System-level analysis of strategies for biodegradable plastics production from microalgae

Abstract

Fossil-fuel-based plastics have contributed significantly to global warming and marine pollution, both during their production and disposal. As a viable alternative, microalgae-based biodegradable plastics offer an environmentally sustainable solution owing to the rapid growth of microalgae and their ability to absorb CO₂. However, the high price of bioplastics hinders their widespread adoption as a replacement for conventional plastics. In this study, an integrated process (Case 1) for coproducing lactic acid (LA, a monomer of polylactic acid), polyurethane, and azelaic acid (AA), by fully utilizing the major components of microalgae (carbohydrates, triglycerides, and free fatty acids (FFAs)) is proposed. This method significantly improves the economics of bioplastic production. Apart from AA production from FFAs, which is a common process to produce LA and polyurethane, two additional cases are also presented to investigate the environmental and economic impact of FFA utilization: Case 2 consumed FFAs as a heat source and Case 3 externally disposed of FFAs. Comprehensive analyses, including techno-economic analysis and life cycle assessment, were conducted to identify the economic and environmental benefits of the three cases. Case 1 is the most economically advantageous option, with the lowest minimum selling price (MSP) of $1017/ton-LA due to additional revenue from the sales of AA, which is a valuable product. Despite its economic benefit, Case 1 is not environmentally favorable (6.6 kg CO₂ eq./kg-LA). In contrast, Case 2 has the lowest global warming potential (2.3 kg CO₂ eq./kg-LA), equivalent to an annual reduction of 135,865 metric tons of CO₂ emissions in comparison to the conventional LA production process (4.8 kg CO₂ eq./kg-LA); conversely, it has the highest MSP of $1605/ton-LA. This denotes that the proposed process can reduce annual 135,865 tons of CO₂ with competitive price compared to the conventional LA ($1100-1940/ton). The results highlight the inherent tradeoff between economic and environmental viability and provide valuable insights into the commercial development of renewable biodegradable plastics.