Modelagem e simulação termodinâmica para estimativa da energia mínima de regeneração de MDEA saturada no refino de petróleo

Abstract

The regeneration of aqueous solutions of methyldiethanolamine (MDEA) saturated with acid gases such as CO₂ and H₂S represents a significant energy and environmental challenge in petroleum refining. This work estimates the theoretical minimum energy required for this process, in alignment with the principles of energy efficiency and sustainability. Thermodynamic modeling was based mainly on the Electrolyte NonRandom Two-Liquid (eNRTL) model, used to calculate activity coefficients, equilibrium constants, and Gibbs free energy variations (ΔG) in an aqueous MDEA–H₂O–CO₂–H₂S system at temperatures between 393 K and 403 K. The computational implementation in Python enabled the simulation of chemical equilibrium between the initial (saturated) and final (regenerated) states, considering dissociation reactions and ionic interactions. Results indicated a minimum energy of 207.8 kJ to regenerate 100 mol of solution, equivalent to 806.95 kJ/kg of CO₂ removed, corresponding to approximately 6.45% of the actual energy consumption reported in industrial processes (12,500 kJ/kg of CO₂). Sensitivity analyses showed that ΔG_total decreases with higher acid gas loading and elevated temperatures, reaching a maximum at MDEA mole fractions around 0.5. From an economic perspective, the minimum regeneration cost was estimated at R$ 190.53/tCO₂, considering an electricity tariff of R$ 0.85/kWh in Northeastern Brazil, while the actual cost based on reboiler energy consumption reached R$ 2,951.39/tCO₂ — a competitive value in global carbon markets (such as the EU ETS, at around R$ 410/tCO₂). Regeneration proved far more advantageous than replacing MDEA with fresh solvent (R$ 24,000–48,000/tCO₂) and showed potential for reuse of the exhausted MDEA in CO₂ capture from air or flue gases, generating higher-value credits (US$ 170– 500/tCO₂). The findings contribute to the optimization of industrial processes, emission reduction, and alignment with the Sustainable Development Goals, while suggesting future integration with kinetic models, life-cycle assessments, and hybrid regeneration technologies.