Effects of carbon nanofiber on the dissolution and diffusion of CO2 in polypropylene nanocomposites

The effects of nanofiller with elongated structure on the dissolution and diffusion behaviors of CO₂ in polypropylene (PP)/carbon nanofiber (CNF) composites were investigated in this work. The solubility of CO₂ in PP and PP composites containing 5 wt% and 10 wt% CNF was measured by using magnetic suspension balance (MSB) combined with the experimental swelling correction by using a self-designed high-temperature and -pressure view cell at the temperatures of 200 and 220 °C and pressures up to 20 MPa. The diffusion coefficient of CO₂ in PP and PP composites was also determined from the sorption line at CO₂ pressures ranging from 5 to 10 MPa. It was found that the solubility and diffusivity of CO₂ in PP/CNF composites increased with increasing the filler content, which should be mainly attributed to the change of the distribution of free volume in the polymer matrix besides the small amount of adsorption capacity of CO₂ in CNF. A modified Henry model incorporated with Langmuir adsorption factor was proposed to correlate the solubility of CO₂ in the PP/CNF composites with an average relative deviation less than 3%. A new model based on free volume theory incorporated with the diffusion driving force factor was established to correlate the experimental diffusion coefficient of CO₂ in the PP/CNF composites within an average relative deviation of 2%.     

Solubility and diffusion coefficient of supercritical-CO2 in polycarbonate and CO2 induced crystallization of polycarbonate

The solubility and diffusion coefficient of supercritical CO₂ in polycarbonate (PC) were measured using a magnetic suspension balance at sorption temperatures that ranged from 75 to 175 °C and at sorption pressures as high as 20 MPa. Above certain threshold pressures, the solubility of CO₂ decreased with time after showing a maximum value at a constant sorption temperature and pressure. This phenomenon indicated the crystallization of PC due to the plasticization effect of dissolved CO₂. A thorough investigation into the dependence of sorption temperature and pressure on the crystallinity of PC showed that the crystallization of PC occurred when the difference between the sorption temperature and the depressed glass transition temperature exceeded 40 °C (T − T_g ≥ 40 °C). Furthermore, the crystallization rate of PC was determined according to Avrami's equation. The crystallization rate increased with the sorption pressure and was at its maximum at a certain temperature under a constant pressure.     

Carbon dioxide sorption and dilation of poly(lactide-co-glycolide)

Recently, CO₂ has been intensely studied as a promising fluid to process or modify biomaterials. The thermodynamic behavior of CO₂–polymer mixtures plays an essential role in further progress of this field. In this study, CO₂ sorption isotherms and the induced polymer swelling were studied, respectively, by the pressure decay technique and a volumetric approach derived from the ADSA (Axisymmetric Drop Shape Analysis) method used for interfacial tension measurements. The polymer of interest in this work was Poly(lactide-co-glycolide) (PLGA), an important biomaterial already approved by the FDA. To the best of our knowledge, CO₂ sorption and dilation isotherms in PLGA are very limited in the literature. This work provides data for PLGA5050, PLGA7525 and PLA100DL over a useful range of processing conditions (temperatures of 30, 40 and 60 °C, and pressures up to 10 MPa). PLGA is shown to have a relatively high affinity for CO₂ and the resulting volumetric expansion upon CO₂ sorption is closely related to the percentage of the lactide component in the copolymer. The Sanchez–Lacombe equation of state (SLEOS) was applied to correlate the experimental data, and the nearly equivalent fitting quality employing various optimization routes verified that the SLEOS is a robust thermodynamic model to describe the CO₂–polymer mixture. In addition, the combination of a group contribution method and the isobaric density data of the pure polymer obtained by the ADSA offers a simple way of estimating the characteristic parameters for the SLEOS model. The approach is verified by the satisfactory prediction of PMMA density, and then applied to PLGA copolymers.     

Solubility and diffusivity of CO2 in polypropylene/micro-calcium carbonate composites

This work is aimed at studying the effects of the fillers and interface bonding condition between the fillers and polymer matrix on the solubility and diffusivity of CO₂ in polypropylene (PP)/Micro-calcium carbonate (MicroCaCO₃) composites. The solubility of CO₂ in PP and its composites containing 5% and 10% MicroCaCO₃ was determined precisely by using magnetic suspension balance (MSB) combined with experimental swelling correction at 200 and 220 °C and CO₂ pressures up to 22 MPa. It was found that the solubility of CO₂ in the PP/MicroCaCO₃ composites without the interface compatibilizer increased with increasing the filler content, while the CO₂ solubility remained almost unchanged in PP composites with compatibilizer. The Henry's law and a modified Henry's law were used to well correlate the solubility of CO₂ in the PP composites with and without the interface compatibilizer, respectively. The diffusion coefficient of CO₂ in the PP composites was found to decrease with increasing the filler content. The mutual diffusion coefficients of CO₂ in the PP composites can be correlated within an average relative deviation of 10% by the free volume model proposed by Kulkarni and Stern with a parameter accounting for the barrier effect of the filler.     

Measurement of CO2 sorption and PEG 1500 swelling by ATR-IR spectroscopy

In situ high-pressure ATR-IR spectroscopy was applied to simultaneously measure the sorption of CO₂ in polyethylene glycol (PEG) with molecular weight 1500 and the polymer swelling. The band at ca. 2338 cm⁻¹ corresponding to the antisymmetric stretching mode of CO₂ was used to calculate concentration of CO₂ dissolved in PEG while spectral bands of PEG at ca. 1100 cm⁻¹ were used to calculate swelling of PEG as a function of temperature and pressure. This in situ approach allowed to observe CO₂-induced melting of PEG and to assess intermolecular interactions between CO₂ and polymer.The solubility of CO₂ in PEG 1500 was influenced by both pressure and temperature. It remarkably increased with pressure until the CO₂ critical value, then it approached a plateau. Higher solubility was observed at the lower temperature.     

Effect of the porous structure in carbon materials for CO2 capture at atmospheric and high-pressure

Activated carbons prepared from petroleum pitch and using KOH as activating agent exhibit an excellent behavior in CO₂ capture both at atmospheric (∼168 mg CO₂/g at 298 K) and high pressure (∼1500 mg CO₂/g at 298 K and 4.5 MPa). However, an exhaustive evaluation of the adsorption process shows that the optimum carbon structure, in terms of adsorption capacity, depends on the final application. Whereas narrow micropores (pores below 0.6 nm) govern the sorption behavior at 0.1 MPa, large micropores/small mesopores (pores below 2.0–3.0 nm) govern the sorption behavior at high pressure (4.5 MPa). Consequently, an optimum sorbent exhibiting a high working capacity for high pressure applications, e.g., pressure-swing adsorption units, will require a poorly-developed narrow microporous structure together with a highly-developed wide microporous and small mesoporous network. The appropriate design of the preparation conditions gives rise to carbon materials with an extremely high delivery capacity ∼1388 mg CO₂/g between 4.5 MPa and 0.1 MPa. Consequently, this study provides guidelines for the design of carbon materials with an improved ability to remove carbon dioxide from the environment at atmospheric and high pressure.     

Ovicidal activities of supercritical CO2 and N2O on Ascaris suum eggs

This study examined whether supercritical CO₂ and N₂O fluids are effective in inactivating Ascaris suum eggs, which were chosen as a model for parasite eggs. The treatments were carried out in a multibatch apparatus, in which, the eggs could be placed atop a solid surface (non-immersed condition) or in aqueous solution (immersed condition). Various CO₂ and N₂O phases—including gas (6 MPa, 30 °C), liquid (8 MPa, 30 °C), subcritical (10 MPa, 30 °C), and supercritical (10 MPa, 37 °C)—were tested with exposure times ranging from 1 to 20 min. Supercritical CO₂ and N₂O both showed a similar, strong ovicidal effect, requiring only 1 min in non-immersed conditions and 5 min in water-immersed conditions to achieve a 2.4-log inactivation. Subcritical CO₂ and N₂O showed a weaker ovicidal effect. The effect was significantly reduced for the gas and liquid phases, compared with the supercritical phases. This study reports that supercritical CO₂ and N₂O can be effectively employed as a non-thermal treatment technique to control parasite egg contamination in fecal matter and food.     

Phase equilibria of the propylene glycol/CO2 and propylene glycol/ethanol/CO2 systems

The high-pressure vapour–liquid phase equilibria (P–T–x–y) of the binary mixture propylene glycol/CO₂ have been experimentally investigated at temperatures of (398.2, 423.2 and 453.2) K over the pressure range from (2.5 to 55.0) MPa using a static-analytic method. Furthermore, the high-pressure vapour–liquid phase equilibria (P–T–x–y) of the ternary mixture propylene glycol/CO₂/ethanol at constant temperatures of (398.2, 423.2 and 453.2) K and at constant pressure of 15.0 MPa have been determined using a static-analytic method. Initial concentrations of components in propylene glycol (PG)/ethanol (EtOH) mixture vary from 10 up to 90 wt.%. In general, for binary system it was observed that the solubility of CO₂ in the heavy propylene glycol reach phase increases with increasing pressure at constant temperature. On the contrary, the composition of gaseous phase is not influenced by the pressure or the temperature. On average the solubility of PG in light phase of CO₂ amounts to 30 wt.%. The system behaviour at temperature of 398.2 K was investigated up to 70.0 MPa and a single-phase region was not observed. Above the pressure 60.0 MPa a single-phase region of the system was observed for the temperature of 423.2 K. For the temperature of 453.2 K the single-phase was observed above the pressure of 48.0 MPa. For ternary system it was observed that the composition of heavy phase is slightly influenced by the temperature when the mass fraction of EtOH in initial mixture is higher than 50 wt.%. If the mass fraction of PG in initial mixture is higher than 50 wt.%, the composition of heavy phase is not influenced by the temperature anymore. The composition of the PG, EtOH and CO₂ in light phase remains more or less unchanged and it is not influenced by the conditions.     

Hydrogen storage in CO2-activated amorphous nanofibers and their monoliths

Amorphous carbon nanofibers (CNFs), produced by the polymer blend technique, are activated by CO₂ (ACNFs). Monoliths are synthesized from the precursor and from some ACNFs. Morphology and textural properties of these materials are studied. When compared with other activating agents (steam and alkaline hydroxides), CO₂ activation renders suitable yields and, contrarily to most other precursors, turns out to be advantageous for developing and controlling their narrow microporosity (<0.7 nm), V_DR(CO₂). The obtained ACNFs have a high compressibility and, consequently, a high packing density under mechanical pressure which can also be maintained upon monolith synthesis. H₂ adsorption is measured at two different conditions (77 K/0.11 MPa, and 298 K/20 MPa) and compared with other activated carbons. Under both conditions, H₂ uptake depends on the narrow microporosity of the prepared ACNFs. Interestingly, at room temperature these ACNFs perform better than other activated carbons, despite their lower porosity developments. At 298 K they reach a H₂ adsorption capacity as high as 1.3 wt.%, and a remarkable value of 1 wt.% in its mechanically resistant monolith form.     

Combined high hydrostatic pressure and carbon dioxide inactivation of pectin methylesterase,polyphenol oxidase and peroxidase in feijoa puree

A combined treatment of high hydrostatic pressure (HHP) and dense phase carbon dioxide (DPCD) was investigated to inactivate pectin methylesterase (PME), peroxidase (POD) and polyphenol oxidase (PPO) in feijoa (Acca sellowiana) puree. The treatments were HHP (HHP); carbonation and HHP (HHPcarb); carbonation + addition of 8.5 mL CO₂/g puree into the headspace of the package and HHP (HHPcarb + CO₂). The different samples were treated at 300, 450 and 600 MPa, for 5 min.The residual POD and PPO activity decreased in the order HHP > HHPcarb > HHPcarb + CO₂ at all pressures used. Treatments with HHP at 300 MPa increased POD activity to 140%. The residual PME activity of HHPcarb and HHPcarb + CO₂ samples at 600 MPa (45–50%) was significantly (p < 0.05) lower than for HHP treatment (65%).The simultaneous application of HHP and DPCD seems to synergistically enhance the inactivation of the enzymes studied, the CO₂ concentration being a key process factor.     

Density and viscosity of the binary polyethylene glycol/CO2 systems

Density of CO₂ saturated solutions of polyethylene glycols (PEGs) of different molecular weight was measured in pressure range from 8.0 MPa up to 47.7 MPa at a temperature of 343 K by a volumetric method. To validate the method density of pure CO₂ was measured at different pressures and a temperature of 293 K. The results were compared to the literature data and the accuracy was better than 2%. The density was between 1.17 g/mL for PEG 1000/CO₂ at 14.5 MPa and 1.78 g/mL for the system PEG 4000/CO₂ at 35 MPa. Further, the data were compared to results, obtained by a gravimetric method using magnetic suspension balance (MSB).Viscosity of CO₂ saturated solutions of polyethylene glycols (PEGs) of different molecular weight at different pressures and at a temperature of 343 K was measured using a high pressure view cell. Also a temperature impact on the viscosity of pure PEGs was observed at ambient pressure. After saturating PEG 1500 with 10 MPa of CO₂ pressure its viscosity decreases from 76.6 mPa s to 2.24 mPa s at 333 K. Further addition of CO₂ and increasing the pressure results in even lower viscosity and the highest viscosity reduction was reached at the highest pressure; at 35 MPa viscosity of the system PEG 1500/CO₂ is only 0.665 mPa s.     

Preparation in supercritical CO2 of porous poly(methyl methacrylate)–poly(l-lactic acid) (PMMA–PLA) scaffolds incorporating ibuprofen

Partially biodegradable porous scaffolds incorporating bioactive molecules prepared by clean techniques posses an enormous interest in tissue engineering applications. Poly(methyl methacrylate)–poly(l-lactic acid) (PMMA–PLA) blends were submitted to CO₂ supercritical conditions (P = 160–260 bar, T = 60 °C) after certain time and then rapidly depressurized to obtain porous structures that have been related with the supercritical parameters and to the polymer blend composition. In some cases ibuprofen was also incorporated to the formulations previously to the CO₂ treatment and studied the appropriate conditions for avoiding its extraction in SCCO₂. Scaffolds purity, thermal transitions, swelling and degradation behaviour, and the ibuprofen release were also studied to determine the appropriate scaffolds with a desired porosity for cell seeding. Cell culture was performed on the selected porous scaffolds using human fibroblast examined by scanning electron microscopy (SEM).     

Response surface optimization of Smyrnium cordifolium Boiss (SCB) oil extraction via supercritical carbon dioxide

In this study, the essential oil of aerial parts of a species of a plant called Smyrnium cordifolium Boiss (SCB) was extracted by supercritical CO₂. The essence was analyzed by the method of GC/MS. Design of experiments was carried out with response surface methodology by Minitab 16 software to optimize four operating variables of supercritical carbon dioxide (SC-CO₂) extraction (pressure, temperature, CO₂ flow rate and extraction dynamic time). This is the first report announcing optimization of the operation of supercritical extraction of SCB in laboratorial conditions. Optimizing process was done to achieve maximum yield extraction. Independent variables were dynamic time (t_d), pressure (P), temperature (T) and flow rate of SC-CO₂ (Q) in the range of 30–150 min, 10–30 MPa, 40–60 °C and 0.5–1.7 ml/min, respectively. The experimental optimal recovery of essential oil (0.8431, w/w%) was obtained at 13.43 MPa, 40 °C, 150 min (dynamic) and 1.7 ml/min (CO₂ flow rate).     

Formation of PVP hollow fibers by electrospinning in one-step process at sub and supercritical CO2

It was well known that electrospinning is one of the simple technical methods for the production of polymer nanoparticles and nanofibers. Various polymers have been successfully electrospun into ultrafine particles and fibers in recent years mostly in solvent solution and some in melt form. In this work, hollow fibers with walls made of organic polymer composites have been formed by electrospinning in a single processing step under pressurized carbon dioxide (CO₂). The experiments were conducted at 313 K and ∼8 MPa. The capability and feasibility of this technique was demonstrated by the production of polyvinylpyrrolidone (PVP) fibers whose size and wall thickness could be independently varied by controlling a set of experimental parameters. The PVP fibers had an average pore diameter 2–4 μm. At low pressures (<5 MPa; subcritical conditions), the solid fibers were formed, the baloon-like structures of PVP was formed with increasing pressure of CO₂ at 8 MPa (supercritical condition)     

Frequency response of microcantilevers immersed in gaseous,liquid, and supercritical carbon dioxide

The frequency response of ferromagnetic nickel microcantilevers with lengths ranging between 200 μm and 400 μm immersed in gaseous, liquid and supercritical carbon dioxide (CO₂) was investigated. The resonant frequency and the quality factor of the cantilever oscillations in CO₂ were measured for each cantilever length in the temperature range between 298 K and 323 K and the pressure range between 0.1 MPa and 20.7 MPa. At a constant temperature, both the resonant frequency and the quality factor were found to decrease with increasing pressure as a result of the increasing CO₂ density and viscosity. Very good agreement was found between the measured cantilever resonant frequencies and predictions of a model based on simplified hydrodynamic function of a cantilever oscillating harmonically in a viscous fluid valid for Reynolds numbers in the range of [1;1000] (average deviation of 2.40%). At high pressures of CO₂, the experimental Q-factors agreed well with the predicted ones. At low CO₂ pressures, additional internal mechanisms of the cantilever oscillation damping caused lowering of the measured Q-factor with respect to the hydrodynamic model predictions.     

Near-infrared spectroscopic solubility measurement for thermodynamic analysis of melting point depressions of biphenyl and naphthalene under high-pressure CO2

Melting temperatures of organic solids are often depressed by high-pressure CO₂ due to a dissolution of CO₂ in the molten organic compounds. For thermodynamic analysis of the melting point depression, solubilities of CO₂ in molten biphenyl and naphthalene were measured by near-infrared spectroscopy at various temperatures and pressures up to 20 MPa. Molarity of the organic component was determined from the 3ν_CH absorption band, and that of CO₂ from the 2ν₁ + ν₃ band. Mole fraction of CO₂ in the liquid phase was found to be an increasing function of the pressure up to 0.6 at 20 MPa and a weakly decreasing function of the temperature. The solubility data were used for modeling of the mixtures by the Peng–Robinson equation of state with a binary interaction parameter k₁₂. Calculation of the solid–liquid–gas phase equilibrium for the model fluid qualitatively described a large decrease in the melting temperature with increasing pressure up to 10 MPa followed by a small change at higher pressures. The melting point change was interpreted by the two competing effects: hydrostatic pressure effect increases the melting point by ca. 8 °C at 20 MPa, whereas CO₂ solubility effect reduces it by ca. 30 °C. Decomposition of the solubility effect into ideal and non-ideal mixing parts revealed that the non-ideality increases the melting point by more than 10 °C.     

High pressure densities of carbon dioxide + dipentaerythritol hexaheptanoate: New experimental setup and volumetric behavior

To perform an appropriate selection of the lubricants in air conditioned systems working with carbon dioxide as refrigerant, the thermodynamic behavior of the CO₂ + lubricant systems must be well known. In this work we present a new setup to prepare compressed gas–liquid mixtures and to determine the high pressure density by using an automated densimeter HPM and two syringe pumps. To analyze the reliability of the procedure proposed, we have determined the densities and mixing volumes of four CO₂ + n-decane mixtures. We have found a good agreement with previous literature data. In addition new density values are reported for the binary system CO₂ + dipentaerythritol hexaheptanoate (DiPEC7) at several temperatures and pressures from 10 MPa to 120 MPa.     

Gas sorption studies on a highly-thermostable microporous Zn(II) coordination polymer constructed from 2D honeycomb layers

By combining experiment with molecular simulation, the CO₂ sorption performance of a 2D honeycomb layered coordination polymer, {[Zn₂(bpydb)₂(H₂O)₂](DMA)₃(H₂O)}_n (1) (bpydb = 4,4′-(4,4′-bipyridine-2,6-diyl) dibenzoate) was systematically investigated. The desolvated 1 not only shows high CO₂ capacity (72.5 cm³/g at 273 K and 42.9 cm³/g at 298 K) with a moderate high zero-coverage adsorption enthalpy (29.7 kJ/mol), but also exhibits excellent CO₂/N₂ selectivity around room temperature. To better understand the adsorption behaviors and adsorption sites for CO₂ in 1, GCMC simulations were carried out, which indicate that the open metal sites between two adjacent layers account for the high CO₂ sorption capacity and strong CO₂ binding ability. Moreover, the thermal stability of 1 was further confirmed by the TGA and VT-PXRD, which indicate that 1 could be thermally stable up to 400 °C.     

Hydrogen solubility in CO2-expanded 2-propanol and in propane-expanded 2-propanol determined by an acoustic sensor

Hydrogen solubility in CO₂-expanded 2-propanol and in propane-expanded 2-propanol was obtained by an acoustic technique described elsewhere [L. Zevnik, J. Levec, Gas expanded liquids: Determination of the volumetric expansion by an acoustic technique, J. Supercrit. Fluids (2007), in press]. Solubility in CO₂-expanded 2-propanol at expansion coefficients V/V₀ = 2 and 4 was determined at 298 and 313 K. H₂ solubility was determined also in liquid CO₂ at 298 K and partial pressure of H₂ up to 6 MPa. Solubility in propane-expanded 2-propanol with V/V₀ = 2 and 4 was measured at 333, 353 and 393 K. Hydrogen mole fraction in liquid propane was obtained at 333 K and partial pressure of H₂ up to 5 MPa. For both expanded liquids the results show that hydrogen concentration increases with increasing V/V₀ ratio and with increasing temperature. It is demonstrated, however, that the acoustic technique is a reliable method for determination of gas composition and that it can be also implemented in various fields of gas processing.     

Phase equilibrium of the CO2/glycerol system: Experimental data by in situ FT-IR spectroscopy and thermodynamic modeling

Phase equilibrium experimental data for the CO₂/glycerol system are reported in this paper. The measurements were performed using an in situ FT-IR method for temperatures ranging from 40 °C to 200 °C and pressures up to 35.0 MPa, allowing determination of the mutual solubility of both compounds. Concerning the CO₂ rich phase, it was observed that the glycerol solubility in CO₂ was extremely low (in the range of 10⁻⁵ in mole fraction) in the pressure and temperature domains investigated here. Conversely, the glycerol rich phase dissolved CO₂ at mole fractions up to 0.13. Negligible swelling of the glycerol rich phase has been observed. Modeling of the phase equilibrium has been performed using the Peng–Robinson equation of state (PR EoS) with classical van der Waals one fluid and EoS/G^E based mixing rules (PSRK and MHV2). Satisfactory agreement was observed between modeling results and experimental measurements when PSRK mixing rules are used in combination with UNIQUAC model, although UNIFAC predictive approach gives unsatisfactory representation of experimental behavior.