H2O-CO2 Mixtures Research Articles

New and accurate thermodynamic property data of CO2-EGS relevant working fluids with data fitted to existing thermodynamic models

The article presents a new setup for the accurate measurements of the phase behaviour of CO2 mixtures relevant to CCS as well as a CO2-H2O working fluid for EGS, designed to cover the temperature range from -60 to 200 °C and up to 100 MPa in pressure. Included in the article are a description of the experimental setup, methodology, and results of the experimental campaign conducted in the SINTEF Energy Research labs for the EnerGizerS project. Phase equilibrium of the CO2-water system has been investigated at the temperature of 50 °C and pressures between 1 and 17.5 MPa, using the analytical isothermal technique. These measurements are compared and verified against the existing data, followed by a presentation of the fit of GERG-2008/EOS-CG for CO2 and H2O. The maximum mole fraction of water in the CO2H2O mixture at measured conditions should not exceed 0.35 % and even less than 0.3481 % at 7.8 MPa to maintain the vapour phase of the mixture. The accuracy with respect to GERG-2008/EOS-CG varies from 1.044 % to 10.683 % near the critical values of sCO2. The estimated uncertainty of the setup is 31 mK for temperature measurements, from 0.4 to 2.5 kPa for pressure measurements and from 0.2 to 2.1 % of total combined relative uncertainty as regards the mole fraction. Despite the fact that the EGS reservoir could reach conditions above 150 °C and 50 MPa, lower values were adopted to validate the setup at 50 °C. Knowledge gaps at higher pressure and temperature values are still in dire need of filling.

Molecular dynamics insights into gas-water interfacial tension: Optimizing hydrogen storage in subsurface conditions

This study presents a comprehensive analysis of interfacial tension (IFT) between pore water and hydrogen-cushion gas mixtures in subsurface porous media, a key variable in the distribution of gas mixtures for hydrogen storage. Employing molecular dynamics simulations, we developed two IFT models at 20 MPa and 373 K: one for an H2–CO2–H2O system and another for an H2–CH4–H2O system. The models reveal that increasing cushion gas concentration reduces gas-water IFT. Notably, for H2–CO2–H2O mixtures, the IFT substantially decreases with CO2 concentration up to 40%, after which the reduction rate diminishes. In H2–CH4–H2O mixtures, the IFT decreases linearly with CH4 concentration. The study attributes these variations to local density distributions and molecular orientation effects. Specifically, CO2 adsorption at the interface up to 40% concentration significantly lowers IFT, while CH4 adsorption proportionally decreases IFT. The influence of CO2 on water molecule orientation at the interface, in contrast to the non-effect of CH4, is also critical in enhancing IFT reduction. Our results also highlight the reduction of H2 self-diffusion at the interface caused by CO2 and CH4, an essential factor in optimizing subsurface hydrogen storage operations.

T–x diagrams for the CO2–H2O system: The importance of water content in CO2 transportation for carbon capture and storage

AbstractWhen water is present in a CO2 pipeline, corrosion or plugging can occur due to the formation of liquid water or gas hydrate, respectively. Understanding how corrosion and hydrate plugging can be avoided is important for enhanced oil recovery and carbon dioxide capture and storage processes. If the CO2 is sufficiently dried prior to transportation, the formation of these problematic free‐water phases can be avoided. In this work, isobaric T–x diagrams were developed from the P–T diagram for the CO2–H2O binary system. Pressures ranging from just below the lower quadruple point to above the lower critical end point were studied. These diagrams are meant to give the reader a better conceptual understanding of how the water composition in CO2–H2O mixtures will influence phases that form at different temperatures and pressures. The diagrams are analyzed from the perspective of flow assurance in CO2 transportation.

Application of absorption-line blackbody distribution functions for H2O-CO2 mixtures for the spectral integration of the radiative transfer equation with the SLW model

This study presents the generation and evaluation of absorption-line blackbody distribution functions for mixtures (ALBDF-M) of CO2 and H2O. These functions are employed in the spectral integration of the radiative transfer equation in the framework of the spectral line-based weighted-sum-of-gray-gases (SLW) model. The proposed approach avoids the need to model the mixture of gases when dealing with ALBDFs obtained for pure H2O and CO2 species, which is the methodology currently adopted in the SLW literature. The ALBDF-M can be used with any development of the SLW model to manage local variations of the thermodynamic state conditions. In the present study, both the rank (RC-) and the locally correlated (LC-) SLW methodologies are employed with the ALBDF-M for an uncouple solution of an axisymmetric field that is representative of the combustion of ethylene diluted with H2O. Comparisons with line-by-line (LBL) solutions show that using the ALBDF-M provides an improvement in the accuracy when compared to the standard methodology to combine the ALBDFs generated for CO2 and H2O individually.

New gas radiation model of high accuracy based on the principle of weighted sum of gray gases

The standard WSGG (Weighted Sum of Gray Gases) model is very fast and simple but can lead to relatively high discrepancies in the computation of the radiative heat transfer. A new model of high accuracy relying on the principle of the WSGG model is proposed. Contrary to the standard WSGG model, the pressure absorption coefficient depends here weakly on the temperature while the weighting factor is not predefined by a mathematical function. Mathematical properties on the model parameters are obtained and we show that all the model parameters can be determined from only one of them. This last is reconstructed with an efficient inverse algorithm from the total radiative heat source data computed with the LBL method using HITEMP 2010. We propose an efficient method to find good initial guesses (of the model parameters) leading to the best accuracy of the model. It is shown, on 17 selected 1D cases representative of the combustion of CO2H2O mixtures, that the maximum relative errors on the radiative heat source for the new model (based on 6 gray gases) does not exceed 3.5% (for these 17 cases) whereas for the standard WSGG model, these errors vary up to 14.5% (five cases have errors higher than 10.0% and nine cases have errors between 5.0% and 10.0%). The accuracy of the total radiative heat flux is also greatly enhanced with the new model. We also show that the present model is robust and can be used in 3D geometry.

Applications of weighted-sum-of-gray-gas model with soot to an experimental aero-engine combustion chamber

Due to the importance of radiation during combustion in the aero-engine, the weighted-sum-of-gray-gas (WSGG) model considering both gas and soot is applied to the combustion modelling for an experimental aero-engine in this work. Five gray gases are chosen to resolve the absorption coefficients of CO2-H2O mixture, with which the Planck-mean absorption coefficients of soot are used for the spectral consideration of gas-soot mixture. Together with the discrete ordinate method, the radiation effects using WSGG model on the combustion are presented. Comparisons are made between full-scale combustion simulations without radiation and those with radiation from gas only or gas-soot mixture. Results show that radiation from either gas or gas-soot mixture leads to no more than 3% differences in temperature and 5% differences in species concentrations. However, the temperature of combustor liner walls in the primary zone (i.e., the main combustion region) is significantly altered with an average of 100 K rise when considering radiation from gas only and a maximum of 500 K rise when considering radiation from gas-soot mixture. Results also show that the temperature of combustor liner walls with radiation from gas-soot mixture becomes more well-distributed than that either without radiation or with radiation from gas only.

New gas radiation model based on the principle of weighted sum of gray gases. Application to CO2–H2O mixtures at high temperature

A new gas radiation model based on the principle of weighted-sum-of-gray-gases (WSGG) is proposed. It is shown that expressing the weighting factors as linear functions of the temperature is more suitable than the fourth-order polynomial dependence to the temperature that is commonly adopted in the WSGG model. Using an efficient inverse algorithm, it was estimated a set of twelve spatially nonconstant parameters of the new model based on four gray gases, namely the coefficients of the linear functions and the pressure absorption coefficients. The inverse algorithm is based on the adjoint state of the radiative transfer equation (RTE) using as data the total radiative heat source instead of the total gas emissivity data. The parameters are fitted using data generated with line-by-line (LBL) simulations based on HITEMP2010. In the present work, the proposed gas radiation model is applied to determine the parameters of H2O–CO2 mixtures at atmospheric pressure with partial pressure ratio equal to 2, within the range of temperature between 400 K and 1800 K and for thicknesses of the gas layer up to 3.0 m. By applying the inverse algorithm to a given case, the present gas radiation model has the level of accuracy of the LBL method. The application of the same parameters to other test cases does not lead to the same level of accuracy, since the parameters obtained are spatially dependent. However, averaging these parameters in the inverse algorithm results in a gas radiation model with spatially constant parameters. When applied to several (1-D and 3-D) test cases in the conditions for which the parameters were obtained, this led to a significant reduction in the normalized errors on the radiative heat source and, for many of these cases, on the radiative heat flux compared to that obtained with the standard WSGG model.

A Full-Spectrum Correlated K-distribution Based Interpolation Weighted-Sum-of-Gray-Gases model for CO2-H2O-soot mixture

The Weighted-Sum-of-Gray-Gases (WSGG) method is extensively employed in laboratorial and industrial radiative calculations due to its simplicity and negligible memory requirement. For a CO2-H2O-soot mixture, the superposition model is usually applied to obtain the radiative property of participating medium, which leads to a substantial increase in computing resources. To improve the computational efficiency of existing WSGG methods without significantly reducing accuracy, a Full-Spectrum Correlated K-distribution based interpolation WSGG (iWSGG) method is proposed here. In this method, a CO2-H2O-soot mixture is represented by 8 gray gases, whose absorption coefficients are obtained by linear interpolation, rather than the superposition method. The accuracy and efficiency of iWSGG are evaluated in 3 1D and 3 2D sooting flames. The results show that iWSGG demonstrates good accuracy as compared to the benchmark line-by-line solution in fuel-oxidizer and dry oxy-fuel sooting flames. The computational time of iWSGG is about 1/12 of that of WSGG with 5, 5, and 4 gray gases representing CO2, H2O and soot, and 2/5 of that of WSGG with 5 and 4 gray gases representing CO2-H2O mixture and soot.

Evaluation of two plumes jet plasma reactor for plasmolysis of H2O vapor and CO2 combinations – Optimization study

AbstractA custom design multi‐flying jet plasma torches (MFJPT) reactor was tested for plasmolysis of water vapor and mixtures of water vapor‐carbon dioxide in a series of experimental investigations at various reactor operational parameters. Experimentation plans were applied within the range of induced power (100–300 watts) and various vapor/gas throughputs. The produced gases were analyzed through online gas chromatography. The results of water vapor plasmolysis in two schemes demonstrated the production of 1337 ppm of hydrogen from water vapor/argon and 1665 ppm from applying a water vapor/argon/CO2 combination. Valuable hydrocarbon gases (e.g., Ethane, Ethylene/Acetylene) were generated and detected at higher conversions upon introducing H2O vapor, argon, and CO2 mixtures. The experimental data were trained through machine learning and a Gaussian Process Regression (GPR) model has fitted the data quite well. Ultimately, optimization study outcomes are presented through a color heat‐map for system scaling‐up purposes.

Thermodiffusion of CO2 in Water by Nonequilibrium Molecular Dynamics Simulations

The components of a fluid mixture may segregate due to the Soret effect, a coupling phenomenon in which mass flux can be induced by a thermal gradient. In this work, we evaluate systematically the thermodiffusion of the CO2-H2O mixture, and the influence of the geothermal gradient on CO2 segregation in deep saline aquifers in CO2 storage. The eHeX method, a nonequilibrium molecular dynamics simulation approach, is judiciously selected to simulate the phenomenon. At 350 K, 400 bar, and CO2 mole fraction of 0.02 (aquifer conditions), CO2 accumulates on the cold side, and the thermal diffusion factor is close to 1 in a number of force fields. The lower the temperature, the higher is the separation and the thermal diffusion factor. In colder regions, water self-association is stronger, whereas the CO2-H2O cross-association and the CO2-CO2 interactions enhance at higher temperatures. Thermodiffusion and gravitational segregation have opposite effects on CO2 segregation. At typical subsurface conditions, the Soret effect is more pronounced than gravity segregation, and CO2 concentrates in the top (colder region). Our work sets the stage to model the effect of electrolytes on CO2 segregation in subsurface aquifers and other areas of interest.

Non-destructive analysis of a mixed H2O–CO2 fluid in experimental noble-metal capsule by means of freezing and high-energy synchrotron X-ray diffraction

High-pressure high-temperature syntheses that involve volatile-bearing aqueous fluids are typically accomplished by enclosing the samples in gas-tight welded shut noble-metal capsules, from which the bulk volatile content must be extracted to be analyzed with mass spectroscopy, hence making the analysis non-replicable. Here we describe a novel non-destructive method that ensures the identification and the quantitative estimate of the volatiles directly in the sealed capsule, focusing on fluid H2O–CO2 mixtures equilibrated with graphite at conditions of geological interest (1 GPa, 800 °C). We used a high-energy (77 keV) synchrotron X-ray radiation combined with a cryostat to produce X-ray diffraction patterns and X-ray diffraction microtomographic cross-sections of the volatile-bearing samples down to –180 °C, thus encompassing the conditions at which crystalline phases-solid CO2 and clathrate (CO2 hydrate)-form. The uncertainty of the method is < 15 mol%, which reflects the difference between the volatile proportion estimated by both Rietveld refinement of the diffraction data and by image analysis of the microtomograms, and the reference value measured by quadrupole mass spectrometry. Therefore, our method can be reliably applied to the analysis of frozen H2O–CO2 mixtures and, moreover, has the potential to be extended to experimental fluids of geological interest containing other volatiles, such as CH4, SO2 and H2S.

Dissolution losses of metallurgical cokes in CO2-H2O mixtures

ABSTRACT Influences of the gas mixtures of carbon dioxide and water vapor with different water vapor content on the thermal properties of cokes were studied at 1,373 k using a high-temperature gas-solid reaction device to clarify the action mechanism of water vapor in the dissolution loss of metallurgical coke in the blast furnace. Furthermore, the reaction depth and the microstructure of coke samples with different water vapor content were studied. The results showed that the reactivity of cokes was significantly improved by steam, and coke strength after the reaction was significantly weakened. Cokes with strong reactivity were more affected by water vapor. When H2O content was 0 and 11.1%, the reactivity indices of cokes with strong reactivity were 2.03 and 1.67 times that of cokes with poor reactivity, respectively. The influence of H2O on the strength ratio of two kinds of cokes after the reaction was ignored when H2O content exceeded 50.1%. The analysis of coke reaction depth after the reaction under different H2O content showed that the solution loss reaction between H2O and coke is mainly concentrated on the coke surface, while CO2 can penetrate into the coke to react. In addition, by comparing two kinds of coke with different reactivity, it is found that coke with higher reactivity is more sensitive to water vapor. The micromorphologies of cokes after reactions showed that water vapor significantly affected the pore and pore sizes of cokes. When water vapor content increased, the pore sizes of cokes increased, with the thinner pore wall and the increased number of new pores.

A Compact WSGG Formulation to Account for Inhomogeneity of H2O–CO2 Mixtures in Combustion Systems

Abstract An alternative weighted-sum-of-gray-gases (WSGG) model is proposed with a single set of constant pressure-based absorption coefficients that accounts for different mole fraction ratios (MRs) of H2O–CO2. The method requires no further interpolation, which in turn brings not only less uncertainty into the model but also simplifies its use. The hitemp2010 spectral database along with the line-by-line (LBL) integration is employed to generate a set of accurate total emissivities from which the WSGG coefficients are fitted. The fitting procedure employs a novel formulation to account for the MR dependence, leading to a more compact set of WSGG correlations when compared to the alternatives available in the literature. The new formulation takes advantage of the weak interdependence of temperature and molar fraction ratio in the weight factors and therefore separates their effects by two independent correlations. As oxy-fired combustion usually occurs in two distinct scenarios, dry- and wet-flue gas recirculation (FGR), the paper also proposes two other sets of coefficients intended to support the MR ranges corresponding to these specific conditions. Comparisons made against the benchmark LBL integration and other WSGG models, for one- and three-dimensional calculations, show the satisfactory level of accuracy of the proposed sets of correlations. In particular, the three-dimensional test case illustrates that the new model is also applicable to conditions observed in air–fuel combustion.

Metasomatic modification of Sr isotopes in apatite as a function of fluid chemistry

Apatite is a ubiquitous accessory mineral in crustal rocks. The Sr-isotope record of apatite has a wide range of applications in earth science studies. However, apatite has been documented to be easily altered by certain fluids. Currently, the impact of metasomatic alteration on Sr-isotopic abundances in apatite is not well known. In order to better understand this issue, well-characterized fluorapatite grains have been metasomatized experimentally at a temperature of 800 or 600 °C and a pressure of 200 MPa. Fluids used included a CO2-H2O mixture and NaF-, CaCl2-, and HCl-bearing solutions, all of which were doped with a standard solution with a known 87Sr/86Sr ratio. In the fluorapatite + CO2-H2O experiments, the fluorapatite grains were not altered by the fluids; thus, their Sr isotope compositions were generally kept unchanged. However, the other fluids induced partial to complete alteration of fluorapatite. In experiments involving the NaF- or HCl-bearing solutions, the Sr content remained constant or was increased in altered areas of the fluorapatite, and the Sr isotopes underwent changes with partial isotopic signature of the reacting solutions. In experiments involving CaCl2, the Sr content was decreased in the altered fluorapatite because high Ca activity in the solution caused Ca to replace Sr on the Ca site. Notably, the Sr isotopic ratios are still changed, although to a relatively small extent. The efficient Sr isotopic exchange between fluid and apatite is attributed to the rapid transport rate of Sr between the reaction-interface fluid and bulk fluid surrounding the apatite. This experimental study demonstrates that the response of apatite Sr isotopes to metasomatic alteration is mainly controlled by the chemistry of fluids. Overall, Sr isotopes become susceptible to hydrothermal alteration once the apatite is chemically reactive with the fluids. Therefore, it is important to evaluate the fluid-rock history, especially the conjectured fluid composition before using Sr isotopes from apatite as a geochemical tracer.

Bi4TaO8Cl/Bi heterojunction enables high-selectivity photothermal catalytic conversion of CO2-H2O flow to liquid alcohol

The high-selectivity solar-driven catalytic production of value-added fuels, such as liquid alcohol from CO2, represents an ideal energy storage and conversion pathway. However, catalysts facilitating a practical CO2 reduction approach are currently unavailable. The present work addresses this issue by developing a novel Bi4TaO8Cl/Bi heterojunction. The Bi4TaO8Cl/Bi heterojunction photocatalysts exhibit remarkable photon-to-thermal conversion and can attain a heating rate as great as 160.64 °C/s under solar irradiation with average light intensity of 365 mW/cm2, which is significantly greater than the 40.94 °C/s heating rate attained by pristine Bi4TaO8Cl photocatalysts. The proposed photothermal catalyst overcomes the high CO production obtained via conventional Bi4TaO8Cl photocatalysts, and thereby obtains high liquid alcohol (methanol and ethanol) selectivities of 92% and 76% under broadband and strictly visible light irradiation, respectively, for CO2-H2O mixtures in a flow reactor at a temperature of 200 °C. Analyses demonstrate that the superior CO2 reduction performance of the Bi4TaO8Cl/Bi heterojunction photocatalysts can be attributed to increased optical absorption, bidirectional charge transfer across the Bi4TaO8Cl/Bi interface, and the surface plasma resonance of the Bi nanoparticles. Accordingly, this work provides a novel strategy for the production of value-added liquid fuels in future CO2 conversion processes.

Thermodynamic modeling of iron and zinc reduction from B&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; ‒ CaO ‒ Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; ‒ ZnО melt by СО ‒ CO&lt;sub&gt;2&lt;/sub&gt; and H&lt;sub&gt;2&lt;/sub&gt; ‒ Н&lt;sub&gt;2&lt;/sub&gt;О mixtures

The paper presents the thermodynamic modeling results of zinc and iron reduction from B2O3 ‒ CaO ‒ Fe2O3 ‒ ZnО melts by CO ‒ CO2 and H2 ‒ H2O mixtures containing 0 – 60 % CO2 (H2O) at 1273 – 1673 K using a technique describing the reduction of metals from an oxide melt by gas in bubbling processes, under conditions that provide an approximation to real systems. Its originality is equilibrium determination for each individual portion of gas supplied into the working fluid. The reducible metals oxides content in each calculation cycle is taken from the previous data. During the calculations, changes in the content of zinc (СZnO ) and iron (СFe2O3 , СFe3O4 and СFeO ) oxides in the melt and the degree of their reduction were estimated. When using CO or H2 as a reducing agent, this process proceeds in three stages. In the first stage, Fe2O3 is reduced to Fe3O4 and FeO. CFe2O3 values decrease to almost zero, while CFe3O4 and CFeO increase simultaneously. By the end of the stage, СFe3O4 reaches its maximum value. At the second stage, the Fe3O4 → FeO transition occurs, when СFeO values reach its maximum. At these stages, there is a slight increase in the CZnO . At the third stage, the values CFeO and CZnO decrease, and iron and zinc are reduced. An increase in temperature dramatically reduces the gas consumption for zinc reduction by 2 – 3 times, and the replacement of CO with H2 reduces it by less than 20 %. In the presence of oxidizing agents (CO or H2O), only zinc is reduced. The process ends when the final content of zinc oxide in the melt corresponds to the equilibrium with the initial gas composition. The higher the temperature, the less CZnO is. The obtained data are useful for the development of technologies for the selective recovery of metals.

A highly active and durable electrode with in situ exsolved Co nanoparticles for solid oxide electrolysis cells

This work demonstrates that a double perovskite Sr2Fe1.3Co0.2Mo0.5O6-δ (SFCM) with exsolved Co nanoparticles has enhanced the reaction activity and durability of solid oxide electrolysis cells (SOECs) for electrolysis of H2O, CO2 or CO2–H2O mixture. The Co nanoparticles are in situ exsolved from the parental SFCM in 10% H2–90% N2, as confirmed by analyses of XRD, XPS, TEM and SEM, and they can keep stable in the atmosphere of 50% CO2–50% H2 or 50% CO2–50% CO. The cells with a configuration of SFCM‖La0.8Sr0.2Ga0.83Mg0.17O3-δ (LSGM)‖SFCM demonstrate excellent electrochemical performances in electrolysis. For example, polarization resistances of the electrolyzer are as low as 0.24 Ω cm2 in 50% H2O-50% H2 under open-circuit voltage. In addition, the cells for CO2/H2O co-electrolysis at 800 °C shows a reasonable durability at different current densities of 0.3, 0.6, 0.9, 1.2, 1.5, 1.8 A cm−2, and 1.0 A cm−2 for ~110 h s. Electrochemical impedance spectroscopy and distributed relaxation time analysis indicates that electrode surface exchange and diffusion are the rate-limiting steps in the electrolysis of CO2/H2O, and the resistances of these steps can be significantly decreased by the in situ exsolved Co nanoparticles from SFCM electrode, thereby providing higher activity and better stability.

A new line-by-line methodology based on the spectral contributions of the bands

This study presents a new methodology to solve thermal radiation in participating gases, the spectrally reduced integration (SRI), which employs a non-uniform spectral discretization to considerably reduce the computational cost of the line-by-line (LBL) solution while still maintaining good levels of accuracy. This non-uniform spectral mesh is generated from discretization schemes based on the spectral contributions of the bands, which apply less or more refined spectral resolution depending on the importance of the bands to the radiative transfer. Based on this methodology, several schemes were initially proposed and evaluated for a homogeneous H2O-CO2 mixture test case. Results showed that the most refined schemes were able to generate highly accurate results three to five times faster than the reference LBL solution, while the coarser schemes were still interesting alternatives for faster but still reliable calculations. In fact, a compromise between the accuracy of the SRI solution and the total number of spectral intervals was observed in all the tested schemes. The SRI method also presented similarly promising results when solving non-homogeneous test cases. Finally, the present study also develops two alternatives to address the need of a priori evaluation of the spectral contributions of the bands when using the discretization schemes. These two methodologies produced surprisingly accurate solutions of the non-homogeneous test cases, each with its own advantages and disadvantages, and could be applied together to further simplify the use of the SRI in highly accurate coupled combustion problems.

Application of ePC_SAFT-MB EoS in prediction of VLE for CO2+MDEA+H2O ternary and H2O+MDEA+CO2-CH4 quaternary mixtures

The present study aims to implement an electrolyte EoS developed in our previous work [A. Raeispour Shirazi, M. N. Lotfollahi, Fluid Phase Equilib., 502 (2019) 112289] to model the vapor-liquid equilibria (VLE) of CO2 solubility in aqueous N-methyldiethanolamine (MDEA) solution (CO2+MDEA+H2O ternary mixture) as well as H2O+MDEA+CO2-CH4 quaternary mixture. The proposed electrolyte PC-SAFT+MSA+Born equation of state ((ePC_SAFT-MB) consists of PC-SAFT equation of state, the mean spherical approximation (MSA) term and the Born term. First, an appropriate association scheme for water is specified via performing VLE calculations for H2O-CO2 binary mixture and without any adjustment in binary interaction parameter (BIP). By determining the proper association scheme for water (4C), the BIPs of H2O-CO2, MDEA-CH4 and CH4-H2O binary mixtures are adjusted with binary VLE experimental data. In what follows, the nonelectrolyte PC-SAFT EoS is applied considering the obtained BIPs to predict 162 selected data points of bubble pressure for H2O-MDEA-CO2 ternary system in a wide range of temperature (298-413 K), MDEA concentration (18.7-48.8 wt.%) and CO2 loading (0.0001-1.5). The average absolute relative deviation (AAD%) for the calculation results is obtained 25.9%. In order to consider the ions interactions in the solution and to improve the precision of calculations, Born and MSA contributions are added to PC-SAFT EoS. By adjusting two BIPs (kMDEAH+−−CO2and kMDEAH+−HCO3−) and without any readjustment of other BIPs, the AAD% is obtained 15.3%. Finally, the obtained BIPs between the molecular and ionic species for proposed ePC_SAFT-MB EoS are employed to predict the VLE of H2O-MDEA-CO2-CH4 quaternary mixture without any readjustment in BIPs. For this case, the AAD% of 28.05% indicates the reliability of proposed ePC_SAFT-MB EoS for the prediction of H2O-MDEA-CO2-CH4 quaternary VLE results.

Sustainable approach of high-pressure agave bagasse pretreatment for ethanol production

Agave bagasse is one of the most abundant lignocellulosic residues readily available for valorization. The agave bagasse was pretreated by applying high-pressure CO2–H2O mixture at temperatures ranging from 150 to 190 °C for a residence time varying from 10 to 50 min. Subsequently, solid phase obtained from pretreatment was subject to enzymatic hydrolysis at high solid loadings. Under optimal conditions, the process integrating pretreatment followed by enzymatic hydrolysis yielded 75.8 mol% of the polysaccharides present in the biomass converted into oligo- or monosaccharides, providing 110.5 g/L of reducing sugars. The monosaccharides present in the obtained hydrolysate were successfully fermented into ethanol, demonstrating the feasibility of performing its biological conversion to commercial biofuels or biochemicals. Thereby, the present study has demonstrated the proof of concept of use of more sustainable high-pressure CO2–H2O pretreatment in the context of lignocellulosic residual biomass valorization based on the biochemical sugar platform.