Artículos SCI

In this paper, the thermal degradation properties of Viton A and Fluorel are investigated by both isoconversional and combined kinetic analysis methods using non-isothermal thermogravimetry technique. It has been found that the heating rate has little affect on the degradation residue of Fluorel and Viton A, where around 1.3% char was formed for Fluorel and 3.5% for Viton A. Different from the literature, the decomposition of Viton A should be considered as an overlapped dehydrofluorination and carbon chain scission process, with activation energy of 214 +/- 11 and 268 +/- 13 kJ mol(-1), respectively. The effect of dehydrofluorination on degradation of Fluorel is not so significant due to low content of H, and hence, it could be considered as a single-step mechanism with average activation energy of 264 +/- 14 kJ mol(-1). The thermal stability of Fluorel is much better than that of Viton A, and the predicted half-life is around 218 min for Fluorel and 49 min for Viton A at 420 A degrees C, which are consistent with experimental values. If using a single-step model as in the literature for Viton A, its half-life at 420 A degrees C would be underestimated for > 20%.

The share of renewable energies is growing rapidly, partly in response to the urgent need for mitigating CO2 emissions from fossil fuel power plants. However, cheap and efficient large-scale energy storage technologies are not yet available to allow for a significant penetration of renewable energies into the grid. Recently, a potentially low-cost and efficient thermochemical energy storage (TCES) system has been proposed, based on the integration of the calcium-looping (CaL) process into concentrated solar power plants (CSPs). The CaL process relies on the multicycle carbonation/calcination of CaO, which can be derived from calcination of widely available, cheap, and nontoxic natural limestone (CaCO3). This work explores the effect on the multicycle activity of limestone-derived CaO of thermal pretreatment under diverse atmospheres and the addition of nanosilica, which would be expected to hinder CaO grain sintering. Importantly, optimum CaL conditions for CSP energy storage differ radically from those used in the application of the CaL process for CO2 capture. Thus, calcination should be ideally carried out under low CO2 partial pressure at moderate temperature (below 750 degrees C), whereas CO2 concentration and temperature should be high for carbonation in order to maximize thermoelectric efficiency. When limestone is subjected to carbonation/calcination cycles at these conditions, its performance is critically dependent on the type of pretreatment. Our results indicate that the multicycle CaO activity is correlated with the size of the particles and the CaO pore size distribution. Thus, CaO activity is impaired as particle size is increased and/or CaO pore size is decreased. These observations suggest that pore plugging poses a main limitation to the multicycle performance of limestone-derived CaO at the optimum CaL conditions for TCES in CSPs, which is supported by scanning electron microscopy analysis. Strategies to enhance the performance of natural limestone at these conditions should be therefore oriented toward minimizing pore plugging rather than CaO grain sintering, which stands as the main limitation at CaL conditions for CO2 capture.