To produce ethylene oxide (EO) and ethylene glycols (EGs) from ethanol by dehydration to ethylene and using oxygen as the oxidizing agent.
Modern EO/EG plants are highly integrated units where EO produced in the EO reaction system can be recovered as glycols (MEG, DEG and TEG) with a co-product of purified EO, if desired. Process integration allows for significant utilities savings as well as the recovery of bleed streams as high-grade product, which would otherwise be recovered as a lesser grade product. The integrated plant recovers all MEG as fibergrade quality product and EO product as low-aldehyde product. The total recovery of the EO from the reaction system is 99.7% with only a small loss as heavy glycol residue.
A heated mixture of ethanol vapor and steam is fed to an adiabatic dehydration reactor (1). The steam provides heat for the endothermic reaction and pushes the reaction to 99+% conversion of ethanol with 99+% selectivity to ethylene. Recovered H2O is stripped of light ends (2) and recycled as process steam. Product ethylene is compressed and put through a water wash (3) before passing to the ethylene oxide reactor section.
Ethylene and oxygen, in a dilute gas mixture of mainly methane or nitrogen, along with carbon dioxide (CO2) and argon, are fed to a tubular catalytic reactor (4). The reaction heat is removed by generating steam on the shell side of the reactor while the reaction temperature is controlled by adjusting the pressure of the steam. The EO produced is removed from the excess gas by scrubbing with water (5) after heat exchange with the reactor feed gas.
Byproduct CO2 is removed from the scrubbed gas (6, 7) before the recovered reaction gas is recompressed and returned to the reactor loop, along with the fresh ethylene and oxygen, which are controlled to achieve the desired concentrations in the EO reactor inlet gas.
The EO is steam stripped (8) from the scrubbing solution and recovered as a concentrated water solution (9) that is suitable as feed to a glycol plant (11) or to an EO purification system (10). The stripped water is cooled and returned to the scrubbing column.
The glycol plant feed, along with any high-aldehyde EO bleeds from the EO purification section, are sent to the glycol reactor (12). A multieffect evaporator train (13, 14, 15) is used to remove the bulk of the water from the glycols. The glycols are then dried (16) and sent to the glycol distillation train (17, 18, 19) where the MEG, DEG and TEG products are recovered and purified.
Product quality: The SD process has set the industry standard for fibergrade quality MEG. When EO is produced as a co-product, it meets the low-aldehyde specification requirement of 10-ppm maximum, which is required for EO derivative units.
Yield: The ethanol-to-glycols yield is 0.95 kg of total glycols per kg of ethanol (190 proof; 95 wt% ethanol). The ethanol yield for EO production is 0.68 kg of EO per kg of ethanol.
Licensor: Scientific Design Co., Inc.