Techno-economic and carbon footprint assessment of methyl crotonate and methyl acrylate production from wastewater-based polyhydroxybutyrate (PHB)

This paper assesses whether a cleaner and more sustainable production of the chemical building blocks methyl crotonate (MC) and methyl acrylate (MA) can be obtained in an innovative process in which resource consumption, waste generation and environmental impacts are minimized by using polyhydroxybutyrate (PHB) produced from wastewater as feedstock. For this purpose, conceptual process design, process modelling, economic and carbon footprint assessments of five conversion alternatives for wastewater-based PHB to MC or MA are performed. The PHB conversion step is modelled based on experimental data for both intracellular and extracellular feedstock. Results show that, despite the lower reaction selectivity of the direct conversion of intracellular PHB to MC or MA, this route is economically and environmentally preferred because no intensive downstream process is required for cell release after wastewater fermentation. The lowest total production costs are achieved when dry intracellular PHB is used as feedstock: 1.31 €/kg MC and 2.89 €/kg MA. However, the use of aqueous PHB as starting material leads to minimal carbon footprint due to lower energy demand: 3.25 kg CO2-eq/kg MC and 8.78 kg CO2-eq/kg MA, respectively. A sensitivity analysis is conducted to evaluate the eco-efficiency of the PHB conversion routes when the co-products methyl 3-hydroxubutyrate, crotonic acid and propylene are sold.