Determination of Amine Volatility for CO2 Capture

Thu Nguyen

January 10, 2008

The University of Texas at Austin

Professor Gary Rochelle

Outline

Scope of Present Work – determine MDEA and PZ volatility

Experimental Apparatus – introduce FTIR setup & operation

Theory – use Raoult’s Law to measure volatility: partial pressure & activity coefficient)

Results – explore volatility in terms of loading, temperature, & amine concentration

Future Work -- outline of activities planned

Scope of Present Work

Determine PZ and MDEA volatility in blends of varying amine concentrations

1) Explore volatility in terms of Partial Pressure and Activity Coefficient

2) Ask how do these parameters behave with

i. CO2 loading

ii. Temperature

iii. Varying amine concentration

3) Run experiments at 40ºC and 60ºC

Experimental Apparatus – Stirred Reactor Coupled with FTIR Analysis

-apparatus allows simultaneous measurements of CO2 solubility and amine volatility

-sample line & FTIR are both kept at elevated operating temperature (180ºC) to eliminate condensation / adsorption of vapor amine to surface

-FTIR is capable of performing multi-component analysis

-gas is returned back to reactor at ~55ºC higher than reactor temp. to avoid rapid condensation / loss of amine species

Theory

-activity coefficient is calculated using modified Raoult’s law

yi P =γi * xi * Po

yi : vapor phase mole fraction of species i (FTIR)

P : total pressure at equilibrium (reactor pressure)

γi : activity coefficient of species i (to be determined)

xi : liquid phase mole fraction of species i (Amine Titration)

Po: vapor pressure of species i (DIPPR database)

Vapor Pressure Equation (DIPPR Thermodynamic Database)

Pvap (Pa) = exp [A + B/T + C(ln T) + DTE] where T is in Kelvin

Pvap = exp [70.5 -7914/T – 6.65(ln T) + 5.21e-18(T)6 for PZ

Pvap = exp [253.1 -18378/T – 34(ln T) + 2.34e-5(T)2 for MDEA

model confirmed to provide good consistent estimates of vapor pressures within 283K – 785K range (includes experimental

temperatures)

Figure 1. PZ Volatility

Figure 2. Apparent PZ Activity Coefficient

Figure 3. MDEA Volatility

Figure 4. MDEA Activity Coefficient

Conclusions

PZ Partial Pressure

~2.2-19.3 ppm (40ºC) 15-66 ppm (60ºC)

MDEA Partial Pressure

~5.2-6.9 ppm (40ºC) 24.8-28.6 ppm (60ºC)

-Continue amine volatility measurements for:

-other blends of varying amine concentrations-focus on volatility in absorber lean & wash water stream-focus on volatility at stripper unit -ROC16 solution

-Modeling experimental results to obtain activity coefficient prediction models

-NMR Analysis

-Heat Capacity Measurements

Future Work