Investigating best available technique for CO2 chemical absorption: solvent selection based on empirical surrogate model and exergy loss

Abstract

The carbon dioxide concentration in the atmosphere has reached extremely high levels, generating environmental concerns. Unfortunately, despite the climate change, CO2 is not included nowadays as a key environmental issue in Best Available Technique (BAT) reference documents (BREF). Industrially, the widespread industrial technology to capture CO2 is the chemical absorption using aqueous monoethanolamine (MEA) at 30%wt, which is the basis of comparison for novel alternative techniques in the literature and seems a suitable candidate to be proposed as Best Available Technique. Nevertheless, there is an intense research to find alternative solvents that decrease the energy consumption for carbon capture and many solvents are claimed in the literature to outperform MEA. A novel empirical surrogate model and exergy balances are used to confirm that MEA is still the best candidate to be proposed as Best Available Technique. The surrogate model proposed in this study properly regresses the CO2 gas liquid equilibrium data. The regressed parameters of the model are tabulated in this study for many aqueous alkanolamines and their mixtures, being the basis for computationally inexpensive chemical absorption column design. The surrogate model parameter considering the temperature is related with the chemical absorption energy and the consumed energy for solvent recovery. The obtained results show that none of the considered alkanolamine outperforms MEA in all the considered aspects, i.e. energy and solvent flowrate. MEA minimum flowrate is 15.62 mol solvent/mol gas and its heat of absorption regression parameter is − 27,745 J/mol. The proposed mathematical method is useful as a fast assessment for other novel alternatives that will be proposed in the future, providing energetically more efficient and cleaner technologies for CO2 capture.