Catalytic Dehydration of Glycerine to Acrolein

The biodiesel production yields glycerine as a by-product in quantities around 10 vol% of produced biodiesel. Acrolein can be obtained from glycerine by a dehydration reaction. Catalytic processes in gas phase have been developed to obtain acrolein from a renewable feedstock using heterogeneous catalysts. The main process variables are the reaction temperature, the concentration of glycerol in water, and the space velocity in fixed-bed reactors. A thermodynamic study of the equilibrium has been made to estimate the conversion to equilibrium as a function of temperature. The reactors have been heated usually between 523 and 603 K. Generally, an aqueous glycerol solution is preheated in a preheating zone at a temperature enough to vaporize the feedstock, between 473 and 533 K, depending on the concentration of reactant required in the feed. Some of the most active catalysts in the gas-phase reaction (yield >70%) were NH 4 -La- β zeolite, Pd/LaY zeolite, hierarchical ZSM-5, WO 3 /ZrO 2 , WO 3 /TiO 2 , ZrOx-NbOx, WOx-NbOx, WO 3 SiO 2 /ZrO 2 , NbOx-WOx/Al 2 O 3 , H 3 PO 4 -MCM-41, SAPO-40, NbPSi, Pd-H 3 PW 12 O 40 / Zr-MCM-41, H 3 PW 12 O 40 /Cs-SBA-15, H 3 PW 12 O 40 /Nb 2 O 5 , Cs-doped H 4 SiW 12 O 40 / Al 2 O 3 , H 4 SiW 12 O 40 /TiO 2 , and H 4 SiW 12 O 40 /SiO 2 .