Heterogeneous Catalyzed Macromolecular Hydrogenations in Oscillating Systems
An examination of novel oscillatory (alternating gas and liquid phase) reactors and heterogeneous catalysts for multi-phase macromolecular reactions was carried out. A monolith-containing square die with Pd/Al2O3 catalysts was used to successfully hydrogenate poly(styrene) (PS). The inherent pulse behavior of the extruder was found to be sufficient to approach intrinsic kinetics at low polymer concentrations. At higher (10 wt% PS) concentrations, forced pulsing was shown to have a greater impact on observed reaction rates. Selectivity with this extruder-fed reactor was better than with a stirred tank in all cases, due to a more plug-flow-like residence time distribution. While accurate control over the exit distribution of forced pulses was difficult due to gas back mixing, an optimal frequency of forced pulsation was observed for the 10 wt% PS system.
Mesoporous catalysts for macromolecular hydrogenations were synthesized and tested for PS hydrogenation. They were shown to be more active than microporous catalysts. The type of support was shown not to have a large influence on activity, but high dispersion of the active metal was critical. The addition of a second inactive metal did improve hydrogenation selectivity, but it was observed that having a chloride-free support is even more important in achieving high activity.
For the hydrogenation of a low molecular weight species (?-methylstyrene) (AMS) in a piston oscillating monolith reactor (POMR), oscillations gave improvements in reaction rate of up to 84%. With no oscillations, the activity was still higher than in a stirred tank operated at an equivalent power per unit volume. Selectivity in the POMR was as good as or better than in a stirred tank. It was also found that the Pd crystallite size had a large influence on activity.
For the hydrogenation of soybean oil, the POMR gave a higher activity than a stirred tank at identical conditions. The hydrogenation rate increased by as much as 112% with oscillations. It was shown that this improvement was unrelated to external mass transfer; rather it arised from improved intraparticle mass transfer limitations or surface wetting. Sereo-selectivity was largely unaffected by the reactor system but was instead dependent on intraparticle diffusion lengths.
Advisor:Kalliat Valsaraj; Paul Russo; Richard Bengtson; F. Carl Knopf; Kerry Dooley
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:03/05/2008