April 1, 2013
Make byproduct-free monoethylene glycol in one reactor. The conventional process for producing monoethylene glycol (MEG) is the noncatalytic hydration of ethylene oxide (EO). This process typically makes MEG with ≈90% selectivity. The byproducts are diethylene glycol (DEG, ≈9% selectivity) and triethylene glycol (TEG, ≈1% selectivity). This mix of products can be good or bad, depending on the producer’s situation.
For example, because of the high cost of ethylene in Western Europe, a producer there may want to make the byproducts because they have value as specialty chemicals. In contrast, a Middle Eastern producer, with low-cost ethylene, may not want to deal with the small-volume DEG and TEG markets and would choose a method that does not make DEG and TEG.
About 5 years ago, Shell Chemical developed the OMEGA process, which converts EO to MEG with 100% selectivity. The Shell route is based on the initial conversion of EO to ethylene carbonate (EC) via its reaction with CO2. In a second reactor, EC is hydrolyzed to MEG in 100% yield. The released CO2 is recycled to the first reactor.
This method improves the MEG yield but increases capital expense because two reactors are needed. H. J. van Milligen and P. Veenstra disclose a one-reactor version of this process.
The inventors used computer simulations to obtain their examples. The simulated reactor is subdivided by baffles into several continuously stirred tank reactor (CSTR) zones. The vapor phases from the last three CSTRs were combined with makeup CO2 and fed to the first CSTR. Vapor from the third CSTR was vented.
All of the reactors were operated at 2.0 MPa (gauge). The reaction temperature was increased stepwise from 100 °C in the first CSTR to 150 °C in the last one. The carboxylation and hydrolysis catalysts were KI and K2MoO4, respectively.
EO, makeup CO2, water, carboxylation catalyst, and hydrolysis catalyst were fed to the first CSTR in a 1.0:0.5:1.8:0.014:0.0029 mol ratio. No more water or catalyst was added to any of the reactors. Selectivity to MEG was 99.2%. EO losses through the vent amounted to 1.6% of the total EO feed. (Shell Oil [Houston]. US Patent 8,329,959, Dec. 11, 2012; Jeffrey S. Plotkin)