Catalytic Oxidative Dehydration of Butanol Isomers: 1-Butanol, 2-Butanol and Isobutanol

The catalytic production of economically important four-carbon olefins was achieved through catalytic oxidative dehydration of 1-butanol, 2-butanol, and isobutanol using a millisecond contact time reactor.  Both alumina foam and rhodium-alumina foam catalysts convert these four-carbon alcohols into four-carbon olefins, with contact time equal to 25 ms over a wide range of equivalence ratios (f) from 0.176 to  6.338 (or C/O_air ratio from 0.0659 to 2.11) . The cracking of the carbon backbone was found to be minimal.   A mixture of butene isomers was obtained due to the isomerization of the carbocation intermediates.  The degree of this isomerization was determined by analyzing the ratios of butenes/(total olefins), 1-butene/2-butene, cis-2-butene/trans-2-butene, and isobutene/(linear butenes).  In addition, a reaction mechanism of the catalytic oxidative dehydration of butanol in short contact times was proposed.  In this mechanism, the C-O bond of the majority of butanol was broken to form olefinic species on the alumina surface.  These surface olefinic species would undergo successive oxidation to form CO and/or CO₂, depending on the availability of oxygen.