Corrosion evaluation of MEA solutions by SEM-EDS, ICP-MS and XRD

Georgios Fytianos

Seniz UcarAndreas Grimstvedt Hallvard F. Svendsen

Hanna Knuutila

8th Trondheim Conference on CO2 Capture, Transport and Storage. TCCS-8 16 - 18 June 2015

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Outline

• Introduction

• Motivation

• Methodology

• Results

• Conclusions

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Amine treating Units

Although the continuous improvement in the capture efficiency there are various operational problems such as corrosion of process equipment and solvent degradation

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Degradation and Corrosion

Amine degradation:• Decreases the efficiency of CO2 capture

• Solvent loss• Unwanted compounds and emissions

Corrosion:• Severe operational problems• Increases the maintenance budget

Corrosion and Degradation are closely tied

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Research Motivation

Process parameters that determine the extent of corrosion:

1. Temperature

2. CO2 loading

3. Amine type and concentration

4. Degradation products Little information on corrosivity

available 

Degradation ProductsWe tested different acids: Some of them increase corrosion

Other Degradation Compounds: We tested 12 compounds

Degradation Products CASOZD 497-25-6HEEDA 111-41-1

HEIA 3699-54-5

HEI 1615-14-1HEF 693-06-1HEA 142-26-7

BHEOX 1871-89-2

HEPO 23936-04-1

HEGly 5835-28-9DEA 111-42-2Bicine 150-25-4

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Degradation products

• We chose 3 techniques to evaluate corrosion

ICP-MSSEM-EDS

XRD

After a first screening, we chose two degradation products:

Corrosion Evaluation: Overview

Weight loss technique with metal coupons is one of the most used for the calculation of the corrosion rate.

A number of electrochemical methods for corrosion measuring exist potentiodynamic polarization techniques are among the most popular

When studying corrosion it is of great importance to examine

• Corrosion rate• Kinetics• Corrosion products• Corrosion type• Links between degradation products and corrosion

Corrosion Evaluation: Overview

ICP-MS : Inductively Coupled Plasma Mass

Total Metal Concentration in the liquid gives information about the relative corrosivity

SEM- EDS : Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy

Surface morphology- Elemental Mapping (homogeneous corrosion or not)

XRD : X-ray Powder Diffraction

Identification of corrosion products

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Methodology

Experimental Setup

• Stainless steel cylinders (316 stainless steel tubes with an outer diameter of ½ inch and equipped with Swagelok® end caps)

• 9 g of loaded solution injected into the cylinder(30wt% MEA+1wt% degradation product)

• Cell put in forced convection oven at 135 o C

• Experiments run for 5 weeks (two replicates)

• Samples analysed for Fe, Cr and Ni by ICP-MS as an indication of corrosivity

• LC-MS analysis for MEA and degradation products

• SEM-EDS for surface characterization

• XRD for corrosion products identification

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Results

Degradation

MEA concentration after 5 weeks for the different solutions

HeGly (1wt%) Bicine (1wt%)

Week 2 0.48% 0.77%

Week 5 0.06% 0.59%

Thermal Stability

Corrosion Results

Metal Concentration

MEA MEA+HeGly MEA+Bicine0

200

400

600

800

1000

1200

FeNiCr

Solutions

mg/

L

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Surface morphology

(A) before the experiment, (B) End of exp. MEA solution (C) End of exp. MEA+bicine, (D) End of exp. MEA+HeGly

Scale bars denote 100 µm

Elemental mapping

wt % MEA MEA+Bicine MEA+ HeGly

Fe 64.6 63.8 64.4

Cr 18.3 18.0 18.2

Ni 12.5 13.1 12.8

Mo 2.4 2.6 2.5

Mn 1.6 1.6 1.6

Si 0.4 0.5 0.4

Corrosion Products

• XRD data showed formation of highly crystalline siderite, FeCO3, on the cylinder surfaces for all the solutions.

• Additional low intensity peaks at 43.5° associated with elemental iron, Fe, were observed in the presence of 1 wt% degradation product+MEA solutions.

MEA+HeGly

MEA+Bicine

MEA

LIQUID SAMPLE• Liquid sample analysis with ICP-MS can work as a first

screening of relative corrosivity among solutions

• ICP-MS alone is not enough to study corrosion in post-combustion CO2 capture

STAINLESS STEEL• SEM itself can be used for surface morphology but does not

give any details about the composition of the surface.

• EDS can be used for elemental composition

Conclusions

• The combination of ICP-MS, SEM-EDS and XRD was used for corrosion evaluation of MEA solutions.

• ICP-MS: Additon of Bicine or HeGly increases the corrosion

• SEM-EDS: Surface morphology of 316 SS changed with addition of degradation product

• Overall the results from SEM support the findings from the liquid analyses since ICP-MS showed higher relative corrosivity with the addition of HeGly and bicine.

Acknowledgements

The work is done under the SOLVit SP4 project, performed under the strategic Norwegian research program CLIMIT. The authors acknowledge the partners in SOLVit, Aker Solutions, Gassnova, EnBW and the Research Council of Norway for their support.

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Thank you for your attention

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APPENDIX

• Degradation Products Structure

• Materials and Methods

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Degradation Products

Eirik F. da Silva et. al. : Understanding MEA degradation in post-combustion CO2 capture

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Materials and Methods• A high resolution Thermo Fischer Element 2 (Bremen, Germany) ICP-MS was used

for the analysis of metals in the liquid samples. The solutions were analyzed for Fe, Cr, and Ni by ICP-MS as an indication of corrosivity. For the ICP-MS analysis each sample was mixed at room temperature and 100 μL was pipetted into a sample tube. 100 μL of concentrated HNO3 (ultra pure) are added and everything was diluted to 10 mL with water. Finally this solution was further diluted resulting in a total dilution of 10000 (1 +9999).

• Both SEM and EDS characterization were carried out by using a Hitachi S-3400N scanning electron microscope. For this purpose small pieces were cut from the cylinders and their surfaces were cleaned with ethanol to remove any deposited corrosion product prior to scanning. An acceleration voltage of 20.0 kV and a working distance of 10.0 μm were used, and samples were placed on stubs and scanned without coating. Aztec Energy software was used to process the EDS data.

• Qualitative characterization of deposited corrosion products was conducted via powder X-Ray Diffraction (XRD) (D8 Advance DaVinci, Bruker AXS GmBH). The pattern was collected in the 2θ range of 20-80° using a Cu X-ray tube, with a step size of 0.013° and a step time of 0.78 s. Precipitates formed on cylinder walls were collected gently after air-drying, and crushed with a mortar and pestle before XRD analyses. The PDF-4+ database (from the International Centre for Diffraction Data) was used for species identification.