Chapters authored
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
Sustainable Synthesis of Pyridine Bases from Glycerol
Catalytic processes have been developed to obtain pyridine bases from glycerol, either by direct conversion or with acrolein as an intermediate. When producing acrolein as an intermediate, the reaction may proceed in a single reactor at temperatures above 400°C in co-feeding with ammonia. A system of two interconnected reactors can also be used: one reactor performs the catalytic dehydration of glycerol to acrolein, while in the second reactor acrolein reacts with ammonia to form pyridine bases. Both processes require the use of solid acid catalysts, for which ZSM-5 zeolite-based catalysts are the most studied. In the direct reaction between glycerol and ammonia, the most active catalysts were Cu/HZSM-5 and the composite zeolite HZSM-5/11. In the two-step systems, the dehydration of glycerol to acrolein over a HZSM-5 zeolite modified by alkali treatment or over a HZSM-22 zeolite modified by an alkali-acid treatment as catalysts in the first reactor, in combination with a Zn impregnated acid-treated-HZSM-5 zeolite have shown to be efficient catalyst pairs for the synthesis of pyridine bases from glycerol in two-step processes. When using acrolein or acrolein diacetals, the most active catalysts were a 4.6%Cu–1.0%Ru/HZSM-5 zeolite in the presence of hydrogen, and a ZnO/HZSM-5-At-acid zeolite.
Part of the book: Ethanol and Glycerol Chemistry