April 2, 2012
Use olefin metathesis to make neohexene from isobutylene. Manufacturers are giving a great deal of attention to methods for producing propylene that use olefin interconversion technologies, such as olefin metathesis and olefin cracking. Phillips first used olefin metathesis commercially in the mid-1960s to convert propylene to ethylene and butenes. Now, however, many companies are carrying out the reverse process by combining ethylene and butenes to make propylene. This procedure is becoming increasingly important as propylene prices continue to rise. Manufacturers are developing other olefin metathesis processes for converting low-value olefins to higher-value olefins.
Many years ago, Phillips invented a two-step route to neohexene (3,3-dimethyl-1-butene, in which isobutylene was dimerized to diisobutylene, and diisobutylene was metathesized with ethylene. The fragrance industry uses neohexene as an intermediate in musk manufacture. Neohexene is also of interest as a gasoline blending stock because it has a research octane number of almost 112.
J. M. Basset and co-inventors disclose a new catalyst system that can convert isobutylene to neohexene in one step. The catalyst is made by grafting tungsten hydride onto an alumina support. In an example, isobutylene is fed to a reactor that contains 500 mg tungsten hydride alumina catalyst at a rate of 1.52 mol/(mol W·min), a temperature of 150 °C, and a pressure of 0.1 MPa. Isobutylene conversion is initially 40%, but after 5 h, the conversion rate stabilizes at 10%. The selectivity to neohexene is 21%. The process produces significant amounts of neohexene isomers 2,3-dimethyl-1-butene (33%) and 2,3-dimethyl-2-butene (8%), but the inventors state that these compounds and unreacted isobutylene can be separated and recycled to the reactor. (BP Oil International [Middlesex, UK]. US Patent 8,119,852, Feb. 21, 2012; Jeffrey S. Plotkin)