LCA-Guided Optimization of the Preparation of Alginate-Based Heterogeneous Catalysts

Alginates are polysaccharides extracted from brown algae, readily available at low cost. As chiral anionic polymers, they can be crosslinked by divalent metal cations to form gels with high surface area and abundant carboxylate groups. These properties make alginate-based gel beads good candidates as heterogeneous catalysts for enantioselective reactions since their structure provides multiple interaction sites with the substrates, facilitating enantioselective processes. This thesis aims to integrate Life Cycle Assessment (LCA) methodology into the optimization of the catalytic process, building upon the group’s previous work on the Friedel-Crafts alkylation of nitrostyrenes with indoles as the benchmark reaction. LCA is a standardised methodology, following the ISO 14040 framework, used to evaluate the environmental impact of a process from raw material extraction to disposal. A previous LCA study conducted within the group identified ethanol, used during solvogel preparation, as the environmental hotspot of the process. Therefore, the main goal of this work is to eliminate, or at least reduce, the use of ethanol from the protocol while maintaining the catalytic performance previously achieved. In the catalyst preparation, ethanol replaces water (the gelification medium), converting the hydrogel to a solvogel usable in reactions occurring in organic solvents, such as the THF used in the benchmark process. Through exploration of solvent exchange protocols and additives, e.g. molecular sieves, this work demonstrates that ethanol can be avoided entirely, converting the hydrogel directly into a THF solvogel. The results obtained are comparable to those of the ethanol-based protocol, leading to a more sustainable catalytic system guided by the LCA framework. Further studies can be done to extend this ethanol-free protocol to a broader scope of Friedel–Crafts type reactions and integrate LCA-guided optimization within alginate-based heterogeneous catalyst systems.