable oil, and gases. The oil (“bio-oil”) is a mixture of thousands of compounds. Some of the compounds are soluble in water (aqueous), while others are not (organic), so depending on the processing conditions (fast or slow pyrolysis) the oil can be a single emulsified phase or several phases. A complex process, it needs to be studied experimentally using several approaches and many scales ranging from nano (atomic) level to single particle level to the reactor level.

In my doctorate research, I designed a reactor system to study pyrolysis at different pressures to distinguish primary depolymerization reactions from secondary reactions and the phenomenon of micro-explosion, which releases aerosols made up of large chemical intermediate compounds.

Main photo with two inset photos in the upper left and right. The main photo (labeled A) shows a small aluminum cylinder (A1) with a blue pressure gauge (A2) attached on the top, a coil wrapped in gray tape (A5) attached on the left over a glass tube (A4), a black handle with electrical connections attached on the right, and steel tubing (A3) connected on the bottom of the frame leading to a black vacuum line. Inset photo on the upper left (labeled B) shows a glass tube (B1) with copper coil (B2) covering the top and bottom of the tube. Inside the tube is a pipe with a window, inside of which is a small platinum coil. The inset photo in the upper right (labeled C) shows the aluminum cylinder with the small steel pipe (C2) emerging from it with a window inside of which is a platinum coil (C1) inside of which is a long thin quartz tube and a thin pink wire leading up the steel pipe into the platinum coil holding the quartz tube.

(A) Modified pyroprobe captive sample reactor used for this study. The custom aluminum housing (A1) holds the pyroprobe inside a glass culture tube (A4, B1), sealed with a rubber gasket to the body. The glass tube is chilled by insulated 3/8” copper chilling loop (A5) at -7 °C. There are lines leading to the vacuum pump and gas sampling port (A3) as well as a vacuum gauge (A2). (B) Alternative chilling loop (B2) to allow for video recording of the solid sample. (C) Pyroprobe exposed to display thermocouple placement. Two thermocouples measure temperature in the gas (C2) and sample wall (C1).

Photo looking down the end of an open black pipe (represented by concentric, ripple-like circles of a blue/gray blurry background), inside of which is a red hot flat heating element on top of which is a quartz plate with a brown pile of powder that extends beyond the diameter of the pipe. A pink wire leads into the brown pile and smoke is coming off of the pile.

Visualization of a pile of wood powder pyrolyzing and releasing vapors from the intermediate melt phase.

Computational Fluid Dynamics (CFD)

Simulation of multiscale chemical reaction systems is a powerful tool to understand and design systems when coupled with and verified by experimental data. It can be used to study the effect of physical parameters on effective reaction rates. In biomass pyrolysis, I have participated in collaborative efforts to couple single particle CFD biomass pyrolysis models with reactor-scale discrete element models (DEM) to understand the effect of morphological particle distributions on the product yields. I have also worked on CFD for catalyst modeling.

Figure of five subplots with a blue ellipsoidal-cylindrical particle with ribbed sides and holes in the top indicating long pores inside the particle. The particle color indicates heat transfer into particle, and ends of the particle are red indicating more heat transfer at the porous ends. A left y-axis labeled 'Velocity magnitude (m/s)' ranges from 0 (dark purple) to 2.3  (white) and ranges in color from dark purple to red to orange to yellow to white. A right y-axis labeled 'Heat flux (MW/m2)' ranges from 0 (dark blue) to 1.0 (red) and ranges in color from dark blue to turquoise to green to yellow to orange to red. The (A) and (D) subplots show top-flow configurations. The (B), (C), and (F) subplots show top-flow configurations. Outside the particle is blue gas which changes color to red and yellow as it moves away from the particle indicating increasing gas speed as distance from particle increases.

Simulated heat transfer into 0.5 mm long wood particles at Pr = 0.5 and Re = 100. (A) Aspen particle in top-flow configuration. (B) Aspen particle in side-flow 1 configuration. (C) Aspen particle in side-flow 2 configuration. (D) Pine particle in top-flow configuration. (F) Pine particle in side-flow configuration. In all cases, the narrow regions of the leading edge of the particle achieve highest interfacial heat transfer. Depressed regions of the particle surfaces, such as area within partial lumen on the particle exterior display, relatively lower localized interfacial heat transfer due to the low local fluid velocities within the boundary layer.

Reaction Engineering

Chemical reaction rates are difficult to study in complex, realistic systems with crude raw feedstocks. By coupling CFD simulations described above with experimental data, we can isolate and extract kinetic reaction information and push the limits of understanding in these areas.

Areas of Expertise

  • Computational modeling: Kinetic modeling of catalytic reactions and biomass pyrolysis (Matlab + COMSOL)

  • Scientific reactor design: Novel design concepts for studying specific chemical reaction or physical phenomena

Education

  • Ph.D., Chemical Engineering, Washington State University, 2017

  • B.S., Chemistry, University of Dallas, 2011

Associations and Accreditations/Memberships

  • American Institute of Chemical Engineers

  • American Chemical Society

Featured Publications

  1. "Estimation of Interfacial Heat Transfer Coefficients for Biomass Particles by Direct Numerical Simulation Using Microstructured Particle Models," ACS Sustainable Chemistry & Engineering (2017) 

  2. "Effect of Vacuum on the Fast Pyrolysis of Cellulose: Nature of Secondary Reactions in Liquid Intermediate," Industrial & Engineering Chemistry Research (2017)

  3. "Effect of Temperature and Heating Rate on Product Distribution from the Pyrolysis of Sugarcane Bagasse in a Hot Plate Reactor," Journal of Analytical and Applied Pyrolysis (2017) 

  4. "Chemical and morphological evaluation of chars produced from primary biomass constituents: Cellulose, xylan, and lignin," Biomass and Bioenergy (2017) 

  5. "Micro-explosion of liquid intermediates during the fast pyrolysis of sucrose and organosolv lignin," Journal of Analytical and Applied Pyrolysis (2016)

  6. "Cellulose-Lignin Interactions during Slow and Fast Pyrolysis," Journal of Analytical and Applied Pyrolysis (2015) 

  7. "Impact of Combined Acid Washing and Acid Impregnation on the Pyrolysis of Douglas Fir Wood," Journal of Analytical and Applied Pyrolysis (2015)

  8. "Effect of particle size on the composition of lignin derived oligomers obtained by fast pyrolysis of beech wood," Fuel (2014)

  9. "Effect of Pyrolysis Temperature and Sulfuric Acid During the Fast Pyrolysis of Cellulose and Douglas Fir in an Atmospheric Pressure Wire Mesh Reactor," Energy Fuels (2014)

  10. "Slow and fast pyrolysis of Douglas-fir lignin: Importance of liquid-intermediate formation on the distribution of products," Biomass and Bioenergy (2014)

  11. "Effect of Cellulose Crystallinity on Solid/Liquid Phase Reactions Responsible for the Formation of Carbonaceous Residues during Slow Pyrolysis," Industrial & Engineering Chemistry Research (2014)

  12. "Novel concept for the conversion of wheat straw into hydrogen, heat, and power: A preliminary design for the conditions of Washington State University," International Journal of Hydrogen Energy (2013)

  13. "Secondary Vapor Phase Reactions of Lignin-Derived Oligomers Obtained by Fast Pyrolysis of Pine Wood," Energy Fuels (2013)

  14. "Effect of cellulose crystallinity on the formation of a liquid intermediate and on product distribution during pyrolysis," Journal of Analytical and Applied Pyrolysis (2013)

  15. "Effect of the Fast Pyrolysis Temperature on the Primary and Secondary Products of Lignin," Energy Fuels (2013)

Book Chapters

  1. "Chapter 2: Converting Composting Facilities into Biorefineries," in Advancing Organics Management in Washington State (2016)

  2. "Chapter 26: Pyrolysis of Lignocellulosic Biomass: Oil, Char and Gas," in Bioenergy: Biomass to Biofuels (2014)

Awards and Honors

  • Frontier-Labs Young Scientist Award, poster award, Pyro 2016 (2016)

  • Alaska Airlines Biofuels Travel Grant (2016)

  • Outstanding Reviewer Status, Biomass and Bioenergy (2015) 

  • Hydrogen Student Contest, 2nd place (2012)

  • Melvin and Ruth Smith Scholarship, Washington State University Dept. of Chemical Engineering (2012) 


Please contact me with research questions, ideas for collaborations, and questions about pyrolysis or catalysis projects at NREL. Please do NOT contact me directly for jobs—see instead information on NREL's Director's Postdoctoral Fellowship program or on NREL Careers in general.