Patent Watch
April 27, 2009
Nonacetone routes to phenol continue to be developed. Almost all of the world’s phenol is manufactured by the cumene-based acetone coproduct process. In this process, cumene is formed by alkylating benzene with propylene, then oxidized with air to form cumene hydroperoxide (CHP). Concentrated CHP is cleaved to yield the coproducts phenol and acetone. This type of technology is called a “2-for-1” process.
Most 2-for-1 processes are considered to be low-cost routes, but they require that the market demand for both products grow in the same ratio as they are produced. In the case of phenol and acetone, there is concern that the phenol market will outpace the acetone market because of the strong growth of bisphenol A for the polycarbonate market. (Bisphenol A requires 2 equiv of phenol for every 1 equiv of acetone.) Thus, to keep up with phenol demand, too much acetone will be produced, causing its price to decline. Declining acetone prices will penalize phenol costs because acetone is taken as a byproduct credit. In addition, the price of propylene has increased sharply above historic levels as a result of strong polypropylene demand.
In 2007, Shell Chemical announced its intention to commercialize a new phenol process in Asia that will mitigate the problem of acetone oversupply. This process is believed to involve co-oxidation of cumene and sec-butylbenzene to give phenol and with acetone and methyl ethyl ketone (MEK) as byproducts. sec-Butylbenzene can be made by alkylating benzene with straight-chain butenes. Now, ExxonMobil appears to be developing another route to phenol that will coproduce cyclohexanone instead of acetone or MEK.
T.-J. Chen and colleagues at ExxonMobil Chemicals disclose a catalyst that facilitates the hydroalkylation of benzene to cyclohexylbenzene (CHB, 1) in good selectivity. Peroxidation of CHB gives CHB peroxide, which in turn can be decomposed to produce 1 equiv of phenol and 1 equiv of cyclohexanone. Cyclohexanone is an important raw material for making adipic acid and caprolactam.
The key to this invention is the finding that contacting benzene and hydrogen with a bifunctional catalyst that consists of a hydrogenation metal such as palladium and a molecular sieve of the MCM-22 family gives high selectivities to CHB. The inventors also found that the molar ratio of the metal to the molecular sieve significantly affects the selectivity to CHB.
In one example, two catalysts, each composed of 2 g of 0.3 wt% Pd supported on γ-Al2O3, were prepared. One catalyst (A) was copelletized with 1.6 g of MCM-49 catalyst, whereas the other sample (B) was copelletized with 4.8 g of MCM-49. The Al/Pd mol ratios were 50:1 and 150:1 in catalysts A and B, respectively.
Both catalysts were tested under the same conditions. Benzene was fed at a rate of 0.08 mL/min and hydrogen was fed at 10 mL/min. The reaction temperature was 150 °C, and the gauge pressure was 1034 kPa. Both catalysts gave about the same conversion (42.5–43.5%), but selectivity to CHB was much better with catalyst B (78%); catalyst A gave only 70.8% selectivity. The major byproducts in both cases were dicyclohexylbenzene and lower amounts of cyclohexane. (ExxonMobil Chemical Patents [Houston]. World Patent WO2009038900, March 26, 2009; Jeffrey S. Plotkin)
View patent information from CAS.
What do you think of Patent Watch and Noteworthy Chemistry? Let us know.