Reformation extraction
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Recently, the non-aromatic content in the benzene product from my benzene column has been high, and the replacement of stripped benzene still fails to meet specifications. Is this because the boiling points of C6 non-aromatics and benzene are very close?
Perform a compositional analysis on the non-aromatic components; based on the analysis results, just look up the physicochemical properties of those compositions to find out. The importance and necessity of analyzing chemical enterprises can be seen from problem identification.
Analyze whether it is light non-aromatic or heavy non-aromatic Light non-aromatics are a problem related to the extraction process, while heavy non-aromatics result from poor reactions; there is also a possibility of carryover.
A PONS analysis was conducted, and the composition of the benzene extracted from the top of the column was almost identical to that of the benzene obtained from the side stream of the 6-layer tray column. Can it be inferred that there is a problem in the rectification section of the benzene column?
Check whether the extraction efficiency is poor. Is there a stripping tower? If so, what is the efficiency of stripping?
Compared to normal operating conditions of the product, it’s necessary to check whether there are any changes in the aromatic content of the extracted feedstock, whether the temperature at the sensitive plate in the extraction tower fluctuates, as well as parameters such as the solvent ratio and the feed temperature of the lean solvent. All these factors must be examined one by one
Benzene products contain non-aromatic compounds, and it is not possible to replace them through stripping. Based on the experience from my workshop, this is due to insufficient bottom temperature in the stripper; as a result, all of the non-aromatic compounds cannot be stripped up to the top tank, which leads to non-aromatic hydrocarbons being present in the feed to the recovery tower. Another possibility is that the temperature at the top of the water stripping tower is low, preventing all of the non-aromatic compounds in the wash water from being stripped and entering the recovery tower. (The process may vary.)
According to the original poster, your unit likely employs liquid-liquid extraction rather than extractive distillation. The main reason is that in terms of extraction efficiency, the recovery rate takes precedence over purity. It is recommended to allow a slightly higher proportion of benzene to be fed into the raffinate oil during the extraction stage. Additionally, water removal should be enhanced prior to the benzene purification stage; meanwhile, the temperature range for side-drawing in the benzene distillation stage should initially be set narrowly and then gradually widened based on the desired purity level.