(25g) CO2 Absorption In Blends of Piperazine and Piperazine Derivatives

Piperazine (PZ) is a good amine solvent for CO₂ capture because it has high absorption rate, great cyclic CO₂ capacity and excellent thermal stability. However the application of PZ is limited by the window of solid solubility in water. To accurately screen amine solvents which have better solubility in water, CO₂ solubility and absorption/desorption rate in the blend of PZ and 2-methylpiperazine (2-MPZ) as well as the blend of PZ, 1-methylpiperazine (1-MPZ) and 1,4-dimethylpiperazine (1,4-DMPZ) was measured in a Wetted Wall Column (WWC). The results were compared to those for 8 molal (m) PZ. 4 m PZ / 4 m 2-MPZ was found to have about 5 % higher CO₂ capacity but 15 % lower absorption rate than 8 m PZ. 3.75 m PZ / 3.75 m 1-MPZ / 0.5 m 1,4-DMPZ has a CO₂ capacity 10 % higher than 8 m PZ while retaining the same absorption rate. Quantitative ¹H and ¹³C NMR studies were performed on 8 m 2-MPZ at different CO₂ loading and 40 °C to understand the speciation. It was found that the methyl group greatly hindered the formation of carbamate on the adjacent amino group. The unhindered monocarbamate accounts for more than 80 % of the total carbamate at rich CO₂ loading. With all the experimental data, thermodynamic and kinetic models are under development using Aspen Plus^® to represent CO₂ solubility and rate in PZ/2-MPZ and PZ/1-MPZ/1,4-DMPZ.