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>_a) 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, CO₂, CH₄, HCHO, CH₃OH, HCOOH, and CH₃COOH, 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 K₂CO₃, 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 K₂CO₃ 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