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- Strontium-doped lime catalysts for biodiesel production: activity and stability during soybean oil methanolysisPublication . Dias, Ana Paula Soares; Puna, Jaime; Neiva Correia, Maria Joana; Gomes, João; Bordado, JoãoBiodiesel produced by alcoholysis of vegetable oils is a low carbon fuel, which can replace the fossil diesel in internal combustion engines. CaO is a cheap and environmentally benign material showing interesting catalytic performances in the methanolysis reaction of vegetable oils. However, the reaction rate is slower than the conventional homogeneous-catalyzed by sodium methoxide. In order to improve the catalytic activity, lime catalyst (commercial) was doped with different amounts of strontium. The catalysts, prepared by wet impregnation using aqueous solutions of nitrate salt, were calcined at 575 °C and 800 °C. The physical-chemical characterization of catalysts showed that the doping element had an apparently null effect on the basicity assessed by Hammett indicators. The Ca(OH)2, with weak basicity, formed in the Sr-modified catalysts eventually masked the Sr effect on the basicity. In the tested conditions, all the prepared catalysts were active allowing fatty acid methyl esters’ (FAME) yields higher than 94%. The catalyst stability tests, performed without intermediate reactivation, showed that Sr dopant promoted accelerated decay due to calcium diglyceroxide formation which is leached into the reaction medium. High temperature calcination had a negative effect on the catalyst stability due to the formation of Ca(OH)2. Such undesired effect was prompted by the Sr dopant.
- The role of alkali dopants on the oil methanolysis behavior of lime catalyst: activity & stabilityPublication . Soares Dias, A. P.; Puna, Jaime; Gomes, João; Ramos, Marta; Rijo, Bruna; Bordado, JoãoHeterogeneous basic catalysts, namely calcium oxide, are referred to as promising catalysts for biodiesel (FAME, fatty acid methyl esters) production since they can be easily separated from the reaction medium allowing them to operate in a continuous mode. Despite the relatively high catalytic activity of calcium catalysts, they present slower alcoholysis rates than homogeneous conventional catalysts (sodium or potassium methanoate). In order to improve the catalytic activity, CaO-based catalysts, modified with alkali elements (Li, Cs, Sr, and Mg) were prepared. Dopant element contents of 10% and 30%, as weight basis (5–50% molar), were introduced by wet impregnation using aqueous solutions of nitrate salts. The effect of calcination temperature (575°C and 800°C) on both activity and stability was studied. All the prepared catalysts, raw and alkali modified, showed pKa<15.0 when characterized by Hammett indicators in methanolic solution. Such basicity is characteristic of Ca hydroxide, thus indicating that the catalysts surfaces were covered with Ca-OH species. FAME yield, in soybean oil methanolysis, higher than 96% was obtained for the first batch reaction for all the tested catalysts showing that alkali dopants have an almost nihil effect on the catalysts performances. The deactivation tests performed with catalysts without intermediate reactivation showed that calcination temperature plays a major role in stability as it enhances the formation of calcium diglyceroxide. The presence of Ca hydroxide in fresh catalysts appears to be responsible for fast deactivation. The dopant elements prompt the catalysts deactivation. Catalysts calcined at higher temperatures showed slower deactivation, which can be due to the formation of larger particles, thus reducing the contact with the formed glycerin. Alkali dopants enhanced the CaO sintering for the highest calcination temperature. Calcium diglyceroxide formed during the reaction is responsible for deactivating the catalyst, due to leaching, and such effect is prompted by alkali dopants.
- Calcium rich food wastes based catalysts for biodiesel productionPublication . Catarino, Maria Alice; Ramos, M.; Soares Dias, A. P.; Santos, Maria Teresa; Puna, Jaime; Gomes, JoãoBiodiesel produced from food wastes can help to solve several environmental issues: anthropogenic carbon emissions due to fossil fuels combustion and waste management. Biodiesel was produced using waste frying oils (WFO) and calcium rich food wastes such as mollusk, shrimp, eggs shells and cuttlebone to produce calcium based heterogeneous catalysts by calcination. The characterization of chalky white calcined powders by XRD showed diffraction lines typical of lime but some samples were slightly contaminated with calcite. The powders with low crystallinity showed high hydration rate presenting XRD features ascribable to nanocrystals of calcium hydroxide. The post reaction samples presented mainly lines due to calcium diglyceroxide and methoxide. Thermograms of used catalysts showed some weight loss of these calcium compounds, confirming the presence of such phases. All prepared catalysts were effective in catalyzing the methanolysis of soybean oil. A FAME yield around 96% was obtained after 2.5 h of reaction. When using WFO, the FAME yield was only 65% with simultaneous production of soap. The use of WFO and soybean oil mixtures attenuates the loss of catalytic performances. The obtained glycerin's presented a light color characteristic of heterogeneous catalyzed processes. FTIR spectra of glycerin's showed some features belonging to matter organic non glycerin and methanol. The catalyst reutilization without intermediate reactivation indicated that catalysts are somewhat stable. When WFO was used, the reused catalysts showed improved performance probably due to the formation of calcium diglyceroxide. Nevertheless, calcium diglyceroxide is bound to promote homogeneous catalysis and consequent deactivation.