Published January 1975
Shortages of conventional feedstocks for the production of ethylene, together with their increasing costs encourage the investigation of alternative sources of this olefin and its derivatives. In this connection, a Union Carbide patent covers a one-step method of making ethylene glycol from CO and H2 synthesis gas. On the basis of the somewhat fragmentary process information in this patent, a very rough study of the economic potentialities of such an operation has been attempted. The results indicate that the process may prove to be quite attractive.
The Union Carbide patent covers use of a complex rhodium catalyst (such as rhodium dicarbonyl acetylacetonate complexed with 2-hydroxypyridine or pyrocatechol) and a reaction diluent such as tetrahydrofuran. Preferred reaction conditions are stated to be: 160 to 300 C, 150 to 405 bars pressure, 1:5 to 5:1 molal ratio of H2 to CO in the synthesis gas fed, and a rhodium contnent of 0.00001 to o.1 wt% in the total reaction mixture. The required liquid residence time depends on the reaction conditions used; it can range from 2 to 48 hours.
The principal reaction products are polyols (mostly ethlene glycol, with smaller amounts of propylene glycol and glycerine). These may total from 60 to over 90 wt% of the oxygenated liquid reaction products. Other products formed included methanol, methyl formate, ethanol, and water. Methane and formaldehye are essentially absent.