Estimation of the through-plane thermal conductivity of polymeric ion-exchange membranes using finite element technique

The aim of this study is to calculate the through-plane thermal conductivity of commercial polymeric ion-exchange membranes. Different membranes were considered to study the influence of membrane properties on the thermal conductivity values. In particular we focused on reinforcement, ion exchange capacity and membrane density and thickness. For this purpose, we use a simple experimental setup and a numerical simulation to estimate the thermal conductivity from the experimental temperature profiles. Once the system is calibrated, the model includes as the only unknown parameter the membrane thermal conductivity. To validate the method, the thermal conductivity of the well-known Nafion membranes has been determined, a very good agreement was achieved in context from reliable literature values. The study also provides the thermal conductivity of other polymeric ion-exchange membranes with great potential in diverse applications under non-isothermal conditions. The calculated thermal conductivity for the different ion-exchange membranes is in the range from 0.04 Wm(-1) K-1 to 0.42 Wm(-1) K-1. The results show that the reinforcement leads to lower values of thermal conductivity whereas a higher density or heterogenous structure leads to higher thermal conductivity values. The approach presented here, combining experimental and simulation techniques, may provide a basis for confirming the effect of the polymeric ion-exchange membrane properties on the thermal conductivity and may shed light on the best choice for the electrolyte of membrane-based applications performance under non-isothermal conditions. Published by Elsevier Ltd

The Pioneer anomaly in the context of the braneworld scenario

We examine the Pioneer anomaly - a reported anomalous acceleration affecting the Pioneer 10/11, Galileo and Ulysses spacecrafts - in the context of a braneworld scenario. We show that effects due to the radion field cannot account for the anomaly, but that a scalar field with an appropriate potential is able to explain the phenomena. Implications and features of our solution are analyzed.Comment: Final version to appear at Classical & Quantum Gravity. Plainlatex 19 page

Nanoemulsion stability: experimental evaluation of the flocculation rate from turbidity measurements

The coalescence of liquid drops induces a higher level of complexity compared to the classical studies about the aggregation of solid spheres. Yet, it is commonly believed that most findings on solid dispersions are directly applicable to liquid mixtures. Here, the state of the art in the evaluation of the flocculation rate of these two systems is reviewed. Special emphasis is made on the differences between suspensions and emulsions. In the case of suspensions, the stability ratio is commonly evaluated from the initial slope of the absorbance as a function of time under diffusive and reactive conditions. Puertas and de las Nieves (1997) developed a theoretical approach that allows the determination of the flocculation rate from the variation of the turbidity of a sample as a function of time. Here, suitable modifications of the experimental procedure and the referred theoretical approach are implemented in order to calculate the values of the stability ratio and the flocculation rate corresponding to a dodecane-in-water nanoemulsion stabilized with sodium dodecyl sulfate. Four analytical expressions of the turbidity are tested, basically differing in the optical cross section of the aggregates formed. The first two models consider the processes of: a) aggregation (as described by Smoluchowski) and b) the instantaneous coalescence upon flocculation. The other two models account for the simultaneous occurrence of flocculation and coalescence. The latter reproduce the temporal variation of the turbidity in all cases studied (380 \leq [NaCl] \leq 600 mM), providing a method of appraisal of the flocculation rate in nanoemulsions

Optimization of Li4SiO4 synthesis conditions by solid state method for maximum CO2 capture at high temperature

The aim of this research work is to optimize the synthesis of Li4SiO4 by solid state method to maximize CO2 capture. This includes evaluating the main characteristics of the synthesised material which enhance CO2 uptake performance. Starting from Li2CO3 and SiO2 pure reagents, the effect of the sintering process conditions (heating rate, synthesis temperature and holding time) of the previously mixed powders has been studied. The samples were characterized by N2 physisorption, particle size distribution and X-ray diffraction. The evaluation of the CO2 uptake performance of the samples has been carried out at 600ºC in a thermobalance under a flow of almost pure CO2. Unreacted Li2CO3 is present at low synthesis temperatures, and its content in the synthesised material decreases when higher temperatures are used, so complete conversion to Li4SiO4 is reached at 900°C. At this temperature, the maximum CO2 uptake was found 20%, although it was yet far from the stoichiometric CO2 uptake value of 36.7%. The holding time at a synthesis temperature of 900ºC was then varied and a maximum CO2 uptake of 30.5% was obtained for a holding time of 2 h. Lastly, under optimised synthesis temperature and holding time conditions, the heating rate was varied. A value of 5 oC/min was found as the optimum one as the use of either lower or higher heating rates have a negative effect on CO2 uptake performance. As crystalline phases, particle size and BET surface area were very similar among all prepared samples at 900º C, crystal size was identified as the main physical property that could explain the CO2 uptake performance of the samples, i.e., the lower crystal size, the higher CO2 uptake.The financial support of the Research Centre for Carbon Solutions (RCCS) at Heriot-Watt University is gratefully acknowledged. M.T. Izquierdo thanks the Spanish Ministry of Education, Culture and Sports for the financial support under “Salvador Madariaga” programme for senior researchers (ref no. PRX17/00264). A. Turan acknowledges the financial support for this research from The Scientific and Technological Research Council of Turkey (TÜBİTAK) under 2219 scholarship programme (application no: 1059B191600366 and 2016/1).Peer reviewe

Optimization of Li₄SiO₄synthesis conditions by a solid state method for maximum CO₂ capture at high temperature

The aim of this research work is to optimize the synthesis of Li4SiO4 by a solid state method to maximize CO2 capture. This includes evaluating the main characteristics of the synthesised material which enhance the CO2 uptake performance. Starting from Li2CO3 and SiO2 pure reagents, the effect of the sintering process conditions (heating rate, synthesis temperature and holding time) of the previously mixed powders has been studied. The samples were characterized by N2 physisorption, particle size distribution and X-ray diffraction. The evaluation of the CO2 uptake performance of the samples has been carried out at 600 °C using a thermobalance under a flow of almost pure CO2. Unreacted Li2CO3 is present at low synthesis temperatures, and its content in the synthesised material decreases when higher temperatures are used, so complete conversion to Li4SiO4 is reached at 900 °C. At this temperature, the maximum CO2 uptake was found to be 20%, although it was yet far from the stoichiometric CO2 uptake value of 36.7%. The holding time at a synthesis temperature of 900 °C was then varied and a maximum CO2 uptake of 30.5% was obtained for a holding time of 2 h. Finally, under the optimised synthesis temperature and holding time conditions, the heating rate was varied. A value of 5 °C min-1 was found as the optimum one as the use of either lower or higher heating rates has a negative effect on the CO2 uptake performance. As crystalline phases, the particle size and BET surface area were very similar among all the prepared samples at 900 °C; the crystal size was identified as the main physical property that could explain the CO2 uptake performance of the samples, i.e., the lower the crystal size, the higher the CO2 uptake

High-temperature CO2 capture by Li4SiO4 sorbents: effect of CO2 concentration and cyclic performance under representative conditions

10 Figuras, 1 TablaThis study investigates CO2 capture on in-house-prepared Li4SiO4, a commercial Li4SiO4, and a commercial-derived CaO under the same experimental conditions in order to compare their performance with emphasis on the in-house-prepared Li4SiO4. The selected commercial Li4SiO4 was unsuitable for CO2 absorption–emission due to the insignificant CO2 uptake after regeneration. The commercial-derived CaO absorbs 41 wt %, which was the highest CO2 uptake among the studied samples. However, this sample underwent a severe decay after 12 carbonation–regeneration cycles despite the mild regeneration conditions used (700 °C under N2), reaching an almost constant CO2 uptake value (10 wt % after 18 cycles). The in-house-prepared Li4SiO4 absorbs 30 wt %, which was near the theoretical CO2 uptake for Li4SiO4. After an initial loss of CO2 uptake from near 30% to 26%, the performance of in-house-prepared Li4SiO4 was maintained after 16 cycles under the same conditions as those used for CaO. The effect of CO2 concentration on CO2 uptake was to obtain the inversion temperature for practical CO2 concentrations. Due to the significant differences among inversion temperatures from different equilibrium plots, experimental inversion temperatures were obtained by the temperature-programmed technique for absorption under a CO2 concentration of 4% and for emission under a CO2 concentration of 70%, giving 525 and 660 °C, respectively. A cyclic test was conducted with in-house-prepared Li4SiO4: absorption at 520 °C under a CO2 concentration of 4% and regeneration at 675 °C under a CO2 concentration of 70%. Under these mild thermal conditions the sample did not exhibit a CO2 uptake decay, indicating that this sorbent could be efficiently used for high-temperature CO2 capture from power plant flue gas.Financial support of the Research Centre for Carbon Solutions (RCCS) at Heriot-Watt University is gratefully acknowledged. M.T.I. thanks the Spanish Ministry of Education, Culture and Sports for financial support under the “Salvador Madariaga” programme for senior researchers (ref no. PRX17/00264).Peer reviewe