Cellulose pyrolysis kinetics in a simulated solar environment

Abstract

The instrumentation and methods required to study rapid, radiative decomposition of highly reactive biopolymers are described and used to determine the kinetic parameters for the pyrolysis of Avicel PH105 microcrystalline cellulose. Experiments were carried out at heating rates greater than 2 K/s in a specially fabricated thermogravimetric analyzer system which employed a 30-kWe/2-kWth downward-facing beam, arc-image furnace as a heat source. The thermogravimetric data were interpreted assuming a simple, single-step reaction mechanism and using a nonlinear least-squares kinetic analysis. Based on the results, an apparent activation energy of 100.5 ± 3 kJ/mol, a preexponential factor of In [A (s'1)] = 14 ± 0.5, and nearly a first-order ( = 0.9 ± 0.05) reaction were obtained. The extent of char formation was determined experimentally and found to be in the range 6.6-8.4% by weight of original dry material depending upon the prevailing reaction conditions.

A model for primary and heterogeneous secondary reactions of wood pyrolysis

“…Murty and Blackshear [38] also observed an increase in reaction rate constant at a particular temperature on passing from the surface to the center of the specimen and Stamm [39] has described experiments in which the rate of reaction was increased when products were not free to escape, effects that could be called autocatalytic. Tabatabaie et al [40] call attention to the fact that their high temperature decomposition of cellulose in the Fast-TGA sample boat may have been affected by autocatalysis (perhaps by the presence of organic acids such as formic and acetic acids in the volatile pyrolysis products). Autocatalysis is promoted by the presence of the lid which hinders easy escape of the primary vapours from within the sample boat into the inert carrier gas stream [41].…”

Review of Heat Transfer Research for Solar Thermochemical Applications

“…The bulk kinetic reaction approach for modeling the reactor scale systems is described here. Experimental investigations of reaction kinetics are typically performed using thermogravimeters [64][65][66][67][68][69][70][71][72] or laboratory scale reactors, including fluidized beds [73][74][75], stabilized beds [76][77][78], and monolithic structured reactors [79][80][81][82][83]. Reaction kinetic modeling associated with each of these practices requires special attention to the corresponding experimental conditions.…”

“…For monolithic reactors with small reactive surface area or small samples used in thermogravitometers the species concentra- [65,[68][69][70]. However, for larger scale reactors, such as fluidized or stabilized beds with large reactive surface area, the species concentration gradient is significant in the flow direction, and a control volume approach combined with Eq.…”

“…The solar thermogravimetric analyzer, or solar TGA, is a unique device to study the global kinetics of solid-state reactions in an environment similar to that expected in a solar reactor. As first described by Tabatabaie-Raissi et al [68,69], the solar TGA is a directly irradiated, insulated cavity in which material samples are heated and reaction rates are determined from gravimetric measurements. They measured the kinetics of decomposition of zinc sulfate and pyrolysis of cellulose and discuss the necessity for accurate calibration and measurement of transient temperature and weight change.…”

“…As in all high-temperature measurements, conduction along the probe, radiation exchange with the surroundings, and contact resistance must be accounted for in converting the raw data to an accurate estimate of measured temperature. Additionally, due to the rapid heating and cooling rates (i.e., from solar furnaces, solar simulators, or benchtop-scale imaging furnaces), errors due to sensor time lag are often significant [68,69]. The time constant is not known a priori in radiative systems and, thus, must be measured in a carefully designed experiment that replicates the heat transfer modes in the planned operational environment.…”