Ambiente e Sustentabilidade | Artigos em revistas internacionais / Papers in international journals
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- Phase equilibrium of n-Nonane + n-Decane for low-temperature thermal energy storage: insights into odd–even effectsPublication . Sequeira, Maria Carolina; Nikitin, Timur; Caetano, Fernando J. P.; Diogo, Herminio; Fareleira, João; Fausto, RuiThe present article presents the solid–liquid phase diagram of a binary system composed of an n-alkane with an odd number of carbon atoms, namely, n-nonane (n-C9), with an even-numbered one, namely n-decane (n-C10). This work is part of a series of phase equilibrium studies on n-alkanes for low-temperature thermal energy storage (TES) applications. The ultimate purpose of this work is to investigate the adequacy of this binary system to be used as a Phase Change Material (PCM) at low temperatures. Additionally, along the equilibrium studies on linear alkanes, an interesting feature has emerged: the solid–liquid phase diagrams of binary n-alkane systems apparently show a striking dependence on the odd or even number of carbon atoms in their chains. The phase diagram for the system n-C9 + n-C10 has primarily been obtained using Differential Scanning Calorimetry (DSC), whose results have been complemented by Hot-Stage Microscopy (HSM) and low-temperature Raman Spectroscopy results. The DSC analysis provided both the temperature and enthalpy values for the observed solid–liquid and solid–solid phase transitions. The n-C9 + n-C10 binary system seems to display a peritectic solid–liquid phase diagram at low temperatures. The peritectic temperature found was 222.41 K, with a peritectic composition around xnonane = 0.60. Those results confirmed the initial suggestions that this would be a peritectic system, based on previously observed odd–even effects on phase equilibrium behavior of alkane mixtures. The goal of this work is to extend new insights into the solid–liquid phase equilibrium behavior of the binary system n-C9 + n-C10, a topic not yet covered in the literature. This information, consequently, provides practical and essential information on the potential use of this system as PCM for low-temperature TES applications. Additionally, it contributes to support the important discussion on the effect of odd–even number of carbons of the individual n-alkanes in the solid–liquid phase equilibrium behavior of their binary mixtures. The solid–liquid diagram of this system is being published for the first time, as far as the authors are aware.
- Solid-liquid phase diagram of the dimethyl + dipropyl adipates system: application to low-temperature thermal energy storagePublication . Sequeira, Maria Carolina; Nikitin, Timur; Caetano, Fernando J. P.; Diogo, Herminio; Fareleira, João; Fausto, RuiThe present study is the continuation of our research work on di-n-alkyl adipates and their potential as phase change materials (PCM) for low-temperature thermal energy storage (TES). The solid–liquid phase diagram for the binary system composed of dimethyl adipate (DMA) and dipropyl adipate (DPA) is presented and analysed. In a previous study, we explored a particular binary system of n-alkyl adipates, namely diethyl and dibutyl adipates, and demonstrated that these compounds possess underappreciated potential as PCMs at sub-zero temperatures. The goal of the current work is to expand on this research by contributing new phase equilibrium data and deepening our understanding of the fundamental thermodynamics governing low-temperature phase behaviour in di-n-alkyl-adipates. The phase diagram for the DMA + DPA binary system was obtained using three complementary techniques: differential scanning calorimetry (DSC), hot-stage microscopy (HSM), and Raman spectroscopy. DSC analysis of sixteen compositions, including the two pure compounds, provided both the temperature and enthalpy values for the solid–liquid and solid–solid phase transitions. The binary system displays eutectic behaviour at low temperatures, with the eutectic point found at 252.83 K and a composition of approximately xDPA = 0.77. Raman spectroscopy confirmed that the system is characterized by a non-isomorphic eutectic phase diagram, indicating differences in the crystal structures of the solid phases. The liquidus line of the binary phase diagram was successfully described using a suitable fitting equation, yielding a root mean square deviation of 0.65 K, indicating excellent agreement between the experimental data and the theoretical model. This fitting also allowed an accurate prediction of the eutectic composition and temperature. A Tammann diagram is also presented, further confirming the eutectic composition and associated enthalpy. This work addresses a gap in the literature by presenting, for the first time, the solid–liquid phase equilibrium behaviour of the DMA + DPA binary system (including the detailed solid–liquid phase diagram of the system). The findings provide valuable insight into the potential use of this system as PCM for sub-zero TES applications, supporting their consideration in future thermal energy storage technologies.