Evaluation and optimization of the environmental performance of PHA downstream processing

Abstract

Biobased and biodegradable materials such as polyhydroxyalkanoates (PHA) have great potential as an alternative for conventional oil-based plastics in consumer goods and medical applications, but their total market share is still marginal due to their high production costs. Downstream processing, with high energy demand and significant requirements in oil-derived solvents and chemicals, has been identified as one bottleneck in the PHA value chain. Hence, a thorough study of the environmental performance of PHA recovery processes is essential to promote their applicability. This work provides valuable insights on PHA downstream processing environmental hotspots and how to optimize them accordingly. Eight PHA downstream alternative processes for both high-grade and low-grade purification are evaluated from a techno-economic and an environmental perspective, assessing scale-up possibilities and challenges. To reach this goal, both scenario definition and process design were supported by a systematic review of available PHA downstream methods and related life cycle assessments. Methods relying on solvent extraction require large amounts of energy for solvent recovery, and thus, their higher performance in impurity removal also entails larger costs and impacts in all categories, when compared to mechanical disruption or chemical digestion. Therefore, solvent extraction is only recommended for those cases where a higher quality is required, or solvents can be reasonably obtained from an integrated biorefinery. Chemical digestion can be optimized by adding a chemicals recovery unit, while mechanical disruption appears to be the most promising technology in terms of environmental performance. Through this technoeconomic and environmental assessment, it is proved that PHAs can be attractive materials for a sustainable bioeconomy if the process and product design incorporate life cycle assessment such as the developed in this work