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AUTHORS have shown that soy-based biodiesel (a mixture of methyl esters derived from vegetable oils) can be oxidized to valuable olefins and olefinic esters efficiently and fairly selectively. The reaction is conducted in an autothermal catalytic reactor, in which heat is supplied by the exothermic oxidation reactions, not by external heaters.
To carry out the oxidation process, AUTHORS uses an automotive fuel injector to spray droplets of biodiesel, which consists of methyl oleate, methyl linoleate, and related compounds, onto the walls of the reactor where the droplets vaporize. A mixture of the organic material and air is then passed over a catalyst that contains a few percent of rhodium and cerium supported on alumina.
By adjusting the ratio of biodiesel to oxygen (C/O) in the feed stream, the team is able to control the oxidation process and reactor conditions, such as catalyst temperature, and thereby tune the product distribution. For example, at a C/O ratio of roughly 1.3, the reaction yields about 25% ethylene and smaller concentrations of propylene, 1-butene, and 1-pentene. In contrast, at a C/O ratio of 0.9, the product stream consists mainly of hydrogen and CO.
The team notes that C2 to C5 products consist almost exclusively of olefins, whereas longer chain products include olefins and olefinic esters. The researchers report that at all C/O ratios, the process yields less than 13% CO2 (an unwanted product). They add that the catalyst remains stable and resists deactivation by carbon buildup even under extreme conditions.
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