KAUST team seeks improved catalysts for Lebedev ethanol-to-butadiene process for renewable rubber
Butadiene, an essential component of synthetic rubber, is currently produced by the petrochemical industry from fossil reserves. Butadiene can also be produced from ethanol by one of two primary methods: Lebedev, which converts ethanol over one catalyst in one reactor, and Ostromisslensky, which converts a mixture of ethanol and acetaldehyde in a two-reactor system. A 2017 analysis by a Ukrainian/French team (Kyriienko et al.) suggested that the Lebedev method holds more potential than the Ostromisslensky.
The basic Lebedev process, developed in the 1930s, includes (1) acetaldehyde (AA) formation from ethanol (EtOH); (2) aldol condensation of AA to crotonaldehyde; (3) Meerwin-Ponndof-Verley (MPV) reduction of crotonaldehyde with ethanol to crotyl alcohol and AA; and (4) dehydration of crotyl alcohol to 1,3-butadiene. Selectivity of the process depends upon the nature, strength and amount of acidic and basic sites on the catalyst surface, according to Kyriienko et al.
The conventional Lebedev process is driven by silica-magnesia catalysts that are produced by an unusual method called wet kneading. The method involves combining solid catalyst precursors in water under continuous mixing. However, improved wet-kneaded catalysts have mainly been discovered by trial and error.
Now, researchers at KAUST, with colleagues in the Netherlands, are using solid-state nuclear magnetic resonance spectroscopy to study silica-magnesia catalyst formation under real wet-kneading conditions. A paper on their work appears in Nature Catalysis.
Crucially, they showed that magnesium silicates on the silica particles tend to produce ethylene as an undesired side product. With that understanding, the team could synthesize just the catalyst particles that are active for butadiene production and avoid the particles that produce ethylene, Chung said. The team also showed that the best catalysts also had certain active sites in very close proximity.
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