Supercritical CO2 Environment Research Articles

Corrosion Behavior of N80 Steel in Underground Supercritical CO2 Environments

Corrosion Behavior of N80 Steel in Underground Supercritical CO2 Environments

Prediction and modeling of tie-dye polyester fabric's texture and color feature in supercritical carbon dioxide

To mitigate the water-intensive challenges of tie-dye clothing production and address the absence of objective evaluation for finished products, we have explored the correlation between tie-dye techniques in supercritical carbon dioxide (SC-CO2) and image patterns. Employing digital image processing, we extracted the average HSV three-component value of the valid tie-dye area, the proportion of incompletely dyed area in the HSV color space, and the initial three texture features of the digital tie-dye image using the Tamura method. We scrutinized five factors in the supercritical CO2 dyeing process: rotational speed, dyeing temperature, dyeing pressure, dye concentration, and dyeing time. The single-factor climbing test revealed that temperature and pressure are the predominant factors influencing tie-dyeing performance. We propose a correlation between the texture parameters of tie-dyeing and the swelling effect of polyester fabric in a supercritical CO2 environment. Subsequently, we conducted two-factor tests on temperature and pressure to investigate their specific effects on the parameters of supercritical polyester tie-dyeing. The results indicated significant changes in regularity, saturation, and the proportion of undyed area with variations in dyeing temperature and pressure. Building upon these findings, we developed an artificial neural network for predicting tie-dye dyeing temperature and pressure in supercritical CO2, utilizing features regularity, saturation, and proportion of undyed area as inputs. In the 105st round, experimental results demonstrated an accuracy of 0.99445, substantiating the efficacy of tie-dye pattern features in supercritical CO2 for technique forecasting.

Atomic insights into the corrosion behavior of Fe-Cr alloys in supercritical CO2 environment

In this work, the corrosion process of Fe-Cr alloys in flowing CO2 was simulated using molecular dynamics within an extended ReaxFF force field. The effects of Cr content, temperature variations, impurity gases and vacancy defects were discussed. The corrosion process was dominated by oxidation and carburization reactions, with the oxidation rate higher than carburization rate, resulting in the formation of a carbide layer within the central region between two oxide layers. The increase in Cr content tended to decelerate corrosion, while raising temperature aggravated the corrosion of Fe-Cr alloy. The presence of O2 and SO2 impurities was found to thicken the corrosion layer, in contrast to the effects of CO and H2O impurities. A notable finding highlighted the positive influence of 2% vacancy defects in enhancing the corrosion resistance of the Fe-Cr alloy. The Al2O3 coating achieved a good corrosion protection by inhibiting the dissociation of CO2.

Corrosion behavior of eutectic high-entropy alloys in supercritical CO2 environments

This study explores the corrosion resistance of AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) in supercritical CO2 (S–CO2). The corrosion behavior was meticulously examined under conditions of 500 °C and 25 MPa CO2 over a duration of 800 h. The formation of distinct passivation layers on the face-centered cubic (FCC) and body-centered cubic (BCC) B2 phases was observed, leading to a cooperative passivation effect of Al and Cr. The protective Al2O3 oxide layers, which were dense and continuous, played a crucial role in inhibiting carburization and further oxidation, thereby significantly enhancing the corrosion resistance. Interestingly, no carburization was observed in this study.

Evaluation of coated steels in supercritical CO2

AbstractThe carburizing supercritical CO2 (sCO2) environment limits the use of lower cost steels in the lower temperature (450–650°C) portions of the sCO2 Brayton cycle because of concerns about internal carburization and embrittlement. Results on a ferritic–martensitic steel and conventional and advanced austenitic steels at 450–650°C in 30 MPa sCO2 with and without 1% O2 and 0.1% H2O additions have indicated that sCO2 environments will have lower maximum operating temperatures compared to steam plants. Pack Al and Cr coatings were evaluated at 650°C on T91 and 316H substrates and showed some benefit for up to 2000 h at 650°C, especially without impurities. However, characterization indicated Al2O3 was not formed and Cr‐rich carbides formed in the Cr coatings. With the addition of impurities in the sCO2, the coatings were less protective at 650°C. Subsequent exposures at 600°C in sCO2 showed similar behavior. Postexposure evaluations included measuring the bulk C content and room temperature tensile properties. Improvements were indicated but the tensile results were complicated by the high temperature pack coating process affecting the substrate properties.

Corrosion mitigation behavior of mild steel in supercritical CO2 environments with varying the solution volume

The corrosion behavior of X70 steel in CO2 saturated water at 60 °C and 10 MPa was investigated by limiting the exposed solution volumes. When the specific solution volume to the exposed area was smaller than 10 mL/cm2, it revealed the formation of protective FeCO3 layer, leading to a significant corrosion reduction. The time-sensitive nucleation and the spatial growth of FeCO3 grains governed the overall performance of corrosion product layers. The solution volume dependency was further explained by a diffusion-controlled deposition mechanism. It suggested a possible way to prevent CO2 corrosion in harsh environments by generating stable FeCO3 layers.

Temperature and Reaction Time’s Effects on N80 Steel Corrosion Behavior in Supercritical CO2 and Formation Water Environments

In the present study, an immersion experiment was carried out to examine how N80 steel corrodes when exposed to formation water containing dissolved CO2 and supercritical CO2 (Sc-CO2) along with water vapor. We employed electrochemical and surface analysis methods to examine the influence of various factors, including the temperature and duration of immersion, on the extent of corrosion. The results show that the corrosion patterns of N80 steel in a supercritical CO2 environment and CO2-saturated formation water differed significantly. The presence of similar corrosion features was suggested by the constant structure of the corrosion products identified in the formation water. However, the morphology of the corrosion product was complex in the supercritical CO2 environment, exhibiting features of pitting and localized corrosion. Furthermore, a non-linear trend in the corrosion rate was observed between 40 °C and 120 °C. Specifically, the rate of corrosion declined from 40 °C to 80 °C, but it then resumed its growth from 80 °C to 120 °C. These findings suggest that very high temperatures could lead to the destruction of corrosion products and subsequently enhance the corrosion process.

DNS of a non-premixed CH4/O2 flame in a supercritical CO2 environment

3D Direct Numerical Simulation (DNS) is performed to investigate turbulent non-premixed methane oxy-combustion in a CO2-rich environment at supercritical conditions (300 bar). The study focuses on a shear-layer configuration typical of slot burners, where the central slot carries the fuel and the oxidant mixture O2/CO2 flows on both sides of the central jet. The simulation solves the compressible Navier–Stokes equations coupled with the translated volume formulation of the Peng–Robinson cubic equation of state (VTPR-EoS), utilizing a reduced 23-species kinetic scheme derived from the ARAMCO 2.0 complete mechanism. The extremely high pressure results in turbulent scales smaller than those observed at lower pressures. Both premixed and diffusion flame zones are identified, with heat primarily released in non-premixed rich regions, leading to a CO mass fraction of up to 0.55. The flow exhibits uphill (counter-gradient) diffusion for both CO2 and H2O, primarily influenced by the interaction of binary diffusion coefficients and individual species chemical potential gradients. Values in the range of 2.52−2.62 are obtained for the fractal dimension of temperature iso-surfaces. Mixture fraction probability density functions (PDFs) are compared with the standard presumed β−PDF, revealing an underestimation of mixing. Differently from flames at atmospheric pressures, the Dufour effect in the energy diffusion flux, is not negligible. Furthermore, fugacity coefficients must be considered in the calculation of chemical species kinetic rates.

Corrosion Evolution mechanism of N80 tubing steel under supercritical CO2 and H2S environment

The corrosion evolution mechanism of N80 tubing steel in 8 MPa supercritical CO2 and 0.1 MPa H2S environment was investigated. The results show that although the corrosion rate of N80 steel decreases with the prolonged corrosion time, it still maintains a high level of about 1.06 mm/y after a long period of 360 h. As the corrosion progresses, the corrosion products change from FeS to a mixture of FeS and FeCO3. The corrosion form of N80 steel changes from uniform corrosion to localized corrosion. The origin credited for localized corrosion is the detachment of large particles of FeS in the early corrosion stage. A double-layer film consisting of an outer layer of FeS and an inner layer of FeCO3 forms in the area of corrosion pits after a prolonged period of corrosion, which provides protection for the substrate, thereby causing the decrease of localized corrosion rate of N80 steel.

Corrosion behaviors of iron in a supercritical CO2 environment: a molecular dynamics study

Corrosion behaviors of iron in a supercritical CO2 environment: a molecular dynamics study

Insights into the effect of H2S on the corrosion behavior of N80 steel in supercritical CO2 environment

In this study, the corrosion behavior of N80 steel exposed to 80 bar supercritical CO2 and 0–15 bar H2S environments was investigated by weight loss test, surface analysis, water chemistry simulation, corrosion thermodynamic and kinetic calculations. The results show that a very low H2S pressure of 0.004 bar in supercritical CO2 environment boosts the corrosion rate of N80 steel, whereas the rate is considerably reduced with further increasing the H2S pressure. The variation of corrosion rate with H2S pressure largely depends on the changes in cathode process and overall protectiveness of corrosion product film caused by H2S. As the H2S pressure rises, the evolution of corrosion product film on the steel is as follows: FeCO3 dominated film below 0.16 bar H2S, FeCO3 and FeS mixed film within 0.16–4 bar H2S, and FeS dominated film over 4 bar H2S. Benefiting from the integrity of film structure and the uniformity of film composition, N80 steel experiences uniform corrosion in the formation environment of FeCO3 or FeS dominated film. However, the localized corrosion easily occurs in the formation environment of FeCO3 and FeS mixed film owing to the loss of film integrity induced by uneven precipitation of FeCO3 inside the corrosion product film.

Dielectric barrier discharge plasma treatment of catalysts and the effect on isomerised rice bran oil

SummaryDielectric barrier discharge (DBD) plasma is an emerging technology applied in multiple industries in recent years. In this work, DBD plasma was used instead of a traditional heating activation catalyst and applied in the field of rice bran oil (RBO) conjugation. Linoleic acid (LA) in rice bran oil generated a series of compounds with π‐double bonds at the basic site of the catalyst and finally shed with the catalyst to produce conjugated linoleic acid (CLA). Ru‐Pd/USY was prepared by the primary wet impregnation method, and Ru‐Pd/USY was treated at a power of 180 W, a discharge time of 150 s and an electrode spacing of 2.5 cm. The Ru‐Pd/USY morphology and internal composition were analysed by scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The catalyst was isomerised with RBO in a supercritical CO2 environment, and the conversion of linoleic acid (LA) in Pd‐Ru/USY RBO after DBD treatment reached 67.4 ± 0.8%, and the finished oil met the edible standard.

Effect of Flow on the Corrosion Behavior of Pipeline Steel in Supercritical CO2 Environments with Impurities

Corrosion is a major concern in transmission pipelines that transport captured CO2. While dry CO2 is noncorrosive, significant corrosion has been reported in dense-phase CO2 with trace amounts of water and impurities such as O2, H2S, SOx, and NOx. The aim of this work is to improve our understanding of the physicochemical aspects of the corrosion of carbon steels in the high-pressure environments associated with CO2 transmission pipelines. The effect of flow on the corrosion of X65 carbon steel was investigated in a series of autoclave tests with different combinations of impurity concentrations in supercritical CO2 conditions (8 MPa and 35°C). The corrosion rate of specimens was determined by weight loss measurements. The surface morphology and composition of the corrosion product layers were characterized using surface analytical techniques (scanning electron microscopy, eneregy dispersive x-ray spectroscopy, and Raman microscopy). Localized corrosion was measured via surface profilometry after corrosion products were removed. Results showed that no corrosion was observed in the supercritical CO2 with 650 ppmv of water, 50 ppmv SO2, and 100 ppmv NO, but corrosion occurred when SO2 concentration was increased to 4,500 ppmv and 40,000 ppmv of O2 was added to the system. The presence of flow significantly accelerated the corrosion of carbon steel. Furthermore, localized corrosion was observed in the presence of both O2 and flow.

Epitaxial supercritical fluid processing of ZIF-8 membranes towards efficient C3H6/C3H8 separation

Although having shown promising prospects in diverse gas separations, sustainable fabrication of high-performance metal-organic framework (MOF) membranes remains a significant challenge towards applications. In the present work, epitaxial supercritical fluid (SCF) processing was developed for preparing highly C3H6-permselective ZIF-8 membranes through depositing ZIF-8 seed layers followed by epitaxial supercritical growth in supercritical CO2 (scCO2) environments. Our results indicated that maintaining scCO2 in the gas-like region was indispensable for preparing ZIF-8 membranes with desired microstructure and superior C3H6/C3H8 separation (i.e., C3H6 permeance and C3H6/C3H8 selectivity). Simultaneously, unreacted 2-methylimidazole ligands could be fully recycled and reutilized after epitaxial SCF processing. The present study sheds light on the future prospects for sustainable production of versatile high-performance MOF membranes.

Supercritical CO2‐assisted Ru‐Pd/USY synchronised isomerisation to produce rice bran oil rich in conjugated linoleic acid

SummaryIn this work, the catalytic efficiency and influencing factors of supported bimetallic catalysts for the synchronised isomerisation of rice bran oil (RBO) to produce conjugated linoleic acid (CLA)‐rich RBO under supercritical conditions were investigated. The morphology and internal composition of the metal catalysts were analysed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which revealed that Ru and Pd were successfully supported by ultra‐stable Y(USY). The catalyst and oil were synchronously isomerised in the supercritical CO2 environment, and the change in the fatty acid composition of the oil was measured by gas chromatography. The results showed that when the CO2 pressure was 8.0 MPa, the catalyst addition was 5% and the reaction temperature was 160 °C, the conversion of linoleic acid in the RBO catalysed by Ru‐Pd/USY was 68.25 ± 0.08%, and the produced oil met the edible standard.

Electrochemical Study of Pitting Corrosion of Corrosion Resistant Alloys in Supercritical CO2 Environment

Various types of corrosion resistance alloys such as 13 Cr, Super 13 Cr, and duplex stainless steels are typically used in oil and gas and CO2 capture and storage applications, especially the injection section, where the pipeline could be exposed to aqueous phase and the risk of localized corrosion is of high concern. The composition of these materials is engineered to provide high corrosion-resistant properties. The operating conditions in the above-mentioned applications can include high CO2 pressure and high temperature leading to the “so-called” supercritical CO2 condition. Under the supercritical CO2 conditions, the pH of the aqueous phase in the system can be as low as pH ~ 3 buffered by the dissolved CO2. The environment can also contain high salinity, and therefore, the passive layer on the stainless steel might be locally damaged resulting in pitting corrosion. While there are numerous studies available on the localized corrosion of different stainless steels in chloride-containing aqueous environment, the number of studies in supercritical CO2 conditions is limited. The objective of this work is to understand the effect of supercritical CO2 on the localized corrosion mechanism of corrosion resistant alloys.Three different types of corrosion resistant alloys (13 Cr, Super 13 Cr, and duplex stainless steel) are studied under CO2 pressure (0 to 14 MPa) and at high temperature (150˚C) in 5 wt.% NaCl solution. The experiments are conducted in a high-pressure autoclave system at a consistent initial pH for comparison. The electrochemical behavior and the pitting corrosion are studied using cyclic potentiodynamic polarization and potentiostatic measurements. The surface of each specimen is investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) before and after the electrochemical experiments to characterize the microstructural and localized corrosion features, respectively. All the tested materials show passive behavior under the conditions of the current study, however the pitting potential decreased in this order: duplex, Super 13 Cr and 13 Cr stainless steel.

Initial stages of oxide growth on AM stainless steel exposed to a supercritical CO2 environment

Wrought and additively manufactured (AM) 316 L stainless steel samples were exposed to a simulated Brayton cycle supercritical CO2 (sCO2) environment, at temperature of 450 °C and pressure of 76 bar in 99.999% CO2 for 2 weeks. The ground surfaces of wrought and AM 316 L specimens had average oxide thickness of 95 and 51 µm, respectively, composed primarily of Fe and Cr oxides. An as-printed AM 316 L sample was also exposed to the sCO2 environment and exhibited negligible oxidation during the 2-week exposure because of a thick Cr rich Mn silicate native oxide covering most of surface.

Synthesis of single-atom dispersed Co-NC catalytic materials in supercritical CO2 environment with inorganic salt precursor

Supported single-atom catalytic materials (SACMs) have aroused extensive interest due to their remarkable properties. Herein, a novel method was proffered to prepare Co-NC SACMs using custom-designed N-doped carbon (NC) as support, CoCl2 as the precursor in supercritical CO2 with appropriate co-solvent. It was found that when ethanol was used as co-solvent, nanoparticles were obtained while only Co single-atom was obtained when N, N-Dimethylformamide (DMF) was used as co-solvent. Both the theoretical loading and the deposition time influenced the Co loading a lot, and the maximum Co loading was as high as 1.71 wt%. Strong acid, strong alkali, corrosive solvent, and high-temperature treatment were avoided in the whole process. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM), X-ray photoelectron spectroscopy (XPS), Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), and Energy Dispersive X-ray spectroscopy (EDX) were conducted to confirm the existence and uniform distribution of Co atoms over the N-doped carbon materials. The conversion rate of 90.0% and selectivity of 86.0% were obtained for the solvent-free selective oxidation of benzyl alcohol to benzaldehyde at 70 °C and 1 h using the Co-NC SACMs.

Interfacial tension and equilibrium contact angle of lipids on polished glass in supercritical CO2

Better understanding of the wettability behavior of lipids on different surfaces is needed for supercritical CO2 (SC-CO2) fractionation of lipid mixtures using packed columns. This study aimed to determine the interfacial tension (IFT) and equilibrium contact angle (CAeq) of oleic acid (OA) and canola oil (CO) on polished glass in SC-N2 and SC-CO2 environments at 40, 60, 80 °C and 16, 20, 24 MPa. IFT and CAeq were determined using pendant drop and height/width methods, respectively. IFT values decreased with pressure due to the increase in CO2 density. CAeq values of lipids in SC-CO2 exhibited three different patterns: complete, complete-partial, and partial wettability at different conditions due to the solubility of SC-CO2 in lipid and vice versa, and formation of thin vapour film on glass surface. Novel phenomena of formation of satellite droplets, SC fluid cavity, bouncing and sliding of CO droplet on glass in SC-CO2 were observed.

Effect of Flow Rate on the Corrosion Behavior of API 5L X80 Steel in Water-Saturated Supercritical CO2 Environments

The effect of the water-saturated supercritical carbon dioxide (scCO2) flow rate on the corrosion behavior of API 5L X80 steel at a temperature of 35°C and pressure of 80 bar was investigated. Tests were performed with the samples attached to a rotating shaft inside an autoclave. Results indicate that increasing the scCO2 flow rate had no significant influence on the general/localized corrosion rate under the various dynamic conditions considered. The average general corrosion rate was 0.064 mm/y, while the average measured pitting penetration rates were one order of magnitude higher. The size of the corrosion features on the surface of the samples, which were believed to provide an indication as to the size of the condensed water droplets, was much smaller than the calculated critical droplet size needed to be displaced by the flow, supporting the theory as to why flow rate had little effect on the corrosion response.