Siderite corrosion protection for carbon steel infrastructure in post-combustion capture plants

International Journal of Greenhouse Gas Control 58 (2017) 232–245

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International Journal of Greenhouse Gas Control journal homepage: www.elsevier.com/locate/ijggc

Siderite corrosion protection for carbon steel infrastructure in post-combustion capture plants Kyra L. Sedransk Campbell ∗ , Louis C.Y. Yu, Daryl R. Williams Department of Chemical Engineering, Imperial College, South Kensington Campus, London, SW7 2AZ, United Kingdom

a r t i c l e

i n f o

Article history: Received 28 November 2016 Received in revised form 16 January 2017 Accepted 31 January 2017 Available online 7 February 2017 Keywords: Post-combustion CO2 capture Amine Siderite Corrosion Carbon steel

a b s t r a c t To mitigate CO2 release, large-scale post-combustion capture with amine solvents is essential. To achieve capital cost savings, carbon steel infrastructure can replace stainless steel if corrosion by CO2 -loaded amine solvents is controlled. A coating, to protect the carbon steel, formed using an amine (or additive) is beneficial because it can be regenerated. Siderite has been shown to form a protective crystalline product layer, created when Fe oxidised at the surface reacts with carbonate ions. Tertiary or sterically-hindered CO2 -loaded amine solutions can form this layer. Herein siderite was prepared on carbon steel substrates from 5 M methyldiethanolamine (MDEA), 5 M 2-amino-2-methyl-1-propanol (AMP), and 1 M K2 CO3 at 40 and 80 ◦ C. At 40 ◦ C, K2 CO3 produced the most successful protective siderite layer; by contrast, the amine solutions developed layers with interlocking crystals at 80 ◦ C. After siderite formation, these substrates were tested in 2.5 M MEA and AEPZ, both highly corrosive but with more desirable capture kinetics. At 80 ◦ C, substrates pre-treated with MDEA or AMP showed good resistance against the corrosive actions of MEA and AEPZ for four weeks. The siderite layer reduced Fe oxidation at the surface and ingress of solution species thereby ceasing contact and corrosion. © 2017 Elsevier Ltd. All rights reserved.

1. Introduction The continued growth of the global population and its increasing demand for energy has been a major contributor to greenhouse gas emissions, resulting in global climate change. With such significant environmental damage and devastating weather-related effects worldwide, it is imperative that emissions are reduced in order to minimise further damage to the environment. The sources of these emissions, namely CO2 , are principally from three sectors: manufacturing, energy production, and transport (Sreenivasulu et al., 2014). Because of their fixed position, establishing a flue gas treatment for manufacturing and energy industries is the most sensible first step towards reducing CO2 emissions. Post-combustion CO2 capture (PCCC), using aqueous amine solvents, is an existing technology and is readily adaptable to current plant infrastructure. Flue gas streams containing CO2 first pass through an absorption stage (Fig. 1) (MacDowell et al., 2010; Boot-Handford et al., 2014) where the ‘lean’ amine solvent travels counter currently to react with the CO2 in the flue gas. The solution exits the absorber as loaded or a ‘rich’ amine solution. This ‘rich’ solution is passed through a

∗ Corresponding author. E-mail address: [email protected] (K.L. Sedransk Campbell). http://dx.doi.org/10.1016/j.ijggc.2017.01.018 1750-5836/© 2017 Elsevier Ltd. All rights reserved.

heat exchanger into the desorber (stripper) where CO2 is removed from the solvent at elevated temperatures. The now ‘lean’ solution passes back through the heat exchanger for reuse in the absorber. While this is the most effective and economical method of PCCC currently ready for large-scale deployment, capital and operational costs remain a deterrent. The cost of the former is due to the use of stainless steels, which are employed because of their relative resistance to corrosion. This material of choice for most PCCC plant infrastructure is a historical one, from the natural gas sweetening industry, where cost was a less significant concern. Alternative materials must be considered to replace stainless steel to reduce the high capital cost. A novel approach is the pre-treatment of carbon steel using amines, or other common additives, known to promote the growth of corrosion inhibiting product layers. While amines are not inherently corrosive, but rather are alkalinic, chemical absorption of CO2 can result in corrosive behaviours (Hatcher et al., 2014; Gouedard et al., 2012; Rennie, 2006; Zheng et al., 2016a). However, certain types of amines will promote the formation of product layers, which act as physical barriers separating the metal substrate from the solution. The best performing product is siderite (FeCO3 ), which has been proven to reduce corrosion of carbon steels (Zheng et al., 2016a, 2016b; Yu et al., 2016a). The formation of this FeCO3 layer acts as a physical barrier between underlying steel and the amine solution (Ruzic et al.,

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233

Fig. 1. Schematic of amine solvent PCCC system (MacDowell et al., 2010).

2006; Tanupabrungsun et al., 2013), thereby reducing the oxidation of Fe at the surface. Two distinct categories of corrosive behaviours on carbon steel have been established: one in which there is the potential to inhibit corrosion and the other to exacerbate it (Yu et al., 2016a; Sedransk Campbell et al., 2016). Primary (1◦ ) and secondary (2◦ ) amines react directly with CO2 to form carbamates (Eqs. (1)–(4)), which in turn promote the formation of iron oxide corrosion products (Sedransk Campbell et al., 2016; Gunasekaran et al., 2013a). Monoethanolamine (MEA) is an industry benchmark 1◦ amine (Gunasekaran et al., 2013a) and one of the most corrosive upon CO2 loading, where the formation of carbamates was found to further intensify corrosion (Guo and Tomoe, 1999; Xiang et al., 2014). By contrast to 1◦ and 2◦ amines, tertiary (3◦ , e.g. methyldiethanolamine MDEA) and sterically-hindered (SH) amines generally do not engage in direct capture (Sartori and Savage, 1983; Kohl and Nielsen, 1997). Rather, CO2 hydrolyses with water to form bicarbonate and carbonate species (Eqs. (5)–(6)). In the case of SH amines, particularly 2-amino-2-methyl1-propanol (AMP), a hybrid capture mechanism has been suggested involving direct capture and formation of an unstable carbamate (Eq. (7)) with subsequent hydrolysis to produce carbonates (Eq. (8)) (Yamada et al., 2011; Stowe et al., 2015). This makes these amines less desirable for the process of CO2 capture as they exhibit reduced reaction rates with CO2 (Couchaux et al., 2014). The practice of blending a 3◦ or SH amine with either a 1◦ or 2◦ amine has been used to improve kinetics (Jacques-Derks, 2006; Sodiq et al., 2014). RNH2 + CO2 → RNH2 COO

(1)

RNH2 + RNH2 COO → RNH+ + RNHCOO− 3

(2)





RR NH + CO2 → RR NHCOO

(3)

RR NH + RR NHCOO → RR NH+ + RR NCOO− 2

(4)

CO2 + H2 O → H2 CO3

(5) + HCO− 3

(6)

AMP(aq) + CO2(g) → AMPCOO− (aq)Unstable

(7)

AMPCOO− + H2 O(l) → AMPH+ + HCO2− 3 (aq) (aq)Unstable

(8)

 

 

RR R N + H2 CO3 → RR R NH

+

From 3◦ and SH amines, the capture mechanism is a source of carbonate (CO3 2− ) species, alongside those formed in the hydrolysis of CO2 with water (Eq. (9)–(10). With two sources of CO3 2− , the high concentration, and in some cases saturation, in solution provides sufficient reactants with Fe2+ ions oxidised at the metal surface for the formation of siderite (Eqs. (11)–(12)) (Zheng et al., 2016c; Farelas et al., 2013). H2 O(l) + CO2(g) → H+ + HCO− 3(aq) (aq) 2− + HCO− 3 → H + CO3 2+

Fe(s) → Fe 2+

Fe

+ 2e

+ CO2− 3(aq)

−

→ FeCO3(s)

(9) (10) (11) (12)

The formation of siderite layers on steel has been well documented for MDEA and AMP. Corrosion rates (mm y−1 ) of carbon steel C1018 in CO2 rich MDEA at 80 ◦ C were the lowest recorded against a selection of benchmark industry amines (MEA > AMP > piperazine (PZ)) (Gunasekaran et al., 2013b). This positive effect has been directly attributed to the FeCO3 formed in MDEA solutions (Guo and Tomoe, 1999), via the potential to form bicarbonate derivatives which result from the 3◦ capture mechanism (Choi et al., 2013; Yu et al., 2016a). Similarly, stericallyhindered amine AMP loaded with CO2 over a range of 30 ◦ C–80 ◦ C has been found to be significantly less corrosive on carbon steel C1020 through the growth of FeCO3 (Veawab et al., 1999). One area of interest is establishing the solubility product (KSP ) of FeCO3 and its impact on such systems. Some single parameters have been studied, where solubility decreases with increasing temperature. However limited data is available on the effect of Fe2+ and CO3 2− concentration on KSP (Sun et al., 2009); and virtually no research addressing the influence of amines in solution on KSP . There are other factors affecting a systems ability to produce stable FeCO3 in more industrially relevant environmental conditions. The presence of O2 and heat stable salts in MDEA-CO2 systems have been shown to slightly increase corrosion rates on carbon steel (Choi et al., 2010). This is attributed to reduced stability of FeCO3 corrosion inhibition layers (Choi et al., 2010; Xiang et al., 2015), though a specific mechanism is not entirely understood. Ionic solutions are a highly regarded alternative to amine solvents for their robustness against thermal and oxidative degradation (Sun et al., 2009). The Benfield process utilises aqueous

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potassium carbonate (K2 CO3 ) to increase the rate of CO2 dissolution forming bicarbonate and potassium ions in solution (Eq. (13)) (Lee et al., 2013; Stolaroff, 2013). Additionally beneficial in surface corrosion inhibition is the formation of FeCO3 from the excess CO3 2− with oxidised Fe2+ ions in solution (Sedransk Campbell et al., 2016). 2− + 2K+ + CO2− 3(aq) + H2 O(l) + CO2(g) → 2K(aq) + 2HCO3(aq) (aq)

(13)

While the use of stainless steels offers a longer track record of use, costs of corrosion monitoring are still significant. Stainless steels are more likely to undergo catastrophic corrosive failures rather than the general corrosion common to carbon steels, in addition to the initial substantial capital investment required (Ohmi et al., 1993; Billingham et al., 2011). As such, a range of approaches to corrosion reduction have been trialled. Specific to PCCC amine solvents, vanadium and arsenic based additives have been used as corrosion inhibitors (DuPart et al., 1993); however, there are significant environmental considerations and consequences. Polymer resins have been used in some industrial instances, and while reported in some cases to withstand stripper conditions, a susceptibility to localized damage is very concerning and dangerous (Smith et al., 2010). Furthermore, these methods pose a range of concerns including the loss of time and money. A recent report has studied the possibility of semi in situ coating of carbon steel using siderite promoting amines and subsequently testing the layers resilience against more aggressive amines (Zheng et al., 2016c). Dense layers of siderite with cubic crystal habits were grown on A106 carbon steel coupons in solutions of 30% by weight piperazine (PZ) and 10% by weight NaHCO3 at 80 ◦ C for 2 days (Zheng et al., 2016c). It was reported that subsequent soaking of the protected A106 coupons in MEA at 80 ◦ C for 9 and 48 days resulted damage to the siderite crystals via dissolution (Zheng et al., 2016c). While it is widely recognized that PZ has the potential to form excellent siderite (Yu et al., 2016b), the environmental concerns due to nitrosamine formation paired with the operational constraints limit the possibilities of its widespread use (Li et al., 2013; Fine et al., 2011). The study herein, operates on a similar principle using the tendency for 3◦ and SH amines (and ionic salts) to form initial FeCO3 layers on steel surfaces in situ. This allows the surface passivation of steel to take place during PCCC operation albeit at a lower efficiency, due to slower CO2 uptake kinetics of these species. However, the pre-treatment solution can then be replaced with a more corrosive, and efficient amine solution, for a longer period of time. Corrosive amines MEA and aminoethylpiperazine (AEPZ) were trialled in this study. This process was assessed at both 40 and 80 ◦ C to evaluate the possibilities for a wider range of PCCC infrastructure than has been addressed in the limited existing studies. The use of this process industrially could cycle at intervals, if necessary, to allow regeneration of the FeCO3 layer growth without the significant downtime required for such methods as polymer coatings.

2. Methods Aqueous amine solutions were made from 2-amino-2methyl-1-propanol (AMP, ≥90% Sigma), methyldiethanolamine (MDEA, ≥99% Sigma) potassium carbonate (K2 CO3 , ≥98% Sigma), monoethanolamine (MEA, ≥99% Sigma) and 1-(2aminoethyl)piperazine (AEPZ, ≥99% Sigma) with deionized water. All solvents were used as received. Corrosion coupons of carbon steel C1018 (76.25 × 12.62 × 1.63 mm, 98.83–99.13% Fe, 0.18% C, 0.6–0.9% Mn, ≤0.04 P and ≤0.05 S, Alabama Specialty Metals) were first washed with acetone and air dried then weighed. Five coupons were mounted on a custom made PTFE coupon mount (Imperial College Department of Chemical Engineering Workshop).

Three 2 L pre-treatment solutions of 5 M AMP, 5 M MDEA and 1 M K2 CO3 (lower concentration due to solution saturation limits) were prepared in custom glass reactors. Solutions were purged of oxygen by continuously bubbling nitrogen gas (N2 ) at 50 mL min−1 for four hours at room temperature. The solutions were subsequently loaded by bubbling CO2 at 100 mL min−1 for two hours at either 40 or 80 ◦ C, as dictated by the experiment, at atmospheric pressure. Solutions of AMP at 40 ◦ C often crystallized locally making the solution unmanageable and unrealistic for implementation industrially, as such this case was excluded. The temperature was maintained using a hot plate (IKA) with individual water baths with a height equal to the reaction vessels and a temperature probe inside the reaction solution. Upon completion of loading, the coupon mount was submerged into the pre-treatment solution. Throughout the experiment, CO2 was continuously bubbled into the solution at a rate of 50 mL min−1 to maintain CO2 saturation. After the seven days allocated for pre-treatment one coupon was removed, the solution was then sampled and changed to either 2.5 M MEA or AEPZ, at the same temperature as pre-treatment. The new solutions were loaded with CO2 and maintained using the same protocol. Each subsequent week, one coupon was withdrawn for four weeks and the liquid sampled at the same interval. After removal, the coupons were first weighed, then washed with deionized water and acetone, then reweighed. As the varied experimental conditions have the potential to both produce and destroy material, net coupon weight change provides a simple means to gauge the rate of material size change (MSC, mm y−1 ). This is calculated from the difference between coupon initial mass (mINITIAL ) and final mass (mFINAL ), divided by coupon initial surface area (A), density (␳) and the time spent in solution (t) (Eq. (14)) (Yu et al., 2016a, 2016b). Rate of MSC





mm y−1 =

mINITIAL − mFINAL At

(14)

The coupons were cut to 5 × 5 mm, coated in 10 nm thick gold and mounted on aluminium stubs for imaging using scanning electron microscopy (SEM) (JEOL 6400). The surface composition was also measured using Energy Dispersive X-ray (EDX) against a Co standard. Coupons analysed using X-ray diffraction (XRD) were mounted on sample holders. Scans were run between 2␪ angles 10◦ –100◦ at a step size of 0.334 and scan time 40 s (PAnalytical X-Pert X-Ray Diffractometer). 3. Results and discussion 3.1. Coupon mass change Using traditional immersion techniques, it is standard protocol to assess the changes in mass of the coupons. As both weight gains and losses can be observed when carbon steel is treated with amines (Gunasekaran et al., 2013b; Cummings et al., 2005), the rate of MSC (Eq. (14)) was used to represent this change. As this is based on the standard equation used for corrosion rate, a positive value for rate of MSC indicates overall material loss and a negative value indicates overall material gain. To establish the impact of a pre-treatment process, control experiments were run where the carbon steel sample was only cleaned (no pre-treatment) before being immersed in either 2.5 M MEA or AEPZ. For solutions of 2.5 M MEA the change in mass measured indicates a loss of mass overall at both 40 and 80 ◦ C (Fig. 2A and B). At 40 ◦ C the consistent loss for weeks one, two, and four suggests that the corrosion continues, essentially, at a continuous rate. Interestingly, at 80 ◦ C the trend is dramatically different where an initially high loss of mass is observed in the first week. The sub-

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Fig. 2. Rate of MSC (mm y−1 ) on carbon steel with (5 M MDEA, 5 M AMP −80 ◦ C only, 1 M K2 CO3 all for one week at noted temperature) and without pre-treatment under the following conditions for four weeks: (A) 2.5 M MEA at 40 ◦ C, (B) 2.5 M MEA at 80 ◦ C, (C) 2.5 M AEPZ at 40 ◦ C, (D) 2.5 M AEPZ at 80 ◦ C. Overlaid on each subfigure is the Rate of MSC for one week of each pre-treatment course (listed on the right) where solid lines indicate the average and dashed lines are used to indicate one standard deviation above and below this value.

sequent week the rate decreases significantly and remains at this lower value. By contrast, samples immersed in 2.5 M AEPZ show a slightly more corrosive effect at 40 ◦ C, rather than 80 ◦ C (Fig. 2C and D). Interestingly, both cases show a decreasing rate of loss, i.e. a reduction in corrosion rate, over the four week period. This pattern of behaviour has been observed in experiments of MEA at 1, 3 and 5 M at 120 ◦ C (Yu et al., 2016a). By increasing the concentration of amines and hence loaded solution corrosivity, this phenomenon can be likened to an increase in solution temperature and therefore the corrosion rate. In stronger corrosive conditions, the initial material loss is higher due to faster rate of oxidation. However with a higher concentration of free Fe ions in solution, the driving force for corrosion product precipitation on the carbon steel surface is increased leading to an apparent decreased corrosion rate. The impact of weight loss or gain for each of the pre-treatment methods was analysed. Coupons were measured after the one week pre-treatment period. The results are shown with labels on the right side of each subfigure in Fig. 2. Horizontal solid lines are used to indicate the mean with one standard deviation in both directions demarcated using dashed lines. At 40 ◦ C (Fig. 2A and C), 5 M MDEA shows a significantly higher rate of MSC than 1 M K2 CO3 , which shows little deviation from the original mass. This suggests that 5 M MDEA at 40 ◦ C is likely not particularly effective in the formation of a product layer, and in fact the pre-treatment process may be detrimental to the stability of the coupon surface. However, at an increased temperature of 80 ◦ C (Fig. 2B,D) 1 M K2 CO3 proved less effective than either 5 M MDEA or AMP, which both show apparent weight gains as recorded by the rate of MSC. In almost all cases, there is a demonstrable and positive impact from the use of coupon pre-treatment. For both MEA and AEPZ at 40 ◦ C the use of either pre-treatment method lowers the rate of MSC, but a loss of mass remains clearly apparent. Against 2.5 M MEA, all samples subjected to pre-treatment show continuing improvement over the course of the four weeks (Fig. 2A). In fact, by the third week the rates appear commensurate with those obtained for a single week’s change in 1 M K2 CO3 . These improvements in

rate of MSC are not observed with the same pre-treatment methods at 40 ◦ C when trialled against 2.5 M AEPZ (Fig. 2C). In this case the rate appears relatively constant and 5 M MDEA is clearly less effective than 1 M K2 CO3 . The relative lack of efficacy of 5 M MDEA is not surprising given that in after one pre-treatment a weight loss far more significant than for 1 M K2 CO3 was observed. At increased temperatures of 80 ◦ C the pre-treatment methodology appears more effective, reducing the rate of MSC so far as to indicate weight gain on the coupon in some cases. Against 2.5 M MEA (Fig. 2B) and AEPZ (Fig. 2D), this is true for almost all weeks measured when a pre-treatment of either a 5 M MDEA and AMP solution was used. The efficacy of a 1 M K2 CO3 pre-treatment is strongly evident. This is particularly true for the case of 2.5 M AEPZ at 80 ◦ C, where the results with 1 M K2 CO3 are commensurate with no pre-treatment whatsoever. Overall, the efficacy of the pre-treatment course alone after

3.2. Solution Fe concentration In the corrosion reaction of carbon steel, Fe is the primary metal oxidised at the surface. The oxidation results in the release of Fe ions into solution, which was measured by sampling the bulk solution each week and analysed with ICP-OES. Other metals also found in C1018 carbon steel including Al, Mn, Cr were also tested but no measurements indicated any concentration higher than the instrumentation error. Without the presence of any pre-treatment procedure, samples at 40 ◦ C for both MEA and AEPZ show the highest Fe ion concentration after the first week of the study (Fig. 3A and C). The concentration drops in both cases for the three subsequent weeks, though AEPZ remains consistently higher than MEA. The process of pre-treatment itself results in some Fe ions oxidised at the surface of the metal coupon, subsequently raising the overall bulk concentration after one week. At 40 ◦ C, 1 M K2 CO3 shows a lower overall bulk Fe ion concentration. This is likely due to the relative concentration of carbonate species (CO3 2− ) in solution available for rapid

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Fig. 3. Fe ion concentration (mg L−1 ) on carbon steel with (5 M MDEA, 5 M AMP, 1 M K2 CO3 all for one week at noted temperature) and without pre-treatment under the following conditions for four weeks: (A) 2.5 M MEA at 40 ◦ C, (B) 2.5 M MEA at 80 ◦ C, (C) 2.5 M AEPZ at 40 ◦ C, (D) 2.5 M AEPZ at 80 ◦ C. Overlaid on each subfigure is the Rate of MSC for one week of each pre-treatment course (listed on the right) where solid lines indicate the average and dashed lines are used to indicate one standard deviation above and below this value.

reaction with Fe. As K2 CO3 is simply a salt species, CO3 2− is much more readily available whereas MDEA must undergo a slow reaction process (Eqs. (5) and (6)) to create a similar concentration, resulting in a build-up of Fe ions in the bulk solution during this time. For the solution which was pre-treated with K2 CO3 at 40 ◦ C and subsequently immersed in 2.5 M MEA at 40 ◦ C (Fig. 3A), the concentration of Fe ions in the bulk is definitively lower than the untreated coupon for the first two weeks. However, a build-up of Fe ions in solution is occurring and, in fact, surpasses the untreated case for the second two weeks. By contrast the pre-treatment with 5 M MDEA maintains a concentration lower than without the pretreatment for the four weeks tested, though a small increase in Fe ion concentration is observed. A different behaviour is observed for the case of pre-treatment against 2.5 M AEPZ at 40 ◦ C (Fig. 3C). The use of 1 M K2 CO3 at 40 ◦ C provided no significant difference from the untreated case for the first two weeks tested. However, in the final two weeks a decrease in concentration of Fe ions, below the untreated case, is observed. By contrast the pre-treatment with 5 M MDEA at 40 ◦ C, generally, shows a higher concentration of Fe ions in solution than the untreated coupon. In fact, the Fe ion concentration starts high and remains relatively stable; this is in contrast to the case where no pre-treatment was employed and the concentration decreased in the latter weeks. As such, the pre-treatment has an adverse effect on Fe ion concentration in the bulk for some of these cases; however, the influence on overall corrosion is more complex and will be discussed in the next section. At an increased temperature of 80 ◦ C, solutions containing coupons submerged in 2.5 M MEA show consistency in the Fe ion concentration recorded across the four weeks. This concentration is lower than that achieved for comparable tests at 40 ◦ C, until the final week where the values become commensurate. As was observed for MEA, the concentration of Fe ions in solution for the 2.5 M AEPZ 80 ◦ C case remains relatively constant throughout the experiment. The pre-treatment process, as was apparent at 40 ◦ C,

also results in the release of some Fe ions into the bulk solution. The Fe ion concentration is reversed for MDEA and K2 CO3 at the elevated temperature of 80 ◦ C. The increased rate of reaction of MDEA at a higher temperature likely contributes to this, thereby resulting in a higher CO3 2− concentration than the K2 CO3 solution has readily available. Notably, AMP shows an even higher Fe ion concentration, suggesting that the formation of CO3 2− species may in fact be slower than by MDEA. For solutions tested against 2.5 M MEA, the pre-treatment procedures show only a minimal impact on Fe ion concentration. Unlike MEA, the benefit of pre-treatment appears highly beneficial in reducing the concentration of Fe ions in the bulk for 2.5 M AEPZ solutions at 80 ◦ C. The least effective of the three treatments is 1 M K2 CO3 . In this case, the Fe ion concentration build-up reaches almost the same levels as a sample without pre-treatment within four weeks. By contrast, both 5 M MDEA and AMP show a lasting efficacy. While some increase in Fe ion concentration is observed, after four weeks the concentration is still nearly only 5% of the concentration for a sample which did not receive any pre-treatment. 3.3. Coupon surface analysis 3.3.1. 2.5 M MEA and AEPZ Imaging using SEM was used in consort with XRD analysis to ascertain the chemical surface changes occurring. The control studies indicating the impact of 2.5 M MEA and AEPZ over a four week period are presented first for studies conducted at both 40 and 80 ◦ C. Carbon steel coupons in 2.5 M MEA at 40 ◦ C showed the formation crystalline structures within the first week, with good surface coverage apparent (Fig. 4A). Further inspection shows a mixture of crystalline forms which are common to both ferrous oxides (Fig. 4B needle/bladed crystals, (Li et al., 2013)) and siderite (Fig. 4C (Li et al., 2013)). After one week, evidence of siderite by XRD (Fig. 5A) supports the SEM image analysis, where a similar spectra is still appar-

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Fig. 4. SEM images of a carbon steel coupon after one week in a 40 ◦ C solution of 2.5 M MEA showing the formation of siderite crystals where (A) 500×, (B) 2000×, (C) 4000×.

Fig. 5. XRD spectra of carbon steel coupons after (A) one week in 2.5 M MEA at 40 ◦ C (B) four weeks in 2.5 M MEA at 40 ◦ C and (C) four weeks in 2.5 M MEA at 80 ◦ C. Relevant reference spectra are included.

ent after the fourth week (Fig. 5B). The formation of siderite by a 1◦ amine appears contradictory to the mechanisms previously explored (Eqs. (1) and (2)). However, the CO3 2− molecules formed in solution are due to the reaction between water and CO2 (Eqs. (9) and (10)). Additionally, the conditions for siderite formation must be at least somewhat favorable in 2.5 M MEA. By contrast, the formation of crystalline layers is not apparent at the increased temperature of 80 ◦ C. The probability of siderite formation is reduced at this elevated temperature due to a reduced concentration of CO2 in solution (MacDowell et al., 2010). Rather than siderite, the predominant species identified is ferrite, with indications from XRD of a nominal amount of hematite (Fe2 O3 ) present (Fig. 5C) after four weeks. These observations are consistent with the previously observed reduction in Fe ion concentration over four weeks at 40 ◦ C (Fig. 3A). A high initial concentration at the first week is caused by oxidation of Fe at the surface. Subsequent growth of these crystal structures contributes to some retardation in oxidation of Fe from the surface, though the porosity limits the efficacy. This combined, with reaction of Fe in solution to form various species, results in the observed decrease in Fe ion bulk concentration. However, it is likely that an equilibrium is becoming established and that a net flux of Fe ions will remain thereby not fully restricting corrosion on the surface but reducing it. At an increased temperature of 80 ◦ C, 2.5 M MEA is not strongly corrosive with little change in the Fe ion concentration. This is corroborated by the continued presence of ferrite (not cementite) detected by XRD, and the emergence of some hematite at the fourth week.

In comparison to MEA, 2.5 M AEPZ shows very significant surface damage at both 40 and 80 ◦ C (Fig. 6A–D). The results from XRD corroborate this visual observation. After week one, samples at both temperatures have a spectrum consistent with ferrite. However, in subsequent weeks the spectra show small but distinct peaks attributed to cementite (Fe3 C) (Fig. 6E, F). In an unadulterated coupon, cementite would be found in subsurface layers as a result of the manufacturing process. Due to the apparently corrosive effect, the labile Fe at the surface has been oxidised leaving cementite exposed (Berntsen et al., 2013). Therefore, a reduced flux of Fe ions would be expected from the surface of the metal coupon.

3.3.2. One week pre-treatment Three pre-treatment solutions were trialled to reduce the corrosive effects: 5 M MDEA, 5 M AMP, and 1 M K2 CO3 . Two samples (except AMP) of each solution were tested for one week, one at 40 ◦ C and one at 80 ◦ C. For the amine solutions 5 M MDEA and 5 M AMP a crystalline structure is observed for the one-week tests carried out at 80 ◦ C (Fig. 7B and D), but not at 40 ◦ C (Fig. 7A). The rhombohedral shape of the crystals observed is consistent with the formation of the most common siderite habit (Webmineral, 2015; Graf, 1961; Han et al., 2009), and confirmed with XRD (Fig. 7C and E). The crystals themselves appear to be larger, after one week, in solutions containing 5 M MDEA at 80 ◦ C. Siderite was observed to form in K2 CO3 at both 40 ◦ C and 80 ◦ C (Fig. 7F–H). Notably, both amine solutions result in more interlocked layers of crystals; whereas the crystals formed on the surface of the carbon steel in K2 CO3 are less well developed with significant

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Fig. 6. Carbon steel samples immersed in 2.5 M AEPZ are shown with imaging by SEM (at 500× with a 2000× inset image) in (A) one week at 40 ◦ C, (B) one week at 80 ◦ C, (C) four weeks at 40 ◦ C, (D) four weeks at 80 ◦ C. Spectra using XRD spectra for week four are shown in (E) for 40 ◦ C and (F) for 80 ◦ C. Relevant reference spectra are included.

inter-crystal spacing. The spacing seems a more significant problem at 80 ◦ C than 40 ◦ C. 3.3.3. Impact of one week pre-treatment at 40 ◦ C The pre-treatment of 5 M MDEA at 40 ◦ C failed to yield siderite formation on the surface. However, rate of MSC and Fe ion concentration in solution show that there is still some benefit where apparent corrosion rates decrease somewhat. Little observable

change to the surface, using SEM, is seen across weeks one through four after subsequent immersion in 2.5 M MEA at 40 ◦ C (Fig. 8A and B). Using XRD the only crystalline species on the surface detected is ferrite (Fig. 8C). While no apparent protective crystalline layer is observed, pre-treatment in 5 M MDEA showed a significantly reduced concentration of Fe ions in solution throughout the four weeks tested. Additionally, the product species formed on untreated coupons

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Fig. 7. SEM images of carbon steel samples immersed in pre-treatment solutions for one week and respective XRD spectra are shown: (A) 5 M MDEA at 40 ◦ C 1000×, (B) 5 M MDEA at 80 ◦ C 500× with 2000× inset, (C) MDEA XRD spectra, (D) 5 M AMP at 80 ◦ C 500× with 2000× inset, (E) AMP XRD spectra, (F) 1 M K2 CO3 at 40 ◦ C 500× with 2000× inset, (G) 1 M K2 CO3 at 80 ◦ C 500× with 2000× inset, (H) K2 CO3 XRD spectra. Relevant reference spectra are included.

tested against 2.5 M MEA at 40 ◦ C are not observed here. The reason for this result remains somewhat unclear, however it is evident that MEA is unable to react as easily with the surface after it has been exposed to MDEA. An explanation could be as simple as the presence of an amorphous thin film providing some surface protection. The robustness of 1 M K2 CO3 siderite layer formed at 40 ◦ C was tested against 2.5 M MEA 40 ◦ C and shows extremely rapid destruc-

tion. After only one week in solution the destruction is visually evident (Fig. 8D). The previously rhombohedral siderite crystals are now damaged, deformed, and irregular. This was confirmed by XRD where the reduction of the siderite signals in each subsequent week is significant (Fig. 8F). The overall protection to carbon steel provided by pretreatment with 1 M K2 CO3 is in doubt when compared to the control sample tested in 2.5 M MEA at 40 ◦ C with no pre-treatment. While

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Fig. 8. Carbon steel samples tested against 40 ◦ C 2.5 M MEA after (A) one (1000×) and (B) four (1000×) weeks with a 5 M MDEA pre-treatment and (C) XRD spectra for all four weeks; (D) one (500×) and (E) three (500×) weeks with a 1 M K2 CO3 pre-treatment and (F) XRD for all four weeks. For XRD spectra after pre-treatment, week one is black, two is blue, three is green, and four is red (spectra plotted individually are included in Supplementary information), relevant reference spectra are included.

the K2 CO3 offers an initial protection from oxidation at the surface, it is destroyed yielding increasing concentration of Fe ions in solution. However, this increase may be due to that dissolution process and not due to continuing oxidation at the surface. However, there is no evidence to suggest continued nucleation and growth of siderite after the initial pre-treatment. By contrast, 2.5 M MEA at 40 ◦ C naturally grows a siderite layer, albeit much more slowly, but offering longer term protection even with some initial oxidation at the surface. The limited efficacy of a 5 M MDEA solution pre-treatment at 40 ◦ C, is particularly evident when tested against a 2.5 M AEPZ solution. Even after one week immersion in this solution the presence of cementite is apparent using XRD (Fig. 9C). The uncovering of cementite is of interest because it has been previously reported that it can act as a porous substrate from which FeCO3 is able to nucleate and grow from Farelas et al. (2013). Imaging, using SEM, after two weeks shows the destruction to the carbon steel surface though a very small region of a layer remains intact (Fig. 9A). This layer observed adds credence to the hypothesis that an amorphous film may be present after exposure to MDEA at 40 ◦ C, providing some protection (Fig. 9C). This layer is no longer apparent at four

weeks (Fig. 9B). The removal of this product is likely from poor adhesion and perhaps dissolution into the solution. The degradation of siderite formed in the 1 M K2 CO3 pretreatment is more significant against AEPZ, than MEA. The siderite is significantly reduced over the four weeks (Fig. 9D–F). With a high initial Fe ion concentration, while the formation of the layer is strongly evident during the pre-treatment process its porosity yield significant oxidation of Fe at the surface. However, as with the untreated case, reduced flux of Fe ions into solution and consumption of Fe ions results in an overall reduced Fe ion concentration in the bulk of the solution. While 2.5 M AEPZ at 40 ◦ C did this untreated, the addition of the 1 M K2 CO3 pre-treatment layers improved the results further. 3.3.4. Impact of one week pre-treatment at 80 ◦ C The siderite layer formed during the one week pre-treatment process on carbon steel coupons in 5 M MDEA at 80 ◦ C is maintained very well during exposure to 2.5 M MEA for four weeks. Good surface coverage remains present (Fig. 10A) and only in the final week (Fig. 10B) does some surface debris on the crystals become visible at a high magnification. The source of the debris is most likely siderite precipitated into and re-deposited from the solution. The crystal

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Fig. 9. Carbon steel samples tested against 40 ◦ C 2.5 M AEPZ after (A) two (500×) and (B) four (2000×) weeks with a 5 M MDEA pre-treatment, (C) XRD spectra for all four weeks; (D) one (1000×) and (E) four (2000×) weeks with a 1 M K2 CO3 pre-treatment and (F) XRD for all four weeks − labelled backwards. For XRD spectra after pre-treatment, week one is black, two is blue, three is green, and four is red (spectra plotted individually are included in Supplementary information), relevant reference spectra are included.

structure is clearly well intact with no apparent increase in intercrystal spacing. Assessment of XRD spectra shows strong continued indication of siderite (Fig. 10C), and notably little diminishing of the siderite signal with respect to that of ferrite. While the siderite crystals formed in 5 M AMP appeared smaller from the pre-treatment process, they appear as effective through the four week trial tested against 2.5 M MEA at 80 ◦ C. After two weeks the crystals appear to form less of a layer. However, the crystals are still interlocked, only showing a somewhat less smooth surface on the individual crystals themselves (Fig. 10D). After two more weeks a bit more wear to the edges of the crystals is evident due to exposure to 2.5 M MEA at 80 ◦ C (Fig. 10E). This is likely the result of some dissolution of the siderite back into the solution. This prevalence of this may stem from the less well formed crystals at the outset. However, there are clear and strong siderite signals across all four weeks after pre-treatment (Fig. 10F) indicating no significant damage to the barrier layer overall. However, the comparative lack of surface coverage and development of siderite crystals in the 1 M K2 CO3 solution formed at 80 ◦ C results in a less robust protection against 2.5 M MEA at 80 ◦ C. After only one week’s exposure, deterioration of the layer, and crystals themselves, is evident with diminishing crystal size and increasing inter-crystal spacing (Fig. 10G). This trend continues with significantly damaged crystals after only three weeks (Fig. 10H). While

the SEM images are illustrative, the XRD spectra show this disappearance clearly (Fig. 10I) with unique siderite peaks decreasing and ferrite ones increasing. Notably, the reduction is less dramatic than for the comparable case where 1 M K2 CO3 at 40 ◦ C was used as a pre-treatment against 2.5 M MEA solution at 40 ◦ C. The impact of a 5 M MDEA pre-treatment before a four week trial against 2.5 M AEPZ at 80 ◦ C is similarly effective (Fig. 11A) as was observed for MEA, again with surface coverage maintained. However, the same degree of surface debris is not observed, even after four weeks (Fig. 11B). The XRD spectra also indicate no deterioration of the siderite signal (Fig. 11C). In the comparative case where pre-treatment with 5 M AMP at 80 ◦ C was trialled the results are very similar for AEPZ as MEA. Images from SEM show the less smooth crystal formations (Fig. 11D), with nominal increasing roughness after exposure at four weeks (Fig. 11E). Spectra for the first three weeks show little diminishing siderite signal, though a decrease is visible in the fourth week of exposure to AEPZ (Fig. 11F). The destruction of the crystalline layer grown in a 1 M K2 CO3 solution at 80 ◦ C is significant after exposure to 2.5 M AEPZ at 80 ◦ C. After only one week, sections of the crystalline layer peel and flake off (Fig. 11G). This mechanical disruption to the surface exposes the underlying carbon steel to AEPZ. Subsequently, oxidation of Fe at the surface leads to uncovering the underlying cementite by three

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Fig. 10. Carbon steel samples tested against 80 ◦ C 2.5 M MEA after (A) two (500×) and (B) four (6000×) weeks with a 5 M MDEA pre-treatment, (C) XRD spectra for all four weeks; (D) one (500×) and (E) four (4000×) weeks with a 5 M AMP pre-treatment and (F) XRD for all four weeks; (G) one (2000×) and (H) three weeks (2000×) 1 M K2 CO3 pre-treatment and (I) XRD for all four weeks. For XRD spectra after pre-treatment, week one is black, two is blue, three is green, and four is red (spectra plotted individually are included in Supplementary information), relevant reference spectra are included.

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Fig. 11. Carbon steel samples tested against 80 ◦ C 2.5 M AEPZ after (A) two (500×, 2000× inset) and (B) four (2000×) weeks with a 5 M MDEA pre-treatment, and (C) XRD spectra for all four weeks; (D) two (2000×) and (E) four (2000×) weeks with a 5 M AMP pre-treatment and (F) XRD for all four weeks; (G) one (500×, inset 2000×) and (H) four (500×) weeks 1 M K2 CO3 pre-treatment and (I) XRD for all four weeks. For XRD spectra after pre-treatment, week one is black, two is blue, three is green, and four is red (spectra plotted individually are included in Supplementary information), relevant reference spectra are included.

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weeks (Fig. 11I). This dramatic degree of damage to the surface is widespread after four weeks (Fig. 11H). The behaviours using all three pre-treatment approaches at 80 ◦ C offer some level of protection against the oxidation of Fe at the surface of the carbon steel coupon. Particularly worthy of note is the difference in performance of the siderite layer formed using 1 M K2 CO3 at 80 ◦ C compared to the 5 M amines solutions. When subjected to 2.5 M MEA at 80 ◦ C there is an initial increase and then very definite decrease in the Fe ion concentration in the bulk. Tied with the imaging done by SEM, it is clear that some product remains on the surface. It is likely that the initial layer formed does not remain wholly intact. Rather, the gaps allow continued oxidation of the surface of the coupon. However, the increase in concentration of Fe in solution allows for formation of more siderite. But it is clear that such precipitation of crystals is not nearly as good a protection mechanism, as is obtained by a well formed layer under controlled conditions. As such the Fe ion concentration decreases but in a longer study could very well oscillate. Comparatively when tested against AEPZ, the concentration of Fe ions simply rises. While a similar phenomenon occurs initially, the constitution of the solution containing AEPZ clearly makes it such that the reformation and precipitation of siderite is thermodynamically unfavourable. This is supported by the dramatically different images showing a level of damage to the coupon surface, and evidence of cementite, not seen in the comparable MEA case. The results of 5 M MDEA and 5 M AMP forming siderite protective layers at 80 ◦ C appear comparable. What is distinct is how these layers perform when tested against 2.5 M MEA versus AEPZ. When tested against MEA both types of protective layers result in similar Fe ion concentrations in the bulk, where fluctuations are within a relatively low range over the four weeks. As such, while the siderite crystal nucleation and growth is clearly somewhat different this does not impact the overall protective effect. Moreover, with such low concentrations even if some net flux of Fe ions is occurring it must be very minimal. This points to a reasonably robust protective mechanism. The impact of these protective siderite layers on carbon steel for 2.5 M AEPZ solutions is more demonstrable. However, the slight increase in Fe ion concentration in the bulk cannot be ignored in parallel with the appearance of some wear on the crystals. While the increase in Fe ion concentration may be due simply due to mechanical wear and the release of some Fe ions back into solution from the siderite, the long term effect could be sufficient damage to allow exposure to the bare carbon steel surface. 4. Conclusions There is significant potential for the use of carbon steel infrastructure in post-combustion capture plants where siderite provides a protective barrier on the surface. While absorber temperatures of 40 ◦ C, show less potential for the formation of robust siderite layers, warmer sections of the infrastructure are promising. In this proof of concept study, it was demonstrated that the use of 3◦ and SH amines offer the opportunity to grow siderite layers on carbon steel, while some CO2 capture can take place. Subsequently, more efficient solvents can replace the pre-treatment solution and the siderite layers appear to be sufficiently robust to withstand the corrosive nature of more efficient amines. This exciting result establishes the groundwork for further studies in how to optimize such a system for industrial application. Acknowledgements The authors would like to acknowledge the Imperial College Department of Materials X-ray Diffraction and Electron Microscopy

facilities, as well as the Department of Chemical Engineering’s Analytical Laboratory and Mechanical Workshop. Dr. Sedransk Campbell would like to thank the Royal Society and EPSRC for support of her Dorothy Hodgkin Research Fellowship. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ijggc.2017.01. 018. References Berntsen, T., Seiersten, M., Hemmingsen, T., 2013. Effect of FeCO3 supersaturation and carbide exposure on the CO2 corrosion rate of carbon steel. Corrosion 69 (6), 601–613. Billingham, M.A., Lee, C.H., Smith, L., Haines, M., James, S.R., Goh, B.K.W., Dvorak, K., Robinson, L., Davis, C.J., Peralta-Solorio, D., 2011. Corrosion and materials selection issues in carbon capture plants. Energy Procedia 4, 2020–2027. Boot-Handford, M.E., Abanades, J.C., Anthony, E.J., Blunt, M.J., Brandani, S., Mac Dowell, N., Fernández, J.R., Ferrari, M.C., Gross, R., Hallett, J.P., Haszeldine, R.S., 2014. Carbon capture and storage update. Energy Environ. Sci. 7 (1), 130–189. Choi, Y.S., Duan, D., Nesic´ı, S., Vitse, F., Bedell, S.A., Worley, C., 2010. Effect of oxygen and heat stable salts on the corrosion of carbon steel in MDEA-based CO2 capture process. Corros. Sci. 66 (12). ´ S., Duan, D., Jiang, S., 2013. Mechanistic modeling of carbon steel Choi, Y.S., Neˇsic, corrosion in a MDEA-based CO2 capture process. Corrosion 69, 551–559. Couchaux, G., Barth, D., Jacquin, M., Faraj, A., Grandjean, J., 2014. Kineitcs of carbon dioxide with amines. I. Stopped flow studies in aqueous solutions. A review. Oil & gas science and technology—revue d’IFP energies nouvelles. Institut Franc¸ais du Pétrole 69 (5), 865–884. Cummings, A.L., Waite, S.W., Nelsen, D.K., 2005. Corrosion and corrosion enhancers in amine systems. In: MPR Services Inc. Presentation, The Brimstone Sulfur Conference. DuPart, M.S., Bacon, T.R., Edwards, D.J., 1993. Understanding corrosion in alkanolamine gas treating plants: part 1 & 2. Hydrocarb. Process. 75–80, 89–94. Farelas, F., Brown, B., Nesic, S., 2013. Iron carbide and its influence on the formation of protective iron carbonate in CO2 corrosion of mild steel. NAC International Corrosion 2013 Conference & Expo. 2291. Fine, N.A., Goldman, M.J., Rochelle, G.T., 2011. Formation of nitrosamines in amine scrubbing with piperazine and monoethanolamine. 2nd Post Combustion Capture Conference. IEAGHG. Gouedard, C., Picq, D., Launay, F., Carrette, P.L., 2012. Amine degradation in CO2 capture 1. A review. Int. J. Greenh. Gas Control. 10, 244–270. Graf, D.L., 1961. Crystallographic tables for the rhombohedral carbonates. Am. Mineral. 46, 1283–1316. Gunasekaran, P., Veawab, A., Aroonwilas, A., 2013a. Corrosivity of single and blended amines in CO2 capture process. Energy Proc. 37, 2094–2099. Gunasekaran, P., Veawab, A., Aroonwilas, A., 2013b. Corrosivity of single and blended amines in CO2 capture process. Energy Proc. 37, 2094–2099. Guo, X.-P., Tomoe, Y., 1999. The effect of corrosion product layers on the anodic and cathodic reactions of carbon steel in CO2-saturated mdea solutions at 100 ◦ C. Corros. Sci. 41 (7), 1391–1402. ´ S., 2009. Chemistry and structure of Han, J., Young, D., Colijn, H., Tripathi, A., Neˇsic, the passive film on mild steel in CO2 corrosion environments. Ind. Eng. Chem. Res. 48 (13), 6296–6302. Hatcher, N.A., Jones, C.E., Weiland, G.S., Weiland, R.H., 2014. Predicting corrosion rates in amine and sour water systems. Optimised Gas Treat. Jacques-Derks, P.W., 2006. Carbon Dioxide Absorption in Piperazine Activated N-Methyldiethanolamine. PhD Thesis. The University of Twente. Kohl, A., Nielsen, R., 1997. Gas Purification. Gulf Publishing Company Houston, Texas, USA. Lee, D.K., Min, D.Y., Seo, H., Kang, N.Y., Choi, W.C., Park, Y.K., 2013. Kinetic expression for the carbonation reaction of K2CO3/ZrO2 sorbent for CO2 capture. Ind. Eng. Chem. Res. 52, 9323–9329. Li, L., Voice, A.K., Li, H., Namjoshi, O., Nguyen, T., Du, Y., Rochelle, G.T., 2013. Amine blends using concentrated piperazine. Energy Proc. 37, 353–369. MacDowell, N., Florin, N., Buchard, A., Hallett, J., Galindo, A., Jackson, G., Adjiman, C.S., Williams, C.K., Shah, N., Fennell, P., 2010. An overview of CO2 capture technologies. Energy Environ. Sci. 3 (11), 1645–1669. Ohmi, T., Ohki, A., Nakamura, M., Kawada, K., Watanabe, T., Nakagawa, Y., Miyoshi, S., Takahashi, S., Chen, M.S., 1993. The technology of chromium oxide passivation on stainless steel surface. J. Electrochem. Soc. 140 (6), 691–1699. Rennie, S., 2006. Corrosion and materials selection for amine service. Institute of Materials Engineering Australasia Ltd. Mater. Forum 30. ´ S., 2006. Protective iron carbonate films—part 1: Ruzic, V., Veidt, M., Nˇesic, mechanical removal in single-phase aqueous flow. Corrosion 62 (5), 419–432. Sartori, G., Savage, D.W., 1983. Sterically hindered amines for carbon dioxide removal from gases. Ind. Eng. Chem. Res. 22 (2), 239–249. Sedransk Campbell, K.L., Zhao, Y.C., Hall, J.J., Williams, D.R., 2016. The effect of CO2-loaded amine solvents on the corrosion of a carbon steel stripper. Int. J. Greenh. Gas Control 47, 376–385.

K.L. Sedransk Campbell et al. / International Journal of Greenhouse Gas Control 58 (2017) 232–245 Smith, L., Billingham, M., Barraclough, C., Lee, C.H., Milanovic, D., Peralta-Solario, D., James, S.R., Goh, B.K.W., Dvorak, K., Robinson, L., Davis, C.J., 2010. Corrosion and materials selection in CCS systems. Int. Energy Agency Greenh. Gas (IEAGHG). Sodiq, A., Rayer, A.V., Abu-Zahra, M.R.M., 2014. The kinetic effect of adding piperazine activator to aqueous tertiary and sterically-hindered amines using stopped-flow technique. Energy Proc. 63, 1256–1267. Sreenivasulu, B., Gayatri, D.V., Sreedhar, I., Raghavan, K.V., 2014. A journey into the process and engineering aspects of carbon capture technologies. Renew. Sustain. Energy Rev. 41, 1324–1350. Stolaroff, J., 2013. Carbonate Solutions for Carbon Capture: A Summary. Lawrence Livermore National Laboratory, Livermore, CA. Stowe, H.M., Vilciauskas, L., Paek, E., Hwang, G.S., 2015. On the origin of preferred bicarbonate production from carbon dioxide (CO2) capture in aqueous 2-amino-2-methyl-1-propanol (AMP). Phys. Chem. Chem. Phys. 17, 29184–29192. Sun, W., Nesic, S., Woollam, R.C., 2009. The effect of temperature and ionic strength on iron carbonate (FeCO3) solubility limit. Corros. Sci. 51, 1273–1276. Tanupabrungsun, T., Brown, B., Nesic, S., 2013. Effect of pH on CO2 corrosion of mild steel at elevated temperatures. Inst. Corros. Multiph. Technol. 2348. Veawab, A., Tontiwachwuthikul, P., Chakma, A., 1999. Influence of process parameters on corrosion behavior in a sterically hindered amine-CO2 system. Ind. Eng. Chem. Res. 38, 310–315. Webmineral, 2015. Mineralogydatabase. Xiang, Y., Yan, M.C., Choi, Y.S., Young, D., Nesic, S., 2014. Time-dependent electrochemical behaviour of carbon steel in MEA-based CO2 capture process. Int. J. Greenh. Gas Control 30, 125–132.

245

Xiang, Y., Choi, Y.S., Yang, Y., Neˇsic, S., 2015. Corrosion of carbon steel in MDEA-based CO2 capture plants under regenerator conditions: effects of O2 and heat-stable salts. Corros. Sci. 71 (1). Yamada, H., Matsuzaki, Y., Higashii, T., Kazama, S., 2011. Density functional theory study on carbon dioxide absorption into aqueous solutions of 2-amino-2-methyl-1-propanol using a continuum solvation model. J. Phys. Chem. 115, 3079–3086. Yu, L.C.Y., Sedransk Campbell, K.L., Williams, D.R., 2016a. Using carbon steel in the stripper and reboiler for post-combustion CO2 capture with aqueous amine blends. Int. J. Greenh. Gas Control 51, 380–393. Yu, L.C.Y., Sedransk Campbell, K.L., Williams, D.R., 2016b. Carbon steel corrosion in piperazine-promoted blends under CO2 capture conditions. Int. J. Greenh. Gas Control (Available online). Zheng, L., Landon, J., Matin, N.S., Thomas, G.A., Liu, K.L., 2016a. CO2 loading-dependent corrosion of carbon steel and formation of corrosion products in anoxic 30 wt.% monoethanolamine-based solutions. Corros. Sci. 102, 44–54. Zheng, L., Landon, J., Matin, N.S., Thomas, G.A., Liu, K.L., 2016b. Corrosion mitigation via a pH stabilization method in monoethanolamine-based solutions for post-combustion CO2 capture. Corros. Sci. 106, 281–292. Zheng, L., Landon, J., Matin, N.S., Liu, K., 2016c. FeCO3 coating process toward the corrosion protection of carbon steel in a postcombustion CO2 capture system. Ind. Eng. Chem. Res. 55, 3939–3948.