Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
Practical Applications of Raman Spectroscopy for Process Analysis
Brian J. Marquardt, Charles Branham and David J. VeltkampCenter for Process Analytical Chemistry
University of Washington
Bernd WittgensSINTEF, Trondheim, Norway
Materials and Chemistry
CPAC Satellite Workshop 2007, RomeAbsorption process for removal of
CO2 from flue gas
2 MEA + CO2 MEACOO- + MEAH+
Cold
Hot
Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
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?
Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
MEA, CO2, H2O
MEA, CO2, H2O, HCO3
-, CO3-,
MEACOO-, MEAH+
Raman Shift (cm-1)
Equilibrium of MEA and CO2
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 H2CO3 H+ + HCO3
- 2 H+ + CO32-
For > 0,5MEACOO- + H2O HCO3
- + MEAH+
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500 1000 1500 2000 2500 Raman Shift (cm-1)
Inte
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Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
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
Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
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
Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
Gas/Liquid Reactor Setup
Liquid InletGas
Inlet
Ballprobe
Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
Raman Sampling Probe
Stainless steal probe
Sapphirelens
Focuspoint
Fibre optic
Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
Raman Spectra: Pure components
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• Water• Mono Ethanolamine (MEA)• Methyl-di-ethanolamine (MDEA)
Raman Shift (cm-1)
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Raman Shift (cm-1)
Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
Raman Spectra: Absorption mixtures
Raman Shift (cm-1)
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• 70% Water - 30% MEA• 70% Water - 22% MEA – 8% MDEA
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Raman Shift (cm-1)
Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
MEA, Water and CO2 - Challenge: Comparison of standards to reaction
Raman Shift (cm-1)
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• Water• MEA
Time• 2.5• 10• 30• 50
Sapphire
Raman Shift (cm-1)
Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
MEA, Water and CO2 - Pressure step 10/0.69 ,32/2.2 and 58/3.99 psi/bar(g)
Raman Shift (cm-1)
Inte
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• 0 psi• 10 psi• 32 psi• 58 psi• 58 psi (no flow)
0 10 20 30 40 50 60 70 80 90 1000.6
0.8
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x-axis (unk.)
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PCA Analysis of ROI
Raman Shift (cm-1)
Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
CO2 and MEA at 30 psi / 2.1 bar(g)
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Time (min)• 2.5• 10• 17• 25• 40• 47• 55
Raman Shift (cm-1)
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)
0 20 40 60 80 100 1200.8
1
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2.2x 10
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x-axis (unk.)
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PCA Analysis of ROI
Raman Shift (cm-1)
Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
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
Materials and Chemistry
CPAC Satellite Workshop 2007, Rome
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