Problems with MTBE decarboxylation step 5
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A refining-type MTBE plant has a catalytic distillation column. The carbon pentane content in the feed reached 2.3 wt%, and it is expected that the purity of the MTBE product will be very low. The current problem is how to remove this portion of C5 hydrocarbons (primarily isopentane). Option 1: Install a fifth-decarbonation column in the vapor separation unit to ensure that the content of pentane in the mixed C4 stream fed into MTBE meets the required standards. Option 2: After extracting the MTBE product from the bottom of the column, add another fifth-decarbonation column. Please discuss the advantages and disadvantages of these two options to determine which one is more feasible It would be even better if you have experience in actual production in this area. Because I am merely conducting simulated calculations and lack practical experience. There is one more thing that’s not clear; in my calculations, I found that the C5 components in MTBE can exit the tower along with C4 and methanol, which ensures that the purity of MTBE at the bottom of the tower is sufficient. Then why do many people say that the C5 compounds in the feed almost always end up in the MTBE at the bottom of the tower? Couldn’t they just be vaporized and removed? I hope everyone will be kind enough to share their advice. Thank you!
I’m a newcomer and don’t know much about this, but I’ve seen that in many plants, scheme one is used whenever carbon and pentane need to be removed; however, there are also quite a few plants that do not remove pentane. Some of the pentane reacts with methanol in the reactor, which affects purity
When the carbon pentane content in the feed gas for the gas phase process exceeds 2–3%, a carbon pentane removal tower is generally installed to meet the requirements regarding the carbon pentane level in liquefied gas for household use or vehicle use, as well as the requirements for subsequent separation of carbon tetrahydrocarbons. If the pentane content is not high, in order to save energy and reduce consumption, it may be possible to omit the pentane tower; some plants even shut down such towers. A high content of C5 compounds can affect the purity of MTBE; the temperature at the bottom of the tower and the catalyst also come under influence. If MTBE is used in blended gasoline, a slightly lower purity is not a problem. Since I am not an on-site staff member, I kindly ask the experts for their corrections.
This post was last edited by k68315404 on 2011-8-23 08:18. It’s the first method used in our factory. The average boiling point of C5 is around 35°C, while that of C4 is around 0°C; the difference between the two is approximately 35°C. During the separation of MTBE products, C5 does not flow out of the tower along with C4, but rather only from the bottom of the tower. The boiling point of C5 is lower than that of MTBE; therefore, C5 does not flow out smoothly from the bottom of the tower. A large amount of C5 must first accumulate in the retention section of the tower before it can be discharged from the bottom, and the sensitive temperature of the tower will be higher than usual.
If MTBE purity is required, it is advisable to install a decarbonization column in the gas separation unit; otherwise, C5 entering the MTBE unit will react with methanol to produce TAME, and this along with MTBE reaching the bottom of the column will affect the purity of MTBE
During the separation of MTBE products, C5 does not flow out from the top of the tower along with C4; it can only flow out from the bottom of the tower. The boiling point of C5 is lower than that of MTBE
Our company uses C5 columns for removal, which improves the purity of the MTBE feed right from the start.
When C5 and C4 enter the reaction tower together, TAME may be formed; its boiling point seems to be higher than that of MTBE, which affects the purity of MTBE. It was said on the 6th floor that C5 has a lower boiling point than MTBE; therefore, C5 will come out along with C4 and methanol, and won’t flow out from the bottom of the tower
It’s fine to produce TAME; the MTBE product at the bottom of the tower is used to blend with gasoline. What concerns me is the impact that C5 compounds might have on the etherification process. Some people say it could cause blockages in the catalyst pores, but isn’t the etherification of light gasoline also a form of C5 etherification? The suppliers of the MTBE production technology say that they add an additional tower to separate out the C5 compounds after the MTBE is produced. We are only responsible for the engineering aspects, so there’s not much more to say. I’m still a bit worried, though.
Recommended Option 2: If desorption is done first, the energy consumption will be too high. You can calculate it based on your own material flow rate
Regarding the choice of tower, if the C5 content in the raw material is not too high (1–2.5%), most of the C5 can be distilled out at the top of the tower; as a result, the purity of the MTBE product will not be too low, generally ranging from 94% to 97%, making it suitable for use in oil blending.