Crude benzene hydrogenation
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Dear experts: In the hydrogenation of crude benzene, we use sulfolane to extract aromatics and water to recover sulfolane. Does the amount of water used for sulfolane recovery affect the purity of pure benzene? Note: We have been using sulfolane for almost a year now; the water injection volume is around 7,000, the top temperature of the benzene tower is kept at around 85 degrees, and the temperature of the sensitivity plate is maintained at around 99.5 degrees. However, the purity of our pure benzene is only between 99.96% and 99.98%, falling short of the 99.99% target. The content of non-aromatic compounds in the 300BT product is only 0.01%. Why is this? In the past, we were able to keep these parameters under control, with the purity of pure benzene reaching 99.99%, but now that’s no longer possible. I recall that the poor extraction efficiency of sulfolane, along with inadequate recovery rates, were to blame. Is my analysis incorrect? Someone told me that the amount of water used in sulfolane treatment does not affect the purity of pure benzene!
What are the components of crude benzene? There are many reasons why the content does not meet the standards; it is recommended to have the laboratory analyze what kinds of impurities are present in order to determine the cause
The test results show the presence of non-aromatic compounds. Correction: The temperature at the top of the benzene tower is 95 degrees. Additionally, the temperature difference between the temperature of the tray layer measured at the tower top and that of the sensitive tray is 3.5–4.0 degrees
The results of the analysis cannot be trusted completely; there might be other impurities as well sometimes
1. It might be caused by an excessive accumulation of non-aromatics; you should have a top benzene extraction line to remove a small amount of it. 2. Analytical test error 3. High water content in the solvent
The amount of water injected does not affect the purity of pure benzene; however, if too much water is used, it may cause sulfolane to be carried away, leading to an excess level of toluene sulfide； It also increases the energy consumption for operating the recovery tower. If too little solvent is used, it will affect the quality of the poor solvent, which in turn affects the extraction efficiency. Reasons for the decrease in pure benzene purity: 1. Improper operation of the extraction tower. 2. The benzene taken out from the benzene tower contains too much non-aromatic content; it should be discharged into the raw material tank. 3. After being used for an extended period, the sulfolane’s extraction capacity declines, so it needs to be regenerated.
Reply to 1# supei*ong: 7000 units of what? ? ? If it’s in kg/h, then you’re pouring in too much water; it should be 700, right?
You were doing well before, so identify where the change occurred – were it the process parameters or the water injection volume? Is it still a raw material issue? Do I also need to check for changes in operations, etc.? Find a problem and the problem will be solved; actually, this could serve as an excellent QC topic! !
The extractant we use is NFM; we are still learning about sulfolane.
Reply to 9# ys362: What is the temperature of the NFM feed material at your facility? What is the benzene content in non-aromatic compounds, and what is the purity of pure benzene? Thank you. I’ve just started working with benzene hydrogenation; I’d appreciate some guidance
Reply to 3# supei*ong: The purity of pure benzene is insufficient; there are basically two possibilities: 1. Non-aromatic compounds are present in the pure benzene. 2. Toluene is present in pure benzene; it does not seem that the second scenario applies at present. Personally, I think the non-aromatic compounds are found in the tower top reflux. So, there are basically two possible explanations: 1. The extraction of non-aromatic compounds by sulfolane in the extraction tower is incomplete. 2. The non-aromatic content in the reflux at the top of the benzene tower increases. For item 2, the reflux tank can be drained. In both of the above cases, I believe the main reason is that sulfolane does not extract non-aromatic compounds thoroughly, which allows such compounds to enter the benzene column; this in turn leads to an increase in the amount of non-aromatic components in the overhead reflux, resulting in the presence of non-aromatic substances in pure benzene. It is recommended to start from the following aspects: 1. Increase the solvent ratio. 2. Take a sample of the solvent for analysis to determine whether there are any changes in its components and whether its extraction capacity has declined. 3. I’m not sure how your company recycles solvents – is it on a continuous basis or periodically? It is recommended to regenerate the solvent in small amounts on a continuous basis to maintain its effectiveness. The regeneration system regularly discharges solvent waste. 4. Slightly increase the temperature of the sensitive plate in the extraction tower to raise the benzene content in the non-aromatics. . The above items can be tested one by one. . The specific details aren’t very clear, but I hope this can help with your question.