Glycerol dehydration to acrolein was studied with three catalysts using zeolite-Y. This zeolite in its protonic form (HY), with La (LaY) and Pd with La (Pd/LaY), was characterized by X-ray diffraction (XRD), Fourier-transform-infrared spectroscopy (FTIR) with pyridine, BET, Scanning Electron Microscope (SEM)-Energy-Dispersive Spectroscopy X-ray (EDS) and the catalytic activity tests were carried out under H 2 atmosphere. It was found that La ions exchanged in the zeolite-Y resulted in the improvement of both glycerol conversion and yield to acrolein, also a relatively constant glycerol conversion was achieved up to three hours, due to the presence of Pd on the catalyst and H 2 in the feed. The comparison of the calculated and experimental yields obtained from the catalytic tests of the Pd/LaY catalyst indicates a greater activity for the reaction to acrolein than for the reaction to acetol. The calculated equilibrium yields of the dehydration reaction from glycerol to acrolein, acetol, ethanal, methanol, and water and the experimental yields of a Pd/LaY catalyst were compared. Thermodynamically, a complete conversion of glycerol can be achieved since the general system remains exothermic and promotes the path to acetol below 480 K. Above this temperature the system consumes energy and favors the production of acrolein, reaching its maximum concentration at 600 K.
The study of the deactivation of HY zeolites in the dehydration reaction of glycerol to acrolein has represented a challenge for the design of new catalysts. HY zeolites with SiO2/Al2O3 molar ratios between 3.5 and 80 were studied. The solids were characterized by XRD, N2 physisorption, SEM-EDXS, Raman and UV-vis spectroscopies, infrared spectroscopy of pyridine (FTIR-Py) and catalytic activity tests from 250 °C to 325 °C. It was found that the total amount of acid sites per unit area of catalyst decreased as the SiO2/Al2O3 molar ratio increased from 3.5 to 80, resulting in the decrease in the initial glycerol conversion. The initial acrolein selectivity was promoted with the increase of the Brønsted/Lewis acid sites ratio at any reaction temperature. The deactivation tests showed that the catalyst lifetime depended on the pore structure, improving with the presence of large surface areas as evidenced by the deactivation rate constants. The characterization of the deactivated catalysts by XRD, N2 physisorption and thermogravimetric analysis indicated that the deposition of coke resulted in the total obstruction of micropores and the partial blockage of mesopores. Moreover, the presence of large mesopores and surface areas allowed the amount of coke deposited at the catalyst surface to be reduced.
The transesterification of used soybean oil with methanol was carried out over hydrated lime (HL), Ca(OH)2, and its decomposition products in the 200–500 °C range. The catalysts were characterized by X-ray powder diffraction (XRD), thermogravimetric analysis, and scanning electron microscopy. The XRD powder patterns demonstrated that the pristine sample consisted of a mixture of calcium hydroxide and calcite. It was noticed that the coexistence of CaO, Ca(OH)2, and CaCO3 remained up to 400 °C. At 500 °C, Ca(OH)2 is transformed into CaO so that this and CaCO3 are the only remaining phases. In the transesterification reaction, the influence of calcination temperature, reaction time, catalyst amount, methanol:oil ratio, and reaction temperature was studied. Full conversion of the raw materials into biodiesel (BD) was obtained with the fresh HL. In order to determine any change in the solid, it was recovered after 10, 30, and 60 min of reaction and analyzed by XRD analysis. Only Ca(OH)2, CaCO3, and traces of monohydrocalcite were detected. From the results it was demonstrated that the active phase for biodiesel production was calcium hydroxide. Furthermore, the catalyst was used up to three times without deactivation. A simple, economic, and environmentally friendly way to obtain biodiesel was developed considering (a) used soybean oil, considered waste, was employed as raw material, (b) hydrated lime is cheap and readily available, and (c) full conversion of the raw materials into BD was achieved with the as-received HL.
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-
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