Alternative Polyhydroxybutyrate Solvent Extraction: a Process Simulation Study

Polyhydroxybutyrate (PHB) is a possible sustainable alternative to fossil-based plastic, today the cause of one of the primary forms of pollution in the world, since it is biodegradable, recyclable and compostable. Furthermore, PHB can be accumulated in several bacterial strains as a product of their metabolic activity. Solvent extraction (SE) is the most used technique, thanks to the high recovery yields and purity, to extract PHB from bacteria. In particular, a two-step SE is required: the accumulated PHB in the bacterial biomass is firstly dissolved in a solvent to obtain a mixture rich in PHB; then, an anti-solvent is added to reduce the total solubility allowing the biopolymer to precipitate and to be recovered from the residual biomass. However, despite its wide application, the SE technique is characterised by several limitations, such as the high cost and the use of halogenated solvents (i.e. chloroform). In this work, a non-halogenated based extraction process for PHB recovery from wet bacterial biomass is proposed. Simulations were carried out using butyl acetate (BA) as solvent and hexane (HEX) as anti-solvent. The process scheme also includes a distillation column and a cooling system (when necessary) to recover both the solvent and the anti-solvent. The effects of the PHB solubility during the precipitation step and the solvent recovery on process performance were investigated. The recovery yield was higher than 90% and increased as the solubility decreased. The simulation results highlighted that the proposed strategy is an effective and sustainable alternative to conventional processes for PHB recovery.