Gas-liquid Equilibrium Research Articles

Improvement Wilson equation (K-Values) of gas-liquid equilibrium for Advancing Estimating Bubble Point Pressure

Knowing the bubble point pressure of the oil reservoirs is a key factor for the petroleum engineers in order to optimize the development of the oil field starting from the discovery phase till the abandonment. Thus any considerable error in estimating the bubble point pressure will lead to errors in the production and reservoirs engineering calculations. More than six hundred Egyptian oil samples of PVT analysis were used to improve the Wilson equation (K-Values) for estimating bubble point pressure. None of the published bubble point pressure correlations is particularly accurate when applied to Egyptian crude oils. Experimental work was conducted in PVT- Services Center of Egyptian Petroleum Research Institute (EPRI). In this work, the K-values correlation proposed by Wilson equation was modified by adding new terms such as API, GOR, and heptanes plus-fraction (C7+) of compositional analysis of the reservoir fluid. Multiple non-linear regression analysis is used to calculate the new equation constant after adding the new terms. The statistical error analysis shows that the Correlation coefficient , the average percent relative error , the standard deviation and the average absolute percent relative error of the modifying are 99.75 %, 1.77%, 8.08%, and 6.84 %, respectively. This correlation of K-factor can be applied not only to low and moderate pressure but also to higher pressures up to (4500 psi) by this modification. Evaluation among the bubble point pressure calculated from the modified Wilson equation and the literature published ones were done. Results confirm that the modified Wilson equation is more accurate one and it can be used for estimating the reservoir fluids characteristics in the absence of data measurement.

New process development and process evaluation for capturing CO2 in flue gas from power plants using ionic liquid [emim][Tf2N

Abstract Using the ionic liquid [emim][Tf2N] as a physical solvent, it was found by aspen plus simulation that it was possible to attempt to capture CO2 from the flue gas discharged from the coal-fired unit of the power plant. Using the combination of model calculation and experimental determination, the density, isostatic heat capacity, viscosity, vapor pressure, thermal conductivity, surface tension and solubility of [emim][Tf2N] were obtained. Based on the NRTL model, the Henry coefficient and NRTL binary interaction parameters of CO2 dissolved in [emim][Tf2N] were obtained by correlating [emim][Tf2N] with the gas–liquid equilibrium data of CO2. Firstly, the calculated relevant data is imported into Aspen plus, and the whole process model of the ionic liquid absorption process is established. Then the absorption process is optimized according to the temperature distribution in the absorption tower to obtain a new absorption process. Finally, the density, constant pressure heat capacity, surface tension, thermal conductivity, viscosity of [emim][Tf2N] were changed to investigate the effect of ionic liquid properties on process energy consumption, solvent circulation and heat exchanger design.The results showed that based on the composition of the inlet gas stream to the absorbers, CO2 with a capture rate of 90% and a mass purity higher than 99.5% was captured; These results indicate that the [emim][Tf2N] could be used as a physical solvent for CO2 capture from coal-fired units.In addition,The results will provide a theoretical basis for the design of new ionic liquids for CO2 capture. Graphical Abstract. The Aspen Plus simulation uses ionic liquid [emim] [Tf2N] to absorb CO2 from flue gases and investigates the effects of ionic liquid properties on process energy consumption, solvent cycling and heat exchanger design. Finally, CO2 with a capture rate of 90% and a mass purity higher than 99.5% was captured. This result will provide a theoretical basis for the design of new ionic liquid capture CO2.

Solubility and mass transfer of H2, CH4, and their mixtures in vacuum gas oil: An experimental and modeling study

Abstract In this work, the solubility data and liquid-phase mass transfer coefficients of hydrogen (H2), methane (CH4) and their mixtures in vacuum gas oil (VGO) at temperatures (353.15–453.15 K) and pressures (1–7 MPa) were measured, which are necessary for catalytic cracking process simulation and design. The solubility of H2 and CH4 in VGO increases with the increase of pressure, but decreases with the increase of temperature. Henry's constants of H2 and CH4 follow the relation of ln H = − 413.05/T + 5.27 and ln H = − 990.67/T + 5.87, respectively. The molar fractions of H2 and system pressures at different equilibrium time were measured to estimate the liquid-phase mass transfer coefficients. The results showed that with the increase of pressure, the liquid-phase mass transfer coefficients increase. Furthermore, the solubility of H2 and CH4 in VGO was predicted by the predictive COSMO-RS model, and the predicted values agree well with experimental data. In addition, the gas–liquid equilibrium (GLE) for H2 + CH4 + VGO system at different feeding gas ratios in volume fraction (i.e., H2 85% + CH4 15% and H2 90% + CH4 10%) was measured. The selectivity of H2 to CH4 predicted by the COSMO-RS model agrees well with experimental data. This work provides the basic thermodynamic and dynamic data for fuel oil catalytic cracking processes.

Processes and Their Limitations in Oxygen Depolarized Cathodes: A Dynamic Model-Based Analysis.

Oxygen depolarized cathodes (ODCs) are key components of alkaline fuel cells and metal-air batteries or of chlor-alkaline electrolysis, but suffer from limited oxygen availability at the reaction zone. Dynamic analysis is a highly suitable approach to identify the underlying causes, especially the limiting steps and process interactions in such gas diffusion electrodes. Herein, a one-dimensional, dynamic, three-phase model for analyzing the oxygen reduction reaction in silver-based ODCs is presented. It allows for a detailed evaluation of the electrochemical reaction, the mass transport processes, and their interaction. The model also reveals that the depletion of reactant oxygen in the liquid electrolyte is caused by the current-dependent change of the gas-liquid equilibrium as the limiting subprocess. The phase equilibrium, in turn, depends on the slow mass transport of water and hydroxide ions in the liquid phase. Key parameters are the location or size of the gas-liquid interface within the electrode. Profiles of local concentrations and partial pressures of different species reveal a steep gradient of oxygen in the liquid phase, but no limitation in oxygen mass transport in the gas phase. Dynamic simulations with potential steps allowed the identification of different time constants to separate overlapping processes. Accordingly, the mass transport of water and hydroxide ions was identified as the slowest process that strongly influenced the dynamic response of all species, including oxygen, and of the current. The characteristic time constant of the mass transport of water and hydroxide ions across the liquid phase within the ODC is determined to be τ ≈0.176 s, whereas the time constant of oxygen mass transport into the reaction zone is several magnitudes smaller: τ ≈1.70×10-6 s. Finally, a sensitivity analysis confirms that the overall performance is best improved by adjusting mass transport properties in the liquid phase.

Partitioning characteristic of chlorine ion in gas and solid phases in process of desulfurization wastewater evaporation: model development and calculation.

Since the promulgation of "Water Pollution Control Action Plan " in China, zero liquid discharge of desulfurization wastewater has become a new trend of power plant water pollution control. Aiming at the application of desulfurization wastewater evaporation technology using high-temperature flue gas, simulation and experimental research on quantifying and predicting gas-solid partitioning of chlorine ion under different operation conditions are carried out in this paper. The gas-liquid equilibrium theory is applied to the complex mixed salt system; based on state equation, the semi-empirical model of gas-solid phase partitioning coefficient of chlorine ion is calculated, with high degree of fitting range from 180 to 380°C. The essential effects of pH, Cl- concentration, and total dissolved solids (TDS) on the gas-solid phase partitioning coefficient of chlorine ion are investigated. The study provides key data for the application of evaporation technology using high-temperature flue gas, obtaining the quantification and prediction of chlorine ion volatilization during desulfurization wastewater evaporation.

Air‐drying with ionic liquids

SignificanceIonic liquids (ILs) are employed for air‐drying for the first time. The experimental gas–liquid equilibrium (EQ) of N2/O2 + [EMIM][BF4] and N2/O2 + [EMIM][BF4] + H2O systems under a broad temperature range are measured. The new modified UNIFAC‐Lei model is successfully extended to predict the N2/O2‐IL‐H2O system based on extensive phase EQ data. The air‐drying experiment using [EMIM][BF4] as an absorbent is conducted, confirming that this new technology is effective and efficient. © 2018 American Institute of Chemical Engineers AIChE J, 65: 479–482, 2019

Production of 160 mg/L ozone water using circulating water electrolysis system

A circulating water electrolysis system was developed to produce highly concentrated O3-dissolved water (ozone water). It enabled the production of 160 and 112 mg/L ozone water in batch and continuous-withdrawal operation, respectively. The ratios of the actual gas-phase O3 concentrations to those calculated from the dissolved O3 concentration using Henry's law at 1 atm were about 0.5, suggesting the supersaturation of ozone water. Once the O3 gas dissolved in the electrolysis cell operated at 0.15 MPa/G, it should have taken time for the ozone water to reach the gas-liquid equilibrium. The electric conductivity of the ozone water increased to 1.2 mS/cm and the formation of ClO2 was observed at the end of the run. The electrophoretic migration of Cl− ions from the catholyte to the ozone water is considered to be the cause of this impurity. The time dependence of the dissolved O3 concentration and the maximum dissolved O3 concentration obtained in the experiment were well reproduced by a circulating water electrolysis simulator.

Pentafluoroethane Dehydration with Ionic Liquids

Ionic liquids (ILs) were proposed as promising separating agents for the hydrofluorocarbons (HFCs) pentafluoroethane (R125) dehydration. Taking into account the H2O solubility and selectivity of H2O to R125 in a variety of IL candidates, we determined the hydrophilic [EMIM][BF4] as a satisfactory absorbent. Besides, some theoretical insights into separation mechanism at the molecular level were explored by means of the combination of COSMO-RS model and quantum chemistry calculation. The gas–liquid equilibrium (GLE) data for the binary R125-[EMIM][BF4] and ternary R125-H2O-[EMIM][BF4] systems were measured, and the experimental data were compared with the predicted results by COSMO-RS model. The R125 dehydration experiment with IL was carried out. Furthermore, the continuous processes for R125 dehydration with [EMIM][BF4] and the conventional benchmark solvent tetraethylene glycol (TeEG) as absorbents were simulated and optimized with the rigorous equilibrium (EQ) stage model, in which COSMO-SAC model was selected. It was confirmed that the R125 gas dehydration with IL presented in this work is a typical process intensification technology.

Comprehensive solubility of N2O and mass transfer studies on an effective reactive N,N-dimethylethanolamine (DMEA) solvent for post-combustion CO2 capture

The physical solubility and mass transfer performance of CO2 absorption into aqueous N,N-dimethylethanolamine (DMEA) solution were comprehensively studied in the present work. The physical solubility (Henry’s law constant (He)) was measured using a stirred cell reactor for pure DMEA and aqueous DMEA at temperatures from 293.98 to 333.03 K. Then, the physical solubility of CO2 was obtained based on the “N2O analogy” method. Furthermore, He was correlated successfully by using an empirical polynomial model with an average absolute relative deviation (AARD) of 4.23%. The mass transfer performance was studied in a laboratory scale structured packing absorption column at DMEA concentration of 1–4 kmol/m3, liquid feed temperature of 293.15–333.15 K, liquid flow rate of 3.90–11.7 m3/m2-hr, CO2 partial pressure of 6–20 kPa, lean CO2 loading of 0.050–0.300 mol/mol, over the inert gas flow rate range of 26.11–43.52 kmol/m3-hr. Based on the experimental values of He for CO2 into aqueous DMEA solution, the effect of the gas concentration of A in gas-liquid equilibrium (yA∗) on gas phase volumetric overall mass transfer coefficient (KGav) was considered in this study, but found to be an insignificant influence that can be ignored. Analogously, an attempt to correlate the mass transfer coefficient KGav and outlet concentration of CO2 (yout) using semiempirical models as function of the mentioned operational parameters was conducted. The predictive correlations for KGav and yout of the DMEA-CO2-H2O system in structured packing column are KGav=L0.230.6144aeq-aC/pCO2+0.02327 and lnyout=lnyin-0.77PVGΩL0.230.6144aeq-aC/pCO2+0.02327, with acceptable AARDs of 4.59% and 1.48%, respectively.

Thermodynamic assessment of MVR implementation in multistage evaporation plants

A study on process alternatives for reducing steam consumption was carried out in a multistage evaporation system of a chlorine–alkali industrial complex. A phenomenological model was developed, based on the mass and energy balances and on gas–liquid equilibrium correlations for the ternary mixture of caustic soda, sodium chloride and water. The design specifications of the plant were adopted as a reference to validate the mathematical model, which comprises 153 nonlinear equations. Different process conditions were simulated by taking into account the most important process variables and their effect on steam consumption. Differently from previously published studies, in which the conservation laws are mainly focused on the heat exchangers and their optimization, the present study considers the whole multistage evaporation unit. The model also enabled to evaluate the effect of changes in the plant configuration, either by considering a side product stream at a specified concentration, designated to another production unit in the industrial complex, or by including mechanical vapor recompression, which has proven to be a better solution to reduce steam consumption from the energy and exergy points of view. Results indicate an expressive decrease in steam consumption to around 1% of the original configuration. Moreover, from the exergy perspective, if the power generation is considered, the MVR is a better choice from the energy and exergy point of view.

A novel acid catalyst based on super/subcritical CO 2 -enriched water for the efficient esterification of rosin

Rosin esters are widely applied as masticatory substances and beverage stabilizers, while classical acid-catalysed processes will lead to metal residue or environmental issues. Super/subcritical CO2–enriched high temperature liquid water (HTLW) as a green acid catalyst in the esterification reaction of rosin with glycerol was investigated. The pH of CO2–H2O binary system, as calculated based on gas–liquid equilibrium, charge balance and chemical equilibrium equations, ranged from 3.49 to 3.70 depending on the reaction conditions, indicating effective acid catalysis. Response surface methodology experiments showed the optimum conditions were 3.5 h, 3.9 MPa CO2 pressure, a rosin-to-glycerol molar ratio of 1.32 and 269°C, and an enhanced esterification yield of 94.74% was achieved, which was superior to that obtained using a ZnO catalyst. It was found that the esterification kinetics was a pseudo first-order reaction, and the enthalpy and entropy of activation were calculated using the Arrhenius–Polanyi equation. The presence of super/subcritical CO2-enriched HTLW catalyst can decrease the activation energy and significantly accelerate the reaction rate.

Immiscibility of Liquid Phases and Liquid–Liquid Critical Phenomena in Aqueous Solutions of Sodium and Potassium Phosphates

Phase equilibria were studied in aqueous solutions of sodium and potassium phosphates at elevated temperatures (to 425°C) and pressures (to 63 MPa). Experimental data were obtained on the transformation of gas–liquid equilibria into heterogeneous equilibria of two liquid phases with increasing pressure, which ends in the critical phenomena of immiscibility (L1 = L2). Based on the experimental and literature data, it was concluded that the binary water–salt systems containing KH2PO4, K2HPO4, K3PO4, NaH2PO4, and Na2HPO4 are characterized by phase diagrams of the first type [1, 2], which have two critical invariant end points: N (G–L1 = L2) and R (G = L1–L2).

Solid–Liquid–Gas Equilibrium of Methane–n-Alkane Binary Mixtures

In this work, a solid-phase thermodynamic model is coupled with the Soave–Redlich–Kwong (SRK), Peng–Robinson (PR), and Perturbed Chain-Statistical Associating Fluid Theory (PC-SAFT) equations of state (EoS) to model the solid–liquid–gas equilibrium (SLGE) of binary methane (CH4) mixtures with normal alkanes (n-alkanes). The mixtures considered include n-alkanes from n-C6H14 up to n-C36H74. The predictive capabilities of each combined model are validated against available experimental data and vary substantially as the asymmetry of the binary mixture, with respect to the size of the molecules involved, increases. Several aspects of the models, such as the use of binary interaction parameters (BIPs) fitted to experimental vapor (or gas)–liquid equilibrium (VLE/GLE) data and the importance of specific terms of the solid-phase model, are studied to showcase their effect on the accuracy of the calculations. In this way, modifications on the basic combined models are applied. A specific volume translation strat...

Absorption, desorption and interaction of SO2 with the binary system tetraethylene glycol + dimethyl sulfoxide

ABSTRACTThe gas-liquid equilibrium (GLE) data were determined for the mixture SO2 + N2 in the binary system of tetraethylene glycol (TeEG) + dimethyl sulfoxide (DMSO) at T = 298.15–313.15 K and p = 123.15 kPa with the SO2 partial pressures of 0.4–150 Pa. From GLE data, Henry’s law constants (HLCs) were obtained. When the SO2 concentration in the gas phase was designed at ySO2 = 500 ppmv, the SO2 solubility in the binary system is located in a minimum of 9.36 mol m−3 in TeEG and a maximum of 80.34 mol m−3 in DMSO. The SO2 absorption process was reversible from the five absorption–desorption cycles, and the solvents could repeat utilisation without obvious loss of absorption capacity and the homologous SO2 desorption efficiency was nearby 98.7%. Furthermore, the spectral consequences illustrated that H-bonding was formed among TeEG, DMSO and SO2.

Encapsulation of Ionic Liquids with an Aprotic Heterocyclic Anion (AHA-IL) for CO2 Capture: Preserving the Favorable Thermodynamics and Enhancing the Kinetics of Absorption

The performance of an ionic liquid with an aprotic heterocyclic anion (AHA-IL), trihexyl(tetradecyl)phosphonium 2-cyanopyrrolide ([P66614][2-CNPyr]), for CO2 capture has been evaluated considering both the thermodynamics and the kinetics of the phenomena. Absorption gravimetric measurements of the gas-liquid equilibrium isotherms of CO2-AHA-IL systems were carried out from 298 to 333 K and at pressures up to 15 bar, analyzing the role of both chemical and physical absorption phenomena in the overall CO2 solubility in the AHA-IL, as has been done previously. In addition, the kinetics of the CO2 chemical absorption process was evaluated by in situ Fourier transform infrared spectroscopy-attenuated total reflection, following the characteristic vibrational signals of the reactants and products over the reaction time. A chemical absorption model was used to describe the time-dependent concentration of species involved in the reactive absorption, obtaining kinetic parameters (such as chemical reaction kinetic constants and diffusion coefficients) as a function of temperatures and pressures. As expected, the results demonstrate that the CO2 absorption rate is mass-transfer-controlled because of the relatively high viscosity of AHA-IL. The AHA-IL was encapsulated in a porous carbon sphere (Encapsulated Ionic Liquid, ENIL) to improve the kinetic performance of the AHA-IL for CO2 capture. The newly synthesized AHA-ENIL material was evaluated as a CO2 sorbent with gravimetric absorption measurements. AHA-ENIL systems preserve the good CO2 absorption capacity of the AHA-IL but drastically enhance the CO2 absorption rate because of the increased gas-liquid surface contact area achieved by solvent encapsulation.

Competition between surfactants and apolar fragrances in micelle cores

The impact of surfactant structure and composition on the micellar partitioning of hydrophobic fragrance molecules was studied. Based on molecular diffusion coefficients derived from self-diffusion NMR spectroscopy the partition coefficient KM between water and micellar phases turned out to be directly proportional to the octanol-water partition coefficient PO/W of the fragrance molecules. By partially replacing the main surfactant sodium laureth sulfate with low- and high-molecular weight co-surfactants a shift of the fraction of fragrance molecules towards the water phase could be observed. The shift is related to a change in the hydrophobic environment inside the micelles as evidenced by fluorescence spectroscopy. A micellar affinity factor was defined and free energy differences were calculated that take into account the compatibility between solute and micellar core. A variation of micellar affinity of up to a factor of 10 was observed between various surfactant systems and mixtures, affecting significantly the proportions of the fragrance molecules in micellar and water phases. According to the Henry’s law constant, the availability of volatile fragrance molecules in the aqueous phase has a direct impact on the headspace concentration in a liquid-gas equilibrium. The shift of fragrance molecules towards the water phase and a subsequent concentration increase in the gas phase was experimentally confirmed by dynamic headspace measurements. The selection of type and composition of surfactant has thus a direct consequence on the concentration of volatiles in the gas phase and on the final perceived fragrance intensity.

Experimental research of fouling layer and prediction of acid condensation outside heat exchanger used in coal-fired boiler

Research on the fouling layer covering heat exchangers is of practical value to increase the efficiency of heat exchangers and even that of boiler, especially when considering coupled effects of ash deposition and acid condensation. The field experiments are carried out using a special designed pipe in a 300 MW sub-critical unit. The effects of internal Reynolds number of water (Rewater), inlet temperature of water (Tin), flue gas temperature (Tgas) and external Reynolds number of flue gas (Regas) on heat transfer efficiency have been analyzed via the calculation of fouling factor (ε) as well as external Nusselt number of flue gas (Nugas). Apart from this, the 1-D model to describe the acid condensation has been built in light of the thermodynamic results of water vapor and sulfuric acid vapor obtained by former research. In this model, both gas-liquid equilibrium effect and multi-component diffusion effect have been well considered. Furthermore, the acid condensation can be influenced to different extents by the exterior wall temperature of the pipe, acid vapor and water vapor contents of flue gas. Consequently, the efficiency of heat exchangers is enhanced by the rise of exterior wall temperature according to the experimental results and acid condensation analysis.

Syngas Dehydration with Ionic Liquids

This work deals with the feasibility of ionic liquids (ILs) as an alternative drying agent to the conventional solvent (methanol) in the application of syngas dehydration. The screening of ILs by COSMO-RS model shows that [EMIM][Tf2N] is the suitable absorbent for syngas dehydration among various possible ILs. The gas–liquid equilibrium (GLE) experiments for the CO (H2)–[EMIM][Tf2N] systems were carried out. The experimental data were compared with the predicted results by the UNIFAC-Lei model. The syngas drying experiments with [EMIM][Tf2N] showed the excellent gas dehydration performance of ILs. On this basis, the conceptual process of syngas dehydration with [EMIM][Tf2N] was simulated and optimized with the rigorous equilibrium stage (EQ) model, where the UNIFAC-Lei model parameters were embedded. It was found that the gas dehydration process with IL exhibits unique advantages in energy consumption, equipment cost, and dehydration performance when compared to the conventional benchmark methanol process...

Modeling and Simulation of a Three Phase Fixed Bed Catalytic Reactor for the Hydrogenation of 2-ethyl-hexenal

The aim of this work is the investigation, by modelling and simulation, of the liquid phase hydrogenation of 2-ethyl-2-hexenal to 2-ethyl-hexanol, over a modern Cu-Ni catalyst, in an industrial tri-phase trickle bed reactor. The chemical kinetics, hydrodynamic parameters and mass transfer coefficients were evaluated from published data. The mathematical model of the process takes into consideration intraparticle and interphase concentration gradients. The calculated temperature evolution along the catalytic reactor is in a good agreement with measured values from an industrial plant. The results indicate that critical kinetic step of the process is the hydrogen transfer toward the inner catalyst surface and that the process occurs close to gas-liquid equilibrium. The degree of catalyst pellet utilization, evaluated by internal effectiveness factors, is relatively low, being mainly dependent on rapid exhaust of dissolved hydrogen inside the catalyst pellet. The presented results could be useful in process analysis, optimization and control studies.

Thermodynamic modeling of hydrate formation conditions using different activity coefficient models in the presence of tetrahydrofuran (THF)

The clathrate hydrate is a major problem in gas transportation lines and on the other hand, can be used as a tool for natural gas storage. Moreover, it could be used for gas separation such as monoxide and dioxide carbon from combustion chambers. In this work, a thermodynamic model is developed to calculate gas hydrate formation conditions of single and binary gases in the absence and presence of the thermodynamic promoter such as tetrahydrofuran (THF). A three-phase solid–liquid–gas equilibrium calculation is carried out so that the van der Waals–Platteeuw model is applied for the hydrate phase, SRK EoS for the gas phase and the different activity coefficient models such as local composition and group contribution models for the aqueous solution. The binary interaction parameters for the present activity coefficient models are adjusted through the optimization of the hydrate formation data for the single gases in the presence and absence of THF. Using the local composition and group contribution models, allows one to compare the calculated results with experiment through the percent of Absolute Average Deviation (AAD %)-in pressures and temperatures of the gas hydrate formation conditions so that it is observed the present results are in a good agreement with the experiment.