Carbonaceous solid acids for glycerol acetylation: From waste-derived biochars to engineered graphenes

The oversupply of glycerol from biodiesel production poses economic and environmental challenges. Glycerol acetylation to acetins (mono-, di-, tri-) is a promising valorization route. This review explores carbonaceous solid acids, including biochars, graphene-based materials, CNTs, and hybrids, for glycerol acetylation. Analysis from 2000 to 2025 using PRISMA identifies correlations between acid-site density, morphology, and catalytic outcomes. Biochars offer low-cost, sustainable solutions but face stability issues. Graphene-based catalysts and CNTs provide high conversion but struggle with scaling. Hybrid systems optimize performance, yet gaps in experimental standardization, deactivation mechanisms, and crude glycerol adaptation remain. Addressing these challenges will enhance industrial viability.