CO2 capture using aqueous 1-(2-Hydroxyethyl) piperidine and its blends with piperazine: Solubility and enthalpy

Abstract

In this article, equilibrium CO2 solubility in aqueous 1-(2-Hydroxyethyl) piperidine (HEP) solutions pertaining concentrations (1, 2, 3) mol/L in the temperature range (303.15–323.15) K, and CO2 partial pressure range 0.1–100 kPa are presented. HEP; being a tertiary alkanolamine, its rate of CO2 absorption is comparatively slower than primary or secondary alkanolamine. Piperazine (PZ), a rate promoter was added to HEP in 1:4 mol ratio to form blends having enhance rate of CO2 absorption. Equilibrium CO2 solubility in four different aqueous blends; (0.8 mol/L HEP + 0.2 mol/L PZ), (1.6 mol/L HEP + 0.4 mol/L PZ), (2.4 mol/L HEP + 0.6 mol/L PZ), (3.2 mol/L HEP + 0.8 mol/L PZ) were measured over the temperature range of (303.15–323.15) K and CO2 partial pressure spanning over 0–70 kPa. Equilibrium constant for deprotonation reaction of HEP was estimated by measuring pKa of aqueous HEP solution at 298.15, 303.15, 313.15, 323.15 and 333.15 K. Experimentally obtained CO2 solubility data for single and blended amine solutions were correlated efficiently using activity coefficient model with AAD % of 3.76 and 3.22, respectively. Speciation of both single and blended amine solutions in their equilibrated liquid phase were predicted. Interaction parameters obtained through thermodynamic modelling of equilibrium solubility data for single and blended amine solutions were used to predict the enthalpy of CO2 absorption.