Increasing CO2 Pressure Research Articles

Synthesis of TiO2-polymer nanocomposite in supercritical CO2 via RAFT polymerization

Polymer chains of PMMA were grown from nano titania (n-TiO2) spherical surfaces by the Reversible Addition Fragmentation Chain Transfer Polymerization process (RAFT) using the green solvent, supercritical carbon dioxide (scCO2). The RAFT agent (1), 4-cyano-4-(dodecylsulfanylthiocarbonylsulfanyl)pentanoic acid, with an available carboxyl group was first coordinated to the n-TiO2 surface, with the SC(SC12H25) moiety subsequently used for RAFT polymerization of MMA to form the n-TiO2/PMMA nanocomposites. The livingness of polymerization was verified using GPC, while the morphology of the nanocomposites was studied using thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and dynamic light scattering (DLS). The rate of polymerization and molecular weights at different pressures in scCO2 and in non-pressurized and pressurized organic solvent (THF) were compared, showing that increased CO2 pressure provided a higher rate of polymerization and longer chain lengths indicating the utility of this approach.

Carbon dioxide‐induced crystallization in poly(L‐lactic acid) and its effect on foam morphologies

AbstractThe effect of carbon dioxide (CO2) on the physical properties of poly(L‐lactic acid) (PLLA) and on the formation of crystalline domains was investigated. The presence of CO2 in the matrix was found to induce crystallization in PLLA, with the crystallinity increasing with increasing CO2 pressure. The combination of saturation conditions and formation of crystalline domains was studied for its effect on the formation of porous morphologies in PLLA. Moreover, the effect of CO2 on PLLA properties and formation of porous structures was further exploited by first creating crystalline domains in samples using CO2 at various pressures at 25 °C and then re‐saturating the same samples with CO2 at a constant pressure of 2.8 MPa and 0 °C. This paper reports on the solubility of CO2 at 25 and 0 °C in PLLA, crystallization and subsequent effect on foam morphologies when processed using different saturation cycles. Unique and intriguing morphologies were obtained by specifically controlling the properties of PLLA. Copyright © 2010 Crown in the right of Canada. Published by John Wiley & Sons, Ltd

Effect of supercritical CO2 on three‐dimensional colloid arrays of PS‐MA–EGDMA

AbstractUsing emulsifier‐free emulsion polymerization method, monodispersed crosslinked poly(styrene‐co‐methacrylic acid‐co‐ethylene glycol dimethacrylate) colloid microspheres were synthesized. The microspheres were treated in supercritical carbon dioxide (SCCO2) after they have self‐assembled into ordered three‐dimensional (3D) colloid arrays. The CO2 absorbed into the polymer microspheres enhances chain segments mobility and reduces the glass transition temperature (Tg) of polymer, which induce the microspheres coalesce at the relatively low temperature. The coalescence degree of microspheres was studied by varying the experimental temperature, pressure, and exposure time in SCCO2. The results were shown by scanning electron microscopy (SEM). Further, the lattice spacing of the assembled 3D colloid microspheres was calculated from the SEM images. It was illustrated that the coalescence degree enhanced with the increase of CO2 pressure; however, this tendency became weak when CO2 pressure reached a certain value. Extending exposure time in SCCO2 or elevating temperature can also increase coalescence degree, and the effect of temperature is more significant. It is believed that these results will make sense when the polymer microspheres are considered to be used as templates in SCCO2; meanwhile, it raises a new method about tuning the final morphology of the stabilized colloidal crystals and porous materials via controlling the coalescence degree with the assistance of SCCO2. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Achievement of a Homogeneous Phase in Ternary Ionic Liquid/Carbon Dioxide/Organic Systems

A few years ago, it was found that carbon dioxide (CO2) is able to induce in ternary ionic liquid (IL) + organic systems, a “two-phase (L + V)−three-phase (L1 + L2 + V)−two-phase (L1 + L2)” transition by pressure increase. In the two liquid phase region (L1 + L2), one of the phases did not contain any IL. Therefore, the organic compound could be separated from the IL at increased CO2 pressure without any IL contamination. However, the occurrence of a homogeneous phase by further pressure increase, a so-called L1 + L2 → L transition, in the same systems was never observed before. Here, we demonstrate that in addition a third phase transition is possible upon further CO2 pressure increase, where the two liquid phases (L1 + L2) can be forced to form one homogeneous liquid phase (L). This phenomenon has promising implications for reactions and separations in systems using ILs.

Effect of operating conditions on the physical and chemical CO2 absorption through the PVDF hollow fiber membrane contactor

Porous polyvinylidene fluoride (PVDF) hollow fiber membranes were fabricated via a wet phase-inversion process and used in the gas–liquid membrane contactor for physical and chemical CO2 absorption. Effect of different operating parameters such as absorbent temperature, CO2 pressure, absorbent flow rate and long-term operation on the CO2 flux of the membrane were investigated. The characterization results showed that the prepared membrane possess small pore size with high surface porosity and wetting resistance, which are favorable for gas absorption application. Results of CO2 absorption experiments revealed that in case of physical absorption with distilled water, CO2 solubility was the key parameter which significantly affected the membrane CO2 flux. A significant increase in the CO2 flux was observed by increasing CO2 pressure and decreasing the absorbent temperature. However, in case of chemical absorption with NaOH (1 M), the reaction rate was dominant, where the CO2 flux was significantly increased by increasing the absorbent temperature. It was also found that when the liquid contacted the outer skin layer of the hollow fiber membrane, the operation was stable at the same gas and liquid pressure without bubble formation in the liquid phase. In addition, the results of long-term study demonstrated that the membrane performance was maintained constant for long-term operation. The initial flux reduction was found to be about 30% within the 23 h of physical absorption, and 20% of gradual reduction within 80 h of chemical absorption.

Rheological and Dielectric Behavior of Polyisoprene under Pressurized Carbon Dioxide

For a well-entangled polyisoprene (PI; molecular weight = 260k) equilibrated under pressurized carbon dioxide (CO2) at 25 °C, linear viscoelastic and dielectric data, respectively, were measured with a stress-controlled rheometer and a dielectric bridge being equipped with respective high-pressure cells. The viscoelastic and dielectric data shifted to higher frequencies with increasing CO2 pressure, indicating that the pressurized CO2 dissolved into PI thereby accelerating the global motion of PI. For those data at various CO2 pressure, time-CO2 pressure superposition held well and a single master curve was obtained, and the horizontal/vertical shift factors were consistent for the viscoelastic and dielectric data. These results indicated that the dissolved CO2 behaved just as an ordinal solvent to accelerate the global motion of PI as in ordinary solutions. In fact, the dynamic tube dilation (DTD) relationship between the viscoelastic and dielectric data, known to be valid for ordinary solutions/bulk of linear PI, was found to work also the PI/CO2 system, which confirmed the simple solvent role of the pressurized CO2 for the global motion of PI. Thus, the knowledge for ordinary polymer solutions would work for processing of polymer/CO2 systems.

Hydrogenation of nitrile in supercritical carbon dioxide: a tunable approach to amine selectivity

The use of supercritical carbon dioxide (scCO2) on the hydrogenation of benzonitrile was investigated over Pd and other metal catalysts. Without any additive, benzonitrile was hydrogenated to benzylamine with high conversion (90.2%) and selectivity (90.9%) using the Pd/MCM-41 catalyst. A strong influence of CO2 pressure on the conversion and selectivity were observed. As the CO2 pressure increases, the conversion was increased, and after reaching the maximum at around 8–10 MPa, it decreased. Moreover, simply by tuning the CO2 pressure, it is possible to obtain benzylamine or dibenzylamine. For instance, at lower pressure CO2 acts as a protecting agent, leading to the formation of the primary amine, but at higher pressure, the yield of primary amine as well as the solubility of the imine intermediate in CO2 increases, which results high selectivity for dibenzylamine. A plausible mechanism has been proposed to show the role of CO2 on the selectivity toward primary and secondary amines. The results confirm that the presence of CO2 is mandatory for the formation of benzylamine with high selectivity. Furthermore, the other reaction parameters, such as reaction time, H2 pressure, temperature etc., also affect the conversion as well as selectivity of benzylamine. This process has been extended to the hydrogenation of a series of different nitrile compounds.

Understanding Biphasic Ionic Liquid/CO2 Systems for Homogeneous Catalysis: Hydroformylation

A biphasic ionic liquid (IL) and compressed carbon dioxide system has a number of advantages for efficient homogeneous catalysis. The hydroformylation of 1-octene to nonanal catalyzed by a rhodium−triphenylphosphine complex was used as a model reaction to illustrate the effects of carbon dioxide in a biphasic ionic liquid/CO2 system using the model ionic liquid, 1-hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf2N]). Detailed phase equilibrium studies were conducted to determine volume expansion of the IL phase and the multiphase equilibria and mixture critical points between the reactant, product, and IL with CO2 and syngas (CO/H2). These data ultimately affect the concentration of the reactant and, thus, the apparent reaction rate. The viscosity of the IL with CO2 pressure was measured and demonstrates the dramatic decrease with increasing CO2 pressure. The self-diffusion coefficient of the ionic liquid and 1-octene were measured and indicate a large increase with CO2 pressure (so...

Capillary Pressure and Wettability Behavior of CO2 Sequestration in Coal at Elevated Pressures

SummaryEnhanced coalbed-methane (ECBM) recovery combines recovery of methane (CH4) from coal seams with storage of carbon dioxide (CO2). The efficiency of ECBM recovery depends on the CO2 transfer rate between the macrocleats, via the microcleats to the coal matrix. Diffusive transport of CO2 in the small cleats is enhanced when the coal is CO2-wet. Indeed, for water-wet conditions, the small fracture system is filled with water and the rate of CO2 sorption and CH4 desorption is affected by slow diffusion of CO2. This work investigates the wetting behavior of coal using capillary pressures between CO2 and water, measured continuously as a function of water saturation at in-situ conditions. To facilitate the interpretation of the coal measurements, we also obtain capillary pressure curves for unconsolidated-sand samples. For medium-and high-rank coal, the primary drainage capillary pressure curves show a water-wet behavior. Secondary forced-imbibition experiments show that the medium-rank coal becomes CO2-wet as the CO2 pressure increases. High-rank coal is CO2-wet during primary imbibition. The imbibition behavior is in agreement with contact-angle measurements. Hence, we conclude that imbibition tests provide the practically relevant data to evaluate the wetting properties of coal.

Thermodynamical studies of irreversible sorption of CO2 by Wyodak coal

Differential scanning calorimetry (DSC), temperature programmed desorption mass spectrometry (TPD-MS) and small angle neutron scattering (SANS) were used to investigate CO 2 uptake by the Wyodak coal. Adsorption of carbon dioxide on Wyodak coal was studied by DSC. The exotherms evident at low temperatures are associated with the uptake of CO 2 suggesting that carbon dioxide interacts strongly with the coal surface. Reduction in the value of the exotherms between the first and second runs for the Wyodak coal suggests that some CO 2 is irreversibly bound to the structure even after heating to 200 °C. DSC results also showed that adsorption of CO 2 on the coal surface is an activated process and presumably at the temperature of the exotherms there is enough thermal energy to overcome the activation energy for adsorption. The adsorption process is instantly pursued by much slower diffusion of the gas molecules into the coal matrix (absorption). Structural rearrangement in coal by CO2 is examined by change in the glass transition temperature of coal after CO2 uptake at different pressures. The amount of gas dissolved in the coal increases with increasing CO2 pressure. TPD-MS showed that CO2 desorption from the Wyodak coal follows a first order kinetic model. Increase in the activation energy for desorption with pre-adsorbed CO 2 pressure suggests that higher pressures facilitate the transport of CO 2 molecules through the barriers therefore the amount of CO2 uptake by the coal is greater at higher pressures and more attempts are required to desorb CO2 molecules sorbed at elevated pressures. These conclusions were further confirmed by examining the Wyodak coal structure in high pressure CO 2 by SANS.

Contact Angle of Water on Polystyrene Thin Films: Effects of CO2 Environment and Film Thickness

We examine the contact angle of water droplets on polystyrene (PS) thin films of varying thicknesses supported by silicon wafers under both air and pressurized carbon dioxide (CO2) environments. At 23 degrees C, the contact angle is found to increase upon increasing CO2 pressure in the vapor regime and then levels off in the liquid CO2 regime. A macroscopic model based on Young's equation and the geometric-mean method for interfacial tensions, and long-range van der Waals interactions, correctly predicts the trends and the magnitude of the contact angle dependence on pressure, although deviations occur at high CO2 activities. The contact angle was also found to depend on film thickness, h, when h was comparable to or smaller than 50 nm. Specifically, the contact angle decreases with decreasing PS film thickness. This behavior could be accounted for with the use of a model that incorporates the effects of film thickness, CO2 pressure, and the long-range van der Waals potential.

Hydroformylation of Cyclohexene with Carbon Dioxide and Hydrogen Using Ruthenium Carbonyl Catalyst: Influence of Pressures of Gaseous Components

Hydroformylation of cyclohexene was studied with a catalyst system ofRu3(CO)12 and LiCl using H2 and CO2 instead of CO in NMP. The influence of H2 andCO2 pressures on the total conversion and the product distribution was examined. It wasshown that increasing total pressure of H2 and CO2 promoted the reverse water gas shiftreaction and increased the yield of cyclohexanecarboxaldehyde. Its hydrogenation tocyclohexanemethanol was promoted with increasing H2 pressure but suppressed withincreasing CO2 pressure. Cyclohexane was also formed along with those products and thisdirect hydrogenation was suppressed with increasing CO2 pressure. The roles of CO2 as apromoter as well as a reactant were further examined by phase behavior observations andhigh pressure FTIR measurements.

Carbonate binders by “cold sintering” of calcium carbonate

The solubility of calcium carbonate (limestone) particles depends on the amount of CO2 dissolved in the water, which is a function of temperature and the pressure of CO2 that is in equilibrium with water. At a constant temperature, increasing CO2 pressure increases the solubility of CaCO3, and decreasing CO2 pressure favours the crystallisation of CaCO3. This dissolution–crystallisation behaviour of CaCO3 can be used in the development of carbonate binders—a process called “cold sintering”—of limestone. This paper examines the effect of a range of parameters on the cold sintering process of limestone powder. The parameters studied are CO2 gas pressure (atmospheric, 10 atm and 35 atm), exposure time (0–90 min), post-compaction pressure (10 and 15 MPa) and compact pressing time (10–60 min). The water/limestone powder ratio was kept constant at 0.2 (by weight). The compressive strength of the limestone compacts was used as a measure of the efficiency of the carbonate binder formation process, and scanning electron microscopy was used to study the microstructural developments. The results show that carbonate binders can be produced by cold sintering of limestone powder. Exposure of limestone compacts to high CO2 pressure followed by post-compaction at high mechanical pressure, enhances the strength of the compact. From the microstructural data, it is evident that newly formed calcium carbonate crystal growths are responsible for the strength improvements observed. The amount of water that is used in the limestone powder mixture is one factor that controls the quantity of the cementing phase. Future work has to be focussed on the application of methods to further increase the solubility of calcium carbonate, as the amount of calcium carbonate available for recrystallisation is important in producing a strong binder.

Density measurement of polymer/CO2 single‐phase solution at high temperature and pressure using a gravimetric method

AbstractThe densities of two polymer/CO2 single‐phase solutions, poly(ethylene glycol) (PEG)/CO2 and polyethylene (PE)/CO2, were measured at temperatures higher than melting temperature of the polymer under CO2 pressures in the range 0–15 MPa using a newly‐proposed gravimetric method. A magnetic suspension balance (MSB) was used for the density measurement under the high pressure CO2: A thin disc‐shaped platinum plate was submerged in the considered polymer/CO2 single‐phase solution in the MSB high‐pressure cell. The weight of the plate was measured while keeping CO2 pressure and temperature in the sorption cell at a specified level. Since the buoyancy force exerted on the plate by the polymer/CO2 solution reduced the apparent weight of the plate, the density of the polymer/CO2 solution could be calculated by subtracting the true weight of the plate from its measured weight. Experimental results showed that the density of PE/CO2 solution increased with the increase of CO2 pressure and the density of PEG/CO2 solution decreased with the increase of CO2 pressure. To differentiate the effect of CO2 dissolution in polymer from that of mechanical pressure, the density of polymer/CO2 solution was compared with the density of neat polymer under the given mechanical pressure, which was calculated using the Sanchez–Lacombe equation of state and Pressure–Volume–Temperature data of the polymer. The comparison could elucidate that the dissolution of CO2 in polymer reduced density of both PEG/CO2 and PE/CO2 systems but the degree of CO2 induced‐density reduction was different between two polymer/CO2 systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Numerical modeling of fluid–rock chemical interactions at the supercritical CO2–liquid interface during CO2 injection into a carbonate reservoir, the Dogger aquifer (Paris Basin, France)

A project of geological CO2 storage in the deep Dogger aquifer in the Paris Basin (France) is under development. Before effective containment can be assured, investigations need to be carried out on reservoir behavior when subjected to physical, chemical and mechanical perturbations induced by CO2 injections. The aim of this study is to present the numerical results of two CO2 injection scenarios, firstly with CO2-saturated water and secondly with pure supercritical CO2. The simulation results confirm the high reactivity of CO2-saturated water, which can dramatically damage the reservoir structure. On the other hand, supercritical CO2 injection appears to be weakly reactive, with a limited modification of well injectivity. Supercritical CO2 reacts differently to CO2-saturated solution: firstly, it dissolves into aqueous solution and it increases both water acidity and mineral dissolution potential, favoring augmented porosity. Following this step, numerical simulations demonstrate that hydraulic processes induced by supercritical CO2 injection are accompanied by a desiccation phenomenon of the porous medium. Irreducible water, entrapped in pores, sustains the increase in CO2 pressure. When the pressure is sufficiently high and under a continuous dry (without water vapor) CO2 flux, an evaporation process starts leading to the precipitation of salts and possibly other secondary minerals. Although there has been little focus on this desiccation process in the literature until now, it nevertheless must constitute an important risk of both a modification in porosity and well injectivity.

Dynamics of CO2-Plasticized Electron Transport in Au Nanoparticle Films: Opposing Effects of Tunneling Distance and Local Site Mobility

The electron-transport properties of unlinked and linked solid-state films of very small “Au38” nanoparticles (monolayer protected clusters, or MPCs) remarkably change in opposing directions upon contact with increasing pressures of CO2 gas (0∼6.6 MPa). Electronic conductivities (σEL) of dropcast, unlinked Au MPC films increase up to 31-fold with increasing CO2 pressure, while σEL of dithiol-linked Au MPC films decreases with increasing CO2 pressure. In conductivity by electron hopping between electron donor and acceptor Au MPC cores, the organic protecting ligands serve as a solvent shell whose properties influence the dynamics of electron transport. Exposure of Au MPC films to CO2 and consequent swelling by CO2 (or organic vapor) sorption into the monolayers changes two key factors: core edge-to-edge electron tunneling distances (dHOP) and a previously underappreciated effect of dimension and/or frequency of local core thermal motions. Swelling induces increases in both, but depending on which factor i...

Recovering coal bed methane from deep unmineable coal seams and carbon sequestration

Published data from nearly 2,000 coal samples comprising 250 coal beds from 17 states, representing many of the coal producing horizons in the USA, shows moderate correlation (0.7) between depth and methane content for high volatile coal ranks. Low-volatile rank coals average the highest methane content, 12.74 m?/ton (450 ft?/ton), subbituminous rank coals the lowest, <0.71 m?/ton (<25 ft?/ton). Experimentation under replicated in situ conditions of triaxial stress, pore pressure and temperature on Pittsburgh No. 8 coal indicate permeability decreases with increasing CO2 pressure, with an increase in strain in the coal associated with its swelling.

Dielectric Behavior of cis-Polyisoprene in Carbon Dioxide under High Pressure

Dielectric measurement was conducted for cis-polyisoprene (PIP) in carbon dioxide (CO2) at high pressures. CO2 is dissolved in PIP more with increasing pressure, and this dissolution is expected to affect the chain dynamics. In our experimental window, the PIP chains having type-A dipoles parallel along their backbone exhibited the dielectric dispersion reflecting their global motion. This dispersion shifted to higher frequencies with increasing CO2 pressure. Time - CO2 pressure superposition was found to hold well, which suggests that the global motion of the chain is accelerated by CO2 without any heterogeneity in space and along the chain backbone. The vertical shift factor (intensity shift factor) for this superposition gave the CO2 concentration in PIP. The plasticizing capability of CO2 evaluated from the horizontal shift factor (frequency shift factor) was found to be a little larger than that of tetradecane in the same range of concentration. No peculiarity was found for plasticizing ability of CO2 even in the supercritical state (at a pressure of 10 MPa).

Selective hydrogenation of citral with transition metal complexes in supercritical carbon dioxide

Abstract The activity and selectivity of the transition metal complexes formed from Ru, Rh, Pd and Ni with triphenylphosphine (TPP) have been investigated for hydrogenation of citral in supercritical carbon dioxide (scCO2). High activities are obtained with Ru/TPP and Pd/TPP catalysts, and the overall activity is in the order of Pd≈Ru > Rh > Ni. The Ru/TPP complex is highly selective to the formation of unsaturated alcohols of geraniol and nerol. In contrast, the Pd/TPP catalyst is more selective to partially saturated aldehydes of citronellal. Furthermore, the influence of several parameters such as CO2 and H2 pressures, N2 pressure and reaction time has been discussed. CO2 pressure has a significant impact on the product distribution, and the selectivity for geraniol and nerol can be enhanced from 27% to 75% with increasing CO2 pressure from 6 to 16 MPa, while the selectivity for citronellol decreases from 70% to 20%. Striking changes in the conversion and product distribution in scCO2 could be interpreted with variations in the phase behavior and the molecular interaction between CO2 and the substrate in the gas phase and in the liquid phase.

Impact of different pressures and exposure times of a simulated carbon dioxide pneumoperitoneum environment on proliferation and apoptosis of human ovarian cancer cell lines

This study aimed too evaluate the proliferation and apoptosis of human ovarian cancer cell lines HO8910 and SKOV3 after exposure to a simulated laparoscopic carbon dioxide (CO2) pneumoperitoneum environment at different pressures and lengths of exposure time. The effects of the simulated laparoscopic CO2 pneumoperitoneum environment at different CO2 pressures (0-16 mmHg) and exposure times (1-4 h) on tumor cell growth and apoptosis were assessed by 3-[4,5-Dimethylthiazol]-2; 5-diphenyltetrazolium bromide (MTT) chromometry and proliferative index (PI) staining or Annexin V and PI double-staining flow cytometry. Cells cultured in a standard environment were used as the control group. In this study, HO8910 cell growth tended to slow down with the increase in CO2 pressure and exposure time. A significantly lower PI was observed at 72 h of culture after exposure to both 8 and 16 mmHg of pressure, as compared with the control and 0 mmHg pressure group (p < 0.05). The PI of SKOV3 cells tended to decline after exposure. Significantly lower PI was observed in the group with exposure to 16 mmHg for 4 h over a 72-h period, as compared with the control groups exposed to 0 mmHg (p < 0.05). The inhibition of cell growth was associated with an increase in the proportion of cells at stage G1. The apoptotic index and the percentage of apoptotic cells tended to increase with an increase in pressure and a prolonged time of exposure. The results suggest inhibited cell proliferation and increased cell apoptosis of human ovarian cancer cells were positively related to CO2 pressure and exposure time.