1. Practical Applications of Raman Spectroscopy for Process Analysis
Brian J. Marquardt, Charles Branham and David J. Veltkamp
Center for Process Analytical Chemistry
University of Washington
Bernd Wittgens
SINTEF, Trondheim, Norway

2. Absorption process for removal of CO2 from flue gas
Cold
2 MEA + CO MEACOO- + MEAH+
Hot

3. Why is this reaction important?
Environmental implications of CO2 release from the burning of fossil fuels
Need for efficient chemical processing to effectively reduce excess stack emissions into the environment
Raman could be a useful tool for monitoring the absorption of C02 and absorbent performance in real-time for process control
Can Raman be an effective sensor for monitoring both gas emission (CO2, SO2, …) and absorbent quality/capacity simultaneously in a wet scrubber to improve efficiency and control?

4. Equilibrium of MEA and CO2
MEA, CO2, H2O
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Intensity (counts) ) 1 -
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Intensity (counts)
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Raman Shift (cm
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Raman Shift (cm -
Intensity (counts) ) 1
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MEA, CO2, H2O,
HCO3-, CO3-,
MEACOO-,
MEAH+
Water • •
Methyl
12000
Methyl Ethanolamine
8000
Diethylanolamine
6000
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10000 • •
Water
Diethylanolamine •
Methyl
6000 •
Methyl Ethanolamine
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Currently, the reaction is modeled based on the CO2 concentration in the gas phase. The equilibrium reactions in the liquid phase are:
CO2 + 2 MEA MEAH+ + MEACOO-
CO2 + H2O H2CO H+ + HCO H+ + CO32-
For a > 0,5
MEACOO- + H2O HCO3- + MEAH+
Raman Shift (cm-1)

5. Raman Analysis of Gas/Liquid Reactor at Ambient and Elevated Pressure
Evaluate Raman as an online tool for evaluating gas scrubber absorbent performance
Experiments were performed in a gas/liquid reactor at ambient and elevated pressures
Efficient and reproducible sampling was needed to interrogate both the liquid and gas phases of the reaction

6. Experimental 785 nm Raman System
Ballprobe connected inline with high pressure fitting
Laser power = 160 mW at sample, -50º C detector temp.
Exposure time 6 sec, 5 accums./spectrum (30 sec/spectrum)
Charge reactor with 20 mL of absorbent and H2O
Mono ethanolamine (MEA)
Methyl-di-ethanolamine (MDEA)
Bubble CO2 gas at pressure through absorbent while collecting Raman data
Pressure range 5 – 60 psi CO2 / 0.35 – 4.13 bar(g)
Monitor reaction with Raman to determine absorbent CO2 saturation point at a given partial pressure of CO2

7. Gas/Liquid Reactor Setup
Ballprobe
Liquid
Inlet
Gas
Inlet

8. Raman Sampling Probe Sapphire lens Focus Fibre optic point
Stainless steal probe

9. Raman Spectra: Pure components
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Water
Mono Ethanolamine (MEA)
Methyl-di-ethanolamine (MDEA)
Raman Shift (cm-1)
Intensity (counts)
Raman Shift (cm-1)

10. Raman Spectra: Absorption mixtures
70% Water - 30% MEA
70% Water - 22% MEA – 8% MDEA
3000
Intensity (counts)
2000
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Raman Shift (cm-1)
Raman Shift (cm-1)

11. MEA, Water and CO2 - Challenge: Comparison of standards to reaction
12000
Water
MEA
Time
2.5 10 30 50
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Intensity (counts)
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Sapphire
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Raman Shift (cm-1)
Raman Shift (cm-1)

12. MEA, Water and CO2 - Pressure step 10/0. 69 ,32/2. 2 and 58/3
MEA, Water and CO2 - Pressure step 10/0.69 ,32/2.2 and 58/3.99 psi/bar(g)
7000
0 psi
10 psi
32 psi
58 psi
58 psi (no flow)
PCA Analysis of ROI
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Intensity (counts)
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Raman Shift (cm-1)
Raman Shift (cm-1)

13. CO2 and MEA at 30 psi / 2.1 bar(g)
Time (min)
2.5 10 17 25 40 47 55
PCA Analysis of ROI
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Intensity (counts)
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Raman Shift (cm-1)
Raman Shift (cm-1)

14. Summary
Initial experiments indicate that Raman is an effective analysis tool for following these CO2 absorption reactions
More experiments need to be performed to evaluate and modify the reactor to ensure good gas mixing with the liquid absorbent
Problems with foaming and liquid evacuating the cell
By optimizing the reactor system it should improve the reproducibility of both the reaction and the optical sampling and lead to more consistent results
A successful demonstration of Raman applied to a liquid/gas reactor to improve process control of a reaction at moderate pressure

15. Future work Calibration for online detection of amine concentrations
Identification of species in reactions
Identify relation between reaction kinetics and observed results from PCA
Utilize GC for online sampling of CO2 inlet and outlet concentration
Apply in-situ fluorescence sensor or FT-IR for gas analysis