CO2 solubility in tetrabutyl ammonium bromide (TBAB) and ethylene glycol deep eutectic solvents in the presence of N-methyl diethanolamine (MDEA): experimental study and thermodynamic modeling

Abstract

The growing need for efficient carbon dioxide (CO₂) capture technologies has spurred research into novel solvents as alternatives to traditional methods. While ionic liquids (ILs) have shown promise, their high cost and complex synthesis hinder widespread application. Deep eutectic solvents (DESs), formed by simple mixing of a hydrogen bond donor and acceptor, have emerged as cost-effective and readily synthesized candidates for CO₂ absorption. Characterized by melting points lower than their components, DESs can exist in the liquid phase under ambient conditions. This study experimentally investigated the solubility of CO₂ in a specific DES composed of TetraButyl Ammonium Bromide (TBAB) and ethylene glycol (EG) in a 1:4 M ratio at temperatures of 313.15 K, 328.15 K, and 343.15 K, across a pressure range of 0.1–5 MPa. To further enhance CO₂ uptake, the effect of incorporating Methyl DiEthanolAmine (MDEA) at concentrations of 5, 10, and 15 wt% into the DES was also evaluated. The experimental results demonstrated a significant enhancement in CO₂ absorption with increasing pressure and decreasing temperature. Notably, the addition of MDEA led to a marked improvement in the CO₂ absorption capacity of the DES + MDEA mixture. Vapor-liquid equilibrium data for the studied systems were thermodynamically modeled using the Soave-Redlich-Kwong (SRK) equation of state for the vapor phase fugacity and the Non-Random Two-Liquid (NRTL) model for the liquid phase activity coefficients. The excellent agreement between the model predictions and the experimental data highlights the significant potential of TBAB:EG (DES), particularly when enhanced with MDEA, for efficient CO₂ capture applications.