Practical Applications of Raman

Transcription

1 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

2 Absorption system Clean Flue gas Sweet natural gas Lean amine CO 2 to sequestration Absortion column Desorption column Flue gas Raw natural gas Loaded amine Reboiler

3 Raman Analysis of Gas/Liquid id 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 the reaction

4 10000 Reaction of Methyl Ethanolamine (MEA) and CO 2 Hot MEA + CO 2 + H 2 O HCO3 - + MEAH + Cold Intensity (counts) Raman Shift (cm -1 )

5 Why is this reaction important? Environmental implications of CO 2 release from the burning of fossil fuels Need for efficient chemical processing to effectively reduce excess stack emissions into the environment Removal of C0 2 from natural gas Raman could be a useful tool for monitoring the absorption of C0 2 and absorbent performance in real-time for process control Can Raman be an effective sensor for monitoring both gas emission (CO 2, SO 2, ) and absorbent quality/capacity simultaneously in a wet scrubber to improve efficiency and control?

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 H 2 O Methyl ethanolamine (MEA) Methyl diethanolamine (MDEA) Bubble CO 2 gas at pressure through absorbent while collecting Raman data Pressure range 5 60 psi CO 2 Monitor reaction with Raman to determine absorbent CO 2 saturation point at a given partial pressure of CO 2

7 Gas/Liquid Reactor Setup

8 Raman Sampling Probe

9 Reactant Stds: Raman Spectra Intensity (counts) Water Methyl Ethanolamine Methyl Diethanolamine Raman Shift (cm -1 )

10 Reactant Raman Spectra (counts) 70% % Water - 30% MEA 70% Water - 22% MEA 8% MDEA Intensity Raman Shift (cm -1 )

11 Gas/Liquid Reactor Setup

12 CO 2 and H 2 O Raman Spectrum ROI of Dissolved CO (counts) Intensity PSI 32 PSI 60 PSI Raman Shift (cm -1 )

13 MEA, Water and CO 2 - Challenge: Comparison of standards to reaction water MEA (counts) Intensity Time Sapphire Raman Shift (cm -1 )

14 MEA, Water and CO 2 - Pressure step 10,32 and 58 psi (counts) psi 10 psi 32 psi 58 psi 58 psi (no flow) Relative Intensity 2.4 x 105 PCA Analysis of ROI Intensity x-axis (unk.) Raman Shift (cm -1 )

15 CO 2 and MEA at 30 psi (counts) Intensity Time (min) Relative Intensity 2.2 x 105 PCA Analysis of ROI x-axis (unk.) Raman Shift (cm -1 )

16 CO 2, MEA and MDEA at 30 psi (counts) Intensity Time (min) arb. units PCA Analysis of ROI x-axis (unk.) Raman Shift (cm -1 )

17 Summary Initial experiments indicate that Raman is an effective analysis tool for following these CO 2 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 podu yof 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

18 Work in progress Designed single test reactor (3 rd 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