APPLICATIONThe Badger/Niro Para-xylene Crystallization processrecovers high-purity para-xylene from aromaticsstreams. This technology is particularly attractive whenthe feed has over 70% para-xylene. Such concentratedstreams are available from UOPs PX-PlusTM process,which selectively disproportionates toluene to para-xylene and benzene. Similar concentrated para-xylenestreams can be generated from the HySorbTM process,which involves adsorptive concentration of para-xylene.With such feeds, this para-xylene crystallization tech-nology achieves 99.9+% product purity, with highrecovery and lower consumption of utilities than anycompeting process.

In xylenes streams from naphtha reformers, isomer-ization units, and other equilibrium-limited processes,the para-xylene content of the C8 aromatics is typicallynear 22%. In a new grassroots facility operating onthese traditional feeds, adsorption by UOPs ParexTM

process is typically chosen over crystallization forrecovering para-xylene because, for this low-purityfeed, crystallization is limited to a recovery of about60%, while the Parex process can achieve 99.9% purityat 97% recovery per pass.

With feed para-xylene concentrations of 70% or more,recoveries above 95% become possible with crystalliza-tion. With these higher concentration para-xylenefeeds, high recoveries can be achieved using a singlerefrigerant compressor system, thus avoiding the needfor expensive cascaded-refrigerant systems using twocompressors and two refrigerants.

When PX-Plus processing is used, Badger/Niro crystal-lization is typically the most economical way to makethe final purification of the para-xylene. The integrateddesign of these UOP and Badger/Niro technologies iscurrently available for license as the PX-Plus XPTM

process. The Badger/Niro Para-xylene Crystallizationand PX-Plus processes can also be integrated into an

existing aromatics complex using a number of differentflow schemes. One example is shown above.

Because the Badger/Niro technology is based on con-tinuous suspension crystallizers, like all traditionalpara-xylene crystallization installations, it can be usedto revamp traditional units. The unit can be revampedfor higher product purity and increased throughput withconventional feedstock purity, or for very largeincreases in capacity with the higher concentrationpara-xylene feedstocks available when combined withan adsorption or PX-Plus unit. Another revamp scenarioinvolves lowering an existing Parex units productpurity in conjunction with increasing throughput, androuting this lower purity product to a new Badger/Nirocrystallization unit. The best alternative is determinedby the specific project objectives and the limitationsinvolved with the existing installation.

PROCESS DESCRIPTIONThe process designs for Badger/Niro Para-xyleneCrystallization units are based on the use of vertical-vessel, scraped-surface crystallizers, and wash columns.The simplest form of this technology is shown in theflow scheme on the following page. The crystallizerscreate a slurry of high-purity para-xylene crystals in amother liquor. This slurry is fed to Niro wash columnswhere the crystals are separated from the mother liquor,and melted for the final product.

BADGER/NIRO PARA-XYLENECRYSTALLIZATION PROCESS

AROMATICS AND DERIVATIVES

PX-Plus Fractionation Badger/NiroCrystallization

Parex

Isomar

Toluene Benzene

para-Xylene

Mixed Xylenes

PX-Plus Process with Badger/Niro Crystallization

Inside the wash col-umn, the crystals aremechanically pushedupward, and themother liquor iswashed away coun-tercurrently from thecrystals with product-purity para-xyleneflowing downward.

This wash para-xylene is recovered because it freezes asit heats the crystals up to the melting point of pure para-xylene. The crystals enter the top head and are fluidizedby circulating product-purity para-xylene liquid. Theresulting slurry leaves the wash column and enters a heatexchanger where the crystals are melted. The net productpara-xylene is split off, and the rest of the melt is recircu-lated back to the top head of the wash column for thefluidization of more crystals. Because the crystal washingis countercurrent, the washing is very complete, and thus,the product purity is very high. With the wash recoveredinternally, there are no processing costs for wash recoveryas there are with either centrifuges or filters.

In all forms of this technology, the consumption of utili-ties is minimal because the para-xylene is crystallizedonly once, there is effective heat integration, and washrecovery is done without additional refrigeration or otherutilities. The optimal implementation of this technologydepends on the feed purity, para-xylene recovery, andthroughput objectives of the project.

ECONOMICSAn existing Parex-based aromatics complex was evaluatedwith the objec-tive of increas-ing thepara-xyleneproduction by65% whilemaintainingoverall para-xylene productpurity at 99.8%.The increased

2001 UOP LLC. All rights reserved.This information is not to be taken as a warranty or representation for which UOPassumes legal responsibility nor as permission or recommendation to practice anypatented invention without a license. It is offered solely for your consideration.

uopTM

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UOP 2699C-18a 0201AD1Q

production was achieved with the addition of a PX-PlusXP process scheme and replacement of the existing ben-zene and toluene columns. The simple return on investmentfor the expansion was calculated to be an attractive 63%.

A summary of the investment cost and utility requirementsfor a typical Badger/Niro Para-Xylene Crystallizationunit is given below. The basis for this design is 400,000MTA of para-xylene product from a 90% para-xylenefeed at 93.5% recovery. The product purity is 99.9+%,and the purity of the mother liquor stream is 37% para-xylene. The estimated inside battery limits erected cost forthe unit assumes construction on a US Gulf Coast site inthe fourth quarter 2000.

EEC, ISBL US$ MM 20.4 (including refrigerant inventory)

Utilities, per MT PX productElectric, kWh 49LP Steam, kg 75

The steam can be at any pressure above atmospheric, so it can often be supplied by low-level waste heat.

EXPERIENCEThe Badger Technology Center of Washington GroupInternational and Niro Process Technology combinedtheir crystallization and wash column technologies in1993 with the formation of an alliance. Since that time,five design packages have been sold for para-xylenepurification. The first commercial unit started up in mid-1999.

UOP now offers the Badger/Niro technology for installa-tion in series with PX-Plus or HySorb processes, as wellas for crystallization or Parex-unit-based aromatics com-plex revamps.

FOR MORE INFORMATIONFor more information, contact your UOP representative orUOP at:

Phone: 847-391-2000Fax: 847-391-2253

Feed M

M

Crystallization

Refrigerant

MotherLiquor

Wash ColumnPurification

para-Xylene

M

Melter

Process Flow Scheme

Parex

XyleneSplitter

Isomar

Carom/Sulfolane

ReformateSplitter

BenzeneColumn

TolueneColumn

Raffinate

Benzene

Toluene

para-Xylene

Light Ends

DeheptanizerColumn

A9+ Byproduct

Aromatics Complex