Innovations in p-Xylene Recovery

16 April Hotel Le Meridien New DelhiGTC Technology Day

C5

Aromatics

Extraction

Toluene

Conversion

Benzene C

olu

mn

Tolu

ene C

olu

mn

Xyle

ne C

olu

mn

Benzene

C6 -C7 raffinate

C9+

Paraxylene

Hydrotreated

Naphtha

Xylene

Isomerization

Catalytic

Reformer

C5

Xyle

ne C

olu

mn

C9+

Refo

rmate

Split

ter

Paraxylene

Recovery

Dehepta

niz

er

Paraxylene Recovery in an Aromatics Complex

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• Boiling points of C8 aromatic isomers are too close for distillation to be used

• Freezing points far enough apart to use crystallization

Boiling Point, °C

Ethylbenzene

Paraxylene

Metaxylene

Orthoxylene

136.0

138.3

139.1

144.3

Freezing Point, °C

-95.0

+13.2

-47.9

-25.2

C8 Aromatic Isomers - Separation Methods

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Suspension Crystallization (GTC’s CrystPX):

– Pure PX is crystallized from a solution of the C8 isomer mixture

– Solid crystals separated from remaining liquid (mother liquor) using centrifuges

– Continuous process

Static Melt Crystallization:

– Solutions containing C8 isomer mixture are repeatedly cooled and heated in tubes to

enrich PX to final purity

– Batch process

Types of PX Crystallization

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1957 first unit built2000 – GTC

partnership with Lyondell

2002 – largest-in-the-world centrifuges and

crystallizers; eliminated external

wash

2006 - Introduced unique slurry system,

(now 2 drums with single point of refrigeration)

Original Arco Process (now Lyondell) was identical in all

practical aspects to Amoco process (now BP)

GTC Partner with Lyondell for CrystPX

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2013 – Isom catalyst produces high purity

benzene at 99.9% without extraction; operates >

70% EB conversion

2014 – Advanced distillation systems to

greatly cut energy consumption in

fractionation sections

2015 – Enhanced mixing system and scraper design

for reduced equipment count

GTC - Leader in innovation

Continued technology advancement

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- 12 licensees, all awarded in competitive bidding

- 4 operational plants with reliable partners

GTC Licensing Experience

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Mixed Xylenes Feed

(from xylene column) CentrifugeCentrifuge

Refrig 1 Refrig 2

Crystallizer

First Stage

Crystallizer

Second Stage

Para-lean xylenes to

isomerization

Paraxylene Product

PX MELT

Wash

PX MELT

(recycle)

(Slurry)

(Slu

rry)

(Cake)

(Cake)

Traditional (1957 vintage) 2-Stage Process for PX Recovery From Dilute Feedstocks

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• Much larger and more reliable equipment:

– First generation process produced ~3,100 MTY / crystallizer

– Modern process produces >100,000 MTY / crystallizer

– Higher speed and more reliable crystallizer scraper system

• PX product washing instead of toluene/C5 wash

• Intermediate process stages via slurry drums to preserve the energy from the cold stage

(gaining an additional stage)

• Single point of refrigeration. No cooling required beyond the crystallizers

Improvements to Process

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Cold Stage

High Purity Paraxylene

Production StageIntermediate Stage

(Cake)

Centrifuge

Centrifuge

Refrig

Crystallizer

Cold Stage

Para-lean Xylenes to

Isomerization

Paraxylene

Product

PX MELT

PX Wash

(Cake)

(Cake)

(Slurry)

(Slurry)

(Slu

rry)

Centrifuge

Slurry

Drum

Slurry

Drum

Mixed Xylenes Feed (from

Xylene Column)

CrystPX Process for PX Recovery from Dilute Feedstocks

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Paraxylene

Product

Primary Centrifuge

High Purity Paraxylene Production Section Paraxylene Recovery Section

PX-lean

Filtrate

PX Melt

PX Wash

Feed

Drum

PX Rich Feed

Secondary

Centrifuge

(Cake)

(Cake)

(Slu

rry)

(Slurry)

(Slu

rry)

1- Stage CrystPX Process For PX Recovery From Enriched Feedstocks

GTC Technology Day

• As a mixture of xylenes is cooled, PX crystallization occurs when

the concentration of PX reaches the solubility of PX in the mother

liquor.

• PX crystals separate from solution and leave other xylenes in the

mother liquor. The crystals are nearly pure PX. As temperature

decreases, more and more crystals separate.

• As temperatures continue to decrease, a second component may

reach its solubility limit and begin to crystallize. This temperature is

the eutectic point. Paraxylene crystals under

microscope

How Does PX Crystallization Occur?

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• Crystallizers

• Scraped Surface, Jacketed

• Centrifuges

• Screen Bowl

• Pusher

Major Equipment

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Crystallizers

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Ice Formation with Scraping Action

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Mechanical Design

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Pusher Centrifuges

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Feeding, distribution & main

dewateringDischarge washing intermediate

dewateringFinal

dewatering

Wash liquid

SolidsFiltrate

100% liquid saturation level

Pusher Centrifuge Cross Section – Details

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Screen Bowl Centrifuge

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Screen Bowl Centrifuge

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Giant Xylene Column

Reformate Xylene

Feed

Para-lean xylenesDeC7 Column

Light Ends

C9+

Adsorption

Toluene

Extract

Raffinate

Desorbent

Desorbent

Finish

Column

Paraxylene

Product

Isomerization

Complicated simulated moving bed;

high risk of failing to meet PX purity

PX Separation Technology – Adsorption

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• Lower installed cost

• Equipment easily procured

• Feed preparation requirements are relaxed, and

insensitive to most common feed impurities

• Highest product purity

• Convenient to add incremental capacity

• No expensive adsorbent and desorbent required

• Simple concept for easy operation

• Lower per-pass recovery results in increased

recycle to Isomerization Unit.

Advantages Disadvantages

Advantages of 2-Stage Crystallization Compared to Adsorption Process

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• Fewer equipment pieces result in the lowest investment cost

• Less equipment leads to lower maintenance and production costs

• Stable operation with simple process controls; product quality maintained by paraxylene wash rate

• Highly efficient refrigeration system requires minimum cooling water consumption

• Turndown operation permissible; operating flexibility and simplicity

• Enriched feedstock results in high recovery

Advantages of 1- Stage Crystallization Process From Enriched Feedstocks

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• Crystallization units often mischaracterized as outdated; however, modern designs

offer:

– Higher equipment reliability and reduced maintenance requirements

– Larger-scale equipment and reduced equipment count

– Higher efficiency based on newer configurations and processing schemes

Crystallization Modern Designs

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C5

Aromatics

Extraction

Toluene

Conversion

Tolu

ene C

olu

mn

BenzeneC6 -C7 raffinate

C9+

Paraxylene

Hydrotreated

Naphtha

Xylene

Isomerization

Catalytic

Reformer

Xyle

ne C

olu

mn

C9+

Refo

rmate

Split

ter

Paraxylene

Recovery

Dehepta

niz

er

Benzene C

olu

mn

Xyle

ne C

olu

mn

PRU (Largest-in-the-world commercial size

equipment)

PRU (Largest-in-the-world commercial size

equipment)

PRU “1-time freezing of crystals with optimum

application of refrigerant energy

Distinctives of GTC’s PX Technology

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C5

Aromatics

Extraction

Toluene

Conversion

Tolu

ene C

olu

mn

BenzeneC6 -C7 raffinate

C9+

Paraxylene

Hydrotreated

Naphtha

Xylene

Isomerization

Catalytic

Reformer

Xyle

ne C

olu

mn

C9+

Refo

rmate

Split

ter

Paraxylene

Recovery

Dehepta

niz

er

Benzene C

olu

mn

Xyle

ne C

olu

mn

“GTC-DWC for Energy

Savings”

BTX

Columns

Reformate

Splitter

Deheptanizer

Xylene Column

(GTC-TWDC

to segregate streams by PX

and EB content)

Distinctives of GTC’s PX Technology

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C9+

Catalytic

Reformer

C5

Aromatics

Extraction

Toluene

Conversion

Tolu

ene C

olu

mn

BenzeneC6 -C7 raffinate

C9+

Paraxylene

Hydrotreated

Naphtha

Xyle

ne C

olu

mn

Refo

rmate

Split

ter

Paraxylene

Recovery

Dehepta

niz

er

Benzene C

olu

mn

Xyle

ne C

olu

mn

Isom (higher EB

conversion)

Xylene

Isomerization

High-purity benzene by direct

fractionation

Distinctives of GTC’s PX Technology

GTC Technology Day

• Historical traditional method for PX production has been crystallization

• Adsorption processes have enjoyed popularity due to advantages over first-

generation crystallization technologies

• Updated design features, improved equipment, and world-scale designs are making

crystallization once again desirable

• GTC has capable technical staff station locally, to ensure reliable operation

• CrystPX℠ is state-of-the-art for advancement in PX crystallization

Conclusions

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