Kinetic modeling and simulation: Pyrolysis of Jatropha residue de-oiled cake

An improved kinetic model based on thermal decomposition of biomass constituents, i.e. cellulose, hemicellulose and lignin, is developed in the present study. The model considers the independent parallel reactions of order n producing volatiles and charcoal from each biomass constituent. While estimating the kinetic parameters, the order of degradation of biomass constituents is also checked and found to be matching with the order of degradation reported in the literature. The results of thermo-gravimetric analysis of Jatropha de-oiled cakes are used to find the kinetic parameters. The experimental runs are carried out using a thermo-gravimetric analyzer (TGA 4000, Perkin Elmer). TGA study is performed in a nitrogen atmosphere under non-isothermal conditions at different heating rates and the thermal decomposition profiles are used. The model is simulated using finite difference method to predict the pyrolysis rate. The corresponding parameters of the model are estimated by minimizing the square of the error between the model predicted values of residual weight fraction and the experimental data of thermogravimetry. The minimization of square of the error is performed using non-traditional optimization technique logarithmic differential evolution (LDE).     

Physical and electrochemical characterization of nanocomposites formed from polythiophene and titaniumdioxide

A simple method for covering titanium dioxide particles with a polythiophene film by chemical preparation was developed. The resulting nanocomposites consisted of a titanium dioxide core with a grain size of 25-250 nm and a polythiophene shell between 1 and 2 nm thickness. The composites were characterized by scanning electron microscopy, thermogravimetry, X-ray photoelectron spectroscopy, cyclovoltammetry, impedance spectroscopy and photocurrent spectroscopy. The content of polythiophene in the composite (determined by thermogravimetry), was between 2% and 5%. Disk-like electrodes were prepared by pressing and then characterized by various electrochemical methods. A reversible redox potential of the polythiophene of +1.0 V (NHE) was determined by cyclic voltammetry. The reduced form of polythiophene behaved as a p-type semiconductor so that the composite with n-type TiO₂ contained the properties of a p/n-junction. In the photocurrent spectra (depending on the applied potential), the characteristic anodic peaks of the TiO₂ at λ=320 nm and cathodic peaks of the polythiophene around λ=500 nm were found. A new cathodic peak observed at 370 nm was explained as a new feature of the pn interface.     

Pt-Ba/alumina NOx storage-reduction catalysts: Effect of Ba-loading on build-up, stability and reactivity of Ba-containing phases

A series of Pt-Ba/Al₂O₃ catalysts with Ba-loadings in the range 4.5–28 wt.% has been prepared by wet impregnation of Pt/Al₂O₃ with barium acetate (Ba(Ac)₂) as Ba precursor. The build-up and thermal stability of the deposited Ba-containing species was followed by means of XRD and thermogravimetry (TG) combined with mass spectroscopy (MS). Samples were characterized before and after thermal treatment (calcination). The study showed that the thermal stability of the Ba-containing phases depends on their interaction with the alumina support and the presence of dispersed platinum. In calcined catalysts, three different Ba-containing species could be distinguished based on their crystallinity and thermal stability. The relative concentration of these species varied with the Ba-loading. The first layer of Ba-containing species, corresponding to saturation of the alumina surface with Ba(Ac)₂, contained up to 12.5 wt.% of Ba in the form of amorphous BaO. Increasing the Ba-loading further resulted in 5–6 wt.% of Ba in the form of amorphous carbonates with relatively low thermal stability (LT-BaCO₃). At Ba-loadings higher than about 16 wt.%, crystalline barium carbonate became discernible which exhibited remarkably higher thermal stability (HT-BaCO₃). NO_x storage tests accomplished by exposing the catalysts to pulses of NO in oxygen containing carrier gas at 300 °C indicated that from all characterized Ba-containing phases, LT-BaCO₃ possesses the highest reactivity for NO_x storage, i.e. LT-BaCO₃ is transformed most rapidly to Ba(NO₃)₂.     

Phase development in normal and ultra high performance cementitious systems by quantitative X-ray analysis and thermoanalytical methods

Quantitative X-ray diffraction (QXRD) and thermogravimetry (TG) methods are used to determine the phase development up to 28 days of hydration in normal and ultra high performance cementitious systems (UHPC) that do not contain aggregate. The phase development in ultra high performance cementitious formulation is quantitatively and kinetically different from that in normal concrete formulation. This is related to the different components employed and their associated reactions. For both formulations the most remarkable changes of the phase contents are recorded between the first and second hydration day and up to the seventh day. After the seventh day less phase content changes are measured. Because of the non sufficient water amount for hydration, considerable amount of cement remains non hydrated in the UHPC formulation. The portlandite content, which is present in the UHPC specimen, gives evidence for non complete pozzolanic reactions even after 28 days of hydration, whereas the absence of calcite in the UHPC specimen indicates an insignificant carbonation in this specimen.     

Modulated thermogravimetry in analysis of decomposition kinetics

Optimal constants in physicochemical models describing decomposition kinetics are searched for from thermogravimetric information by the method of nonlinear regression. The method requires an iterative numerical solution of differential equations for non-isothermal kinetics. The technique of conjugate functions is used to provide a fast quadratic convergence of the iterations.The method is described in detail for the cases where input information represents either derivatives of mass loss or perturbations of these derivatives caused by sinusoidal modulation of linear temperature-time relationships. In both cases two-stage decomposition with two parallel (independent) reactions is considered as a numerical example. The discussion is mainly focused on the analysis of the perturbations (modulations).In the case of modulated thermogravimetry, a relative error in the calculated activation energy is approximately equal to a relative error in the approximation of the perturbations. That is why activation energy can be calculated with high accuracy. Moreover, the conclusion about the adequacy of evaluated models can be made immediately after a visual verification of the approximation error.Two-stage decomposition of cotton is used as an experimental example. The only curve of the perturbations measured at one heating rate is used for calculating the kinetic constants. This curve contains information about mass loss in the hidden form. Nevertheless, one can ensure that the used mathematical models with the obtained kinetic constants are able to approximate not only the curve of mass loss subjected to the handling but also a curve measured at another heating rate. The high predictive force of modulated thermal analysis promises to be an obvious alternative to the classical technique. The weak sensitivity of predictions made by modulated thermogravimetry to a form of models used is a very important distinction for the wide application of this analysis in different fields of chemical engineering.     

Water – an important parameter for the preparation and proper use of certified reference materials

Property values of powdered certified reference materials (CRMs) are very often related to dry mass. The dry mass is indirectly determined by measuring the moisture content of the sample. The most commonly used methods are the drying oven method and the Karl Fischer titration (KFT). It is well known that these two methods may give different values for the moisture/water content. In this study thermogravimetry was used to simulate the drying oven method and to investigate the reasons of the differences between both moisture/water content determination methods. A mass spectrometer coupled to a thermobalance (TGMS) added further useful information regarding the release of volatile substances and the decomposition of the material during the drying process.     

Electrochemical behavior of uranium(VI) in 1-butyl-3-methylimidazolium chloride and thermal characterization of uranium oxide deposit

The electrochemical behavior of uranyl nitrate in 1-butyl-3-methylimidazolium chloride at glassy carbon working electrode has been investigated in the temperature range 343-373 K by transient electrochemical techniques such as cyclic voltammetry, chronopotentiometry and square wave voltammetry. Influence of bulk concentration of uranium and temperature on the electroreduction and transport properties of U(VI) in bmimCl has been examined. Diffusion coefficient (D) and the energy of activation (E_a) of U(VI) in bmimCl has been estimated and is of the order of ∼10⁻⁸ cm²/s and 54 kJ/mol, respectively. Reduction of U(VI) takes place through an irreversible single step two-electron transfer to UO₂ deposit at glassy carbon working electrode. Thermal analysis of the uranium oxide indicated the entrapment of nearly 5% of electrolyte, bmimCl, during electrodeposition, which decomposes in the range 553-653 K.     

Simulated delayed coking characteristics of petroleum residues and fractions by thermogravimetry

Simulated delayed coking characteristics of five petroleum residues from various sources in China and four fractions from one of the residues were investigated by thermogravimetry (TG), and interactions among the fractions were thus revealed. Results showed that properties of these petroleum residues and fractions varied over a broad range. The coke yields from residues were closely related to their carbon residues and those from the fractions varied much. Apparent thermal-cracking activity was in the order saturates > aromatics > resins > asphaltenes, while actual overall cracking intensity appeared in reverse order when measured by the heat effect derived from differential thermal analysis (DTA). The apparent cracking reactions of the fractions and their parent residue could be described in first order kinetics in two coking temperature zones with activation energies being 75–120 kJ mol^− 1 and 130–210 kJ mol^− 1. Saturates promoted coke formation from other fractions, while aromatics inhibited coke formation from both resins and asphaltenes; the coke yield from a residue was smaller than that by physical summation based on residue's compositional fractions. It is thus possible to inhibit coke formation and enhance liquid distillate production by delayed coking of certain mixed petroleum residues.     

Mechanical,thermal and morphological properties of durian skin fibre reinforced PLA biocomposites

Durian skin waste generated by durian fruit or Durio zibethinus Murray show potential as a new reinforcement based-natural fibre. Similar to other lignocellulosic fibre, durian skin fibre (DSF) is capable in reinforcing polylactic acid (PLA) through extrusion and injection moulding processes for various applications. In current study, the effects of fibre content and pre-treatment using 4% sodium hydroxide (NaOH) on DSF were investigated on impact and thermal properties of PLA biocomposites. Treated DSF significantly enhanced the properties of PLA biocomposites as compared to untreated biocomposite. PLA can be replaced by 30 wt% DSF for similar impact performance. Thermogravimetry analysis (TGA) demonstrated that pre-treated DSF improved the thermal stability of PLA biocomposite. Differential scanning calorimetry (DSC) showed the presence of pre-treated DSF minimally enhanced the glass transition temperature (T_g), crystallization temperature (T_c) and melting temperature (T_m) relative to untreated DSF which suggests on better reinforcement with NaOH pre-treatment.     

Research into the kinetics of COS elimination from syngas at moderate temperatures

Thermogravimetry at constant temperature and programmed temperatures is used to study reaction kinetics and possible mechanism of COS desulfurization using ferric oxide as the main active component. The apparent reaction activation energy is smaller in hydrogen atmosphere than in nitrogen. The desulfurization reaction of COS takes place easily in a hydrogen atmosphere. At the same time, the influence of the reducing temperature on the desulfurizing reaction was also studied in the TGA apparatus and was shown to play an important part for ferric desulfurization. The optimum temperature for the reducing reaction is under 360 °C. The kinetics of the COS removal reaction are approximately first-order. When the reaction gas contains hydrogen, the apparent reaction activation energy is 12.36 kJ mol⁻¹, in contrast to 21.92 kJ mol⁻¹ in the absence of hydrogen.