Recovery of polyhydroxybutyrate (PHB) from Cupriavidus necator biomass by solvent extraction with 1,2-propylene carbonate

An integrated procedure for the recovery of polyhydroxybutyrate (PHB) produced by Cupriavidus necator based on the extraction with 1,2-propylene carbonate was evaluated. The effect of temperature (100-145 degrees C) and contact time (15-45 min), precipitation period, and biomass pretreatments (pH shock and/or thermal treatments) on PHB extraction efficiency and polymer properties was evaluated. The highest yield (95%) and purity (84%) were obtained with the combination of a temperature of 130 degrees C and a contact time of 30 min, with a precipitation period of 48 h. Under these conditions, PHB had a molecular weight of 7.4 x 105, which was the highest value obtained. Lower values (2.2 x 10(5)) were obtained for higher temperatures (145 degrees C), while lower temperatures resulted in incomplete extraction yields (45-54%). No further yield improvement was achieved with the pH/heat pretreatments, but the polymer's molecular weight was increased to 1.3 x 10(6). The PHB physical properties were not significantly affected by any of the tested procedures, as shown by the narrow ranges obtained for the glass transition temperature (4.8-5.0 degrees C), melting temperature (170.1-180.1 degrees C), melting enthalpy (77.8-88.5 J/g) and crystallinity (55-62%). 1,2-Propylene carbonate was shown to be an efficient solvent for the extraction of PHB from biomass. The precipitation procedure was found to highly influence the polymer recovery and its molecular weight. Although polymer molecular weight and purity were improved by applying pH/heat pretreatment to the biomass, the procedure involves the use of large amounts of chemicals, which increases the recovery costs and makes the process environmentally unfriendly.