Principle of dehydration in the C4 light-end removal column after MTBE etherification
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The carbon tetrahydrocarbon composition of our company’s product is similar to that of the carbon tetrahydrocarbon phase after MTBE etherification (the difference being the presence of isobutylene). After washing, it enters a dehydration tower (with a top pressure of 0.64 Mpa and a bottom temperature of 86 degrees Celsius). The water content in the feed to the tower is 400 PPm, and there is no significant reduction in the water content at the tower bottom; this suggests a problem with the phase separator at the bottom of the tower. The principle of dehydration is said to be based on the azeotropy between water and tetrahydrofuran; those who are familiar with this process could please provide some explanation. Thank you
Trace water is a light component in C4; after it becomes concentrated at the tower top, it becomes supersaturated and forms free water, which is then discharged from the reflux tank along with the aqueous phase. Was the reflux tank drained in a timely manner? Is the tower top at full reflux? Is there any material being extracted from the top of the tower? Please explain in detail.
The reflux tank is essentially the feed dehydration tank; the water level in it is continuously drained, so there is no significant increase in the water level. There is a non-condensable gas vent valve on the top of the tank, designed to be used during startup, and it remains open at all times to stabilize the tower pressure.
We conducted a comparison with a unit at our factory that has a similar number of columns; the temperature at the bottom of your column is a bit high, while the pressure is low. If there is no non-condensable gas in the system, try turning off the vent valve of the reflux tank.
I’m not sure what the composition of your raw materials is, and what are the results of the tower top analysis? Just by looking at your reboiler temperature and tower pressure, it seems that the reflux ratio and steam volume are too high. In our case, the tower pressure is 0.69 Mpa, the reboiler temperature is 69°C, and the reflux ratio is 150:1. Isobutane accounts for 15% of the feedstock entering the tower. I suggest you increase the tower pressure first and see.
In my opinion, it’s due to an overload in the gas-liquid phase of the tower; with a bottom temperature of over 80 degrees and a vaporization rate of 0.64 kilograms, too much heat is absorbed during reflux, which makes it easy for the conditions at the bottom of the tank to become unsuitable. I’m not sure by how much the water level exceeds the standard