Effect of Cosolvent Concentration on Phase Behavior for the Poly(isodecyl acrylate) in Supercritical Carbon Dioxide,Propane, Propylene,Butane, 1‐Butene and Dimethyl Ether

High pressure phase behavior data of mixtures of poly(isodecyl acrylate) [P(IDA)] in supercritical carbon dioxide, dimethyl ether (DME), propane, propylene, butane and 1‐butene have been studied. The phase behaviors for these binary and ternary systems are shown for temperatures below ca. 200°C and pressures up to ca. 1920 bar. The location of the P(IDA)+CO₂ cloud‐point curve shifts to lower temperatures and pressures when isodecyl acrylate (IDA) or DME is added to the P(IDA)+CO₂ solution. High pressure phase behaviors for IDA in supercritical carbon dioxide were also performed for temperature ranging from 40–120°C and pressures from 38–217 bar. The experimental results in this work are modeled using the Peng‐Robinson equation of state.     

Sorption and Diffusion of Supercritical Carbon Dioxide in a Biodegradable Polymer

A gravimetric method was used to study the sorption and diffusion of supercritical carbon dioxide in a temperature range from 40°C to 80°C and a pressure range from 8.0 to 18.0 MPa in a biodegradable polymer, namely poly(butylene adipate-co-terephthalate) (PBAT). The PBAT presented Fickian behavior and Fick's diffusion model was applied to determine the amount of carbon dioxide present in the samples after a predetermined exposure time as well as the diffusion coefficients. The variations of diffusion coefficients of CO₂ for the sorption under supercritical conditions and desorption at ambient conditions as well as equilibrium sorption amounts of CO₂ with variations of pressure and temperature were determined and compared.     

Fabrication of fluorographene nanosheets with high yield and good quality based on supercritical fluid-phase exfoliation

This article presents a novel and simple method of supercritical fluid-phase exfoliation to fabricate fluorographene (FG) nanosheets with high yield and good quality. After soaking with supercritical CO₂ and glycol at 10 MPa and 50 °C for 24 h, fluoride graphite powder was exfoliated by the intercalated CO₂ and glycol molecules during an abrupt depressurization step. Here, supercritical CO₂ acted as a penetrant and glycol acted as a “molecular wedge” to exfoliate fluoride graphite very well. The properties of FG nanosheets were detected by TEM, AFM, UV spectra, FTIR, XPS, Raman spectra, and XRD, which show the possibility of producing thickness-controlled FG nanosheets by varying numbers of supercritical CO₂ process and the high yield of pure FG nanosheets of 32 wt%, four times higher than that of the sample treated only by the traditional method of sonication. Its simplicity, high productivity, low cost, and short processing time make this technique suitable for large-scale manufacturing of FG nanosheets.     

Spectral characteristics of subcritical carbon dioxide in nanopores

Coherent anti-Stokes Raman scattering spectra measured within the Q-branch of the vibrational transition ν₁ are used to gain insights into the state of carbon dioxide molecules in nanopores of Vycor™ glass at room temperature (20.5°C) and a subcritical temperature of 30.5°C and gas pressures up to the saturation point P _sat for each temperature. Along with the main spectral component, belonging to gaseous CO₂ molecules, the spectra recorded at pressures close to P _sat feature a second (low-frequency) component. The second component is associated with the contribution from the CO₂ molecules trapped inside pores. A spectral deconvolution with account for the interference of these two bands makes it possible to estimate the spectral characteristics of the second (low-frequency) component at each temperature. At 20.5°C, the bandwidth of the low-frequency component decreases with CO₂ pressure, a behavior that can be explained by the transition of CO₂ from the adsorbed to the condensed state in the pore. At the subcritical temperature of 30.5°C, the spectral width of the second component is pressure-independent and close to the value measured in the bulk of the supercritical fluid, a result likely associated with a low-temperature shift of the critical point of the substance trapped in nanopores.     

A Study of ibuprofen solubility in supercritical carbon dioxide by Fourier-transform infrared spectroscopy

In the work, a method of study of solubility of pharmaceutical substances in high-pressure gases and supercritical media with Fourier-transform IR spectroscopy has been developed. An investigation of the process of ibuprofen dissolution in supercritical carbon dioxide (SC CO₂) in a real-time scale has been performed. On the basis of analysis of the time dependences of the integral intensities of the selected IR-absorption bands of ibuprofen on the value of the initial weighed portion the value of solubility (molar fraction) of ibuprofen in SC CO₂ at a temperature of 35°C and pressure of 15.0 MPa was obtained, being equal to (8.9 ± 1.6) × 10^?3.     

Conference Report

Soil from Free-Air Carbon dioxide Enrichment (FACE) plots (FAL, Braunschweig) under ambient air (375 ppm; δ¹³C–CO₂?9.8‰) and elevated CO₂ (550 ppm; for six years; δ¹³C–CO₂?23‰), either under 100% nitrogen (N) (180 kg ha^?1) or 50% N (90 kg ha^?1) fertilisation treatments, was analysed by thermogravimetry. Soil samples were heated up to the respective temperatures and the remaining soil was analysed for δ¹³C and δ¹⁵N by Isotope Ratio Mass Spectrometry (IRMS). Based on differential weight losses, four temperature intervals were distinguished. Weight losses in the temperature range 20–200 °C were connected mostly with water volatilisation. The maximum weight losses and carbon (C) content were measured in the soil organic matter (SOM) pool decomposed at 200–360 °C. The largest amount of N was detected in SOM pools decomposed at 200–360 °C and 360–500 °C. In all temperature ranges, the δ¹³C values of SOM pools were significantly more negative under elevated CO₂ versus ambient CO₂. The incorporation of new C into SOM pools was not inversely proportional to its thermal stability. 50% N fertilisation treatment gained higher C exchange under elevated CO₂ in the thermally labile SOM pool (200–360 °C), whereas 100% N treatment induced higher C turnover in the thermally stable SOM pools (360–500 °C, 500–1000 °C). Mean Residence Time of SOM under 100% N and 50% N fertilisation showed no dependence between SOM pools isolated by increasing temperature of heating and the renovation of organic C in those SOM pools. Thus, the separation of SOM based on its thermal stability was not sufficient to reveal pools with contrasting turnover rates of C.     

The system Na2CO3–MgCO3 at 3 GPa

It was suggested that Na–Mg carbonates might play a substantial role in mantle metasomatic processes through lowering melting temperatures of mantle peridotites. Taking into account that natrite, Na₂CO₃, eitelite, Na₂Mg(CO₃)₂, and magnesite, MgCO₃, have been recently reported from xenoliths of shallow mantle (110–115?km) origin, we performed experiments on phase relations in the system Na₂CO₃–MgCO₃ at 3?GPa and 800–1250°C. We found that the subsolidus assemblages comprise the stability fields of Na-carbonate?+?eitelite and eitelite?+?magnesite with the transition boundary at 50?mol% Na₂CO₃. The Na-carbonate–eitelite eutectic was established at 900°C and 69?mol% Na₂CO₃. Eitelite melts incongruently to magnesite and a liquid containing about 55?mol% Na₂CO₃ at 925?±?25 °C. At 1050 °C, the liquid, coexisting with Na-carbonate, contains 86–88?mol% Na₂CO₃. Melting point of Na₂CO₃ was established at 1175?±?25 °C. The Na₂CO₃ content in the liquid coexisting with magnesite decreases to 31?mol% as temperature increases to 1250°C. According to our data, the Na- and Mg-rich carbonate melt, which is more alkaline than eitelite, can be stable at the P–T conditions of the shallow lithospheric mantle with thermal gradient of 45?mW/m² corresponding to temperature of 900 °C at 3?GPa.     

Aerogel–copper nanocomposites prepared using the adsorption of a polyfluorinated complex from supercritical CO2

A supercritical deposition method has been used to synthesize aerogel?Ccopper nanocomposites. Carbon, resorcinol?Cformaldehyde, and silica aerogels (CAs, RFAs, and SAs) were impregnated with a new polyfluorinated copper precursor (CuDI6), which has a high solubility in supercritical carbon dioxide (scCO₂). Adsorption isotherms of CuDI6 onto various aerogels from scCO₂ were determined at 35?°C and 10.6?MPa using a batch method which is based on the measurement of the fluid phase concentration. The relative affinity between CuDI6 and different aerogels changed in the following order: CA?>?RFA?>?SA. The effect of temperature on the adsorption isotherms for the CuDI6?CCO₂?CCA system was also studied at 35 and 55?°C and at a CO₂ density of 736.1?kg/m³. The CuDI6 uptake at a particular CuDI6 concentration increased with increasing temperature. Adsorbed CuDI6 was found to convert into Cu and Cu/Cu₂O nanoparticles on the aerogel supports after chemical or thermal treatments at ambient pressure and at temperatures ranging from 200 to 400?°C.     

Melting and subsolidus phase relations in the system K2CO3–MgCO3 at 3 GPa

ABSTRACT

As part of an investigation of carbonate systems under mantle pressures and temperatures, phase relations in the K₂CO₃–MgCO₃ system have been studied at 3?GPa and 800–1300°C. Subsolidus assemblages comprise the stability fields of K₂CO₃?+?K₂Mg(CO₃)₂ and K₂Mg(CO₃)₂?+?MgCO₃ with the transition boundary near 50?mol% K₂CO₃ in the system. The K₂CO₃–K₂Mg(CO₃)₂ eutectic is located at 840°C and 52?mol% K₂CO₃. The K₂CO₃ content in the melt coexisting with potassium carbonate increases to 85?mol% as temperature increases to 1050°C. K₂CO₃ remains solid up to 1250 and melts at 1300°C. K₂Mg(CO₃)₂ melts incongruently at 890°C to produce magnesite and a liquid containing 51?mol% K₂CO₃. As temperature increases to 1300°C, the K₂CO₃ content in the liquid coexisting with magnesite decreases to 27?mol%.     

Polyester Fabric’s Fluorescent Dyeing in Supercritical Carbon Dioxide and its Fluorescence Imaging

As one of the most important coumarin-like dyes, disperse fluorescent Yellow 82 exhibits exceptionally large two-photon effects. Here, it was firstly introduced into the supercritical CO₂ dyeing polyester fabrics in this work. Results of the present work showed that the dyeing parameters such as the dyeing time, pressure and temperature had remarkable influences on the color strength of fabrics. The optimized dyeing condition in supercritical CO₂ dyeing has been proposed that the dyeing time was 60 min; the pressure was 25 MPa and the temperature was 120 °C. As a result, acceptable products were obtained with the wash and rub fastness rating at 5 or 4–5. The polyester fabrics dyed with fluorescent dyes can be satisfied for the requirement of manufacturing warning clothing. Importantly, the confocal microscopy imaging technology was successfully introduced into textile fields to observe the distribution and fluorescence intensity of disperse fluorescent Yellow 82 on polyester fabrics. As far as we know, this is the first report about supercritical CO₂ dyeing polyester fabrics based on disperse fluorescent dyes. It will be very helpful for the further design of new fluorescent functional dyes suitable for supercritical CO₂ dyeing technique.     

Stepwise synthesis of fine crystalline Ce-doped yttrium aluminum garnet in water medium in subcritical and supercritical conditions

In this paper the continuous stepwise method of a production of fine crystalline yttrium aluminum garnet doped with cerium (YAG: Ce³⁺) in supercritical water fluid (SCWF) are represented. The synthesis was carried out in water medium in two stages: first in subcritical conditions and then in an atmosphere of supercritical water fluid. The stoichiometric mixture of yttrium oxide and aluminum hydroxide in a water solution of cerium nitrate was maintained the certain time at 280°C and under vapor water pressure 6.3 MPa. Then temperature and pressure were risen up to a supercritical condition (T = 392–400°C, P_{H2 O}P_{H_2 O} = 22 MPa). The concentration of cerium ions in reaction medium was changed in the interval 0.012–0.706 wt %. The products, obtained on various stages of synthesis, were investigated by physical-chemical methods. During the first stage, the crystals of boehmite and yttrium hydroxide under hydrothermal conditions were arising, and eventually poorly formed YAG: Ce³⁺ were appearing. At this stage, the diffusion of cerium ions into intermediate products takes place. Because of this, at the second step of synthesis, in supercritical conditions, YAG: Ce³⁺, phosphor with high luminescence intensity at 530 nm, was obtained. In supercritical conditions well-faceted crystals of 0.5–3.0 μm with rhombododecahedral habitus were produced.     

The Ca-looping process for CO<Subscript>2</Subscript> capture and energy storage: role of nanoparticle technology

The calcium looping (CaL) process, based on the cyclic carbonation/calcination of CaO, has come into scene in the last years with a high potential to be used in large-scale technologies aimed at mitigating global warming. In the CaL process for CO₂ capture, the CO₂-loaded flue gas is used to fluidize a bed of CaO particles at temperatures around ~?650 °C. The carbonated particles are then circulated into a calciner reactor wherein the CaO solids are regenerated at temperatures near ~?950 °C under high CO₂ concentration. Calcination at such harsh conditions causes a marked sintering and loss of reactivity of the regenerated CaO. This main drawback could be however compensated from the very low cost of natural CaO precursors such as limestone or dolomite. Another emerging application of the CaL process is thermochemical energy storage (TCES) in concentrated solar power (CSP) plants. Importantly, carbonation/calcination conditions to maximize the global CaL-CSP plant efficiency could differ radically from those used for CO₂ capture. Thus, carbonation could be carried out at high temperatures under high CO₂ partial pressure for maximum efficiency, whereas the solids could be calcined at relatively low temperatures in the absence of CO₂ to promote calcination. Our work highlights the critical role of carbonation/calcination conditions on the performance of CaO derived from natural precursors. While conditions in the CaL process for CO₂ capture lead to a severe CaO deactivation with the number of cycles, the same material may exhibit a high and stable conversion at optimum CaL-CSP conditions. Moreover, the type of CaL conditions influences critically the reaction kinetics, which plays a main role on the optimization of relevant operation parameters such as the residence time in the reactors. This paper is devoted to a brief review on the latest research activity in our group concerning these issues as well as the possible role of nanoparticle technology to enhance the activity of Ca-based materials at CaL conditions for CO₂ capture and energy storage.     

An investigation of the dissolution of acetylsalicylic acid in supercritical carbon dioxide

The dissolution of acetylsalicylic acid in supercritical carbon dioxide (SC–CO₂) is investigated using Fourier transform IR spectroscopy. Temporal dependences of integrated intensities of the absorption band of acetylsalicylic acid (ASA) near 1199 cm^–1 are measured for various ASA charges placed into a cuvette. Molar fractions of ASA in the saturated solution in SC–CO₂ are determined at a temperature of 40°C and pressures of 10.0 and 15.0 MPa, and the components are 2.10 ± 0.25 × 10^–4 and 11.0 ± 1.5 × 10^–4, respectively.     

Green preparation of Pd nanoparticles on SBA-15 via supercritical fluid deposition and application on Suzuki–Miyaura cross-coupling reaction

A well-dispersed green Pd/SBA-15 catalyst with an average size of 13.7 nm and 492.6 m²/g BET surface area is prepared via supercritical fluid deposition method with a new bipyridyl precursor that enables reduction at mild conditions at 80 °C and 17.2 MPa. The catalytic performance of Pd/SBA-15 prepared using scCO₂ with hydrogen reduction was assessed for Suzuki–Miyaura coupling reaction of bromobenzene and phenylboronic acid that was chosen as a model coupling reaction. The catalyst was tested in six different solutions and in three organic and inorganic bases during reactions. In general, the effect of bases is investigated when solvents are held constant and K₂CO₃ appears to have the best results in the activity studies used. For each of the 3 bases used, the highest catalytic activity was reached as the result of the solvent system being ethanol/water (1:1). The highest catalytic conversion was obtained in the ethanol-K₂CO₃ solvent-base pair. The catalyst synthesized in this study exhibited high activities and TON value was found as 160.8 at room temperature.     

Thermal Decomposition Behavior of a Heterocyclic Aramid Fiber

Heterocyclic aramid fibers are one of the high-performance fibers with excellent mechanical and thermal properties. In this article, the thermal decomposition behaviors of a type of the fibers were studied in nitrogen and air by pyrolysis/gas chromatography–mass spectrometry (Py/GC-MS), thermal gravimetric analysis–differential thermal analysis/Fourier transform infrared spectroscopy (TGA-DTA/FTIR), and thermal gravimetric analysis–differential thermal analysis/mass spectrometry (TGA-DTA/MS). The results showed that under nitrogen atmosphere, the thermal decomposition mainly happened between 520°C and 580°C, the temperature of the maximum weight loss rate was 550°C, and the weight remaining at 800°C was 58%. HCN, NH₃, NO₂, NO, CO₂, CO, H₂O, and some other compounds containing benzene rings were detected by the TGA-DTA/FTIR. Among these released chemicals, the intensity of the absorption peak assigned to CO₂ was the strongest. These chemicals were also identified by the TGA-DTA/MS. The Py-GC/MS analysis revealed that the number of chromatographic peaks increased with the increase of temperature. Most of the pyrolysis products were produced between 550°C and 600°C, which represented the major pyrolysis process. Moreover, the detection of benzene ring containing compound fragments reflected the process of the molecular chain scission. In air atmosphere, the thermal decomposition mainly happened between 500°C and 680°C. The maximum weight loss rate was observed at 600°C, and almost 100% weight was lost at 900°C. NH₃, NO₂, CO₂, and H₂O were detected by the TGA-DTA/MS, and the ion current intensity of CO₂ was again the strongest with a strong oxidation reaction at around 670°C. It was speculated that the thermal decomposition began with the breaking of the bonds between PPTA (poly-p-phenylene terephthalamide) blocks and heterocyclic blocks at high temperature. Then, with the increase of temperature, the chemical bonds inside the PPTA blocks and heterocyclic blocks were broken. In this process, free radicals that led to restructuring and new breakages to produce micromolecular products were introduced.     

Conversion of brown coal in sub- and supercritical water at cyclic pressurization and depressurization

The conversion of brown coal in sub- and supercritical water at 310–460°C and pressures up to 30 MPa in the cyclic pressurization and depressurization modes is studied. The temperature dependences of coal organic matter (COM) conversion and the yield of volatile and condensed products are obtained. The temperature dependence of the yield of condensed substances has a maximum at 370°C. The fraction of high-molecular substances in condensed products is increased with increasing temperature. The cumulative conversion of COM into volatile and condensed products upon heating to 460°C was 31.4 and 8.6%, respectively. According to the data of mass spectrometry analysis of volatile products and the elemental analysis of the initial coal, carbonaceous residue after the conversion, and condensed products, 82.3% of oxygen and 74.7% of sulfur, are removed from COM. CO₂ and H₂S are the main products of the conversion of oxygen- and sulfur-containing groups.     

The Effect of Supercritical CO2 on the Macromolecules Parallel Conformation and Its Relation to the Electrical Conductivity and Dielectric Behavior of Epichlorohydrin Terpolymer

The effect of supercritical CO₂ on the electrical conductivity of poly(epichlorohydrin–Ethylene oxide–Allyl glycidal ether) terpolymer is investigated using dielectric spectroscopy. Impedance measurements were carried out in the frequency range from 100–10 MHz and the temperature range of ?35–70°C with intervals of 5°C. The experimental results of the dielectric constant and the dielectric loss were fitted with the Cole–Cole equation to obtain the maximum relaxation frequencies of the different relaxation processes. As a result of the CO₂ treatment process, enhancement in the polymer chain mobility without noteworthy change in the glass transition temperature was determined. In addition, the level of the DC conductivity and the dielectric strength were increased. These effects were attributed to improvement in the chain dynamics, which arises from enhancement in the parallel conformation of macromolecules.     

Fabrication of highly porous bioresorbable polymer matrices using supercritical carbon dioxide

A new method for fabrication of highly porous bioresorbable polymer structures on the basis of various aliphatic polyesters for tissue engineering has been successfully designed and worked out. It has been shown that injection of polymer compositions plasticized in sub- or supercritical carbon dioxide into press forms at temperatures from 20 to 40°C through a nozzle of a certain diameter under atmospheric or elevated (up to 6 MPa) CO₂ pressure allows obtaining polymer matrices with a desired structure and morphology and mean porosity of up to 96 vol % with high reproducibility and avoiding the use of toxic organic solvents. The effect of chemical composition and molecular mass of starting polymers, as well as temperature and CO₂ pressure in the reaction cell and the receiver, on the morphology and internal structure of fabricated samples was studied using the method of scanning-electron microscopy.     

The transformation of <Emphasis Type="Italic">n</Emphasis>-alkanes on H-forms of zeolites under supercritical conditions

The skeleton isomerization of n-butane, n-hexane, and n-heptane was studied under supercritical conditions on H-forms of zeolites mordenite, beta, and ZSM-5 over the temperature and pressure ranges 260–450°C and 80–130 atm. The isomerization of n-hexane and n-heptane was accompanied by side processes such as oligomerization and cracking. The selectivity of formation of branched isomers of these hydrocarbons did not exceed 70 and 30%, respectively. The catalyst with the most stable operation was pentasil ZSM-5, but the selectivity of formation of branched isomers on it did not exceed 30% even at 260–280°C and decreased to 3% as the reaction temperature increased to 400–450°C. The fraction of aromatization products was then more than 15%. A study of the influence of C₆–C₇ n-alkane additives on the isomerization of n-pentane on mordenite in the H-form under supercritical conditions at 260°C and 120 atm showed that a gradual decrease in the activity of this catalyst in the isomerization of n-pentane was related to the formation of heavier hydrocarbons.     

Experimental study of influence of temperature on fuel-N conversion and recycle NO reduction in oxyfuel combustion

Coal combustion in O₂/CO₂ environment was examined with a bituminous coal in which the gas-phase and char combustion stages were considered separately. The effects of temperature (1000–1300 °C) and the excess oxygen ratio λ (0.6–1.4) on the conversion of volatile-N and char-N to NOx were studied. Also, the reduction of recycle NOx by fuel-N was investigated under various conditions. The results show that fuel-N conversion to NO in O₂/CO₂ is lower than that in O₂/N₂. In O₂/CO₂ atmosphere, the volatile-N conversion ratios vary from 1–7% to 15–24% under fuel-rich and fuel-lean conditions, respectively. The char-N conversion ratios are 11–28% and 30–50% under fuel-rich and fuel-lean conditions, respectively. The influences of temperature on the conversion of volatile-N to NO under fuel-rich and fuel-lean conditions are contrary. A significant difference for char-N conversion in fuel-rich and fuel-lean conditions is observed. The experimental data of recycle NO reduction indicate that the reduction of recycle NO by gas-phase reaction can be enhanced by volatile-N addition in fuel-lean condition at high temperature, while in fuel-rich condition, the volatile-N influence cancelled out and the overall impact is small. NO/char reaction competes with the conversion of fuel-N to NO at higher temperatures.