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- Author or Editor: J. Sempere x
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Abstract
The role of domestic journals in disseminating research results in the filed of Earth Sciences in Spain is discussed. The analysis is based on bibliometric indicators of Spanish scientific production, as well as on the opinion of Spanish researchers in this field, obtained through a specially designed survey. A reasonable correspondence has been found between the results of bibliometric analysis and scientists' judgements. Results show that 69% of Spanish articles in Earth Sciences were published in Spanish journals during the period 1990–1994. Scientists use both national and international journals to communicate, their research results, although due to the nature of the discipline, geographically oriented and therefore mostly devoted to local problems, they use basically domestic journals. In terms of international visibility, although none of the Spanish journals in this field is covered by the SCI, most of them are covered by some of the most representative international databases in the field concerned. The study points out the importance of domestic journals in the field of Earth Sciences in Spain.
Abstract
For a great number of European safety groups, reaction calorimetry is the key technique for analysis of the main reaction in the risk assessment of chemical processes. A comparison of calorimetric studies of model reactions, the N-oxidation of two substituted pyridines with hydrogen peroxide, made by several European groups, can open the door to standardization of the methodologies used. However, the intrinsic experimental complexity of the model reactions, which included dosing at high temperature, a multiphase system and evaporation, and the different evaluation criteria, produced a considerable dispersion between the results obtained by the various groups.
Abstract
The non-parametric kinetics (NPK) method has been recently developed for the kinetic treatment of thermoanalytical data. The most significant feature of this method is its ability to provide information about the reaction kinetics without any assumptions either about the functionality of the reaction rate with the degree of conversion or the temperature. This paper presents the results of the application of the method to adiabatic calorimetry. Some data have been obtained by numerical simulation, but also the thermal decomposition of DTBP, a well known first order reaction, has been studied, being the obtained results in good agreement with literature.
Abstract
Titanium nitride and carbide oxidation have been studied using TG and DSC. Titanium nitride shows a oxidation behavior were both techniques detect a unique phenomenon. Titanium carbide shows a variable behavior depending on the heating rate and sample size. Low masses and heating rates provide similar results to titanium nitride. However, using moderate sample sizes and scanning rates a two-stage oxidation is observed. The first step is extremely fast and exothermic, consuming the oxygen trapped inside the nanoparticle bed. The second is controlled by the diffusion of the oxygen and CO2 through the sample. Thermal safety conclusions are extracted from this observation. Energies of activation calculated using traditional kinetic models are lower than those found in the literature, being an indication of the influence of the specific surface of the material.
Abstract
A small scale (100 mL) calorimeter is developed. It includes a glass vessel submerged in a thermostatic bath, a compensation electrical heater, and a control system. The typical operation mode consists on introducing the solvents and part of the reactants into the vessel, to stabilise a temperature of the bath (T j) some degrees below the desired process temperature (T p) and to adjust the reaction mass temperature (T r) to T p using the electrical heater. An oscillating set point is established for Tr, which produces an oscillating response of the applied compensation power (Q c). Finally, the rest of reactants are dosed to the vessel. A small deviation of T r and T p is observed. Even though it can be avoided improving the tuning of the controller, it can be useful for enhancing the calculation of the heat capacity of the reaction mixture (C P). The signals of T r, Q c and T j are processed on-line using the FFT (Fast Fourier Transform) method as the mathematical tool used to analyse the data obtained, producing accurate values of the heat evolved (Q c) by the process, the heat transfer coefficient (UA), and the heat capacity of the reaction mixture (C P).
Abstract
This paper explains why directly agitated test cells are sometimes required in order to obtain good adiabatic calorimetry data that can be used with confidence to predict large scale plant behaviour. Experiments for methyl methacrylate polymerisation are reported. Simple procedures are presented for calculating genuine thermo-kinetic parameters from data which includes energy dissipation from the stirrer drive system.
Abstract
The aim of this work is basically centred in the improvement of the obtention of the peroxides precursors of macrocyclic lactones (C11 and C16) through the Story synthesis useful as raw materials for high performance linear polyesters. As a starting point, the yield has been increased respect to the classic synthesis using mild and intrinsically safer reactants. Concretely, a yield of 55% in triperoxide of cyclohexanone has been achieved using 35% hydrogen peroxide and phosphotungstic acid as catalyser. For this intention two factorial experimental designs, fractional and complete, have been carried out. The analytical method adequate for the reactive system studied (HPLC-UV-RI) has been chosen as well as the optimal operating conditions. A quantification of the risk on the first part of the reaction in calorimetric terms has been performed.
Abstract
Traditionally, the kinetic treatment of adiabatic calorimetry data has been based on the results of one or more experiments, but always with the assumption of the kinetic model that the reaction follows to calculate the kinetic parameters. In this paper a method for the determination of the activation energy that uses a set of adiabatic calorimetry data is developed. To check the method, the thermal decompositions of two peroxides were studied.
Abstract
Copper chromite catalysts were prepared by using a new metal organic precursor, M(OR)n, which was dissolved in organic solvent, hydrolysed and condensed to form inorganic polymers containing M-O-M linkages. In the cases of Ba and Mn promotion, the corresponding metal oxide was admixed to the copper-chromium solution prior to gelification. After drying in helium atmosphere, the precursor was subjected to thermal treatment at different temperatures (373-873 K) and in different atmospheres (air, nitrogen or hydrogen). Both the catalysts and the industrial Engelhard catalyst were characterized by various techniques (TG-DTA, HTXRD, IR, BET, metallic copper surface area and porosimetry measurements) and evaluated for ester hydrogenation.
