(25f) CO2 Solubility In Aqueous Amines at High Temperature and Pressure

CO₂ Solubility in Aqueous
Amines at High Temperature and Pressure

Qing Xu,
Gary T. Rochelle, gtr@che.utexas.edu

Department of Chemical
Engineering

The University of Texas
at Austin

Amine based post-combustion CO₂ capture is one of
the most effective ways to reduce the CO₂ emission. Various aqueous
amines have been investigated by researchers. However previous vapor-liquid
equilibrium measurements mostly focused on absorber conditions at 40 to 70 °C with an exception of
aqueous MEA.

This paper presents total pressure and CO₂
partial pressure data for CO₂ loaded aqueous amines at 100-160 °C, 100- 2800 kPa. 7 m (molality, mole/kg
water) monoethanolamine (MEA) was chosen as the
benchmark and the base line solvent. 8-10 amine solvents with various CO₂
loadings were screened, including MEA, piperazine
(PZ), 1-methyl-piperazine (1MPZ), 2-methyl-piperazine (2MPZ), diglycolamine (DGA), dimethyl-piperazine
(DMPZ) and blends of selected above amines. These VLE measurements at high
temperature contribute to thermodynamics at stripper and reclaimer
conditions. Combined with the low temperature data these measurements also give
a good interpolated prediction for the mid-temperature range.

The calculated results for 7 m
MEA match well with literature. The regressions based on data from 40 to 160 °C gave models for CO₂
partial pressure over loaded aqueous amines and the models predict the data
well. The CO₂ partial pressure mainly depends on the type of amine,
temperature and CO₂ loading (mol CO₂/mol alkalinity). The
concentration of amines does not have an obvious effect on CO₂
partial pressure. Heat of absorption for CO₂ loaded aqueous amines
was also derived from these models and compared in this paper. Heat of
absorption is an important factor in predicting the energy consumption in the
stripping process.