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- Biodiesel glycerin valorization into oxygenated fuel additivesPublication . Soares Dias, A. P.; Fonseca, Frederico G.; Catarino, Mónica; Gomes, Joãorequires costly purification before commercialization. Production of oxygenated fuel additives is a potential route for glycerin valorization. Glycerin acetylation was carried out over heterogeneous acid catalysts (15%, glycerol weight basis) using glacial acetic acid (molar ratio=9). The catalysts, containing different amounts of phosphate species (P/Si from 10 to 20 atomic ratio), were prepared by wet impregnation of commercial silica with aqueous solutions of diammonium phosphate and ortho-phosphoric acid. X-ray diffraction patterns of calcined solids presented amorphous patterns like raw silica. The prepared catalysts presented, at 120 degrees C, glycerol conversion higher than 89.5% after 1 h of reaction, been diacetin the major product, with triacetin selectivities lower than 26.1%. Diacetin selectivity was found to be almost invariant with catalyst acidity thus underlining the relevance of catalyst porosity due to the large acetins molecules sizes. The slow rate of triacetin diffusion in narrow pores of catalyst might be responsible for the relatively low yield obtained. Surface phosphate species showed a slow rate of leaching in the reaction medium showing high catalyst stability.
- Co-processing lard soybean oil over Ca-based catalysts to greener biodieselPublication . Soares Dias, A. P.; Catarino, Mónica; Gomes, JoãoFatty Acid Methyl Esters (FAME) were produced from lard/soybean oil (SBO) mixtures using a calcium-based heterogeneous catalyst. The green catalyst was prepared by scallop shell calcination at a relatively low temperature (800 degrees C) to minimize energy consumption. Images from Scanning Electron Microscopy showed agglomerates of a few tens micrometers with rhombohedral calcite crystallites studded with lime. X-ray diffractogram of fresh catalyst presented overlapped patterns of calcite and lime In tested conditions (methanol reflux temperature, 5% (fat mass basis), methanol fat = 12 molar ratio, and 150 min), the FAME yield reached 95% (mass) with SBO. However, only 75% FAME yield was obtained from pure lard since the active sites of the catalyst were partially neutralized by lard acidity. Co-processing lard/SBO mixtures attenuated the undesirable fat acidity drawback allowing FAME yields around 90% for mixtures containing less than 50% (mass) of lard. The low-grade fat content of the processed mixture showed no impact on the glycerin quality. Co-processing lard/SBO is a smart strategy to overcome the low-grade fats acidity in biodiesel production process thus providing a more sustainable biodiesel production route.
- 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.