Water-saturated Supercritical CO2 Research Articles

Inhibition of N80 steel corrosion in impure supercritical CO2 and CO2-saturated aqueous phases by using imino inhibitors

Steel corrosion has been widely investigated during supercritical CO2 phase with various impurities in carbon capture and storage system; however, the use of inhibitors to suppress steel corrosion has been rarely studied. This work investigated the corrosion inhibition effect of imidazoline and piperazine on N80 steel in water-saturated supercritical CO2 phase and supercritical CO2-saturated aqueous phase with impurities (SO2, NO2, and O2). Results showed that the inhibition efficiency of piperazine increased from 64% to 86% in the aqueous phase when the piperazine concentration increased from 300ppm to 1000ppm. In all cases, the inhibition efficiency in the supercritical CO2 phase was lower than that in the aqueous phase under the same test conditions. By contrast, the inhibition effect of imidazoline was negligible, and severe localized attacks were found within deep pits in supercritical CO2 and aqueous phases. Based on the pH measurement results, piperazine exhibited remarkable neutralization effect and thus could be a potential pH stabilizer. Fe3C possibly resided on the steel surface, and Fe2(SO4)3 was confirmed in the product scale. Nevertheless, steel corrosion inhibition in impure supercritical CO2 phase remains challenging.

Interaction between hydroxyl group and water saturated supercritical CO 2 revealed by a molecular dynamics simulation study

Molecular dynamics simulations were performed to investigate hydroxyl groups-CO2 interactions. Three silica surfaces with different hydroxyl group structures were selected and the effect of pressure was studied in the range of 4.8–32.6 MPa. Radial distribution functions especially for OsOc pair show evidence for hydrogen bonds between hydroxyl groups and CO2 molecules. The hydrogen bonds structure was analyzed using the mean number of hydrogen bonds. Pressure and hydroxyl group structures were found to affect H-bonding structure. These findings provide new insight for CO2-hydroxyl group interactions to better understand the effects of CO2 in carbon capture and sequestration process.

Reactivity of micas and cap-rock in wet supercritical CO2 with SO2 and O2 at CO2 storage conditions

Seal or cap-rock integrity is a safety issue during geological carbon dioxide capture and storage (CCS). Industrial impurities such as SO2, O2, and NOx, may be present in CO2 streams from coal combustion sources. SO2 and O2 have been shown recently to influence rock reactivity when dissolved in formation water. Buoyant water-saturated supercritical CO2 fluid may also come into contact with the base of cap-rock after CO2 injection. Supercritical fluid-rock reactions have the potential to result in corrosion of reactive minerals in rock, with impurity gases additionally present there is the potential for enhanced reactivity but also favourable mineral precipitation.The first observation of mineral dissolution and precipitation on phyllosilicates and CO2 storage cap-rock (siliciclastic reservoir) core during water-saturated supercritical CO2 reactions with industrial impurities SO2 and O2 at simulated reservoir conditions is presented. Phyllosilicates (biotite, phlogopite and muscovite) were reacted in contact with a water-saturated supercritical CO2 containing SO2, or SO2 and O2, and were also immersed in the gas-saturated bulk water. Secondary precipitated sulfate minerals were formed on mineral surfaces concentrated at sheet edges. SO2 dissolution and oxidation resulted in solution pH decreasing to 0.74 through sulfuric acid formation. Phyllosilicate dissolution released elements to solution with ∼50% Fe mobilized. Geochemical modelling was in good agreement with experimental water chemistry. New minerals nontronite (smectite), hematite, jarosite and goethite were saturated in models. A cap-rock core siltstone sample from the Surat Basin, Australia, was also reacted in water-saturated supercritical CO2 containing SO2 or in pure supercritical CO2. In the presence of SO2, siderite and ankerite were corroded, and Fe-chlorite altered by the leaching of mainly Fe and Al. Corrosion of micas in the cap-rock was however not observed as the pH was buffered by carbonate dissolution. Ca-sulfate, and Fe-bearing precipitates were observed post SO2-CO2 reaction, mainly centered on surface cracks and an illite rich illite-smectite precipitate quantified. Water saturated impure supercritical CO2 was observed to have reactivity to rock-forming biotite, muscovite and phlogopite mineral separates. In the cap-rock core however carbonates and chlorite were the main reacting minerals showing the importance of assessing actual whole core.

Effect of impurity on the corrosion behavior of X65 steel in water-saturated supercritical CO2 system

A range of impurities from various CO2 capture processes may exist in supercritical CO2 transport pipeline in carbon capture and storage process. In this regard, the corrosion behavior of X65 steel in water-saturated supercritical CO2 containing O2, H2S, SO2 or NO2 impurity was investigated using weight loss measurement and surface characterization. The corrosion impact factor was defined which showed that NO2 or SO2 had the greatest influence on the corrosion of X65 steel, followed by H2S and O2. Localized corrosion occurred in water-saturated supercritical CO2 system containing NO2 with or without other impurities. Low concentrations of impurities could notably change the corrosion rate and the characteristics of corrosion scale via changing the corrosion mechanism, and thus the corrosion effect of CO2 weakened in water-saturated supercritical CO2 system containing impurities.

Ab initio thermodynamics of magnesium carbonates and hydrates in water-saturated supercritical CO2 and CO2-rich regions

ab initio Thermodynamics is used to determine how free energies of magnesium carbonates and hydrates in a CO2-rich environment change with water concentration across a range temperature and pressure relevant to geochemistry and carbon sequestration (275K to 375K and pCO2 of 1 to 210bar). The methodology is based on first principles density-functional theory (DFT) calculations of the total energies and vibrational entropy of periclase, magnesite, brucite, nesquehonite, and hydromagnesite coupled to the experimental chemical potentials of CO2 and H2O. The impact of water in supercritical CO2 (scCO2), even though less than 1% at saturation, is found to have a significant impact on the stability of hydrated carbonate minerals. Hydromagnesite and nesquehonite are found to be more thermodynamically stable than periclase and brucite in water-saturated scCO2 and hence may be expected to result kinetically from carbonation of these minerals during CO2 sequestration. Under dehydrating conditions nesquehonite destabilizes rapidly, whereas hydromagnesite is much more likely to persist in a CO2-rich environment, consistent with the observations that hydromagnesite is widespread in nature and nesquehonite is relatively rare.

Synergistic effect of O2, H2S and SO2 impurities on the corrosion behavior of X65 steel in water-saturated supercritical CO2 system

The synergistic effect of O2, H2S and SO2 impurities on the corrosion behavior of X65 steel corrosion was evaluated in the water-saturated supercritical CO2 system. Weight loss measurements showed that the synergistic effect of multiple impurities significantly increased the corrosion rate of steel. Surface characterization of corrosion scales using SEM, EDS and XRD showed that low concentrations of impurities notably changed the characteristics of corrosion scales. The interactions among O2, H2S and SO2 resulted in additional formation reactions of elemental sulfur, sulfuric acid and water and consequently accelerated the corrosion of steel consistent with the high synergistic interaction impact factors.

Effect of O2 and H2S impurities on the corrosion behavior of X65 steel in water-saturated supercritical CO2 system

The corrosion behavior of X65 steel in water-saturated supercritical CO2 containing O2 and/or H2S impurities was investigated by means of weight loss measurements and surface characterization. The results showed that the addition of O2 or H2S impurities increased the corrosion rate of X65 steel in water-saturated supercritical CO2 system. The effect of H2S on the corrosion of X65 steel was greater than that of O2. The corrosion was more severe with the coexistence of O2 and H2S. The change in corrosion behavior was attributed to the fact that low concentrations of O2 and/or H2S can notably change the corrosion mechanism.

The effect of O2 content on the corrosion behaviour of X65 and 5Cr in water-containing supercritical CO2 environments

The general and localized corrosion behaviour of X65 carbon steel and 5Cr low alloy steel were evaluated in a water-saturated supercritical CO2 environment in the presence of varying concentrations of O2. Experiments were performed at a temperature of 35°C and a pressure of 80bar to simulate the conditions encountered during CO2 transport and injection. Results indicated that increasing O2 concentration from 0 to 1000ppm caused a progressive reduction in the general corrosion rate, but served to increase the extent of localized corrosion observed on both materials. Pitting (or localized attack) rates for X65 ranged between 0.9 and 1.7mm/year, while for 5Cr rose from 0.3 to 1.4mm/year as O2 concentration was increased from 0 to 1000ppm. General corrosion rates were over an order of magnitude lower than the pitting rates measured. Increasing O2 content in the presence of X65 and 5Cr suppressed the growth of iron carbonate (FeCO3) on the steel surface and resulted in the formation of a corrosion product consisting mainly of iron oxide (Fe2O3). 5Cr was shown to offer more resistance to pitting corrosion in comparison to X65 steel over the conditions tested. At concentrations of O2 above 500ppm 5Cr produced general corrosion rates less than 0.04mm/year, which were half that recorded for X65. The improved corrosion resistance of 5Cr was believed to be at least partially attributed to the formation of a Cr-rich film on the steel surface which was shown using X-ray photoelectron spectroscopy to contain chromium oxide (Cr2O3) and chromium hydroxide (Cr(OH)3). A final series of tests conducted with the addition of 1000ppm O2 in under-saturated conditions (water content below solubility limit) revealed that no corrosion was observed when the water content was below 1200ppm for both materials.

Understanding the Influence of SO2and O2on the Corrosion of Carbon Steel in Water-Saturated Supercritical CO2

In this work, the general and localized corrosion behavior of X65 carbon steel in water-saturated supercritical CO2 conditions containing O2 and SO2 at 35°C and 80 bar is evaluated. The results ind...

Relating iron carbonate morphology to corrosion characteristics for water-saturated supercritical CO2 systems

The changes in general and localised corrosion rates (via gravimetric analysis and non-contact profilometry, respectively) of carbon steel are quantified as a function of time in water-saturated supercritical CO2 condition, affording particular attention to surface pitting at various stages throughout the 168-h experiment. It was observed that two distinctly different surface degradation and corrosion product precipitation mechanisms were occurring on the steel surfaces, which were believed to be influenced by the volume of condensed water. The results are supported with scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy coupled with selected area electron diffraction (SAED) measurements.

Contact angle measurement ambiguity in supercritical CO2–water–mineral systems: Mica as an example

The current ambiguity on wettability of minerals in CO2–brine systems under the geological CO2 sequestration (GCS) reservoir conditions imparts the greatest uncertainty in predicting capillary behavior controlling safe-storage of CO2. To address this issue we conducted a series of experiments using muscovite as a representative of common aluminosilicate minerals. Based on new experimental results we identified several possible causes of the ambiguity problem in contact angle (CA) measurements. We also found that reaction with water-saturated supercritical (sc) CO2 (but not with scN2) phase severely roughened the muscovite surfaces, largely increased CA hysteresis and CO2 adhesion. Although some methodological influences on contact angle uncertainty can be reduced, the high surface-energy of clean and pristine aluminosilicate minerals have strong tendency to adsorb oppositely changed molecules and particles to reduce their surface energy, resulting in less reproducible CA values. Giving the fact that such clean and pristine mineral surfaces do not exist in real reservoirs, our future investigations shall focus on improving understanding of the effect of long-term CO2–mineral–brine reactions on reservoir wettability under realistic reservoir geochemical conditions.

Injection and Monitoring at the Wallula Basalt Pilot Project

Abstract Continental flood basalts represent one of the largest geologic structures on earth but have received comparatively little attention for geologic storage of CO2. Flood basalt lava flows have flow tops that are porous, permeable, and have large potential capacity for storage of CO2. In appropriate geologic settings, interbedded sediment layers and dense low-permeability basalt rock flow interior sections may act as effective seals allowing time for mineralization reactions to occur. Previous laboratory experiments showed the relatively rapid chemical reaction of CO2-saturated pore water with basalts to form stable carbonate minerals. However, recent laboratory tests with water-saturated supercritical CO2 show that mineralization reactions occur in this phase as well, providing a second and potentially more important mineralization pathway than was previously understood. Field testing of these concepts is proceeding with drilling of the world's first supercritical CO2 injection well in flood basalt being completed in May 2009 near the township of Wallula in Washington State and corresponding CO2 injection permit granted by the State of Washington in March 2011. Injection of a nominal 1000 MT of CO2 was completed in August 2013 and site monitoring is in progress. Well logging conducted immediately after injection termination confirmed the presence of CO2 predominantly within the upper flow top region, and showed no evidence of vertical CO2 migration outside the well casing. Shallow soil gas samples collected around the injection well show no evidence of leakage and fluid and gas samples collected from the injection zone show strongly elevated concentrations of Ca, Mg, Mn, and Fe and 13C/18O isotopic shifts that are consistent with basalt-water chemical reactions. If proven viable by this field test and others that are in progress or being planned, major flood basalts in the U.S., India, and perhaps Australia would provide significant additional CO2 storage capacity and additional geologic sequestration options in regions of these countries where conventional storage options are limited.

Clay Hydration/dehydration in Dry to Water-saturated Supercritical CO2: Implications for Caprock Integrity

Injection of supercritical CO2 (scCO2) for the geologic storage of carbon dioxide will displace formation water, and the pore space adjacent to overlying caprocks could eventually be dominated by dry to water- saturated scCO2. Wet scCO2 is highly reactive and capable of carbonating and hydrating certain minerals, whereas anhydrous scCO2 can dehydrate water-containing minerals. Because these geochemical processes affect solid volume and thus porosity and permeability, they have the potential to affect the long-term integrity of the caprock seal. In this study, we investigate the swelling and shrinkage of an expandable clay found in caprock formations, montmorillonite (Ca-STx-1), when exposed to variable water-content scCO2 at 50°C and 90bar using a combination of in situ probes, including X-ray diffraction (XRD), in situ magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), and in situ attenuated total reflection infrared spectroscopy (ATR-IR). We show that the extent of montmorillonite clay swelling/shrinkage is dependent not only on water hydration/dehydration, but also on CO2 intercalation reactions. Our results also suggest a competition between water and CO2 for interlayer residency where increasing concentrations of intercalated water lead to decreasing concentrations of intercalated CO2. Overall, this paper demonstrates the types of measurements required to develop fundamental knowledge that will enhance modeling efforts and reduce risks associated with subsurface storage of CO2.

Fayalite dissolution and siderite formation in water-saturated supercritical CO2

Olivines, significant constituents of basaltic rocks, have the potential to immobilize permanently CO2 after it is injected in the deep subsurface, due to carbonation reactions occurring between CO2 and the host rock. To investigate the reactions of fayalitic olivine with supercritical CO2 (scCO2) and formation of mineral carbonates, experiments were conducted at temperatures of 35°C to 80°C, 90atm pressure and anoxic conditions. For every temperature, the dissolution of fayalite was examined both in the presence of liquid water and H2O-saturated scCO2. The experiments were conducted in a high pressure batch reactor at reaction time extending up to 85days. The newly formed products were characterized using a comprehensive suite of bulk and surface characterization techniques: X-ray diffraction, Transmission/Emission Mössbauer Spectroscopy, Scanning Electron Microscopy coupled with Focused Ion Beam, and High Resolution Transmission Electron Microscopy. Siderite with rhombohedral morphology was formed at 35°C, 50°C, and 80°C in the presence of liquid water and scCO2. In H2O-saturated scCO2, the formation of siderite was confirmed only at high temperature (80°C).Characterization of reacted samples in H2O-saturated scCO2 with high resolution TEM indicated that siderite formation initiated inside voids created during the initial steps of fayalite dissolution. Later stages of fayalite dissolution result in formation of siderite in layered vertical structures, columns or pyramids with a rhombus base morphology.

Rotor design for high pressure magic angle spinning nuclear magnetic resonance

High pressure magic angle spinning (MAS) nuclear magnetic resonance (NMR) with a sample spinning rate exceeding 2.1kHz and pressure greater than 165bar has never been realized. In this work, a new sample cell design is reported, suitable for constructing cells of different sizes. Using a 7.5mm high pressure MAS rotor as an example, internal pressure as high as 200bar at a sample spinning rate of 6kHz is achieved. The new high pressure MAS rotor is re-usable and compatible with most commercial NMR set-ups, exhibiting low 1H and 13C NMR background and offering maximal NMR sensitivity. As an example of its many possible applications, this new capability is applied to determine reaction products associated with the carbonation reaction of a natural mineral, antigorite ((Mg,Fe2+)3Si2O5(OH)4), in contact with liquid water in water-saturated supercritical CO2 (scCO2) at 150bar and 50°C. This mineral is relevant to the deep geologic disposal of CO2, but its iron content results in too many sample spinning sidebands at low spinning rate. Hence, this chemical system is a good case study to demonstrate the utility of the higher sample spinning rates that can be achieved by our new rotor design. We expect this new capability will be useful for exploring solid-state, including interfacial, chemistry at new levels of high-pressure in a wide variety of fields.

A thermodynamic model for predicting mineral reactivity in supercritical carbon dioxide: I. Phase behavior of carbon dioxide–water–chloride salt systems across the H2O-rich to the CO2-rich regions

Phase equilibria in mixtures containing carbon dioxide, water, and chloride salts have been investigated using a combination of solubility measurements and thermodynamic modeling. The solubility of water in the CO2-rich phase of ternary mixtures of CO2, H2O and NaCl or CaCl2 was determined, using near infrared spectroscopy, at 90atm and 40 to 100°C. These measurements fill a gap in the experimental database for CO2–water–salt systems, for which phase composition data have been available only for the H2O-rich phases. A thermodynamic model for CO2–water–salt systems has been constructed on the basis of the previously developed Mixed-Solvent Electrolyte (MSE) framework, which is capable of modeling aqueous solutions over broad ranges of temperature and pressure, is valid to high electrolyte concentrations, treats mixed-phase systems (with both scCO2 and water present) and can predict the thermodynamic properties of dry and partially water-saturated supercritical CO2 over broad ranges of temperature and pressure. Within the MSE framework the standard-state properties are calculated from the Helgeson–Kirkham–Flowers equation of state whereas the excess Gibbs energy includes a long-range electrostatic interaction term expressed by a Pitzer–Debye–Hückel equation, a virial coefficient-type term for interactions between ions and a short-range term for interactions involving neutral molecules. The parameters of the MSE model have been evaluated using literature data for both the H2O-rich and CO2-rich phases in the CO2–H2O binary and for the H2O-rich phase in the CO2–H2O–NaCl/KCl/CaCl2/MgCl2 ternary and multicompontent systems. The model accurately represents the properties of these systems at temperatures from 0°C to 300°C and pressures up to ~4000atm. Further, the solubilities of H2O in CO2-rich phases that are predicted by the model are in agreement with the new measurements for the CO2–H2O–NaCl and CO2–H2O–CaCl2 systems even though the new data were not used in the parameterization of the model. Thus, the model can be used to predict the effect of various salts on the water content and water activity in CO2-rich phases on the basis of parameters determined from the properties of aqueous systems. Given the importance of water activity in CO2-rich phases for mineral reactivity, the model can be used as a foundation for predicting mineral transformations across the entire CO2/H2O composition range from aqueous solution to anhydrous scCO2. An example application using the model is presented which involves the transformation of forsterite to nesquehonite as a function of temperature and water content in the CO2-rich phase.

Reaction of water-saturated supercritical CO2 with forsterite: Evidence for magnesite formation at low temperatures

The nature of the reaction products that form on the surfaces of nanometer-sized forsterite particles during reaction with H2O-saturated supercritical CO2 (scCO2) at 35°C and 50°C were examined under in situ conditions and ex situ following reaction. The in situ analysis was conducted by X-ray diffraction (XRD). Ex situ analysis consisted of scanning electron microscopy (SEM) examination of the surface phases and chemical characterization of precipitates using a combination of confocal Raman spectroscopy, 13C and 29Si NMR spectroscopy, and energy-dispersive X-ray spectroscopy (EDS). The results show that the forsterite surface is highly reactive with the primary reaction products being a mixture of nesquehonite (MgCO3·3H2O) and magnesite (MgCO3) at short reaction times (∼3–4days) and then magnesite (MgCO3) and a highly porous amorphous silica phase at longer reaction times (14days). After 14days of reaction most of the original forsterite transformed to reaction products. Importantly, the formation of magnesite was observed at temperatures much lower (35°C) than previously thought needed to overcome its well-known sluggish precipitation kinetics. The conversion of nesquehonite to magnesite liberates H2O which can potentially facilitate further metal carbonation, as postulated by previous investigators, based upon studies at higher temperature (80°C). The observation that magnesite can form at lower temperatures implies that water recycling may also be important in determining the rate and extent of mineral carbonation in a wide range of potential CO2 storage reservoirs.

In Situ Infrared Spectroscopic Study of Brucite Carbonation in Dry to Water-Saturated Supercritical Carbon Dioxide

In geologic carbon sequestration, whereas part of the injected carbon dioxide will dissolve into host brine, some will remain as neat to water saturated supercritical CO(2) (scCO(2)) near the well bore and at the caprock, especially in the short term life cycle of the sequestration site. Little is known about the reactivity of minerals with scCO(2) containing variable concentrations of water. In this study, we used high-pressure infrared spectroscopy to examine the carbonation of brucite (Mg(OH)(2)) in situ over a 24 h reaction period with scCO(2) containing water concentrations between 0% and 100% saturation, at temperatures of 35, 50, and 70 °C, and at a pressure of 100 bar. Little or no detectable carbonation was observed when brucite was reacted with neat scCO(2). Higher water concentrations and higher temperatures led to greater brucite carbonation rates and larger extents of conversion to magnesium carbonate products. The only observed carbonation product at 35 °C was nesquehonite (MgCO(3)·3H(2)O). Mixtures of nesquehonite and magnesite (MgCO(3)) were detected at 50 °C, but magnesite was more prevalent with increasing water concentration. Both an amorphous hydrated magnesium carbonate solid and magnesite were detected at 70 °C, but magnesite predominated with increasing water concentration. The identity of the magnesium carbonate products appears strongly linked to magnesium water exchange kinetics through temperature and water availability effects.

Impact of SO 2 concentration on the corrosion rate of X70 steel and iron in water-saturated supercritical CO 2 mixed with SO 2

The corrosion behavior of X70 steel and iron in water-saturated supercritical CO 2 mixed with SO 2 was investigated using weight-loss measurements. As a comparison, the instantaneous corrosion rate in the early stages for iron in the same corrosion environment was measured by resistance relaxation method. Surface analyzes using SEM/EDS, XRD and XPS were applied to study the morphology and chemical composition of the corroded sample surface. Weight-loss method results showed that the corrosion rate of X70 steel samples increased with SO 2 concentration, while the corrosion rate increased before decreasing with SO 2 concentration for iron sample. Comparing resistance relaxation method results with weight-loss method results, it is found that the instantaneous corrosion rate of iron is much higher than the uniform corrosion rate of the iron tablet specimens which are covered with thick corrosion product films after a long period of corrosion. The corrosion product films were mainly composed of FeSO 4 and FeSO 3 hydrates. The possible reaction mechanism under such environment was also analyzed, and the electrochemical reaction between the dissolved SO 2 in the condensed water film with iron is the critical reaction step.

Cosolvent effect of water in supercritical carbon dioxide facilitating induced crystallization of polycarbonate

AbstractWater‐induced crystallization of polycarbonate (PC) was investigated in water‐saturated supercritical CO2 (scCO2) in the range of 80–160°C and 12–20 MPa, with the help of differential scanning calorimetry and wide‐angle X‐ray diffraction. Compared with pure scCO2, the enhanced plasticizing effect of water‐saturated scCO2 reduced the energy‐barrier for the motion of polymer chains, hence increased the crystallization rate of PC, and reduced the pressure threshold for crystallization from 14 to 12 MPa. On the other hand, the presence of water did not affect the thermodynamics of PC crystallization in scCO2. A 3D‐diagram was established to show the relationship between crystallization and solubility parameter of mixed supercritical fluid at different temperatures and pressures. The results show clearly that the PC has a wider range of crystallization temperature and pressure in water‐saturated scCO2 than in pure scCO2, mostly because the addition of water increased significantly the solubility parameter of mixed supercritical fluid, and decreased the difference in solubility parameter between PC and water‐saturated scCO2. POLYM. ENG. SCI., 47:1338–1343, 2007. © 2007 Society of Plastics Engineers