Enhancing PHAs Production Sustainability: Biorefinery Design through Carbon Source Diversity

Abstract

In this work, we propose a Mixed Integer Nonlinear Programming (MINLP) model to determine the optimal sustainable design of a poly(hydroxyalkanoate)s (PHAs) production plant configuration and its heat exchanger network (HEN). The superstructure-based optimization model considers different carbon sources as raw material: glycerol (crude and purified), corn starch, cassava starch, sugarcane sucrose and sugarcane molasses. The PHA extraction section includes four alternatives: the use of enzymes, solvent, surfactant-NaOCl or surfactant-chelate. Model constraints include detailed capital cost for equipment, mass and energy balances, product specifications and operating bounds on process units. To assess the feasibility of the PHA plant, we considered the Sustainability Net Present Value (SNPV) as the objective function, a multi-criteria sustainability metric that considers economic, environmental and social pillars. The Net Present Value (NPV) was also calculated. SNPV metric provides useful insights on sustainable PHA production, as the optimal technological route results in the sugarcane-surfactant-chelate option, rather than the sugarcane-enzyme pathway which proves more economically profitable, but with higher environmental impacts. Moreover, inclusion of HEN design significantly improves the objective function value, mainly due to a 24% carbon footprint impact reduction.