Experimental Study on Vapor-Liquid and Solid-Liquid Equilibria Data for the Regeneration of Biobased Solvents Guaiacol and 2,2,5,5-Tetramethyl Oxolane in Biorefinery Processes

Solvent regeneration is crucial after liquid-liquid extraction (LLX). This study investigates the vapor-liquid equilibria (VLE) and solid-liquid equilibria (SLE) for regenerating guaiacol and 2,2,5,5-tetramethyl oxolane (TMO) following LLX. The deep eutectic solvent (DES) composed of lactic acid and choline chloride was regenerated by LLX with these biobased solvents after biomass delignification. Both crystallization and evaporation methods have been considered for solvent regeneration. The experimental SLE study in the guaiacol-lactic acid system reveals a solid solution formation, with significant nonideality in the liquidus and solidus lines at guaiacol weight fractions around 0.80 to 1. A two-step crystallization process is conceptualized, concentrating guaiacol in the solid state, obtaining noticeable reductions in HMF and furfural concentrations in the solid phase, with guaiacol yields of 57.0% in the first stage and 39.8% in the second stage. Additionally, vapor pressures of guaiacol (400.59-439.67 K) and TMO (318.43-372.16 K) have been measured to facilitate solvent regeneration simulations via evaporation or distillation. Antoine parameters were fitted for both solvents to experimental vapor pressure data, with an average deviation of 0.05 K for guaiacol and 0.07 K for TMO.