Selective hydrogenation of 1,5,9-cyclo-dodecatriene towards cyclo-dodecene

• Published in: Applied catalysis. A, General Vol. 343; no. 1; pp. 87 - 94
• Main Authors: Gaube, J., David, W., Sanchayan, R., Roy, S., Müller-Plathe, F.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.07.2008; Elsevier
• Subjects: 1,5,9-Cyclo-dodecatriene; Catalysis; Chemistry; Cyclo-dodecene; Exact sciences and technology; General and physical chemistry; Hydrogenation; Kinetics; Reaction engineering; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Cyclo-dodecene; 1,5,9-Cyclo-dodecatriene; Kinetics; Hydrogenation; Reaction engineering; Heterogeneous catalysis
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2008.03.025

A cyclo-dodecene yield ≥90% can be attained in liquid phase hydrogenation of 1,5,9- cis, trans, trans-cyclo-dodecatriene on Pd catalysts of eggshell type if the hydrogen concentration is kept at a low level. Ab initio Hartree–Fock calculations of the molecular structures of cyclododecadienes have pointed at the crucial role of both cyclododecadienes and hydrogen adsorption on nanostructured surfaces of palladium. ▪ The liquid phase hydrogenation of 1,5,9- c, t, t-cyclo-dodecatriene (CDT) and of cyclododecadienes (CDD) towards cyclo-dodecene (CDE) using a Pd/Al 2O 3 catalyst of egg-shell type has been studied in discontinuous operation at different hydrogen pressures and for stepwise reduced hydrogen pressure. The yield of CDE is considerably increased if the hydrogen concentration and consequently the rate of hydrogenation are markedly reduced. By this means a CDE yield of 93% at a (CDT + CDD) conversion of 98% could be reached. Because of the low hydrogenation rate the conversion is not influenced by mass transfer effects. For discussion the partial hydrogenation of CDT is compared with the hydrogenation of cyclo-octadiene for which a cyclo-octene yield of >99% is attainable at a much higher reaction rate. In order to understand the partial hydrogenations of cyclo-octadiene and of CDD ab initio Hartree–Fock calculations have been carried out to study the structure of these molecules. On this basis a hypothesis for the lower selectivity of CDT-hydrogenation towards CDE compared to that of cyclo-octadiene towards cyclo-octene is presented. The increase of CDE selectivity with decreasing hydrogen pressure is traced back to the increased rate of the isomerization of t, t- and c, t-CDDs towards the more strongly adsorbed c, c-CDDs. The results of the presented study clearly show that the realization of an industrial process of the selective hydrogenation of CDT towards CDE using a simple catalytic reactor is possible. Concepts are proposed for discontinuous and for continuous procedure.