5 research outputs found
Kinetic Modeling of Cellulose Fractional Pyrolysis
The kinetics of cellulose
fractional pyrolysis was studied for
the first time in the temperature range of 200–900 °C,
with 25 °C increment under nitrogen atmosphere. A detailed analysis
of the major and minor pyrolysis products was performed using a System
for Thermal Diagnostic Studies (STDS) and FTIR techniques. A semiglobal
kinetic model was proposed, with products grouped into kinetic lumps,
based on their formation profile similarity. Kinetic parameters (pre-exponential
factor <i>A</i> and activation energy <i>E</i><sub>a</sub>) for formation of major products grouped into heavy
volatiles 1 lump (levoglucosan and anhydrosugars) and light volatiles
2 lump (furans and carbonyls) were obtained based on the performed
experimental studies. The final model accurately predicts not only
the weight loss, the temperature-distribution of major lumped products,
and the total yields of tar and gases from the fractional pyrolysis
of cellulose but also shows a good performance toward literature data
for experimental studies of others
Low-Temperature Pyrolysis of Woody Biomass in the Thermally Thick Regime
Pyrolysis of biomass is a thermal
degradation process in the absence
of oxygen, producing gas, tar, and char. The product distribution
depends on pyrolysis conditions (heating rate, peak temperature, particle
size). In this work, the decomposition of dried poplar wood cylinders
of 1.9 cm diameter is investigated under conditions favoring production
of “biochar” for soil amendment, that is, in the thermally
thick regime with maximum temperature <450 °C. The intraparticle
temperature history was measured using a thin sheathed thermocouple.
Time-resolved mole fractions of light pyrolysis species, CO, CO<sub>2</sub>, CH<sub>4</sub>, HCHO, CH<sub>3</sub>OH, HCOOH, and CH<sub>3</sub>COOH, were measured by FTIR analyzer. Tar was collected and
identified by GC/MS, and yields of gas, tar, and char are reported.
The experiments were compared to the predictions of a one-dimensional
model proposed by Park, W. C.; Atreya, A.; and Baum, H. R. (2010)
and implemented in Comsol Multiphysics commercial software. Sensitivity
to model parameters was determined. The timing of gas production relative
to temperature changes supports the view that exothermic processes
are caused by decomposition of an intermediate solid, after the main
volatiles release
Pyrolysis of Potassium-Doped Wood at the Centimeter and Submillimeter Scales
The
effect of potassium additives on pyrolysis of poplar was investigated
at 427 °C, both at the submillimeter scale, through thermogravimetric
analysis (TGA), and at the centimeter scale, through pyrolysis of
wood cylinders in a turbulent reactor. Internal temperatures and time-resolved
rates of production of gases and light volatiles were measured in
the centimeter-scale study. The potassium level in the samples was
varied through vacuum treatment with distilled water or solutions
of KCl or K<sub>2</sub>CO<sub>3</sub>, resulting in potassium levels
of approximately 100, 4500, and 7000 ppm (dry, mass basis). At the
centimeter scale, potassium addition had a dramatic effect on conversion
time and on the magnitude of exothermic temperature excursions, as
well as a significant effect on the yields of gases and light volatiles.
Consistent with the literature, submillimeter-scale TGA experiments
with external temperature control also indicated a catalytic effect
of the potassium additives, with K<sub>2</sub>CO<sub>3</sub> more
effective than KCl in promoting pyrolysis and char formation
Effect of Particle Size on Low-Temperature Pyrolysis of Woody Biomass
When
biomass is thermochemically processed, the size of the biomass
particles affects processing time requirements and yields. This study
investigates the effects of particle size at the centimeter scale
on pyrolysis through both experimental and modeling approaches, with
three types of woody biomass; poplar, pine sapwood, and pine heartwood.
Large (<i>D</i> = 3.81 cm) and small (<i>D</i> = 2.54 cm) wood spheres were pyrolyzed under thermally thick conditions
at three final pyrolysis temperatures in a reactor with turbulent
gas flow; the same wood materials were also pyrolyzed in a thermogravimetric
analyzer (TGA), under kinetic control. The experiments were simulated
using a previously published 1-dimensional pyrolysis model, which
includes transport and kinetics of solid to vapor reactions for biomass
components. Particle size had a strong effect on devolatilization
timing and also affected the yields of some species. The model was
successful at predicting the qualitative features and approximate
magnitudes of quantities such as temperature overshoot, product yields
for thermally thick particles, and devolatilization timing in both
TGA and thermally thick particles. However, the dependence of yields
and timing on wood type and particle size were not reproduced by the
model
Molecular Products and Fundamentally Based Reaction Pathways in the Gas-Phase Pyrolysis of the Lignin Model Compound <i>p</i>‑Coumaryl Alcohol
The fractional pyrolysis
of lignin model compound para-coumaryl
alcohol (<i>p</i>-CMA) containing a propanoid side chain
and a phenolic OH group was studied using the System for Thermal Diagnostic
Studies at temperatures from 200 to 900 °C, in order to gain
mechanistic insight into the role of large substituents in high-lignin
feedstocks pyrolysis. Phenol and its simple derivatives <i>p-</i>cresol, ethyl-, propenyl-, and propyl-phenols were found to be the
major products predominantly formed at low pyrolysis temperatures
(<500 °C). A cryogenic trapping technique was employed combined
with EPR spectroscopy to identify the open-shell intermediates registered
at pyrolysis temperatures above 500 °C. These were characterized
as radical mixtures primarily consisting of oxygen-linked conjugated
radicals. A comprehensive potential energy surface analysis of <i>p-</i>CMA and <i>p-</i>CMA + H atom systems was performed
using various DFT protocols to examine the possible role of concerted
molecular eliminations and free-radical mechanisms in the formation
of major products. Other significant unimolecular concerted reactions
along with formation and decomposition of primary radicals are also
described and evaluated. The calculations suggest that a set of the
chemically activated secondary radical channels is relevant to the
low temperature product formation under fractional pyrolysis conditions