(556b) Kinetics and Energetics of Biomass Pyrolysis By Pulse-Heated Analysis of Solid Reactions (PHASR)

Thermochemical conversion of lignocellulosic biomass utilizes high temperature chemical decomposition to produce liquids via pyrolysis, solids via torrefaction, or gases via gasification which are subsequently converted to liquid biofuels or biochemical^[1]. However, these systems are comprised of thousands of molecules and millions of chemical reactions within three phases, making them intractable by conventional research techniques. In this presentation, utilization of an isothermal biomass kinetics reactor called “PHASR” (Pulse-Heated Analysis of Solid Reactions) enables millisecond time-resolved measurement of 100-200 chemical compounds produced from cellulose at 300-550 °C^[2]. The design of the technique and its performance are presented. The requirements for elimination of transport (heat and mass) artifacts are identified along with experimental measurement identifying the kinetic transition between transport- and reaction-controlled conditions; biomass films reacting at 500 °C must be thinner than 70 µm. The experimental kinetics of cellulose conversion indicate a key cellulose initiation mechanism transition at 467 °C, wherein the low temperature intra-chain initiation mechanism (E_a,app 23.2±1.9 kcal/mol, k₀ 2.0 × 10⁷ s^-1) is converted to a high temperature intra-chain initiation initiation mechanism (E_a,app 53.7±1.1 kcal/mol, k₀ 2.4 × 10¹⁶ s^-1)^[3]. The mechanisms of cellulose initiation and further reaction to volatile products are discussed in relation to the measured energies.

[1] "Top Ten Fundamental Challenges of Biomass Pyrolysis," M.S. Mettler, D.G. Vlachos, P.J. Dauenhauer, Energy & Environmental Science 2012, 5, 7797-7809.

[2] "Millisecond Pulsed Films Unify the Mechanisms of Cellulose Fragmentation," Christoph Krumm, J. Pfaendtner, P.J. Dauenhauer, Chemistry of Materials 2016, 28(9), 3108-3114.

[3] "Energetics of Cellulose and Cyclodextrin Glycosidic Bond Cleavage," Cheng Zhu, Christoph Krumm, Greg Facas, Matthew Neurock, Paul J. Dauenhauer Reaction Chemistry and Engineering 2017. DOI: 10.1039/C6RE00176A