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- 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.
- Catalyzed pyrolysis of coffee and tea wastesPublication . Rijo, Bruna; Soares Dias, A. P.; Ramos, Marta; Jesus, Nicole de; Puna, JaimeThe pyrolysis of food waste has a double environmental advantage as it contributes to the management and treatment of waste and allows the production of renewable fuels. Spent coffee and tea grounds, were characterized by thermogravimetry to determine their composition and evaluating the pyrolysis kinetics of each lignocellulosic pseudocomponent and pyrolyzed in a fixed bed reactor. Tea grounds had about twice the cellulose and higher pyrolysis activation energy than the coffee grounds sample. At 673 K the pyrolysis of the coffee grounds led to a 42% bio-oil yield while the tea grounds produced only 18% of liquid product, which is compatible with its higher cellulose content and the higher activation energy for pyrolysis. The alkaline carbonates used as pyrolysis catalysts led to an increase in the production of a gaseous product, bio-gas, with a reduction in the production of bio-oil but accompanied by a significant increase in the volatile fraction of the produced bio-oils. Pyrolysis data shows that both coffee and tea residues can be used as raw materials to produce pyrolysis bio-oil and that low-value materials such as alkaline carbonates can be used as pyrolysis catalysts improving the characteristics of bio-oils produced such as acidity and volatility.