May 20, 2013
Oxidative dehydrogenation is the key to butadiene production. The sudden availability of inexpensive ethane from shale gas is reinvigorating the US petrochemical industry. The switch to ethane as a steam-cracker feedstock, however, has a downside. As more US ethylene plants take advantage of low ethane prices, smaller amounts of propylene and butadiene are coproduced.
For propylene, the supply gap is closed by propylene production from fluid catalytic cracking units in refineries. In addition, numerous “on-purpose” propylene technologies have been developed and commercialized over the past 10 years.
Refineries, however, are not a potential supply source for butadiene, so manufacturers are contemplating on-purpose butadiene technology. Dehydrogenation of butane and butane has been used (and is still used in very small plants in Russia) to make butadiene. A key challenge to this strategy is that this reaction is equilibrium-controlled, and butane and butene conversions per pass are relatively low. One way around this limitation is to use oxidative dehydrogenation.
C. Shin and co-inventors developed catalysts for oxidatively dehydrogenating 1-butene with excellent conversion and selectivity. The catalysts are based on bismuth, molybdenum, and iron (BMF) oxides. In the patent’s examples, 1-butene is oxidatively dehydrogenated in a stainless steel pipe reactor at atmospheric pressure.
In one example, 0.5 g BMF oxide catalyst (1.0:1.0:0.75 Bi/Mo/Fe mol ratio) is added to the reactor and activated at 450 °C under nitrogen and oxygen for 2 h. 1-Butene, air, and water (1.0:3.75:5.0 mol ratio) are mixed and passed over the catalyst at a weight-hourly space velocity of 2.4 h–1 at 420 °C. 1-Butene conversion is 75.5% after 400 min. Butadiene selectivity is 95.9%, for an overall yield of 72.4%.
In a comparative experiment, the same catalyst without iron gave good selectivity to butadiene but only 37.4% 1-butene conversion. In another experiment, a BMF (1.0:1:0:0.65) catalyst was tested for deactivation. This catalyst deactivated very little over a 120-h reaction time. (Korea Kumho Petrochemical [Seoul]. US Patent 8,420,878, April 16, 2013; Jeffrey S. Plotkin)