Separation of Crotonic Acid and 2-Pentenoic Acid Obtained by Pyrolysis of Bio-Based Polyhydroxyalkanoates Using a Spinning Band Distillation Column

Searching for renewable alternatives to produce platform chemicals, various biomasses have shown great potential as feedstock for value-added chemicals. For instance, biomass obtained by aerobic digestion of wastewater is rich in the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Pyrolysis of PHBV yields a mixture of crotonic acid (CA) and 2-pentenoic acid (2-PA). Application of CA and 2-PA as bio-based monomers requires purification. Purification by distillation is challenging as the high melting point of CA (72 °C) in combination with the high polymerization potential limits the temperature window for distillation severely. This study has experimentally explored the use of a spinning band distillation column (SBC) under vacuum operation to separate these acids. The thermodynamic feasibility for distillation was first studied by measuring vapor-liquid equilibrium data at relevant pressures of 50 and 100 mbar. The separation in the SBC was accomplished at 50 mbar and 40-110 °C for about 5 h. A successful recovery of CA with a high purity of >98% was achieved using a synthetic mixture of acids with a mass ratio of 80/20 (CA/2-PA). Actual pyrolyzate mixtures obtained by pyrolysis of the biomass and extracted pure PHBV were also fed to the distillation column and resulted in separation of CA with purities of 96 and 93%, respectively.