(582ah) Glycerol Valorization to Oligomers of Glycerol By Etherification over Supported Sr and Ca Catalysts

Increasing demands for alternative fuels, such as biofuel, has led to the large surplus of glycerol, generated as a byproduct in conventional biodiesel production. The glycerol valorization could help the cost reduction of biofuel and, consequently, make the production process of biofuel more economically favorable.

In this work, glycerol oligomers synthesized from the catalyzed etherification of glycerol were studied using supported Sr and Ca catalysts. These catalysts were obtained with impregnation of strontium onto γ-alumina (γ-Al₂O₃) and zeolite LTA substrates in 2M Sr(NO₃)₂ or 1M Ca(NO₃)₂ solutions. Effect of calcination temperatures of these supported catalysts, from 500°C to 700°C, on the resultant conversion efficiency of glycerol to oligomers and the selectivity of linear and branched oligomer to cyclic ones were investigated. Various instruments including BET, TPD, XRD, FT-IR and SEM were employed to characterize the obtained solid catalysts. With Sr supported on γ-alumina catalyst (Sr/γ-Al₂O₃), the catalyzed etherification reactions were proceed optimally at 260°C with 2.5 wt% Sr/γ-alumina calcined at 500°C under the inert atmosphere. Under optimal reaction conditions, a conversion efficiency of glycerol near 82% glycerol cold be obtained after 4-h reaction. Moreover, a selectivity near 90% of di- and tri-glycerol in linear and branched forms over the cyclic form could be achieved. In contrast, calcination of Sr on zeolite LTA (Sr/LTA) catalysts at 600°C would be ideal for the production of glycerol oligomers. The optimal reaction condition would fall at (1) catalyst loading at 2 wt% of glycerol, (2) reaction temperature at 240°C, and (2) 6 h for reaction. Under these conditions, a conversion efficiency about 90% for glycerol and the 95% selectivity of di- and tri-glycerol could be achieved. In contrast, the Ca-supported zeolite LTA gave only about 60% conversion of glycerol.

Keywords: glycerol, diglycerol, triglycerol, γ-alumina, zeolite LTA, etherification, strontium, biodiesel.