The pyrolysis process of wood biomass samples under isothermal experimental conditions—energy density considerations: application of the distributed apparent activation energy model with a mixture of distribution functions

This work deals with the isothermal pyrolysis of Pine and Beech wood samples and kinetic studies, using the thermo-analytical technique, at five different operating temperatures. Pyrolysis processes were investigated by using the distributed apparent activation energy model, which involves the complex mixture of different continuous distribution functions. It was found that decomposition processes of wood pseudo-components take place in different conversion areas during entire pyrolyses, whereby these areas, as well as the changes in apparent activation energy (E _a) values, are not the same for softwood and hardwood samples. Bulk density (Bden) and energy density (ED) considerations have shown that both biomass samples suffer from low Bden and ED values. It was concluded that pyrolysis can be used as a means of decreasing transportation costs of wood biomass materials, thus increasing energy density. The “pseudo” kinetic compensation effect was identified, which arises from kinetic model variation and wood species variation. In the current extensive study, it was concluded that primary pyrolysis refers to decomposition reactions of any of three major constituents of the considered wood samples. Also, it was established that primary reactions may proceed in parallel with simultaneous decomposition of lignin, hemicelluloses and cellulose in the different regions of wood samples, depending on the operating temperature. It was established that endothermic effects dominate, which are characterized with devolatilization and formation of volatile products. It has been suggested that the endothermic behavior that arises from pyrolyses of considered samples may indicate the endothermic depolymerization sequence of cellulose structures.     

Investigation of the thermal degradation process of polystyrene brominated on the ring

The results of investigation of the degradation process of polystyrene brominated on the ring via an ionic route have been presented. Using thermogravimetric (TG) and differential thermal analysis (DTA) methods, the course of degradation of polymer samples with different bromine content has been described. Introducing of bromine on the aromatic ring influenced the initial decomposition temperature (IDT) and the temperature corresponding to the maximum of decomposition rate (T _m). The samples have been pyrolyzed at 300°C and some pyrolysis products were identified by means of gas chromatography/mass spectrometry. Finally, the possible mechanism of degradation was presented.     

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.     

Thermal decomposition of C3-substituted peroxyacyl nitrates

The gas phase thermal decomposition rates of C₃-substituted peroxyacyl nitrates, RC(O)OONO₂ have been measured at ambient temperature (287–298 K) and 1 atm. of air. Two saturated compounds (PnBN, R = n-C₃H₇- and PiBN, R = i-C₃H₇-) and two unsaturated compounds (MPAN, R = CH₂=C(CH₃)- and CPAN, R = CH₃CH=CH-) have been studied. In the narrow temperature range studied, thermal decomposition rates for PiBN, PnBN and MPAN exhibited linear Arrhenius behavior with, in units of 10^-4 s^-1, and at 298 K, k = 2.2 for PiBN, 2.3 for MPAN, and 2.7 for PnBN. The thermal decomposition rate of CPAN was 1.6 x 10^-4 s^-1 at 291.6 K and 1.73 x 10^-4 s^-1 at 293.2 K. These thermal decomposition rates are of the same magnitude as that for PAN, R = CH₃. Implications for the atmospheric persistence of C₃- substituted peroxyacyl nitrates are briefly discussed.     

Evolution of gaseous products from biomass pyrolysis in the presence of phosphoric acid

Slow pyrolysis experiments of China fir (Cunninghamia lanceolata) wood were performed in a vertical tubular furnace at various heating rates. The raw material was pretreated by impregnation with phosphoric acid solutions of various concentrations for given times. The evolution of the gaseous products CO, CO₂, H₂ and CH₄ was analyzed online by using gas spectrometry to investigate the effect of phosphoric acid on the pyrolytic gaseous products of biomass. The addition of phosphoric acid was shown to significantly reduce the pyrolysis temperature necessary for the production of CO, CO₂ and H₂ gases, and the pyrolysis variables exerted an influence on the amount of the gases released. Moreover, phosphoric acid appreciably depressed the CO, CO₂ and CH₄ production, and promoted H₂, especially when a higher heating rate was employed. This suggested that phosphoric acid catalyzed both the primary thermal decomposition of biopolymers and the secondary reactions that took place among the pyrolytic vapor products.     

Model-free method for isothermal and non-isothermal decomposition kinetics analysis of PET sample

Pyrolysis, one possible alternative to recover valuable products from waste plastics, has recently been the subject of renewed interest. In the present study, the isoconversion methods, i.e., Vyazovkin model-free approach is applied to study non-isothermal decomposition kinetics of waste PET samples using various temperature integral approximations such as Coats and Redfern, Gorbachev, and Agrawal and Sivasubramanian approximation and direct integration (recursive adaptive Simpson quadrature scheme) to analyze the decomposition kinetics.The results show that activation energy (E_α) is a weak but increasing function of conversion (α) in case of non-isothermal decomposition and strong and decreasing function of conversion in case of isothermal decomposition. This indicates possible existence of nucleation, nuclei growth and gas diffusion mechanism during non-isothermal pyrolysis and nucleation and gas diffusion mechanism during isothermal pyrolysis. Optimum E_α dependencies on α obtained for non-isothermal data showed similar nature for all the types of temperature integral approximations.     

Oxime-trimethylsilylation method for analysis of wood pyrolysate

Oxime-trimethylsilylation (TMS) method was applied to the analysis of wood pyrolysate. Quantitative determination of hydroxycarbonyls such as glycolaldehyde, which are important pyrolysis products of wood polysaccharide, is difficult as indicated by the gas chromatography–mass spectrometry (GC–MS) and ¹H NMR analysis of glycolaldehyde. Glycolaldehyde decomposed into formic acid and the unknown compound with molecular weight of 72 at the injector in its GC analysis. ¹H NMR analysis of glycolaldehyde in acetone-d₆ indicated the complex mixture with its dimerization products. Glycolaldehyde was quantified precisely as oxime-TMS derivative (E/Z-mixture) of the monomer by GC after oximation with hydroxylamine hydrochloride and the following trimethylsilylation with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA). With this method, the other carbonyls such as furfural, 5-hydroxymethylfurfural and hydroxyacetone could also be determined as their oxime-trimethylsilylated derivatives. Furthermore, anhydrosugars such as levoglucosan and levomannosan in wood pyrolysate were also determined, simultaneously, as their TMS derivatives. Finally, oxime-TMS method is proposed as a quantification method of the pyrolysis products derived from wood polysaccharide.     

Thermal and pyrolysis studies of copolyesters

Random copolyesters of dimethyl terephthalate (DMT), ethylene glycol (EG), and butane-1,4-diol (BD) and the homopolyesters poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) have been subjected to degradation and pyrolysis studies. Differential thermal analysis (DTA) showed that the decomposition temperature is dependent on the percentage of EG and BD present in the copolyesters. Thermal volatilization analysis (TVA) also showed that the decomposition temperature is dependent on the percentage of EG and BD present in the copolyesters. The trend for the decomposition temperatures obtained from TVA studies for these copolyesters is similar to such other thermal properties as melting temperature T_m, ΔH_f, ΔH_c, etc. The subambient thermal volatilization analysis (SATVA) curves obtained for these polymers are also presented. The SATVA curve is the fingerprint of the total volatile products formed during the degradation in high vacuum. The isothermal pyrolysis of these materials was carried out in high vacuum at 450°C. The products formed were separated in a gas chromatograph and were subsequently identified in a mass spectrometer. The major pyrolysis products from PBT were butadiene and tetrahydrofuran, whereas those from PET were ethylene and acetaldehyde. The ratio of acetaldehyde to ethylene increases with the EG content in the copolyester, suggesting a different decomposition mechanism compared to the decomposition mechanism of PBT and PET.     

Complex formation and degradation in poly(acrylonitrile‐co‐vinyl acetate) containing copper nitrate

The pyrolysis of polymers containing metal nitrates may provide a relatively simple, rapid, and advantageous method of producing high‐temperature superconductors (HTSCs). The advantage lies in the ability to use conventional polymer processing or microlithographic patterning before pyrolysis. A copolymer of acrylonitrile and vinyl acetate [P(AN‐VA)], a well‐known fiber‐forming polymer, was investigated as a potential HTSC precursor. Complex formation with the highly polar acrylonitrile groups was expected to enhance atomic‐level mixing and hinder nitrate recrystallization. The metal nitrates were found to have a profound effect on P(AN‐VA) pyrolysis. P(AN‐VA) containing copper nitrate (CuN) exhibited complex formation and an exothermic decomposition that began at about 170 °C (reaction 1‐CuN). Reaction 1‐CuN had a heat of about 3.5 kJ/g_NO3 and a mass loss of about 0.99 g/g_NO3. As reaction 1‐CuN also involved the nitrile groups, it disrupted the nitrile cyclization reaction at about 290 °C. For a P(AN‐VA)/CuN ratio of 2/1, there was no nitrile cyclization, and the thermooxidative degradation temperature was reduced by approximately 200 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1023–1032, 2004     

Thermal behavior and degradation mechanism of poly(bisphenyl acryloxyethyl phosphate) as a UV curable flame-retardant oligomer

Poly(bisphenyl acryloxyethyl phosphate) (BPAEP) was blended in different ratios with urethane acrylate EB220 to obtain a series of UV curable flame-retardant resins. The thermal degradation mechanisms of their cured films in air were studied by thermogravimetric analysis, in situ FTIR and direct pyrolysis/mass spectrometry measurements. The results showed that BPAEP/EB220 blends have lower initial decomposition temperatures (T_di) and higher char residues than pure EB220, while BPAEP has the lowest T_di and the highest char residue. The degradation process of BPAEP was divided into three characteristic temperature regions, attributed to the decomposition of phosphate, ester group and alkyl chain, and aromatic structure in the film.     

CO2 production from degraded woods via a novel integrated pyrolysis-combustion process

The process of combustion produces minimal amounts of CO₂ for conventional radiocarbon dating, making it difficult to estimate the age of the archaeological wood. Thus, the objective of this paper is to introduce a novel integrated pyrolysis-combustion process that will maximize the production of CO₂. Degraded wood samples were assumed to be archaeological samples for this study, namely Karas (Aquilaria malaccensis), Meranti (Shorea acuminate) and Setumpol (Hydnocarpus spp.) were used for this process. The process of CO₂ production was optimized by the application of design of experiment (DOE) and response surface method. The mathematical model was examined using the analysis of variance (ANOVA) at 5% level of significance. The temperature during the pyrolysis process, retention time and flow rates for the carrier gas (argon) were found to have a positive influence on the production of CO₂. A second-order model was obtained to predict the production of CO₂ as a function of temperature, retention time and flow rate. Optimum conditions for the production of CO₂ were obtained at a pyrolysis temperature of 300 °C, 20 min retention and 980, 984 and 987.6 ml/min argon flow rate for Karas, Meranti and Setumpol, respectively. The optimized yields of carbon dioxide produced were 82.57, 79.7 and 84% for Karas, Meranti and Setumpol, respectively. The different yields of carbon dioxide were due to the carbon content in the individual samples.     

Die thermische Zersetzung der Erdalkalinitrate

Zusammenfassung Die Zersetzung von Calcium-, Strontium- und Bariumnitrat wurde thermogravimetrisch untersucht. Die Zersetzungstemperaturen wurden bei einer Erwärmungsgeschwindigkeit von 5° C/min festgestellt und isotherme Messungen in einem breiterem Temperaturintervall ausgeführt. Die Bedingungen, bei welchen Ba(NO₃)₂ quantitativ zu BaO₂ zerfällt, werden angegeben und der Einfluß der Menge des Nitrates, der Atmosphäre (O₂, N₂) und der Schmelze auf die Zersetzungsgeschwindigkeit untersucht.

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The decomposition of calcium, strontium and barium nitrates has been studied by thermogravimetric analysis. The decomposition temperature has been determined at a heating rate of 5° C/min and isothermal measurements are given for various temperatures. The experimental conditions for quantitative transition of Ba(NO₃)₂ to BaO₂ are given. The influence of different factors such as the quantity of nitrates, atmosphere (nitrogen, oxygen) and melt on the decomposition have been determined.

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Mit 6 Abbildungen

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Auszug aus einem Teil der Magisterarbeit vonF. Lazarini.     

Studies on the thermal decomposition of the silver group of alkali metal nitritocobaltates(III)

The thermal decomposition of nitritocobaltate(III) of the silver group of general formula M₂Ag[Co(NO₂)₆] (where M = K⁺, NH⁺₄, Rb⁺ or Cs⁺) has been investigated. Based on the thermal curves of the investigated compounds and chemical and diffractometric analysis, the mechanism of thermal decomposition has been determined. The results obtained indicate that the decomposition proceeds in three stages. As a result of decomposition in the first stage (300°C), nitrates of alkali metals, metallic silver and Co₃O₄ are formed. In the second stage (500°C), a partial decomposition of nitrates to alkali metal oxides occurs, and in the third stage the products are alkali metal oxides, silver and Co₃O₄. This paper also presents the dependence of the decomposition temperature of nitritocobaltates(III) of the silver group on the ionic radius of the outer-sphere cation.     

Thermal behaviour of arsenic oxides (As2O5 and As2O3) and the influence of reducing agents (glucose and activated carbon)

In this paper the thermal behaviour of pure arsenic oxides (As₂O₅.aq and As₂O₃) and the influence of the presence of reducing agents (glucose or activated carbon) on the thermal behaviour of the arsenic oxides are studied through thermogravimetric (TG) analysis.The TG experiments with pure As₂O₅.aq reveal that the reduction reaction As₂O₅→As₂O₃+O₂ does not take place at temperatures lower than 500 °C. At higher temperatures decomposition is observed. Pure As₂O₃, however, is already released at temperatures as low as 200 °C. This release is driven by temperature dependent vapour pressures.Comparing these results with earlier observations concerning the thermal behaviour of chromated copper arsenate (CCA) treated wood, suggests that wood, char and pyrolysis vapours form a reducing environment that influences the thermal behaviour of arsenic oxides. Therefore, the influence of the presence of reducing agents on the thermal behaviour of As₂O₅.aq is studied. First, TG experiments are carried out with mixtures of As₂O₅ and glucose. The TG and DTG curves of the mixture are not a simple superposition of the curves of the two pure constituents. The interaction between As₂O₅.aq and glucose results in a faster decomposition of arsenic pentoxide. This effect is more pronounced if the purge gas nitrogen is mixed with oxygen. Second, TG experiments are performed with mixtures of As₂O₅ and activated carbon. The presence of activated carbon also promotes the volatilisation of arsenic for temperatures higher than 300 °C, probably through its reducing action.Extrapolation of the thermal behaviour of these model compounds to the real situation of pyrolysis of CCA treated wood confirms the statement that the reduction of pentavalent arsenic to trivalent arsenic is favoured by the reducing environment, created by the presence of wood, char and pyrolysis vapours.     

Pyrolysis of metal impregnated biomass: An innovative catalytic way to produce gas fuel

An innovative way of catalysis was investigated for its potential to reduce the amount of condensable hydrocarbons produced during the pyrolysis of oak wood. The experiments were carried out in a horizontal tubular reactor, fed with a controlled flow rate of nitrogen and equipped with accessories to collect char, liquid and gaseous products. Pyrolysis was performed at 700 °C with different wood sample series impregnated with either Ni or Fe nitrates (in aqueous solution) and by varying the metal concentration in the wood. In the blank run the biomass was acid-washed to determine the impact of demineralization. The influence of the metal type and content introduced into the wood to reduce the fraction of condensable organic compounds produced during pyrolysis was determined.Depending on the experimental conditions, the gas yield increases from 20.0 to 33.1%. Condensable hydrocarbons are cracked into gaseous components and the concentration of H₂ is significantly increased, by 260% compared to the reference sample. In particular, the Ni-loaded wood samples give much higher H₂ yields than the Fe-loaded ones under similar conditions but less toxic products are formed with the latter. These results show that biomass impregnation with either nickel or iron salts is a promising way to reduce the fraction of condensable organic compounds produced during pyrolysis.     

Effect of iron-containing catalysts on thermal decomposition of cured GAP-AP propellants

The effects of various burning rate catalysts on thermal decomposition of cured glycidyl azide polymer (GAP)-ammonium perchlorate (AP) propellants have been studied by means of thermal analysis and a modified vacuum stability test (MVST). Four types of iron-containing catalysts examined in this paper are catocene, ferrocenecarboxaldehyde (FCA), ferrocene, and ferric oxide. Results of differential thermal analysis (DTA) and thermogravimetric analysis (TG) revealed that the catalysts play an important role in the decomposition of both AP and GAP. The peak decomposition temperature (T _m) of DTA curves and onset decomposition temperature (T _o) of TG patterns considerably shifted to a lower temperature as the concentration of catalysts increased in the propellants. The endothermic temperature of AP, however, is unaffected by the presence of burning rate catalysts in all cases. The activation energy of decomposition of the propellants in range of 80 to 120°C is determined, based on the MVST results.     

Pyrolysis of chromated copper arsenate (CCA) treated wood waste at elevated pressure: Influence of particle size, heating rate, residence time, temperature and pressure

Lab-scale pyrolysis experiments with weathered CCA treated wood chips have been performed and the influence of particle size, residence time (10-40 min), heating rate (5-20 °C/min), temperature (330-430 °C) and pressure (0 bar, 5 bar) has been investigated. Few data, covering the pyrolysis of weathered wood was found in the literature and the literature data on pyrolysis experiments with a controlled CCA wood input, showed that results were often highly affected by experimental uncertainty. In order to reduce the uncertainty on the results, a thorough characterization of the wood input has been performed and a ratio method has been proposed which allows to study the effect of particle size on arsenic and chromium volatilization. Larger wood particles show a higher arsenic and chromium retention during pyrolysis which is attributed to the higher mass transfer resistance in these particles. Residence time has a limited effect on arsenic retentions. Increasing heating rate results in a limited increase in arsenic retentions and a more profound increase in chromium retentions. The latter is attributed to a lower average particle temperature during heating caused by the thermal lag in larger particles. Elevated pressure results in a significant increase of arsenic retentions, which is probably due to higher mass transfer resistance. Increasing temperature results in a slight decrease in arsenic retentions till 390 °C, with a sharp decrease at higher temperatures. Chromium retentions are less affected by increasing temperature, especially at higher temperatures. To conclude, a mechanism is proposed for the volatilization of chromium and arsenic during low temperature pyrolysis of CCA wood. Mass transfer resistance and the formation of As₄O₆ are crucial for the control of arsenic volatilization, while heat transfer resistance and thermal lag are more important for the control of chromium volatilization.     

Effect of sample layer thickness and temperature rise time on the pyrolysis temperature of cellulose

The temperature profiles throughout a rapidly heated sample layer were calculated as functions of time and sample thickness using the one-dimensional heat equation. The rates of decomposition throughout the layer were then calculated using the Arrhenius equation. The decomposition temperature, T_1/e, for a layer is defined as the temperature at which a fraction of 37% of the material is not yet decomposed. The theoretical results are used to predict T_1/e in cellulose for different Curie-point temperatures and heating rates. In general, T_1/e increases with increasing heating rates. In vacuum Curie-point pyrolysis (e.g., pyrolysis-mass spectrometry) of thin samples (thickness < 0.04 mm), T_1/e is almost uniform throughout the sample. When loss of heat occurs due to an ambient gas (e.g., pyrolysis-gas chromatography) the temperature rise time increases so the decomposition proceeds at a lower temperature; this is most pronounced at the outside of a very thick layer.     

Thermal stability of flexible polyurethane foams containing modified layered double hydroxides and zinc borate

Abstract

Flexible polyurethane foams (FPUFs) have been modified to contain layered double hydroxides (LDHs) by dihydrogen phosphate (H₂PO₄ ^?). The thermal stability of the prepared foams has been characterized using thermogravimetric analysis (TGA) at 5, 10, 20, 30, and 40?°C/min heating rates. The experimental data indicate that the temperature range for the two pyrolysis stages of FPUF is about 212–350?°C and 350–565?°C, respectively. Integral programmed decomposition temperature (IPDT) has been calculated according to the measured data, which was found that the IPDT of the modified FPUF was increased to 526?°C. Additionally, the thermal stability of FPUF composite has been also evaluated by the activation energy (E) on the basis of the pyrolysis kinetics of FPUF composites during thermal decomposition using Coats–Redfern integral method. These results manifest that the presence of intercalated LDHs enhances the thermal stability of FPUF.     

Preparation of New Solid Bases Derived from Supported Metal Nitrates and Carbonates

A highly basic solid catalyst was obtained by dispersing nitrates or carbonates of alkali metals such as KNO₃, CsCO₃ over alumina and zirconia at the surface density of 10-15 × 10¹⁸ cations m^-2 and heating them at 773-873 K in an inert atmosphere. The temperature is far below the decomposition temperatures of the nitrates and the carbonates. Based on the temperature-programmed decomposition (TPD) experiments, two types of decomposition process are suggested; a bulk decomposition and an anion decomposition. Generation of a strong basicity relates to the anion decomposition. The basic center may be composed of the oxygen anions liberated from the decomposition of the nitrate or carbonate anions that are dissociatively adsorbed on the support surface during the preparation. These catalysts effectively catalyzed the double bond isomerization of aliphatic hydrocarbons and bicyclic hydrocarbons at moderate temperature.