Equation-of-state calculations of chemical reaction equilibrium in nonideal systems

In order to calculate accurately chemical-reaction equilibria of a system over a wide range of temperatures and pressures, one must account for the non-idealities of the system. In this work, a method is developed to predict accurately chemical-reaction equilibria and phase equilibria of a system using an equation of state to account for the nonidealities. The general formalism for a multicomponent system with multiple reactions is presented. Three widely used cubic equations of state are used to calculate the physical properties of the species. The proposed method is applied to the water-gas shift reaction, to the decomposition of methylcyclohexane, and to the reaction of carbon monoxide with hydrogen sulfide over a wide range of temperatures and pressures.     

Critical parameters of mixtures of carbon dioxide and ethane

This paper deals with an evaluation of the critical parameters reported for mixtures of carbon dioxide and ethane. Equations are presented for the critical parameters as a function of the concentration.     

Characterization of chromia scales formed in supercritical carbon dioxide

Abstract

Initial experimental work at 700°–800 °C is in progress to develop a lifetime model for supercritical CO₂ (sCO₂) compatibility for a 30-year lifetime of a >700 °C concentrated solar power system. Nickel-based alloys 282, 740H and 625 and Fe-based alloy 25 are being evaluated in 500-h cycles at 1 and 300 bar, and 10-h cycles in 1 bar industrial grade CO₂. The alloys showed similar low rates of oxidation in 1 and 300 bar CO₂ in 500-h cycles at 750 °C. However, in 10-h cycles, alloy 25 showed accelerated attack at 700° and 750 °C. Transmission electron microscopy scale cross-sections on alloy 25 after 1000 h at 700 °C in sCO₂ and in air only showed a small row of carbides beneath the scale in the former environment. Similar characterisation was performed on alloys 625 and 282 after sCO₂ exposure at 750 °C.     

超临界二氧化碳流动和换热研究进展

综述了国际上对超临界二氧化碳管内换热和压降特征的研究。提供了多种公开发表的超临界流体在冷却工况下的换热关联式及单相压降关联式,将实验关联式的计算结果与文献中的实验数据进行对照,在此基础上对关联式的准确性进行了讨论。同时指出了现有研究内容的不足。     

The viscosity of liquid carbon dioxide

The viscosity coellicient of carbon dioxide in the liquid phase has been measured by means of a vibrating-wire viscometer at temperatures of 220, 230, 240, 2411, 260, and 380 K. The measurements extended beyond both phase transition lines into the coexistence region (superheated liquid) and into the solid range (undercooled liquid). At 3811 K. the measurements extended only to 3511 MPa since no density data are available for high pressures. The accuracy of the measurements is estimated to be I % The agreement with the data of Ulybin and Makarushkin is rather good, but our values are in general a few percent lower than those of Diller and Ball. The results show, for the most part, a linear pressure dependence for the various isotherms, with a common intersection with the negative pressure axis of 113.7 MPa. The fluidity, the reciprocal of the viscosity, shows a linear dependence of the molar volume in adjacent density ranges. After reduction of the molar volume with the volumes of close packing, two sets of linear functions result, with common intersections of the axis forV/V ₀=1.31 andV/V ₀=1.40.Paper presented at file Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Hydrogen component fugacities in binary mixtures with carbon dioxide: Pressure dependence

The fugacity coefficients of hydrogen in binary mixtures with carbon dioxide were measured isothermally using a physical equilibrium technique. This technique involves the use of an experimental chamber which is divided into two regions by a semipermeable membrane. Hydrogen can penetrate and pass through the membrane, while carbon dioxide cannot. During the approach to equilibrium, the pressure of pure hydrogen on one side of the membrane approaches the partial pressure of hydrogen in the mixture on the other side of the membrane. This allows a direct measurement of the hydrogen component fugacity at a given mixture mole fraction. In this study, results are reported for measurements made on the hydrogen + carbon dioxide binary at 130°C (403 K), with total mixture pressure of 3.45, 5.17, 8.62, 10.34, and 13.79 MPa. General trends in the experimental results are discussed, and comparisons are made with predictions from the Redlich-Kwong, Peng-Robinson, and extended corresponding-states models.     

超声强化超临界二氧化碳除锈除油污

结合超声清洗的优势与超临界二氧化碳的特性,设计出超声强化超临界二氧化碳复合清洗实验平台,超声换能器最大发射声功率为1 200 W,换能器每工作10 s停止20 s,即一个工作周期为30 s。利用实验平台开展了CD03钢片表面除锈实验,使用ZEISSMerlin高分辨率热场发射扫描电镜对CD03钢片表面进行扫描电子显微镜(Scanning Electronic Microscopy, SEM)和能谱(Energy Dispersive Spectrometer, EDS)分析,实验结果表明,随着清洗时间的延长,铁锈在超声作用下逐渐剥落,超声作用适当的工作周期数后,清洗效果达到最佳,超声作用时间太长会造成对钢片基体的损伤。利用实验平台开展了碳钢片表面油污清除实验,使用徕卡光学显微镜对清洗后的碳钢片做表面形貌观察,利用JA2003电子天平等手段对清洗效果进行了计算分析,同样,超声强化超临界二氧化碳油污清洗也存在一个最佳清洗时间。但是,不同污染所需的最佳清洗时间不同,甚至可以相差很大。在实际的清洗中要先根据污染物的类别确定最佳清洗时间,然后进行清洗。     

超临界二氧化碳微细管内冷却换热研究

对超临界二氧化碳在微细竖直圆管内冷却条件下的对流换热进行了数值模拟研究,分析了不同管径、进口雷诺数及不同的热流率对超临界二氧化碳对流换热的影响,考察管内局部流体温度、湍动能、湍流雷诺数的变化。湍流模型采用低雷诺数YS模型。研究表明,在临界温度区域比较大的截面,超临界二氧化碳局部传热系数达到最大值,同时管内传热受湍流雷诺数影响较大。     

Synthesis of epoxy ferrite nanocomposites in supercritical carbon dioxide

A series of epoxy ferrite nanocomposites (EFNCs) was synthesised through dispersing ferrite nanoparticles (5.0 phr, parts per hundred of resin) into diglycidylether of bisphenol A (0.1 mol) in supercritical carbon dioxide at 85 ± 1°C, 1600 psi over 1 h followed by curing with triethylene tetramine (15 phr) at 40 ± 1°C. For this purpose, ferrite nanoparticles were synthesised through size-controlled precipitation method. The size of ferrite nanoparticles was calculated through XRD and further verified through transmission electron microscopy. The synthesised EFNCs were characterised through UV-Vis, FT-IR, laser-induced breakdown spectra, X-ray diffraction, scanning electron microscopy and vibrational sample magnetometry. The results showed that, with the decrease in size, the concentration of ferrite nanoparticle in EFNCs was increased ranging 3.843–4.042 phr. This resulted in a substantial increase in the compression, tensile, impact strength and Rockwell hardness of EFNCs. The effect of particle size on wear behaviour of EFNCs was investigated at various combinations of hydraulic end load ranging 1.0–3.0 bar and disc speed 230 rpm, which showed that a decrease in the size of ferrite nanoparticles imparts a remarkable reduction in wear volume over epoxy composite. All such EFNCs showed superparamagnetic behaviour with saturation magnetisation ranging 15.8–39.91 emu g^?1.     

Shear viscosity coefficients of compressed gaseous and liquid carbon dioxide at temperatures between 220 and 320 K and at pressures to 30 MPa

The shear viscosity coefficients of compressed gaseous and liquid carbon dioxide hav been measured with the torsional piezoelectric crystal method at temperatures between 220 and 320 K and at pressures to 30 MPa. The dependencies of the viscosity on pressure, density, and temperature and the dependencies of the fluidity (inverse viscosity) on molar volume and temperature have been examined. The measurements on the compressed liquid were correlated with a modified Hildebrand equation.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Solubilities of long-chain hydrocarbons in carbon dioxide

Heavy hydrocarbons are becoming an increasingly important problem for the natural gas industry as it develops more costly gas reserves, such as those in the deep Gulf of Mexico. The waxy substances precipiate during natural gas processing, causing blockage of transmission pipelines. Knowledge of the solubility behavior of these hydrocarbon solids is therefore necessary to develop solutions to the solid deposition problem. This work reports solid-supercritical fluid equilibrum data for long-chain n-alkanes in carbon dioxide, a component of natural gas, over a range of temperatures and pressures that are typical of natural gas processing. A flow apparatus was used to measure the solubility, and the data were correlated by the Patel-Teja equation of state. Satisfactory agreement was obtained between calculated and experimental values, so the equation of state may be used to estimate the conditions for solid deposition and the amounts of solids formed at typical processing conditions.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Specific heats (C v) of saturated and compressed liquid and vapor carbon dioxide

Specific heats of saturated liquid carbon dioxide (C _sat) have been measured in the temperature range 220 to 303 K. Specific heats at constant volume (C _v) have been measured at 12 densities ranging from 0.2 to 2.5 times the critical density in the temperature range 233 to 330 K, with pressures varying from 3.4 to 32 MPa. The measurements have been conducted in an adiabatic constant-volume calorimeter of conventional design. Uncertainty of the specific heats is estimated to not exceed 2.0%. Comparisons are made with an extended Benedict-Webb-Rubin equation of state and with the results of other workers.     

Low temperature metal oxide film deposition and reaction kinetics in supercritical carbon dioxide

An effective method is developed for low temperature metal oxide deposition through thermal decomposition of metal diketonates in supercritical carbon dioxide (scCO₂) solvent. The rates of Al(acac)₃ (Aluminum acetyl acetonate) and Ga(acac)₃ (Gallium acetyl acetonate) thermal decomposition in scCO₂ to form conformal Al₂O₃ and Ga₂O₃ thin films on planar surfaces were investigated. The thermal decomposition reaction of Al(acac)₃ and Ga(acac)₃ was found to be initialized at  150 °C and 160 °C respectively in scCO₂ solvent, compared to  250 °C and 360 °C in analogous vacuum-based processes. By measuring the temperature dependence of the growth rates of metal oxide thin films, the apparent activation energy for the thermal decomposition of Al(acac)₃ in scCO₂ is found to be 68 ± 6 kJ/mol, in comparison with 80–100 kJ/mol observed for the corresponding vacuum-based thermal decomposition reaction. The enhanced thermal decomposition rate in scCO₂ is ascribed to the high density solvent which effectively reduces the energy of the polar transition states in the reaction pathway. Preliminary results of thin film deposition of other metal oxides including ZrO_x, FeO_x, Co₂O₃, Cr₂O₃, HfO_x from thermal decomposition of metal diketonates or fluorinated diketonates in scCO₂ are also presented.     

Universal crossover behavior of fluids and fluid mixtures in the critical region

A new universal scaled equation of state for one-component fluids, binary mixtures, and ionic solutions, which represents the thermodynamic behavior of fluids in a wide range of temperatures and densities including the critical region, is proposed. Near the critical point this equation reduces to a theoretically based scaled equation including the leading nonasymptotic (Wegner) correction and a correction accounting for the asymmetry of fluids with respect to the critical isochore. Far away from the critical point the new equation goes over into the classical Landau expansion (van der Waals equation). The new equation is applied to represent experimental P-V-T data for H₂O and CO₂, as well as to represent C _v,x data for dilute aqueous solutions of NaCl. A crossover from fluctuation to mean-field behavior is observed at increased concentrations of NaCl. A universal crossover function for the heat capacity C _v,x of one-component fluids and binary mixtures is presented.     

Processing behaviors of thin-film pentacene and benzene-1,4-diboronic acid in supercritical carbon dioxide

This research investigates the feasibility of using supercritical carbon dioxide (scCO₂) as a green solvent for processing organic thin film semiconductor, such as pentacene, and a potential molecular modifier for use in electronic device applications. Benzene-1,4-diboronic acid (BDBA) was selected as a molecular modifier in this work due to its electron deficient nature, which can potentially enhance pentacene's physical, chemical or electronic properties by changing its structure in the solid state. In this study, the solubilities of BDBA and pentacene in scCO₂ are measured as individual compounds and as co-solutes, at 313 K, using ultraviolet (UV) spectroscopy. Methanol co-solvent effects on solubility have also been characterized for each compound. The results show that BDBA is insoluble in pure scCO₂ up to 1.82 × 10⁷ Pa. However, with a small amount of methanol added to the mixture, BDBA becomes soluble in solution with a solubility of 3.81 × 10^− 4 mol/l at 9.00 × 10⁶-Pa-pressure. In contrast, pentacene is only soluble in scCO₂ at pressures above 1.10 × 10⁷ Pa, and its solubility is decreased upon addition of methanol due to the non-polar nature of pentacene. When a pentacene thin film is treated with BDBA in scCO₂/methanol solution, BDBA sorption is observed at pressures as low as 8.80 × 10⁶ Pa. Based on these results, it is concluded that treatment of pentacene thin films in scCO₂ is a promising approach that can be optimized for BDBA and other similar molecular modifiers, to produce multi-component organic thin film devices.     

Thermodynamic and transport properties of fluids and fluid mixtures in the extended critical region

A practical representation of the thermodynamic properties and the transport coefficients related to diffusion, heat conduction, and their cross-processes in pure fluids and binary mixtures near the liquid-vapor critical line is developed. Crossover equations for the critical enhancement of those coefficients incorporate the scaling laws near the critical point and are transformed to the regular background far away from the critical point. The crossover behavior of the thermal conductivity and the thermal diffusion ratio in binary mixtures is also discussed. A comparison is made with thermal-conductivity data for pure carbon dioxide, pure ethane, and carbon dioxide add ethane mixtures.     

Vapor-liquid equilibrium,coexistence curve,and critical locus for binary HFC-32/HFC-134a mixture

Two kinds of equilibrium measurements of binary R-32/134a mixtures were carried out. The vapor-liquid equilibria were measured by the static method in the temperature range between 283 and 313 K. On the basis of the present experimental data, the temperature dependence of the binary interaction parameterk ₁₂ for two equations of state, namely, the Soave-Redlich-Kwong equation and Carnahan-Starling-De Santis equation, was discussed. The vapor-liquid coexistence curve near the critical point was also measured by the observation of meniscus disappearance. The critical temperatures and critical densities of 30 and 70 wt% R-32 mixtures were determined on the basis of the saturation densities along the coexistence curve in the critical region. In addition, a correlation of the critical locus for this mixture is proposed as a function of composition.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Vapor-liquid equilibria for the ternary system N2 + CO2 +n-C4H10 at 250 and 270 K1

The system studied was nitrogen + carbon dioxide +n-butane at 250 and 270 K and at pressures from 1.5 to 14 MPa. The Peng-Robinson equation was used to model the results, since it is the most widely accepted equation of state in the gas processing industry. In general, the predictions are most accurate at low and moderate pressures and poorest at high pressures, especially near the critical region.     

Influence of physical state of intercalating agents on intercalation process of high speed airflow pretreated montmorillonite in supercritical carbon dioxide

The work aimed at studying the effect of scCO₂ processing technology on basal spacing, surface morphology and thermal stability of sodium montmorillonite (MMT) that were pretreated with high speed airflow pulverization method and then modified using myristyltrimethylammonium bromide (MTAB) and tetradecyltrihexylphosphonium chloride (TDTHP) with scCO₂ as the medium. X-ray diffraction (XRD) showed that physical state of intercalating agents played an important role on the intercalation process in scCO₂. Solid-state MTAB could hardly intercalate into the interlayer of pretreated MMT (PMMT), though addition of co-solvent benefited the intercalation to some extent. However, liquid TDTHP could intercalate into the interlayer of PMMT easily even without co-solvent and the basal spacing of TDTHP-modified PMMT was larger than that of MTAB-modified PMMT. Scanning electron micrographic (SEM) showed the large compact structure for MMT broke into small random structures after airflow processing and some smaller tactoids and more dispersed structures can be observed for both MTAB-modified PMMT and TDTHP-modified PMMT compared to unprocessed MMT. For TDTHP–PMMT, many clay platelets that were separated from the tactoidal structure and more dispersed structure were observed, which may be helpful for MMT exfoliation and dispersion in polymers. Thermogravimetric analysis (TG) demonstrated that TDTHP-modified PMMT was up to 100 °C more stable than MTAB-modified PMMT. These results are very important and relevant to the preparation and application of MMT/polymer nanocomposites.     

Analytical Equation of State for Solid-Liquid-Vapor Phases

A simple analytical equation of state has been proposed for describing the phase behavior of three thermodynamic states (solid, liquid, and vapor) of matter. In terms of reduced parameters, it can be written as: