| Selective hydrogenation of the olefin residing within nitrile butadiene rubber (NBR) yields an elastomer that possesses remarkable thermal and oxidative stability. A new generation of homogeneous catalysts have been identified for the reaction, having the general form OsHCl(CO)(L)(PCy;The rates of hydrogenation supported by 2a are superior to those produced by RhCl(PPh;A spectroscopic analysis of HNBR produced using 2a revealed no evidence for the reduction of the copolymer's nitrile unsaturation to amine. However, the olefin hydrogenation was accompanied by an undesirable crosslinking reaction that was not observed for the rhodium catalysts. Detailed studies of the effect have indicated that elevated pressures and minimized catalyst concentrations suppress, but do not eliminate, the crosslinking process. By monitoring the evolution of the side-reaction product with time, it has been connected to the presence of residual olefin. Various mechanisms by which the cross-linking process could occur have been explored.;An alternative to batch HNBR production has been explored in the form of a continuous, plug-flow reactor configuration. The design considerations underlying the new production strategy have been detailed along with criteria used for its evaluation. To demonstrate the operating principles of the new approach, a bench-scale prototype has been constructed and assessed according to these standards. The breadth and form of the residence time distribution afforded by the unit have been measured and related to its hydrogenation performance. The data suggests that HNBR may be synthesized efficiently by this method. |
