992 resultados para 48-406
Resumo:
Fil: Starcenbaum, Marcelo. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.
Resumo:
A comparative study of the influence of three different acid solids as catalysts (conventional zeolites Z15c with Si/Al = 19.5 and Z40c with Si/Al = 48.2, and a hierarchical zeolite Z40c-H with Si/Al = 50.0) for the etherification of glycerol with benzyl alcohol was performed. The catalytic activity and selectivity of these zeolites was elucidated at different catalyst contents. Three different ethers (3-benzyloxy-1,2-propanediol, which is a mono-benzyl-glycerol ether (MBG) and 1,3-dibenzyloxy-2-propanol, which is a di-benzyl-glycerol ether (DBG) and dibenzyl ether (DBz) were identified as the main products. MBG was the major product of the reaction catalyzed by the microporous Z15c zeolite with low Si/Al molar ratio, whereas DBG was formed in higher yield with the use of microporous Z40c and hierarchical Z40c-H zeolites, both of them having a similar high Si/Al molar ratio (≈50). MBG is a value-added product and it is obtained with good yield and selectivity when using the conventional zeolite Z15c as a catalyst. Under the best conditions tested, i.e., 25 mg of catalyst for 8 h at 120 °C, a 62% of conversion was obtained without the need of solvent, with an excellent 84% selectivity toward the MBG and no formation of DBz.
Resumo:
When the European Council meets in December, it will face a range of decisions which will lay the foundations for Europe's defence posture and role in the wider world for decades to come, perhaps even beyond the remainder of this century. The Lisbon Treaty has, for the first time, equipped the EU with the range of means to meet that role in practice. The question that remains to be answered is whether Europe's leaders have the political will to implement those means in full.
