April 4, 2011
Make cyclohexylbenzene from benzene with this new catalyst. The conventional commercial route to phenol is the Hock process. It starts with cumene, made by alkylating benzene with propylene, and produces 1 equiv each of phenol and acetone. Making two products in one process seems attractive in concept, but in practice two-for-one processes work well only when market requirements for both products are growing at about the same rate. Phenol demand is currently outpacing acetone demand; and there are fears that acetone will be in significant oversupply, which will lower its price.
For years, the petrochemical industry has looked for routes that substitute propylene with other olefins that give other coproducts. For example, adding straight-chain butenes to benzene gives n-butylbenzene, which upon oxidation and rearrangement gives phenol and 2-butanone. The problem with this process is that demand for 2-butanone is very limited.
Oxidation and subsequent rearrangement of cyclohexylbenzene, however, give phenol and cyclohexanone. Cyclohexanone is needed in large volumes as a feedstock for adipic acid and caprolactam, monomers for nylon-6,6 and nylon-6, respectively. The challenge to commercializing this route is to find an efficient way to make cyclohexylbenzene.
T.-J. Chen and co-inventors found that Pd/Al2O3 copelletized with the correct amount of MCM-22 family molecular sieves effectively converts benzene and hydrogen to cyclohexylbenzene. They postulate that some of the benzene is partially hydrogenated to cyclohexene, which adds to the remaining benzene to form cyclohexylbenzene.
To demonstrate the sensitivity of the catalyst to the Pd/Al2O3:MCM-49 ratio, the inventors prepared two catalysts. Both contained 2 g of 0.3 wt% Pd/Al2O3, but catalyst A was made by adding 1.6 g MCM-49 and catalyst B by adding 4.8 g MCM-49. Benzene at 0.08 mL/min and hydrogen at 10 mL/min were passed over both catalysts. The reaction temperature was 150 °C, and the pressure was 1034 kPag. Both catalysts promoted about the same benzene conversion (42.5–43.5%), but catalyst B was superior in terms of selectivity to cyclohexylbenzene: 78.0% versus 70.8% for catalyst A. (ExxonMobil Chemical Patents [Houston]. US Patent 7,910,779, March 22, 2011; Jeffrey S. Plotkin)