Point Of CO2 Research Articles

Assessment of the potential models of acetone/CO2 and ethanol/CO2 mixtures by computer simulation and thermodynamic integration in liquid and supercritical states

Binary mixtures of CO(2) with ethanol and with acetone are studied by computer simulation, including extensive free energy calculations done by the method of thermodynamic integration, at 313 K, i.e., above the critical point of CO(2) in the entire composition range. The calculations are repeated with three different models of acetone and ethanol, and two models of CO(2). Comparisons of the molar volume of the different systems as well as of the change of their molar volume accompanying the mixing of the two components with experimental data reveal that, among the model pairs tested, the best results are obtained if both components are described by the Transferable Potentials for Phase Equilibria (TraPPE) force field. Around the ethanol/acetone mole fraction of 0.05 all ethanol/CO(2) and almost all acetone/CO(2) model pairs considered predict the existence of a sharp maximum of the molar volume. Due to the lack of experimental data in this composition range, however, these predictions cannot be verified/falsified yet. Most of the model pairs considered also predict limited miscibility of these compounds, as seen from the positive values of the free energy change accompanying their mixing, and the miscibility gap is located at the same composition range as the aforementioned molar volume maximum.

Experimental determination and modeling of the phase behavior for the selective oxidation of benzyl alcohol in supercritical CO 2

In this study the phase behavior of mixtures relevant to the selective catalytic oxidation of benzyl alcohol to benzaldehyde by molecular oxygen in supercritical CO 2 is investigated. Initially, the solubility of N 2 in benzaldehyde as well as the dew points of CO 2–benzyl alcohol–O 2 and CO 2–benzaldehyde–water ternary mixtures were experimentally determined. The cubic plus association (CPA) equation of state was used to model the phase behavior of the experimentally investigated systems as well as the phase behavior of relevant mixtures that can exist inside the reactor during the reaction time. In this direction, the CPA binary interaction parameters were estimated from the corresponding binary systems and the phase behavior of two ternary systems, i.e. CO 2–benzyl alcohol–O 2 (reacting mixture) and CO 2–benzaldehyde–water (mixture of products) as well as the phase behavior of multicomponent mixtures containing both reactants and products were predicted. CPA was proved to be a versatile model that can predict the complex phase behavior of the aforementioned systems. The results reveal that the ternary mixture of products (CO 2–benzaldehyde–water) and the intermediate multicomponent mixtures containing both products and reactants require lower pressure than the corresponding mixture of the reactants (CO 2–benzyl alcohol–O 2) in order to be in a single phase.

Comparative Study of Pt/Pd and Pt–Rh/Pt Thermocouples

The Pt/Pd thermocouple has demonstrated superior thermoelectric drift and homogeneity performance over conventional Pt–Rh/Pt thermocouples. Here, we present a systematic comparison of the drift and homogeneity performance of Pt/Pd and Type R thermocouples by ageing the thermocouples at 1350 °C for a total of 500 h and measuring the performance at regular intervals during this time. The thermocouples studied were one Pt/Pd thermocouple, one Type R thermocouple and one ‘special’ Type R thermocouple which was given the same preparatory annealing treatment as the Pt/Pd thermocouple prior to use. The thermoelectric stability of each thermocouple was measured at the freezing point of Ag (961.78 °C) and the melting point of Co–C eutectic (1324.29 °C). The thermoelectric homogeneity of the thermocouples was also measured. Two difference methods were used by withdrawing the thermocouple from the Ag cell and by moving a localized heat source along the thermocouple. The long-term drift of the Pt/Pd thermocouple was around 50 mK (Ag) and 65 mK (Co–C) after the first 100 h ageing at 1350 °C, followed by a further 25 mK (Ag) and 35 mK (Co–C) over the subsequent 400 h ageing. This drift performance and inhomogeneity were an order of magnitude lower than for the two Type R thermocouples. The Type R thermocouple which was given the ‘special’ preparatory treatment was about 50 % more stable than the conventional Type R thermocouple.

High-pressure phase equilibrium for the hydroformylation of 1-octene to nonanal in compressed CO 2

The hydroformylation reaction in supercritical carbon dioxide or CO 2-expanded liquids (CXLs) has many advantageous properties. However, accurate phase behavior and equilibrium must be known to properly understand and engineer these systems. In this investigation, the vapor–liquid equilibrium and mixture critical points of CO 2 systems with 1-octene, nonanal, 1-octene and nonanal mixtures, and mixtures of 1-octene, nonanal and syngas (CO/H 2) were measured at 60 °C up to 120 bar of pressure. The Peng–Robinson equation of state with van der Waals two-parameter mixing rule was employed successfully to correlate the binary mixture data and predict the ternary mixture data. The presence of CO/H 2 pressure increased the mixture critical points and decreased the volume expansion at any given pressure. In an actual reaction, the mixture critical point would increase throughout the reaction, while the volume of the liquid phase would decrease. These data will aid the understanding and reaction engineering for the hydroformylation reaction in CO 2-expanded liquids and supercritical fluids.

Combining geologic data and numerical modeling to improve estimates of the CO2 sequestration potential of the Rock Springs Uplift, Wyoming

Abstract We present results from the first stages of a detailed three dimensional analysis of the geologic CO 2 sequestration potential of the Rock Springs Uplift (RSU), located in south-western Wyoming. This site is of particular interest because of the collocated 2.1 GW Jim Bridger coal burning power plant and the possibility of additional power plants being developed in the area to take advantage of the abundant coal reserves in the RSU region (i.e. the Southern California Edison CEPL project). The Rock Springs Uplift is a huge asymmetric dome structure with two superior target sequestration reservoirs located beneath a 1500 m thick sequence of Cretaceous shale. The target reservoirs, the Weber Sandstone and Madison Limestone, with thicknesses of greater than 200m and 75m respectively, are located at depths where pressures are well above the critical point of CO 2 . Seismic data reveal that the structure of the RSU creates an ideal trap for buoyant supercritical CO 2 . The target reservoirs currently contain high salinity sour brines (35,000-80,000 ppm) with little or no economic value. Reservoir continuity inferred from well logs and cores and high average measured porosity (10%) and permeability (10-75 md) led to initial screening estimates on the order of 26 billion tons of CO 2 for the storage capacity of the structure. This paper focuses on calculations that will help to refine the initial capacity estimates through the use of high resolution multiphase numerical models. First we present an analysis using a system level simulator, CO2-PENS, to differentiate between two injection depths in the Weber on the basis of the costs associated with on-site drilling and pipelines for a range of permeabilities. The deeper site is analogous to the subsurface near the Jim Bridger Power Plant (JBPP), while the shallower site is analogous to the crest of the RSU. Results of this analysis show that deeper injection may be more cost effective. Next, we develop a 3-D computational hydrostratigraphic model and simulate injection of CO 2 near the Jim Bridger Power Plant. Utilizing existing seismic and wellbore data, a geologic framework model has been created in EarthVision (i.e., 3D model building and visualization software). From this model, hydrostratigraphic units were extracted and a 3-D computational mesh for a 16×16 km section of the RSU structure was constructed. This model is used to simulate injection of 80% of the total CO 2 emissions from the 2.1 GW JBPP (483 kg/s or 15 Mt/year) into the Weber formation for two cases. The first case assumes a very high permeability in the Weber and needs only one injection well, while the second case assumes a lower permeability and uses 9 injection wells. The major differences between these two examples are the amount of CO 2 that dissolves into the formation brines and the areal extent of the resulting plumes. Because the low permeability case requires more injectors, the injected CO 2 is exposed to a larger volume of reservoir rock and leads to a higher percentage of the total injected CO 2 being dissolved in the formation water. The focused injection for the high permeability case leads to more CO 2 remaining in the supercritical state and longer up-dip transport. Finally, both cases show that both diffusive and advective transport into the surrounding strata may significantly increase the storage potential of the RSU.

Estimating Plume Volume for Geologic Storage of CO2 in Saline Aquifers

Estimating Plume Volume for Geologic Storage of CO 2 in Saline Aquifers Christine Doughty Earth Sciences Division Lawrence Berkeley National Laboratory July 2008 Typically, when a new subsurface flow and transport problem is first being considered, very simple models with a minimal number of parameters are used to get a rough idea of how the system will evolve. For a hydrogeologist considering the spreading of a contaminant plume in an aquifer, the aquifer thickness, porosity, and permeability might be enough to get started. If the plume is buoyant, aquifer dip comes into play. If regional groundwater flow is significant or there are nearby wells pumping, these features need to be included. Generally, the required parameters tend to be known from pre-existing studies, are parameters that people working in the field are familiar with, and represent features that are easy to explain to potential funding agencies, regulators, stakeholders, and the public. The situation for geologic storage of carbon dioxide (CO 2 ) in saline aquifers is quite different. It is certainly desirable to do preliminary modeling in advance of any field work since geologic storage of CO 2 is a novel concept that few people have much experience with or intuition about. But the parameters that control CO 2 plume behavior are a little more daunting to assemble and explain than those for a groundwater flow problem. Even the most basic question of how much volume a given mass of injected CO 2 will occupy in the subsurface is non-trivial. However, with a number of simplifying assumptions, some preliminary estimates can be made, as described below. To make efficient use of the subsurface storage volume available, CO 2 density should be large, which means choosing a storage formation at depths below about 800 m, where pressure and temperature conditions are above the critical point of CO 2 (P = 73.8 bars, T = 31 o C). Then CO 2 will exist primarily as a free-phase supercritical fluid, while some CO 2 will dissolve into the aqueous phase. A mass balance for CO 2 may be written as M = V + V where M is the total mass of CO 2 injected, φ is the porosity of the storage formation, S g is the saturation of free-phase CO 2 (that is, the fraction of pore space filled with free-phase CO 2 ), S l = 1 – S g is the saturation of the aqueous phase (water plus dissolved salt plus dissolved CO 2 ), ρ g and ρ l are densities of the CO 2 and aqueous phases, respectively, X l is the mass fraction of CO 2 dissolved in the aqueous phase, and V is plume volume. Angle brackets represent a spatial average over the plume. The first term of Equation (1) represents the mass of free-phase CO 2 and the second term the mass of dissolved CO 2 . Assuming that φ, S , ρ, and X l are not correlated enables the angle brackets to be dropped,

Impact of fluorine on the phase behavior of bis- p-tolyl propane in supercritical CO 2, 1,1-difluoroethane, and 1,1,1,2-tetrafluoroethane

Fluorine substitution on a solute can have a significant effect on solute solubility in a given solvent and fluorine substitution on a solvent can also have a significant effect on solvent quality. The effect of fluorine is demonstrated with the phase behavior data for bis( p-tolyl)propane (BTP) compared to bis( p-tolyl)hexafluoropropane (BTHFP) in supercritical carbon dioxide, 1,1-difluoroethane (F152a), and 1,1,1,2-tetrafluoroethane (F134a). Semifluorinated BTHFP is more soluble than non-fluorinated BTP in all three solvents, especially CO 2. The CO 2–BTP system exhibits solid solubility behavior while the CO 2–BTHFP system exhibits liquid–liquid–vapor (LLV) behavior near the critical point of CO 2. Although the two dipolar hydrofluorocarbons (HFC) are better solvents than CO 2 for these two aromatic solid compounds, F152a is the superior HFC solvent, especially for BTP, because F152a has a smaller molar volume and a larger effective dipole moment than F134a. LLV behavior is also observed for the F134a–BTP system near the critical point of F134a although the F134a–BTHFP, F152a–BTP, and F152a–BTHFP systems all appear to exhibit type-I phase behavior and no liquid–liquid immiscibility near the respective critical points.

Numerical simulation of supercritical CO 2 injection into subsurface rock masses

Carbon dioxide (CO 2) is considered to be one of the greenhouse gases that may contribute most to global warming on the earth. Disposal of CO 2 from stationary sources into subsurface structures has been suggested as a possible means for reducing CO 2 emissions into the atmosphere. However, much remains to be done in the issues regarding the safety and reliability of CO 2 geological sequestration. In this study, we have developed a simulation code by using the mathematical model of two phase flow in porous media to analyze the flow dynamics in the subsurface. The equation of state for CO 2 covering the fluid region from the triple point to the supercritical region is employed to model the states of CO 2 gas, liquid and supercritical state. The correct understanding of the CO 2 state under the geological formation condition is an important factor to predict the injection pressure and CO 2 fluid permeation because the fluid density has a great effect on the injection behavior. The numerical simulation was implemented under several geological conditions including gas, liquid and supercritical states to examine the optimal injection condition. Comparing the numerical results obtained using the equation of state for CO 2 with those obtained using the ideal gas equation, it has been shown that the difference in the injection pressure appears to be significant near the condition of the critical point of CO 2 and the phase equilibrium curves between the gas and liquid states. The numerical simulation has been implemented to examine the effect of the reservoir condition on the injection behavior. The injection pressure is decreased at the lower reservoir temperature and higher hydrostatic pressure condition. The CO 2 permeation is also strongly affected by the reservoir condition, and the spatial CO 2 saturation becomes higher with increasing reservoir temperature. It has been demonstrated that the simulation code developed in this study may be useful to provide knowledge required to select the reservoir condition for CO 2 geological sequestration.

Carbon materials syntheses using dielectric barrier discharge microplasma in supercritical carbon dioxide environments

In this study, carbon materials syntheses using a dielectric barrier discharge (DBD) microplasma in supercritical carbon dioxide (scCO 2) environments are reported. The dependencies of the carbon materials synthesis processing on the environmental temperature, environmental pressure and power frequency were investigated. In contrast to atmospheric-pressure CO 2 environments, in which no carbon materials could be fabricated, it was possible to fabricate various carbon materials, such as amorphous carbon, graphite and nanostructured carbon materials, using scCO 2 as a processing medium and a raw starting material. In particular, in the vicinity of the critical point of CO 2, the quantity of carbon nanostructured materials, such as carbon nanotubes and carbon nanohorns, was larger than under other scCO 2 conditions. It is supposed that the high density and molecular clustering caused by supercritical conditions may affect the formation of such carbon nanostructured materials. In addition, we found that by varying the power frequency, the form of the synthesized carbon materials could be changed.

Chemical and stable isotopic constraints on the nature and origin of volatiles in the sub-continental lithospheric mantle beneath eastern China

We report concentrations and stable isotopic data of CO 2 , CO, CH 4 , H 2 O and H 2 volatile species from mantle xenoliths hosted in Cenozoic basalts in eastern China. The volatiles are extracted by stepwise heating and mostly released in two temperature intervals, ∼ 400–600 °C and ∼ 800–1200 °C, respectively. We identified two types of volatiles: (1) “initial" volatiles, which were originally dissolved in crystal structures and trapped in fluid inclusions in the interiors of mineral crystals, are released at the 800–1200 °C interval, and composed of H 2 (66.6 mm 3.STP/g on average), CO 2 (50.7), CO (35.8) and CH 4 (0.6). The δD and δ 13C of CH 4 exhibit “normal" mantle signatures. However, variable δ 18O of CO 2 (0.6‰ to 16.6‰) and lighter δ 13C values of CO 2 and CO point to the involvement of a recycled crustal component. We interpret the latter as subducted oceanic crust with terrigenous sediments. (2) metasomatic volatiles, which were incorporated into minerals as fluid inclusions at edges and healed fractures of the recrystallizing minerals probably during mantle metasomatism, are released at the 400–600 °C interval, and composed mainly of CO 2 (∼ 9.82 mm 3.STP/g on average) with minor CO, H 2 and CH 4 , and are characterized by δ 13C of biogenic CH 4 , lighter and variable δD of H 2 O (− 110.7‰ to − 280.9‰), lighter δ 13C of CO 2 and CO and variable δ 18O of CO 2 (1.0‰ to 11.5‰), suggesting that the metasomatic volatiles may have originated form devolatilization of altered recycled oceanic crust with terrigenous sediments. We speculate that the metasomatic volatiles could have come from dehydration of the subducted paleo-Pacific lithosphere that lies horizontally in the transition zone beneath eastern China. Such recycled crustal fluids may have been important in metasomatizing the sub-continental lithosphere beneath eastern China and in causing thinning of the lithosphere and associated magmatism in the Mesozoic.

4312 高圧水中におけるCO_2スラリーの放出実験(S59-1 温室効果ガス排出抑制技術(1),S59 温室効果ガス排出抑制技術)

Ocean storage of carbon dioxide (CO_2) is one of greenhouse gas control technologies. The authors have proposed a CO_2 sending method for ocean storage using a mixture of liquid CO_2 and dry ice, CO_2 slurry. Releasing experiments of CO_2 slurry using a high-pressure tank was carried out to observe the behavior of CO_2 slurry released in highly pressurized water. CO_2 slurry was prepared by melting of dry ice in a chamber at the triple point of CO_2, -56 degrees of Celsius. Descending of CO_2 slurry drops in water was observed. However, releasing of cold CO_2 slurry caused the formation of tubular ice at the releasing nozzle, which narrowed the flow of CO_2 slurry to form slurry drops with a diameter smaller than the nozzle hole. The result implies that the formation of tubular ice at the nozzle should be reduced to control the size of slurry drops.

Ultrasound speed and absorption study in near-critical CO 2: A sensor for high-pressure application

This paper reveals an ultrasonic sensor assembly for accurate determination of the speed of sound and sound attenuation (acoustic energy losses) in dense fluids. It was constructed by means of commercially available 200 kHz emitting/receiving piezoelectric transducers equipped with a special acoustic matching layer. The construction allows changing the distance between transducers without dismantling a high-pressure vessel. This experimental technique makes it possible to determine the sound absorption coefficient, indispensable information for the acoustic determination of gas composition and other properties related to the sound absorption coefficient. The assembly was successfully applied for measuring the speed of sound and sound amplitude in CO 2 between 298 and 343 K and 6–14 MPa. The measurements of sound amplitude resulted in accurate location of the critical point of CO 2 because in the vicinity of the critical point a decrease of sound signal amplitude is far more significant than a decrease of sound speed.

On point orbits of the Co2-minimal parabolic geometry

The orbits of certain subgroups of Co 2, Conway's second largest simple group, on the points of Co 2's minimal parabolic geometry are determined. This information is used in [6,7] to analyse a grap associated with the Baby Monster group.

Medium temperature carbon dioxide gas turbine reactor

A carbon dioxide (CO 2) gas turbine reactor with a partial pre-cooling cycle attains comparable cycle efficiencies of 45.8% at medium temperature of 650 °C and pressure of 7 MPa with a typical helium (He) gas turbine reactor of GT-MHR (47.7%) at high temperature of 850 °C. This higher efficiency is ascribed to: reduced compression work around the critical point of CO 2; and consideration of variation in CO 2 specific heat at constant pressure, C p, with pressure and temperature into cycle configuration. Lowering temperature to 650 °C provides flexibility in choosing materials and eases maintenance through the lower diffusion leak rate of fission products from coated particle fuel by about two orders of magnitude. At medium temperature of 650 °C, less expensive corrosion resistant materials such as type 316 stainless steel are applicable and their performance in CO 2 have been proven during extensive operation in AGRs. In the previous study, the CO 2 cycle gas turbomachinery weight was estimated to be about one-fifth compared with He cycles. The proposed medium temperature CO 2 gas turbine reactor is expected to be an alternative solution to current high-temperature He gas turbine reactors.

Solubility of semi-fluorinated and nonfluorinated alkyl dichlorobenzoates in supercritical CO 2

Isopleths and solution densities, from ∼25 to 100 °C, are reported for mixtures of CO 2 with semi-fluorinated and nonfluorinated propyl, butyl, octyl, and decyl 2,5-dichlorobenzoates. The maxima in the pressure–composition ( P– x) isotherms for the alkyl 2,5-dichlorobenzoates range from 70 to 600 bar and the maxima increase with increasing alkyl chain length at each temperature. When the alkyl side chains are semi-fluorinated, the P– x maxima range from 60 to 175 bar over the same temperature range as with the nonfluorinated analogs. The P– x maxima of the semi-fluorinated 2,5-dichlorobenzoates in CO 2, first decrease as the benzoate alkyl chain is increased from propyl to butyl, but then increase as the alkyl chain length is further increased from butyl to octyl to decyl, although the differences in the maxima at a given temperature between these four semi-fluorinated benzoates are not as great as that observed with the nonfluorinated analogs. Also, the alkyl 2,5-dichlorobenzoate–CO 2 mixtures exhibit three-phase, liquid–liquid–vapor (LLV), equilibria near the vapor pressure curve and critical point of CO 2 whereas three phases are not observed for the semi-fluorinated analogs.

Application of emulsion of dense carbon dioxide in electroplating solution with nonionic surfactants for nickel electroplating

An electroplating reaction using nickel was carried out in an emulsion of dense carbon dioxide (CO 2) and an electroplating solution with nonionic surfactants. The current efficiency and electrical resistance values were measured as a function of CO 2 volume fraction in the emulsion with three kinds of surfactants. These results show that dense CO 2 beyond the critical point of CO 2 is effective to form an emulsion for the electroplating reaction. The nonionic surfactant octa(ethylene oxide) dodecyl ether, two kinds of poly (ethylene oxide)-b-poly (propylene oxide) with molecular weights of 745 and 950, respectively, were employed for emulsification. Moreover, a hydrophilic CO 2-philic balance of the surfactants strongly influences on the stability of the emulsion. On the basis of the electrical conductivity measurements, the emulsion was classified into a CO 2 in water (C/W) type with the CO 2 volume fraction ranging from 0 to 80%. Compared to electroplating from the only solution, higher quality nickel films have been prepared by this method. The nickel films that were produced have a higher uniformity, a smaller grain size (sub-100 nm), and a significantly higher Vickers hardness.

Equilibrium and kinetics properties of p-dichlorobenzene and toluene on silica gel in dense CO 2 by chromatography analysis

The adsorption equilibrium constant and kinetics properties for p-dichlorobenzene and toluene on silica gel adsorbent in the subcritical and supercritical CO 2 have been measured by an impulse chromatography technique. The experiments were performed at temperatures of 298.15, 208.15, 318.15 K and pressures of 75–178 bar. A series fit method was applied to treat the chromatography peak. The adsorption equilibrium constant increased with temperature and decreased with pressure under the experimental conditions. The fluid density is found to be the main controlling factor determining the adsorption equilibrium constant. The dependence of the kinetics properties, dispersion coefficient and intraparticle effective diffusivity, on temperature and pressure has been investigated. The pore diffusion is the main diffusion mechanism within the pore medium. The partial molar volume (PMV) and partial molar enthalpy (PME) for p-dichlorobenzene in supercritical CO 2 have also been evaluated from the adsorption equilibrium constants obtained in this work. Very large and negative values for the two partial molar properties were obtained near the critical point of CO 2.

Effects of drought on photosynthesis in grapevines under field conditions: an evaluation of stomatal and mesophyll limitations.

The effect of diffusional and photochemical limitations to photosynthesis was assessed in field-grown water-stressed grapevines (Vitis vinifera L.) by combined measurements of gas exchange and chlorophyll fluorescence. Drought was slowly induced, and the progressive decline of photosynthesis was examined in different grapevine cultivars along a continuous gradient of maximum mid-morning values of stomatal conductance (g), which were used as an integrative indicator of the water-stress conditions endured by the leaves. Initial decreases of g were accompanied by decreases of substomatal CO2 concentration (Ci), the estimated chloroplastic CO2 concentration (Cc) and net photosynthesis (AN), while electron transport rate (ETR) remained unaffected. With increasing drought, g, AN, Ci and Cc further decreased, accompanied by slight decreases of ETR and of the estimated mesophyll conductance (gmes). Severe drought led to strong reductions of both g and gmes, as well as of ETR. The apparent carboxylation efficiency and the compensation point for CO2 remained unchanged under severe drought when analysed on a Cc, rather than a Ci, basis, suggesting that previously reported metabolic impairment was probably due to decreased gmes.

IR spectroscopic study of NO and CO adsorptions on nonstoichiometric nickel–copper manganites

The adsorptions and co-adsorption of nitric oxide and carbon monoxide on nonstoichiometric nickel and nickel–copper manganites have been investigated in situ by transmission infrared spectroscopy. Time-dependent and temperature-dependent data have been acquired to investigate the nature of the molecule–surface interactions. The surface chemistry of NO was found to be particularly rich, involving numerous surface species (mononitrosyls, dinitrosyls, adsorbed N2O, nitrites/nitrates), whereas that of CO was somewhat simpler. The competitive adsorption of NO and CO was evidenced. However, with time, NO tended in all cases to colonize the surface of the samples, and Cu+ cations were shown to be the only access points of CO to the surface of such oxides in the presence of NO. Finally, a time sequence of reactions was shown in the case of NO adsorption.

Effect of supercritical carbon dioxide on morphology development during polymer blending

AbstractSupercritical carbon dioxide (scCO2) was added during compounding of polystyrene and poly(methyl methacrylate) (PMMA) and the resulting morphology development was observed. The compounding took place in a twin screw extruder and a high‐pressure batch mixer. Viscosity reduction of PMMA and polystyrene were measured using a slit die rheometer attached to the twin screw extruder. Carbon dioxide was added at 0.5, 1.0, 2.0 and 3.0 wt% based on polymer melt flow rates. A viscosity reduction of up to 80% was seen with PMMA and up to 70% with polystyrene. A sharp decrease in the size of the minor (dispersed) phase was observed near the injection point of CO2 in the twin screw extruder for blends with a viscosity ratio, ηPMMA/ηpolystyrene, of 7.3, at a shear rate of 100 s−1. However, further compounding led to coalescence of the dispersed phase. Adding scCO2 did not change the path of morphology development; however, the final domain size was smaller. In both batch and continuous blending, de‐mixing occurred upon CO2 venting. The reduction in size of the PMMA phase was lost after CO2 venting. The resulting morphology was similar to that without the addition of CO2. Adding small amounts of fillers (e.g. carbon black, calcium carbonate, or nano‐clay particles) tended to prevent the de‐mixing of the polymer blend system when the CO2 was released. For blends with a viscosity ratio of 1.3, at a shear rate of 100 s−1, the addition of scCO2 only slightly reduced the domain size of the minor phase.