Mixture Of CO Research Articles

Synthesis and characterization of mixed ligands based Co(II)-based coordination polymers and study their photochemically antibiotic degradation

Two Co(II)-based coordination polymers （CPs）, denoted as [Co4(NPDA)4(bmb)2·3H2O]n (1) and [Co(CHDA)(bmb)]n (2) (bmb = 4, 4́-bis(2-methylimidazol-3-ium-1-yl) biphenyl; H2NPDA = 1,4-naphthalenedicarboxylic acid; H2CHDA = 1,4-cyclohexanedicarboxylic acid), were obtained from mixtures of Co(NO3)2·6H2O and H2NPDA and bmb for 1 or H2CHDA and bmb for 2 with good yields (67 % and 53 %). Single crystal XRD shows a quadruply acetate-bridged Co(II)···Co(II) center for 1 with distorted triangular bipyramid surrounding of Co atom, while 2 shows a cis-configured octahedral N2O4 coordination for Co. Thermal gravimetric analysis confirms the water content of 1 and shows remarkable thermal stabilities, with a decomposition for 1 at around 400 °C and 450 °C for 2. 1 and 2 were used as catalysts for the photochemical degradation of the antibiotics secnidazole (SIZ), nitrofurazone (NFZ), sulfasalazine (SLA), and furazolidone (FZD). Using 1 at a dosage of 10 mg/L allowed a degradation efficiency of 92.3 % for 30 ppm NFZ at 6.5 pH. A proposed photodegradation mechanism was investigated through radical trapping experiments.

Promoter Impact on 5Ni/SAPO-5 Catalyst for H2 Production via Methane Partial Oxidation

Compared to steam reforming techniques, partial oxidation of methane (POM) is a promising technology to improve the efficiency of synthesizing syngas, which is a mixture of CO and H2. In this study, partial oxidation of methane (POM) was used to create syngas, a combination of CO and H2, using the SAPO-5-supported Ni catalysts. Using the wetness impregnation process, laboratory-synthesized Ni promoted with Sr, Ce, and Cu was used to modify the SAPO-5 support. The characterization results demonstrated that Ni is appropriate for the POM due to its crystalline structure, improved metal support contact, and increased thermal stability with Sr, Ce, and Cu promoters. During POM at 600 °C, the synthesized 5Ni+1Sr/SAPO-5 catalyst sustained stability for 240 min on stream. While keeping the reactants stoichiometric ratio of (CH4:O2 = 2:1), the addition of Sr promoter and active metal Ni to the SAPO-5 increased the CH4 conversion from 41.13% to 49.11% and improved the H2/CO ratio of 3.33. SAPO-5-supported 5Ni+1Sr catalysts have great potential for industrial catalysis owing to their unique combination of several oxides. This composition not only boosts the catalyst’s activity but also promotes favorable physiochemical properties, resulting in improved production of syngas. Syngas is a valuable intermediate in various industrial processes.

New analytical thermodynamic models developed for pure H2, CH4, CO2 and H2 containing mixtures based on molecular simulations

Pressure-volume-temperature-composition (PVTX) properties of gas mixtures are important to model and predict flow and compression performance in a range of industrial processes. It is time consuming and sometimes impractical to obtain these properties from experiments. Here, molecular dynamics (MD) simulations were conducted to compute the thermodynamic volumetric properties of pure H2, CH4, CO2, and binary mixtures of H2/CH4 and H2/CO2 at temperatures of 310.9–470 K, pressures up to 172 MPa. MD simulation results were used to develop five analytical equations explicit in pressure as a function of density or volume, temperature, and composition, for the pure gases and mixtures. Our simulated results matched very well with the predictions from the established GERG-2008 equation and data published by NIST. The simplified equations of state (EOS) developed in this work will be more computationally efficient than other EOS for mixed systems. This can be significant in reservoir simulations.

Plasma Chemical Looping: Unlocking High-Efficiency CO2 Conversion to Clean CO at Mild Temperatures.

We propose a plasma chemical looping CO2 splitting (PCLCS) approach that enables highly efficient CO2 conversion into O2-free CO at mild temperatures. PCLCS achieves an impressive 84% CO2 conversion and a 1.3 mmol g-1 CO yield, with no O2 detected. Crucially, this strategy significantly lowers the temperature required for conventional chemical looping processes from 650 to 1000 °C to only 320 °C, demonstrating a robust synergy between plasma and the Ce0.7Zr0.3O2 oxygen carrier (OC). Systematic experiments and density functional theory (DFT) calculations unveil the pivotal role of plasma in activating and partially decomposing CO2, yielding a mixture of CO, O2/O, and electronically/vibrationally excited CO2*. Notably, these excited CO2* species then efficiently decompose over the oxygen vacancies of the OCs, with a substantially reduced activation barrier (0.86 eV) compared to ground-state CO2 (1.63 eV), contributing to the synergy. This work offers a promising and energy-efficient pathway for producing O2-free CO from inert CO2 through the tailored interplay of plasma and OCs.

Calculations of solubilities of pure noble gases and He–CO2/CH4/N2 gas mixtures in aqueous solutions with accurate thermodynamic models

Determining solubilities of pure noble gases and He–CO2/CH4/N2 gas mixtures in aqueous solutions is essential for various applications of noble gases in geological processes and for understanding the migration and accumulation of helium. This study developed two thermodynamic models for calculations of solubilities of five pure noble gases (i.e. He, Ne, Ar, Kr, and Xe) and He–CO2/CH4/N2 gas mixtures in water and in aqueous NaCl solution. The first model is constructed by extending the improved SAFT-LJ equation of state (EOS) to five binary H2O-noble gas systems and four ternary systems (i.e. H2O–He–NaCl, H2O–He–CO2, H2O–He–CH4, and H2O–He–N2). Both the non-ideality of aqueous phase and that of vapor phase of these systems were described using the improved SAFT-LJ EOS (φ-φ model). The second model is developed by modifying the gas solubility model proposed by Duan and his coworkers (one type of γ-φ model). The Pitzer theory was used to describe the non-ideality of aqueous phase and the improved SAFT-LJ EOS was used to describe the non-ideality of vapor phase. Both binary adjustable parameters of the improved SAFT-LJ EOS and parameters of the modified solubility model for pure gas were evaluated from experimental solubility data for pure gas. Both models are predictive for solubilities of gas mixtures since there is no need to evaluate their parameters from solubility data of gas mixtures.Comparisons of calculations of two models with experimental data show that both models can well represent solubilities and Henry's coefficients of five noble gases in pure water, as well as the solubility of He in aqueous NaCl solutions over a wide P-T range (273–600 K, 1–2000 bar for the solubility of He in water). The absolute average deviation of the improved SAFT-LJ EOS from experimental solubility data for five noble gases in pure water is 3.14% and that of the modified solubility model is 2.21%. Predictions of the improved SAFT-LJ EOS for Henry's coefficients for He in the He–CO2–H2O system are consistent with available experimental data. According to predictions of the improved SAFT-LJ EOS, Henry's coefficient for He in the He–CO2–H2O system is always lower than that in the He–H2O system at the same depth. Within 0–5 km depth, He solubility of He–CO2 gas mixture is much greater than that of pure He at the same depth and He partial pressure, He solubility of He–N2 mixture is a little greater than that of pure He, and He solubility of He–CH4 mixture is between that of He–CO2 mixture and that of He–N2 mixture. A computer program for calculations of solubilities of pure noble gases and He–CO2/CH4/N2 gas mixtures in pure water and in aqueous NaCl solutions can be obtained from the corresponding author via email.

Catalytic CO2 hydrogenation to hydrocarbon fuels in a potassium ion-conducting reactor

The electrochemically assisted CO2 hydrogenation directly to hydrocarbon fuels was studied, apparently for the first time, over a cheap, widespread and non-precious Fe catalyst in a potassium ion conducting (K-β-Al2O3) reactor, under atmospheric pressure, at relatively low temperatures and using representative concentrated CO2 and H2 gas mixtures and an easily scalable tubular catalyst-electrode configuration. The Fe electrocatalytic film was deposited by dip-coating on a commercial K-β-Al2O3 candle and characterized, both as prepared and after activation and testing, by TPR, TGA, XPS, XRD and SEM-EDX. The optimum operating conditions for both Fe activation (300 ºC, 75% H2, 24 hours) and electropromoted CO2 hydrogenation (300 ºC, 1.5 V, H2/CO2=3) were identified. Long-term tests on electrochemically promoted CO2 hydrogenation to hydrocarbons were performed under selected operating conditions to assess electrocatalyst stability. Both the selectivity to the target product (C5+ hydrocarbons) and the stability of the catalyst can be tuned in situ by modifying the potassium surface coverage via electrochemical pumping of potassium ions through the applied polarization. Finally, as an attempt to improve the catalyst-electrode behaviour, powdered catalysts, based on iron nanoparticles dispersed on KVO3 (a K+ and e- co-conductor) with different Fe loadings (17 and 9 wt%) were prepared and comparatively studied for CO2 hydrogenation to hydrocarbons. The catalyst with higher Fe loading was selected as the most promising, in terms of activity, selectivity and stability, for further catalyst-electrode optimisation by deposition, via dip-coating, of a Fe-KVO3 film on the K-β-Al2O3 candle.

Mechanistic analysis of acid gas storage and oil recovery in naturally fractured reservoirs using single matrix block approach

AbstractThe objective of this study is to assess the storage of acid gas, containing CO2 and H2S, in a depleted naturally fractured reservoir (NFR) using single matrix block (SMB) approach. The acid gas dissolution in oil is considered by Peng‐Robinson equation of state and compositional simulation. The PHREEQC package is used to determine acid gas solubility in formation brine. Three types of acid gases with different compositions are used for this study and their swelling behavior and miscibility in relation to the reservoir oil are analyzed. An SMB model, with a matrix block surrounded by fractures, is constructed, and validated for simulation of a real experiment. The simulation is conducted for synthetic and real reservoir fluids when the oil is in its residual saturation. A sensitivity analysis is performed to study the effects of key parameters, such as acid gas composition, reservoir pressure, permeability, porosity and matrix height on the storage capacity and oil recovery factor. The matrix has a volume of 27 m3 and about half of acid gas storage is achieved in the first 5 years while the simulations are run for 30 years. The results show that up to 90% of remained oil is recoverable, and more than 0.67 kmol of acid gas per cubic meter of matrix is stored whether matrix contains a real oil or a synthetic one. Higher storage is achieved for higher matrix porosities and heights and large H2S proportion in acid gas. In all cases about 10% of acid gas is trapped in water and the remaining 90% is dissolved in oil. The mineral trapping was more active in CO2‐rich acid gases. While about 10 kg of the matrix rock was dissolved in the acidic brine when the acid gas contained H2S, the amount of the dissolved minerals in acidic brine resulted from the injection of CO2‐rich acid gas was more than 16 kg. Finally, this study gives a comparative analysis of the storage performance of acid gas mixture and pure CO2. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

INFLUENCE OF THERMOCHEMICAL NONEQUILIBRIUM ON CHARACTERISTICS OF BOUNDARY LAYER AT FLIGHT IN THE MARTIAN ATMOSPHERE

In framework on the eN-method, comparative calculations of position beginning zone of laminar-turbulent transition completed for two points on landing trajectory of “Pathfinder” spacecraft on surface of the Mars. The calculations used a three-component model of a thermochemical nonequilibrium mixture CO2=CO=O. The set of frequencies of spatial disturbances is determined along neutral curves for first unstable modes of temporary disturbances. The transition Reynolds number Re T was determined from envelopes of families of the N-factor curves at NT=8. In hypersonic regime at M=12:6, taking into account the developed thermochemical nonequilibrium leads to a significant decrease in the static temperature of gas in the lower part of the boundary layer. As a result, beginning of the zone of laminar-turbulent transition shifts downstream by approximately 9% compared to case of a perfect gas.

JWST observations of 13CO2 ice

The structure and composition of simple ices can be severely modified during stellar evolution by protostellar heating. Key to understanding the involved processes are thermal and chemical tracers that can be used to diagnose the history and environment of the ice. The 15.2 µm bending mode of 12CO2 in particular has proven to be a valuable tracer of ice heating events but suffers from grain shape and size effects. A viable alternative tracer is the weaker 13CO2 isotopologue band at 4.39 µm, which has now become accessible at high S/N with the James Webb Space Telescope (JWST). In this study, we present JWST NIRSpec observations of 13CO2 ice in five deeply embedded Class 0 sources that span a wide range in masses and luminosities (0.2–104 L⊙) taken as part of the Investigating Protostellar Accretion Across the Mass Spectrum (IPA) program. The band profiles vary significantly depending on the source, with the most luminous sources showing a distinct narrow peak at 4.38 µm. We first applied a phenomenological approach with which we demonstrate that a minimum of three to four Gaussian profiles are needed to fit the absorption feature of 13CO2. We then combined these findings with laboratory data and show that a 15.2 µm 12CO2 bending-mode-inspired five-component decomposition can be applied to the isotopologue band, with each component representative of CO2 ice in a specific molecular environment. The final solution consists of cold mixtures of CO2 with CH3OH, H2O, and CO as well as segregated heated pure CO2 ice at 80 K. Our results are in agreement with previous studies of the 12CO2 ice band, further confirming that 13CO2 is a useful alternative tracer of protostellar heating and ice composition. We also propose an alternative solution consisting only of heated mixtures of CO2:CH3OH and CO2:H2O ices and warm pure CO2 ice at 80 K (i.e., no cold CO2 ices) for decomposing the ice profiles of HOPS 370 and IRAS 20126, the two most luminous sources in our sample that show strong evidence of ice heating resulting in ice segregation.

Preparation of a membrane-sealed cell for studying catalyst nanoparticles in flowing gas with high vacuum x-ray photoelectron spectrometer.

Here a sealing-style x-ray photoelectron spectroscopy study of the surface of a 1.0 wt. %Ni/TiO2 nanoparticle catalyst in a flowing mixture of CO and O2 at 1bar was performed with a graphene membrane-sealed Si3N4 window-based miniature cell. We report the details on how a commercial Si3N4 window is modified before assembling a graphene membrane, how single-layer graphene membranes are transferred from their metal supports to the modified Si3N4 window, how a modified Si3N4 window covered with a double-layer graphene membrane is assembled onto a blank cell cap, how a nanoparticle catalyst is introduced to the cell cap and then the cell cap is installed onto a cell body to form a complete reaction cell, and how a complete cell is interfaced with a high vacuum chamber of an XPS system before an XPS study of 1.0 wt. %Ni/TiO2 catalyst surface in a flowing mixture for 0.2bar CO and 0.8bar O2 is performed. How the characterization of a catalyst using this type of graphene membrane-sealed Si3N4 window-based miniature cell is relevant to the finding of the actual surface chemistry of a catalyst during catalysis is discussed.

Improved surface activity of lanthanum ferrite perovskite oxide through controlled Pt-doping for solid oxide cell (SOC) electrodes

The development of multi-functional and highly mixed ionic-electronic conductive perovskite oxide-based electrodes is becoming an established trend for designing and developing SOFC/SOEC reversible cells. Ideally, the same material can be employed at both electrodes provided that structural stability, high conductivity and catalytic activity are preserved in different operational atmospheres. Here, controlled Fe substitution with a small extent (0.5 mol%) of platinum at the B-site of a lanthanum strontium ferrite is proposed as an effective method to enhance the original oxide properties as both air and fuel electrode for solid oxide cells. The effects of low Pt-doping on La0.6Sr0.4FeO3-δ structure, morphology and electrocatalytic activity are investigated and discussed. La0.6Sr0.4Fe0.995Pt0.005O3-δ (05P-LSF) is first tested as air electrode, displaying lower area specific resistance as compared to the Pt-free perovskite. 05P-LSF structural stability and conductivity are assessed in 100 % CO2 and 50 % CO2–50 % CO environments. Symmetric devices are then tested as SOECs in 100 % CO2, obtaining a current density output of 1.08 A/cm2 at 1.5 V. Electrochemical impedance spectroscopy (EIS) with distribution of relaxation times analysis (DRT) are used to provide insights on the electrode operation. Pt nanoparticle exsolution at the fuel electrode is induced by voltage application. The device stability under applied voltage is assessed for over 120 h. SOFC/SOEC characterization in a 50 % CO2/50 % CO mixture at 850 °C is also provided, obtaining a maximum power density of 270 mW/cm2 in SOFC mode, and a current density of 0.91 A/cm2 at 1.5 V in SOEC mode.

Auxiliary ligand influence on interpenetration and C2H2/CO2 separation in NDI based isoreticular MOFs

Selective separation of C2H2 from CO2 mixtures promises a critical industrial process to produce high-purity C2H2 but challenging due to their similar physical properties and molecular sizes/shapes. Naphthalenediimide (NDI) ligand-based metal − organic frameworks (MOFs) exhibit potential in selective adsorption of C2H2 due to NDI’s high affinity to C2H2 molecules. Here, three iso-reticular NDI based MOFs (denoted as FJU-109, 110 and 111) are obtained by tuning interpenetration using auxiliary ligands of different lengths. Based on the actual column breakthrough experiments, FJU-111 can achieve separation C2H2/CO2 mixture, with a separation selective of 2.2. Calculation of the binding energy shows that C-H…O interactions between guest and O atom from NDI ligand play a dominant role in elective recognition of acetylene.

Plasma-Driven Efficient Conversion of CO2 and H2O into Pure Syngas with Controllable Wide H2/CO Ratios over Metal-Organic Frameworks Featuring In Situ Evolved Ligand Defects.

While the mild production of syngas (a mixture of H2 and CO) from CO2 and H2O is a promising alternative to the coal-based chemical engineering technologies, the inert nature of CO2 molecules, unfavorable splitting pathways of H2O and unsatisfactory catalysts lead to the challenge in the difficult integration of high CO2 conversion efficiency with produced syngas with controllable H2/CO ratios in a wide range. Herein, we report an efficient plasma-driven catalytic system for mild production of pure syngas over porous metal-organic framework (MOF) catalysts with rich confined H2O molecules, where their syngas production capacity is regulated by the in situ evolved ligand defects and the plasma-activated intermediate species of CO2 molecules. Specially, the Cu-based catalyst system achieves 61.9 % of CO2 conversion and the production of pure syngas with wide H2/CO ratios of 0.05 : 1-4.3 : 1. As revealed by the experimental and theoretical calculation results, the in situ dynamic structure evolution of Cu-containing MOF catalysts favors the generation of coordinatively unsaturated metal active sites with optimized geometric and electronic characteristics, the adsorption of reactants, and the reduced energy barriers of syngas-production potential-determining steps of the hydrogenation of CO2 to *COOH and the protonation of H2O to *H.

Thermodynamic assessment of two-step nucleation occurrence in supercritical fluid

For the crystallization of an API in supercritical CO2, a two – step nucleation mechanism involves the apparition of metastable liquid droplets in the vapour phase composed of the API dissolved in the CO2, before crystallization. To find out the pressure and temperature conditions such a two – step mechanism could be observed, we studied the stability / metastability / instability for {(S)-Naproxen + CO2} and {(RS)-Ibuprofen + CO2} vapour binary mixtures. Thermodynamic computations proposed in the paper, have shown that a mixture of API and CO2 at elevated pressures can be unstable and/or metastable with respect to a liquid-vapour equilibrium and at the same time with respect to a solid-vapour equilibrium. Depending on the degree of supersaturation, such a mixture can potentially first decompose via spinodal decomposition into coexisting liquid and vapour phases, which turn due to nucleation and growth theory to a solid-fluid equilibrium.

Atomic insight into the transport mechanism of CO2/N2 molecules passing through UiO-66/PDMS membranes

Mixed matrix membranes (MMM) prepared by adding MOF filler to polymeric membranes are expected to overcome the trade-off effect inherent in membranes and improved the efficiency of separation and CO2 capture. In this work, concentration-gradient-driven molecular dynamics (CGD-MD) was employed to explore gas permeability of pure CO2/N2 and their mixture in PDMS membrane, UiO-66 membrane and UiO-66/PDMS membrane, respectively. The transport mechanism of gas molecules in the membranes was illustrated from molecular level. Moreover, the simulated permeability and predict permeability were compared to investigate the effect of the porosity at the UiO-66/PDMS interface on gas transport in mixed matrix membrane. The competitive effect between CO2 and N2 molecules in mixture could explain their different permeability in different membranes. The pore sizes distribution map and pore connectivity diagrams within UiO-66/PDMS membrane shown that the relative larger pore size and interconnectivity voids are formed in the interfacial region, and the interfacial porosity formed in UiO-66/PDMS membrane shown a positive effect on pure N2 transport and almost no effect on pure CO2 permeability. While the selectivity of UiO-66/PDMS membrane for the mixed gas case is improved because CO2 increases the retention time of N2 in the membrane and decreases the N2 permeability. This work provides a worthwhile perspective on the design of high-performance membranes for separation.

Experimental assessment of reverse water gas shift integrated with chemical looping for low-carbon fuels

Chemical looping integrated with reverse water gas (CL-RWGS) shift is presented in this study using Cu-based oxygen carrier (OC) supported on Al2O3 has been used to convert the CO2 and H2 mixture stream into a syngas stream with a tailored H2 to CO ratio and relevant conditions. The results demonstrated consistent breakthrough curves during redox cycles, confirming the chemical stability of the material. In 10 consecutive cycles at 600 °C and 1 bar, bed temperatures increased by 184 °C and 132 °C across the bed during oxidation and reduction stages respectively. The cooling effects during RWGS showed a decline in solid temperatures demonstrating the effectiveness of the heat removal strategy while attaining a CO2-to-CO conversion close >48%. The outlet gas maintains a H2/CO ratio above 2, confirming the material's dual role as OC and catalyst. During complete CL-RWGS cycles, varying temperature from 500 °C to 600 °C at a constant H2/CO2 molar ratio (1.3) and pressure (1 bar) reduces the H2/CO molar ratio from 3.14 to 2.35, respectively with a remarkable continuous CO2-to-CO conversion > 40%. The decrease in H2/CO molar ratio with the increase in temperature is consistent with the expected results of equilibrium limited conditions. Additionally, in CL-RWGS cycles, pressure insignificantly affects product molar composition. The study showed the capability of Cu material in converting CO2 into syngas through the CL-RWGS technique.

Hollow fiber gas-diffusion electrodes with tailored crystal facets for tuning syngas production in electrochemical CO2 reduction

Electrochemical reduction of CO2 (CO2RR) in aqueous electrolytes not only relies on advanced gas diffusion electrodes (GDEs) to improve CO2 mass transportation but also efficient electrocatalysts to produce specific products. Herein, to produce syngas (CO and H2 mixture), a facet-orientated zinc nanosheet catalyst was electrodeposited on the Cu hollow fiber GDE via a controllable facile surfactant-assisted method. The introduction of cationic surfactant cetyl trimethyl ammonium bromide (CTAB) could manipulate the nucleation and crystal growth of zinc ions around the GDE during the electrodeposition process, leading to controlled changes in the surface free energy and tuned zinc crystal growth orientation. Consequently, the ZncNS-HF with the largest ratio of Zn (101)/Zn (002), resulted in a high current density of 73.3 mA/cm2 and a high syngas production rate of 1328.6 µmol/h∙cm2 at applied potential −1.3 V (vs. RHE). This comes from the hierarchical structure of HFGDE, which provides sufficient CO2 reaching the catalyst/electrolyte interface, and the well-connected zinc nanosheets contribute to a significant number of active sites for CO2RR. This is the first time to configure flow-through or gas-penetrated HFGDEs with zinc crystal facets controlled nanosheet catalysts for syngas production. This research demonstrates the high potential of nanoengineering catalysts for HFGDEs to achieve high production rates of syngas.

Flexible Co-Ni nanocomposites in situ synthesized on carbon fibers for highly sensitive electrochemical detection of H2O2

In this study, Co-Ni nanomaterials were in situ synthesized on carbon fiber paper substrates, termed Co-Ni paper. Scanning electron microscopy characterization demonstrates fabricated flake-like Co-Ni nanocomposites uniformly distribute on carbon fibers, forming three-dimensional continuous network structure. The fabricated sample is determined to be a mixture of Co, Ni and C elements according to energy-dispersive X-ray spectrometer analysis. Without any pretreatments, Co-Ni paper exhibits excellent electro-oxidation capabilities towards H2O2, such as an excellent detecting performance in a wide linear range of 0‒11.5 mM of H2O2, fast amperometric responses within 1 s, and a low detection limit of 2.53 µM. Along with these intriguing properties, the in situ-synthesized Co-Ni paper has a good anti-interference towards Na2SO4, ZnCl2, glucose and NaCl during H2O2 detection. Moreover, the H2O2 electro-chemical sensor on Co-Ni paper also possesses excellent reproducibility, long-term stability and high mechanical stability. This Co-Ni-paper-based sensor is effective to determine H2O2 in blood samples, thus it is promising for electrochemical H2O2 sensing.

Dry-Cooled Rankine Cycle Operated With Binary Carbon Dioxide Based Working Fluids

The dry-cooled Rankine cycle working with a zeotropic mixture of CO2+C6F6 is influenced by the ambient temperature as air is used as the heat sink. Varying heat sink temperatures allow for operating the cycle under sliding condensation pressure which may benefit a hybrid PV-CSP plant. The study demonstrates the effect of this operation mode on composition shift and condensation pressure and investigates the cycle performance. The results show that defining the turbine design conditions significantly impact whether the system´s thermodynamic performance behaves acceptably in off-design conditions. Operating the turbine which was designed for a big pressure ratio in part-load especially if both, inlet and outlet pressure are at off-design conditions, is not favorable and leads to deteriorated efficiencies. Under some constraints for turbine and heat exchanger design, the proposed cycle enhances the hybrid PV-CSP system.

Experimental investigation of the CO2+SiCl4 mixture as innovative working fluid for power cycles: Bubble points and liquid density measurements

Supercritical CO2 is recognized as a promising working fluid for next-generation of high temperature power cycles. Nevertheless, the use of CO2 mixtures with heavier dopants is emerging as a promising alternative to supercritical CO2 cycles in the recent years for air-cooled systems in hot environments. Accordingly, this work presents an experimental campaign to assess the thermodynamic behaviour of the CO2+SiCl4 mixture to be used as working fluid for high-temperature applications, conducted in the laboratories of CTP Mines Paris PSL. At first, bubble conditions of the mixture are measured in a variable volume cell (PVT technique), then liquid densities are measured with a vibrating tube densimeter, for molar composition in the range between 70 % and 90 % of CO2. The Peng Robinson EoS was fine-tuned on the bubble points obtained, resulting in a satisfactory accuracy level. Finally, a non-conventional methodology has been developed to measure bubble points with the vibrating tube densimeter, whose results are consistent with the VLE data obtained with the standard PVT technique. Thermodynamic analysis in next-generation concentrated solar power plant, at 700 °C turbine inlet, confirms the mixture overcomes 50 % thermal efficiency, providing +4.2 % net electrical output over pure supercritical CO2 at equal thermal power from the solar field.