Binary Mixtures Of Carbon Dioxide Research Articles

Experimental isochoric apparatus for bubble points determination: Application to CO2 binary mixtures as advanced working fluids

Carbon dioxide binary mixtures are increasingly considered as working fluids in transcritical power cycles, due to the capability to perform liquid-phase compression even at high environmental temperatures. However, a robust thermodynamic model is essential for optimal and reliable design conditions. It is widely recognised that fine-tuning the equation of state with experimental vapour-liquid equilibrium data of the mixture significantly enhances its reliability.In this work, a new apparatus dedicated to vapour-liquid equilibrium measurements of mixtures is presented. The proposed method consists of a constant-volume system, where bubble points are identified from the divergence of slope of the isochoric lines between the two-phase and liquid regions, in the temperature-pressure plane. The temperature and pressure limits of the apparatus are 503 K and 25 MPa.Bubble points of CO2 binary mixtures with hexafluorobenzene (C6F6) and n-pentane (C5H12) have been measured and compared with previous literature data for validation purposes. Then, the CO2 mixture with octafluorocyclobutane (c-C4F8) is experimentally studied, addressing a literature gap in bubble point data. The data are used to calibrate the thermodynamic model, leading to affordable design conditions of the power cycle compared to the non-optimised thermodynamics scenario, in a concentrated solar power tower plant.

Optimization of coal desulfurization method by sub/supercritical fluid extraction with binary mixtures of carbon dioxide and ethyl lactate as a solvent

Coal combustion for energy results in the emission of air pollutants such as NOx and SOx, which negatively affect human health and the environment. Reducing toxic gas emissions and ash production is needed to achieve cleaner coal. This study aimed to develop an extraction method for desulfurizing coal with non-toxic solvents before combustion. Mixtures of sub/supercritical carbon dioxide and ethyl lactate (EL) were used at temperatures of 60–80 °C and extraction times of 15–45 min. Box-Behnken design (BBD) was used to assess the influence of the extraction parameters and to optimize the extraction method. The results show that higher temperatures and lower EL content significantly increased desulfurization. The optimal conditions for desulfurization were CO2/EL (95:5, v/v) at 80 °C, 300 bar and 15 min, reducing total sulfur in coal from 1.90 to 0.13% by weight. The extraction was efficient for removing organic sulfur, sulfones and sulfates, whereas there were still traces of sulfoxides and sulfides remaining in the coal after extraction. Moreover, the ash content slightly decreased while the calorific value increased by 8% and 3% by weight, respectively. The use of a temperature less than 100 °C and an extraction time of 15 min make this method "greener" in comparison to other proposed "green" methods, which use temperatures above 200 °C. Thus, the method has the potential to produce clean coal.

Solubility of digitoxin in supercritical CO2: Experimental study and modeling

In this communication, the solubility of digitoxin drug in supercritical CO2 was studied at different operating conditions (311 < T (K) < 343, 120 < P (bar) < 300). The results revealed digitoxin drug solubility (in mole fraction) was between 0.095 × 10−5 to 1.12 × 10−5. In the case of thermodynamic solubility modeling, cubic and non-cubic equation of states i.e. SAFT (statistical associating fluid theory), SRK (Soave-Redlich-Kwong) and sPC-SAFT (simplified perturbed chain SAFT) EoSs and six density-based correlations (Chrastil, Kumar-Johnston (KJ), Mendez-Santiago-Teja (MST), Garlapati and Madras (GM), Bartle et al. and Sung-Shim models) were considered. All used equations indicated reasonable behavior with appropriate accuracy for the solubility of the digitoxin drug. Meanwhile, sPC-SAFT EoS and Kumar-Johnston correlation with AARD% set to 8.96 % and 6.25 %, respectively exhibited greater accuracy in fitting the solubility data. Moreover, total, solvation and vaporization enthalpies of the digitoxin/supercritical carbon dioxide binary mixture were calculated based on KJ, Chrastil and Bartle et al. models.

Calculating Thermodynamic Factors for Diffusion Using the Continuous Fractional Component Monte Carlo Method.

Thermodynamic factors for diffusion connect the Fick and Maxwell-Stefan diffusion coefficients used to quantify mass transfer. Activity coefficient models or equations of state can be fitted to experimental or simulation data, from which thermodynamic factors can be obtained by differentiation. The accuracy of thermodynamic factors determined using indirect routes is dictated by the specific choice of an activity coefficient model or an equation of state. The Permuted Widom's Test Particle Insertion (PWTPI) method developed by Balaji et al. enables direct determination of thermodynamic factors in binary and multicomponent systems. For highly dense systems, for example, typical liquids, it is well known that molecular test insertion methods fail. In this article, we use the Continuous Fractional Component Monte Carlo (CFCMC) method to directly calculate thermodynamic factors by adopting the PWTPI method. The CFCMC method uses fractional molecules whose interactions with their surrounding molecules are modulated by a coupling parameter. Even in highly dense systems, the CFCMC method efficiently handles molecule insertions and removals, overcoming the limitations of the PWTPI method. We show excellent agreement between the results of the PWTPI and CFCMC methods for the calculation of thermodynamic factors in binary systems of Lennard-Jones molecules and ternary systems of Weeks-Chandler-Andersen molecules. The CFCMC method applied to calculate the thermodynamic factors of realistic molecular systems consisting of binary mixtures of carbon dioxide and hydrogen agrees well with the NIST REFPROP database. Our study highlights the effectiveness of the CFCMC method in determining thermodynamic factors for diffusion, even in densely packed systems, using relatively small numbers of molecules.

Understanding the performance of membrane for direct air capture of CO2

AbstractDirect air capture (DAC) of CO2 is becoming increasingly important for reducing greenhouse gas concentrations in the atmosphere. However, the cost and energy requirements associated with DAC make it less economically feasible than carbon capture from flue gases. While various methods like solid sorbents and gas–liquid absorption have been explored for DAC, membrane processes have only recently been investigated. The objective of this study is to examine the separation performance of a membrane unit for capturing CO2 from ambient air. The performance of a membrane depends on several factors, including the composition of the feed gas, pressure ratio, material selectivity, and membrane area. The single‐stage separation process with the co‐current flow and constant permeability flux model is evaluated using a commercial module integrated with a process simulator to separate a binary mixture of carbon dioxide and nitrogen to assess the sensitivity of selectivity on purity and recovery of CO2 in permeate, and power requirement. Additionally, three levels of CO2 reduction from the feed stream to the retentate stream (25%, 50%, and 75%) are studied. A trade‐off between purity and recovery factor is observed, and achieving high purity in permeate requires high concentration in the retentate.

5E (energy, exergy, energy level, exergoeconomic, and exergetic sustainability) analysis on a carbon dioxide binary mixture based compressed gas energy storage system: A comprehensive research and feasibility validation

Recently, the application of carbon dioxide binary working fluids in compressed carbon dioxide energy storage systems has been proposed to improve the system characteristics, especially for the condensation problem of carbon dioxide. Based on the previous research, a more comprehensive 5E (energy, exergy, energy level, exergoeconomic, and exergetic sustainability) analysis on a typical transcritical compressed carbon dioxide energy storage system using carbon dioxide binary working fluid is carried out. Propane, propylene, R32, R161, R1234ze, and R1234yf are chosen to compose the binary working fluid with carbon dioxide, respectively. The effect of changing parameters, including pump pressure ratio, compressor isentropic efficiency, and heat exahcnger1 outlet temperature on system performance, is also analyzed. In addition, the feasibility of applying carbon dioxide binary working fluid at high ambient temperature is investigated. According to the results, the performance of heat exchanger1, heat exchanger2, and pump decreases while the performance of the turbine is improved with a higher refrigerant mass fraction from the point of energy level. The compressor, pump, and turbine show potential for optimization according to their higher process energy level difference. The pump power and system operating pressure is reduced at the cost of reducing round trip efficiency when using carbon dioxide binary working fluid. A 1% improvement in compressor isentropic efficiency leads to an increase of nearly 0.4% in round trip efficiency, albeit with reduced turbine power. Increasing the heat exchanger1 outlet temperature from 305 K to 315 K results in a 1% increase in round trip efficiency but with a decrease in the performance of heat exchanger1. Both increasing compressor isentropic efficiency and heat exchanger1 outlet temperature benefit the system economy and exergetic sustainability. A noticeable decrease in system performance is observed when the ambient temperature shifts from 293 K to 303 K. However, this deterioration can be mitigated by raising the pressure of saturated working fluid gas at the compressor inlet. Propylene, R32, and R1234yf are suitable candidates to address the condensation issue, considering the system performance at high ambient temperatures. This paper extends research on the compressed carbon dioxide energy storage system based on carbon dioxide mixtures and provides a reference for the working fluid selection and system optimization for related research.

A step towards dynamic: An investigation on a carbon dioxide binary mixtures based compressed gas energy storage system using energy and exergy analysis

A dynamic model of a compressed gas energy storage system is constructed in this paper to discover the system's non-equilibrium nature. Meanwhile, the dynamic characteristics of the CO2 binary mixture (i.e., CO2/propane, CO2/propylene, CO2/R161, CO2/R32, and CO2/DME) based system are first studied through energy and exergy analyses. Performance indicators are considered, including round trip efficiency, exergy efficiency, energy density, discharge time, and average power output. The effects of tank volume and ambient temperature on the system performance are analyzed. According to the results, although the round trip efficiency of the CO2 mixture system is reduced by about 0.68%–11.97% compared to pure CO2, the compressor performance and the system pressure stability are improved. When the tank volume increases from 10,000 m3 to 15,000 m3, the system round trip efficiency increases by 0.16%–0.33%. A further improvement of round trip efficiency for the CO2 mixture is found compared to pure CO2 at higher ambient temperature. This paper demonstrates the dynamic operational characteristics of the compressed gas energy storage system when using different CO2 binary mixtures, providing a reference for optimizing related systems. Potential scenarios and applications for the CO2 binary mixture are discussed for future research.

Investigation on solid-liquid equilibrium for binary mixtures of carbon dioxide (R744) and alkanes: Propane (R290) and isobutane (R600a)

The solid-liquid equilibrium (SLE) of binary systems containing carbon dioxide (R744) and alkanes propane (R290) and isobutane (R600a) was experimentally investigated. A novel experimental setup using the cooling curve method was designed, built and verified, enabling SLE measurements at temperatures down to 173 K. The temperature and pressure of the triple point of carbon dioxide (CO2) were measured. The results for R744 and the binary mixture of carbon dioxide and propane were in agreement with the available literature data, demonstrating the accuracy of the experimental setup. Activity coefficients were determined for the binary mixtures studied. The Schröder and Wilson equations were used to calculate solubility over various temperatures and compositions. The Wilson model produced a very accurate correlation for the studied non-ideal binary mixtures, while the Schröder equation did not provide satisfactory results. Determined activity coefficients and SLE curves should be useful for the design of low-temperature refrigeration systems operating on carbon dioxide mixtures with low global warming potential.

Binary mixture of carbon dioxide and dimethyl ether and its properties for use in refrigeration machines

Binary mixture of carbon dioxide and dimethyl ether and its properties for use in refrigeration machines

Analysis of the Efficiency of Technologies for Extraction Carbon Dioxide from Combustion Products

The main purpose of the article is to compare and analyze existing technologies for extracting carbon dioxide from combustion products in relation to mini-CHP plants operating on local fuels. The article presents a brief overview of the main technical features of the implementation of carbon dioxide extraction technologies from gas mixtures. The specific features and limitations for each of the methods are shown. Mathematical modeling of technological processes of adsorption, physical and chemical absorption is carried out on the basis of Aspen Hysys and Aspen Adsorption software packages. When modeling absorption processes, the composition of combustion products characteristic of the actual operating conditions of an energy source on wood chips was considered, while for the adsorption process, the composition of combustion products was simulated by a binary mixture of carbon dioxide and nitrogen with a molar content of 11 and 89 %, respectively. The results of numerical research that were obtained have shown that the highest degree of carbon dioxide extraction from combustion products is 97 %, and it is achieved in the optimal mode of implementation of chemical absorption technology. With the same method, the highest degree of purity of the resulting carbon dioxide is observed, viz. 86 % taking into account water vapor and 99 % if it is dry. The least effective technology for extracting carbon dioxide was the method of physical absorption in a fixed bed, in which the degree of purity of the resulting dry carbon dioxide was 79 %. Therefore, for practical use in the deep utilization of combustion products of mini-CHP plants operating on local fuels, to obtain carbon dioxide with a low content of impurities, it is necessary to apply the method of chemical absorption. The use of physical absorption technology in a fixed bed can be used to reduce energy source emissions or in cases where the degree of purity of carbon dioxide does not matter.

Full coupling of CO2–CH4 transport and sorption with solid deformation in gas shale enhances natural gas recovery and geological CO2 storage capacity

A thermodynamically rigorous constitutive model is used to describe the full coupling among the nonlinear processes of transport, sorption, and solid deformation in organic shale where the pore fluid is the binary mixture of carbon dioxide and methane. The constitutive model is utilized in a numerical solution that simulates injection of carbon dioxide in shale before producing carbon dioxide and methane from the same. The solution considers advection and diffusion as viable mechanisms of pore fluid transport where the latter comprises molecular, Knudsen, and surface diffusion in ultralow permeability shale. Results indicate that gas adsorption would be the main storage mechanism of sequestration in shale which may comprise up to 70% of the stored CO2 mass. A third of this storage capacity could be due to the geomechanical effects. Therefore, complete or partial exclusion of the coupling between sorption and solid phase deformation from the solution would result in underestimation of carbon dioxide storage capacity and natural gas recovery factor of the rock. Surface diffusion, sorption-induced deformation, as well as strain-induced changes in gas sorption capacities, are all conducive to both outcomes. Sensitivity analysis shows that the solution results are most sensitive to changes in adsorption capacities, followed by initial permeability, Young's modulus, Poisson's ratio, surface diffusivities, and initial pore radius.

Preliminary thermodynamic analysis of a carbon dioxide binary mixture cycled energy storage system with low pressure stores

The liquid CO2 energy storage has considerable potential for power supply-demand management, but its low energy density, harsh condensation condition and high operation pressure are substantial obstacles. It is the first time to design energy storage system with high energy density and low-pressure stores by cycling the CO2 binary mixtures. By using CO2 mixtures, the pressure in storage tanks can be as low as ambient pressure (0.1 MPa) and two-tank cold energy storage with liquid storage materials can be used to complete the evaporation and condensation processes of working fluid in subcritical pressure. A large number of refrigerants are discussed and nine of them are selected as preliminary candidate additives into CO2. The performance of newly proposed system cycled with these additives is further analyzed by utilizing an in-house code developed with established thermodynamic models. The numerical results demonstrate that the mass fraction of additives is suggested to be higher than 0.12, otherwise there is high required capacity of cold storage material although a larger energy density. By and large, the mixtures CO2/R161 (0.7/0.3) and CO2/R1270 (0.82/0.18) are the first two most suitable selections among the CO2 mixtures, the round trip efficiency and energy density of which at basic design condition are 52.95% and 29.74 kWh/m3 and 52.12% and 29.83 kWh/m3, respectively. Both the optimal charge and discharge pressures can be identified for round trip efficiency while the energy density increases monotonically with charge pressure and the increasing trend is first steep and gradually becomes slow.

High-Pressure Densities and Excess Molar Volumes for the Binary Mixture of Carbon Dioxide and Hydrogen Sulfide at T = 343–397 K

A few studies have been carried out on the volumetric properties of binary systems of H2S + CO2, which are rich in CO2; however, no volumetric studies for acid gas fluids rich in H2S have been found in the open literature. Herein we report new high-precision density measurements for three compositions (x(CO2) = 0.09822, 0.26989, and 0.49556) for the CO2 + H2S binary system at T = 343–398 K and pressures up to p = 25 MPa. The measured mixture densities were compared to data from Stouffer et al. ( J. Chem. Eng. Data 2001, 46, 1309−1318. DOI: 10.1021/je000182c.) and Nazeri et al. ( Fluid Phase Equilib. 2016, 423, 156−171. DOI: 10.1016/j.fluid.2016.04.024.The measured density data showed agreement within ca. ±2% at high pressures and up to 4% in the vicinity of the critical point or high compressibility region. Additionally, we used our mixtures and interpolated pure fluid densities to calculate the excess molar volumes, to further ascertain the accuracy of the mixing coefficients provided by Kunz and Wagner ( J. Chem. Eng. Data 2012, 57, 3032−3091. DOI: 10.1021/je300655b.). The comparison of the calculated and experimental molar volumes showed good agreement to within ±2 cm3·mol–1, especially in the high-pressure region. Within the study, we considered the COS formation from the reaction of CO2 + H2S, which was a potential explanation for measurement failure in previous studies. The measured equilibrium concentrations of COS were low and showed that the reaction of CO2 + H2S to form COS was not facile at the measured conditions.

Vapor-liquid equilibria for binary systems carbon dioxide + 1,1,1,2,3,3-hexafluoro-3-(2,2,2-trifluoroethoxy)propane or 1-ethoxy-1,1,2,2,3,3,4,4,4-nonafluorobutane at 303.15–323.15 K

The phase behavior of binary mixtures of carbon dioxide (CO2) and hydrofluoroethers (HFEs) has been studied. In particular, experimental vapor-liquid equilibrium (VLE) data for CO2 + 1,1,1,2,3,3-hexafluoro-3-(2,2,2-trifluoroethoxy)propane (HFE-449mec-f) and 1-ethoxy-1,1,2,2,3,3,4,4,4-nonafluorobutane (HFE-7200) at temperatures of 303.15, 313.15, and 323.15 K are reported. The VLE data were measured using a static-type apparatus and then correlated using the Peng-Robinson equation of state with the van der Waals one fluid and Wong-Sandler-NRTL mixing rules. Reasonable correlation results were obtained from the Peng-Robinson equation of state with both the van der Waals one fluid and the Wong-Sandler-NRTL mixing rules. The GC-SAFT-VR equation also gave good predictions of the phase behavior. Additionally, the group contribution SAFT-VR (GC-SAFT-VR) equation was used to predict the experimental VLE in good agreement with the experimental data, as well as the full p,T phase diagram for both systems.

Excess volume, isothermal compressibility, isentropic compressibility and speed of sound of carbon dioxide+n-heptane binary mixture under pressure up to 70 MPa. II. Molecular simulations

Molecular simulations have been performed in this work to provide a microscopic understanding of the experimental results of asymmetric supercritical binary mixtures of carbon dioxide and n-heptane published in the first article of the series [Bazile et al. J. Supercrit. Fluids 140, 218 (2018)]. Interestingly, molecular simulations results compared well with experimental data on density, isothermal compressibility, speed of sound, isentropic compressibility and the corresponding excess properties. In addition, using Kirkwood-Buff theory, computed partial molar volumes are found to be consistent with those obtained indirectly from experimental data. In particular, the negative value of partial molar volume of n-heptane at infinite dilution close to CO2 critical conditions is well captured, confirming the occurrence of a clustering phenomenon at such conditions. Last, computed properties of the cluster indicates a weak cluster with a radius of about 3 nm and a residence time of the CO2 molecules in the cluster of about 25 ps.

Carbon dioxide mixtures for organic power cycles using waste heat sources

The theoretical study proposed here is based on the energy recovery of sensible heat sources of medium and low temperature levels from Rankine power cycles in which binary mixtures of carbon dioxide and organic fluids are the working fluids. In this sense, the impact of these blends on performance parameters in the basic Rankine cycle configuration is addressed, as well as, optimization analyses of global conductance to ensure the highest production of net power cycle. The results allowed identifying what mixtures stand out in each performance indicator, particularly at net power and first law efficiency.

Estimation of kinematic viscosities at high pressures for binary mixtures CO2 + solvent using modified Eyring–Wilson and McAllister models

ABSTRACTThis work reports an estimation of kinematic viscosities at high pressures for binary mixtures of carbon dioxide (CO2) + solvent using the modified Eyring–Wilson model, by introducing each empirical equation as a function of temperature and pressure to both the binary interaction parameters in the Wilson model over wide temperature and pressure ranges. Binary mixtures tested for the estimation are CO2 + acetone, + water, + alcohol, and hydrocarbon with 60 data sets, and the covered temperature and pressure ranges are 296–473 K, and 0.77–120.86 MPa, respectively. The modified Eyring–Wilson model shows reasonable agreements with the experimental data, giving 8.03% of the average absolute relative deviations (AARD) for all the data sets studied. While the accuracy of the McAllister model, also introducing the functions of temperature and pressure to the binary interaction parameters in the same manner as in the Wilson model, showed lower AARD value (6.47%), the significant deviations were seen at higher temperatures. We conclude that the modified Eyring–Wilson with the newly proposed temperature and pressure dependencies of the binary parameters is effective for the estimation of the kinematic viscosities for binary mixtures CO2 + solvent over wide temperature and pressure ranges.

Vapor–Liquid Equilibrium Data for the Carbon Dioxide (CO2) + 1,1,1,3,3-Pentafluorobutane (R365mfc) System at Temperatures from 283.15 to 337.15 K

Isothermal vapor–liquid equilibrium data for the binary mixture of carbon dioxide (CO2) and 1,1,1,3,3-pentafluorobutane (R365mfc) were measured at six isotherms ranging from 283.16 to 337.16 K, at pressures ranging from 0.7 to 9.1 MPa, and are presented. The measurements were performed using a “static-analytic” apparatus, equipped with two capillary ROLSI samplers, with phase analysis performed via gas chromatography. The measured data were correlated using in-house thermodynamic software based on the Peng–Robinson equation of state with the Mathias–Copeman α function and the Wong–Sandler mixing rules incorporating the nonrandom two liquids model.

Capillary Condensation of Binary and Ternary Mixtures of n-Pentane-Isopentane-CO2 in Nanopores: An Experimental Study on the Effects of Composition and Equilibrium.

Confinement in nanopores can significantly impact the chemical and physical behavior of fluids. While some quantitative understanding is available for how pure fluids behave in nanopores, there is little such insight for mixtures. This study aims to shed light on how nanoporosity impacts the phase behavior and composition of confined mixtures through comparison of the effects of static and dynamic equilibrium on experimentally measured isotherms and chromatographic analysis of the experimental fluids. To this end, a novel gravimetric apparatus is introduced and validated. Unlike apparatuses that have been previously used to study the confinement-induced phase behavior of fluids, this apparatus employs a gravimetric technique capable of discerning phase transitions in a wide variety of nanoporous media under both static and dynamic conditions. The apparatus was successfully validated against data in the literature for pure carbon dioxide and n-pentane. Then, isotherms were generated for binary mixtures of carbon dioxide and n-pentane using static and flow-through methods. Finally, two ternary mixtures of carbon dioxide, n-pentane, and isopentane were measured using the static method. While the equilibrium time was found important for determination of confined phase transitions, flow rate in the dynamic method was not found to affect the confined phase behavior. For all measurements, the results indicate qualitative transferability of the bulk phase behavior to the confined fluid.

A high-throughput computing procedure for predicting vapor-liquid equilibria of binary mixtures – Using carbon dioxide and n-alkanes as examples

An automatic high-throughput computing (HTC) procedure is implemented for calculating vapor-liquid equilibrium (VLE) curves of binary systems using molecular dynamics simulation and coarse-grained force field. The HTC procedure builds simulation models, carries out the simulations, and validates the simulations automatically. The procedure is demonstrated by calculating the VLE curves for 16 binary mixtures of carbon dioxide and n-alkanes on 856 state points in the temperature range of 277.2–420.0 K and pressure range of 0.3–25.0 MPa. The averaged uncertainties in predictions are 0.119 MPa for pressure, 0.007 and 0.029 for liquid and vapor CO2 molar fractions, and 0.005 and 0.010 for liquid and vapor densities respectively. The Validation against experiment data on 10 binary systems and 316 state points shows that the predictions are accurate with average deviation of about 5% for CO2 mole fraction and 3.5% for saturated density at pressure range to P < 0.9Pc. This automatic procedure can only be used for the prediction of the vapor-liquid equilibrium. The computed data can be obtained from http://sun.sjtu.edu.cn/msd.