Sustainable and economic analysis of marine macroalgae based chemicals production - Process design and optimization

Abstract

This work proposes a Mixed Integer Nonlinear Programming (MINLP) model to determine the optimal design of macroalgae based chemicals production plants. The superstructure considers two brown marine macroalgae species (Macrocystis pyrifera and Lessonia vadosa) that are used to produce sorbitol for further transformation. Two additional alternatives are included: corn starch as the traditional feedstock to obtain the corresponding sugars and directly buying sorbitol from market. Sorbitol is transformed into isosorbide, a platform molecule, which can be converted into a drug for heart disease (isosorbide dinitrate), a flame retardant, a biopolymer and a biosolvent (dimethyl isosorbide). The Renewable Process Synthesis Index Metric (RePSIM) is used as objective function to address sustainability. Alternatively, Net Present Value (NPV) is also considered to obtain a detailed economic analysis. In terms of sustainability, the production of isosorbide dinitrate is the optimal pathway, albeit it shows a negative RePSIM of −4.30 million USD/yr. On the other hand, the production of dimethyl isosorbide is the optimal configuration taking into account the economic objective function. Its NPV is 44.31 million USD with a production cost of 6.97 USD/kg. It is worth mentioning that the social and environmental aspect of the dimethyl isosorbide production process is positive. In this sense, this chemical can be obtained from marine macroalgae biomass in a profitable way with a process that is socially and environmentally beneficial.