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+

0 500 1000 1500 2000 2500 3000

0

2000

4000

6000

8000

10000

500 1000 1500 2000 2500 Raman Shift (cm-1)

Inte

nsi

ty (

coun

ts)

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

0

2000

4000

6000

8000

10000

12000

0 500 1000 1500 2000 2500 3000

• Water• Mono Ethanolamine (MEA)• Methyl-di-ethanolamine (MDEA)

Raman Shift (cm-1)

Inte

nsi

ty (

counts

)

Raman Shift (cm-1)

Materials and Chemistry

CPAC Satellite Workshop 2007, Rome

Raman Spectra: Absorption mixtures

Raman Shift (cm-1)

0

1000

2000

3000

0 500 1000 1500 2000 2500 3000

• 70% Water - 30% MEA• 70% Water - 22% MEA – 8% MDEA

Inte

nsi

ty (

counts

)

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)

Inte

nsi

ty (

counts

)

0

2000

4000

6000

8000

10000

12000

0 500 1000 1500 2000 2500 3000

• 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

nsi

ty (

counts

)

0

1000

2000

3000

4000

5000

6000

7000

0 500 1000 1500 2000 2500 3000

• 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

1

1.2

1.4

1.6

1.8

2

2.2

2.4x 10

5

x-axis (unk.)

Re

lati

ve

In

ten

sit

y

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)

1500

0

1000

2000

3000

4000

5000

6000

0 500 1000 2000 2500 3000

Time (min)• 2.5• 10• 17• 25• 40• 47• 55

Raman Shift (cm-1)

Inte

nsi

ty (

counts

)

0 20 40 60 80 100 1200.8

1

1.2

1.4

1.6

1.8

2

2.2x 10

5

x-axis (unk.)

Re

lati

ve

In

ten

sit

y

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