November 25, 2013
Make propylene from acetone in one step. US propylene prices are rising because polypropylene demand is strong, and ethane cracking from inexpensive shale gas limits propylene production. Increasing prices make the direct conversion of acetone to propylene increasingly attractive.
In addition to polypropylene manufacture, one major use of propylene is the conventional route to phenol. In this process, benzene is alkylated with propylene to give cumene, which is oxidized to cumene hydroperoxide (CHP). CHP is catalytically rearranged to give 1 equiv phenol and 1 equiv acetone.
Mitsui Chemicals is a major user of this route to phenol. From time to time, depending on market conditions, Mitsui converts coproduct acetone to propylene in two steps. The first step is hydrogenolysis of acetone to isopropyl alcohol (IPA); the second is dehydration of IPA to propylene. The propylene is a feedstock for additional cumene. The decision to reclaim acetone as propylene is driven by the relative market prices of the two commodities.
T. Ohkubo and co-inventors disclose catalysts and operating conditions for converting acetone to propylene in one step with excellent yields. In one example, a fixed-bed reactor is charged with a mixed catalyst that consists of 3.0 g 5% Ag–0.5% In/SiO2 and 1.0 g WO3. Acetone is passed over the catalyst bed at rate of 0.3 g/h at 300 ºC. Hydrogen is allowed to flow through the bed at a pressure of 3.0 MPa and a rate of 22 mL/min. These flow rates correspond to a H2/acetone mol ratio of 11:1. Nitrogen at 50 mL/min is introduced into the reactor between the outlet and a back pressure valve.
After 100 h, acetone conversion is 99.9%, and selectivity to propylene is 93.4%. The same experiment was run with the WO3 replaced by a catalyst with the composition K3PW12O40. With this cocatalyst, propylene selectivity increases to 98.2%. (Mitsui Chemicals [Tokyo]. US Patent 8,552,239, Oct. 8, 2013; Jeffrey S. Plotkin)