Piroska Szabó

Kinetic modeling of biomass pyrolysis

Abstract The thermal decomposition of lignocellulosic biomass materials and their major components is discussed. Thermogravimetric and DSC curves at different T( t ) heating programs were evaluated by the method of least squares. Pseudo-first order models, parallel, successive and competitive reaction schemes and complex reaction networks were employed in the modeling. The following topics are treated: thermal decomposition of cellulose at low (2 °C min −1 ) and high (50–80 °C min −1 ) heating rates; low temperature phenomena; the validity of the Broido-Shafizadeh model; effects of mineral catalysts; cellulose pyrolysis in closed sample holders; thermal decomposition kinetics of xylan, lignin and lignocellulosic plant samples.

Kinetics of the thermal decomposition of cellulose in sealed vessels at elevated pressures. Effects of the presence of water on the reaction mechanism

Abstract The thermal decomposition of Avicel cellulose was studied by non-isothermal differential scanning calorimetry in hermetically sealed sample holders. The experimental results, which were published earlier, showed a marked catalytic effect of the water on the cellulose decomposition. Here we propose a reaction scheme containing two rate determining reactions to describe the result. The corresponding model resulted in a good fit between the experimental and the calculated data. The results indicate that the reaction starts with cellulose hydrolysis which may be followed immediately by decomposition reactions to intermediate products. The intermediates undergo further water-catalyzed decomposition reactions giving char, water and gases. The results may help in the understanding of biomass pyrolysis under experimental or industrial conditions where the thickness of the layer, the size of particles or the enclosure of the reactor keeps part of the water vapor formed during the reaction in the pores or between the particles of the decomposing material.

Thermogravimetric/mass spectrometric characterization of two energy crops, Arundo donax and Miscanthus sinensis

Abstract Two herbaceous plants, Arundo donax and Miscanthus sinensis with high biomass production potential, were studied by simultaneous thermogravimetry/mass spectrometry (TG/MS) in an inert argon atmosphere at a heating rate of 20 °C min−1. The effect of particle size, the partial removal of the minerals by acid- and water-washing, and the effect of potassium carbonate as catalyst were studied. Experiments with covered sample pans were carried out to investigate the effect of secondary tar cracking on the charcoal production. TG/MS supplied intensity profiles of the low molecular weight volatile products as a function of time or temperature. Their comparison to the weight-loss rate curves (DTG) provided information of the details of the degradation mechanism. The amounts of various volatile pyrolysis products were estimated by the integrals of the corresponding mass spectrometric intensities. The factors influencing the char yield were discussed.

Least squares criteria for the kinetic evaluation of thermoanalytical experiments. Examples from a char reactivity study

Abstract The mathematical modeling of the chemical processes is a crucial problem of the thermal analysis. Simple models with few parameters seldom can describe the real complexity of the phenomena arising during the heating of the various substances. In the case of more complex models the determination of the parameters and the validation of the model require the evaluation of carefully designed experimental series. The one-by-one evaluation of the experiments is a mathematically ill-defined problem at a larger number of unknown parameters. The non-statistical experimental errors of the thermal analysis hinder the determination of a single parameter set by the simultaneous least squares evaluation of the experiments. This paper discusses several evaluation techniques for the handling of the non-statistical errors during the least squares evaluation of experimental series. The methods are illustrated by the evaluation of oxidative thermogravimetric experiments of a lignite and a coal char.

Kinetics of the thermal decomposition of cellulose under the experimental conditions of thermal analysis. Theoretical extrapolations to high heating rates

Abstract Thermobalance-mass spectrometer (TG-MS) experiments carried out by the authors in a period of 8 years are reviewed and analyzed. Celluloses and lignocellulosic biomass samples were studied. The data are evaluated by the method of least squares. The results indicate that a single rate-controlling reaction step dominates the kinetics of the cellulose decomposition at low heating rates (2–20°C/min) provided that the heat and mass transport problems are experimentally eliminated and the amount of catalytic impurities is reduced by dilute acid or hot water washing treatments. The kinetic parameters obtained from the experiments with different cellulose and biomass samples evidenced only ca 8% scattering. A simple explanation is given for the kinetic compensation effect observed. Theoretical extrapolations are presented to predict the behavior of extremely small, idealized cellulose samples at high heating rates.

Study of the structure and thermal behaviour of intercalated kaolinites

Intercalation complexes of three different Hungarian kaolinites with hydrazine and potassium acetate were investigated by FT-IR (DRIFT) spectrometry, X-ray diffraction, and thermogravimetry combined with mass spectrometry. Differences were found in the thermal behaviour of the complexes as well as in the rehydration — reexpansion patterns of the heated intercalates. An XRD method is proposed for the distinction of kaolinite and 7.2 Å halloysite present in the same mineral.

The effects of heat and mass transport on the results of thermal decomposition studies: Part 2. Polystyrene, polytetrafluoroethylene and polypropylene

Abstract The thermal decomposition of pure polymer samples was studied at a low heating rate (4°C/min) and with sample masses of 0.3–6 mg in a Perkin-Elmer TGS-2 thermobalance. The various transport effects were distinguished by changing the gas flow from argon to helium, varying the sample mass and geometry and by applying a self-generated atmosphere. Sample masses of 3–6 mg showed marked effects of insufficient heat transfer in a flow of argon. The concentration of the volatile products above the samples did not influence the thermal decomposition. The diffusion problems in the polymer bulk, however, changed the kinetics from first order to zero order in the case of polytetrafluoroethylene, and increased the overall reaction rate of polypropylene. The latter effect was attributed to chain termination caused by the evaporation of small radicals from the thin polypropylene samples.

Reaction Kinetics of the Thermal Decomposition of Cellulose and Hemicellulose in Biomass Materials

Sugar cane bagasse, wheat straw, pine and cotton wood pyrolyxad sis was studied by TGA in argon at heating rates of 5 and 20°C/min. The DTG (-dm/dt) peaks associated with the compoxad nents of an untreated plant material are relatively wide and strongly overlap each other. A reduction in the amount of inorganic ions in the samples by simple water or dilute acid washing procedures resulted in sharper peaks with a better separation. The thermal decomposition of the major biomass components was described, more or less formally, by first orxad der reactions and the DTG curves of the biomass samples were approximated by a linear combination of first order reactions. Good fits between the calculated and the experimental data and good reproducibility of the model parameters were achieved. The kinetic model applied here may serve as a starting point to build more complex models capable of describing the thermal behavior of plant materials during a thermal or thermochemical processing or burning. Theoretically, there is also a possibility to utilise this sort of calculation in the quantitative analysis of the cellulose and hemicellulose content of the lignocellulosic materials.

Pyrolysis-gas chromatographic-mass spectrometric and thermogravimetric-mass spectrometric investigation of brown coals

Abstract Fourteen low-rank coals were subjected to thermogravimetric-mass spectrometric (TG-MS) and pyrolysis-gas chromatographic-mass spectrometric investigations. TG-MS fragment ion curves were used to clarify the thermal decomposition processes taking place during coal pyrolysis. Carbon dioxide production is attributed to the decarboxylation of humic acid content at 300°C and that of other acidic and ester groups up to 500°C. The pyrolytic evolution of alkylarenes seems to be connected with the production of carbon monoxide, through the cleavage of the ketonic carbonyl groups linking the aromatic segments. Methane originates from long-chain alkanes at about 500°C but from alkyl substituents of arenes at higher pyrolysis temperatures. Above 800°C the dehydrogenation process proved to be a consequence of the aromatic ring destruction reaction at aryl ether bonds. The TG-MS curves serve as an adequate basis for the selection of a suitable temperature for fast pyrolysis applied for the characterization of coals. The relative amounts of the isoprenoid and aromatic marker compounds found in the pyrograms at 600°C proved to be related to the rank of the coal. The coal samples investigated have been characterized by the relative amounts of some pyrolysis products considered to be of key importance.

Identification of positive and negative regulatory regions controlling expression of the cartilage matrix protein gene.

A complex pattern of regulation of the cartilage matrix protein gene was revealed by transient expression experiments. A minimal promoter from positions -15 to +64 functioned in chondrocytes and fibroblasts. An enhancer located in the first intron exerted chondrocyte-specific stimulation on the minimal promoter activity. The same fragment, however, had a negative effect in fibroblasts. Between -334 and -15, a silencer was found which inhibited the gene expression driven from its homologous as well as heterologous promoters both in chondrocytes and fibroblasts. Additional positive and negative control regions were mapped further upstream of the promoter.