Evaluation of energy consumption and greenhouse gas emissions from poly(phenyllactic acid) production using sweet sorghum

The extensive use of fossil-based plastics has raised concerns regarding the depletion of fossil resources and the deterioration of the environment. Phenyllactic acid (PhLA), fermented from renewable resources, could be used to produce high-performance bio-plastics able to replace the fossil-based engineering plastics (FBEPs) in many applications. In order to evaluate the environmental performance of poly(PhLA) produced from sweet sorghum, a cradle-to-factory-gate life cycle assessment was performed for two impact categories, namely fossil energy consumption and greenhouse gas (GHG) emissions per kilogram of poly(PhLA). These two impact categories were compared with those of the FBEPs, and with those of the bio-based polylactides (PLA) and poly(hydroxyalkanoate) (PHA). The fossil energy consumption for poly(PhLA) is 24.2 MJ/kg, which is lower than that of the FBEPs and the bio-based PLA and PHA. However, the GHG emissions are 6.2 kg CO2 eq/kg using the current technology; these are higher than those of the FBEPs and bio-based PLA and PHA. The results of a sensitivity analysis show that the GHG emissions become less than those of FBEPs when increasing the efficiency of separation and purification to more than 90.3%, the PhLA yield to more than 20.6%, the sugar extraction rate to 96%, the Brix of sorghum juice to more than 19.4%, and the sorghum yield to more than 79.2 t/ha. These results show that using the poly(PhLA) produced from sweet sorghum to replace the FBEPs has the potential to reduce fossil energy consumption and GHG emissions.