Presence Of scCO2 Research Articles

Characterization of phase structures of a supercritical water/supercritical carbon dioxide/heavy oil system with molecular dynamics simulations

In this work, phase structures of a supercritical water (SCW)/supercritical carbon dioxide (scCO2)/heavy oil system are evaluated and characterized by performing molecular dynamics (MD) simulations. The MD simulation processes are initialized with structures of an oil droplet-in-SCW + scCO2 mixture, and its resultant structure, radial distribution function (RDF), solvation free energy, and cohesive energy density (CED) were then integrated to analyze the simulation results. The SCW and scCO2 are found to disperse into the oil drop and induce the oil swelling through stretching the oil molecules. Both saturates and aromatics can be easily dissolved in an SCW + scCO2 mixture due to the attractive interaction between them, whereas resins and asphaltenes are intended to conduct self-assembly due to their repulsion to the SCW + scCO2 mixture and high CED, resulting in a pseudo-one phase structure of an SCW/scCO2/heavy oil system. The presence of scCO2 can enhance the miscibility of heavy oil with an SCW + scCO2 mixture through intensifying the affinity between heavy oil and solvent(s) as well as destroying the hydrogen bonds by diluting the SCW. Elevating temperature is adverse to the miscible process between heavy oil with an SCW + scCO2 mixture on account of the reduced density of such a mixture. A moderate increase in pressure facilitated dissolution of heavy oil in an SCW + scCO2 mixture; however, an excess increase in pressure can lead to a suppressed miscibility between heavy oil and an SCW + scCO2 mixture since the hydrogen bonding is significantly recovered.

Preparing low-Density microcellular polystyrene foam by in-Situ fibrillated PTFE and supramolecular nucleator TMC-300 in the presence of sc-CO2

A method using in-situ fibrillated polytetrafluoroethylene (PTFE) and octamethylenedicarboxylicdibenzoylhydrazide (TMC-300) supramolecular nucleator was presented to prepare low density polystyrene foams. This study used a torque rheometer in the molten compound preparation of PS/fibrillated-PTFE/TMC-300 composites. Scanning electron microscopy showed in-situ fibrillated polytetrafluoroethylene in Polystyrene melt and a nanofiber network with high aspect ratio. The formation of nanometer-sized fiber networks improved the melt viscoelasticity of matrices which promoted cell nucleation. As the results demonstrated, low-density foams with 11 μm average cell size were obtained using Polystyrene. The self-assembly nucleating agent TMC-300 was then introduced to the composite materials. TMC-300 and polytetrafluoroethylene as a composite cell nucleating agent were used in Polystyrene foams. Meanwhile, their nucleating efficiency was investigated. TMC-300 completed self-assembly in Polystyrene and served as composite nucleating agent in combination with polytetrafluoroethylene. Compared with the sample PS/PTFE-0.5, the average cell size of the sample PS/PTFE-0.5/TMC-2 had a reduction rate of 28.16% from 12.18 μm to 8.75 μm. The cell density increased by an order of magnitude. The composite nucleating agent was successful in controlling Polystyrene foam cell morphology, thus leading to the preparation of low-density Polystyrene microporous foams.

Impact of organic solutes on capillary phenomena in water-CO2-quartz systems

Hypothesis: The migration of supercritical CO2 (scCO2) injected into underground reservoirs as part of carbon capture and storage is influenced by organic contamination affecting mineral wettability. Molecular dynamics (MD) simulations of relevant systems that incorporate representative organic solutes allow detailed investigation of changes in fundamental interfacial and capillary properties. Experiments: We use MD simulations to explore the effects of four organic solutes (quinoline, decanoic acid, coronene, sorgoleone) on the wettability of quartz by water in the presence of scCO2. We examine the impacts of polar, alkyl, and aromatic moieties as well as fluid flow velocity at elevated temperatures and pressures. Findings: Organic molecules accumulate at the water-CO2 interface, where they distribute according to their size and functional groups. Certain organics penetrate the adsorbed water film at the quartz-CO2 interface, revealing two modes of hydrogen bonding between polar organic functional group, water, and quartz surface –OH groups. Interfacial energies and contact angles are minimally impacted by organic adsorption at the water-CO2 interface, possibly due to simultaneous CO2 desorption. Non-equilibrium MD simulations reveal that flow-induced redistribution of organic compounds modulates the radii of curvature of the advancing and receding water-CO2 interfaces. Our results indicate that organic adsorption on water surfaces is likely ubiquitous during multi-phase flow in soils and sedimentary rocks, with implications for the mobilization and transport of organic compounds.

WO3–SiO2 nanomaterials synthesized using a novel template-free method in supercritical CO2 as heterogeneous catalysts for epoxidation with H2O2

A series of tungsten oxide-silica (WO3–SiO2) composite nanomaterials were synthesized through a novel, template-free sol-gel method, in which supercritical-CO2 (scCO2) was utilized as synthesis medium. The efficacy of the synthesis method stems from a tailored reactor design that allows the contact of the reactants only in the presence of scCO2. Selected synthetic parameters were screened with the purpose of enhancing the performance of the resulting materials as heterogeneous catalysts in epoxidation reactions with H2O2 as environmentally friendly oxidant. A cyclooctene conversion of 73% with epoxide selectivity of > 99% was achieved over the best WO3–SiO2 catalyst under mild reaction conditions (80 °C), equimolar H2O2 amount (1:1) and low WO3 loading (~2.5 wt%). The turnover number achieved with this catalyst (TON = 328), is significantly higher than that of a WO3–SiO2 prepared via a similar sol-gel route but without supercritical CO2, and that of commercial WO3. A thorough characterization with a combination of techniques (ICP-OES, N2-physisorption, XRD, TEM, STEM-EDX, SEM-EDX, FT-IR and Raman spectroscopy, XPS, TGA and FT-IR analysis of adsorbed pyridine) allowed correlating the physicochemical properties of the WO3–SiO2 nanomaterials with their catalytic performance. The high catalytic activity was attributed to: (i) the very high surface area (892 m2/g) and (ii) good dispersion of the W species acting as Lewis acid sites, which were both brought about by the synthesis in supercritical CO2, and (iii) the relatively low hydrophilicity, which was tuned by optimizing the tetramethyl orthosilicate concentration and the amount of basic solution used in the synthesis of the materials. Our optimum catalyst was also tested in the reaction of cyclohexene with H2O2, resulting in cyclohexane diol as main product due to the presence of strong Brønsted acid sites in the catalyst, whereas the reaction with limonene yielded the internal epoxide as the major product and the corresponding diol as side product. Importantly, the catalyst did not show leaching and could be reused in five consecutive runs without any decrease in activity.

Dispersion Polymerization of Methyl Methacrylate in Supercritical CO2: A Preliminary Evaluation of In Situ Incorporation of Copaiba Oil

In-situ dispersion polymerization of methyl methacrylate (MMA) in the presence of scCO2 is investigated as an alternative technique to load copaiba (Copaifera ssp.) oil in poly (methyl methacrylate...

Effect of supercritical carbon dioxide over the esterification of levulinic acid with ethanol using montmorillonite K10 as catalyst

Alkyl levulinates are green chemicals that have the ability to modify physical properties of both gasoline and diesel, which makes their use as fuel additives of great importance. An interesting route for their production is the ethyl esterification using solid catalysts, which still needs improvement. The use of supercritical CO2 (scCO2) as solvent may enhance the reaction yield, in such a way that the objective of this work was to combine the use of a solid catalyst (montmorillonite K10) and scCO2 to achieve the esterification of levulinic acid to obtain ethyl levulinate. Moreover, understanding the relationship between the amount of CO2, reactants and the catalyst can be a key to determine how scCO2 works in this type of reaction. The results obtained after a systematic study have shown that the combined effect of scCO2 and montmorillonite K10 allow the obtainment of 90.9 % of conversion after 126 min of reaction at 180 °C, with a molar ratio of 6:1 and 10 wt% of catalyst, while reactions performed using the same conditions and without scCO2 provided 82.9 % of conversion after 138 min. Furthermore, the presence of scCO2 also helped montmorillonite K10 to retain its catalytic activity after 4 reuse cycles, while under the absence of scCO2, a decrease in the levulinic acid conversion was already observed in the first reuse cycle. The results presented in this work are a step further for the use of montmorillonite K10 along with scCO2 in industrial scale.

An Investigation of CO2-Responsive Preformed Particle Gel for Conformance Control of CO2 Flooding in Reservoirs With Fractures or Fracture-Like Channels

Summary Gel treatment is an important technique to solve early CO2 breakthrough and excess–CO2–production problems, caused by the low viscosity and low density of CO2, as well as the heterogeneity of reservoirs with fractures or fracture–like channels. However, there is no reported work on gel that increases its volume after reacting with CO2 (termed CO2–responsive gel) for the conformance control of CO2 flooding. In this paper, the intrinsic properties of a CO2–responsive preformed particle gel (CR–PPG) were evaluated in a water/supercritical–CO2 (scCO2) environment in high–pressure vessels. Continuous scCO2 injection and CR–PPG treatment were conducted in fractured sandstone cores, to probe their plugging performance to scCO2 flow in a high–permeability–contrast system. The volumetric swelling ratio (VSR) of the CR–PPG increased by approximately two times in the presence of scCO2, compared with a sample under similar conditions in the absence of scCO2. The CR–PPG swelling ratio decreased with increasing NaCl concentration. Under the same conditions, the temperature did not have an apparent effect on the swelling ratio after 31 days of swelling. In coreflooding experiments, the placed CR–PPG resisted a considerable pressure up to 617.0 psi before breakthrough. After a shut–in process, CO2–breakthrough pressure was detected at 437.2 psi. It is observed that the shut–in process improved the plugging performance of CR–PPG to CO2 as revealed by the increase in the residual resistance factor. Controlling the shut–in time was found to be effective in augmenting the increase in the residual resistance factor, by increasing the VSR of placed CR–PPG. Resistance of CR–PPG to some real field challenges, including a high pressure gradient and long–term exposure to CO2, was also reported for field–applicability concerns.

Geochemical reactions of Na-montmorillonite in dissolved scCO2 in relevance of modeling caprock behavior in CO2 geological storage

One of the challenges of the present century is to limit the greenhouse gas emissions for the mitigation of climate change which is possible for example by a transitional technology, CO2 geological storage. Clay minerals are considered to be responsible for the low permeability and sealing capacity of caprocks sealing off stored CO2. However, their reactions are not well understood for complex simulations. This work aims to create a kinetic geochemical model of Na-montmorillonite standard SWy-2 supported by solution and mineral composition results from batch experiments. Such experimentally validated numerical models are scarce. Four 70-hours experiments have been carried out at atmospheric conditions, and with CO2 supercritical phase at 100 bar and 80 °C. Solution samples have been taken during and after experiments and their compositions were measured by ICP-OES. The treated solid phase has been analyzed by XRD and ATR-FTIR and compared to in-parallel measured references (dried SWy-2). Kinetic geochemical modelling of the experimental conditions has been performed by software PHREEQC. Experiments and models show fast reactions under the studied conditions and increased reactivity in presence of scCO2. Solution composition results cannot be described by the change of the uncertain reactive surface area of mineral phases. By considering the clay standard’s cation exchange capacity divided proportionally among interlayer cations of Na-montmorillonite, the measured variation can be described on an order of magnitude level. It is furthermore indicated that not only the interlayer cations take part in this process but a minor proportion of other, structural ions as well, differently in the reference and scCO2 environments.

Supercritical Fluid Extractive Regeneration of the Ion-Exchange Catalyst KU-2FPP

The process of supercritical fluid extractive regeneration of the ion-exchange catalyst KU-2FPP was studied. The use of pure supercritical carbon dioxide (SC-CO 2 ) and the one modified with a polar additive (H 2 O) as the extractant in the process at T = 383÷393 K and P = 15÷25 MPa provided an effective removal of non-polar organic compounds and the occurrence of the side carboxylation reaction to form dialkylphthalate. The side reaction was supposed to bear responsibility for the ineffective regeneration in the presence of SC-CO 2 as the extractant. The application of supercritical propane-butane mixture as the extractant (T = 393 K, P = 10÷15 MPa) allowed the catalyst activity to be restored to the level appropriate for the industrial application.

Controlled Formation of Hierarchical Metal–Organic Frameworks Using CO2-Expanded Solvent Systems

It is shown that a crystalline metal–organic framework (HKUST-1) can be rapidly synthesized from a DMSO/MeOH solution with greatly reduced amounts of organic solvents using a supercritical CO2 (scCO2) solvent expansion technique. The precursor solution is stable for months under ambient conditions, and CO2-driven MOF (metal–organic framework) crystallization is achieved under mild conditions (40 °C, 40–100 bar) with excellent reproducibility. As the degree of liquid-phase expansion drives MOF nucleation and growth, the crystallite size and overall yield can be tuned by adjusting the CO2 pressure. Furthermore, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and gas sorption analyses showed that, in the presence of scCO2, HKUST-1 crystallites with a hierarchical pore structure are generated through a postcrystallization etching process. These findings demonstrate that scCO2 is a time- and material-efficient route to MOF synthesis with a high level of control ov...

A novel route to the generation of porous scaffold based on the phase morphology control of co-continuous poly(ε-caprolactone)/polylactide blend in supercritical CO2

Three-dimensional porous polylactide (PLA) scaffolds of almost fully interconnected pores were successfully prepared by extracting the poly(ε-caprolactone) (PCL) phase from co-continuous PCL/PLA blends. Quiescent annealing of the blends in supercritical CO2 (scCO2) prior to the PCL extraction, reported for the first time in this paper, allowed control over the average pore size from 50 to 150 μm of the PLA scaffolds. It was found that the PCL/PLA blend underwent a significant coarsening process in scCO2 under proper condition, which indicated that the CO2 pressure adjustment could be used as an additional effective tool for morphology control and the scaffold structure could be tailored by careful control of annealing time, temperature and CO2 pressure. Moreover, the structure of the blend could be changed at a relative low temperature in the presence of scCO2, this fact added the advantage over the conventional melt-processed treatment, as minimizing the degradation of PLA to maintain the mechanical properties of the scaffolds. A porous PLA scaffold was used to study the NIH 3T3 fibroblast cell culture and the cells successfully proliferated in the scaffold, which suggested biocompatibility and high potential of this scaffold being used in tissue engineering application.

Influence of Supercritical CO2 on the Mobility and Desorption of Trace Elements from CO2 Storage Rock Sandstone and Caprock Shale in a Potential CO2 Sequestration Site in Taiwan

ABSTRACTExcess carbon dioxide emission was considered as the most important cause of increased trend of global warming. Significant amounts of research were devoted to the reduction of CO2 emission and CO2 sequestration. Sequestration of CO2 in empty oil reservoirs was considered as one of the most promising options. However, the effects of metal release and mobility as a result of CO2 injection were not studied in detail, particularly under super-critical CO2 (scCO2) conditions. In this study, the release of selected metals immersed in distilled water for varying amounts of time in the absence and presence of scCO2 was assessed in simulated conditions at 90°C and 24 MPa. Significant increases in dissolution of Fe, Sr, and Ba by 3, 8, and 24 times were found when the storage rock sandstone or caprock shale was immersed in DI water for different time period. However, in the presence of scCO2, the dissolution of these metals was reduced by 80% for Fe, suggesting permanent sequestration of scCO2 into carbonate minerals. The trend in changes of pore water chemistry in the sandstone and shale after being immersed in DI water showed dissolution of Sr-bearing mineral and precipitation of Ba-bearing mineral.

Micronization, characterization and in-vitro dissolution of shellac from PGSS supercritical CO2 technique

The purpose of this investigation was to determine whether shellac, a naturally occurring material with enteric properties, could be processed in supercritical CO2 (sc-CO2) using the particles from gas saturated solution (PGSS) process and how process parameters affect the physico-chemical properties of shellac. In-situ attenuated total reflection fourier transform infra-red (ATR-FTIR) spectroscopy showed that CO2 dissolves in shellac with solubility reaching a maximum of 13% (w/w) at 300bar pressure and 40°C and maximum swelling of 28%. The solubility of sc-CO2 in shellac allowed for the formation of porous shellac structures of which the average pore diameter and pore density could be controlled by adjustment of operating pressure and temperature. In addition, it was possible to produce shellac microparticles ranging in average diameter from 180 to 300μm. It was also shown that processing shellac in sc-CO2 resulted in accelerated esterification reactions, potentially limiting the extent of post-processing “ageing” and thus greater stability. Due to additional hydrolysis reactions enhanced by the presence of sc-CO2, the solubility of shellac at pH 7.5 was increased by between 4 and 7 times, while dissolution rates were also increased. It was also shown that the in-vitro dissolution profiles of shellac could be modified by slight adjustment in operating temperatures.

Green synthesis and catalytic hydrogenation in clean and green solvents

Supercritical carbon dioxide (scCO 2 ) as a green solvent has a characteristic feature that is tunable chem-physical properties, which is incomparable by the conventional organic solvents. For example, its viscosity, density, coefficient of mass and heat transfer, dielectric constant can be adjusted by altering pressure or temperature slightly near the supercritical point. The material synthesis and catalysis reaction in green solvent of scCO 2 have been paid more attention, and achieved some progresses in these years. Catalytic hydrogenation is one of the most prospective reactions in scCO 2 . We have made a wide study on the selective hydrogenation reactions in scCO 2 , and some interesting results have been obtained, such as hydrogenation of unsaturated aldehydes, hydrogenation of benzoic ring of benzoic acid and phenol, hydrogenation of maleic anhydride and the nitro-compounds. The reaction rates of these reactions increase significantly with increasing the pressure of CO 2 , and the product selectivities depend on the CO 2 pressure also. My group focuses our study on the new advancements and new situations of the catalysis hydrogenation in scCO 2 , discuss or reveal the effects of CO 2 pressure on reaction rate and product selectivity as well as the influencing mechanism. Moreover, we also investigate the nanomateirals synthesis in the presence of scCO 2 , and pay more attention to the forming process of the metal oxides and metal nanoparticles.

Electrochemical fixation of CO2 to organohalides in room-temperature ionic liquids under supercritical CO2

The electrochemical properties of novel reaction media, ionic liquid (IL)/supercritical CO2 (scCO2) systems, were evaluated and the electrochemical carboxylation of various organohalides in these systems was demonstrated. Voltammetric studies revealed that the CO2 solubility in an IL such as N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis(trifluoromethanesulfonyl) imide ([DEME][TFSI]) increased in the presence of scCO2. The IL/scCO2 systems were found to be effective for the electrochemical carboxylation of various organohalides.

Comparison Study on CO2-Promoted Crystallization and Melting Behavior of Polypropylene: Homopolymer and Copolymers

Three types of polypropylene, namely propylene homopolymer (HPP), block copolymer of propylene with ethylene (CPP-B) and random copolymer of propylene with ethylene (CPP-R), were melted and isothermally crystallized in a self-designed vessel under supercritical carbon dioxide (Sc-CO2) atmosphere. The melting behavior and crystalline forms of crystallized samples were investigated using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The results showed that the presence of Sc-CO2 could improve the crystallinity for all three polypropylenes, and the promoting effect was more obivious with increasing CO2 pressure. In addition, it was observed that γ-crystals could be obtained in the CPP-B and CPP-R samples crystallized under Sc-CO2, while no γ-crystals were formed in HPP under the given conditions. The relative content of γ-crystals obtained in CPP-R samples was much higher than that of CPP-B, and 100% γ-phase could be formed in the CPP-R sample when subjected to 14 MPa Sc-CO2.

Electrodeposition of high phosphorus Ni–P alloys in emulsified supercritical CO2 baths

The use of an emulsified supercritical CO2 (sc-CO2) bath for electrodeposition of Ni–P alloys was attempted. The material characteristics of the deposits with various P contents, formed by varying the electrolyte composition and deposition current density, were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) for surface morphology and chemical composition and crystal structure analyses. The experimental results showed that the presence of sc-CO2 in the electrodeposition bath could substantially improve the microhardness and the corrosion performance of the as-deposited Ni–P coatings. The roles of phosphorus and carbon in modifying the material properties of the deposits are discussed in detail.

Characterization and supercritical CO2 devulcanization of cryo-ground tire rubber: Influence of devulcanization process on reclaimed material

Abstract Ground truck-tire rubber (GTR) was characterized and subsequently devulcanized in supercritical CO 2 (scCO 2 ) in the presence of Diphenyl Disulfide (DD) as devulcanizing agent. Temperature and pressure were kept respectively at 180 °C and 15 MPa and the ratio between rubber and DD was 10 wt %. The treatment effect on the properties of GTR was widely studied. The reached degree of devulcanization was about 50% with a low amount of sol fraction. The results display that the treatment with the DD in presence of scCO 2 reduces the crosslink density of the GTR, increasing the property of the gel fraction and the compatibility of this material with the raw rubber. The suitability of the devulcanized GTR to be reemployed in new tire blends was investigated through the final mechanical properties. The unreacted DD can strongly affect the revulcanization process and the mechanical properties of the blends containing devulcanized rubber, resulting the only limiting factor for the application of this devulcanization process.

Performance of two immobilized lipases for interesterification between canola oil and fully-hydrogenated canola oil under supercritical carbon dioxide

The performance and stability of Lipozyme RM IM and TL IM for the interesterification between canola oil and fully-hydrogenated canola oil (FHCO) in the presence of SCCO2 were studied using a high pressure batch stirred reactor at 65 °C/17.5 MPa. The influence of exposure time (4, 8, and 12 h) in SCCO2 and pressurization/depressurization cycles of up to 12 times on the enzyme's resultant activity were studied. There was no significant difference (p > 0.05) in the performance of the two enzymes over reaction time, reaching a constant degree of interesterification of about 23% after 2 h. Although FE-SEM images illustrated some morphological changes on the surface of the enzymes after 4 cycles of 7 h each, similar degrees of interesterification were achieved after each cycle. However, the amount of reaction intermediates decreased by 50–60% in the product obtained by using SCCO2-treated enzymes after 12 pressurization/depressurization cycles compared to untreated enzymes, while there were no significant changes in the conformational and morphological structure of the treated enzymes based on FTIR and FE-SEM analysis. Findings enhance our understanding of enzymatic conversions of lipids under high pressure CO2, targeting production of base-stock for zero-trans margarines.

Relative permeability hysteresis and capillary trapping characteristics of supercritical CO2/brine systems: An experimental study at reservoir conditions

We present the results of an experimental study on the effects of hysteresis on capillary trapping and relative permeability of CO2/brine systems at reservoir conditions. We performed thirty unsteady- and steady-state drainage and imbibition full-recirculation flow experiments in three different sandstone rock samples, low- and high-permeability Berea and Nugget sandstones. The experiments were carried out at various flow rates with both supercritical CO2 (scCO2)/brine and gaseous CO2 (gCO2)/brine fluid systems. The unsteady-state experiments were carried out with a wide range of flow rates to establish a broad range of initial brine saturations (Swi). This allowed investigation of the sensitivity of residual trapped CO2 saturation (SCO2r) to changes in Swi. The values were successfully compared with those available in the literature. For a given Swi, the trapped scCO2 saturation was less than that of gCO2 in the same sample. This was attributed to brine being less wetting in the presence of scCO2 than in the presence of gCO2. Post-imbibition dissolution of trapped CO2 and formation of dissolution front was also investigated. During the steady-state experiments, scCO2 and brine were co-injected with monotonically increasing or decreasing fractional flows to perform drainage and imbibition processes. We carried out seven sets of steady-state flow tests with various trajectories generating a comprehensive group of relative permeability hysteresis curves. The scanning curves revealed distinct features with potentially important implications for storage of scCO2 in geological formations. For both series of experiments, the ratio of SCO2r to initial CO2 saturation (1- Swi) was found to be much higher for low initial CO2 saturations. The results indicate that very promising fractions (about 49 to 83%) of the initial CO2 saturation can be stored through capillary trapping.