RESUMO
Sustainability must be always assured in process design. Not rarely, multiple sustainability criteria point oppositely, entailing a need for more systematic and coherent assessments. The Sustainable Process Systems Engineering method is introduced as a two-level hierarchical evaluation of process designs. The first level selects the best design via four-dimensional indicators (environment, efficiency, health-&-safety, and economic), while in the second level, sustainability hotspots of the best design are pinpointed to unveil possible improvements. The method is applied for sustainability assessment of two ethylene oxide processes: the conventional and a novel route employing supersonic separator to prevent ethylene oxide losses using liquid-water injection. Supersonic separator route reduces oxide losses by 83.33 kg/h, representing +0.9% greater ethylene oxide production, 95% less ethylene oxide losses, entailing 2.5% higher net value for 20 operation years despite 0.11% higher investment, and consequently exhibiting the best environmental, technical, health-&-safety and economic performances. Photochemical-oxidation and aquatic-ecotoxicity are environmental indicators with highest improvement due to supersonic separator inclusion. Ethylene oxidation reactor, carbon dioxide stripping-column and cooling-water tower are the main unit-operations with sustainability hotspots.