In the last episode I gave a background of what my senior design project is about. It involves constructing and optimizing a Ethylene Oxide(EO) process unit. Today let’s get into a little more detail about this project, the parameters to optimize and what the general process is like. As you know, this is still a working process and it really interesting to get everything to work. See this post for some background
To start, ethylene and air enters from two separate pipelines at 25 degrees C and 30 bar. In fact, instead of air, the commercial process typically uses 99.5 wt% pure oxygen because it the costs less to run due to the fact that a air purification unit is not required; and upon speaking to our industry consultant, oxygen is readily available to us at the given conditions. It also has 0.5 wt% Argon, which is a inert gas so it doesn’t partake in the chemical reaction. Ethylene and Oxygen goes through a mixer first, which they get mixed together along with the recycled ethylene from later in the process. They’re then fed into a special unit called the Feed Effluent Heat Exchanger (FEHE). FEHE is a really cool unit because it is really efficient and does the job for a separator heater and cooler. Basically, the way FEHE works is that it takes in the cold feed, and uses the heat generated by the exothermic reaction to heat the feed up to the desired temperature, and send the feed into the reactor. The FEHE then cools the hot reaction effluent by using the cold feed. Since the limiting reagent in this reaction is oxygen, we’re going to get unreacted ethylene in the outlet stream, along with product EO, side reaction product CO2 and water, and inert Argon.
Remember the that reactions are C2H4 + 0.5 O2 → C2H4O desired, C2H4 + 3 O2 → 2CO2 + 2H2O undesired, and C2H4O + 2.5 O2 → 2CO2 + 2H2O undesired. A silver catalyst is used for the reaction. It’s the best to make as much EO as possible per pass, while limiting the two undesired reactions.
The reaction takes place in an isothermal reactor. It is Plug Flow Reactor as it is most suitable for gas reactions. The reactor is cooled by 100 degrees C steam constantly to maintain the reaction temperature at 24o degrees C., and it is our goal to determine the reactor sizes. The reactions products were then sent to a absorber and distillation column to obtain a EO purity of 99.5 wt%. Stay tuned for more details.