Patent Watch

June 15, 2009 [Repeated from 12/22/08]

Alkylating benzene with 2-butene boosts phenol prospects. Almost 98% 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, followed by air oxidation to form cumene hydroperoxide (CHP). Concentrated CHP is cleaved to yield coproducts phenol and acetone, which are further purified in a downstream fractionation section.

This kind of technology is called a "two-for-one" process. These processes are generally considered to be low-cost routes, but the market demand for both products must 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 manufacturing polycarbonate. (Bisphenol A requires 2 equiv of phenol for every 1 equiv of acetone.) Thus, to keep up with phenol demand too much acetone would be produced, causing the price of acetone to decline. Declining acetone prices will penalize phenol costs because acetone is taken as a byproduct credit.

To overcome this problem, 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 (SBB) to give phenol with acetone and methyl ethyl ketone (MEK) as byproducts. SBB can be made by alkylating benzene with n-butenes. However, very little information is reported in the literature about using solid catalysts to perform this alkylation. Solid catalysts are routinely used in the production of cumene from benzene and propylene.

J. M. Dakka and colleagues at ExxonMobil Chemical disclose solid catalysts capable of alkylating benzene with 2-butene in good selectivity. For example, a 1.0-g sample of MCM-22 catalyst is loaded into a downflow fixed-bed tubular reactor. The catalyst is dried at 150 °C by flowing nitrogen over it for 2 h. Benzene flow is begun at 7.63 mL/h, and a 2-butene feed (57.1% cis-2-butene, 37.8% trans-2-butene, 2.5% n-butane, 0.8% isobutene–1-butene, and 1.8% others) is introduced at 2.57 mL/h. The benzene/butene mol ratio is maintained at 3:1 for the entire run, and the temperature is adjusted to 160 °C. After 3.8 days on stream, 2-butene conversion is 97.7% and selectivity to SBB is 89.2 wt%. The only other products made in >1% selectivity are dibutylbenzene (8.0 wt%) and tributylbenzene (1.2 wt%). (ExxonMobil Chemical [Fareham, U.K]. Eur. Patent 1984311, Oct. 29, 2008; Jeffrey S. Plotkin)

View patent information from CAS.

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