Why is water injection required in the SED aromatic extraction process?
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In the SED aromatic extraction process, why is it necessary to maintain a certain level in the non-aromatic distillation reflux tank and the solvent recovery reflux tank? Why is it necessary to add water from the outside when there isn’t enough water? Does water play any other roles in extractive distillation beyond reducing the solvent partial pressure in the solvent regeneration tower to improve the stripping efficiency?
The purpose of adding water is to maintain a certain water content in the solvent, which helps improve the selectivity of the solvent and facilitates the separation of aromatics from non-aromatics. Water also acts as a cosolvent. Maintaining a certain liquid level ensures stable water content in the solvent, which is beneficial for the separation of aromatics in the extraction system.
Adding a small amount of water to sulfolane not only improves the selectivity for aromatics but also lowers its melting point. Pure sulfolane has a melting point of about 28°C and freezes quite easily. As the water content increases, the melting point drops rapidly. The water content in commercially available sulfolane is generally 2–3%, with a corresponding melting point of 13–10°C. During operation, the water content in the solvent-rich phase of the system is 0.5–1.0%, with a corresponding melting point of 20–15°C; therefore, in seasons with lower temperatures, it is necessary to ensure that heating systems are activated to prevent the solvent from freezing and blocking the system.
The lower the water content in the solvent, the greater its ability to dissolve hydrocarbons, which helps to avoid the formation of two liquid phases. However, maintaining a water content of 0.5–1.0% is necessary to effectively reduce the temperature at the bottom of the solvent recovery tower, and it also contributes to improving the selectivity of the solvent.
1# weifuwang2008 May I ask the original poster where the injection point is? Could you provide a detailed explanation? Our extraction distillation tower is not filled with water. The product prices fluctuate greatly.
The water injection point is located at the inlet of the pump for the recovery tank in the solvent recovery system; during normal operation, when the liquid levels in the water pack of the recovery tank and that of the non-aromatic distillation recovery tank drop, demineralized water can be added as needed.
The entrained solvent must be washed off; otherwise, there will be significant solvent loss: the levels of solvent in both non-aromatic and aromatic compounds are above the acceptable limits. It shows that the tower was not divided well earlier.
After passing through the regeneration tower, it becomes steam and enters at the bottom of the recycler heater, thereby reducing the partial pressure. 2. It acts as a stirrer, reducing the residence time of the solvent on the surface of the heater tubes and thereby minimizing high-temperature decomposition of the solvent.
The main goal is to improve solvent selectivity; our facility also adds water, using a dedicated water pump to inject desalinated water.
May I ask the original poster: For an aromatic hydrocarbon extraction unit that separates only benzene, with a capacity of 60,000 tons per year for mixed aromatics and a benzene content of 6%, what is the approximate investment required? What separation processes and solvents would be suitable? Thank you! !
The extraction water injection should be the SED device from the Institute of Rock Mechanics. Deoxygenated water should be used. Prevent oxygen from entering the solvent. Depending on the process, the circulation rate of the stripping water accounts for less than 2% of the solvent circulation rate. The water content in the poor solvent is below 1%. The purposes of water injection were all correctly stated by those upstairs. I am a technical specialist in extraction production, so we can exchange more ideas.