Optimization and green metrics analysis of the liquid-phase synthesis of sec-butyl levulinate by esterification of levulinic acid with 1-butene over ion-exchange resins

Abstract

Liquid-phase esterification of levulinic acid (LA) with 1-butene (1B) over ion-exchange resins was studied following an experimental design approach aimed at identifying the optimal conditions to synthesize sec-butyl levulinate (SBL) through the proposed reaction pathway. Experiments were performed in a temperature range of 313–383 K with initial molar ratios of LA to 1B (R°LA/1B) from 0.4 to 3. The optimal experimental conditions determined at 373 K and R°LA/1B = 0.5 render 1B and LA yields to SBL of 48.1% and 76.8%, respectively. Empirical equations relating conditions and yields were obtained, and response surface methodology analysis with subsequent multiobjective optimization allowed identification of optimal conditions to maximize simultaneously the yield of both reactants to SBL—that is high 1B initial concentration and temperature ranging 360–370 K. According to screening experiments, dense polymer network favors SBL formation. Amberlyst™15 was the most promising catalyst among the tested ones, since it yields the highest conversion with very low side reactions extension. A green metrics analysis was performed to ascertain the sustainability of the proposed chemical route and to compare it with previously reported studies for the SBL synthesis. Among the scenarios assessed, the proposed chemical pathway represents the greenest alternative.