Corrosion experiments in amine solutions

Transcription

1 Corrosion experiments in amine solutions Andreas Grimstvedt Process technology SINTEF Materials and chemistry Wenle He Applied mechanics and corrosion SINTEF Materials and chemistry 1

2 Contents of presentation Background Apparatus for corrosion experiments Results experiments MEA Results experiments DETA 2

3 Background Corrosion problem on the equipments in amine based CO 2 capture process Corrosion is influenced by many parameters: Type and concentration of amine Gas concentration (O 2, CO 2 ) Temperature Steel Fluid flow Products from corrosion and degradation Corrosion and degradation inhibitors Complex system Corrosion of steel and degradation of amines: Degradation product can be chelating agents for iron ions. Iron ions can catalyze the degradation of amines. 3

4 Corrosion in aqueous systems with CO 2 2 Fe Fe H + 2e H e 2 Anode reaction Cathode reaction Carbamate (primary and secondary amines) Heat stabile salts Degradation products Break down of protective layer (Fe 2 O 3, Fe 3 O 4,FeCO 3 etc) A. Ikeda, M. Ueda and S. Mukai, CO 2 Behavior of Carbon and Cr Steels, In Advances in CO 2 Corrosion (1984) 4

5 Apparatus and Corrosion rate measurements EC-Rotating disk electrode EC-autoclave, 1L Pipe-autoclave, 1.5L 5L-autoclave RT~80ºC, atm, flow RT~150ºC, 2 bar RT~500ºC, 10 bar RT~500ºC, 10 bar by EC (LPR, EIS) by weight loss by weight loss by weight loss vs time, by EC (LPR, EIS) in 6 bottles vs liquid flow vs time 5

6 Rotating disc electrode 1.61ν δ = ω 1/ 6 1/ 2 D 1/ 3 6

7 EC-autoclave Saturated calomel reference electrode Salt bridge Thermocouple Gas outlet Gas inlet Autoclave Glass beaker Plastic Wood Platinum counter electrode 316 L Working electrode Amine solution Magnet Stirrer and heater 7

8 Experimental work Material Environments Carbon steel: ST 52 Stainless steels: 316L, 13Cr Solutions: Temperature: 40 ºC Gases: Liquid flow: MEA, DETA 30 %, 50 %, new and degraded open air 100 % CO 2 4 % CO 2 +N 2 4 % CO % O 2 rotating disk electrode Corrosion rate measurements Tafel Polarization Linear Polarization Resistance (LPR) Impedance Weight Loss 8

9 Polarization curve on ST 52 in MEA 1.5 St 52 corrosion in 30 % MEA with 4 % CO 2 at 40 ºC, ph E / VSCE i / ma cm -2 Polarization curve Steel St 52 was corroded at low potentials At higher potentials the metal became passive. Potential ph diagram 9

10 Comparison of Corrosion Rates measurements St 52 corrosion in 30 % MEA with 4 % CO 2 at 40 ºC, ph Measurements Tafel Extrapolation Linear Polarization (nondestructive) Impedance (nondestructive) Corrosion rate mm / year Corrosion rates were determined by current, linear polarization resistance and impedance resistance E/ VSCE y = x y = x E/ VSCE y = x Z''/ ohm cm Rs Z'/ ohm cm 2 Rs+Rct E E E E E E E E-04 log ( i /ma cm -2 ) I / Acm -2 10

11 Effect of CO 2 partial pressure and O 2 on corrosion rates St 52 corrosion in 30 % MEA with 4 % CO 2 at 40 ºC, ph Z''/ ohm cm % CO2 4 % CO2 4 % CO2 12 % O Z'/ ohm cm 2 Gas Charge transfer resistance Rct, ohm cm 2 Corrosion rate mm / year 100 % CO % CO % CO % O

12 Effect of MEA concentration on corrosion rates Corrosion in MEA with CO 2 at 40 ºC, 100 rpm Corrosion Rates, mm / year Material St 52 St 52 13Cr Gases/Solution 30% MEA 50% MEA 50% MEA 4% CO % CO %O

13 Corrosion rate/ mm year -1 Effect of amine degradation and flow Corrosion rate/ mm year % CO % O2 4 % CO2 4 % CO % O2 4 % CO Rotation rate/ rpm St 52 corrosion in 30 % MEA with CO 2 at 40 ºC Corrosion rate/ mm year Degraded MEA (air+2% CO 2, 10 days) ph % CO % O2 4 % CO Rotation rate/ rpm Degraded MEA (air, 10 days) ph Rotation rate/ rpm Fresh MEA ph Corrosion rates were increased by amine degradation, flow, oxygen presence 13

14 Corrosion in Diethylenetriamine (DETA) Corrosion rate/ mm y -1 Open air system CO 2 purged through amine CO 2 purged over amine 316L corrosion in 2.5 M DETA at 135 ºC (α=0.5) Corrosion rates were measured by weight loss No Corrosion when oxygen was present! Heavy Corrosion when oxygen was removed. Mainly Corrosion was in the solution. Amine solution 14

15 Polarization curves in DETA C 80 C 316L corrosion in 2.5 M DETA E/ VSCE E/ VSCE i/ ma cm -2 Measurement on Pt i/ ma cm -2 At 80 C the 316L Steel shows active and passive behavior 15

16 Summary experiments Almost no corrosion was observed for 316L and 13 Cr steel in MEA. St 52 was not corroded in MEA without CO 2 present. The corrosion rate of ST 52 was increased with concentration of CO 2 and MEA. Corrosion rate was increased by degradation of MEA. Corrosion rate was increased when O 2 was present. Corrosion rate was increased by increasing fluid convection with O 2 present. 316L was corroded in DETA 16