p-Xylene
| 원료 | Feed | ||||||||||||
| 생산물 | p-Xylene | ||||||||||||
| 적용 | A process for the recovery of the highest purity paraxylene commercially available by crystallization from mixed xylenes. | ||||||||||||
| 설명 | Description: In the two-stage crystallization process, xylenes are cooled by exchange and then charged to the firststage crystallization, which consists of one crystallizer operating at - 40° to - 50° followed by a second crystallizer operated at - 55° to - 70℃. Filtrate from the second stage joins the fresh xylenes going to the first-stage crystallization. The crystallizers are cooled by external refrigeration employing ethylene refrigerant. The final first-stage crystallizer operates within a few degrees of the eutectic temperature of the theoretical maximum. The first-stage crystal slurry flows to a continuous centrifuge where crystals of 85-90% paraxylene are removed from the filtrate. First-stage filtrate is exchanged against feed and then leaves the unit for sale as xylenes or as feed for xylene isomerization unit. The first-stage crystals are melted and then charged to a single second-stage crystallizer, which operates at - 20° to 0℃ depending on the feedstock and desired purity. The crystallizer is cooled externally with propane refrigerant. The crystal slurry flows from the crystallizer to a secondstage continuous centrifuge which separates crystals from liquid. The liquid filtrate, which is fairly high in paraxylene content, is recycled to the first stage. The crystals are washed with toluene in the centrifuge and melted. The paraxylene stream is then fed to a paraxylene-toluene wash and high purity paraxylene is taken as bottoms product. The paraxylene crystallization process is usually employed in conjunction with a xylene isomerization process such as Octafining. Paraxylene is removed from the crystallization feedstock (a mixture of fresh C8 aromatics plus recycle) and the paraxylene-depleted C8 aromatics from crystallization are charged to isomerization where C8 aromatics equilibrium is re-established. Yields: Over 90% of theoretical yield. Utilities (per metric ton 99.5% purity paraxylene):
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| Properties in KDB |
Component Names and Formula
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