Solubility and Heat of Absorption of CO2 into Diisopropylamine and N,N-Diethylethanolamine Mixed with Organic Solvents

Ricardo R Wanderley,Gonzalo J C Ponce,Hanna K Knuutila

doi:10.1021/acs.energyfuels.0c00880

Ricardo R Wanderley, Gonzalo J C Ponce + Show 1 more

Open Access

https://doi.org/10.1021/acs.energyfuels.0c00880

Copy DOI

Abstract

We have evaluated the vapor–liquid equilibrium and heat of absorption of CO2 over water-lean mixtures of the amines diisopropylamine and N,N-diethylethanolamine (DEEA). This extends our previous research on water-lean solvents containing ethanolamine. The organic diluents N-methyl-2-pyrrolidone (NMP) and ethylene glycol (MEG) have been employed for solvent formulation. Since both diisopropylamine (a hindered amine) and N,N-diethylethanolamine (a tertiary amine) react with CO2 to form mainly bicarbonate in aqueous solutions, their behavior in nonaqueous mixtures is quite different from that of monoethanolamine. While MEG seems to maintain the reactivity of both diisopropylamine and DEEA even in nonaqueous mixtures, nonaqueous solvents with NMP act essentially as physical absorbents. This is an important indication that MEG is able to take part in the reaction mechanism between these amines and CO2, perhaps through alkylcarbonate formation, a fact that can be traced back to its relatively low autoprotolysis constant (pKS). This study represents a departure from our previous treatment on loss of CO2 solubility in water-lean solvents with monoethanolamine based on solvation phenomena alone, as it has become clear that the shift in equilibria in solvents with hindered and tertiary amines must account for Le Chatelier’s principle.

Highlights

Water-lean solvents for CO2 absorption are mixtures of amines and organic diluents, which are commonly proposed for addressing some of the issues faced by the standard aqueous amine solvents.[1−3] Seminal works on water-lean solvents include the screenings performed by Woertz[4] and by Rivas and Prausnitz[5] in the 1970s, the kinetic studies performed by Sada et al.[6−9] in the 1980s, and the myriad of solubility studies performed by several authors throughout the last decades of the 20th century.[10−16] In recent years, water-lean solvents have been assessed in terms of their rate of absorption,[17−20] heat of regeneration,[3,21] and proneness for degradation.[22]
Solvents based on organic compounds with low volatility such as N-methyl-2-pyrrolidone (NMP) and ethylene glycol (MEG) deliver interesting performances, as the CO2 solubility in their mixtures with MEA does not decrease as much as it is observed among some esters and ketones assessed by that same investigation
Summarizing the results obtained for water-lean solvents based on diisopropylamine: 1. Shifting from water to NMP and MEG enables the utilization of 10 wt % diisopropylamine while avoiding phase separation in the unloaded solvent and excessive volatilization of the amine

Summary

Introduction

Water-lean solvents for CO2 absorption are mixtures of amines and organic diluents, which are commonly proposed for addressing some of the issues faced by the standard aqueous amine solvents.[1−3] Seminal works on water-lean solvents include the screenings performed by Woertz[4] and by Rivas and Prausnitz[5] in the 1970s, the kinetic studies performed by Sada et al.[6−9] in the 1980s, and the myriad of solubility studies performed by several authors throughout the last decades of the 20th century.[10−16] In recent years, water-lean solvents have been assessed in terms of their rate of absorption,[17−20] heat of regeneration,[3,21] and proneness for degradation.[22]. In a previous study,[32] we have assessed the vapor−liquid equilibrium (VLE) behavior and the enthalpy of CO2 absorption in a series of different water-lean solvents containing ethanolamine (MEA) as the reactant of choice. Solvents based on organic compounds with low volatility such as N-methyl-2-pyrrolidone (NMP) and ethylene glycol (MEG) deliver interesting performances, as the CO2 solubility in their mixtures with MEA does not decrease as much as it is observed among some esters and ketones assessed by that same investigation. The present study intends to address that drawback by introducing two new reactants with vastly different properties than ethanolamine

Methods

Results

Conclusion