What to do if the pressure in the MTBE catalytic distillation tower is high?
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Dear colleagues, experts, and professionals: The MTBE unit in my plant has been in operation for four years, and it is scheduled to undergo maintenance this year. With the hot weather of summer, the pressure in the catalytic distillation tower is increasing day by day; it has risen from an initial level of 0.6 MPa to 0.8 MPa at present, and there is a tendency for it to continue rising. Currently, the feed rate remains stable at 15 t/h; I recall that it was 17 t/h in the year before last, and the pressure never exceeded 0.7 Mpa. It seems that the alcohol-to-olefin ratio is being used more and more frequently in operations. The methanol content in the reaction products, as well as that in the tetrahydrocarbon products after etherification, is around 4%, compared to around 3% before. The reason for increasing the alcohol-to-olefin ratio is that a low amount of methanol in the reaction products leads to a separation in the temperatures of the sensitive plates in the catalytic distillation tower; as a result, the MTBE product contains butane, failing to meet the required 99% quality standard. Another change is that the isobutylene content in the raw material used was previously over 15%, while it is now only 12%. The cooler of the catalytic distillation tower had to be shut down urgently for cleaning due to severe scaling. Initially, after the cleaning, the situation was fairly good with low tower pressure; however, one month later the pressure has remained high. A new pump was installed in the circulating water system, but this also did not yield significant improvements. The return water temperature is around 37 degrees. I was wondering if it’s due to the poor separation efficiency of the catalytic distillation tower over time, and how can the root cause be addressed?
This post was last edited by B0SS on 2016-7-28 at 17:58. I’m seeking help from experts to resolve this issue
Based on what you’ve said, the return temperature of the circulating water is also within normal ranges. What are the specific criteria for controlling the alcohol-to-olefin ratio? Excessive control of this ratio can lead to high tower pressure. What does it mean to separate the temperatures of the sensitive plates? The main reasons for high tower pressure depend on the feed composition, feed condition, and whether there is a large amount of non-condensable gas at the top of the tower.
Now the tower pressure is high, the temperature at the top of the tower is also high, and the cooling effect of the cooler is not satisfactory – it’s a vicious cycle. The alcohol-to-olefin ratio was around 1.2 when operations started, but now efforts to increase the conversion rate have led to a ratio of over 1.4. If the alcohol-to-olefin ratio is reduced, the temperature in the lower section of the tower will be several dozen degrees lower at the three points above the tower bottom, even when the temperature at the tower bottom remains normal. As a result, carbon four and carbon five compounds end up in the product, making it unsuitable for use. Additionally, non-condensable gases are released from the top of the reflux tank, but this has little effect
The percentage of isobutylene in the raw materials is between 12 and 13; the total amount of carbon dioxide and carbon trioxide is less than 1. The reactions in the reactor seem to be proceeding normally, but the pressure in the catalytic distillation tower appears to be quite high
Check whether the pressure, temperature, and flow rate of the circulating water are normal.
Pursuing a high conversion rate does not mean simply increasing the alcohol-to-olefin ratio; it’s likely that your current situation is caused by an excessively high alcohol-to-olefin ratio
But now the alcohol-to-olefin ratio is low, and the temperature distribution inside the tower is very abnormal; as a result, the separation efficiency of the tower is poor, and butane ends up in the MTBE
These are all normal; it’s just that the temperature inside the tower is abnormal, as is the pressure
Is there a problem with the gas-liquid phase distribution?