Aqueous phase hydrogenolysis of glycerol to 1, 2-propanediol without external hydrogen addition

Abstract

Facile aqueous phase hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO), catalyzed by an admixture of 5 wt.% Ru/Al₂O₃ and 5 wt.% Pt/Al₂O₃ catalysts in varying amounts, without externally added hydrogen is reported with comprehensive characterization of liquid and gas phase products. The hydrogen generated in situ by aqueous phase reforming of glycerol was used for the conversion of glycerol to 1,2-PDO and other products. The hydrogenolysis reaction may thus be carried out at moderate inert gas pressure and without a need for external hydrogen addition. During 6 h batch runs, it was observed that the 1:1 admixture (w/w) of the Ru and Pt catalysts showed better performance at 493 K [glycerol conversion (X) = 50.1%, 1,2-PDO selectivity (S) = 47.2%] compared to the individual catalysts [X = 19.3%, S = 50% with 5% Ru/Al₂O₃; X = 18.1%, S = 37% with 5% Pt/Al₂O₃]. A run for glycerol hydrogenolysis with the admixture catalyst in the presence of added hydrogen (41 bar), at otherwise identical operating conditions, showed lower selectivity to 1,2-PDO (31.9%) compared to the run without added hydrogen (47.2%). With external hydrogen addition, the availability of excess hydrogen (in addition to the in situ hydrogen generation) promotes the transformation of CO and CO₂ to methane and other alkanes, adversely affecting the 1,2-PDO selectivity. Finally, the admixture catalyst showed excellent stability as evidenced by several repeatable runs with the recycled catalyst.