Narasi Sridhar

The Electrochemical Reduction of Carbon Dioxide to Formate/Formic Acid: Engineering and Economic Feasibility

The engineering and economic feasibility of large-scale electrochemical reduction of carbon dioxide to formate salts and formic acid is the focus of this Full Paper. In our study we investigated the long-term performance of tin and other proprietary catalysts in the reduction of carbon dioxide to formate/formic acid at a gas/solid/liquid interface, using a flow-through reactor. The overall economics and energy consumption of the process are evaluated through a value chain analysis. The sensitivity of the net present value of the process to various process parameters is examined.

Understanding localized corrosion

The breakdown of a protective passive film leading to accelerated dissolution at localized sites is an important practical issue and a vexing scientific problem. The small dimensions, short timescale, and dynamic interplay between a heterogeneous surface and changing potential and solution concentration gradients complicate the development of a complete understanding of the phenomena. This review touches on some of the recent developments in the field, including scanning tunneling microscopy imaging of the earliest stages of pitting which supports a new model explaining the localization of attack, pitting in thin aqueous layers relevant to atmospheric corrosion, the factors controlling crevice corrosion, and predictive modeling of localized corrosion.

Application of a General Reactive Transport Model to Predict Environment Under Disbonded Coatings

Abstract Understanding the evolution of the chemical environment and potential inside a disbonded region is essential to a quantitative risk assessment of corrosion and stress corrosion cracking of...

Effects of Environmental and Metallurgical Factors on the Stress Corrosion Cracking of Carbon Steel in Fuel-Grade Ethanol

Abstract This paper presents the results of a research program to study the effects of metallurgical variables, ethanol-gasoline blends, dissolved oxygen, and inhibitors on the stress corrosion cracking (SCC) of carbon steel in ethanol. The study utilized both slow strain rate (SSR) and fatigue precracked compact tension (CT) tests to characterize the effect of metallurgical and environmental variables on SCC. Metallurgical factors, including steel grade within a range of pipeline grades, welds, and heat-affected zone, do not appear to have a significant effect on the degree or rate of SCC. In terms of environmental factors, it is shown that SCC does not occur even in a fully aerated condition if the ethanol-gasoline blends contain less than approximately 15 vol% ethanol; SCC susceptibility and crack growth rate are higher in 50 vol% ethanol gasoline blend (E-50) than in either lower or higher ethanol concentration blends; oxygen scavenging can be an effective method to prevent SCC; water content above 4....

Localized Corrosion of Carbon Steel and Its Implications on the Mechanism and Inhibition of Stress Corrosion Cracking in Fuel-Grade Ethanol

Abstract Stress corrosion cracking (SCC) of carbon steel has been observed in fuel-grade ethanol (FGE, C2H5OH). Electrochemical behavior of carbon steel and therefore the role of localized corrosion in SCC has not been studied adequately because of the difficulty in performing electrochemical experiments in resistive environments such as FGE. A microelectrode technique was used in this work to conduct electrochemical studies in simulated FGE (SFGE). It was found that oxygen likely played multiple roles: it participated in the passive film formation in addition to its more commonly observed role in aqueous environments of changing the open-circuit potential (OCP), and it may also participate in the oxidation of ethanol on steel surfaces. A model, based on this dual role of oxygen, was proposed to explain the SCC mechanism of carbon steel in SFGE. The model is supported by the inhibitor evaluation work, which also demonstrated that carbon steel SCC could be inhibited by adding inhibitors.

Corrosion Behavior of Carbon Steel in Acidified, Thiosulfate-Containing Brines

The corrosion rate of carbon steel in acidified, thiosulfate-containing brines increased with thiosulfate content. Thiosulfate also increased the rate of cathodic and anodic reactions, as measured in polarization curves obtained shortly after immersion of the electrode. Current from iron dissolution was balanced by hydrogen evolution and reduction of thiosulfate to produce hydrogen sulfide. Hydrogen sulfide production represented a large fraction of the open-circuit corrosion current. Carbon steel specimens exposed to thiosulfate-containing solutions developed a film on their surface, composed of iron sulfide and cementite. The film was a good conductor of electrons and non-passivating. The rate of cathodic reactions measured for the film-covered electrode was faster than in the absence of the film, suggesting it is a good catalyst for reduction reactions. The ability of acidified, thiosulfate-containing brines to simulate hydrogen sulfide solutions was critically analyzed.

Cathodic degradation mechanisms of pure Sn electrocatalyst in a nitrogen atmosphere

The application of electrocatalysts used at high cathodic overpotentials for the electrochemical reduction of pollutant species such as CO2 has revealed a lack of understanding of the cathodic degradation mechanisms of those materials. Pure Sn is one of the most relevant candidate materials mainly because of its high selectivity for the reduction of CO2 to formic acid and formate salts. Degradation of the electrocatalyst can arise from a combination of cathodic polarization and induced changes to the surface by CO2 reduction products. In this study, the cathodic degradation mechanisms of pure Sn were studied as a function of rotation rate, time, current density, electrolyte concentration, grain size, and orientation in a nitrogen-saturated atmosphere using a rotating disk electrode. Several degradation morphologies were observed, but three were dominant. In the first type, electrochemical alterations of grains with specific orientations produced substantial weight changes, both losses and gains. The second type resulted in an alkali-rich deposit that had a high coverage but produced small weight changes. The third type consisted of carbon-rich stains that typically had a small coverage.

Hydrogen Permeation and Corrosion Fatigue Crack Growth Rates of X65 Pipeline Steel Exposed to Acid Brines Containing Thiosulfate or Hydrogen Sulfide

Corrosion fatigue crack growth rates were obtained for X65 pipeline steel in acid brines containing thiosulfate (S2O32−) or hydrogen sulfide (H2S). Samples were exposed for 72 h at the open-circuit potential to allow bulk hydrogen charging. The corrosion fatigue crack growth rate increased with partial pressure of H2S and correlated with the steady-state flux of hydrogen permeation during corrosion in the same solutions. The rate of hydrogen absorption increased with increasing S2O32− concentration to a maximum at 10−3 M S2O32−, owing to a competition between increased surface concentration of H2S from S2O32− reduction and increased rate of iron sulfide film formation. Corrosion fatigue behavior in S2O32−-containing acidified brines is the same as in solutions with low partial pressures of H2S, in accordance with predictions from the hydrogen permeation results. This suggests that, for corrosion fatigue studies, S2O32− solutions are possible candidates for replacement of H2S gas, as long as the H2S partia...

Effect of Oxygen on Ethanol Stress Corrosion Cracking Susceptibility: Part 1—Electrochemical Response and Cracking-Susceptible Potential Region

It is known that dissolved oxygen promotes stress corrosion cracking (SCC) of carbon steel in fuel-grade ethanol. The effects of oxygen on ethanol SCC were investigated using controlled-potential t...

Effect of Liquid Impurities on Corrosion of Carbon Steel in Supercritical CO2

The increasing urgency to mitigate global warming has driven many efforts to control green house gas emissions. One solution among many is carbon capture and storage. However, CO2 emitters are not necessarily in the close vicinity of potential geologic storage sites. In consequence CO2 will be transported from generation site to storage sites under high pressures. This will necessitate a network of pipelines gathering supercritical CO2 from diverse sources and transporting it through transmission lines to the storage sites. These pipelines will be under corrosion risks, particularly because of possible carryover of trace impurities produced from the different sources, such as water, chloride, NOx , SOx , and O2 . The effects of impurities on corrosion in supercritical CO2 have yet to be evaluated systematically. Corrosion of carbon steel associated with water and impurities in supercritical CO2 was studied by Electrochemical Impedance Spectroscopy in autoclaves. Five impurities were studied by introducing them in the liquid condensed phase: water, amine, HCl, HNO3 and NaOH. Results were analyzed in terms of the phase behavior and speciation.Copyright