Coproduction of Drop-in Biofuels and Biodegradable Plastic Monomers: Process Design and Integrative Analyses

Polyhydroxybutyrate (PHB) is a biopolymer that accumulates in cyanobacteria and other microalgal species. This compound serves as an intracellular carbon storage product in the microorganisms formed during photosynthesis. The microalgal strain Chlorella sorokiniana is known to produce PHB. Eco-friendly bioplastics, such as PHB, have the potential to replace conventional plastics. Lipids in microalgae can also be used to produce biofuels, such as diesel blendstock (DB). In this study, we developed an integrated process for growing microalgae and using them to produce PHB and DB. This techno-economic analysis explores the financial profitability of using open raceway ponds compared to photobioreactors to grow microalgae with nutrient deficiency, with sodium acetate as the carbon source. The heat integration applied in the process decreased the energy requirement, leading to 74.2 and 50.5% reduction in heating and cooling requirements, respectively. The economic aspect was addressed by determining the minimum selling price of PHB, which was estimated to be $8830 per ton compared to the market price of $8500–19,600/ton, demonstrating the reasonableness of this process. This study incorporated a life cycle assessment cradle-to-gate approach to evaluate the environmental impact, considering its life cycle from raw material acquisition to end-of-manufacturing.