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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 NH4-La-β zeolite, Pd/LaY zeolite, hierarchical ZSM-5, WO3/ZrO2, WO3/TiO2, ZrOx-NbOx, WOx-NbOx, WO3-SiO2/ZrO2, NbOx-WOx/Al2O3, H3PO4-MCM-41, SAPO-40, NbPSi, Pd-H3PW12O40/Zr-MCM-41, H3PW12O40/Cs-SBA-15, H3PW12O40/Nb2O5, Cs-doped H4SiW12O40/Al2O3, H4SiW12O40/TiO2, and H4SiW12O40/SiO2.
Part of the book: Glycerine Production and Transformation