Molecular-Level Simulation of Thermogravimetric Analysis (TGA): A Cellulose Pyrolysis Example

Molecular-level Simulation of Thermogravimetric Analysis (TGA):
A Cellulose Pyrolysis Example

Juan C. Lucio-Vega, Scott R. Horton, and Mike T. Klein

Department of Chemical and Biomolecular Engineering, University of Delaware

Thermogravimetric analysis (TGA) of cellulose pyrolysis was simulated using a molecular-level kinetics model.  A temperature ramp between 600-1000°C was imposed in order to achieve the TGA simulation.  The underlying celllose pyrolysis model accounted for polymer polydispersity whose decomposition was described using Flory-Stockmayer statistics and the degree of polymerization [1]. A recursive optimization method was utilized to calculate the degree of polymerization of the starting cellulose from literature bulk properties [1, 2]. The model’s primary reaction pathways for the decomposition allowed for the clipping of the active cellulose by thermolysis in order to create levoglucasan (LGA) and glucose. The chemistry proposed by Lin et al [2] was then applied as secondary reactions where the LGA molecules reacted to produce intermediates and levoglucosenone (LGO). Further breakdown of the LGO molecules formed volatiles, furans, aldehyde, ketones, and char through a series of complex reactions. Linear free energy relationships were applied to minimize the number of model kinetic parameters. Executing the cellulose pyrolysis model in TGA mode provided a prediction of the mass loss, which in turn allowed the model parameters to be optimized to literature TGA data [2]. The optimized model showed good agreement with the experimental trends.

[1] Scott R. Horton, Rebecca J. Mohr, Yu Zhang, Francis P. Petrocelli, and Michael T. Klein. "Molecular-Level Kinetic Modeling of Biomass Gasification." Energy & Fuels 30.3 (2016): 1647-1661.

[2] Yu-Chuan Lin, Joungmo Cho, Geoffrey A. Tompsett, Phillip R. Westmoreland, and George W. Huber, “Kinetics and Mechanism of Cellulose Pyrolysis” Journal of Physical Chemistry 113 (2009): 20097–20107.