CO2-saturated Solution Research Articles

Insights into iron-accelerated gypsum scaling mitigation strategies in nanofiltration membrane process

In this study, the impact of ferric ions on gypsum crystallization and NF membrane performance was investigated to mitigate iron-accelerated gypsum scaling. Gypsum scaling in the presence of ferric ions led to a significant decline in the water flux, but a relatively higher reversible fouling ratio was observed compared to that under individual gypsum and iron-oxide scaling. Ferric ions influenced the crystallization of gypsum on NF membranes by serving as additional nucleation sites, leading to accelerated gypsum scaling. Various mitigation methods (e.g., feed spacers and cleaning processes) were evaluated to effectively control iron-accelerated gypsum scaling. The introduction of spacers exhibited a high mitigation efficiency by enhancing the mass transfer of scalant ions due to changes in the water channel hydrodynamics, but the overall efficiency decreased over time. To enhance the mitigation efficiency, different cleaning methods (e.g., CO2 oversaturated solution, HCl, and NaCl flushing) were conducted with feed spacers. A CO2 saturated solution demonstrated high cleaning efficiency owing to the high turbulence induced by CO2 bubbles, whereas HCl flushing showed negligible efficiency. NaCl flushing exhibited the highest cleaning efficiency through mono/divalent ion-exchange effects on iron-gypsum scaling. This study provides comprehensive insights into iron-accelerated gypsum scaling mitigation strategies for nanofiltration membranes, highlighting the impact of coexisting ferric compounds on gypsum scaling.

Three-Way Control on Product Selectivity in Electrocatalytic CO2 Reduction Reaction Using a Single Molecular Co-NHC Catalyst.

For a long time, molecular electrocatalysts have been developed to reduce CO2 efficiently to value-added products such as CO and HCO2H, along with H2; however, selectivity remained as a major issue. Recent work toward addressing this issue showed that several different catalysts could be used to achieve product selectivity. It is desirable that instead of using different catalysts for specific products, a single catalyst should be able to produce the target products by subtle tuning of the reaction conditions. Toward this objective, herein we presented the organometallic Co electrocatalyst Co-NHCU and successfully utilized it in the electrochemical CO2 reduction reaction (CO2RR) to produce CO, H2, and HCO2H with notable selectivity. The reduction of CO2 selectively produced CO with 81 ± 2% Faradaic efficiency (FE) in the presence of 5% H2O as a proton source. The selectivity was changed toward H2 with 80 ± 3% FE when 1.5 M triethylamine was added as an additive in the presence of 10% H2O as a proton source. In the presence of 1.0 M morpholine as an external additive, the CO2-saturated solution containing 10% trifluoroethanol as a proton source generates 55 ± 5% HCO2H as the predominant product, with H2 as a competitive side product. It was found that the combined effect of the proton source and the additive in association with the nature of the Co-NHCU catalyst changed the selectivity of the products in this reaction.

Flow corrosion simulation study of local defects in CO2 saturated solution

The inner walls of oil and gas transportation pipelines are prone to the formation of localized pitting defects due to the presence of solid particles in multiphase flow. The continuous flow poses a risk of perforation leakage in the pipe wall. To investigate the development of defects under flow corrosion and assess the impact of flow, a multi-field coupling finite element model incorporating fluid dynamics, reactions, and mass transfer was developed. The flow corrosion of local defects with various depths in a CO2-saturated solution was simulated. The calculation of mass transfer in corrosion is coupled with the precise flow field solved by large eddy simulation (LES) method. It has been observed that the distribution of corrosive substances is significantly affected by the flow due to local defects. Within these defects, the maximum concentration of corrosion product Fe2+ is observed on the upstream surface of defects. While the H+ accumulates at the downstream wall, which affects the corrosion rate. The local turbulent state is influenced by the depth of defects, and the interplay of the turbulence intensity with reflux velocity determines the mass transfer.

Influence of temperature on corrosion behavior of additively manufactured SS316L stainless steel in CO2-saturated brine solution

The present study investigates the influence of temperature on corrosion of AM SS316L in CO2 saturated brine solution. As the temperature increased from 25 °C to 70 °C, the corrosion rate rose nearly fivefold, from 1.78 to 10.06 mpy. The pitting potential decreased from 818 mV to 450 mV, with the gap between |Epit – Erep| widening from 669 mV to 853 mV. EIS results corroborated these results, revealing a decline in Rct from 4755 to 858 Ωcm2 and an increase in Yct from 38 to 119 snΩ-1cm−2. Subsequent surface morphology analysis post-corrosion testing revealed increased corrosion severity with rising temperature. In summary, elevated temperature led to increased corrosion rates, more susceptibility to pitting corrosion, and hindered repassivation.

Effect of Crevice Size on Crevice Corrosion of N80 Carbon Steel in CO2-Saturated NaCl-HAc Solution.

The effect of crevice size on the crevice corrosion of N80 carbon steel was investigated by electrochemical measurements and surface analysis in a CO2-saturated NaCl-HAc solution. The N80 carbon steel exhibits a high susceptibility to crevice corrosion in this environment, which can be initiated immediately without an induction period for specimens with crevice sizes of 100 μm, 300 μm, and 500 μm. Typically, crevice solutions become more acidic during crevice corrosion; however, in this study, the crevice solution became alkaline, resulting in galvanic corrosion between the inner and outer steel surfaces and leading to severe crevice corrosion. The pH levels of the crevice solution for specimens with 100 μm and 300 μm crevice sizes are similar, but both are notably higher than that of the specimen with a 500 μm crevice size. As a result, there is no significant difference in the crevice corrosion phenomenon between specimens with 100 μm and 300 μm crevice sizes, but it is more severe than in the specimen with a 500 μm crevice size.

Selective adsorption and corrosion mechanism of SO2 and its hydrates on X65 welded joints steel in CO2-saturated aqueous solution

In this study, the corrosion mechanism in different regions of the welded joints in CO2/SO2 saturated aqueous solution was investigated by electrochemistry and morphological analysis. The results demonstrated that SO2 and its hydrolysis have some adsorption properties and tend to adsorb in the region of the base metal and generated FeS product. A dense corrosion product film could form on this region, effectively reducing the corrosion rate. Due to the selective adsorption which increases the potential difference between different regions of the welded joint, further intensifying the galvanic corrosion and ultimately leading to the failure of the welded joint.

A Comprehensive Investigation into the Corrosion Mechanism of an Electroless Ni–P Coating in CO2-Saturated NaCl Solution: Degradation or Penetration?

A Comprehensive Investigation into the Corrosion Mechanism of an Electroless Ni–P Coating in CO2-Saturated NaCl Solution: Degradation or Penetration?

Dramatic Improvement of Homogeneous Carbon Dioxide and Bicarbonate Electroreduction Using a Tetracationic Water-Soluble Cobalt Phthalocyanine.

Electrochemical conversion of carbon dioxide (CO2) offers the opportunity to transform a greenhouse gas into valuable starting materials, chemicals, or fuels. Since many CO2 capture strategies employ aqueous alkaline solutions, there is interest in catalyst systems that can act directly on such capture solutions. Herein, we demonstrate new catalyst designs where the electroactive molecules readily mediate the CO2-to-CO conversion in aqueous solutions between pH 4.5 and 10.5. Likewise, the production of CO directly from 2 M KHCO3 solutions (pH 8.2) is possible. The improved molecular architectures are based on cobalt(II) phthalocyanine and contain four cationic trimethylammonium groups that confer water solubility and contribute to the stabilization of activated intermediates via a concentrated positive charge density around the active core. Turnover frequencies larger than 103 s-1 are possible at catalyst concentrations of down to 250 nM in CO2-saturated solutions. The observed rates are substantially larger than the related cobalt phthalocyanine-containing catalysts. Density functional theory calculations support the idea that the excellent catalytic properties are attributed to the ability of the cationic groups to stabilize CO2-bound reduced intermediates in the catalytic cycle. The homogeneous, aqueous CO2 reduction that these molecules perform opens new frontiers for further development of the CoPc platform and sets a greatly improved baseline for CoPc-mediated CO2 upconversion. Ultimately, this discovery uncovers a strategy for the generation of platforms for practical CO2 reduction catalysts in alkaline solutions.

Optimizing the resistance of Cr-advanced steel to CO2 corrosion with the addition of Ni

The findings of this study indicate that Cr-advanced steels exhibit increased corrosion resistance when Ni is incorporated into the alloy. To investigate this phenomenon, the corrosion products and corrosion behavior of Cr-advanced steels with varying Ni contents were evaluated in CO2-saturated NaCl solutions at 90 and 180 °C. The underlying corrosion resistance mechanism can be elucidated from two distinct perspectives. At 90 °C, the addition of Ni into Cr-advanced steels causes the transformation of Fe oxides to NiFe2O4, and it offers superior protection for steel. In addition, the NiFe2O4 phase generated with electronegative properties can enhance the adsorption of Fe2+, thereby promoting the precipitation of FeCO3 crystals. Furthermore, the residual Ni in the inner film continues to serve a pivotal role in the filling of a considerable number of pores and cracks. Upon comprehensive evaluation of the associated costs, the Cr-advanced steel with enhanced corrosion resistance through the incorporation of 1.0 wt% Ni content provides a potential alternative to a conventional 3Cr steel in a CO2 environment. On the other hand, at 180 °C, the concentrations of Fe2+ and CO32− are significantly higher than the solubility of FeCO3 in initial corrosion, which is conducive to generate a denser nanometer-size FeCO3 layer with a better protectiveness, and thus, the effect of Ni is significantly weakened.

Evaluation of green corrosion inhibitors of chitosan oligosaccharide derivatives for CO2 corrosion inhibition on 20# carbon steel

Two chitosan oligosaccharide derivatives, VCOS and GCOS, were synthesized and explored as corrosion inhibitors, the synergistic inhibition effect of KI and VCOS was also studied. Their structures were elucidated using Fourier Transform Infrared Spectroscopy and Nuclear Magnetic Resonance. The inhibition efficacy of VCOS+KI and GCOS on 20# steel within an 80℃, 3 wt% NaCl, CO2-saturated solution system was investigated employing various techniques, including gravimetric measurement, electrochemical analysis, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and molecular dynamics simulations. The results reveal that the inhibition efficiency of VCOS is relatively low when it acts alone. When VCOS and KI are combined, they have a good synergistic effect, and the synergistic parameter is the highest at 6.209. In the weight loss experiment, the corrosion inhibition efficiency increased with the concentration of the corrosion inhibitor. The inhibition rates of VCOS+KI and GCOS were 90.5 % and 90.2 %, respectively. The adsorption on 20# steel conformed to the Langmuir isotherm adsorption equation. The measurement results of SEM, Energy Dispersive Spectroscopy, and AFM show that VCOS+KI and GCOS adsorbed on the surface of carbon steel to form a dense inhibitor film, which effectively protected the metal substrate. According to the polarization test results, both VCOS+KI and GCOS are mixed-type inhibitors primarily exhibiting anodic inhibition, with inhibition efficiencies reaching 98.9 % and 95.1 %, respectively. Electrochemical impedance spectroscopy tests showed that with increasing inhibitor concentration and immersion time, Rct increased and Cdl decreased, resulting in a gradual increase in inhibition efficiency and the formation of a dense and stable inhibitor film. The results indicate that VCOS+KI and GCOS are non-toxic, water-soluble, and environmentally friendly inhibitors with good anti-corrosion performance.

Measurement and modeling of the electrical conductivity of organic electrolyte solutions and their mixtures with compressed CO2

The electrochemical carbon dioxide reduction reaction (CO2RR) is of increasing importance for the development of a closed carbon cycle. Here, electrolytes are often used to increase the electrical conductivity and thus the current density. In addition, the use of compressed CO2 and electrolyte-containing organic solvents suppresses hydrogen evolution. However, the electrical conductivity of CO2-saturated electrolyte solutions is mostly unknown. Therefore, their electrical conductivity was investigated in this work at different electrolyte concentrations, pressures (up to 150 bar) and temperatures (298.15 K and 343.15 K). In addition, the simplified Mean Spherical Approximation (MSA-simple) model, supported by ePC-SAFT for density modeling, was used to successfully model the conductivity. The results show that CO2-saturated electrolyte solutions generally exhibit lower conductivities than CO2-free electrolyte solutions. However, at very low electrolyte and CO2 concentrations, the conductivities were higher in CO2-saturated electrolyte solutions than in CO2-free electrolyte solutions, which is a new finding in the literature.

Effect of Oil-Water Intermittent Wetting on Corrosion Inhibition of Carbon Steel in CO2 Environment

ABSTRACT Produced water can cause internal corrosion in oil pipelines. The flow of hydrocarbons and water can result in intermittent surface wetting, which can impact corrosion inhibition. However, this is still poorly understood. This research studies the impact of intermittent wetting and the wettability of the steel surface on corrosion inhibition, utilizing electrochemical techniques. An inhibitor model compound and model oil were employed at 25°C and 55°C in CO2 saturated solutions. Corrosion inhibition varied with temperature and steel surface hydrophobicity, altering inhibition significantly after intermittent contact with hydrocarbon at 55°C. EIS and wettability results revealed distinct protective mechanisms when oil was present.

Unraveling short-term O2 contamination on under deposit corrosion of X65 pipeline steel in CO2 saturated solution

The impact of short-term O2 contamination on the deposit-covered pipeline steel under a CO2-saturated solution was investigated using steel coupon and wire beam electrode. Results show that the brief exposure to O2 destroyed the FeCO3 film, and converted it into porous iron oxides, weakening its protection property. However, upon CO2 reinjection, the dense FeCO3 film regrew soon underneath the damaged FeCO3 layer on the bare steel, restoring its protective properties. Conversely, the localized corrosion beneath the deposits persisted and worsened, fueled by macro-cell current between the bare steel and the deposit-covered steel.

Corrosion inhibition properties of sweet crude oil for carbon steel 1018 in NaCl solution

Abstract Aged oil pipeline production systems, historically designed without corrosion protection due to predominantly oil-wetted conditions, now face significant changes as increased water content in produced oil arises from field maturation. This work investigates the corrosion inhibition properties of sweet crude oil on carbon steel 1018 in a CO2-saturated NaCl solution using electrochemical testing (open circuit potential, polarization resistance, electrochemical impedance, potentiodynamic polarization) and surface characterization (SEM, EDS) techniques at 50 °C and pH 6. Carbon steel specimens were immersed in crude oil for durations ranging from 0 to 144 h before undergoing corrosion testing. Results showed that a 144-h immersion in crude oil led to an 88 % reduction in corrosion rate, comparable to the efficiency of standard quaternary ammonium-based inhibitors. Furthermore, a semi-empirical model predicting uniform CO2 corrosion rates for varying oil immersion durations is proposed and validated by comparing its predictions with experimental data from the electrochemical tests.

An indirect Z-scheme heterostructure of nano-gold layer immobilized Cu-Al-doped SrTiO3 and CoOx-WO3 for photocatalytic CO2 reduction

Perovskite oxides have emerged as promising photocatalysts for CO2 reduction to valuable chemicals and fuels. However, conventional perovskite oxide photocatalysts often suffer from inefficient charge separation and bulk charge recombination, negatively impacting overall photoactivity. In this work, we present a novel immobilized perovskite oxide-based photocatalyst sheet featuring an indirect Z-scheme heterostructure composed of Cu-loaded Al-doped SrTiO3 (Cu-ASTO) and CoOx-loaded WO3 (CoOx-WO3) with an ultrathin (20 nm) gold interlayer serving as a conductive bridge. We tested this photocatalyst sheet in a sealed reactor containing a CO2-saturated aqueous solution of 0.1 M NaHCO3 and a side window to allow irradiation. Under irradiation with a 300 W Xe lamp, the Cu-ASTO/Au/CoOx-WO3 immobilized photocatalyst sheet produced methane (CH4) at a rate of 2.676 µmol cm-2 h−1 and methanol (CH3OH) at 0.517 µmol cm-2 h−1. We attribute the superior activity of this catalyst to the all-solid-state indirect Z-scheme heterostructure that greatly extends the lifespan of photoinduced charge carriers and enhances the CO2 photoconversion reaction. In experiments conducted outside, we demonstrated the immobilized photocatalyst's performance under natural sunlight, producing CH4 at 0.307 µmol cm-2 h−1 and CH3OH at 0.069 µmol cm-2 h−1. This work provides design ideas for developing robust immobilized photocatalyst systems for the scalable operation of the CO2 photoreduction process and broadening the scope of applications for perovskite heterostructure photocatalysts.

Corrosion performance of carbon steel and 304 stainless steel in activated methyldiethanolamine solution using autoclave tests

This study evaluated the corrosion performance of carbon steel (CS) and 304 stainless steel (304 SS) under high temperature and pressure (inside an autoclave) in a CO2-saturated solution of activated methyldiethanolamine (aMDEA). The aim was to determine the effect of temperature, presence of chloride ions, degradation of the aMDEA and amount of dissolved oxygen on the corrosion resistance of these materials. The results indicated that raising the temperature between 50 and 120°C led to a higher corrosion rate of both CS and 304 SS. However, the corrosion rate of 304 SS decreased and remained stable at higher temperatures as the corrosion reaction became mass-controlled. Oxygen loading results in the passivation of both CS and 304 SS. The amine degradation products were found to accelerate the corrosion rate of CS at 50°C due to a chelation effect of iron ions, and also increase the corrosion rate of 304 SS at 120°C by causing the passive film rupture. The SCC test on U-shaped 304 SS samples showed transversal microcracks with a depth of more than 25 µm after 2 months of immersion in an autoclave containing CO2-saturated aMDEA at 120°C, which confirmed the SCC risk of 304 SS.

The corrosion and tribological behaviors of DLC film in CO2 saturated NaCl solution with high Cl− concentration

The failure of pipelines during oil and gas exploitation is a pressing issue in the oil and gas industry. The high permeability of chloride ions (Cl−) alters the corrosion morphology of the N80 substrate and diminishes its ability to impede the penetration of corrosive substances. This study aims to deposit DLC films on the inner surface of N80 pipeline using plasma enhanced chemical vapor deposition (PECVD), and investigate the corrosion and friction behavior of DLC films in CO2 saturated NaCl solutions with varying Cl− concentrations. The results indicate that the change in Cl− concentration possess minimal impact on the DLC film. The corrosion current density of DLC films in CO2 saturated NaCl solution with three different Cl− concentrations is one order of magnitude lower than that of the N80 substrate. Moreover, a transfer film can still form in high-concentration CO2-saturated NaCl solutions, reducing wear. DLC film demonstrates exceptional stability, corrosion resistance, and wear resistance, making it an ideal material for safeguarding pipelines during oil and gas exploitation.

Mechanism of electrochemical carbon dioxide reduction to formate on tin electrode

Carbon dioxide can be electrochemically reduced to formate on tin electrodes. Formate is one of the most economically viable products of CO2 reduction reaction (CO2RR). While CO2 is reduced to formate, hydrogen evolution reaction (HER) occurs concomitantly. The kinetics of CO2RR and HER on the tin electrode was investigated. Potentiodynamic polarization studies were conducted in CO2 saturated and N2 saturated 0.1 M KHCO3 solutions, in the potential range from −0.014 V to −1.59 V vs. RHE. A faradaic efficiency of 93.95 % towards formate production was obtained at −1.09 V vs. RHE. The mass transfer effects and bicarbonate dissociation equilibrium were used to estimate the concentration of the reactants at the electrode surface. Density functional theory calculations indicate that –OCHO intermediate species is thermodynamically favoured, and a four-step reaction with two intermediates is proposed. The proposed mechanism captures the major features of the polarization data. CO2 reduction occurs via two intermediate species, viz. adsorbed H and OCHO species, while HER occurs via Volmer-Heyrovsky steps. The model predicts that in N2 saturated solutions, the fractional surface coverage of adsorbed H reaches a maximum of ∼0.48 at a potential of −0.82 V vs. RHE while in CO2 saturated solutions, the corresponding value is ∼0.29. In addition, the maximum fractional surface coverage of adsorbed OCHO is predicted to be ∼0.12 in CO2 saturated solutions.

Electrochemical corrosion behavior of X80 pipeline steel welded joints fabricated by ultrasound-assisted submerged arc welding in CO2-saturated solution

In this study we investigated the electrochemical corrosion behaviors of X80 pipeline steel welded joints fabricated by ultrasound-assisted submerged arc welded (UASAW) joints in CO2-saturated solution. The microstructures of the UASAW joints were analyzed by using metallographic microscopy. Corrosion behavior of UASAW joints was investigated using immersion test, electrochemical polarization, and electrochemical impedance spectroscopy (EIS). The corrosion morphologies and products were characterized by scanning electron microscopy (SEM), energy dispersive spectroscope (EDS) and X-ray diffraction. Metallographic and the corrosion mechanism of UASAW was systematically studied. The investigation results showed that the microstructure of the UASAW weld zone is mainly composed of acicular ferrite and a little granular bainite. The minimum microhardness is obtained in fusion zone (FZ) because of many alloying elements dominated in the final precipitate distribution. Pitting corrosion resistance of the strong vibration region in FZ is attributed to the decline in active sites of the bainite, the UASAW had beneficial effect on the improvement of pitting corrosion resistance of X80 pipeline steel weldment.

Role of bicarbonate in CO2 corrosion of carbon steel

This study investigates the dual role of bicarbonate in the CO2 corrosion of carbon steel through electrochemical measurements and immersion tests conducted in a CO2-saturated solution. The results show that the critical bicarbonate concentration for the aggressive/inhibitive transition is approximately 0.03–0.05 mol·L−1. Above this concentration, bicarbonate exhibits an inhibitory effect on the CO2 corrosion of X65 steel. The size of FeCO3 particles decreases as the bicarbonate concentration increases, leading to a denser FeCO3 film and enhanced passivation of the steel. However, at concentrations below 0.03 mol·L−1, bicarbonate enhances the CO2 corrosion of carbon steel owing to its participation in cathodic processes.