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Anteprima

ESTRATTO DOCUMENTO

A D

ROMATICS AND ERIVATIVES

P P

TM

AREX ROCESS

resins, and films. Para-xylene is converted to tereph-

A

PPLICATION thalic acid (TPA) or dimetheyl terephthalate (DMT),

UOP’s Parex process is an innovative adsorptive separa- which are then reacted with ethylene glycol to form

tion method for the recovery of para-xylene from polyethylene terephthalate (PET) which is the raw

mixed xylenes that offers high product purity, high material for most polyesters.

product recovery, high on-stream efficiency, and

extended adsorbent life. “Mixed xylenes” refers to a P D

ROCESS ESCRIPTION

aromatic isomers that includes ethyl ben-

mixture of C

8 The separation takes place in the adsorption chambers.

zene, para-xylene, meta-xylene, and ortho-xylene. Each adsorbent chamber is divided into a number of

These isomers boil so closely together that separating adsorbent beds. Each bed of adsorbent is supported

them by conventional distillation is not practical. The from below by specialized internals or grids, which are

Parex process provides an efficient means of recovering designed to produce highly efficient flow distribution.

para-xylene using a solid zeolitic adsorbent which is Each internals assembly is connected to the rotary valve

selective for para-xylene. Unlike conventional chro- by a bed line. The internals between each adsorbent bed

matography, the Parex process simulates the counter- are used to inject or withdraw liquid from the chamber

current flow of a liquid feed over a solid bed of while simultaneously collecting liquid from the bed

adsorbent. Feed and products enter and leave the adsorbent above and redistributing the liquid over the bed below.

bed continuously, at nearly constant compositions. This

technique is called simulating-moving-bed separation. A typical Parex unit has 24 adsorbent beds with 26 sets

of chamber internals, and 24 bed

In a modern aromatics complex, Parex Process lines connecting the beds to the

the Parex unit is located down- rotary valve. Due to practical con-

Concentrated

stream of the xylenes column De Extract

so Rotary

rb struction considerations, most

Extract

en Valve

and is integrated with an t Extract

Ext Parex units consist of two adsorp-

Column

rac t

unit. The feed to the

TM

Isomar Desorbent tion chambers in series with 12

xylenes column consists of the d

Fee beds each.

+ aromatics product from a

C e

t

na Concentrated

8 ffi Raffinate

Ra

unit and the

CCR Platforming

TM Raffinate In the Parex process, there are four

Adsorbent Raffinate

Chamber Column

xylenes produced in a Tatoray

TM Feed major streams that are distributed

Pumparound Pump

unit. The C fraction from the to the adsorbent chamber by the

8

overhead of the xylenes column rotary valve. These “net” streams include:

is fed to the Parex unit, where high-purity para-xylene 1. Feed in – mixed xylenes feed

is recovered in the extract. The Parex unit raffinate is 2. Dilute extract out – para-xylene product diluted

aromatic

sent to the Isomar unit, where the other C

8 with desorbent

isomers are converted into additional para-xylene and 3. Dilute raffinate out – ethyl benzene, meta- and

recycled back to the xylene column. The Parex process ortho-xylene diluted with desorbent

is designed to recover over 97 wt-% of the para-xylene 4. Desorbent in – recycle desorbent from the frac-

from the feed in a single pass while delivering product tionation section

purity of 99.9 wt-% or better. At any given time, only four of the bed lines are active,

The high purity para-xylene recovered in the Parex carrying the net streams into and out of the adsorbent

process is used for the production of polyester fibers, chamber. The rotary valve is used to periodically switch


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DETTAGLI
Corso di laurea: Corso di laurea in chimica industriale e tecnologie del packaging
SSD:
Università: Parma - Unipr
A.A.: 2007-2008

I contenuti di questa pagina costituiscono rielaborazioni personali del Publisher Atreyu di informazioni apprese con la frequenza delle lezioni di Chimica industriale II e studio autonomo di eventuali libri di riferimento in preparazione dell'esame finale o della tesi. Non devono intendersi come materiale ufficiale dell'università Parma - Unipr o del prof Moggi Pietro.

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