Semi-quantitative and multivariate analysis of the thermal degradation of carbon-oxygen double bonds in biomass

The aim of this paper was to investigate biomass pyrolysis using diffuse reflectance infrared Fourier transform (DRIFT) studies. The pyrolysis tests were conducted in a nitrogen atmosphere from room temperature (RT) to 600 °C. Infrared techniques provide fast, low-cost and non-destructive analysis. A combination of qualitative and quantitative analysis was applied. Pyrolysis was conducted in an environmental chamber which enabled in-situ spectral measurement. The mass of samples used in DRIFT tests was 3.0 ± 0.1 mg. A semi-quantitative analysis of the oxidation stage was performed for each biomass sample. For a variety of biomass samples, pyrolysis in the temperature range of 250–350° lead to an increase in carbon-carbon double bonds which were formed from cellulose decomposition. The research results showed that the wavenumber assigned to the CO band in carboxylic acids and esters (1742 cm^?1) depends on the temperature and varies with different biomass samples. Also, the intensity of the CO band for ketones and aldehydes (1665 cm^?1) varies with the type of biomass and the pyrolysis temperature. Principal component analysis (PCA) gave information about the similarity of reactions occurring during the pyrolysis of various biomass samples. Efficient conversion of biomass resources to energy requires accurate and detailed knowledge of chemical behaviour during degradation.     

Experimental and modeling study of the thermal decomposition of methyl decanoate

The experimental study of the thermal decomposition of methyl decanoate was performed in a jet-stirred reactor at temperatures ranging from 773 to 1123 K, at residence times between 1 and 4 s, at a pressure of 800 Torr (106.6 kPa) and at high dilution in helium (fuel inlet mole fraction of 0.0218). Species leaving the reactor were analyzed by gas chromatography. Main reaction products were hydrogen, carbon oxides, small hydrocarbons from C₁ to C₃, large 1-olefins from 1-butene to 1-nonene, and unsaturated esters with one double bond at the end of the alkyl chain from methyl-2-propenoate to methyl-8-nonenoate. At the highest temperatures, the formation of polyunsaturated species was observed: 1,3-butadiene, 1,3-cyclopentadiene, benzene, toluene, indene, and naphthalene. These results were compared with previous ones about the pyrolysis of n-dodecane, an n-alkane of similar size. The reactivity of both molecules was found to be very close. The alkane produces more olefins while the ester yields unsaturated oxygenated compounds.A detailed kinetic model for the thermal decomposition of methyl decanoate has been generated using the version of software EXGAS which was updated to take into account the specific chemistry involved in the oxidation of methyl esters. This model contains 324 species and 3231 reactions. It provided a very good prediction of the experimental data obtained in jet-stirred reactor. The formation of the major products was analyzed. The kinetic analysis showed that the retro-ene reactions of intermediate unsaturated methyl esters are of importance in low reactivity systems.     

A model for the devolatilization of a coal particle sufficiently large to be controlled by heat transfer

This study follows previous experimental work showing that the shrinking-core model applies to the pyrolysis (i.e., heating in the absence of oxygen) of particles (diam. ≈ 14 mm) of a bituminous coal or a lignite in a fluidized bed at 700-950 °C. These experimental facts are in accord with the production of volatile matter being endothermic and not thermoneutral, as often assumed. Also, the rate at which volatile matter is produced in the presence of oxygen (i.e., devolatilization) or in its absence (pyrolysis) is demonstrated here to be controlled not at all by mass transfer, but by heat conduction to a moving reaction front inside a coal particle, provided its diameter exceeds ∼3 mm. The resulting steady-state model of devolatilization indicates that six dimensionless groups are required to describe the rate of

(I)     

Study on the thermal decomposition of NaBH4 catalyzed by ZrCl4

The catalytic effect of zirconium tetrachloride (ZrCl₄) on the thermal dehydrogenation of NaBH₄ has been studied. The ZrCl₄ reduced to ZrCl₂ and metallic zirconium which exhibit the high catalytic activity during thermal dehydrogenation. The activation energy corresponding to dehydrogenation of NaBH₄ is remarkably reduced to 180 kJ/mol in the presence of a catalyst as compared to pure-NaBH₄ which was found to be 275 kJ/mol under the similar experimental conditions. The reduced activation energy leads to decreased onset dehydrogenation temperature (<300 °C). A substantial amount of sodium remained at the end of the dehydrogenation of catalyzed sample. The low-temperature dehydrogenation of catalyzed NaBH₄ could be useful to manage the evaporation of sodium metal.     

Investigation of the thermal properties of a Li-ion pouch-cell by electrothermal impedance spectroscopy

Electrothermal impedance spectroscopy (ETIS), is introduced as a new measurement method and thermal parameters derived from a pouch-type lithium-ion cell are presented. ETIS is a valuable tool for (i) the determination of the thermal impedance and (ii) the validation of thermal models. The excitation signal applied to the cell during measurement does not cause a change in entropy, thus facilitating the parameter identification of a thermal model for heat conduction and thermal capacity.ETIS can be applied to measurements in time domain and in frequency domain. Both approaches are presented and a combination further improves measurement time and accuracy.     

Study on the evolution of the chemical structure characteristics of high rank coals by simulating the ScCO2-H2O reaction

ABSTRACT

To study the influence of CO₂ on the structure of a coal reservoir during CO₂ geological storage-enhanced coalbed methane recovery (CO₂-ECBM), two high rank coals from the Qinshui basin were exposed to supercritical CO₂ (ScCO₂) and water for 240 h in a laboratory high-pressure supercritical geochemical reactor to simulate the reaction of ScCO₂-H₂O-coal under three burial depths. The changes in the chemical structure of the coals before and after reaction were evaluated by Fourier transform infrared spectroscopy (FTIR). The results show that the ScCO₂-H₂O treatment has a substantial influence on the coal structure, reducing the aromaticity and the degree of aromatic ring condensation, increasing the hydrocarbon-generating potential and improving the maturation level of the coals. The ScCO₂-H₂O system mainly affects the organic functional groups of coals through the chemical reactions: swelling effect, bond dissociation reaction, hydrolysis and substitution reaction. The results of peak fitting show that the ScCO₂-H₂O treatment can significantly reduce the intensities of the bands associated with in-plane -CH₂- vibrations and oxygenated groups (especially C-O groups), but increase the intensities of the aliphatic hydrocarbon and hydroxyl group bands. The changes in the functional group contents after the ScCO₂-H₂O treatment varied between the different rank coals. The effect of temperature and pressure on the functional group contents after reaction is complicated, and it is affected by the macromolecular structures of the raw coals and the sensitivities of the chemical reactions to temperature and pressure. However, there is a critical depth that provides the optimum influence of temperature and pressure on the structure of the organic matter in coal. This paper aims to provide a theoretical foundation for the study of the changes in the coal matrix structure during the long-term storage of CO₂ in coal seams.     

Surface-induced thermal decomposition of [Ru(dcbpyH)2-(CN)2] on nanocrystalline TiO2 surfaces: Temperature-dependent infrared spectroscopy and two-dimensional correlation analysis

Thermal degradation mechanism of the self-assembled thin films of [Ru(dcbpyH)₂-(CN)₂] (Ruthenium 505, R505) anchoring on TiO₂ surfaces via its carboxylate group has been examined by temperature-dependent diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The CN stretching bands of R505 at 2000-2100 cm⁻¹ appeared to change drastically at ≈140 °C on TiO₂ surfaces, whereas a major CN peak at ∼2090 cm⁻¹ disappeared at a much higher temperature above ≈250 °C in their solid states. Two-dimensional (2D) correlation analysis was introduced to explain the thermal desorption behaviors of the Ruthenium dye. Multiple peaks of the CN stretching vibrations are more clearly resolved in the 2D correlation analysis. More complicated features in the CN stretching vibrational spectra on TiO₂ than those of the solid states suggest a substantial interaction of the CN groups with the TiO₂ surfaces.     

Production of COx-free hydrogen by the thermal decomposition of methane over activated carbon: Catalyst deactivation

Hydrogen, an environment-friendly energy source, is deemed to become strongly in demand over the next decades. In this work, CO_x-free hydrogen was produced by the thermal catalytic decomposition (TCD) of methane by a carbon catalyst. Deactivated catalysts at four-stage of progressive were characterized by nitrogen sorption and scanning electron microscopy. TCD of methane at 820 and 940 °C was about 13- and 8-folds higher than non-catalytic decomposition, respectively. High temperatures positively affected the kinetics of hydrogen production but negatively influenced the total amount of hydrogen and carbon products. The total pore volume was a good indicator of the total amount of hydrogen product. Catalyst activity was decreased because of the changes in the catalyst's textural properties within three ranges of relative time, that is, 0 to 45, 0.45 to 0.65, and 0.65 to 1. Models for specific surface area and total pore volume as functions of catalyst deactivation kinetics were developed.     

Optical measurement of thermal contact conductance between thin,waferlike solid samples by using laser AC heating and reflectance thermometry: Reconsideration of the loading method for the samples

A noncontact optical technique for measuring the thermal contact conductance between two thin, waferlike solid samples was developed. In this technique, one solid surface is heated with a modulated laser beam; the corresponding temperature modulation of the other solid surface across their interface is monitored by using the reflectance of a probe laser beam. Each sample can become slightly bent if its edge is compressed by the sample holder, so the contact pressure between the samples (in the range of 0.8 to 10 MPa) was calculated by elastic and plastic numerical analyses. By using the calculated contact pressure, the correlation between contact pressure and thermal contact conductance could be determined more accurately. Also, the appropriate thickness of the glass plates used to fix the samples was derived by calculating the thickness where the local contact pressure is almost the same as the averaged pressure. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(6): 498–512, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10049     

In situ spectroelectrochemical measurements during the electro-oxidation of ethanol on WC-supported Pt-black. Part II: Monitoring of catalyst aging by in situ Fourier transform infrared spectroscopy

As a continuation of a project on the spectroelectrochemical analysis of long-term behaviour of WC-supported Pt electrocatalysts (for SFG results, see part I: [1]), in this paper we report in situ FT-IR spectroscopy experiments, carried out during prolonged electro-oxidation of ethanol on Pt-black. From the analytical point of view, as expected, FT-IR spectra showed the presence of adsorbed acetic acid and ethanol, in addition to the well-known, dominant species: linearly adsorbed CO (2044-2063 cm⁻¹) and solution-phase CO₂ (2345 cm⁻¹). As far as quantitative spectroscopic results are concerned, a notable sensitivity of the interfacial chemistry to catalyst aging could be highlighted by this approach. The spectra recorded in three subsequent series of potential-cycling experiments showed a clear-cut dependence of spectral patterns and peak intensities, on the applied potential and on the oxidation duration. Qualitative spectral changes seem to suggest - coherently with in situ SFG results obtained with the same system [1] - that electrocatalyst aging correlates with a higher surface coverage with ethanol as compared with acetic acid. Quantitative analysis, based on fitting with Lorentzian lineshapes, yields information that can be used as a molecular-level diagnostic of the modification of the catalyst-adsorbate structure.     

Characterization and voltammetric behavior of PtyMozOx/C electrodes prepared by the thermal decomposition of polymeric precursors

Carbon-supported catalysts containing platinum and molybdenum oxide are prepared by thermal decomposition of polymeric precursors. The Pt_yMo_zO_x/C materials are characterized by energy dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray diffraction. The catalysts present a well-controlled stoichiometry and nanometric particles. Molybdenum is present mainly as the MoO₃ orthorhombic structure, and no Pt alloys are detected. The voltammetric behavior of the electrodes is investigated; a correlation with literature results for PtMo/C catalysts prepared by other methods is established. The formation of soluble species and the aging effect are discussed.