Supercritical Fluid Systems Research Articles

The retention factors and partial molar volumes of cycloartenyl ferulate at infinite dilution in supercritical carbon dioxide: Measurements and correlation

The retention factors and infinite dilution partial molar volumes of a solute in supercritical fluid are crucial for understanding solute–solvent interactions, analyzing pressure effects on chemical reactions, and optimizing industrial processes. Despite their importance, there is a notable scarcity of available data on retention factors and infinite dilution partial molar volumes in supercritical fluid systems. This study presents the first experimental data on the retention factors and partial molar volumes of cycloartenyl ferulate at infinite dilution in supercritical carbon dioxide. The retention factors were measured across temperatures ranging from 308.15 to 353.15 K and pressures of 8.20 to 31.03 MPa using supercritical fluid chromatography. The infinite dilution partial molar volumes were determined by taking the partial derivative of the retention factors with respect to the density of carbon dioxide. The obtained infinite dilution partial molar volumes range from −1.64 × 10−2 to 4.10 × 10−4 m3/mol, with large negative values observed near the critical point of carbon dioxide, indicating strong solvent–solute interactions. In this study, a new correlation model successfully predicts the experimental infinite dilution partial molar volumes with an average absolute relative deviation of 2.3 % over 86 data points.

Flow regimes and heat transfer mechanisms affecting supercritical transition in microchannels

Supercritical carbon dioxide (sCO2) exhibits unique thermophysical and transport properties, which have the potential to enhance a wide range of thermal systems. Significant property variations accompanying the pseudocritical transition preclude accurate and generalized predictions of heat transfer, particularly at the microscale. A novel method for investigating fundamental fluid flow and heat transfer mechanisms through heat transfer coefficient measurements and side-view high-speed (8000 fps) schlieren imaging was developed. Experiments are conducted in a square microchannel (Dh=500μm) at reduced pressure near unity (PR=1.05) over a range of heat and mass fluxes (qc″=1.3−82.6 Wcm−2; G=280−1380 kgm−2s−1). Non-uniform density profiles within the boundary layer and distinct, freely mixed liquid-like and gas-like packets at various stages of pseudocritical transition were observed. Three flow regimes were identified as a function of heat flux with unique convection boundary layer characteristics. Transport of liquid-like and the production of gas-like sCO2 at the wall were found to be the primary mechanisms affecting heat transfer and were quantified using a modified form of the Richardson number. The experimental approach and mechanistic insight developed herein provide a basis for high-fidelity heat transfer models for the design of supercritical fluid systems.

Investigation of the Mixing Mode of Oil Displacement Using Supercritical Fluid Systems From Low-Permeability Reservoirs of the Terrigenic Type

Investigation of the Mixing Mode of Oil Displacement Using Supercritical Fluid Systems From Low-Permeability Reservoirs of the Terrigenic Type

Universal Two-Component Dynamics in Supercritical Fluids.

Despite the technological importance of supercritical fluids, controversy remains about the details of their microscopic dynamics. In this work, we study four supercritical fluid systems—water, Si, Te, and Lennard-Jones fluid—via classical molecular dynamics simulations. A universal two-component behavior is observed in the intermolecular dynamics of these systems, and the changing ratio between the two components leads to a crossover from liquidlike to gaslike dynamics, most rapidly around the Widom line. We find evidence to connect the liquidlike component dominating at lower temperatures with intermolecular bonding and the component prominent at higher temperatures with free-particle, gaslike dynamics. The ratio between the components can be used to describe important properties of the fluid, such as its self-diffusion coefficient, in the transition region. Our results provide an insight into the fundamental mechanism controlling the dynamics of supercritical fluids and highlight the role of spatiotemporally inhomogeneous dynamics even in thermodynamic states where no large-scale fluctuations exist in the fluid.

Numerical study on the heat transfer deterioration and its mitigations for supercritical CO2 flowing in a horizontal miniature tube

Responding to the rapid growth of size reduction in engineering systems, it is crucial to explore the safety performance of supercritical fluid systems in miniature tubes. In this paper, numerical studies are conducted to explore the performance of baffles on heat transfer deterioration (HTD) mitigations for supercritical CO2 (sCO2) flowing in a horizontal mini tube using RNG k-e turbulence model with enhanced wall treatment (EWT). Three kinds of baffle arrangements: in-lined, staggered and centred, with the same blockage ratio (BR = 0.25) are selected to explore their performance on HTD mitigation. Thethermo-hydraulic performances of the baffled tubes are examined using the dimensionless parameters based on normalized Nusselt numbers and Fanning friction factors,Nu/Nu0,f/f0andPEC=(Nu/Nu0)/(f/f0)1/3. The results reveal that unlike the in-lined and staggered baffles, the centred baffles induce jet impingements directly onto the tube walls and generate significant amounts of transverse fluid velocity near the tube wall (which exceeds that in the core region),making it the most influential baffle arrangement on the HTD mitigations. The effects of baffles on buoyancy flow under a wide range of heat and mass fluxes are explored based on Jackson’s criterion (Gr/Re2<103). It is observed that the Gr/Re2 increases at a relatively lower rate in baffled tube than in the smooth tube under increased heat flux variation whereas it decreases at a higher rate than the smooth tube under increased mass flux variation, thus revealing the buoyancy weakening effects of baffles. Finally, the baffle’s performance on HTD mitigation when the tube is further miniaturized is explored and the results unveil that miniaturization weakens buoyancy, and there exists a certain mini size (D = 0.5 mm) at which buoyancy influence completely vanishes, and the effect of baffles on HTD mitigation becomes insignificant.

Performance Enhancement for Tungsten-Doped Indium Oxide Thin Film Transistor by Hydrogen Peroxide as Cosolvent in Room-Temperature Supercritical Fluid Systems.

In this study, hydrogen peroxide (H2O2) cosolvent, which was dissolved into supercritical-phase carbon dioxide fluid (SCCO2), is employed to passivate excessive oxygen vacancies of the high-mobility tungsten-doped indium oxide without any essential thermal process. With the detailed material analysis, the internal physical mechanism of the cosolvent effect or the interaction between the cosolvent solution and supercritical-phase fluid is well discussed. In addition, the optimized result has been applied for the thin film transistor device fabrication. As a result, the device with SCCO2 + H2O2 treatment exhibits the lowest subthreshold swing of 82 mV/dec, the lowest interface trap density of 8.76 × 1011 eV-1 cm-2, the lowest hysteresis of 47 mV, and an excellent reliability and uniformity characteristic compared with any other control groups. Besides, an extremely high field-effect mobility of 98.91 cm2/V s can also be observed, while there is even a desirable positive shift for the threshold voltage. Notably, compared with the untreated sample, the highest on/off current ratio of 5.11 × 107 can be achieved with at least four orders of magnitude enhancement by this unique treatment.

The flow transition characteristics of supercritical CO2 based closed natural circulation loop (NCL) system

Supercritical fluid based natural circulation loop (NCL) systems have been proposed and used in many energy conversion systems in recent years. Supercritical fluid systems can contribute to new generation system design as well as thermo-hydraulic theories of functional fluids. In this study, the flow transition characteristics of supercritical CO2 based NCL system are discussed both numerically and experimentally. Numerical models with variable heat input conditions are simulated, which are focused on the flow transitions during the input changes. It is found that the supercritical NCL flow is very sensitive to heat influx changes. The numerical results are also discussed together with experimental results on the general trends in this study. Experimental results show that besides several kinds of transition flows, the heating control and cooling control can be both effective during the continuous operations of a supercritical loop system. The heater/cooler effect and parameter analysis are also conducted, which contributes to the design of active control of supercritical NCL system.

Fabrication of carbon nanomaterials using supercritical states of ethanol and binary system of ethanol and carbon dioxide for LSI interconnects

The fabrication and filling of carbon nanomaterials (CNMs) into nanoholes and trenches using supercritical method were achieved for the first time at substrate temperatures of 500–700 °C and pressures of 10–20 MPa. Two supercritical fluid systems were examined: (1) ethanol and carbon dioxide were used as the carbon source and supercritical fluid, respectively, and (2) ethanol was used as both the carbon source and supercritical fluid. Multiwalled carbon nanotubes with diameters of 8–20 nm were also confirmed to be formed. The present work introduces a new technique of preparing CNMs for application as large-scale integration interconnects.

Mesoscopic coarse-grained representations of fluids rigorously derived from atomistic models.

Mesoscopic models are widely used to study complex organization and transport phenomena in chemical and biological systems. Defining a rigorous procedure by which a mesoscopic coarse-grained (CG) representation for a fluid can be constructed from an atomistic fine-grained (FG) model is a long-standing question in the field. The connection of these CG models with the FG level of description, which might be built by CG mappings from the FG model, is often unclear. The present paper introduces a new CG mapping scheme that uses dynamically self-consistent smooth centroidal Voronoi tessellation to address this challenging problem. The new mapping scheme is applied to the coarse-graining of supercritical Lennard-Jones fluid systems at different CG resolutions under both quiescent conditions and non-equilibrium shear flow. The method generates continuous, stable, and ergodic CG trajectories and quantitatively captures the slow collective motions of the underlying FG fluids. A parameterization of the CG models from the mapped CG trajectory is then developed based on the Mori-Zwanzig formalism. The Generalized Langevin Equation describes the dynamics of CG variables, and the parameterized result is shown to reproduce the structural and dynamical correlations of the CG system. The new dynamical mapping scheme and the parameterization protocol open up an avenue for direct bottom-up construction of mesoscopic models of fluids in a Lagrangian description.

TiO2 Solubility and Nb and Ta Partitioning in Rutile‐Silica‐Rich Supercritical Fluid Systems: Implications for Subduction Zone Processes

AbstractTo understand Ti, Nb, and Ta mobility in supercritical fluids and Nb/Ta fractionation in subduction zones, we conducted piston cylinder experiments to determine rutile (TiO2) solubility and Nb and Ta partition coefficients (Dru/sf Nb and Dru/sf Ta) in rutile (ru)‐silica‐rich supercritical fluid (sf) systems at 1.5–2.5 GPa and 920–1150 °C over variable fluid chemistries including solute (SiO2 ± albite component), H2O, Cl, and F contents. Under the investigated conditions, TiO2 solubility in the supercritical fluids varies from 761 ± 107 to 9795 ± 448 ppm; Dru/sf Nb and Dru/sf Ta vary from 12 ± 1 to 208 ± 30 and 34 ± 5 to 2464 ± 140, respectively. Higher solute, Cl, and F contents in the systems and higher temperatures result in higher TiO2 solubilities and lower Dru/sf Nb and Dru/sf Ta, and thus, fluid chemistry and temperature exert main controls on Ti, Nb, and Ta mobility. In all cases, Dru/sf Nb/Dru/sf Ta &lt; 0.70, suggesting that supercritical fluids released from subducting slabs are higher in Nb/Ta relative to their protoliths. Therefore, such fluids are expected to result in higher Nb/Ta ratios in mantle wedges and arc magmas. Although Ti, Nb, and Ta could be mobile in supercritical fluids, Nb/Ta ratios in primitive arc basalts compared to those in mid‐ocean ridge basalts show that only ~10% of arc basalts are possibly disturbed by solute‐rich supercritical fluids during their generation. Therefore, if the fluids released from subducting slabs are dominantly supercritical, then most of them must be stable only in narrow P‐T spaces and hence too short‐lived to ascend very far into mantle wedges.

An equation of state for predicting the thermodynamic properties and vapour–liquid partitioning of aqueous Ge(OH)4 in a wide range of water densities

Although germanic acid is an important compound in many engineering and natural aqueous environments, its exact stoichiometry, structure and stability are insufficiently known. To fill this gap, we combined theoretical quantum chemistry simulations of Ge speciation and structure with a recently developed equation of state for aqueous neutral species, applied to available experimental GeO2(s) solubility measurements. Results allow generation of a consistent set of thermodynamic properties of Ge(OH)4(aq) over a large T–P-fluid density range (298–900K, 0.1–300MPa, and 0.01–1.0gcm−3). These properties enable quantitative predictions of Ge transport and its fractionation from similar elements (e.g. Si) in aqueous vapour–liquid and supercritical fluid systems.

Estimation of Binary Infinite Dilute Diffusion Coefficient Using Artificial Neural Network

In this study, the use of the three-layer feed forward neural network has been investigated for estimating of infinite dilute diffusion coefficient ( D12 ) of supercritical fluid (SCF), liquid and gas binary systems. Infinite dilute diffusion coefficient was spotted as a function of critical temperature, critical pressure, critical volume, normal boiling point, molecular volume in normal boiling point, molecule diameter, Lennard-Jones’s (LJ) energy parameter, temperature and pressure. For each set of SCF, liquid and gas systems a three-layer network has been applied with training algorithm of Levenberg-Marquard (LM). The obtained results of models have shown good accuracy of artificial neural network (ANN) for estimating infinite dilute diffusion coefficient of SCF, liquid and gas binary systems with mean relative error (MRE) of 2.88 % for 231 systems containing 4078 data points (mean relative error for ANN model in SCF, liquid and gas binary systems are 3.00, 2.99 and 1.21 %, respectively)

The concept of the Iceland deep drilling project

Calculations discussed in the Iceland Deep Drilling Project feasibility study in 2003 indicated that, for same volumetric flow rate of steam, a geothermal well producing from natural supercritical fluid would have the potential to generate power outputs an order of magnitude greater than from conventional high-temperature wells (240–340°C). To reach supercritical hydrous fluid conditions in natural geothermal systems requires deep drilling to a minimum depth of some 3.5–5km were temperature conditions can be expected to range between 400 and 600°C in reasonably active high-temperature fields. Three geothermal fields in Iceland, Reykjanes, Hengill and Krafla, were selected as suitable locations for deep drilling to test this concept in search of natural supercritical geothermal fluid systems.

Infinite dilution partition coefficients of benzene derivative compounds in supercritical carbon dioxide + ionic liquid systems: 1-butyl-3-methylimidazolium chloride [bmim][Cl], 1-butyl-3-methylimidazolium acetate [bmim][Ac] and 1-butyl-3-methylimidazolium octylsulfate [bmim][OcSO4

Infinite dilution partition coefficients of benzene and benzene derivative compounds (chlorobenzene, bromobenzene, toluene, ethylbenzene, benzaldehyde, benzyl alcohol and phenol) between supercritical carbon dioxide and ionic liquids (1-butyl-3-methylimidazolium chloride [bmim][Cl], 1-butyl-3-methylimidazolium acetate [bmim][Ac] and 1-butyl-3-methylimidazolium octylsulfate [bmim][OcSO4]) were measured with a packed-column chromatographic technique. The Sanchez–Lacombe equation of state was used to correlate the data and could describe the qualitative changes of the infinite dilution partition coefficients over a wide range of temperatures (313–352K) and pressures (5–15MPa). A linear solvation energy relationship (LSER) model, LSER-δ, was developed for compressible phases that uses solute, solvent and ionic liquid solubility parameters. Partition coefficients were generally in the order of solute volatility with the exception of hydrogen bonding solutes. LSER solute volume (McGowan's volume, V) and solute dipolarity/polarizability (S) greatly affected the partition coefficient values. It was found that the McGowan's volume can be considered as a function of the CO2 solubility parameter, which may be helpful in extending LSER theory to supercritical fluid systems. Both models could describe the partition coefficient well and were useful in understanding some of the interactions of the solute with the supercritical CO2 and ionic liquid phases.

Diamond Synthesis from Graphite in the Presence of Water and SiO2: Implications for Diamond Formation in Quartzites from Kazakhstan

Recent studies of microdiamonds from orogenic belts related to continental collisions induced experimentalists to explore new crystallization media possible for diamond synthesis. This has led to considerable progress in diamond-synthesis experiments under high pressures and high temperatures. Diamond was found to grow in a wide variety of systems, which drastically differ from the metal-solvent-catalyst media that have been known since the 1950s in industrial diamond syntheses. The newer systems include a variety of melts consisting of silicate, carbonate, sulfur-carbon, as well as carbon-oxygen-hydrogen (C-O-H) supercritical fluid systems in the presence of different oxides. Our experimental program has focused on systems compositionally approximating natural sites of ultrahigh-pressure metamorphic rocks, where abundant microdiamonds occur. Yet to be explored are SiO2-rich systems that constitute an important diamond-bearing lithology in the world-famous Kokchetav ultrahigh-pressure metamorphic (UHPM) terrane. The purpose of this study is to determine what effect the presence of SiO2 has on the synthesis of diamond from C-O-H supercritical fluid. Experiments performed in a Walker-style multianvil apparatus at T = 1450-1500°C and P = 8-8.5 GPa on the Si-C-O-H system at different levels of oxygen fugacity (fO2) have led us to the conclusion that diamond crystallization requires more reduced media than its counterpart synthesized in Mg-C-O-H and Ca-Mg-C-O-H systems at similar pressures, temperatures, and times.

A comparison between semi-empirical and molecular-based equations of state for describing the thermodynamic of supercritical micronization processes

Recently, supercritical fluids have been widely studied as media for fine particle formation and the thermodynamic description of multi-phase and multi-component systems are of fundamental importance for exploiting the use of supercritical fluid processes at industrial level. This paper compares the capability of three equations of state, based on different physical models, for describing phase equilibrium of systems containing compressed gases and supercritical fluids. In particular, a semi-empirical Peng–Robinson, a lattice based Sanchez–Lacombe and an off-lattice theory, such as perturbed-hard-sphere-chain theory, were used. Calculations were performed for vapor–liquid equilibria for organic solvent–supercritical anti-solvent systems, solid–fluid and solid–liquid–fluid equilibria for solute–supercritical fluid systems, and solid–liquid–fluid equilibria for solute–solvent–anti-solvent ternary systems. For binary organic solvent–supercritical fluid systems, all equations of state fairly reproduce both equilibrium and volumetric properties. For the solid-supercritical fluid systems, the binary interaction parameters were obtained by fitting solubility experimental data; these values fairly reproduce melting point depression at high-pressure only when cubic equation of state and off-lattice model were used. Phase behaviors of ternary systems were calculated using binary interaction parameters fitted on binary systems. Solubility of high molecular weight compounds in solvent–anti-solvent systems are fairly reproduced only by the perturbed hard sphere equation of state. The comparison between the three models was performed in terms of statistical errors and methods for parameter determination. The results here reported may give useful information in order to select the more appropriate and suitable model for reasonably representing the phase behaviors involved in micronization processes.

A comparison between semi-empirical and molecular-based equations of state for describing the thermodynamic of supercritical micronization processes

Recently, supercritical fluids have been widely studied as media for fine particle formation and the thermodynamic description of multi-phase and multi-component systems are of fundamental importance for exploiting the use of supercritical fluid processes at industrial level. This paper compares the capability of three equations of state, based on different physical models, for describing phase equilibrium of systems containing compressed gases and supercritical fluids. In particular, a semi-empirical Peng–Robinson, a lattice-based Sanchez–Lacombe and an off-lattice theory, such as Perturbed-Hard-Sphere-Chain theory, were used. Calculations were performed for vapor–liquid equilibria for organic solvent–supercritical antisolvent systems, solid–fluid and solid–liquid–fluid equilibria for solute–supercritical fluid systems, and solid–liquid–fluid equilibria for solute–solvent–antisolvent ternary systems. For binary organic–solvent–supercritical fluid systems, all equations of state fairly reproduce both equilibrium and volumetric properties. For the solid–supercritical fluid systems, the binary interaction parameters were obtained by fitting solubility experimental data; these values fairly reproduce melting point depression at high pressure only when cubic equation of state and off-lattice model were used. Phase behaviors of ternary systems were calculated using binary interaction parameters fitted on binary systems. Solubility of high molecular weight compounds in solvent–antisolvent systems are fairly reproduced only by the perturbed-hard-sphere equation of state. The comparison between the three models was performed in terms of statistical errors and methods for parameter determination. The results here reported may give useful information in order to select the more appropriate and suitable model for reasonably representing the phase behaviors involved in micronization processes.

Large-aperture variable-volume view cell for the determination of phase-equilibria in high pressure systems and supercritical fluids

A high-pressure, variable-volume view cell incorporating a custom engineered, optically transparent sapphire piston is described. The view cell has an unbroken field of vision that enables the entire sample volume to be observed at all times. When lit from the rear of the cell, a near perfect view of any physical transition or change in state is available to the experimenter. The system has been shown to be particularly suitable for the determination of phase equilibria and cloud point measurements in supercritical fluid systems and has been rated for experiments up to 400 bar, 200 °C.

Thermodynamics of diamond nucleation on the nanoscale.

To have a clear insight into the diamond nucleation upon the hydrothermal synthesis and the reduction of carbide (HSRC), we performed the thermodynamic approach on the nanoscale to elucidate the diamond nucleation taking place in HSRC supercritical-fluid systems taking into account the capillary effect of the nanosized curvature of the diamond critical nuclei, based on the carbon thermodynamic equilibrium phase diagram. These theoretical analyses showed that the nanosize-induced interior pressure of diamond nuclei could drive the metastable phase region of the diamond nucleation in HSRC into the new stable phase region of diamond in the carbon phase diagram. Accordingly, the diamond nucleation is preferable to the graphite phase formation in the competing growth between diamond and graphite upon HSRC. Meanwhile, we predicted that 400 MPa should be the threshold pressure for the diamond synthesis by HSRC in the metastable phase region of diamond, based on the proposed thermodynamic nucleation on the nanoscale.

Nanothermodynamic analysis of the low-threshold-pressure-synthesized cubic boron nitride in supercritical-fluid systems

A thermodynamic model in nanoscale was developed to elucidate the nucleation of the cubic boron nitrides (c-BN) synthesized in the high-pressure and high-temperature (HPHT) supercritical-fluid systems under the conditions of the low-threshold-pressure (from 2.0±0.1 to 3.0 GPa) and low-temperature (1300–1500 K). Notably, taking the nanosize-induced interior pressure into account, the nucleation of c-BN could be driven to the new stable region from the metastable region in the general accepted equilibrium phase (P,T) diagram of BN proposed by Corrigan and Bundy, upon HPHT supercritical-fluid systems. The threshold pressure of the formation of c-BN was calculated based on our model, and these results are in excellent agreement with the experiment.