Chemical Thermodynamics Research Articles

Modeling of Vapor-Liquid Equilibrium for Electrolyte Solutions Based on COSMO-RS Interaction

The modeling of phase equilibrium for electrolyte solutions plays an important role in chemical thermodynamics. Modeling and calculation of the vapor-liquid equilibrium (VLE) for an electrolyte solution are studied in this paper. The influence mechanism for the microscopic interaction on the macroscopic VLE is further studied by COSMOtherm. Then, a developed model is proposed. The interaction parameters in the model are linked to the COSMO interaction energy (H_int). The interaction equations are remodeled using 1stopt software, and components are used to replace the “interaction parameters” used in a previous model. The developed model can be used to successfully predict VLE data for electrolyte solutions based on the α and hi parameters.

Sublimation/vaporization and solvation enthalpies of monosubstituted pyridine derivatives

Different sectors, including medicine and display technology, utilize substituted pyridines. To establish the quality of products manufactured from pyridines, chemical thermodynamics of the solvation and evaporation enthalpies of the pyridines are crucial. The solvation and evaporation enthalpies of the monosubstituted pyridine derivatives were determined in this study. The enthalpy of solvation of the pyridines was determined using the additive scheme method and the solution calorimetry methods. The evaporation enthalpy of the pyridine derivatives was also calculated using solution calorimetry and transpiration methods. As a consequence, solution calorimetry's additive scheme and the transpiration methods were used to determine the 2-iodopyridine's vaporization enthalpy for the first time. The study's sublimation/vaporization enthalpy values were extremely accurate and closely matched those found in the literature. As a result, the impacts of the different attached groups to the pyridine molecule as well as the enthalpies of evaporation and solvation of the monosubstituted pyridine were investigated.

Oxidative torrefaction of densified woody biomass: Performance, combustion kinetics and thermodynamics

Torrefaction in partially oxidative atmospheres is a non-traditional approach to the thermal pre-treatment of biomass. Despite the potential benefits arising from this compared to traditional torrefaction undertaken under costly inert atmospheres, the literature lacks data on the combustion and kinetic analyses of densified biomass torrefied under partially oxidative conditions comparable to those of (reusing) combustion flue gases. This paper, therefore, investigates the effects of partially oxidative atmosphere on the chemical functionality, combustion kinetics and thermodynamics of densified (Australian) woody biomass. Torrefaction was conducted at 250, 275, 300 °C for 30min under both inert and partially oxidative atmosphere (O2: 5 vol%, N2 balance). The kinetic parameters were derived from iso-conversional method over the entire conversion range. Results show that solid biofuel torrefied under partially oxidative atmospheres has superior chemical functionality (e.g., less oxygenates and higher thermal stability), but comparable physical properties to inert atmospheres. In addition, improved thermodynamic features and lower combustion activation energy for partially oxidative torrefied biomass was observed. Overall, the results suggest that the use of partially oxidative atmospheres for torrefaction not only produce a high quality solid biofuel but can also improve process efficiency by using waste heat and flue gases from other combustion processes to thermally pre-treat biomass.

Inactivation kinetics and thermodynamics assessments of Geobacillus stearothermophilus during thermal sterilization for products safety

Chemical kinetics and thermodynamics provide modes and mechanisms for the thermal death of microbial spores. In this study, the effect of thermal inactivation on Geobacillus stearothermophilus, a highly heat-resistant bacterial species, was studied over the temperature range of 95, 100, 105, and 110 °C and holding sterilization periods of 10, 15, 20, 25, 30, and 45 min by the application of mathematical analysis of kinetic and thermodynamic properties. Thermal death rate constant, k, for the best kinetic order of sterilization ranged between 0.0431 to 0.1581 min−1 with the energy of activation, Ea, estimated to be 115.96 kJ/mol. Two primary thermal death kinetic models were applied (log-linear first order and the nonlinear Weibull). Weibull's model provided more reliable kinetic parameters to predict the effect of thermal treatments. Concave curves (α >1) were predicted with the Weibull's model for 100, 105, and 110 °C (1.57, 1.26, and 1.22 respectively), indicating the susceptibility of spores to lethal treatment. The rate parameter, ɸ (first reduction time) decreased with increasing thermal heating (28.80 min (95 °C), 21.08 min (100 °C), 14.61 min (105 °C), and 9.65 min (110 °C)) following the paths of the D-values (about 7 min to attain 88% spores’ destruction after 110 °C heating) of the log-linear kinetic model. Thermal death time (TDT) for the complete destruction of spores was predicted to be after 40 min at 110 °C. The z-value was 23.31 °C, indicating the sterilization temperature that must be attained for one log destruction of spores. The heat of activation showed endothermic reactions for all temperatures (∆H ranged 112.90 – 112.78 kJ/mol), Gibb's free energy of activation, ∆G, ranged from 325 – 333.74 kJ/mol (indicating a non-spontaneous reaction), and the entropy of activation (∆S) showed reversibility of reaction (∆S < 1) for all the thermal temperatures.

Chemical thermodynamics for growing systems

We consider growing open chemical reaction systems (CRSs), in which autocatalytic chemical reactions are encapsulated in a finite volume and its size can change in conjunction with the reactions. The thermodynamics of growing CRSs is indispensable for understanding biological cells and designing protocells by clarifying the physical conditions and costs for their growing states. In this paper, we establish a thermodynamic theory of growing CRSs by extending the Hessian geometric structure of nongrowing CRSs. The theory provides the environmental conditions to determine the fate of the growing CRSs; growth, shrinking, or equilibration. We also identify thermodynamic constraints: one to restrict the possible states of the growing CRSs and the other to further limit the region where a nonequilibrium steady growing state can exist. Moreover, we evaluate the entropy production rate in the steady growing state. The growing nonequilibrium state has its origin in the extensivity of thermodynamics, which is different from the conventional nonequilibrium states with constant volume. These results are derived from general thermodynamic considerations without assuming any specific thermodynamic potentials or reaction kinetics; i.e., they are obtained based solely on the second law of thermodynamics.

In situ synthesis of Al2O3–SiC powders via molten-salt-assisted aluminum/carbothermal reduction method

Al 2 O 3 –SiC composite powder (ASCP) was successfully synthesized using a novel molten-salt-assisted aluminum/carbothermal reduction (MS-ACTR) method with silica fume, aluminum powder, and carbon black as raw materials; NaCl–KCl was used as the molten salt medium. The effects of the synthesis temperature and salt-reactant ratio on the phase composition and microstructure were investigated. The results showed that the Al 2 O 3 –SiC content increased with an increase in molten salt temperature, and the salt–reactant ratio in the range of 1.5:1–2.5:1 had an impact on the fabrication of ASCP. The optimum condition for synthesizing ASCP from NaCl–KCl molten salt consisted of maintaining the temperature at 1573 K for 4 h. The chemical reaction thermodynamics and growth mechanism indicate that the molten salt plays an important role in the formation of SiC whiskers by following the vapor-solid growth mode in the MS-ACTR treatment. This study demonstrates that the addition of molten salt as a reaction medium is a promising approach for synthesizing high-melting-point composite powders at low temperatures.

New Possibilities of the CpFit Program for Approximating Heat Contents and Heat Capacities

Created in 2016 at Moscow State University’s Laboratory of Chemical Thermodynamics, the CpFit program is designed to approximate experimental data on the heat contents and isobaric heat capacities of individual substances using third-generation CALPHAD models that include weighted sums of Einstein functions. It supports approximating anomalies in heat capacity according to excess contributions. Support for robust regression and the ability of users to specify arbitrary anomalous contributions to heat capacity in the interpreted Lua programming language have also been added to the CpFit program. CpFit is a cross-platform free software distributed under the GNU GPL 2 license.

The role of source emissions in sulfate formation pathways based on chemical thermodynamics and kinetics model

Sulfate is a major PM2.5 constituent and poses a significant threat to ecosystems and human health, which has attracted lots of attention to the sulfate formation mechanism. In recent years, there has been great scientific interest in the multiphase oxidation of SO2 in aqueous aerosol particles. Many factors are involved in the reaction process, including precursor SO2, oxidants/catalysts, and aerosol acidity, which are three channels closely related to the source emission. The conjoint analysis of source emissions and sulfate aqueous formation can provide a scientific basis for designing effective strategies, though the related research is extremely limited. Here, we applied an improved solute strength-dependent chemical Thermodynamics & Kinetics model (for aqueous pathway contribution) and the Partial Target Transformation-Positive matrix factor model (for source apportionment) to explore the role of source emission in sulfate aqueous formation. The results indicated H2O2 aqueous oxidation was the dominant pathway (65.9 %), and secondary nitrate source may grow together with sulfate formation from H2O2 pathway. H2O2 and TMI pathways were related to higher SOR (sulfur oxidation rate). TMI pathway was significant in summer (54.6 %) and increased with secondary sources and vehicle exhaust. NO2 pathway was more significant at low secondary source and high coal combustion (higher contribution of NO2 pathway appeared in winter, 24.7 %). While high formation rate of the O3 pathway always occurred at low source levels. Coal combustion and vehicle exhaust showed obvious effects on sulfate aqueous formation. Notably, aerosol acidity is a significant factor related to sources and plays a key role in sulfate formation. The result also suggested aerosol pH may be more important than the amounts of substances involved in the oxidation reaction. The findings in this work can provide useful information for better understanding sulfate aqueous formation and offer a scientific basis for designing strategies for air pollution control and sulfate mitigation.

Multi-component analysis, molecular model construction, and thermodynamics performance prediction on various rejuvenators of aged bitumen

The molecular dynamics (MD) simulation method is proved as an efficient tool to explore the intermolecular interaction between rejuvenators and aged bitumen, but the simple “single-molecule” model of rejuvenator would bring the inaccuracy to simulation outputs due to a huge difference with its realistic multi-component chrematistic. This study aims to in-depth analyze the chemical components of four commonly-used rejuvenators with the Gas chromatography-mass spectrometry (GC–MS) method, and propose their multi-component molecular models for the first time. Further, MD simulations are performed on the multi-component models of various rejuvenators to anticipate and compare their atomic-level properties. The GC–MS results reveal that the chemical components of petroleum-based rejuvenators are more complicated than the bio-oil (BO). The alkane, naphthenic, and aromatic molecules are the main constituents of engine-oil (EO), naphthenic-oil (NO), and aromatic-oil (AO) rejuvenators. The experimental density results validate the reliability of these multi-component molecular models of four rejuvenators. From the MD simulations outputs, there is a significant difference in the energetic indices, cohesive energy density (CED), solubility parameter δ, volumetric parameters, dynamic behaviors, structural indicators, expansion coefficient (α and β), and isobaric heat capacity (Cp) between the multi-component models of four rejuvenators. However, the multi-component molecular model of aromatic-oil based on the GC–MS method is not accurate because the polycyclic aromatic molecules with heavy-weight are not detected and considered. This study detects the difference in chemical components and thermodynamics properties between four rejuvenators and proposes their more realistic multi-component molecular models for further MD simulations on the rejuvenation of aged bitumen.

Problem Solving Thinking Skills: Effectiveness of Problem-Solving Model in Teaching Chemistry College Students

Problem-solving is considered one of the thinking skills that must be possessed in 21st-century education because problem-solving skills are needed to solve all problems that arise. This study aims to describe problem-solving thinking skills as a manifestation of the effectiveness of problem-solving models in college student chemistry learning. The research method uses descriptive research with a quantitative approach. The design used is One Group Pretest-Posttest Design. This research was conducted in the chemistry department Universitas Negeri Surabaya with the subjects of 31 college students who programmed basic chemistry courses on chemical thermodynamics. Measurement of problem-solving thinking skills using a paper-pen test (pretest and posttest) in the form of an essay. This research findings show that: (1) Each indicator of problem-solving thinking skills of trained college students gets percentage, namely understanding problems 76.08%, planning problem solving 80.65%, implementing problem-solving 85.49%, drawing conclusions 78.50%, and evaluating problem-solving results 68.22%; and (2) N-gain scores for each indicator of problem-solving thinking skills obtained have medium and high criteria. Based on the research results, the problem-solving model has been effective in improving college students' problem-solving thinking skills.

Hessian geometric structure of chemical thermodynamic systems with stoichiometric constraints

We establish a Hessian geometric structure in chemical thermodynamics, which describes chemical reaction networks (CRNs) with equilibrium states. In our setup, the ideal gas assumption and mass action kinetics are not required. The existence and uniqueness condition of the equilibrium state is derived by using the Legendre duality inherent to the Hessian structure. The entropy production during a relaxation to the equilibrium state can be evaluated by the Bregman divergence. Furthermore, the equilibrium state is characterized by four distinct minimization problems of the divergence, which are obtained from the generalized Pythagorean theorem originating in the dual flatness. For the ideal gas case, we confirm that our existence and uniqueness condition implies Birch's theorem, and that the entropy production represented by the divergence coincides with the generalized Kullback-Leibler divergence. In addition, under mass action kinetics, our general framework reproduces the local detailed balance condition.

A Density Functional Theory Investigation of the Fragmentation Mechanism of Deprotonated α-Alanine

In this paper, density functional theory (DFT) was applied to study the isomerization process and fragmentation mechanism of deprotonated α-alanine ions ([α-Ala–H]–) at B3LYP/6-311++G(2df,2pd) level. Taking a2, the lowest energy of the [α-Ala–H]– isomers as the zero point, the potential energy profiles of the [α-Ala–H]– in isomerization, H2O- and NH3-loss reaction pathways were plotted using Relative Gibbs free Energies (R.G.) relative to a2 as the reference point. In the isomerization process, the reaction barrier (ΔG≠) required for hydrogen transfer is higher than other ones. From the perspective of chemical reaction thermodynamics, Path 11 of deamination to p3 is the only positive spontaneous pathway among all H2O- and NH3-loss pathways; and from the perspective of reaction kinetics, the dominant path is Path 2 of H2O-loss pathways ( = 53.65 kcal•mol-1). In addition, the effect of temperature on reaction pathways and dissociative products were also investigated. The results show that temperature has little effect on H2O- and NH3-loss pathways.

Chemical thermodynamics of ternary M-An(VI)-CO3 system (M = Mg, Ca, Sr, and Ba)

Abstract This review provides an overview of the chemical thermodynamics on ternary earth-alkaline metal-actinyl-tricarbonate systems (i.e., M-AnO2-CO3, M = Mg, Ca, Sr, and Ba) and discusses the aqueous complexation and dissolution/precipitation equilibrium for these ternary aqueous systems. The aqueous ternary U(VI) carbonate species are remarkably predominant in the U(VI) speciation under natural environmental conditions at ambient temperature and moderate ionic strength condition, while the omnipresence, according to recent studies, would be hindered by an increase in temperature and ionic strength. With respect to the ternary solid U(VI) carbonate phases, most of the previously reported data have been focused on physical properties and thus a notable lack of available data on chemical thermodynamic properties, i.e., solubility product constant, has been identified. Nevertheless, substantial influences of these ternary M-AnO2-CO3 systems on the aqueous speciation and the solubility limiting phase under the natural environmental condition are taken into account according to the thermodynamic calculation. The authors point out that the completeness of the chemical thermodynamic model for predicting the chemical behavior of actinides in nature can be further improved on the basis of a sufficient understanding of ternary M-AnO2-CO3 systems.

The practicality and effectiveness of case study-based module on chemical thermodynamics course (ideal and real gases) as learning tool during the COVID-19 pandemic

The case study-based module on chemical thermodynamics course (ideal and real gases) was developed to fulfill the needs of undergraduate students in online learning during the COVID-19 pandemic. The purpose of this study was to test feasibility of case study-based module. The case study-based module refers to the 4D model (define, design, develop, and disseminate) by integrating the one group pretest-posttest design at the develop stage. The feasibility of the module was measured through validity, practicality and effectiveness using validation sheet, evaluation test sheet and questionnaire sheet. Data were analyzed descriptively, quantitatively (Wilcoxon Signed Rank Test) and qualitatively. The case study-based module was suitable for one of learning tools, which was proven by the findings that 1) meets valid and reliable criteria, 2) meets practical criteria with support for general achievements students’ very positive response to the aspects of module (construction, material, motivation and case study), and 3) meets the effective criteria by increasing the average score pretest-posttest in medium category which contains the cognitive level of analyze-C4, evaluate-C5, and create-C6. The implication of development case study-based module can facilitate students in online learning during the COVID-19 pandemic so that they will successfully reach the course learning outcomes of Chemical Thermodynamics, which includes mastery of knowledge about main principles of thermodynamics, ability to solve science and technology problems, ability to use information and communication technology based learning resources, make decisions based on the relationship of concepts with laboratory activities, and practice responsibility.

Targeting Atmospheric Oxidants Can Better Reduce Sulfate Aerosol in China: H2O2 Aqueous Oxidation Pathway Dominates Sulfate Formation in Haze.

Particulate sulfate is one of the most important components in the atmosphere. The observation of rapid sulfate aerosol production during haze events provoked scientific interest in the multiphase oxidation of SO2 in aqueous aerosol particles. Diverse oxidation pathways can be enhanced or suppressed under different aerosol acidity levels and high ionic strength conditions of atmospheric aerosol. The importance of ionic strength to sulfate multiphase chemistry has been verified under laboratory conditions, though studies in the actual atmosphere are still limited. By utilizing online observations and developing an improved solute strength-dependent chemical thermodynamics and kinetics model (EF-T&K model, EF is the enhancement factor that represents the effect of ionic strength on an aerosol aqueous-phase reaction), we provided quantitative evidence that the H2O2 pathway was enhanced nearly 100 times and dominated sulfate formation for entire years (66%) in Tianjin (a northern city in China). TMI (oxygen catalyzed by transition-metal ions) (14%) and NO2 (14%) pathways got the second-highest contributions. Machine learning supported the result that aerosol sulfate production was more affected by the H2O2 pathway. The collaborative effects of atmospheric oxidants and SO2 on sulfate aerosol production were further investigated using the improved EF-T&K model. Our findings highlight the effectiveness of adopting target oxidant control as a new direction for sustainable mitigation of sulfate, given the already low SO2 concentrations in China.

Pressurized turbulent premixed CH4/H2/air flame validation using OpenFOAM

In this study, we use the Algebraic Flame Surface Wrinkling (AFSW) model to conduct numerical simulations of the PSI (Paul Scherrer Institute) high pressure, turbulent premixed Bunsen flame experiments. The AFSW model was implemented in the open-source computational fluid dynamics solver OpenFOAM, and the numerical simulations were performed using a two-dimensional axial-symmetric model with the standard k–ɛ turbulence model with wall functions. The numerical simulations were performed for two different fuel/air mixtures, namely, 100% CH4 volumetric ratio and 60% CH4 + 40% H2 volumetric ratio. The thermophysical and transport properties of the mixture were calculated as a function of temperature using the library Cantera (an open-source suite of tools for problems involving chemical kinetics, thermodynamics, and transport processes), together with the GRI-Mech 3.0 chemical mechanism. It was found that the outcome of the AFSW model implemented in OpenFOAM was in good agreement with the experimental results, quantitatively and qualitatively. Further assessment of the results showed that, as much as the chemistry, the turbulence model and turbulent boundary/initial conditions significantly impact the flame shape and height.

Liquid organic hydrogen carriers: Development of a thermodynamic and kinetic model for the assessment of hydrogenation and dehydrogenation processes

Liquid organic hydrogen carriers (LOHCs) are drawing interest as a viable storage technology because of many favourable characteristics, such as high gravimetric and volumetric energy density. However, technological readiness is still limited, and very few kinetic and thermodynamic models are currently available. This paper aims to provide a complete and reliable model for the catalytic hydrogenation and dehydrogenation of a 0H-NEC/12H-NEC system following a general chemical thermodynamics approach that could easily extend to other LOHCs. The insurgence of already documented high-temperature phenomena has been taken into account by introducing two novel modifications to the base model, making the model reliable over a wide temperature range. First, the model identifies a maximum rate constant reached for a threshold temperature; secondly, it evaluates thermodynamic equilibrium conditions to account for a maximum H2 uptake.

The chemical thermodynamics and diamagnetism of n-alkanes. Calculations up to n-C110H222 from quantum chemical computations and experimental values

Free energies, enthalpies of formation, enthalpies of combustion, and entropy of n-alkanes have been determined using quantum-chemical computations. After determination of the scaling factor between experimental results vs ab-initio computations, we are able to give various values corresponding to these thermodynamic properties up to n-C110H222. The same procedure is applied concerning data of diamagnetism of n-alkanes up to n-C30H62.

Effect of Carburizing Helium Environment on Corrosion Behavior of the High-Temperature Alloys for High-Temperature Gas-Cooled Reactor

The primary coolant of High-Temperature Gas-cooled Reactor (HTGR) is expected to contain impurities that can make corrosion to structural metallic materials at elevated temperatures. According to the chemical thermodynamics and kinetics, the carbon activity of helium can be calculated, and it is indicated that a high “CH4/H2O” ratio may lead to severe carburizing of the alloys. On this basis, corrosion tests were conducted on the three heat-resistance alloys Inconel 617, Hastelloy X, and Incoloy 800H at 950°C using helium environment with impurities, and mainly the effect of carburization was investigated. The corrosion samples were observed by Scanning Electron Microscopy (SEM) with Energy Disperse Spectroscopy (EDS), Electron Probe Microanalyzer (EPMA), and Carbon-sulfur Analyzer. These all alloys showed the oxidation and carburizing behavior, in which the carburized depth of Hastelloy X was shallow due to the dense oxide scale.

Effect of Strain on the Electronic Structure and Phonon Stability of SrBaSn Half Heusler Alloy.

This paper presents the strain effects on the structural, electronic and phonon properties of a newly proposed SrBaSn half Heusler compound. Since it is stable considering chemical thermodynamics, we tested its strength against uniform strain w.r.t phonon spectrum and it produces a direct bandgap of 0.7 eV. The direct bandgap reduces to 0.19 eV at −12% strain beyond which the structure is unstable. However, an indirect gap of 0.63 eV to 0.39 eV is observed in the range of +5% to +8% strain and afterwards the strain application destabilizes the structure. From elastic parameters, the ductile nature of this material is observed.