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- Calcium diglyceroxide as a catalyst for biodiesel productionPublication . Catarino, Mónica Inês; Martins, Susana; Ana Paula Soares Dias; Pereira, Manuel; Gomes, JoãoCalcium diglyceroxide (CaD) was used as the catalyst for biodiesel production through oil methanolysis. It was evaluated its catalytic behavior, its air expo- sure tolerance, and the Ca leaching. CaD catalyst was synthesized from food waste scallop shell derived CaO (obtained by calcination at 900 degrees C) by contacting with a mixture of equal volumes of glycerin and methanol at 65 degrees C for 2 h. The CaO obtained by calcination of scallop shell was used as reference catalyst. In standard reaction conditions (2.5 h, methanol reflux temperature, 5 wt% (oil basis) catalyst loading, and methanol: oil = 12:1 moral ratio), CaD presented lower catalytic activity than CaO (FAME yield of 92% against 99%, respectively). 24 h repined CaD presented improved catalytic behavior probably due to the formation of surface Ca - OH groups, achieving 96% of FAME yield. Thermogravimetry (TG) data showed that inorganic residue was larger for biodiesel than for glycerin, being CaD catalyst more soluble than CaO. Data showed that CaD is unstable under reaction conditions, suffering leaching, but the absence of Matter Organic Non-Glycerol (MONG) in the glycerin phase allows to neglect the homogeneous contribution of the leached catalyst. CaD formation during reaction contributes to FAME contamination with Ca and promotes catalyst deactivation thus being an undesired occurrence.
- 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.