Process Simulations of the Direct Non-Aqueous Gas Stripping Process for CO₂ Desorption

The integration of the direct steam stripping (DSS) process with organic working fluids promises a significant reduction in the energy penalty for CO₂ capture processes. This work investigates the mechanisms of mass transfer enhancement in the direct pentane stripping (DPS) process using simulation methods. Through regressing the molecule-molecule interaction parameters, a quaternary system thermodynamic model (QSTM) is developed to successfully predict the vapor-liquid equilibrium of the amine/CO₂-pentane/H₂O system. Three typical solvents, monoethanolamine (MEA), methyldiethanolamine (MDEA), and 2-amino-2-methyl-1-propanol (AMP), are studied in this work. The DPS process using 30 wt % MEA, AMP, and MDEA exhibits solvent regeneration energies of 2.55, 2.65, and 2.01 GJ/t of CO₂, respectively, under the optimal conditions, which are 34, 32, and 48% lower than that of the conventional MEA-based process, respectively. DPS using MDEA shows an energy advantage over the other two solvents because of the high CO₂ equilibrium partial pressure and low reaction heat of MDEA. The temperature and CO₂ partial pressure profiles along the stripper reveal a flashing process at the top of the stripper, leading to the intensive desorption of CO₂. Furthermore, DPS exhibits a low-temperature regeneration property, which owes to the high volumetric mass transfer driving force provided by pentane. To achieve a minimum solvent regeneration energy, DPS exhibits a lower CO₂ lean loading compared to DSS, which is of benefit in lowering the investment of the absorber and the heat exchangers. In the future, a techno-economic analysis on DPS is recommended to prepare it for large-scale implementation.