Finding Sustainable Deep Eutectic Solvents for an Efficient Separation of CO₂ and NH₃ in Melamine Production with Soft-SAFT

Industrial processes frequently release tail gases containing harmful components, such as carbon dioxide (CO₂) and ammonia (NH₃), with significant environmental implications. Effective separation and recovery of these gases are critical for reducing pollution and enhancing resource efficiency. This paper investigates the use of deep eutectic solvents (DESs) to capture and separate CO₂ and NH₃ from melamine production tail gases, offering an alternative to traditional methods such as coproduction systems and water scrubbing. Choline chloride ([Ch]-Cl)-based solvents with ethylene glycol (EG), urea (UR), and glycerol (GL) are assessed for selective gas absorption using the soft-SAFT Equation of State (EoS). This approach has been used to model the solubility of CO₂ and NH₃ in these DESs and evaluate key properties, including absorption isotherms, enthalpy, entropy of dissolution, effective Henry's constants, and ideal selectivity. Results reveal that the presence of EG enhances the NH₃ absorption capacity, while UR shows higher CO₂ absorption. From this information, the competitive selectivity in a standard melamine tail gas mixture (60% NH₃ and 40% CO₂ in mole fraction) and DESs has been predicted. Among them, [Ch]-Cl:EG shows the best selectivity, and the 1:7 proportion provides the optimal value for NH₃/CO₂ separation. This work highlights the potential of DESs for efficient gas separation, emphasizing the utility of molecular modeling as a precursor to experimental validation in the design of sustainable separation processes.