Search Results (142)

Currently, there is no existing methodology within commercially available software packages for accurately simulating the gradual evaporation of the aqueous phase in batch thermomechanical dehydration processes involving highly stable water-hydrocarbon emulsions. This limitation constitutes a significant obstacle to the widespread industrial implementation of a promising approach for liquid hydrocarbon waste disposal, which relies on the evaporation of the aqueous phase under intensive stirring conditions, ultimately producing a hydrocarbon product with residual water content. In this study, the widely used Aspen HYSYS V12 software was employed to model these processes. The primary objective was to identify the most appropriate thermodynamic model accurately describing vapor–liquid phase transitions during the boiling of the aqueous phase in highly stable water–hydrocarbon emulsions, with water content ranging from 2 to 60% by weight. The modeling of the gradual boiling process was divided into several sequential stages, each representing a single evaporation step. The initial feedstock temperature was set at 90 °C, with subsequent stages involving temperature increments of 5 °C until the residual water content in the product fell below 0.5% by weight. Four thermodynamic models were evaluated for their ability to predict phase equilibria: Peng–Robinson, Wilson, UNIQUAC, and NRTL. It was observed that the Peng–Robinson model poorly describes the dehydration process, as it predicts water evaporation only at 100 °C, which contradicts experimental evidence indicating that evaporation occurs over a broader temperature range. The Wilson model significantly overestimates boiling points, reaching values up to 290 °C. Although the UNIQUAC model accurately reflects the process at higher water contents, it results in elevated energy consumption, necessitating substantial superheating of the feedstock up to 220 °C. The NRTL model provided the best correlation (among studied thermodynamic models) with experimental data, providing an average relative deviation of 3.68% and effectively capturing the two-stage evaporation mechanism: initial removal of free water at 100–110 °C, followed by bound moisture evaporation at temperatures approaching 160 °C. Vaporization rates were also examined across all models. The Peng–Robinson approach predicted the highest vaporization peaks but was the least representative of actual process conditions. Notably, in the NRTL model, the peak vaporization rates were 1.9 to 2.7 times higher than those estimated using the UNIQUAC and Wilson models. This parameter is critical for the optimal selection and design of subsequent condensation equipment. Based on these findings, the NRTL thermodynamic model is recommended for the industrial-scale implementation of thermomechanical dehydration processes involving heavy hydrocarbon feedstocks, given its accuracy in modeling phase transitions and the temperature-dependent vapor generation rates derived from sequential equilibrium flash calculations. Full article

Fatty alcohols and aliphatic hydrocarbons occur abundantly in nature and serve as critical feedstocks for the surfactant and fuel industries, respectively. However, their industrial-scale separation and purification are significantly hampered by high boiling points and the formation of complex azeotropes. To address these challenges, this study explores a five-column high-vacuum pressure-swing distillation (HVPSD-5C) strategy. Vapor–liquid equilibrium (VLE) analysis of the key components (n-hexanol, n-octanol, n-dodecane, and n-tridecane) validated the thermodynamic viability of the process and established optimal operating conditions. To further enhance efficiency, a heat-pump-integrated configuration (HPI-HVPSD-5C) featuring vapor recompression and heat integration was designed, optimized, and evaluated. Comparison with the baseline HVPSD-5C process demonstrates that the HPI-HVPSD-5C configuration significantly improves sustainability and economics, reducing the total annual cost (TAC) by 17.48%, CO₂ emissions by 16.09%, and energy consumption cost by 12.79%. These findings provide a robust framework for the efficient separation of fatty alcohols from aliphatic hydrocarbons, offering a valuable reference for the purification of other pressure-sensitive azeotropic mixtures. Full article

Fully compressible two-phase flow configurations present many challenges for numerical modelling, requiring the development of Real Fluid Models (RFMs) able to simulate flows in subcritical, transcritical and supercritical regimes. Such an RFM has been recently developed at IFPEN based on physical properties lookup tables, mainly for binary and ternary chemical systems. This paper proposes an Artificial Neural Network (ANN) approach to overcome the limitations of lookup tables of thermodynamic properties and to apply RFM to multi-species combustion. A methodology for generating an optimized data set by combining a vapor–liquid equilibrium (VLE) thermodynamic solver and the in situ adaptive tabulation (ISAT) method is developed. It aims to improve the neural network training process for two-phase combustion simulations where many species are present. This ANN methodology has been implemented in the CONVERGE CFD solver and validated using a mixing layer (LOX/GH₂) benchmark from the literature relevant to rocket conditions, and an academic gaseous (H₂/O₂) case relevant to hydrogen combustion. The results show that this ANN approach makes H₂ combustion simulation possible when coupled to the RFM framework and using a 10-species kinetic mechanism. Full article

This study investigates the feasibility of treating acidic gases produced in oilfields using a novel method that combines cavitation-jet reactor (CJR) technology with electric arc discharge (EAD). The integration of these two approaches enhances the ionization process by converting neutral gas molecules into chemically reactive ion-radical and radical fragments. These highly reactive species eventually recombine, creating new chemical compounds and simpler molecules from incoming acid gas and water vapor. Theoretical validation and experimental demonstration have revealed possible mechanisms and pathways of low-temperature plasma-chemical processes resulting from the synergistic effects of cavitating-jet flow and arc discharge on the molecular degradation of neutral gaseous molecules, such as hydrogen sulfide and carbon dioxide in water vapor, which lead to the generation of new compounds. Research indicates that the most effective method for processing associated petroleum gas (APG) involves minimizing the sequential nature of chemical reactions in low-temperature non-equilibrium plasma environments, thus eliminating the need for costly and complex catalysts. Additionally, studies have shown that the cavitation-jet flow of a gas–vapor–liquid mixture, when combined with an electric arc discharge in the truncated region of the low-temperature plasma of CJR, results in the synthesis of hydrogen, two forms of S₈ (S₈^I and S₈^II), crystalline carbon, and its organic derivatives containing oxygen and nitrogen, specifically methanol, ethanol, acetone, and acetonitrile. The data obtained suggest that the generation of low-temperature plasma in the cavitation-jet chamber, induced by an electric discharge, is essential for the production of reaction products, such as hydrogen, sulfur, and oxygen- and nitrogen-containing derivatives of organic carbon, when water vapor and acid gas molecules traverse the reactor. Full article

The rapid evaporation of liquid droplets across a normal shock wave is a phenomenon of critical importance in advanced propulsion and clean energy systems, such as NH₃ supersonic separation. The conventional Spalding d²-law is commonly used to model such phenomena, but it is not suitable for predicting the complete vaporization of sub-micron droplets, particularly as evaporation approaches the free-molecular regime. To address this issue, this paper introduces a novel time-dependent one-dimensional CFD model, which is used to analyze the shock structure, the non-equilibrium heat and mass transfer between the liquid and gas phases, and the evolution of the droplets’ size through the shock. The model describes the evaporation of NH₃ sub-micron droplet sprays across a stationary normal shock for various fractions of the liquid phase. The Gyarmathy evaporation model is utilized to accurately account for the transition from diffusion-governed to free-molecular regimes, alongside a new two-phase Rankine–Hugoniot shock jump formulation. The study reveals the influence of a steady normal shock on the physical structure of a droplet-laden flow, including the existence of an initial droplet size swelling through the shock, and quantifies the subsequent complete evaporation of the suspended droplets. The maximum swelling throughout the shock is up to 17%, which corresponds to the case with 8% liquid phase mass fraction in the flow. The model provides acceptable accuracy in calculating the two-phase parameters in high-speed flows and can be extended for modeling more complex, multidimensional detonation and propulsion systems. Full article

Biodiesel is a biofuel commonly produced through transesterification, also known as alcoholysis. In this process, triglycerides react with short-chain alcohols (alkyl–OH), producing a mixture of fatty acid esters and glycerol. These esters and glycerol are only partially miscible, leading to the formation of two liquid phases during product separation. Therefore, it is important to experimentally determine liquid–liquid (LLE) and/or vapor–liquid–liquid equilibrium (VLLE) data to better understand the transesterification process and to support improvements in reaction rate, selectivity, reactor and mixture simulation, optimization, and separation processes. This work aimed to experimentally measure and thermodynamically model the LLE and VLLE of alkyl palmitate + alkyl–OH + glycerol systems at 101.3 kPa. For the LLE at 318.15 K, the binodal curve was determined, and tie-line compositions were measured in a jacketed equilibrium cell. These data were subjected to quality tests and used to calculate separation factors. For the VLLE, calibration curves were constructed, and experimental data were obtained in a modified Othmer ebulliometer and subsequently tested for consistency. Thermodynamic modeling was performed using γ–γ (LLE) and γ–γ–φ (VLLE) approaches with the Non-Random Two-Liquid (NRTL) activity coefficient model. The experimental and modeling results were analyzed using phase diagrams (triangular and 3D prism representations) and showed that it is possible to clearly separate the palmitate-rich and glycerol-rich liquid phases. In the VLLE, it was observed that the alkyl–OH is essentially pure in the vapor phase. For both types of equilibria, deviations in liquid-phase compositions (LLE), bubble temperatures, and vapor-phase compositions were below 2.0%, indicating that the NRTL model is capable of accurately describing the phase behavior of these systems. The phase equilibria of the methyl/ethyl palmitate–methanol/ethanol–glycerol system were studied using molecular dynamics (MD). The analyses based on the radial distribution function (RDF), spatial distribution function (SDF) and interaction energies showed that methanol and ethanol interact more strongly with glycerol than with palmitates. As a result, the glycerol-rich phase contains more methanol or ethanol, which can significantly reduce costs in the biodiesel purification step. Full article

Methanol is a liquid fuel with high oxygen content and the potential for a closed-loop carbon-neutral production cycle. To investigate the mixture formation and combustion characteristics of a heavy-duty Port Fuel Injection (PFI) methanol engine, a three-dimensional numerical simulation model was established using the CONVERGE 3.0 software. Multi-cycle simulations were performed to analyze the influence of wall film dynamics on engine performance. The results indicate that the “adhesion–evaporation” equilibrium of the intake port wall film determines the in-cylinder mixture concentration. Due to the high latent heat of vaporization of methanol, severe wall-wetting occurs during the initial cycles, causing the actual fuel intake to lag behind the injection and leading to an overly lean mixture and misfire. Regarding injection strategies, the open valve injection (OVI) strategy utilizes high-speed intake airflow to reduce wall adhesion and improve fuel transport efficiency compared to closed valve injection. OVI refers to the fuel injection strategy that injects fuel into the intake port during the intake valve opening phase. The open valve injection strategy (e.g., SOI −500° CA) demonstrates distinct superiority over closed valve strategies (SOI −200°/−100° CA), achieving a 75% reduction in wall film mass. The long injection duration and early phasing allow the high-speed intake airflow to carry fuel directly into the cylinder, significantly minimizing wall film accumulation and avoiding the “fuel starvation” observed in closed-valve strategies. Additionally, OVI fully utilizes methanol’s latent heat to generate an intake cooling effect, which lowers the in-cylinder temperature and helps suppress knock. Furthermore, a dual-injector strategy is proposed to balance spatial atomization and rapid fuel transport, which achieves a 66.7% increase in the fuel amount entering the cylinder compared with the original strategy. This configuration effectively resolves the fuel induction lag, achieving stable combustion starting from the first cycle. Full article

Accurate knowledge of phase behavior in polyolefin–solvent mixtures is critical for ensuring stable operation and safe scale-up of industrial solution polymerization processes. The binary (n-hexane + ethylene/1-octene copolymer, POE96k-10) and ternary (α-olefin + n-hexane + POE96k-10) phase behaviors were investigated via a visual high-pressure cell (POE96k-10: M_w = 96 kg·mol^–1, M_w/M_n = 3.87, 1-octene mole fraction = 10.31 mol%) at temperatures of 380~480 K and pressures as high as 14 MPa. To systematically analyze the effects of α-olefin mass fraction and type on phase transition, four industrially relevant α-olefins (ethylene, 1-butene, 1-hexene, and 1-octene) were investigated. The results show that the phase transition temperature and pressure for liquid–liquid and liquid–vapor transitions show an approximately linear dependence on α-olefin mass fraction. Ethylene, 1-butene, and 1-hexene lower the phase transition temperature, whereas 1-octene increases it. Ethylene exhibits a strong anti-solvent effect, significantly lowering the transition temperature while increasing the phase transition pressure. The modified Sanchez-Lacombe equation of state (MSL EOS) effectively correlates and reproduces the phase equilibrium data of the α-olefin + n-hexane + POE96k-10 ternary systems, though its accuracy decreases with increasing α-olefin chain length. Full article

This article evaluates and develops a thermodynamic steady-state model, analyzing the thermodynamic properties of ammonia–ionic liquid (NH₃–IL) working pairs for use in high-temperature (>100 °C) absorption heat pumps. Given the increasing need for energy savings and reductions in greenhouse gas emissions, this is becoming an important consideration in the context of industrial facilities. Prior work on ammonia–ionic liquid (IL) pairs has largely focused on lower supply temperatures and offers no quantitative criteria connecting IL properties to high-temperature (>100 °C) cycle design. This article presents calculations based on correlations in the literature to determine the vapor pressures of pure ionic liquids using a modified Redlich–Kwong equation of state; the vapor–liquid equilibrium (VLE) of NH₃/[emim][SCN] and NH₃/H₂O mixtures in the NRTL model; the specific heats of pure ionic liquids (ILs); the specific heat capacities of NH₃–IL and NH₃–H₂O mixtures; and the excess enthalpy (HE) for NH₃/[emim][SCN] and NH₃/[emim][EtSO₄] as a function of temperature and composition, using a combination of NRTL + Gibbs–Helmholtz and Redlich–Kister polynomials. The calculations confirm the practically zero volatility of ionic liquids in the generator. This preserves the high purity of the ammonia vapor above the NH₃/[emim][SCN] solution (y₁ ≥ 0.997 over a wide range of temperatures and concentrations) and enables the rectification process in the generator to be omitted. The specific heat capacity of pure ionic liquids (ILs) has been shown to be 52–63% lower than that of water. Mixtures of ammonia (NH₃) and ILs with a mass fraction of 0.5/0.5 have a specific heat at 120 °C that is 34–37.5% lower than that of the ammonia–water (NH₃–H₂O) solution. This directly translates into a reduction in the power required in the generator. Excess enthalpy results show moderate or strongly negative values within the useful temperature and concentration range, indicating the exothermic nature of the mixture. At the same time, the NH₃/[emim][EtSO₄] mixture is characterized by a decrease in enthalpy with increasing temperature, suggesting that benefits for the COP of the system can be obtained. Based on these calculations, criteria for selecting ionic liquids for use in high-temperature absorption pumps were formulated: negligible volatility, a low specific heat capacity for the mixture, and a strongly negative excess enthalpy, which decreases with temperature, at the operating temperatures of the absorber and generator. Full article

Phase equilibrium calculations are crucial in chemical engineering design and optimization processes. The PC-SAFT equation of state (EoS) can precisely calculate phase equilibrium, but is relatively complex and computationally intensive. Surrogate models are mathematically simple models that map or regress the input–output relationships of more complex, computationally demanding models. This work employs XGBoost and a hybrid XGBoost-artificial neural networks (XGBoost-ANN) model as surrogate models to replace PC-SAFT EoS calculations for the vapor–liquid equilibrium (VLE) of binary associating systems. This work investigates the VLE of five binary associating systems using data generated by the PC-SAFT EoS. The surrogate models take temperature, pressure, liquid phase mole fractions, and the PC-SAFT parameters for binary associating systems as inputs, and predict the vapor phase mole fractions. Both surrogate models significantly reduce the computational time for calculating VLE data compared to the PC-SAFT EoS, while achieving good prediction results. Full article

The vapor–liquid equilibrium (VLE) data of the binary acetonitrile + water system and three ternary systems containing ionic liquids (ILs): acetonitrile + water + 1-butyl-3-methylimidazolium chloride ([C₄mim][Cl]), + 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄mim][BF₄]), and + 1-hexyl-3-methylimidazolium chloride ([C₆mim][Cl]) were experimentally measured at low pressures. In addition, the literature VLE data for the binary systems acetonitrile + [C₄mim][Cl], acetonitrile + [C₄mim][BF₄], and acetonitrile + [C₆mim][Cl] were adopted for model correlation. The NRTL and e-NRTL models were employed to correlate the binary data. The experimental results demonstrate that the presence of ILs causes a pronounced salting-out effect on acetonitrile, significantly increasing its relative volatility with respect to water. The separation performance of the three ILs for the acetonitrile + water mixture decreases in the order: [C₄mim][Cl] > [C₆mim][Cl] > [C₄mim][BF₄]. Full article

2-Methyl-3-butenenitrile, a key intermediate in the industrial production of Nylon-66, is often accompanied by two other by-products, 2-methyl-2-butenenitrile and 2-pentenenitrile, which have been proven to affect the production yield and quality of Nylon-66. Pure 2-pentenenitrile is a commercial synthetic intermediate for many chemical products and bioactive substances. As important foundational data for designing large-scale separation and purification processes for these three compounds are lacking, the saturated vapor pressure of pure 2-pentenenitrile was measured over the temperature range 298.5 K to 401.4 K, and vapor–liquid equilibrium (VLE) data for the binary systems (2-methyl-3-butenenitrile + 2-pentenenitrile, 2-methyl-2-butenenitrile + 2-pentenenitrile) were determined at pressures of 50.0 kPa and 100.0 kPa. In order to better utilize these experimental data for the design of large-scale separation distillation processes, the experimental saturated vapor pressure data of pure 2-pentenenitrile were well correlated using the Antoine equation, yielding an average relative deviation of 0.92%. For all binary systems, the thermodynamic consistency of the VLE results was verified using both the point test and the direct test. The binary VLE data were correlated with the Wilson and NRTL activity coefficient models, and the corresponding model parameters were obtained by regression, which can help to obtain complete data in the whole mole fraction range for industrial separation design. Full article

This study proposes an analytical model for the long-term prediction of boil-off gas (BOG) generation in cryogenic storage tanks. The model assumes a saturated liquid and a superheated vapor under open-vent conditions. Heat ingress is estimated using steady-state thermal conduction analysis, and evaporation is then computed from thermodynamic equilibrium. In the first stage, a thermal resistance network quantifies the heat flux transferred to the liquid and vapor regions inside the tank. The network represents external convection, insulation conduction, and internal convection as thermal resistances. In particular, natural convection on the external and internal tank walls, as well as heat transfer at the liquid–vapor interface, are incorporated through appropriate convective heat-transfer correlations. In the second stage, the temporal variations in temperature and phase change of the vapor and liquid are computed. Each phase is modeled as a lumped mass at equilibrium, and the heat ingress obtained from the thermal resistance network is used to simulate the temperature evolution and evaporation process. A numerical model is also developed to capture the time-dependent variations in liquid and vapor heights and the corresponding BOG generation. The proposed model is applied to a 1.0 m³ liquid nitrogen storage tank and validated through comparison with the BoilFAST and SINDA/FLUINT models. The results confirm the validity of the model in terms of heat ingress, vapor temperature evolution, and BOG history. This study provides a practical framework for predicting long-term evaporation phenomena in cryogenic storage tanks and is expected to contribute to the thermal design and performance evaluation of cryogenic storage systems. Full article

The ability to predict the vapor pressure and vapor-phase composition of hydrocarbon mixtures (such as jet fuel, sustainable aviation fuel or its un-refined precursors) and partially vaporized hydrocarbon mixtures is important to simulations of processes that involve vaporization such as distillations, flash points, combustion properties of partially vaporized fuels, etc. Raoult’s Law provides a simple algebraic formula relating liquid composition and temperature to vapor composition and pressure. However, Raoult’s Law is not accurate at low mole fractions, which is typical for complex mixtures such as fuels. A common approach to correcting Raoult’s Law is to apply a scale factor, a so-called activity coefficient. Numerous models exist for predicting activity coefficients. Here we benchmark against the UNIFAC model, which predicts activity coefficients based on mole fractions, group fractions, Van der Waals volume and surface area and temperature-dependent interaction terms between groups. While this approach is truly predictive, its accuracy at very low mole fractions has not been validated, and it is computationally intensive, particularly for simulations (especially optimizations) that require vapor composition or pressure within the inner-most loop. Here we present an alternative correction to Raoult’s law, where the vapor pressure of the i^th component is represented by a modified form of the Clausius–Clapeyron equation. The reference temperature ($T_{ref}$) is replaced by a simple algebraic function that converges to $T_{ref}$ as $x_i$ approaches 1 while smoothly increasing from this value as $x_i$ decreases. Simultaneously, the heat of vaporization ($\mathsf{\Delta }{H}_{vap,i}\left(T\right)$) term is replaced by another simple algebraic expression that converges to $\mathsf{\Delta }{H}_{vap,i}\left(T\right)$ as $x_i$ approaches 1 while smoothly decreasing as $x_i$ decreases. In this model, the temperature-dependent heat of vaporization is tuned at each temperature such that the Clausius–Clapeyron equation reproduces the correct vapor pressure of the neat material, while the parameterized algebraic corrections are tuned to vapor pressure data of mixtures involving n-pentane, toluene, and dodecane, where the mole fractions of n-pentane and toluene are maintained below 10%_mol. Validation of the resulting model is accomplished by comparing modeled vapor–liquid equilibrium systems with experimental measurements. This approach improves the accuracy and computational efficiency of volatility predictions, thereby supporting the development, certification, and adoption of sustainable aviation fuel. Full article

Since H₂O and Ethylene Glycol Monomethyl Ether (EM) form a minimum-boiling azeotrope, 1-pentanol, 1-hexanol, and 1-heptanol are selected as entrainers to separate the azeotropic mixture (H₂O/EM) using azeotropic distillation. The binary vapor liquid equilibrium (VLE) data were determined at 101.3 kPa, including H₂O/EM, EM/1-pentanol, EM/1-hexanol, EM/1-heptanol, H₂O/1-pentanol, H₂O/1-hexanol and H₂O/1-heptanol. Meanwhile, the Herington area test was used to validate the thermodynamic consistency of the experimental binary data. The VLE data for the experimental binary system were analyzed using the NRTL, UNIQUAC, and Wilson activity coefficient models, showing excellent agreement between predictions and measurements. Finally, molecular simulations were employed to calculate interaction energies between components, providing insights into the VLE behavior. The azeotropic distillation process was simulated using Aspen Plus to evaluate the separation performance and determine the optimal operating parameters. Therefore, this study provides guidance and a foundational basis for the separation of H₂O/EM systems at 101.3 kPa. Full article