María A. Sánchez

Reef-forming polychaetes outcompetes ecosystem engineering mussels

In order to understand changes in the functioning and the community structure of intertidal ecosystem in sewage-impacted sites, a long-term monitoring coverage study (2004-2011) was carried out on abrasion platforms of the SW Atlantic. The intertidal zone is characterized by the mytilid Brachidontes rodriguezii, an ecosystem engineer. Since the austral spring of 2008, a demographic explosion of an invader polychaetes, Boccardia proboscidea, has produced massive biogenic structures around the sewage discharge outfall. Cover percentage of this polychaete reached almost 100% in sewage-impacted sites but low or no coverage at all in Reference Sites. The density of B. rodriguezii declined due to the biogenic reefs stifles these mytilids. The massive settlement of B. proboscidea among mussels, the rapid growth and the tube construction smothers the mussels in sewage-impacted sites.

Influence of the operating conditions and kinetic analysis of the selective hydrogenation of methyl oleate on Ru–Sn–B/Al2O3 catalysts

The influence of the operating conditions and preparation methods of Ru–Sn–B/Al2O3 catalysts on the activity and selectivity for the hydrogenation of methyl oleate to oleyl alcohol was studied. It was found that catalysts prepared by incipient wetness (IW) are more active and selective than those prepared by co-impregnation. This better performance is possibly due to a lower level of residual chlorine. The experiences of hydrogenation of methyl oleate showed that activity increases as the reaction temperature increases while the selectivity to oleyl alcohol has a maximum value. This could be due to the higher activation energies for the hydrogenolysis of carboxymethyl groups than those found for C=C double bonds hydrogenation. The increase in operating pressure has a positive effect on the activity but it influences selectivity time patterns in a more complex way. Experiments carried out by varying methyl oleate/n-dodecane ratio show that the selectivity and conversion not depend on this parameter. A simple kinetic model is proposed.

Ru-Sn-B/Al2O3 Catalysts for Selective Hydrogenation of Methyl Oleate: Influence of the Ru/Sn Ratio

This study focuses on the influence of the Ru/Sn ratio on the catalytic hydrogenation of methyl oleate to oleyl alcohol using Ru-Sn-B catalysts, notably on the catalytic activity and selectivity. Sn addition acts positively over the oleyl selectivity by reducing the rates of C=O and C=C saturation but also decreases the global activity. The catalyst with the highest activity and selectivity towards oleyl alcohol is Ru(1%)-Sn(2%)-B/Al2O3. At a low Sn loading (0.5%) the catalyst has high activity for hydrogenation of the carbonyl group and the carbon-carbon double bond. As a consequence stearyl alcohol is produced with high yield. At a high Sn content (4%) the catalyst has lower selectivity to oleyl alcohol due to its low capacity for hydrogenating the carbonyl group. However it has enough activity for hydrogenating the C=C double bonds to produce the saturated methyl ester.