June 24, 2013
C1 chemistry leads to acetic acid–derived ethanol. C1 chemistry is undergoing something of a renaissance. In the United States, the availability of inexpensive natural gas is spurring this interest; in China, the driving force is easy access to low-cost coal.
Gas is converted to synthesis gas (syngas) by reforming; syngas is made from coal by gasification. Syngas can be used to make chemicals or fuels, including methanol. The second-largest use of methanol is the manufacture of acetic acid. Methanol is carbonylated to give acetic acid in >99% yield; thus acetic acid is based 100% on C1 chemistry.
V. J. Johnson and colleagues at Celanese, the world’s largest producer of acetic acid, extended the range of chemicals and fuels produced via C1 chemistry. The inventors found catalysts and operating conditions that promote the hydrogenolysis of acetic acid to ethanol in good yields. Ethanol is conventionally made by hydrating ethylene or by fermenting sugar or starch.
In one of the patent’s examples, the catalyst was 10 wt% cobalt and 1 wt% palladium on graphite. The catalyst (50 mL) was added to a tubular reactor with a 30-mm i.d. The feed liquid (predominantly HOAc) was vaporized and charged to the reactor with hydrogen in helium carrier gas. The average gaseous hourly space velocity was ≈2500 h–1, the temperature 250 °C, and the pressure 22 bar. The resulting feed stream consisted of ≈4.4–13.8 mol% HOAc and ≈14–77 mol% hydrogen.
HOAc conversion was 18.5%, and selectivity to EtOH was 97.5%. In a similar experiment, with silica as the catalyst support instead of graphite, HOAc conversion was 71% with 96% selectivity. (Celanese International [Dallas]. US Patent 8,450,535, May 28, 2013; Jeffrey S. Plotkin)
[See next week’s Patent Watch for another example of products made by C1 chemistry.—Ed.]
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