Octyl levulinate biolubricant production from levulinic acid esterification over ion exchange resins: Role of morphology and reaction thermodynamics

Abstract

Synthesis of biolubricant octyl levulinate (OL) through liquid-phase esterification of levulinic acid with 1-octanol over ion-exchange resins (IERs) was studied. OL possesses excellent properties for application as biomass-derived lubricant, like moderate viscosity, high viscosity index, and low volatility, and it can be considered a completely renewable value-added product, ready for mass-consumption. An unprecedented catalytic screening using acidic IERs revealed that the present reaction is sensitive to catalyst morphology, with structures easing molecular accessibility towards active sites being more active than IERs with greater active sites concentrations. The most active IERs were the gel-type resin Dowex®50Wx2, a micro-structured resin with low-density polymer regions, and the hyper-crosslinked macroreticular resin Macronet™ MN500, with highly exposed acid sites due to large macropore-sized cavities. Equilibrium conversions were experimentally determined in a batch reactor at 2.5 MPa and 353 − 393 K, with values ranging 35–97 %, revealing a slight exothermic character for the reaction. Thermodynamic equilibrium properties for the reaction were determined experimentally for the first time. Enthalpy, entropy, and Gibbs free energy changes of reaction at 298.15 K were estimated to be −(6.9 ± 0.3) kJ/mol, (5.051 ± 0.016) J/(mol·K), and −(8.5 ± 0.3) kJ/mol, respectively.