Cascade Valorization of 5-Hydroxymethylfurfural (HMF) to Monomers and Furanic/Tetrahydrofuranic Diethers Bio-fuels

5-hydroxymethylfurfural (HMF) represents a valuable platform-chemical for the synthesis of monomers and bio-fuels. Thus, the present work proposes, for the first time, a cascade process for the synthesis of diol monomers and furanic/tetrahydrofuranic diethers as novel bio-fuels starting from HMF. In the first step, the selective hydrogenation of HMF in ethanol to give 2,5- bis(hydroxymethyl)furan (BHMF) or 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF) was carried out by properly tuning the reaction conditions in the presence of 5 wt% Ru/C as catalyst, reaching the highest yields of 80 and 93 mol%, respectively. These diols are strategic precursors for two scarcely investigated ethoxylated bio-fuels, 2,5-bis(ethoxymethyl)furan (BEMF) and 2,5- bis(ethoxymethyl)tetrahydrofuran (BEMTHF). Thus, in the second step, the etherification of both pure BHMF and BHMTHF to give BEMF and BEMTHF, respectively, was studied. The zeolite HZSM-5 (Si/Al = 25) allowed the achievement of the highest BEMF yield of 74 mol%. Analogous results were also obtained starting from crude BHMF. On the contrary, BEMTHF was not obtained by the direct etherification of BHMTHF, but a preliminary study showed the possibility of synthesising BEMTHF by the 5 wt% Ru/C catalyzed hydrogenation of BEMF. Finally, the stability of the tested catalysts was investigated, showing that they maintained the activity almost constant up to five recycle runs, thus resulting recyclable.