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.