ABSTRACT
Abstract Transient infrared studies of partial oxidation over 2 wt% Rh/Al2O3 showed that the total oxidation of propylene to CO2 occurred at a higher rate than the partial oxidation to propylene oxide; total and partial oxidation occurred in parallel pathways at 250 oC. Temperature-programmed desorption revealed that adsorbed propylene oxide can convert to other C3 oxygenates such as acetone and propanal. The parallel reaction pathways for partial and total oxidation on Rh/Al2O3 suggest that selective poisoning of the total oxidation sites could be a promising approach to obtain high selectivity toward propylene oxide under high propylene conversion. Introduction Propylene oxide (PO) is an important intermediate in the manufacture of a wide range of valuable products: propylene glycol, ethers, isopropanolamines, and various propoxylated products for polyurethanes (1). The current processes for the large scale synthesis of PO include (i) the chlorohydrin process and (ii) the peroxide process (1, 2). Chlorohydrin process:
Peroxide process:
H3C C H
CH2 ROOH
R'COOH O
H3C C H
O ROH
+ cat
+ R'COOH
The disadvantage of the chlorohydrin process is the use of toxic, corrosive, and expensive chlorine; the major drawback of the peroxide process is the formation of co-oxidates in larger amounts than the desired PO. The direct epoxidation of propylene using O2 (i.e., partial oxidation of propylene) from air has been recognized as a promising route.
