Showing papers on "Enthalpy published in 2021"

Co-pyrolysis of sewage sludge and low-density polyethylene – A thermogravimetric study of thermo-kinetics and thermodynamic parameters

Abstract: This study investigates, for the first time, the thermal behaviors, kinetics and thermodynamics of sewage sludge (SS) and low-density polyethylene (LDPE) and their blends during co-pyrolysis. SS and LDPE co-pyrolysis were examined through thermogravimetric analysis (TGA) using different mixtures and multiple heating rates method. A positive interaction caused by the co-pyrolysis of SS and LDPE has been confirmed by the improved weight loss rate and devolatilization. Discrepancies between theoretical and experimental TGA/DTG curves as a measurement of the extent of synergic effect proved the existence of chemical interactions during the co-pyrolysis between the SS and LDPE blends of 1:1 and 1:2 ratios. The activation energy and reaction order for raw materials and their blends were studied by Coats-Redfern model. SS and LDPE blend of 1:1 ratio was optimal as it decreased the activation energy. Meanwhile, kinetics and thermodynamics were obtained from Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and Starink methods. Where the activation energies (76.73–355.83 kJ/mol), Gibbs free energy (116.92–123.04 kJ/mol) and lower difference of enthalpy (ΔH=∼6 kJ/mol) showed a promising potential to convert abundant and low-cost bio-solid wastes into bioenergy. This study provides a theoretical groundwork for co-pyrolysis of SS and LDPE.

Kinetic and thermodynamic analyses of dried oily sludge pyrolysis

Abstract: Oily sludge has the potential to utilize in pyrolysis process effectively because of higher product recovery and lower harmful emissions. Due to the complex nature of reactions, it is necessary to evaluate the thermo-kinetic behavior of the process to make it commercially feasible. This study includes thermal degradation behavior, the kinetic and thermodynamic analysis of dry oily sludge by applying Friedman and Vyazovkin method (model-free approach), and Coats-Redfern method (model-fitting approach) with the help of thermogravimetric analysis TGA at different heating rates (5, 20, 40 °C/min). The active region was from 20 to 60% conversion range because the maximum conversion occurs in this region. The overall activation energy decreases as the conversion increases from a lower range (60%) to a higher range (80%) for all satisfied models. The estimated range of pre-exponential coefficient for each model was to 4.91E+15 to 2.30E-01min−1 in the conversion range of 20–60% and 9.80E+02 to 4.89E-04min−1 in the conversion range 60–80%. The overall value of the change in enthalpy ΔH and change in Gibbs free energy ΔG decrease as the conversion increases from the lower range to the higher range.

Thermal degradation characteristics and kinetic study of camel manure pyrolysis

Abstract: An alternate and sustainable utilisation of camel dung waste has been investigated in this study. The pyrolysis degradation characteristics of camel dung have been investigated using a thermogravimetric analyser and the same has been compared with the gasification decomposition behaviour of the dung. The pyrolysis analyses were performed at heating rates of 10, 20, and 50 K/min from room temperature to 1173 K under an inert N2 atmosphere. The pyrolytic kinetics were estimated using different models such as Coats-Redfern, Friedman, Distributed activation energy, Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa, and Starink. The average activation energy values were consistent (162–172 kJ/mol) for all the models. Comparison of pyrolysis kinetics with gasification kinetics indicated that the camel dung requires more activation energy for the pyrolysis decomposition. The estimated activation energy values and the Kissinger equation were used to determine the thermodynamic properties such as Gibbs free energy, enthalpy, and entropy. The Gibbs free energy and enthalpy values of the pyrolysis degradation were lower than in the case of the gasification decomposition. The details of these kinetic parameters and thermodynamic properties are vital for the design and fabrication of pyrolysis reactors.

Learning to fly: thermochemistry of energetic materials by modified thermogravimetric analysis and highly accurate quantum chemical calculations

Abstract: The standard state enthalpy of formation and the enthalpy of sublimation are essential thermochemical parameters determining the performance and application prospects of energetic materials (EM). Direct experimental measurements of these properties are complicated by low volatility and high heat release in bomb calorimetry experiments. As a result, the uncertainties in the reported enthalpies of formation for a number of even well-known CHNO-containing compounds might amount up to tens kJ mol−1, while for some novel high-nitrogen molecules they reach even hundreds of kJ mol−1. The present study reports a facile approach to determining the solid-state formation enthalpies comprised of complementary high-level quantum chemical calculations of the gas-phase thermochemistry and advanced thermal analysis techniques yielding sublimation enthalpies. The thermogravimetric procedure for the measurement of sublimation enthalpy was modified by using low external pressures (down to 0.2 Pa). This allows for observing sublimation/vaporization instead of thermal decomposition of the compounds studied. Extensive benchmarking on nonenergetic and energetic compounds reveals the average and maximal absolute errors of the sublimation enthalpies of 3.3 and 11.0 kJ mol−1, respectively. The comparison of the results with those obtained from the widely used Trouton–Williams empirical equation shows that the latter underestimates the sublimation enthalpy up to 140 kJ mol−1. Therefore, we performed a reparametrization of the latter equation with simple chemical descriptors that reduces the mean error down to 30 kJ mol−1. Highly accurate multi-level procedures W2-F12 and/or W1-F12 in conjunction with the atomization energy approach were used to calculate theoretically the gas-phase formation enthalpies. In several cases, the DLPNO-CCSD(T) enthalpies of isodesmic reactions were also employed to obtain the gas-phase thermochemistry for medium-sized important EMs. Combining the obtained thermochemical properties, we determined the solid-state enthalpies of formation for nearly 60 species containing various important explosophoric groups, from common nitroaromatics, nitroethers, and nitramines to novel nitrogen-rich heterocyclic species (e.g., the derivatives of pyrazole, tetrazole, furoxan, etc.). The large-scale benchmarking against the available experimental solid-state enthalpies of formation yielded the maximal inaccuracy of the proposed method of 25 kJ mol−1.

Paper title: thermochemical heat storage behavior of ZnSO 4 .7H 2 O under low-temperature

Abstract: Thermochemical heat storage materials for space heating applications such as, ZnSO4 offer high energy storage density, low cost and clean mean of long-term solar energy storage. Herein, we studied the ZnSO4 hydrated salt as potential heat storage material at low temperature and furthermore observed the impact of temperature and concentration on the dehydration/hydration process and enthalpy. The thermal behavior of ZnSO4•7H2O was investigated by applying various dehydration temperatures. The results showed that 85% of water loosed at 100 °C temperature, which released 699 J/g (1.37 GJ/m3) in the dehydration process. The hydration process of ZnSO4.7H2O at 100 °C recovered 541 J/g enthalpies, which delivered 1.1 GJ/m3. Similarly, the dehydration result obtained at 150 °C was the same as showed at 100 °C. However, the enthalpy of hydration was 20% less than prior. The XRD result showed that at higher temperatures agglomeration appeared followed by Van der Waals forces which affect the hydration rate. The result of good cyclability and larger water sorption performance of ZnSO4 make them a promising and suitable for heat storage in space heating application, which can be used as thermochemical heat storage material for thermal storage devices.