Amine-Grafted Heterogeneous Catalysts from Waste for Diols Conversion into Cyclic Carbonates

Abstract

The valorization of cellulose- and starch-based wastes has been investigated through a two-step methodology, aiming at the synthesis of amine grafted chars tested as catalysts in the synthesis of cyclic carbonates from diols and dimethyl carbonate. Catalysts were prepared by subjecting the starting material to mild pyrolysis for obtaining biochars, followed by anchoring of 1,6-diamino-hexane on the surface of the char, performed in H₂O. This protocol has been applied to three different pristine polysaccharides (starch, cellulose, and cellulose acetate) and wastes containing the same (post-use starch-based plastics, fir sawdust, and post-use cigarette filters). The success of the derivatization method was confirmed by XPS and elemental analyses. The obtained catalysts were effective and did not show any significant difference in terms of the catalytic activity. Broad investigation on the reaction scope has been conducted on several mono- and disubstituted, aliphatic, and aromatic 1,2-and 1,3-diols, giving carbonates in high yields and selectivity (up to 96% and 99%, respectively). Quantification of the active site density has also been performed, allowing the calculation of TONs, TOFs, and productivity values for each catalyst. The recyclability of the heterogeneous catalysts has also been proved, and characterization of the recycled materials confirmed this behaviour.