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SELECTIVE HYDROGENATION OF ANHYDRIDES TO LACTONES UNDER SUPERCRITICAL CARBON DIOXIDE MEDIUM
Citation:
SahleDemessie*, E AND U R. Pillai**. SELECTIVE HYDROGENATION OF ANHYDRIDES TO LACTONES UNDER SUPERCRITICAL CARBON DIOXIDE MEDIUM. Presented at AIChE Annual Conference, Indianapolis, IN, November 03 - 08, 2002.
Impact/Purpose:
To inform the public.
Description:
Selective Hydrogenation of Anhydrides to Lactones Under Supercritical Carbon Dioxide Medium
Endalkachew Sahle-Demessie Unnikrishnan R Pillai
U.S. EPA , 26 W. Martin Luther King Dr. Cincinnati, OH 45268 Phone: 513-569-7739
Fax: 513-569-7677
Abstract:
Hydrogenation of aldehydes and anhydrides to their respective alcohols and lactones were studied under sc-CO2 medium. Hydrogenation of cinnamaldehyde to cinnamyl alcohol and citral to geraniol were achieved at mild conditions in sc-CO2. Maleic anhydride (MA) was selectively hydrogenated to either g-butyrolactone (GBL) or succinic anhydride (SAH) at 150-200oC and under supercritical CO2 medium using 2MPa H2 pressure over simple Pd/Al2O3 catalyst. MA hydrogenation over Pd/Al2O3 under conventional liquid phase reaction conditions gave only succinic anhydride. MA conversion is 100% irrespective of the variations in pressure and temperature or the nature of the reaction medium. Product selectivity, however, varies significantly with changes in temperature, pressure as well as the reaction medium. Selectivities under supercritical conditions were different from those obtained under normal liquid phase hydrogenations in organic solvents, showing the potential of the supercritical medium for partial or selective hydrogenations over simple metal catalysts. It is seen that GBL selectivity increases with increase in CO2 pressure. Temperature is critical in obtaining the desired yield or selectivity. GBL yield/selectivity increases with increase in reaction temperature. The results show that the desired product selectivity can be obtained by controlling the temperature and pressure. The selectivity obtained over Pd/Al2O3 may be a consequence of the enhanced reactant-product solubility as well as different reaction energetics in supercritical CO2 medium, which require further studies in detail. The mechanisms and kinetics of catalyst deactivation is also studied. This study demonstrates that selective hydrogenation of a low vapor pressure compound like MA can be successfully carried out in Sc-CO2 medium using a simple supported metal catalyst thereby accomplishing the goal of green chemistry cost effectively. The method has considerable promise for both lab-scale as well as industrial selective hydrogenations of low vapor pressure compounds without employing environmentally harmful organic solvents.