No abstract

We report the synthesis and characterization of new niobium oxyhydroxide catalysts from ammonium niobium oxalate (NH4[NbO(C2O4)2(H2O)](H2O)n) or niobium chloride (NbCl5) precursors. The materials have been modified by incorporating a surfactant, specifically cetyltrimethylammonium bromide, on the catalyst surface to impart partial hydrophobicity to the catalyst. The change in the precursor during the synthesis changes properties associated with the morphology, texture and number of acid sites. These properties provide increased contact at the interface between the hydrophilic and hydrophobic regions to improve the catalytic properties, particularly in biphasic reactions. Acetalization reactions were tested using three different glycerols: commercial glycerol p.a., a crude residual originating from biodiesel production and the same material after desalination. The results show 65 and 60 % conversion for the acetalization under mild reactions conditions.

An alternative route to produce biodiesel is based on esterification of free fatty acids present in byproducts obtained from vegetable oil refining, such as palm oil fatty acid distillate (PFAD). PFAD is a byproduct of the production of edible palm oil, which contains 96 wt.% of free fatty acids. The purpose of this work was to study biodiesel synthesis via esterification of PFAD with methanol and ethanol, catalyzed by commercial immobilized lipases (Novozym 435, Lipozyme RM-IM, and Lipozyme TL-IM), in a solvent-free system. The effects of reaction parameters such as type of lipase, enzyme amount, type of alcohol, alcohol amount, and enzyme reuse were studied. Fatty acid conversion of 93% was obtained after 2.5 h of esterification reaction between PFAD and ethanol using 1.0 wt.% of Novozym 435 at 60°C.

The enzymatic alcoholysis of crude palm oil with methanol and ethanol was investigated using commercial immobilized lipases (Lipozyme RM IM, Lipozyme TL IM). The effect of alcohol (methanol or ethanol), molar ratio of alcohol to crude palm oil, and temperature on biodiesel production was determined. The best ethyl ester yield was about 25 wt.% and was obtained with ethanol/oil molar ratio of 3.0, temperature of 50 degrees C, enzyme concentration of 3.0 wt.%, and stepwise addition of the alcohol after 4 h of reaction. Experiments with 1 and 3 wt.% of KOH and 3 wt.% of MgO were carried out to compare their catalytic behavior with the enzymatic transesterification results. The commercial immobilized lipase, Lipozyme TL IM, showed the best catalytic performance.

Biodiesel may be produced by vegetable oil transesterification, followed by purification steps of product sedimentation and water washing. The occurrence of stable emulsions during the purification steps in the biodiesel production process from castor oil is a severe problem that precludes its use as an industrial raw material. The stability behavior of emulsions formed by castor oil biodiesel−water with 10, 20, and 30% (w/w) water content was studied using laser light profiling. Emulsion stability showed a decrease for emulsions with 10−20% water, but emulsions with 30% water showed a very high stability. Demulsification of water in biodiesel emulsions using microwave irradiation was also investigated as a function of the water content, separation temperature, and stirring speed. Analysis of the separation efficiency results showed that all of the variables were statistically significant but that water content was the most important factor. A comparison of microwave irradiation to gravitational sedimentation showed that a higher separation efficiency is obtained for emulsions submitted to the microwave irradiation.