Shuli Yan

Performance of heterogeneous ZrO2 supported metaloxide catalysts for brown grease esterification and sulfur removal

In order to achieve a viable biodiesel industry, new catalyst technology is needed which can process a variety of less expensive waste oils, such as yellow grease and brown grease. However, for these catalysts to be effective for biodiesel production using these feedstocks, they must be able to tolerate higher concentrations of free fatty acids (FFA), water, and sulfur. We have developed a class of zirconia supported metaloxide catalysts that achieve high FAME yields through esterification of FFAs while simultaneously performing desulfurization and de-metallization functions. In fact, methanolysis, with the zirconia supported catalysts, was more effective for desulfurization than an acid washing process. In addition, using zirconia supported catalysts to convert waste grease, high in sulfur content, resulted in a FAME product that could meet the in-use ASTM diesel fuel sulfur specification (<500 ppm). Possible mechanisms of desulfurization and de-metallization by methanolysis were proposed to explain this activity.

The effect of support material on the transesterification activity of CaO–La2O3 and CaO–CeO2 supported catalysts

The effects of support materials—lanthanum oxide, cerium oxide, zirconium oxide, titanium oxide, γ-alumina, and ZSM-5—on the transesterification activity of CaO–La2O3 and CaO–CeO2 catalysts were investigated. The metal composition and surface acidity (or basicity) of the supported catalysts played a significant role in determining the activity of the catalyst. Results showed that both catalytic activity and basicity of the supported catalysts decreased in the following order: CaO–La2O3/La2O3 ≥ CaO–La2O3/CeO2 > CaO–La2O3/ZrO2 > CaO–La2O3/γ-Al2O3 > CaO–La2O3/ZSM-5 > CaO–La2O3/TiO2. In addition, leaching of Ca species from the catalyst was more pronounced with basic supports. However, Ca leaching could be minimized by coupling with La2O3 or CeO2 on an appropriate support. This was verified in a flow reactor study of the CaO–CeO2/La2O3 catalyst, where, over 200 h of continuous operation, the transesterification yield held constant at 88∼90% while the initial Ca concentration in the product decreased from 194 ppm to below 5.0 ppm after 144 h. This further suggests that Ca leaching had little long-term effect on the overall FAME activity of the catalyst.

Competitive transesterification of soybean oil with mixed methanol/ethanol over heterogeneous catalysts.

Methylesters and ethylesters of fatty acids were synthesized using homogeneous CH(3)ONa and CH(3)CH(2)ONa, anion exchanged resin, and CaO-La(2)O(3) catalysts. Methanol, ethanol, and methanol/ethanol mixtures were used as the alcohol feed for transesterification of soybean oil. With a homogeneous catalyst (CH(3)ONa) there was essentially no difference in conversion rates between methanolysis and ethanolysis in batch reactions. However, with a heterogeneous resin and CaO-La(2)O(3) catalysts, significant differences in the conversion rates between the methanolysis and ethanolysis were observed. The formation rate of methylesters over a CaO-La(2)O(3) catalyst was higher than that of ethylesters, which may be attributable to a steric hindrance effect. Conversely, with a heterogeneous resin catalyst, the conversion rate of ethylester was higher than that of methylesters which may be attributable to the surface hydrophobicity of the anion exchanged resin. When the transesterification of soybean oil was carried out with an equimolar methanol/ethanol mixture, the yield ratio of methylester to ethylester formed within the first 30 min was 2.6 for the homogeneous catalyst (0.3% CH(3)ONa), and 3.4 for the heterogeneous CaO-La(2)O(3)catalyst. These differences in selectivity are likely due to both the higher reactivity of methoxide and to a steric hindrance effect of ethoxide on the catalyst surface. In addition, the transformation of methylester to ethylester was observed when a methanol/ethanol mixture was used.