Corrosive effects of supercritical carbon dioxide and cosolvents on metals

Abstract

With the eventual phase-out of chlorofluorocarbons, and restrictive regulations concerning the use of cleaning solvents such as hydrochlorofluorocarbons, and other volatile organic compounds, it is essential to seek new, environmentally acceptable cleaning processes. In the DOE Complex and in industry, an environmentally sound process for precision cleaning of machined metal parts is one of the issues that needs to be addressed. At Sandia, we are investigating the use of supercritical carbon dioxide (CO2) as an alternative cleaning solvent for this application. Carbon dioxide is nontoxic, recyclable, and relatively inexpensive. Supercritical CO2 has been demonstrated as a solvent for many nonpolar organic Compounds, including hydrocarbon-based machining and lubricating oils. The focus of this work is to investigate any corrosive effects of supercritical CO2 cleaning on metals. Sample coupons of several common metals were statically exposed to pure supercritical CO2, water saturated supercritical CO2, and 10 wt% methanol/CO2 cosolvent at 24,138 kPa (3500 psi) and 323°K (50°C) for 24 hours. Gravimetric analysis and magnified visual inspection of the coupons were performed before and after the exposure tests. Electron microprobe, x-ray photoelectron spectroscopy (XPS), and Auger electron surface analyses were done as needed where visual and gravimetric changes in the samples were evident. The results of these experiments will be reported. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Formation mechanism and protective property of corrosion product scale on X70 steel under supercritical CO 2 environment

“…Two semi-empirical formulas have been introduced to describe the relationship between the Young's modulus and the porosity ɛ, as shown in Eq. (17) and (18) [73]: (18) where E 0 is the Young's modulus of pure FeCO 3 crystal, and b is a tunable parameter. According to Ramachandran et al [73], Eq.…”

“…Therefore, by combining Eq. (18) with Eq. (20), it can be confirmed that the corrosion rate exhibited a logarithmic relationship with the Young's modulus.…”

“…It is well known that dry SC CO 2 is not corrosive [17][18], and a number of investigations have also confirmed that corrosion was insignificant in SC CO 2 /H 2 O systems when the water content is far below its solubility limit in SC CO 2 [13,[19][20][21][22][23][24]. However, drying CO 2 can drastically increase the cost of CCS and hinder its application.…”

Determining the corrosive potential of CO2 transport pipeline in high pCO2–water environments

“…When free water exists in the pipeline, it will be saturated with CO 2 and the corrosion rate will be significant for carbon steel because of the formation of carbonic acid (H 2 CO 3 ). In addition, even though pure, dry CO 2 is not corrosive, there are several studies which provide qualitative evidence for corrosion on carbon steel in water-saturated supercritical CO 2 phase (Russick et al, 1996;Propp et al, 1996;McGrail et al, 2009). Thus, to be able to consider the corrosion risk in such pipelines, quantitative evaluation of corrosion in both CO 2 -saturated water and water-saturated CO 2 phases will be needed.…”

Current and future corrosion challenges for a reliable and sustainable development of the chemical, refinery, and petrochemical industries

“…Corrosive attacks can be observed in water saturated CO 2 environments on carbon steel and some aluminum or copper alloys [14]. An important point to determine the corrosivity of supercritical CO 2 media, concerns the mechanisms of formation of free water.…”