Steps in a minefield

Thermal Degradation Kinetics and FT-IR Analysis on the Pyrolysis of Pinus pseudostrobus, Pinus leiophylla and Pinus montezumae as Forest Waste in Western Mexico

For the first time, a study has been carried out on the pyrolysis of wood residues from Pinus pseudostrobus, Pinus leiophylla and Pinus montezumae, from an area in Western México using TGA analysis to determine the main kinetic parameters (Ea and Z) at different heating rates in a N2 atmosphere. The samples were heated from 25 °C to 800 °C with six different heating rates 5–30 °C min−1. The Ea, was calculated using different widely known mathematical models such as Friedman, Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose. The Ea value of 126.58, 123.22 and 112.72 kJ/mol (P. pseudostrobus), 146.15, 143.24 and 132.76 kJ/mol (P. leiophylla) and 148.12, 151.8 and 141.25 kJ/mol (P. montezumae) respectively, was found for each method. A variation in Ea with respect to conversion was observed with the three models used, revealing that pyrolysis of pines progresses through more complex, multi-stage kinetics. FT-IR spectroscopy was conducted to determine the functional groups present in the three species of conifers. This research will allow future decisions to be made, and possibly, to carry out this process in a biomass reactor and therefore the production of H2 for the generation of energy through a fuel cell.

Aromatic C-Nitroso Compounds and Their Dimers: A Model for Probing the Reaction Mechanisms in Crystalline Molecular Solids

This review is focused on the dimerization and dissociation of aromatic C-nitroso compounds and their dimers, the reactions that could be used as a convenient model for studying the thermal organic solid-state reaction mechanisms. This molecular model is simple because it includes formation or breaking of only one covalent bond between two nitrogen atoms. The crystalline molecular solids of nitroso dimers (azodioxides) dissociate by photolysis under the cryogenic conditions, and re-dimerize by slow warming. The thermal re-dimerization reaction is examined under the different topotactic conditions in crystals: disordering, surface defects, and phase transformations. Depending on the conditions, and on the molecular structure, aromatic C-nitroso compounds can associate to form one-dimensional polymeric structures and are able to self-assemble on gold surfaces.

Thermal analysis during partial carbonizing process of rhubarb, moutan and burnet

Control of temperature and duration of partial carbonization for Chinese medicines have been mainly based on experience of the processors. No quantitative methods and parameters are available that can be used to precisely control the temperature and determine the energy changes during the process. In our research, with a simulated atmosphere air condition, the partial carbonization processes of three Chinese herb medicines rhubarb, moutan and burnet were simulated at different heating rates (5, 10 and 20°C • min-1) and analyzed by thermal gravimetric analysis (TGA) to quantify the upper limits of the temperature. The activation energy was calculated with Friedman, Kissinger-Akahira-Sunose (KAS) method and Ozawa-Flynn-Wall (OFW) methods in iso-conversional models and independent parallel reaction model (IPR). The upper temperatures were calculated to be 280, 184 and 246°C for rhubarb, moutan and burnet, respectively, at corresponding conversion rates of 0.4, 0.2 and 0.1. Calculation of the activation energy has been found impossible with the IPR model. Results obtained from the three iso-conversional methods were different. For rhubarb and burnet, the conversion rates at the upper temperature limits were at the highest or second highest activation energy, while for moutan, it was at the lowest value of activation energy. These results confirmed scientific rationales of traditional Chinese medicine theory that rhubarb and burnet be prepared at high temperature and moutan be prepared at medium temperature. Application of thermal analysis techniques would broaden and deepen traditional Chinese medicine research, and are applicable to the processing of medicinal materials including traditional Chinese medicines. Results obtained from the study could provide new ideas and methods for research to modernize the preparation of traditional Chinese medicines.

Oxidation mechanism of porous Zr₂Fe used as a hydrogen getter

We determined the oxidation mechanism of porous ST-198, which mainly comprises Zr2Fe. Oxidation kinetics depended on temperature, oxygen partial pressure, and oxidation extent. The passivation role of oxidation in hydrogen scavenging is probably due to the development of a surface oxide, independent of oxygen concentration. Zr2Fe would be a superior hydrogen getter in oxygen-contaminated environments at high temperatures, as most oxygen will be consumed at the outer shell by mass transfer limitations, protecting the bulk of the getter for hydrogen scavenging.

Clarifications regarding the use of model-fitting methods of kinetic analysis for determining the activation energy from a single non-isothermal curve

Background

This paper provides some clarifications regarding the use of model-fitting methods of kinetic analysis for estimating the activation energy of a process, in response to some results recently published in Chemistry Central journal.

Findings

The model fitting methods of Arrhenius and Savata are used to determine the activation energy of a single simulated curve. It is shown that most kinetic models correctly fit the data, each providing a different value for the activation energy. Therefore it is not really possible to determine the correct activation energy from a single non-isothermal curve. On the other hand, when a set of curves are recorded under different heating schedules are used, the correct kinetic parameters can be clearly discerned.

Conclusions

Here, it is shown that the activation energy and the kinetic model cannot be unambiguously determined from a single experimental curve recorded under non isothermal conditions. Thus, the use of a set of curves recorded under different heating schedules is mandatory if model-fitting methods are employed.

Basics and Applications of Solid-State Kinetics: A Pharmaceutical Perspective**The authors dedicate this review to the memory of Dr. David J.W. Grant who passed away on December 9, 2005. Dr. Grant was an internationally known authority at the University of Minnesota on the solid-state properties of drugs. He will be remembered as a kind, humble, and brilliant scholar

Most solid-state kinetic principles were derived from those for homogenous phases in the past century. Rate laws describing solid-state degradation are more complex than those in homogenous phases. Solid-state kinetic reactions can be mechanistically classified as nucleation, geometrical contraction, diffusion, and reaction order models. Experimentally, solid-state kinetics is studied either isothermally or nonisothermally. Many mathematical methods have been developed to interpret experimental data for both heating protocols. These methods generally fall into one of two categories: model-fitting and model-free. Controversies have arisen with regard to interpreting solid-state kinetic results, which include variable activation energy, calculation methods, and kinetic compensation effects. Solid-state kinetic studies have appeared in the pharmaceutical literature over many years; some of the more recent ones are discussed in this review.