Introduction to pyrolysis of biomass

The pyrolytic properties of biomass are controlled by the chemical composition of its major components, namely cellulose, hemicelluloses and lignin and their minor components including extractives and inorganic materials. Pyrolysis of these materials proceeds through a series of complex, concurrent and consecutive reactions and provides a variety of products.Pyrolysis cellulose at lower temperatures below 300° C involves reduction in molecular weight, evolution of water, carbon dioxide and carbon monoxide and formation of char. On heating at higher temperature 300–500° C, the molecule is rapidly depolymerized to anhydroglucose units that further reacts to provide a XXXX pyrolyXXXXA: still higher temperatures, the anhydrosugar compounds undergo fussion, dehydration disproportionation and decarboxylation reaction to provide a mixture of low molecular weight gaseous and volatile produces. The composition of these produces and mechanism and kinetics of their production are reported.     

Particle size limitations due to heat transfer in determining pyrolysis kinetics of biomass

A simplified heat transfer model is analyzed in order to determine an upper bound for biomass particle size in conducting experimental pyrolysis kinetics. In determining intrinsic kinetic rates, it is desirable that the entire particle be at reactor temperature for the duration of the chemical reaction. By comparing characteristic times for reaction rates versus heat-up rates, an approximate boundary for particle size can be constructed as a function of temperature; above this boundary, the reaction rate is strongly heat transfer dominated, and below the boundary the reaction rate is kinetically controlled. Using parameters for cellulose pyrolysis, it is estimated that a 200 μm particle will be heat transfer limited due to internal heat transfer at temperatures above 500°C. This boundary applies for conditions where the surface of the particle is brought to reactor temperature instantaneously. Using our specific experimental conditions, it is found that the limitations imposed by external transfer are reached before those predicted by assuming that only internal heat transfer is limiting. In examining wood pyrolysis, where a global reaction rate approximation is insufficient, it is experimentally shown that the decomposition for hemicellulose can be transport limited, while cellulose remains in the kinetic controlled regime.     

Fast pyrolysis of biomass

The development of viable fast pyrolysis processes for biomass and other carbonaceous feedstocks will offer significant advantages over conventional pyrolysis, flash pyrolysis and gasification processes with respect to product yield quality and flexibility. Fast pyrolysis is defined and related to other biomass thermochemical conversion processes in some detail. Brief references are made to corresponding coal, hydrocarbon and oil conversion research and development. Proposed mechanisms and chemical pathways are reviewed, potential products. product upgrading and product applications are identified. Fast pyrolysis research is reviewed on both the fundamental bench-scale level and the applied process development level.     

Microwave pyrolysis of biomass

Because of the inherent moisture and large particle size of wood used in the Forest Products Industry, there has been regional interest in exploring the feasibility of processing wood, cellulose, and other such related materials using microwave dielectric-loss heating. A research project was undertaken in the late 1970’s to determine the important variables altering the rate of microwave-induced reactions of this polymeric material. The research presented dates from that period. Reaction proudcts were measured in detail and some optimization of the coupling of the microwave energy to the large particles was studied. Results and principal findings at the time of the study are presented in this paper as well as two papers by the author in the cited literature. Suggestions for future directions for this type of study are also presented.     

Relevance of analytical pyrolysis studies to biomass conversion

The principles and methods of soft ionization mass spectrometry in combination with pyrolysis of macromolecules are outlined. Essential features of the newly developed techniques are the extension of the recorded mass range and the almost exclusive formation of molecular ions of the pyrolyzates. Using field ionization and field desorption mass spectrometry at low and high mass resolution, with electrical and photographic detection, pyrolysis products of biomass were analyzed for the first time. The results of flash pyrolysis by Curie-point heating and thermally programmed degradation of biopolymers are compared.The main topic is the evaluation of the methodology for time- and temperature-resolved pyrolysis. The thermograms and pyrolysis mass spectra obtained enable the study of pyrolysis reactions and the chemical fingerprinting of complex biological matter. The kinetics for the devolatilization of individual chemical species or classes of compounds can be monitored. Curie-point pyrolysis of biopolymers such as kappa-carrageenan and time-programmed degradation of cellulose and lignin are reported. Furthermore, preliminary investigations of pine wood and coal illustrate the potential of the introduced methods.     

Study of the pyrolysis of polystyrenes: I. Kinetics of thermal decomposition

The pyrolysis of polystyrene, studied by isothermal thermogravimetry in the temperature range 300–400°C, obeys the kinetic law dα/dτ = k(1 - α)[1 - α)^2b]^{$\text{1}\text{2}$} or dα/dτ = k(1 - α)tanh β, expressions in which b depends on temperature and (cosh β)^{$\text{1}\text{3}$} = 1 - α.In order to establish the validity of this law in the very large range 0.10 < α < 0.95, it was assumed that the pyrolysis is carried out in three steps: random initiation, depolymerization and termination by disproportionation or combination. In the kinetic expression the term tanh β is proportional to the concentration of radicals and represents the setting up of the steady state. The activation energies obtained for every step agree very well with those given in the literature, whereas the apparent activation energy of the global mechanism was found to be about 43 kcal mol^?1.     

Radiation effects on thermal decomposition of ammonium perchlorate

Thermal decomposition of -irradiated (dose: 0–3.6 MGy) ammonium perchlorate was followed. The dynamic heating (range: 100–220 °C) and IR spectral measurements were carried out simultaneously. Temperature and dose brought a lowering in peak intensity of NH ₄ ⁺ and C10 ₄ ^– ions. Radiolytic products C10₃ and NH₃ are considered to initiate the decomposition process.     

High-temperature gasification kinetics of biomass pyrolysis

The rate of gas formation from wood pyrolysis has been experimentally measured at temperatures from 300°C to 1000°C. The formation rate of specific product gases has been measured rather than the rate of solid weight loss. Even for very fine particles, the rate becomes heat transfer limited a: high temperatures. The product gases also approach thermodynamic equilibrium rapidly at high temperatures. The results are corrected using the experimental residence time distribution.     

Catalytic effects of six inorganic compounds on pyrolysis of three kinds of biomass

Six inorganic compounds, i.e., Na₂CO₃, NaOH, NaCl, Na₂SiO₃, TiO₂ and HZSM-5, have been investigated with regard to their catalytic effects on pyrolysis of three biomass species, i.e., pine wood, cotton stalk and fir wood by thermal analysis experiments. The results show that Na₂CO₃, NaOH, Na₂SiO₃ and NaCl made devolatilization occur at lower temperature regions in the pyrolysis of the three kinds of biomass, whereas TiO₂ and HZSM-5 made that occur at higher temperature regions in the pyrolysis of cotton stalk and had no obvious effects on pyrolysis temperatures of pine wood and fir wood. The basic catalysts NaOH, Na₂CO₃ and Na₂SiO₃ decreased the maximum weight loss rates while NaCl and HZSM-5 increased them and TiO₂ had no obvious effects on them. The four sodium compounds made pyrolysis of the three kinds of biomass more exothermic, which might be due to more char formation, whereas TiO₂ and HZSM-5 had minor effects on reaction heat. The catalytic effects in all aspects were roughly correlated with one another and their relationship with the basicity and acidity of the catalysts were preliminarily described and analyzed.     

Microwave-assisted pyrolysis of biomass: Catalysts to improve product selectivity

This study was intended to evaluate the effects of catalysts on product selectivity of microwave-assisted pyrolysis of corn stover and aspen wood. Metal oxides, salts, and acids including K₂Cr₂O₇, Al₂O₃, KAc, H₃BO₃, Na₂HPO₄, MgCl₂, AlCl₃, CoCl₂, and ZnCl₂ were pre-mixed with corn stover or aspen wood pellets prior to pyrolysis using microwave heating. The thermal process produced three product fractions, namely bio-oil, gas, and charcoal. The effects of the catalysts on the fractional yields were studied. KAc, Al₂O₃, MgCl₂, H₃BO₃, and Na₂HPO₄ were found to increase the bio-oil yield by either suppressing charcoal yield or gas yield or both. These catalysts may function as a microwave absorbent to speed up heating or participate in so-called “in situ upgrading” of pyrolytic vapors during the microwave-assisted pyrolysis of biomass. GC–MS analysis of the bio-oils found that chloride salts promoted a few reactions while suppressing most of the other reactions observed for the control samples. At 8 g MgCl₂/100 biomass level, the GC–MS total ion chromatograms of the bio-oils from the treated corn stover or aspen show only one major furfural peak accounting for about 80% of the area under the spectrum. We conclude that some catalysts improve bio-oil yields, and chloride salts in particular simplify the chemical compositions of the resultant bio-oils and therefore improve the product selectivity of the pyrolysis process.     

Stationary fronts due to weak thermal effects in models of catalytic oxidation

We analyze the possible existence of an infinite number of stationary front solutions in a microkinetic model of a catalytic reaction coupled with weak enthalpy effects in the domain of kinetics bistability. The kinetic model incorporates three steps: dissociative oxygen adsorption, reactant adsorption and desorption, and surface reaction. The infinitude of stationary front solutions emerges due to the lack of intercrystallites communication of surface species in supported catalysts; thermal conductions and gas-phase diffusion are the only means of interaction. Incorporation of surface species diffusion leads to a very slow front motion. We complement this analysis with simulations of stationary states on one- (wire and ring) and two-dimensional (disk) systems which may be subject to control or to fluid flow. These results account for certain experimental results and may have implications for various technological problems.     

The effects of additives on the thermal decomposition of azodicarbonamide

The thermal decomposition of azodicarbanamide containing a promotor and pigments is studied by thermal analysis. The promotor used was the “Standere” 3450 containing zinc and cadmium, the activation energies ranged from 25.1 to 38.2 kJ mol^?1 with different ratios. Six pigments are studied giving a range of activation energy values from 45.3 to 156.8 kJ mol^?1.     

基于TG-FTIR的生物质催化热解试验研究

运用热重－傅里叶红外光谱联用技术(TG-FTIR),以麦秸为研究对象,探讨催化与非催化条件下生物质的热解挥发分析出特性,分析研究热解温度、催化剂种类对生物质热解主要析出产物的影响。通过热重TG和DTG曲线,获得了相关热解特性参数及动力学参数。结果表明,添加NiO和CaO存在两个失重峰,并促进麦秸热解反应进行,降低表观活化能,其中NiO对提高热解析出产率作用更显著。通过红外光谱对热解产物实时测量的分析表明,CO与CO2的析出与失重峰基本一致,而CH4的析出滞后于前两者。添加NiO和CaO有利于减少热解产物中的CO2的浓度,促进挥发分产物CO、CH4的生成。其中CaO更有利于生物质在温度800℃以下的热解性能改善,而NiO在800℃以上具有更好的催化作用。     

升温速率对生物质热解的影响

稻壳、稻秆及麦秆是中国主要的农业废弃物,如何综合、有效地利用这些农业废弃物进行资源化研究显得十分必要。热解是热化学转化中最为基本的过程,是气化、液化及燃烧过程的初始和伴生反应,对热解的分析有助于热化学转化过程控制及高效转化工艺的开发。目前,国内外对生物质及其组分的热解已有大量的研究,但对中国主要的农业废弃物稻壳、稻秆及麦秆的研究较少。本研究利用热重和红外联用技术深入研究了升温速率对三种典型生物质热解气体产物的影响,并对生物质的热解动力学及热解气体产物的析出规律进行实时在线分析。     

The effect of defect structure due to doping and irradiation on the thermal decomposition of potassium chlorate

The thermal decomposition of potassium chlorate was investigated as a function of doping and there seems to be a correlation between the polarizing nature of the dopant cation and the thermal degradation temperature of potassium chlorate. In particular, transition metal cations influence strongly the temperature of decomposition. Irradiation and mechanical shock defects influence also the process. A possible mechanism in terms of the semi-conductive properties of the defective chlorates is discussed.

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Zusammenfassung Die thermische Zersetzung von Kaliumchlorat wurde in Abhängigkeit von der Zugabe von Zusätzen untersucht und es scheint eine Korrelation zwischen der polarisierenden Beschaffenheit des Additivkations und der thermischen Zersetzungstemperatur von Kaliumchlorat zu bestehen. Besonders die Übergangsmetallkationen beeinflussen die Zersetzungstemperatur stark. Bestrahlung und mechanische Stoßdefekte beeinflussen den Vorgang ebenfalls. Ein möglicher Mechanismus wird anhand der Halbleiter-Eigenschaften der defekten Chlorate erörtert.

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Résumé On a étudié la décomposition thermique du chlorate de potassium en fonction de l'ajout d'additifs. Il semble qu'une corrélation existe entre la nature polarisante du cation de l'additif et la température de la dégradation thermique du chlorate de potassium. Enparticulier, ce sont les cations des métaux de transition, qui exercent une forte influence sur la température de décomposition. L'irradiation et des défauts causés par choc mécanique influencent aussi le processus. On discute un mécanisme possible à partir des propriétés semi-conductrices des chlorates présentant des défauts.

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Thermal decomposition of algae bloom biomass

The algae bloom biomass in the water reservoir ‘Rybnik’ is an important problem, and not only in Poland [1,2]. The algae growth in the water affects its odour, colour, taste and quality [3]. Algae bloom biomass removed from water can be treated in the following ways:

disposal in sanitary landfills

storage on special dumping grounds

fermentation

dewatering and incineration

In this paper the physicochemical composition and thermal analysis of the biomass of algae bloom dried at 378 K or in the open air are described. Thermal analytical measurements were made in an air atmosphere.     

Application of off-line pyrolysis with dynamic solid-phase microextraction to the GC–MS analysis of biomass pyrolysis products

Pyrolysis coupled with dynamic solid-phase micro extraction (Py-SPME) followed by GC–MS analysis was applied to the determination of volatile compounds evolved by a micro-scale off-line pyrolysis apparatus, in order to extend the information affordable with this type of analytical equipment. The Py-SPME method with a carboxen/PDMS fiber working in the retracted mode was tested on four biomass samples (switchgrass, sweet sorghum, corn stalk and poplar) for qualitative analysis of semi-volatile pyrolysis products and quantitative determination of main volatiles (C₁–C₄) pyrolysis products. The developed procedure allowed capturing and analysis of all GC analyzable compounds, without memory effects and with good peak resolution also for early GC-eluting compounds. Twelve main volatile pyrolysis products, including hydroxyacetaldehyde and acetic acid, were successfully quantified; in spite of the intrinsic variability introduced by dynamic SPME sampling, results were relatively accurate and consistent with literature data on bench pyrolysis reactors.