Etherification of glycerol by alkaline earth oxides as solid catalysts:kinetics and pilot scale study

Abstract

As the utilization of biodiesel increases, glycerol is expected to be oversupplied since it is a by-product from the transesterification of vegetable oil. Therefore, it is interesting, to increase the use of glycerol by converting to other chemicals. In this work, glycerol etherification catalyzed by alkaline earth oxides was studied. The investigated catalysts (Na₂CO₃, NaOH, CaO, BaO, and MgO) show different activities for the etherification of glycerol at 240 °C and with 2 wt% loading of each types of catalyst. Conversion of glycerol increases with increasing catalyst basicity. The conversion increases in the order: NaOH>Na₂C0₃>BaO>CaO>MgO. Temperature varied from 220 to 250 °C affects the rate of reaction of glycerol to dliglycerol and to other polyglycerols but has no influence on the diglycerol selectivity. The kinetics of reaction of BaO and CaO were also investigated in order to find the reaction rate. The reaction order was found to be first order. The activation energies for the etherification of glycerol using BaO and CaO were 142.6 and 162.3 kJ/mol, respectively. CaO which has satisfied conversion and has commercial advantages was selected to study in pilot scale. A 20 kilogram pilot scale batch reactor was designed and constructed for testing the operating conditions. The pilot scale studies use 2 wt% loading of CaO at 240°C. It was observed that trend of concentration for each component is similar to the previous studies. At 6 h of reaction time, the glycerol conversion is about 39 % and diglycerol concentration is 30 %.