Abstract
Abstract Biodiesel production using acid oils is an important alternative for biofuel cost reduction. However, it is a huge challenge for homogeneous transesterification, the main industrial route commonly used. This paper presents macauba oil with high acidity, 43.90 w/w%, as a potential raw material for biodiesel production. The acidity was reduced to 0.8 w/w% after re-esterification (80 min) with glycerol at high temperature (235 °C), without catalysts. Zinc (powder and coating) and NbOPO4 were also tested as catalysts in comparison with the reaction without a catalyst. Reactions catalyzed by metallic Zn produced a large amount of Zn carboxylate, an undesirable soap, due to the high Zn leaching. In contrast with the literature, Zinc did not show good catalytic activity, as confirmed by the kinetic parameters. NbOPO4 was not a good catalyst, too. Reaction without catalysts was performed using nitrogen as a carrier gas and it was compared with reaction under vacuum to remove co-produced water. Nitrogen showed the best result for re-esterification, avoiding degradation reactions. Triglycerides (TG) were the prevalent products in reactions using nitrogen. After re-esterification, the oil was easily converted into biodiesel with high ester content (98.4%) of methyl ester by alkaline transesterification.
Highlights
Biofuels have been used worldwide to reduce the consumption of fossil fuels and as an effort to minimize climate changes
Glycerol Esterification In order to evaluate the catalyst effect on glycerol esterification of free fatty acids (FFA) present in macauba pulp oil, tests were performed under the same conditions (235+5°C and the nitrogen flow was 1.0 L/min), using different catalysts and without catalyst (Blank)
The acidity of macauba oil was reduced by glycerolysis at 235+5°C, without a catalyst, 80 minutes and nitrogen flux to remove the water generated as a by-product
Summary
Biofuels have been used worldwide to reduce the consumption of fossil fuels and as an effort to minimize climate changes. One possible alternative is to use acid oils, cheaper than neutral vegetable oils, but the acidity makes the conversion process and biodiesel purification difficult. Biofuel produced from vegetable oils and animal fats, is largely produced by the transesterification of triglycerides using mainly alkaline homogeneous catalysts. It can only be efficiently produced if the acidity of the raw material is lower than 2%, a value found only in noble and edible oils. It is possible to use residual and/or non-edible oils for homogeneous transesterification as long as the acidity is reduced to at least 2% (Felizardo et al, 2011)
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