Supplemental Information A. Chemical List Chemical Supplier Purity Piperazine Sigma-Aldrich >99% Ethanolamine Fisher Chemicals >99% Diethanolamine Fisher Chemicals >99% Methyldiethanolamine Sigma-Aldrich >99% 2-amino-2-methyl-1-propanol Sigma-Aldrich >99% Sodium Hydroxide Fisher Chemicals 1 N Sodium Nitrite (Natural) Acros organics 98.5% Sodium Nitrite (N 15 ) Cambridge Isotope Laboratories 97% Sodium Chloroacetate Alfa Aesar 98% N-Nitrosopiperazine Toronto Research Chemicals 98% Nitrosodiethanolamine Toronto Research Chemicals 98% Carbon Dioxide Matheson Tri-Gas 99.99% Table 3: Chemical list for experimental runs B. Mass Spectrometry For HeGly and NHeGly Synthesis HeGly NHeGly Figure 10: High Resolution Mass Spectroscopy of HeGly/NHeGly in MEA
HeGly Figure 11: HeGly peak in High Resolution Mass Spectroscopy of HeGly/NHeGly in MEA NHeGly Figure 12: NHeGly peak in High Resolution Mass Spectroscopy of HeGly/NHeGly in MEA
C. Total Nitrosamine Analysis A schematic for total nitrosamine analysis is shown below. The data from the NO x analyzer shows clear reproducible peaks that are linear with nitrosamine concentration. The response is equivalent across multiple nitrosamines tested. Atmospheric Bypass Ice Water 0-3 ppm NO in N 2 1 SLPM, 1 atm, 10 C Reactor Model 42T Chemiluminescent NO x Analyzer 10-1000 μl sample XX 1 in. OD Reactor ¼ in. Glass Beads 15 ml Reagent 1.1 SLPM N 2 Figure 13: Total Nitrosamine Apparatus (TONO)
2.0 Adjusted Signal (Volts) 1.5 1.0 0.5 0.0 0 10 20 30 40 50 60 70 Time (minutes) Figure 14: Sample responses from injection in the TONO Condition Purity Amount Temperature - 21 C Pressure - 14.7 psig Nitrogen 99.99% 1.1 SLPM Ethyl Acetate 98% 12 ml Acetic Acid 99.85% 2 ml HBr 48% in water 0.4 ml Acetic Anhydride 99% 0.6 ml Table 4: Operating conditions and reagents used in TONO C. Total Aldehyde Analysis A new method was developed for detecting aldehydes and ketones in degraded amine solvents by reaction with 2,4-dintrophenylhydrazine (DNPH) followed by analysis using HPLC. The preparation method was: 1. In a glass HPLC vial, the concentrated amine sample was diluted by a factor of 50X to 500X in 1 ml of 2:1 vol:vol methanol and 10 mm ammonium carbonate buffer. The dilution factor must be sufficient to reduce the total aldehyde content of the sample to less than 3 mmol/kg, the concentration of DNPH that was added to the samples.
2. 0.3 ml of 0.4 wt % DNPH diluted in acetonitrile was then added. The solution was then capped, stirred, and allowed to react at room temperature for 24 hours. 3. The reacted solution was then injected directly on HPLC using an Acclaim Polar Advantage II C18 5 μm 120 Å 4.6 x 150 mm reverse phase column with UV detection at 365 nm, using the eluent ramp shown in Figure 12. DNPH reacts rapidly with aldehydes and slowly with amines. To account for this, a fresh amine sample was prepared and run at the same dilution as the degraded solvent samples. The difference between the expected and observed DNPH peak at 9.1 minutes was used to calculate the total aldehyde concentration of the sample. A 50 mmol/kg sample of MNPZ was prepared in 7.5 M PZ and thermally degraded at 175 C. This was then reacted with DNPH. The reaction mixture was run on HPLC repeatedly for 20 hours after the DNPH was added. Figure 13 shows the initial chromatogram and the chromatogram 20 hours later. The first peak in the chromatogram at 2.5 minutes is postulated to be the DNPH-amine derivative peak. It appears in all DNPH-reacted amine samples and accumulates steadily, as shown in Figure 14. The peak at 3.2 minutes appears only in degraded PZ and MNPZ samples, not in fresh amine samples. Direct injection mass spectroscopy on the degraded MNPZ sample determined that the major product of MNPZ decomposition is 2-piperazinol (2-PZOH), a hemiaminal (Figure 16). This hemiaminal will be in equilibrium with N-(2-ethanal)-ethylenediamine, an aldehyde, as shown in Figure 15. It is postulated that the peak at 3.2 minutes is the DNPH derivative of this product. The peak is fully formed within 12 hours of mixing with DNPH. A prediction of DNPH peak disappearance over time based on the areas of the 2.5 minute and 3.2 minute peaks was compared to the observed DNPH peak. This shows that the DNPH is not reacting with any other unknown products in the thermally degraded MNPZ sample. A regression of the peak area data determined that the 2-PZOH peak followed a calibration curve of 0.0377 mmol/kg/(mau*min).
90 10min: 85% MeOH (vol %) 80 70 60-4 -6 min: 65% MeOH 15 min: 82.5 % 50-4 0 4 8 12 minutes Figure 15: HPLC eluent ramp (vol % MeOH in 10 mm (NH 4 ) 2 CO 3 buffer, 1 ml/min total flow rate) 300 Initial 20 hrs DNPH (9.1 min) mau (365 nm) 200 100 DNPH-PZ-derivative (2.5 min) 0 2-PZOH (3.2 min) 2 4 6 8 10 12 min Figure 16: Chromatograms of DNPH reaction with thermally degraded MNPZ, initially and 20 hours after preparation
9.1 min peak (mau) 150 120 90 60 30 DNPH(9.1 min) and predicted area (--) DNPH-PZ (2.5 min) DNHP-2-PZOH (3.2 min) 30 25 20 15 10 5 2.5 and 3.2 min peaks (mau) 0 0 5 10 15 20 Hours 0 Figure 17: DNPH peak area, DNPH-derivative peak areas, and predicted DNPH peak area based on DNPH-derivative peak areas
Figure 18: High Resolution Mass Spectrometry of 2-PZOH Figure 19: 2-Piperazinol hemiaminal and constituent N-acetal-ethylenediamine aldehyde D. List of Uncommon Abbreviations and Symbols Abbreviation Description Unit NNO Generic nitrosamine - MNPZ n-nitrosopiperazine - NDELA nitrosodiethanolamine - NHeGly nitroso-(2-hydroxyethyl) glycine - HeGly N-(2-hydroxyethyl) glycine - α CO 2 Loading of Amine mol CO 2 /mol N NNO i Initial nitrosamine concentration in decomposition mm kinetics experiments k obs Regressed first order decomposition rate constant in each individual experiment (s -1 )
Par Parameters for regressions using k obs (Temperature, - Concentration, pk a, Loading) k calc The calculated rate constant for a set of experiments (s -1 ) using the regressed models for k obs β The Bronsted slope for pk a dependence - γ The base concentration dependence for nitrosamine - decomposition PZCOO - Piperazine carbamate - PZ(COO - ) 2 Piperazine dicarbamate - H + PZCOO - Protonated Piperazine carbamate (zwitterion) - k 2 Nitrosamine decomposition rate constant after (s -1 M -γ ) accounting for base concentration 2-PZOH 2-piperazinol - NNO ss Nitrosamine steady state concentration in amine (mol/kg) scrubber δ Nitrosamine yield from NO 2 (mol NNO/mol NO 2 ) y NO2 Molar fraction of NO 2 in inlet flue gas (mol NO 2 /mol Flue gas) k Des First order nitrosamine decomposition rate constant in (s -1 ) the desorber τ Des Residence time in the desorber (s) G/L Gaseous molar flow rate over liquid mass flow rate (mol Flue Gas/kg Solvent) t ss Time to reach nitrosamine steady state concentration (s) t tot Total liquid residence time for one pass through amine scrubber (s)