Diffusion Of Supercritical Carbon Dioxide Research Articles

Experimental Study for the Sorption and Diffusion of Supercritical Carbon Dioxide into Polyetherimide.

Supercritical carbon dioxide (SCCO2) is a non-toxic and environmentally friendly fluid and has been used in polymerization reactions, processing, foaming, and plasticizing of polymers. Exploring the behavior and data of SCCO2 sorption and dissolution in polymers provides essential information for polymer applications. This study investigated the sorption and diffusion of SCCO2 into polyetherimide (PEI). The sorption and desorption processes of SCCO2 in PEI samples were measured in the temperature range from 40 to 60 °C, the pressure range from 20 to 40 MPa, and the sorption time from 0.25 to 52 h. This study used the ex situ gravimetric method under different operating conditions and applied the Fickian diffusion model to determine the mass diffusivity of SCCO2 during sorption and desorption processes into and out of PEI. The equilibrium mass gain fraction of SCCO2 into PEI was reported from 9.0 wt% (at 60 °C and 20 MPa) to 12.8 wt% (at 40 °C and 40 MPa). The sorption amount increased with the increasing SCCO2 pressure and decreased with the increasing SCCO2 temperature. This study showed the crossover phenomenon of equilibrium mass gain fraction isotherms with respect to SCCO2 density. Changes in the sorption mechanism in PEI were observed when the SCCO2 density was at approximately 840 kg/m3. This study qualitatively performed FTIR analysis during the SCCO2 desorption process. A CO2 antisymmetric stretching mode was observed near a wavenumber of 2340 cm-1. A comparison of loss modulus measurements of pure and SCCO2-treated PEI specimens showed the shifting of loss maxima. This result showed that the plasticization of PEI was achieved through the sorption process of SCCO2.

Study on the Dissolution and Diffusion of Supercritical Carbon Dioxide in Polystyrene Melts Based on Adsorption and Diffusion Mechanism.

In order to reveal the dissolution process, the adsorption kinetics and diffusion theory are combined and used to describe the adsorption-diffusion mechanism. This can not only predict the solubility of supercritical CO2 in polymer melts but also describe two important parameters of supercritical CO2 in the dissolution process: dissolution amount and dissolution rate, which can provide a good theoretical basis for microcellular foaming. To verify the feasibility and accuracy of the theoretical calculation method, an experimental device for the volume-changing method under static condition was established. The results showed that the theoretical calculation value was in good agreement with the experimental value. In addition, the dissolution amount and dissolution rate of supercritical CO2 in three polystyrene melts with different molecular weights under different temperature and pressure conditions were measured. The results showed that the difference of polystyrene molecular weight can cause the change of dissolution rate during the dissolution process, that is, the larger the molecular weight, the slower the dissolution rate.

Impregnation of mesoporous silica with mangiferin using supercritical CO2

The solvating power and diffusivity of supercritical carbon dioxide (scCO2) have attracted attention in recent years for the impregnation of polymers and porous matrices. This technique provides a final impregnated matrix that is free of solvents and it allows the use of thermosensitive drugs due to the relative low critical point of scCO2.The work reported here concerned the influence of parameters such as pressure, temperature, percentage of co-solvent, depressurization rate and time on the impregnation of mangiferin (MNG) into silica as a porous matrix. Increases in the values of the studied parameters led to an enhanced impregnation of MNG in all cases. Delivery profiles in simulated fluids were obtained. The profile for the gastric fluid shows a gradual release of MNG. The release of MNG in the intestinal fluid was faster than in the gastric fluid. The MNG was more soluble in the intestinal than in the gastric fluid.

The experimental and numerical relation between the solubility, diffusivity and bubble nucleation of supercritical CO2 in Polystyrene via visual observation apparatus

In this work, the solubility and diffusivity of supercritical carbon dioxide (scCO2) in Polystyrene (PS) at different temperatures and pressures were studied using a magnetic suspension balance (MSB). Bubble nucleation and growth in PS/CO2 mixture were investigated via visual observation in a batch foaming system at different temperatures and pressures. A firm relationship between bubble nucleation and growth with solubility and diffusivity was observed. The results show that bubble density during the process can be controlled by changing the temperature and the pressure release rate. Furthermore, bubble growth was simulated considering mass diffusion equations and implicit method. The simulation results were in a good agreement with the experimental data. Finally, the effects of diffusivity and zero shear viscosity on the bubble growth were investigated and it was found that the bubble growth is a diffusion controlled phenomenon.

Enantiomeric separation and quantification of R/S-amphetamine in urine by ultra-high performance supercritical fluid chromatography tandem mass spectrometry

To distinguish between legal and illegal consumption of amphetamine reliable analytical methods for chiral separation of the R- and S-enantiomers of amphetamine in biological specimens are required. In this regard, supercritical fluid chromatography (SFC) has several potential advantages over liquid chromatography, including rapid separation of enantiomers due to low viscosity and high diffusivity of supercritical carbon dioxide, the main component in the SFC mobile phase. A method for enantiomeric separation and quantification of R- and S-amphetamine in urine was developed and validated using ultra-high performance supercritical fluid chromatography-tandem mass spectrometry (UHPSFC-MS/MS). Sample preparation prior to UHPSFC-MS/MS analysis was a semi-automatic solid phase extraction method. The UHPSFC-MS/MS method used a Chiralpak AD-3 column with a mobile phase consisting of CO2 and 0.2% cyclohexylamine in 2-propanol. The injection volume was 2 μL and run-time was 6 min. MS/MS detection was performed with positive electrospray ionization and two multiple reaction monitoring transitions (m/z 136.1 > 119.0 and m/z 136.1 > 91.0). The calibration range was 50–10,000 ng/mL for each enantiomer. The between-assay relative standard deviations were in the range of 3.7–7.6%. Recovery was 92–93% and matrix effects ranged from 100 to 104% corrected with internal standard. After development and validation, the method has been successfully implemented in routine use at our laboratory for both separation and quantification of R/S-amphetamine, and has proved to be a reliable and useful tool for distinguishing intake of R- and S-amphetamine in authentic patient samples.

Solubility and diffusivity of supercritical carbon dioxide in cellulose acetate with cosolvents

The gravimetric procedure was applied to investigate the solubility and diffusivity of supercritical carbon dioxide (SC-CO2) in cellulose acetate (CA). The solubility increases constantly in the initial period and reaches the dissolution equilibrium when the saturation time exceeds 10 h. The solubility decreases gradually from 14.29 wt% to 7.36 wt%, while the saturation temperature increases from 40°C to 70°C. The solubility increases by only 5.63%, while the saturation pressure grows from 10 MPa (12.62 wt%) to 30 MPa (13.33 wt%). The presence of cosolvents, especially ethanol, improves the solubility obviously. The diffusivity is not affected by pressure but increases with the solubility. Scanning electron microscopic images show that the cell densities increase with the content of ethanol, which implies that the higher solubility is in favor of the cell nucleation. The foamed CA with 10 wt% or 20 wt% ethanol has both low density and good impact properties.

Gradient foaming of polycarbonate/carbon nanotube based nanocomposites with supercritical carbon dioxide and their EMI shielding performances

Sorption and diffusion of supercritical carbon dioxide (scCO2) into polycarbonate (PC) nanocomposites loaded with 0, 1 and 2 wt% of multi-walled carbon nanotubes (MWNTs) have been investigated. After determination of the saturation equilibrium, the samples have been saturated with scCO2 to ensure a partial foaming with a density gradient from the surface to the center of the samples and the morphology of the porous materials has been analyzed by SEM. The gradient materials were very advantageous for EMI shielding since the foamed structure at the surface had low dielectric constant and limited the reflection of the EM signal while the presence of highly conductive solid in the middle ensured a high absorption of the electromagnetic radiation.

Solubility and diffusivity of carbon dioxide in St-MMA copolymers

The present study focuses on synthesizing styrene-methylmethacrylate (St-MMA) copolymer particles in a batch reactor using suspension polymerization process at different copolymer compositions. Also for further comparisons, the neat polystyrene (PS) and polymethyl methacrylate (PMMA) were synthesized by the same method. The solubility and diffusivity of supercritical carbon dioxide (scCO2) into the synthesized copolymers at two temperatures (393 and 423)K and pressures in the range from (5 to 12)MPa were measured by a magnetic suspension balance. The Sanchez–Lacombe (SL) equation of state was used to estimate the swelling effect of CO2 on copolymers. The results showed that the solubility and diffusivity of CO2 increased with increasing of CO2 pressure and slightly improved with methyl methacrylate (MMA) content in copolymer. As well as the solubility of CO2 in samples decreased with temperature increment and contrary behavior was observed for diffusivity. Fujita, Maeda and Paul’s diffusion models were combined to estimate the diffusion coefficients for the copolymers and neat polymers.

Sorption and Diffusion of Supercritical Carbon Dioxide into Nitrocellulose with or without Cosolvents

Sorption and diffusion of supercritical carbon dioxide (SC-CO2), SC-CO2 + ethanol, or SC-CO2 + ethyl acetate into nitrocellulose were examined at 40°Cunder 25 MPa for the 0.5–6 h soaking duration using a gravimetric method. A small addition of cosolvent into SC-CO2 leads to a dramatic increase in solubility, desorption diffusivity and sorption diffusivity of CO2 into nitrocellulose. The addition of ethyl acetate or ethanol into SC-CO2 boosts the equilibrium solubility of CO2 in nitrocellulose from 15.74 wt% to 23.52 wt% and from 15.74 wt% to 22.72 wt%, respectively. The desorption diffusivities are found to be higher than the sorption diffusivities due to the plasticizing effect of CO2.

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.

Investigation of sorption and diffusion of supercritical carbon dioxide in polycarbonate

AbstractSorption and desorption of carbon dioxide (CO2) in polycarbonate (PC) with different dimensions were systematically investigated at temperatures of 40, 60, and 80°C; pressures ranged from 7 to 20 MPa; and soaking time ranged from 0.5 to 4 h. The experimental data were analyzed by a mass‐loss analysis. With the assumption of Fickian diffusion, the sorption amount and the sorption diffusivities (Ds) under supercritical conditions, and desorption diffusivities (Dd) under ambient temperature and pressure were determined. The crossover of the sorption isotherms was presented, which indicated that the change of mass transfer mechanism had occurred. It was found that Ds increased with temperature, whereas Dd showed a contrary trend. Moreover, the linear relationship between sorption amount and specific surface area was also observed, which suggested that the specific surface area was one of the important factors on the sorption amount for thick samples in swelling process. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Comparisons of the sorption and diffusion of supercritical carbon dioxide into polycarbonate and polysulfone

Diffusion and interaction of supercritical carbon dioxide (SCCO 2) with polycarbonate (PC) and polysulfone (PSF) is investigated in this study. Experiments on the sorption of SCCO 2 at 40 °C and 20 MPa into these polymers were carried out. Both the sorption amount of SCCO 2 ( M s) and the desorption diffusivity ( D d) were determined by employing Fick's diffusion model. The M s and D d values for SCCO 2 in PC were greater than those in PSF, owing to different interactions of SCCO 2 with the polymers in the sorption process. The FTIR spectroscopy results for both polymers showed that CO 2 desorbed faster from PSF than from PC. This indicated that the carbonyl group in PC had a stronger interaction with SCCO 2. The plasticization effect of SCCO 2 on these polymers was also investigated by comparing the DMA measurement results on pure and SCCO 2 treated polymers. It is shown that PC had a larger shift in glass transition temperature than that of PSF after the SCCO 2 treatment. This implied that there is a greater extent of plasticization on PC.

Measurement and prediction of diffusion coefficients of supercritical CO2 in molten polymers

AbstractThe solubility and diffusivity of supercritical carbon dioxide (sc‐CO2) in low‐density polyethylene (LDPE), high‐density polyethylene (HDPE), polypropylene (PP), ethylene‐ethylacrylate copolymer (EEA) and polystyrene (PS) were measured at temperatures from 150°C to 200°C and pressures up to 12 MPa by using the Magnetic Suspension Balance (MSB), a gravimetric technique for gas sorption measurements. The solubility of CO2 in each polymer was expressed by Henry's constant. The interaction parameter between CO2 and polymer could be obtained from the solubility data, and it was used to estimate the Pressure‐Volume‐Temperature relationship and the specific free volume of polymer/CO2 mixtures. The diffusion coefficients were also measured by the MSB for each polymer. The resulting diffusion coefficients were correlated with the estimated free volume of polymer/CO2 mixture. Combining Fujita's and Maeda and Paul's diffusion models, a model was newly developed in order to predict diffusion coefficients for the polymers studied. Polym. Eng. Sci. 44:1915–1924, 2004. © 2004 Society of Plastics Engineers.

Sorption and diffusion of supercritical carbon dioxide into polysulfone

AbstractSorption and diffusion of supercritical carbon dioxide (SCCO2) into polysulfone (PSF) from 313 K and 20 MPa to 333 K and 40 MPa were investigated in this study. A simple gravimetric method was used to measure the mass gain of SCCO2 in PSF, and the Fick's diffusion model was applied to describe the desorption process. The sorption amount, the sorption diffusivity under supercritical states, and the desorption diffusivity at ambient conditions are presented. Comparisons of the sorption amounts and diffusivities of CO2 for polymers of polycarbonate and PSF are discussed according to the interactions between gas and polymers. The morphology change and plasticization effect attributed to gas sorption in PSF were studied. Effects of glass‐transition temperature and yielding stress for PSF and other polymers were used to describe the difference in their diffusivities for the sorption and desorption processes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 474–482, 2004

Sorption and diffusion of supercritical carbon dioxide in polycarbonate

Sorption and diffusion of supercritical carbon dioxide (SCCO 2) in polycarbonate (PC) at temperatures ranged from 40 to 60 °C and pressures ranged from 10 to 40 MPa are presented in this study. The equilibrium CO 2 sorption in PC specimen with 0.5 mm thickness has been observed at 2 h, and the experimental data were analyzed by a mass-loss analysis. The linear relationship between mass gain and square root of time indicates that SCCO 2 conducted Fickian sorption and desorption in the PC specimen within the experimental conditions. The equilibrium CO 2 sorption amount in PC specimen varies from 7.6 wt.% (at 60 °C and 10 MPa) to 14.7 wt.% (at 40 °C and 40 MPa). Upon plotting the equilibrium sorption amounts against SCCO 2 density, crossover of the sorption isotherms is observed and the change of mass transfer mechanism is suggested. The sorption diffusivities under supercritical conditions as well as the desorption diffusivities under ambient temperature and pressure were determined. The sorption diffusivities increased with temperature and decreased with pressure of SCCO 2, unless the glass transition state of polymer was exceeded. The desorption diffusivities were also observed to increase with CO 2 concentration inside the PC specimen. At lower temperature and pressure, the desorption diffusivity may become larger than that of sorption due to the plasticizing effect.

Investigation of sorption and diffusion of supercritical carbon dioxide into poly(vinyl chloride)

The interaction of supercritical carbon dioxide (scCO 2) with poly(vinyl chloride) (PVC) was systematically investigated. PVC films of 0.5 mm thickness were treated with CO 2 at pressures between 5 and 40 MPa, at temperatures between 40 and 70°C and soaking times between 0.5 and 7 h. The gravimetric desorption data were kinetically and thermodynamically evaluated assuming Fickian diffusion and the morphology changes due to the CO 2 treatment investigated by microscopic methods. The sorbed amount of CO 2, q ( q= g CO2/ g polymer) ranged between 0.03 (5 MPa, 70°C) and 0.13 (15 MPa, 40°C). The desorption diffusivities, D d, were in the order of 0.1×10 −11 m 2/s and decreased with decreasing amounts of CO 2. In contrast, the sorption diffusivities, D s, were markedly higher and varied between 0.7×10 −11 and 2.5×10 −11 m 2/s (20 MPa, 40–70°C). The CO 2 treatment changed the polymer chain structure, macroscopically visualized by the film opaqueness and by the density decrease to 1.05 g/cm 3. Microcellular structures were not detected.

New Chelate Complexes of Copper and Iron: Synthesis and Impregnation into a Polymer Matrix from Solution in Supercritical Carbon Dioxide

New chelate complexes of copper diiminate and iron diiminate were synthesized. Their physical characteristics have been studied. The diffusion of supercritical carbon dioxide (scCO2) into polyarylate (PAR) films and their impregnation with diiminates were investigated. The equilibrium degree of PAR swelling in scCO2 is about 10%. The conditions of impregnation (45 °C, 8 MPa, 1.5 h) were determined. The impregnation was confirmed by the FT-IR spectroscopic data. Thermal reduction of metal ions was investigated. Transformations of the chelate complexes on the polymer-film surface were studied by ESCA. The value of the Auger factor indicates that, after thermal reduction, the copper ion is in a nearly univalent state. The copper content in films is as large as 6.3 wt %; the iron content is 4.5 wt %. The FT-IR and ESCA spectroscopic studies showed that, in the course of impregnation, chelate complexes interact with functional groups of the polymer. Subsequent thermal reduction of metal in air results in diiminate evaporation and thermooxidative degradation with ligand decomposition and enrichment of the surface with metal atoms. According to the SAXS data, the size distribution of metal-containing particles ranges from 20 to 60 nm with a maximum at 34 nm.