Sustainability criteria as a game changer in the search for hybrid solvents for CO2 and H2S removal

Abstract

• Robust multi-criteria screening for CO 2 and H 2 S absorption in water-free solvents. • Polar soft-SAFT validated for a wide range of solvent properties and conditions. • Water-free solvents have a competitive technical edge over aqueous solvents. • Sustainability metrics of water-free solvents calls for greener options. • Holistic solvent evaluation is essential for proper selection. The appearance of hybrid solvents in recent years introduced a potential replacement for aqueous amines for acid gas removal in order to mainly overcome the high energy of regeneration. Yet, the assessment of solvent potentiality remains haphazard with limited information and assessment criteria. In this contribution, we develop and apply a multi-criteria assessment approach built on the use of a molecular-based equation of state, namely, polar soft-SAFT, in combination with sustainability indicators to examine the performance of hybrid solvents for acid gas removal (CO 2 and H 2 S). The first stage of the approach relies on the robust development of the thermodynamic model with available experimental data. Subsequently, with assured fidelity, the model is used in a fully predictive manner to obtain relevant assessment criteria for technical performance evaluation. This is inclusive of standard key performance indicators such as cyclic capacity and energy of regeneration, along with key solvent properties at conditions representative of acid gas removal processes. Additionally, we examine the environmental, health and safety impact of the investigated solvents as a sustainability criteria to select them. This framework has been applied for the first time to six solvents for acid gas removal, including the benchmark solvents aqueous monoethanolamine (MEA) and aqueous diethanolamine (DEA), along with hybrid solvents formulated from chemical solvents such as MEA, or DEA, with physical co-solvents including N-methyl-2-pyrrolidone (NMP), or sulfolane (SFL). The results of the multi-criteria assessment demonstrate that among the six solvents investigated in this work, the overall best performer remains to be the benchmark aqueous MEA. Results also indicate the potentiality of MEA + NMP hybrid solvent in terms of an acceptable compromise between reduced absorption capability and reduced energy of regeneration, compared to aqueous MEA; however, the hybrid solvents fail when applying the sustainability metrics. This work clearly indicates that potential solvents for acid gas removal should be examined following a holistic approach, inclusive of their technical performance and environmental footprint.