Techno-economic analysis of macroalgae biorefineries: a comparison between ethanol and butanol facilities

Abstract

Ulva rigida seaweed is constituted by ulvan, which is a sulfated polysaccharide with uses in a wide variety of applications. After the ulvan-oriented extraction process, a crystalline and recalcitrant residue, the so-called pulp, appears. In this work, this residue was valorized through a multiple-stage process. The total processing of the algae consists of hot water extraction, acid hydrolysis, ABE fermentation, and distillation in order to obtain not only ulvan but also butanol and bioethanol to be used as biofuels by simulating two third-generation algae-based biorefineries in Aspen Plus v10 software. Third-generation plants do not compete with food and algae biomass, and they do not require delignification nor pretreatment steps, which are usually the bottleneck of second-generation plants. A plant producing butanol as biofuel together with diluted ulvan, acetone, and ethanol as byproducts was modelled in Aspen Plus software. Regarding the profitability of the investment, the plants producing bioethanol and butanol were economically feasible. The economic parameters for the bioethanol and butanol plants were as follows: NPV equal to 27.66 M$ and 16.67 M$, and IRR equal to 46% and 37%, respectively. The discounted return period was acceptable for these types of plants, which were 4.11 and 3.16 years for the ABE biorefinery and the bioethanol biorefinery, respectively.