RESUMO
Heterogeneous catalysts consisting of potassium supported on zeolites are active for transesterification, but the effect of zeolite properties is not clearly understood. This work compares catalysts containing 12 wt.% potassium on zeolite sodium A and X (12K/NaA and 12K/NaX) in terms of performance and physicochemical properties. Both catalysts were prepared by ultrasound-assisted impregnation with potassium acetate buffer. 12K/NaA is a better catalyst in transesterification of palm oil, giving a higher biodiesel yield than 12K/NaX in the first run (99.1 ± 0.3 % and 77.9 ± 2.2 %, respectively). From characterization by CO2-TPD, XRD, FTIR, XPS, and SEM-EDS, both catalysts have similar basicity but different dispersion of carbonates and interaction on the zeolites. The 12K/NaA has those species on external surfaces and more monodentate carbonate than 12K/NaX. Ion exchange occurs between potassium ions from the precursor and sodium ions from the zeolite. Moreover, 12K/NaA is more stable, providing higher biodiesel yields in the second and third catalytic cycles.
RESUMO
Zeolite NaY synthesized from a typical procedure could suffer from agglomeration. Adding non-refluxed cogon grass (NG) to the synthesis gel could produce NaY with good dispersion and uniform crystal size. Small molecules produced from cogon grass in alkaline conditions could prevent agglomeration. The obtained zeolite (Y-NG) has a crystallinity and surface area comparable to the synthesis without grass (Y-WG). Y-NG demonstrated similar paraquat adsorption capacity to Y-WG at high initial concentrations. On the other hand, the zeolite from the addition of acid-refluxed grass (Y-RG) has the lowest crystallinity, smallest surface area, and poorest paraquat adsorption capacity. The effect of grass amount on the zeolite structure was studied. One gram of cogon grass was the optimum amount to add to the synthesis gel.