Practical Applications of Raman Spectroscopy for Process Analysis
Brian J. Marquardt & Bernd Wittgens**, Charles Branham and David J. Veltkamp
Center for Process Analytical Chemistry University of Washington ** Sintef, Trondheim, Norway Absorption system
Clean Flue gas CO2 to sequestration Sweet natural gas Lean amine
Desorption Absortion column column
Reboiler Flue gas Raw natural gas Loaded amine RAlifG/LiidRaman Analysis of Gas/Liquid Reactor at Elevated Pressure
Evaluate Raman as an online tool for evaluating gas scrubber absorbent performance Experiments were performed in a gas/liquid reactor at elevated pressures Efficient and reproducible sampling was needed to interrogate both the liquid and gas phases of thihe reaction Reaction of Methyl Ethanolamine
(MEA) and CO2
Hot - + MEA + CO2 + H2O Cold HCO3 + MEAH
10000
8000 counts) ((
6000
Intensity 4000
2000
0 500 1000 1500 2000 2500 3000 Raman Shift (cm-1) 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
Removal of C02 from natural gas
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? 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 Methyl ethanolamine (MEA) Methyl diethanolamine (MDEA)
Bubble CO2 gas at pressure through absorbent while collecting Raman data
Pressure range 5 – 60 psi CO2 Monitor reaction with Raman to determine absorbent CO2 saturation point at a given partial pressure of CO2 Gas/Liquid Reactor Setup Raman Sampling Probe Reactant Stds: Raman Spectra
12000
• Water 10000 • Methyl Ethanolamine • Methyl Diethanolamine
8000 counts) ((
6000
4000 Intensity
2000
0
0 500 1000 1500 2000 2500 3000 Raman Shift (cm-1) Reactant Raman Spectra
• 70% Water - 30% MEA • 70% Water - 22% MEA – 8% MDEA 3000 (counts)
2000 Intensity
1000
0
0 500 1000 1500 2000 2500 3000 Raman Shift (cm-1) Gas/Liquid Reactor Setup CO2 and H2O Raman Spectrum
ROI of Dissolved CO2
1100
4000
1000
900
800
3000
700 (counts)
600
500
2000
1150 1200 1250 1300 1350 1400 1450
Intensity 1382
1000 • 12 PSI • 32 PSI
0 • 60 PSI 1274
200 400 600 800 1000 1200 1400 1600 1800 Raman Shift (cm-1) MEA, Water and CO 2 - Challenge: Comparison of standards to reaction
12000 • water
10000 •MEA
Time 8000 •2.5
(counts) •10 6000 •30 •50
4000 Intensity
2000
0 Sapphire
0 500 1000 1500 2000 2500 3000 Raman Shift (cm-1) MEA, Water and CO 2 - Pressure step 10,32 and 58 psi
7000
5 x 10 PCA Analysis of ROI •0 psi 2.4 2.2 6000 • 10 psi • 32 psi 2 1.8
5000 • 58 psi 1.6
• 58 psi (no flow) 1.4 Relative Intensity Relative 4000 1.2 (counts) 1
0.8 3000
0.6 0 10 20 30 40 50 60 70 80 90 100 x-axis (unk.)
Intensity 2000
1000
0
0 500 1000 1500 2000 2500 3000 Raman Shift (cm-1) CO2 and MEA at 30 psi
5 Time (min) x 10 PCA Analysis of ROI 6000 2.2 •2.5 •10 2 5000 •17 1.8 •25 1.6 4000 •33 1.4 Relative Intensity Relative (counts) • 40 1.2 3000 •47 1 •55 0.8 2000 0 20 40 60 80 100 120 x-axis (unk.) Intensity
1000
0
0 500 1000 1500 2000 2500 3000 Raman Shift (cm-1) CO2, MEA and MDEA at 30 psi
Time (min) PCA Analysis of ROI 0.1 5000 •2.5 •10 0.05 0
4000 •17 •25 -0.05
•33 arb. units -0.1
3000 (counts) • 40 -0150.15
•47 -0.2
•55 -0.25 2000 0 20 40 60 80 100 120 140 160 •73 x-axis (unk.) Intensity
1000
0
0 500 1000 1500 2000 2500 3000 Raman Shift (cm-1) 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 reppodubroducibility yo of bo th the rea ctio n a nd the optical sampling and lead to more consistent results A successful demonstration of Raman applied to a liqq/guid/gas reactor to imp rove p rocess control of a reaction at moderate pressure Work in progress
rd Designed single test reactor (3 generation) “Miniaturized” reactor for improved gas liquid contact Optimize gas/liquid separation Design and application is under patenting Test of new absorber commence in autumn 2008 Conditions: < 1700 Psi Temperature: < 200 C Improve instrumentation for process monitoring Pressure, temperature and flow ABB FT-IR Raman