Presence Of scCO2 Research Articles

Forsterite [Mg2SiO4)] Carbonation in Wet Supercritical CO2: An in Situ High-Pressure X-ray Diffraction Study

Mechanisms controlling mineral stabilities in contact with injected supercritical fluids containing water are relatively unknown. In this paper, we discuss carbonation reactions occurring with forsterite (Mg(2)SiO(4)) exposed to variably wet supercritical CO(2) (scCO(2)). Transformation reactions were tracked by in situ high-pressure X-ray diffraction in the presence of scCO(2) containing dissolved water. Under modest pressures (90 bar) and temperatures (50 °C), scCO(2) saturated with water converted >70 wt % forsterite to a hydrated magnesium carbonate, nesquehonite (MgCO(3) · 3H(2)O), and magnesite (MgCO(3)) after 72 h. However, comparable tests with scCO(2) at only partial water saturation showed a faster carbonation rate but significantly less nesquehonite formation and no evidence of the anhydrous form (MgCO(3)). The presence and properties of a thin water film, observed by in situ infrared (IR) spectroscopy and with isotopically labeled oxygen ((18)O), appears to be critical for this silicate mineral to carbonate in low water environments. The carbonation products formed demonstrated by temperature and water-content dependence highlights the importance of these kinds of studies to enable better predictions of the long-term fate of geologically stored CO(2).

In situ XRD study of Ca2+ saturated montmorillonite (STX-1) exposed to anhydrous and wet supercritical carbon dioxide

Reactions involving supercritical carbon dioxide (scCO2) and a calcium saturated dioctahedral smectite (Ca-STX-1) were examined by in situ high-pressure X-ray diffraction over a range of temperatures (50–100°C) and pressures (90, 125, and 180bar) relevant to long-term geologic storage of CO2. Exposure of Ca-STX-1 containing one water of hydration (1W) to anhydrous scCO2 at 50°C and 90bar produced an immediate increase of ∼0.8Å in the d001 basal reflection that was sustained for the length of the experiment (∼44h). Higher ordered basal reflections displayed similar shifts. Following depressurization, positions of basal reflections and FWHM values (d001) returned to initial values, with no measurable modification to the clay structure or water content. Similar results were obtained for tests conducted at 50°C and higher pressures (125 and 180bar). Exposure of Ca-STX-1 containing two waters of hydration (2W) to scCO2 resulted in a decrease in the d001 reflection from 14.48Å to 12.52Å, after pressurization, indicating a partial loss of interlayer water. In addition, the hydration state of the clay became more homogeneous during contact with anhydrous scCO2 and after depressurization. In the presence of scCO2 and water, the clay achieved a 3W hydration state, based on a d001 spacing of 18.8Å. In contrast to scCO2, comparable testing with N2 gas indicated trivial changes in the d001 series regardless of hydration state (1W or 2W). In the presence of free water and N2, the basal spacing for the Ca-STX-1 expanded slightly, but remained in the 2W hydration state. The experiments show that potential collapse or expansion of the interlayer spacing depends on the initial hydration state of the clay and scCO2, where 1W clay is stable but ≥2W layer clay loses water when exposed to anhydrous CO2. Consequently, the implications of this study depend upon the depth of the caprock. If the caprock is quite deep, then the 1W hydration state is favored and the introduction of dry CO2 could actually help seal the formation. If the caprock is located closer to the surface where 2W or 3W montmorillonite is the predominant form then the introduction of dry CO2 should result in the creation of permeability. Further, these experiments indicate that scCO2 can become intercalated within hydrated clays under conditions proposed for geologic storage of CO2 and act as secondary CO2 traps.

Effect of H 3PO 3 concentration on the electrodeposition of nanocrystalline Ni–P deposited in an emulsified supercritical CO 2 bath

The electrodeposition of Ni–P alloy in an emulsified supercritical carbon dioxide (sc-CO 2) bath was investigated to explore the effect of H 3PO 3 concentration (ranging from 0 to 1.6 M) on the material characteristics of the deposits. The experimental results showed that the P content in the deposit increased with increasing H 3PO 3 concentration in the emulsified sc-CO 2 bath, while the weight gain of the Ni–P film decreased. At the same concentration of H 3PO 3, the significant decreases in weight gain and P content of the Ni–P films deposited in the emulsified sc-CO 2 bath were found, as compared with that plated in the conventional aqueous electrolyte at ambient pressure. X-ray photoelectron analyses revealed that the carbon-containing Ni–P deposit could be obtained in the bath with the presence of sc-CO 2 fluid. Transmission electron microscopy was employed for microstructure analysis. The average grain size of the Ni–P films deposited in the conventional aqueous electrolyte at ambient pressure or in the emulsified sc-CO 2 bath varied, depending on the H 3PO 3 concentration and P content. The Ni–P films deposited from the emulsified sc-CO 2 bath had a higher hardness as compared with that formed in conventional electrolyte. The hardness of Ni–P alloy deposited in the emulsified sc-CO 2 bath was enhanced by the additional solid solution strengthening mechanism.

Preparation and characterization of high melt strength polypropylene with long chain branched structure by the reactive extrusion process

AbstractThe reactive extrusion of maleic anhydride grafted polypropylene (PP‐g‐MAH) with ethylenediamine (EDA) as coupling agent is carried out in a corotating twin‐screw extruder to produce long chain branched polypropylene (LCBPP). Part of PP‐g‐MAH is replaced by maleic anhydride grafted high‐density polyethylene (HDPE‐g‐MAH) or linear low‐density polyethylene (LLDPE‐g‐MAH) to obtain hybrid long chain branched (LCB) polyolefins. Compared with the PP‐g‐MAH, PE‐g‐MAH, and their blends, the LCB polyolefins exhibit excellent dynamic shear and transient extensional rheological characteristics such as increased dynamic modulus, higher low‐frequency complex viscosity, broader relaxation spectra, significantly enhanced melt strength and strain‐hardening behaviors. The LCB polyolefins also have higher tensile strength, tensile modulus, impact strength and lower elongation at break than their blends. Furthermore, supercritical carbon dioxide (scCO2) is constructively introduced in the reactive extrusion process. In the presence of scCO2, the motor current of the twin extruder is decreased and LCB polyolefins with lower melt flow rate (MFR), higher complex viscosity and increased tensile strength and modulus can be obtained. This indicates that the application of scCO2 can reduce the viscosity of melt in extruder, enhance the diffusion of reactive species, and then facilitate the long chain branching reaction between anhydride group and primary amine group. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Solvation structure and dynamics for passivated Au nanoparticle in supercritical CO2: A molecular dynamic simulation

All-atomic molecular dynamics simulations have been performed to study the interfacial structural and dynamical properties of passivated gold nanoparticles in supercritical carbon dioxide (scCO(2)). Simulations were conducted for a 55-atom gold nanocore with thiolated perfluoropolyether as the packing ligands. The effect of solvent density and surface coverage on the structural and dynamical properties of the self-assembly monolayer (SAM) has been discussed. The simulation results demonstrate that the interface between nanoparticle and scCO(2) solvent shows a depletion region due to the preclusion of SAM. The presence of scCO(2) solvent around the passivated Au nanoparticle can lead to an enhanced extension of the surface SAM. Under full coverage, the structure and conformation of SAM are insensitive to the density change of scCO(2) fluid. This simulation results clarify the microscopic solvation mechanism of passivated nanoparticles in supercritical fluid medium and is expected to be helpful in understanding the scCO(2)-based nanoparticle dispersion behavior.

Electroless Ni–B deposition from an emulsified supercritical carbon dioxide bath

The electroless deposition of boron-containing Ni (EN-B) film from a supercritical carbon dioxide (sc-CO 2) bath was introduced. The deposition rate in sc-CO 2 bath was one order of magnitude lower than that at ambient pressure without the presence of sc-CO 2. A more uniform chemical composition of the EN-B film could be obtained if it was deposited in the sc-CO 2 bath. X-ray diffraction analyses revealed that the as-deposited film was amorphous in nature, despite of the deposition condition. Deposition defects such as cracks and voids could be avoided if the deposition was conducted in the sc-CO 2 bath. Crystallization and boride precipitation were found after heat treatment at 400 °C for 1 h. The EN-B film deposited from the sc-CO 2 bath had a higher hardness as compared with that of the normal EN-B coating. A substantial increase in hardness was obtained due to boride precipitation.

Stability of hen egg white lysozyme during denaturation is enhanced by pretreatment with supercritical carbon dioxide

Supercritical carbon dioxide (SC-CO(2)) has been successfully employed in a variety of applications due to its numerous advantages. Despite extensive investigations on the relationship between the activity of enzymes treated with supercritical fluids and supercritical operating conditions, there are no experimental studies that have addressed the effects of supercritical pretreatment on enzyme denaturation. In this study, we have explored the impact of SC-CO(2) pretreatment on the activity and stability of hen egg-white lysozyme during its course of denaturation. Our data indicated no noticeable enhancement in enzyme activity and stability in the presence of SC-CO(2) pretreatment for lysozyme samples denatured in 8 M urea at 50 degrees C and pH 6.2. However, SC-CO(2) pretreated lysozyme samples in 0.067 M phosphate buffer containing dithiothreitol (DTT) (0.1 M DTT, pH 6.2, 25 degrees C or 0.01 M DTT, pH 6.2, 50 degrees C) at 2500 psi and 50 degrees C had better residual activity relative to samples that were not pretreated. In addition, when denaturing at 65 degrees C and pH 9.0, the pretreatment in SC-CO(2) at 2500 psi and 50 degrees C resulted in the best stability of lysozyme. The result of this study may provide supporting evidence that supercritical fluids serve as potential media for enhancing the activity of enzymes used in a variety of biochemical applications.

Stereoselective synthesis of tetrasubstituted olefins via palladium-catalyzed three-component coupling of aryl iodides, internal alkynes, and arylboronic acids in supercritical carbon dioxide

The Pd-catalyzed three-component coupling of readily available aryl iodides, internal alkynes, and arylboronic acids provides a convenient, one-step route to tetrasubstituted olefins in good to excellent yields in scCO 2 using CsOAc as base. The final optimized reaction conditions for the three-component coupling in scCO 2 was determined to be aryl iodides (0.5 mmol), internal alkynes (0.25 mmol), and arylboronic acids (0.5 mmol) in the presence of PdCl 2 (2 mol%) and CsOAc (0.75 mmol) in scCO 2 ( P C O 2 = 7.5 MPa ) at 100 °C for 24 h. The presence of scCO 2 generally substantially improved this Pd-catalyzed system and increased the yields of the desired tetrasubstituted olefins. The reaction involves full cis-addition of internal alkynes and this system in scCO 2 is an effective and environmental friendly alternative to the previous methods involving organic solvent.

Study on selectivity of β-myrcene hydrogenation in high-pressure carbon dioxide catalysed by noble metal catalysts

Hydrogenation of monoterpenes, such as β-myrcene, in high-density carbon dioxide over 0.5 wt.% Pd, or Rh, or Ru supported on alumina was investigated. Hydrogenation catalysed by Rh and Ru is generally faster in a single supercritical (sc) phase (gaseous reagents and solid catalyst) than in a biphasic system (liquid + gas reactants + solid catalyst). The reaction catalysed by Pd occurs faster in two phases. The final composition of the reaction mixture is strongly dependent on the noble metal catalyst used for the reaction. Palladium gives mainly 2,6-dimethyloctane (≈95%), rhodium produces 2,6-dimethyloctane with a yield higher than 40%, and around 40% of 2,6-dimethyloct-2-ene, while ruthenium gives around 10% of 2,6-dimethyloctane and 50% of 2,6-dimethyloct-2-ene leaving the highest amount of unreacted β-myrcene. The Pd catalyst is highly active with an excellent selectivity in enabling the one-pot synthesis of 2,6-dimethyloctane through β-myrcene hydrogenation in the presence of scCO2. The overall activity of the noble metal catalysts decreased in the order Pd > Rh > Ru. The problem of leaching of the active metal from the catalyst rod was also investigated.

Biofilm enhanced geologic sequestration of supercritical CO 2

In order to develop subsurface CO 2 storage as a viable engineered mechanism to reduce the emission of CO 2 into the atmosphere, any potential leakage of injected supercritical CO 2 (SC-CO 2) from the deep subsurface to the atmosphere must be reduced. Here, we investigate the utility of biofilms, which are microorganism assemblages firmly attached to a surface, as a means of reducing the permeability of deep subsurface porous geological matrices under high pressure and in the presence of SC-CO 2, using a unique high pressure (8.9 MPa), moderate temperature (32 °C) flow reactor containing 40 millidarcy Berea sandstone cores. The flow reactor containing the sandstone core was inoculated with the biofilm forming organism Shewanella fridgidimarina. Electron microscopy of the rock core revealed substantial biofilm growth and accumulation under high-pressure conditions in the rock pore space which caused >95% reduction in core permeability. Permeability increased only slightly in response to SC-CO 2 challenges of up to 71 h and starvation for up to 363 h in length. Viable population assays of microorganisms in the effluent indicated survival of the cells following SC-CO 2 challenges and starvation, although S. fridgidimarina was succeeded by Bacillus mojavensis and Citrobacter sp. which were native in the core. These observations suggest that engineered biofilm barriers may be used to enhance the geologic sequestration of atmospheric CO 2.

Dynamic rheology and microstructure of polypropylene/clay nanocomposites prepared under Sc-CO 2 by melt compounding

Polypropylene (PP)/clay nanocomposites were prepared using a twin-screw extruder with the aid of supercritical carbon dioxide (Sc-CO 2). The dynamic rheological properties were measured using a rheometer in the oscillatory mode. X-ray diffraction and transmission electron microscopy were used to characterize the microstructure of extruded nanocomposites. Results showed that an optimized CO 2 concentration existed. When the CO 2 concentration increased up to the optimized level, the nanocomposites tended to be more viscous, especially at low frequency, whereas further increasing the CO 2 concentration resulted in a decrease in the complex viscosity and dynamic moduli. The presence of Sc-CO 2 with a concentration not higher than the optimized level was helpful to promote the degree of dispersion of the nano-clay in PP matrix, but overloading of CO 2 would have a negative effect on the clay dispersion.

Preparation of Budesonide-Poly (Ethylene Oxide) Solid Dispersions Using Supercritical Fluid Technology

The purpose of this study was to investigate the possibility of preparing solid dispersions of the poorly soluble budesonide by supercritical fluid (SCF) technique, using poly (ethylene oxide) (PEO) as a hydrophilic carrier. The budesonide-PEO solid dispersions were prepared, using supercritical carbon dioxide (SC CO2) as the processing medium, and characterized by scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), solubility test and dissolution test in order to understand the influence of the SCF process on the physical status of the drug. The endothermic peak of budesonide in the SCF-treated mixtures was significantly reduced, indicating that budesonide was in amorphous form inside the carrier system. This was further confirmed by SEM and PXRD studies. The enhanced dissolution rates of budesonide were observed from SCF-treated budesonide-PEO mixtures. The amorphous characteristic of the budesonide, the better mixing of drug and PEO powders in the presence of SC CO2, together with the improved wettability of the drug in PEO, produced a remarkable enhancement of the in vitro drug dissolution rate. Thus, budesonide-PEO solid dispersions with enhanced dissolution rate can be prepared using organic solvent-free SCF process.

Transesterification reaction catalysed by Novozym 435 in supercritical carbon dioxide

Transesterification reaction between a substrate having two functional groups (ethylene glycol) with ethyl acetate in the presence of lipase Novozym 435 was carried out to study the effect of supercritical CO 2 (scCO 2) on the conversion and selectivity of the reaction. It was demonstrated that in the presence of scCO 2 the equilibrium conversion could be considerably higher than that in the absence of scCO 2. scCO 2 could also enhance the selectivity of ethylene glycol monoacetate (EGMA) and suppress the formation of ethylene glycol diacetate (EGDA), and selectivity could be tuned by CO 2 pressure.

Enhanced crystallization of bisphenol-A polycarbonate by nano-scale clays in the presence of supercritical carbon dioxide

The crystallization behavior of bisphenol-A polycarbonate (PC) and PC/clay nanocomposites were studied in the presence of supercritical carbon dioxide (SCCO 2) using DSC, WAXD and AFM. In the absence of SCCO 2, nano-scale clay itself does not change the crystallization behavior of PC under our experimental conditions. In the presence of SCCO 2, clay appears to be an efficient nucleating agent and enhances the crystallization of PC. The addition of clay reduces the induction time of crystallization and increases the crystallization rate. The increase in crystallinity with clay depends on the crystallization time. When the crystallization time is sufficient, PC and PC/clay composites tend to have similar crystallinity in the range of 26%. Two melting temperatures are observed during the DSC heating scan, and are mainly associated with the melting of both secondary and primary crystals. Results show that the clay influences the primary crystallization process more than the secondary crystallization process.

Effect of supercritical carbon dioxide on the diffusion coefficient of phenol in poly(bisphenol A carbonate)

AbstractFor some polymers, the rate of solid‐state polymerization (SSP) is higher with supercritical carbon dioxide (scCO2) as the sweep gas than with atmospheric N2. One explanation for this higher rate is that the diffusion coefficient of the condensate molecule is higher in the CO2‐swollen polymer. To investigate this hypothesis, we measured the diffusion coefficient of phenol in poly(bisphenol A carbonate) (BPA‐PC) by carrying out SSP of this polymer under diffusion‐limited conditions. Under these conditions, the diffusion coefficient of the condensate molecule could be calculated from the profile of the molecular weight versus time. The phenol diffusivity was determined between 135 and 180 °C in the presence of N2 at about 1 bar and in the presence of scCO2 at about 138, 207, and 345 bar. The diffusion coefficient of phenol was up to 200% higher in scCO2 than in N2, depending on the temperature and CO2 pressure. With both N2 and scCO2, the activation energy for phenol diffusion in BPA‐PC was larger than the activation energy for the reaction between hydroxyl and phenyl end groups that occurred during SSP of BPA‐PC. As a result, the overall SSP reaction shifted from diffusion control at low temperatures toward chemical‐reaction control at high temperatures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1143–1156, 2003

Intercalated Polymer Nanocomposites Prepared in Supercritical Carbon Dioxide.

ABSTRACTAn alternative route to prepare polymer-clay nanocomposites using supercritical carbon dioxide (scCO2) is described. The presence of clay nanoparticles significantly influences the morphology, foaming process and crystallization of a polymer when processed in scCO2. Intercalated structures are successfully produced in the presence of scCO2 even when favorable interactions between the polymer and the clay are not present. The effect of scCO2 on the intercalation process is analyzed for a variety of polymer systems both with modified and unmodified clays. By controlling the hydrophilicity of the polymer and clay systems, specific understanding of the effect of scCO2 on the structure and morphology of the nanocomposites is obtained. Experimental results show significant increases in the clays d-spacings for scCO2-treated samples. This behavior is consistent regardless of the nature of the polymer, showing significant amounts of intercalation even in purely hydrophobic polymers.

Generation of microcellular foams of PVDF and its blends using supercritical carbon dioxide in a continuous process

Use of supercritical carbon dioxide (scCO 2) as a blowing agent to generate microcellular polymer foams (MPFs) has recently received considerable attention due to environmental concerns associated with conventional organic blowing agents. While such foams derived from amorphous thermoplastics have been previously realized, semicrystalline MPFs have not yet been produced in a continuous scCO 2 process. This work describes the foaming of highly crystalline poly(vinylidene fluoride) (PVDF) and its blends with amorphous polymers during extrusion. Foams composed of neat PVDF and immiscible blends of PVDF with polystyrene exhibit poor cell characteristics, whereas miscible blends of PVDF with poly(methyl methacrylate) (PMMA) yield foams possessing vastly improved morphologies. The results reported herein illustrate the effects of blend composition and scCO 2 solubility on PVDF/PMMA melt viscosity, which decreases markedly with increasing PMMA content and scCO 2 concentration. Morphological characterization of microcellular PVDF/PMMA foams reveals that the cell density increases as the PMMA fraction is increased and the foaming temperature is decreased. This study confirms that novel MPFs derived continuously from semicrystalline polymers in the presence of scCO 2 can be achieved through judicious polymer blending.

Synthesis of controlled‐release products in supercritical medium

AbstractControlled‐delivery products have recently received considerable attention. They prolong the drug's therapeutic effect, keeping its concentration between the therapeutic and toxicity limit. The final product must be free of residual solvent, even with nontoxic solvents, to provide its constant property that does not change with natural evaporation of the solvent. A major cost item in the synthesis of controlled‐release drugs is to remove this solvent to acceptable limits. To eliminate the production step involving the organic solvent from the overall process, the drug was introduced into the polymer matrix using supercritical carbon dioxide (scCO2) as the carrier solvent and swelling agent. This study focuses on the impregnation of a biodegradable polymer matrix with 5‐fluorouracil for chemotherapy and β‐estradiol estrogen hormone therapy. Swelling of the polymer matrix, solubility of drug components in scCO2 and the adsorption isotherm/partition coefficients in the presence of scCO2 were studied. To investigate the single‐component supercritical adsorptive synthesis of controlled‐delivery products, accurate experimental techniques to measure drug‐component solubilities in supercritical fluids and adsorption isotherms in the presence of supercritical fluids were developed. Solubility data of these drugs in scCO2 at 35–55°C and 101–220‐bar were reported. The adsorption equilibrium constants/partition coefficients were presented for these drug components on poly‐dl‐lactide‐co‐glycolide (PLGA) at the same conditions. To understand the effect of operating variables on the total drug loading and to predict the drug‐loading breakthroughs, a flow over a flat plate model was developed that accounts for the polymer swelling, the partitioning of the drug component between the supercritical and polymer phases, and the polymer diffusivity. Experimental isotherm data with and without the polymer were incorporated into the model to isolate the system response from the polymer response to determine impregnation efficiencies.

Enhanced Miscibility of Low-Molecular-Weight Polystyrene/Polyisoprene Blends in Supercritical CO2

While ongoing efforts continue to explore the high-pressure phase equilibria of polymer blends, few studies have attempted to address the impact of a supercritical (sc) fluid on such equilibria. In this work, we report on the phase behavior of an upper critical solution temperature (UCST) polymer blend in the presence of supercritical carbon dioxide (scCO2), a nonselective plasticizing agent. Blends composed of low-molecular-weight polystyrene and polyisoprene have been examined as a function of temperature in scCO2 by visual inspection, small-angle neutron scattering, and spectrophotometry. In the presence of scCO2, the cloud point temperature is depressed by as much as 28 °C, depending on both blend composition and CO2 pressure. Complementary studies performed with nitrogen decouple the plasticization efficacy of CO2 from free-volume compression due to hydrostatic pressure. Existence of a pressure yielding a maximum in CO2-induced cloud point depression is established. These results provide evidence for enhanced polymer miscibility as a result of the plasticizing effectiveness and tunable solubility of scCO2.