Oxidative Degradation and the Oxidation-Reduction Potential of ROC20 Solutions

1. Oxidative Degradation and the Oxidation-Reduction Potential of ROC20 Solutions By Fred Closmann January 10, 2008

2. Summary of Topics Covered • What is Oxidation-Reduction Potential (ORP)? • Why we want to Measure ORP? • How ORP Can Help US? • Review Preliminary Data (ROC20) • Other Findings – High Viscosity Solvent • Possible Future Experiments

3. ORP • According to ASTM method, “the ORP measurement establishes the ratio of oxidants and reductants prevailing within a solution… allows determination of the ability to oxidize or reduce species in solution.” • Reacting species related by Nernst Equation. • Non-selective; all e-transfer reactions influence measurement. • Gross measurement - not initially concerned with exact chemistry. • Standardized method(s) (ASTM)

4. ORP Electrode Standard Hydrogen Electrode We are using Ag/AgCl reference

5. Where is the degradation most likely to occur? Gas w/ 1% CO2 CO2 H2O, O2 Absorber 40-70 °C 1 atm Stripper 120 °C 1 atm Absorber Packing Cross Exchanger Sump Reboiler Flue Gas 10% CO2 5-10% O2 Solvent  = 0.4

6. Why Measure ORP? • Oxidative degradation can occur in the mass-transfer controlled region (Goff). • Allow us to know the potential for and rate of degradation of solvents. • Goal: Develop correlation between ORP and solvent degradation rate. • Secondary Goal: Understand catalytic effect of metals on solvent oxidation. • Real-time data collection (on-line methods).

7. Experiments Conducted to-Date • Baseline: ROC20 formulations (loaded to 0.3 mole/mole based on alkalinity) aerated/stirred in glass reactor at 53.5 °C. • Loaded ROC20 solution augmented with 0.01 mM Cu (added as cupric sulfate). • Rapid shut-down of well-mixed/aerated reactor with loaded ROC20 to understand O2 consumption (absence of copper). • Rapid start-up of reactor (aeration and mixing) from quiescent state (absence of copper). • Viscosity measurements of loaded ROC20 solutions

10. Steady-State Results • *ROC20 solution sat idle in reactor for 3 weeks. • **Viscosity measurements made at 25/40 °C. • NM – Not measured, NA – Not Applicable.

11. Interpretation of Results • Negative ORP not necessarily reduced environment. • Oxygen depleted fast; 90% of ORP change occurs in 24 minutes in quiescent reactor. • Rapid increase (<3 min) in ORP to near-steady state condition (-185 mV) upon reactor start-up. • Copper increases ORP; consistent with previous observations related to formate production (Sexton, 2007). • ROC20 became more viscous after sitting idle (305 cp vs. 18 cp at 25 °C); observation confirmed in experiment without Cu.

12. Potential ORP Experiments • Change reactor conditions improved mixing/aeration, and absence of both. • Addition of metals species including Ferric/Ferrous Iron to ROC20 to observe iron shuttle effect on ORP. • Addition of cobalt and nickel to investigate catalytic effects on ORP. • Addition of Hydrogen Peroxide (H2O2) to create highly oxidative environment - measure ORP and degradation of ROC20.

13. Investigate Potential ROC20 Polymerization Mechanisms • Recreate steps that lead to formation of highly viscous ROC20. • Repeat with ROC20 and other solvents. • Analysis using ORP, cation/anion chromatography, NMR, titration. • Reversible condition? Heat to 120 °C to mimic stripper operation. • Investigate CO2 stripping effects of experiments. Reload back to 0.3 m/m to reverse condition – (completed). • Literature review – formation of urea compound or polymer based on ROC20; propose pathway to creation of polymer.