Biomass conversion to bioplastics: determination of thermodynamic properties and equilibrium of the catalysed sorbitol-to-isosorbide double dehydration reaction

Abstract

This work, which is part of a larger study, is related to the production of polymers and plastics from biomass (known as biopolymers and bioplastics) as an alternative to the use of fossil fuels derived from petroleum as raw materials on an industrial scale. Specifically, it focuses on the synthesis of isosorbide (IB) from sorbitol (SOH). Isosorbide is a molecule that has countless applications and uses. It is a monomer for various bioplastics such as poly-(isosorbide carbonate) (PIC), and it participates in the synthesis of pharmaceutical industry or cosmetic formulation intermediates or products. It can also function as an additive for biofuels or various surfactants. The proposed reaction mechanism to produce isosorbide from sorbitol is the twofold dehydration of sorbitol through 1,4-sorbitan (1,4-ST), catalysed by an acid catalyst. This catalysis is provided by acid solid catalysts, for example ion exchange resins. This study is dedicated to the experimental determination of the equilibrium constant of the aforementioned reactions over the temperature range 130 - 190 °C, as well as the determination of the thermodynamic properties of the system within this temperature range, including enthalpy, entropy, and Gibbs free energy. These thermodynamic properties will be compared with the existing literature as well as with those obtained through estimation from studies conducted in the same research group. The enthalpy and entropy changes of the sorbitol dehydration reactions were estimated to be -(7 ± 2) kJ/mol and (15 ± 4) J/(mol·K) and (23 ± 4) kJ/mol and (73 ± 9) J/(mol·K) for 1,4-ST and 2,5-ST formation respectively. As for the IB formation, enthalpy and entropy changes were set to be (15 ± 5) kJ/mol and (46 ± 11). Being the SOH-to-1,4-ST dehydration exothermic and the SOH-to-2,5-ST and 1,4-ST-to-IB reactions endothermic