February 13, 2012
Make “green” butanol from bioderived ethanol. Biobutanol manufacture is currently being investigated by large energy companies and small biotech startups. These companies want to replace ethanol in gasoline with renewable 1-butanol. Ethanol is easily made from sugars, but it has drawbacks as an oxygenated blending component for gasoline:
- Ethanol is completely water-miscible. Solubility of water in a gasoline blending component is the last thing a refiner wants because any water in the additive causes gasoline storage tanks and pipelines to rust.
- Ethanol has only 70% of gasoline’s energy density.
- Ethanol’s high volatility can be a safety hazard.
Renewable butanol would be a better fuel oxygenate than ethanol on all three counts. Fermenting sugars to produce high yields of butanol, however, has proved difficult.
Inventors T. Tsuchida and S. Sakuma disclose a catalyst system that can couple two ethanol molecules to give relatively high yields of 1-butanol. To prepare their catalyst, they separately dissolve 225.2 g Ca(NO3)2 in 5 L water and 78.87 g (NH4)2HPO4 in 3 L water. Both solutions are added dropwise to aq NH3 at pH 9–11. The mixture is stirred for 1 day, and the precipitate is filtered, dried at 140 °C, and calcined in air at 600 °C for 2 h. The resulting powder has a Ca/P mol ratio of 1.64:1.
The catalyst powder is formed into 14–26 mesh size tablets, which are loaded into a fixed-bed reactor and dried at 500 °C under an Ar–He atmosphere. After this pretreatment, 16 vol% EtOH in the inert carrier gas is allowed to flow over the catalyst bed at 300 °C. The selectivity to 1-BuOH reaches its maximum value, 79.1%, at a contact time of 1.34 s and decreases at longer contact times. At the 1.34-s contact time, byproducts are hexanol (7.3%), octanol (0.8%), and decanol (0.2%). (Kabushiki Kaisha Sangi [Tokyo]. US Patent 8,080,695, Dec. 20, 2011; Jeffrey S. Plotkin)