Supercritical CO2 Environment Research Articles

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.

Cement with bacterial nanocellulose cured at reservoir temperature: Mechanical performance in the context of CO[formula omitted] geological storage

Storing CO2 in deep underground reservoirs is key to reducing emissions to the atmosphere and standing against climate change. However, the risk of CO2 leakage from geological reservoirs to other rock formations requires a careful long-term analysis of the system. Mostly, oil well cement used for the operation must withstand the carbonation process that changes its poromechanical behavior over time, possibly affecting the system’s integrity.This work focuses on the microstructure and mechanical behavior of cement modified with bacterial nanocellulose (BNC) cured at 90 °C, simulating temperature at the reservoir level. The chemo-hydro-mechanical (CHM) coupled behavior of the cement–rock interface is also investigated through numerical analyses.Mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), ultrasonic wave velocity measurement, and unconfined compressive strength (UCS) tests were performed on cement samples subjected to a supercritical CO2 environment. After carbonation, BNC samples show a lower mass gain and lower porosity compared to PC. Permeability based on MIP results indicate that the BNC reduces the permeability of the specimen. XRD quantification shows no substantial difference between the crystalline phases of the two samples. Samples with BNC have lower absolute strength but higher relative increase during carbonation.The numerical study includes a homogenization of the medium considering the contribution of all components. CHM behavior of the cement with BNC is analyzed, and the results show the variations of the physical and chemical properties across the sample. The numerical study shows the advantage of using this type of tool to study realistic CO2 injection scenarios in deep wells.

Influence of H2S on the general corrosion and sulfide stress cracking of pipelines steels for supercritical CO2 transportation

This article presents a literature review and corrosion testing outputs to fill the knowledge gaps about the effect of H2S on corrosion and sulfide stress cracking (SSC) of pipeline steels in supercritical CO2 (s-CO2) environments. In H2O-saturated s-CO2, H2S facilitates the formation of a protective FeS layer with a threshold content less than 50 ppm. Increasing temperature or adding O2 destroys the integrity of FeS layer and remarkably enhances corrosion. The corrosion is likely to be controlled by gas chemical reactions instead of electrochemical reactions. The SSC susceptibility of strained pipeline steels is lower than expected.

Analysis of internal corrosion of supercritical CO2 pipeline

Abstract Carbon capture and storage (CCS) technology is considered to be one of the key technologies to reduce CO2 emissions. This paper reviews the industry corrosion accidents of CCS transportation system, in which the pipeline corrosion risk is analyzed, and the pipeline corrosion theory is summarized. Also, the effect of impurities on gas phase properties is discussed. We analyze the corrosion mechanism of multicomponent impurities on metals in a supercritical CO2 environment from the aspects of corrosion rate and corrosion products. We also describe the mechanism of pitting and stress corrosion of metals in a supercritical CO2 environment. Besides, the formation mechanism of FeCO3 protective layer and the research status of corrosion resistant alloys in supercritical CO2 are reviewed and analyzed. Finally, a series of shortcomings and prospects of the current research are put forward.

Corrosion of SS310 and Alloy 740 in high temperature supercritical CO2 with impurities H2O and O2

This study investigated corrosion performance of SS310 and Alloy 740 in supercritical CO2 with the impurity of 100 ppm H2O or O2 at 600 °C and 30 MPa for up to 1000 h. The addition of 100 ppm H2O remarkably enhanced general and localized oxidations while the presence of O2 led to the opposite tendency. Alloy 740 exhibited better resistance to carburization compared to SS310, possibly due to the higher solubility of carbides in Ni-based alloys than those in Fe-based alloys. Both alloys exhibit near parabolic oxidation behavior and acceptable corrosion resistance in the supercritical CO2 environments.

Oxidation Behavior of Additively Manufactured 316L in a Supercritical CO2 Environment

The general properties of additively manufactured (AM) metals have been fairly well characterized to this point with respect to mechanical behavior and even general corrosion response. However, as the fields of application of AM metals broadens, the need for unique/specialized evaluation is required. For instance, there remains a lack in understanding how AM metals behave under atmospheric corrosion exposure conditions where local heterogeneous environments govern the surface reactivity and susceptibility. Similarly, knowledge gaps exist in specialized environment, for example supercritical CO2 (sCO2). Materials and environment parameters such as composition, pressure, and temperature will influence corrosion susceptibility and/or oxidation properties. As AM metals often display vastly different microstructures from their wrought counterparts due to non-equilibrium cooling during processing, an understanding of their behavior in these environments is critical prior to possible application. Additionally, typical engineering design of oxy-combustion gas turbine systems used in these environments, results in atypical conditions, usually localized, that are well known to affect environmental performance of materials (such as crevices, welds, residual stresses, or galvanic coupling).Austenitic stainless steel, type 316L, specimens made by selectively laser melting (SLM) were exposed with their traditional wrought counterparts for comparison at 450°C and 7.6 MPa in pure sCO2 for one week. SLM samples were exposed in the as printed (a contour scan strategy was used) and the ground (ground to 1200 grit) state and compared to wrought samples ground to 1200 grit. Prior to exposure, samples were partially coated with a zirconia film to establish an initial true height to aid ellipsometry. Post exposure, oxide film thickness was measured with respect to the non-reactive coating height. Preliminary analysis of oxide film thickness measurements performed using ellipsometry showed a thinner oxide film grown on the in-process polished SLM samples (0.66 - 0.79 µm) versus the ground SLM (1.1 µm) or wrought samples (0.8 – 1.22 µm). Additional analysis was performed through scanning electron microscopy and focused ion beam combined with transmission electron microscopy to characterize the oxides formed and elucidate possible microstructural and/or morphological dependence of the film growth.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2020-4568 A

Different Effect Mechanisms of Supercritical CO2 on the Shale Microscopic Structure.

To better understand how supercritical carbon dioxide (CO2) enhances shale gas production, it is necessary to study the interaction of supercritical CO2 with shale and its impact on shale microstructure. The different mechanisms by which supercritical CO2 changes the shale pore structure were studied by X-ray diffraction analyses, scanning electron microscopy (SEM), nuclear magnetic resonance spectroscopy, and low-pressure nitrogen gas adsorption tests on shale samples before and after treatment with different pressures and gases (CO2 and Ar). The results showed that after treatment with CO2, the mineral content of shale changed significantly, and in particular, the proportions of calcite and dolomite decreased. The mineral content of shale changed the most after treatment with supercritical CO2, and the microscopic pores were most observable by SEM. In a gaseous CO2 environment, the effect of CO2 adsorption on shale pores is greater than the effects of gas pressure and dissolution reactions. However, in a supercritical CO2 environment, the changes in shale pore structures are mainly controlled by extraction and dissolution reactions. When shale is exposed to supercritical CO2, the fractal dimensions of adsorption pores and seepage pores decrease, indicating that the specific surface area and roughness of adsorption pores decrease. This implies that the adsorption capacity decreases, and that the complexity of the seepage pores declines, which is conducive for gas migration.

Design and Performance Analysis of a Supercritical Carbon Dioxide Heat Exchanger

This paper presents a preliminary design and performance analysis of a supercritical CO2 (SCO2) heat exchanger for an SCO2 power generation system. The purpose of designing a SCO2 heat exchanger is to provide a high-temperature and high-pressure heat exchange core technology for advanced SCO2 power generation systems. The target outlet temperature and pressure for the SCO2 heat exchanger were 600 °C and 200 bar, respectively. A tubular type with a staggered tube bundle was selected as the SCO2 heat exchanger, and liquefied petroleum gas (LPG) and air were selected as heat sources. The design of the heat exchanger was based on the material selection and available tube specification. Preliminary performance evaluation of the SCO2 heat exchanger was conducted using an in-house code, and three-dimensional flow and thermal stress analysis were performed to verify the tube’s integrity. The simulation results showed that the tubular type heat exchanger can endure high-temperature and high-pressure conditions under an SCO2 environment.

CO2 geological storage: Microstructure and mechanical behavior of cement modified with a biopolymer after carbonation

Large amounts of CO2 could be stored underground in deep rock reservoirs and could help reducing emissions into the environment. Carbon geo-storage technologies have several years in development and new techniques and materials are being studied to make this procedure more effective and less expensive. The risk of leakage from geological reservoirs to other rock formations or even towards the surface means that long-term behavior must be carefully studied. The carbonation of the cement used for sealing the wellbore may compromise the borehole integrity. In light of this problem, this work aims to analyze the poromechanical behavior of cement with and without a new additive in a CO2 environment. Bacterial nanocellulose is a biopolymer that modifies important cement properties such as compressive strength, thermal behavior and hydration degree. Two cement types were studied: class G cement and modified class G cement with bacterial nanocellulose. These samples were submitted to a supercritical CO2 environment (temperatures higher than 32 °C and pressures higher than 8 MPa) during 30 days. Mercury intrusion porosimetry and uniaxial compressive strength tests were performed on these samples to study the effect of carbonation. Both types of cement are affected after carbonation by reducing compressive strength and Young’s modulus (E), however, the strength of modified cement was reduced by 8%, while non-modified cement was reduced by 20%.

Molecular Dynamics of Combustion Reactions in Supercritical Carbon Dioxide. 6. Computational Kinetics of Reactions between Hydrogen Atom and Oxygen Molecule H + O2 ⇌ HO + O and H + O2 ⇌ HO2.

Reactions of the hydrogen atom and the oxygen molecule are among the most important ones in the hydrogen and hydrocarbon oxidation mechanisms, including combustion in a supercritical CO2 (sCO2) environment, known as oxy-combustion or the Allam cycle. Development of these energy technologies requires understanding of chemical kinetics of H + O2 ⇌ HO + O and H + O2 ⇌ HO2 in high pressures and concentrations of CO2. Here, we combine quantum treatment of the reaction system by the transition state theory with classical molecular dynamics simulation and the multistate empirical valence bonding method to treat environmental effects. Potential of mean force in the sCO2 solvent at various temperatures 1000-2000 K and pressures 100-400 atm was obtained. The reaction rate for H + O2 ⇌ HO + O was found to be pressure-independent and described by the extended Arrhenius equation 4.23 × 10-7 T-0.73 exp(-21 855.2 cal/mol/RT) cm3/molecule/s, while the reaction rate H + O2 ⇌ HO2 is pressure-dependent and can be expressed as 5.22 × 10-2 T-2.86 exp(-7247.4 cal/mol/RT) cm3/molecule/s at 300 atm.

Effect of Nb and Ti on Corrosion Characteristics of Low Alloy Steel in Supercritical CO2 Environment

Effect of Nb and Ti on Corrosion Characteristics of Low Alloy Steel in Supercritical CO2 Environment

Effect of high-temperature supercritical carbon dioxide exposure on the microstructure and tensile properties of diffusion-bonded Alloy 690

Alloy 690 was diffusion-bonded and exposed to the high-temperature supercritical CO2 environment, and the effect of exposure on the microstructure and mechanical properties was investigated. In the as-bonded joint, some small carbides are discontinuously arranged along the bonding line. After exposure at 550 °C and 600 °C, the continuous carbides are developed and occupy all the grain boundaries and bonding line. The continuous carbides transform into the discrete large particles when the exposure temperature further increases to 650 °C. With the increase in exposure temperature, the tensile strength and microhardness of the joints decrease, while the elongation first slightly increases and then decreases at 650 °C. For the as-bonded joint and the joints exposed at 550 °C and 600 °C, the fracture occurs at the parent Alloy 690 and the main fracture mode is the ductile dimple fracture. However, for the joint exposed at 650 °C, the fracture occurs at the bond line with a manner of brittle fracture. The degradation of strengths and elongation after exposure to supercritical CO2 at 650 °C were associated with the growth of carbides along the bond line.

Role of residual 2-amino-2-methyl-1-propanol and piperazine in the corrosion of X80 steel within an impure supercritical CO2 environment as relevant to CCUS

The corrosion of steels in the supercritical CO2 environment with impurities in a carbon capture, utilization and storage system has attracted great interests in recent years. In this work, corrosion inhibition mechanisms of the residual 2-amino-2-methyl-1-propanol and piperazine from the CO2 capture process on X80 steel within an impure supercritical CO2 environment were investigated by weight-loss method and surface analysis techniques. The results showed that a small amount of 2-amino-2-methyl-1-propanol had marginal effect on the corrosion of steel. Corrosion rate was decreased as the 2-amino-2-methyl-1-propanol concentration increased further. When 100 ppm 2-amino-2-methyl-1-propanol + 50 ppm piperazine was added, a lowest corrosion rate was observed, reaching 0.41mm/a. Meanwhile, pitting corrosion was observed under all conditions. The combination of 2-amino-2-methyl-1-propanol and piperazine cannot inhibit pitting corrosion efficiently, while flow accelerated the propagation of pits in the presence of 2-amino-2-methyl-1-propanol. FeSO4 was confirmed as the corrosion product for all conditions. RNH3+, PZH+, Fe2O3 and Fe3O4 were detected in the corrosion products depending on the test conditions. The results indicated that the inhibition mechanism of piperazine and 2-amino-2-methyl-1-propanol was attributed to both the neutralization and adsorption effects on the steel surface. A non-uniform adsorption inhibition mechanism is proposed based on these test results.

EPR Diagnostics of D,L-Polylactide Porous Matrices Formed in Supercritical CO2

The regularities of formation of D,L-polylactide porous matrices in supercritical CO2 environment with simultaneous impregnation with paramagnetic biologically active 4-hydroxy-2,2,6,6-tetramethylpiperidine- 1-oxyl (TEMPOL) was studied using spin probe electron paramagnetic resonance (EPR) and optical microscopy. The dependence of the average and local concentration of a dopant on impregnation conditions was assessed. The resulting matrices meet important requirements for porous materials for tissue engineering. Considering that impregnation of a polymer with a paramagnetic compound makes it possible to study the uniform distribution of a dopant in a sample at macroscopic and microscopic levels and to study a structure of a polymer matrix, EPR spectroscopy is a promising method for studying porous polymeric materials formed under supercritical conditions.

Catalytic Effect of Carbon Dioxide on Reaction OH + CO → H + CO2 in Supercritical Environment: Master Equation Study

We investigated the reaction rates of OH + CO → H + CO2 in supercritical CO2 environment with and without additional CO2 molecule included in reactive complex. Ab initio potential energy surfaces previously reported a lower activation barrier and hence a catalytic effect of additional CO2 molecule. Here we solve the steady-state unimolecular master equations based on the Rice-Ramsperger-Kassel-Marcus theory (RRKM) and compare the rates for the two mechanisms. We found that the alternative reaction mechanism becomes faster at high pressure and low temperature, when the concentration of prereactive complex with additional CO2 molecule becomes appreciable. Therefore, this catalytic effect may be important for the chemical processes in CO2 solvent but is unlikely to play a role during combustion.

First-principles study of the products of CO2 dissociation on nickel-based alloys: Trends in energetics with alloying element

Oxidation and corrosion of nickel and Ni-based alloys are a problem for many industrial applications, such as power plants that use supercritical CO2 as the working fluid. In supercritical CO2 environments, CO2 dissociates on the surface forming adsorbed CO and O, which can oxidize the surface. The adsorbed CO can further breakdown via direct CO dissociation or via the Boudouard reaction to form adsorbed C, which can in turn carburize the surface. Understanding how the adsorbed species interact with different Ni-based alloys can help guide the design of future alloys. The interactions of adsorbed O, C, and CO on the (100) and (111) facets of pure Ni and Ni individually alloyed with Al, Co, Cr, Cu, Fe, Mn, Mo, Nb, Ti, V, and W are examined using density functional theory. We find that the binding of CO is energetically similar across all alloy surfaces and both facets, while O binding varies strongly with different metals added to nickel and C binding varies between the different facets but only slightly for different metals alloyed to nickel. The binding of O is weaker on pure Ni and Ni alloyed with Cu, Co, Fe, Al, or Mn and stronger on Ni alloyed with Nb, Cr, Mo, Ti, V, or W, while the binding of C is weaker on the (111) facet than the (100) facet. The difference in the binding energies of the adsorbates across the different alloy surfaces is due mainly to the ensemble effect, rather than the ligand effect. The thermodynamics of CO breakdown are also studied and we find that the breakdown of CO via direct CO dissociation is endothermic on the (111) facet and exothermic on the (100) facet, with the alloy surfaces that bind O strongly having the most exothermic reaction energies. The breakdown of CO via the Boudouard reaction has similar reaction energies across the different alloy surfaces of a single facet and is endothermic on both facets, with the (111) facet being most endothermic. This comprehensive study presents a summary of the current literature as well as a well-rounded view of the products of CO2 breakdown on Ni surfaces alloyed with the most common alloying elements used in industrial applications.

Effects of CO and O2 Impurities on Supercritical CO2 Corrosion of Alloy 625

Corrosion of alloy 625 was investigated in three supercritical CO2 (sCO2) environments: research-grade (RG) (99.999 pct pure), RG + 100 ppm O2 (at.), and RG + 1 pct CO (at.). Samples were exposed to each condition for a total of 1000 hours at 750 °C and 20 MPa. Each sample was analyzed using mass change, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), time-of-flight-secondary ion mass spectroscopy (TOF-SIMS), and Raman spectroscopy. Samples exposed to RG CO2 produced a compact uniform chromia layer. The samples exposed to oxygen-rich CO2 showed a less-uniform oxide with nodules characterized by Ni- and Fe-rich oxides on the surface with enhanced chromia formation beneath. The oxide grown in 1 pct CO exhibited the least protective oxide consisting of a duplex chromia scale with inner equiaxed grain structure and an outer porous layer. RG + 1 pct CO was the only environment in which carbon was observed throughout the oxide, although carbon enrichment was observed at the M-O interface of the oxides produced in RG and RG + 1 pct CO environments. A model for explaining carburization of chromium in sCO2 environments was produced by treating the oxide as a diffusion barrier and considering the chemical equilibrium of CO2 through the Cr2O3 phase.

Understanding the pitting corrosion mechanism of pipeline steel in an impure supercritical CO2 environment

This work was undertaken to investigate the pitting corrosion mechanism of pipeline steel in an impure supercritical CO2 environment by executing experiments with different exposure times and varied rotation speeds. The results revealed that in a water-saturated supercritical CO2-SO2-NO2-O2 environment, the average maximum pitting depth stabilized after three days, which indicated that pits were unstable and cannot rapidly propagate with time while also implying that a local acidification process might not exist. The product accumulation in the pit cavities can eventually prevent the diffusion of the corrosive media and water from the product surface to the metal substrate. The effect of flow on the propagation of pits was marginal, revealing the weak influence of flow on the mass transfer of species through the product scales. The formation of spherical products was possibly attributed to the influence of NO2 on the contact angle of water droplets on the steel surface.