Aromatics 2010

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AROMATICS

Dr I.D.Mall

Department of Chemical Engineering

Indian Institute of Technology Roorkee

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AROMATICS

• Aromatic hydrocarbons especially benzene, toluene,xylene, ethyl benzene are major feedstock for largenumber of intermediates which are used in theproduction of synthetic fibers, resins, synthetic rubber,explosives, pesticides, detergent, dyes, intermediates, etc.

• Styrene, linear alkyl benzene and cumene are the major

consumer of benzene.• Benzene also finds application in the manufacture of

large number of aromatic intermediates and pesticides.

• As per CMAI, demand for benzene is forecast to grow at

an average annual rate of 2.8% per year through 2020resulting in nearly 57 million tonnes of demand by 2020.

• Originally, the aromatics were produced from coal tardistillation, which is byproduct of destructive distillation(carbonisation).

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AROMATICS

• Major application of toluene is as solvent. Other

uses are in the manufacture of benzoic acid, chloroderivatives, nitro toluenes, toluene sulphonic acid,

toluene sulphonamide, benzaldehyde, etc. Xylenes

are another important aromatics

• Amongst the xylenes, about 80% of the production

is of p-xylene. Finds application in the

manufacture of terephthalic acid/DMT.

• o-Xylene used in the manufacture of phthalicanhydride.

• m-xylene Isohthalic acid

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Xylenes

Toluene

Gasoline

Nitrotoluene

Trinitrotoluene

Benzoic acid

Solvents

p-cresol

m-xylene

o-xylene

p-xylene

Toluene

diisocyanate

Isophthalic

acid

Phthalic

anhydride

TPA,

DMT

Motor gasoline

Polyurethane (Rigid foam,

flexible foam, surface coatings)

Explosives

Caprolactam, pharmaceuticals

and flavors, phthalates,

terephthalic acid.

Phenol, sodium benzoate - food

preservatives.

Resins, unsaturated

polyesters, plasticizers,

other esters.

Plasticizers, polyester resins,

alkyl resins, dyes and pigments,

herbicides, isatoic anhydride,

polyester polyols,

phthalimide-fungicides.

Polyester fibers, films,

polyethylene, terephthalate.

Di-tert-butyl-p-cresol (antioxidants)

To

BenzeneProduct Profile

of Aromatics

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CatalystReforming

Extractor

Raffinatewash

column

Water

Non AromaticsRaffinate Wash

ColumnNaphtha

ExtractiveStripper

Extract Reflux

OlefinHydro

Desulphurisation

DieneHydrogenetics

Pyrolysis

SolventRecovery

Steam

ClayTreater

B e n z e n e C o l u m n

T o l u e n e C o

l u m n

C 8 C o l u m n

HeavyEnd

Benzene

Toluene Xylenes,Ethyl

Benzene

Waste

Naphtha

Pyrolysis Gasoline

Solvent

Non-Aromatics

T o l u e n e

Benzene

HeavyEnd Product

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EthylBenzeneColumn

m-xylenecolumn

o-xylene

column

Crystallisationp-xylene

AdsorptionParex

Mixed Xylene

Isomerisation

L i g h t e n d c o l u m n

Recycle forp-xylene

recovery

To flare

p-xylene

IsomerisationSection

Heavy end

Xyleneseparation

Toluenedisprop

ortionation

reactor

XyleneColumn

C9+

Aromatics

p-xylenerich

streamHydrogen

m- and p- xylene

EthylBenzene

Toluene Disproportionation Section

Xylenes,Ethyle

Benzene

Toluene

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Processes Description

Coal Carbonis-

ation (Coke oven plant)

From coke oven plant during carbonisation, light

oil is obtained as by product which containsabout 2-8 kg, 0.5-2 kg, 0.1-0.5 kg of benzene,toluene and xylene respectively per tonne of coal.

Steam cracking ofhydrocar-bons

Steam cracking of naphtha and light hydrocarbonlike ethane and propane produce liquid product

(pyrolysis gasoline) rich in aromatics containingabout 65% aromatics about 50% of which isbenzene. About 30-35% of benzene producedworldwide is from pyrolysis gasoline.

CatalyticReforming

Catalytic reforming is a major conversionprocess, which converts low octane naphtha tohigh-octane gasoline and produce aromatics richin BTX. Major reactions involved aredehydrogenation of naphthalenes to aromatics,isomerisation of paraffins and naphthenes,dehydrocyclisation of paraffins to aromatics, and

hydrocracking of paraffins.

BTX PRODUCTION TECHNOLOGY

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Processes

Description

BP-UOP CyclarProcess

In this process, BTX is produced bydearomatisation of propane and butane. Theprocess consists of reaction system, continuousregeneration of catalyst, and product recovery.Catalyst is a proprietary zeolite incorporatedwith a non noble metal promoter.

Dearomatisationof naphtha

Process consists of extraction of aromatics fromhigh aromatic naphtha feed without priorreforming. The process is useful for naphthahaving high aromatics.

Hydro

dealkylation anddisproportionation

Hydrodealkylation: It involves production of

benzene by dealkylation of toluene either bycatalytic or thermal process. Catalytic process: Hydeal, Deltol Thermal process: HAD (ARCO), THDC Gulf Oil Disproportionation: It involves conversion of

toluene into benzene and xylenes.


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Isomerisationand Isomerprocess

This process consists of conversion of C8 streaminto valuable o- and p- xylene having isomerisationand isomer separation stage.

Mitsubishi's

ZformingProcess

This process uses metallosilicate zeolite catalyst to

promote dehydrogenation of paraffins followed byoligomerisation and dehydrocyclisation of paraffinsfollowed by oligomerisation.

KTIPyroforming

This process uses a shape selective catalyst toconvert C2 and C3 paraffins to aromatics.

Cheveron'sAromaxprocess

It is similar to conventional catalytic reformingprocesses and L-type zeolite catalyst.


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BTX FROM PETROLEUM

• First step in making BTX is to distill off a suitablefraction rich in naphthenes which serves as precursors

for aromatics• Catalytic reforming or steam cracking to produce an

aromatic and pyrolysis gasoline.

• Preliminary treatment of this cut : fractionation and/orselective hydrogenations (essentially pyrolysis gasoline)

• Solvent extraction to eliminate non-aromatics

• Distillation to produce pure benzene and toluene, and incase of reformates used alone or blended with a pyrolysisgasoline

• Distillation aromatic C8 to yield by superfractionationethyl benzene and o-xylene, after passage through aseparation column in a light cut and a heavy cut (splitter)

• Production of p-xylene at low temperature, with a motherliquor by product rich in m-xylene.

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Typical yield of benzene, toluene, xylene in kg per tonne of coalcarbonised is about 2.8, 0.5-2, and 0.1-0.5 kg

Potential Availability of Selected Chemicals

Chemicals Per cent availability

Benzene Toluene

Xylenes

Naphthalenes

Methyl naphthalene

Phenol Cresols & Xylenes

Diphenyl oxide

0.70 0.20

0.05

0.30

0.06

0.02 0.04

0.04

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Aromatic Content of Various Crude Oil

Crude Paraffins Naphthenes Aromatics

Assam Mix, vol.% 32-40 43-52 16-17

Gujarat (North), vol.% 52.50 42.00 5.3

Gujarat (Ankleshwar),vol.%

70.80 25.00 4.2

Bombay High, vol.% 53.70 25.00 21.3

Iranian, wt.% 57.50 31.20 11.4

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Typical Composition of Hydrotreated Pyrolysis Gasoline FeedCharacteristics Hydrotreated C6-C8 Heart cut to Benzene Extraction Unit

Component Wt.%

C5s 1.0 wt.% max.

C9-204 oC 1.0 wt.% max.

Cyclopentane 1.00

C6 Paraffins 10.63

Methyl cyclopentane 10.15

Cyclohexane 2.85

Benzene 24.16

C7 Paraffins 4.90

1,1-dimethyl cyclo, C5 0.17

Cis -1,3-dimethyl cyclo, C5 0.37

Trans- 1,3-dimethyl cyclo, C5 0.30

Cis- 1,2- dimethyl cyclo, C5 0.13

Continue…

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Continue……

Trans- 1,2- dimethyl cyclo, C5 0.54

Methyl cyclohexane 1.12 Ethyl cyclopentane 0.64

Toluene 23.02

C8 Paraffins 1.64

Total dimethyl cyclohexane 0.33 Ethyl cyclohexane 0.03

n-propyl cyclopentane 0.10

Isopropyl cyclopentane 0.07

Total trimethyl cyclopentane 0.57 Ethyl benzene 6.55

Xylenes 9.73

C9 plus 1.00

TOTAL 100.00

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Major Units of Aromatic Complex

• Heavy Naphtha Pre-treatment Unit • Platformer Unit• CCR Unit (Continuous Catalyst

Regenerator) • Recovery Plus. • PSA (Pressure Swing Adsorption) • BTX separation

• Xylene Fractionation Unit • p-xylene and m-xylene separation • Crystalisation, Adsorption

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Separation of Aromatics

• Liquid-liquid extraction (DEG, TEG,Tetramethylene sulfono NMP-EG,

Monomethyl formamide, Morpholine,

DMF, n-methyl pyrolidone NMP• Extractive or azeotropic distillation

• Adsorption

• Crystallization

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PROCESS FLOW

Feed Preparation (Removal of

contaminants S, N, As, Pb)

Temp. control 550 0C

Reactors

Product recovery

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Aromatic production

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Reactions Involved

• Dehydrogenation

Methyl cyclohexane Toluene + H2

MCP Benzene + H2

• Isomerisationn-Hexane Neohexane

• Dehydrocyclisation of paraffins, i-paraffins toaromatics

• n-heptane toluene + H2

• Hydrocracking

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Process Variables

• Temperatures

• Space velocity

• Pressure,

• Hydrogen-hydrocarbon ratio,

• Catalyst type,

• Water/chloride content.

• N + 2A

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Catalyst

• Monometallic(Pt),

• Bimetallic (Pt, Rhenium)

• Multimetallic

• Acid Activity : Halogens/silica incorporated in

alumina base.

• Metallic Function: To promote dehydrogenation andhydrogenation. Also contribute todehydrocyclisation and isomerisation.

• Acid Function : Promotes isomerisation, the initialstep in hydrocracking, participate in paraffindehydrocyclisation.

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p-Xylene plant

• Pretreatment Unit

• Reformer Unit

•Fractionation Units

• Parex Unit

• Isomerisation

X l l

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p-Xylene plant• Pretreatment Unit: This unit is used for

reducing sulphur content to 5 ppm (max.) bydehydro - desulphurisation which takesplace at 330 –370 oC and 24 kg/cm2 pressurein presence of cobalt molybdenum catalyst.

• Reformer Unit: To get maximum amount ofC8 aromatics by reforming process (Processsimilar to described earlier).

• Fractionation Units: For separation of o-, m-,and p-xylenes from combined C8 reformateand isomerisate from isomerisation unit(after clay treatment).

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p-Xylene plant

• Parex Unit: This unit is for the separation ofp-xylene by selective adsorption usingmolecular sieve followed by desorption.Other method for separation of p-xylene is bycrystallisation process.

• Isomerisation: Isomerisation of C8 streamfrom Parex unit rich in m- and o-xylene andethyl benzene to p-xylene, which is sent tofractionation unit for separation of highcomponent. The bottom of the column isrecycled for further recovery of xylenes.

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p-Xylene from Catalytic Reforming

Preheating3 Stage Reactorwith interheater

400-450oC

StabilisationSection

Deheptaniser

ClayTreatment

o-xylenecolumn

Adsorber

Crystallisation

PreheatingIsomerisation

p-xylene

Naphtha

110-145oCCut

Reforming ofNaphtha

Fuel gas Light

reformate

o-xylene

p- and m-xylenes

m-xylene

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p-Xylene Separation Processes


Chevron process Uses crystallisation process for separation. Itis characterised by the use of direct

contact cooling. This is accomplished byinjecting liquid CO2 with feed tocrystallise.

Krupp Process Crystallisation process is used to crystalliser-scrapped chiller.

Amco Process p-xylene is incorporated using two-stagecrystallisation process with its directcooling.

Arco process It uses either two stage or single stagecrystallisation process for separation of p-

xylene followed by toluene distillationcolumn.

Marazen Process Two stage crystallization process using

ethylene gas as a direct refrigerant.

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Continue….

Parex Process

(UOP)

p-xylene is separated by selective adsorption

using zeolite base adsorbent. It usessimulated moving bed, countercurrent andliquid phase adsorption. Desorbent is tolueneor p-diethyl benzene.

Aromax Process

(TorayIndustries)

This process also uses selective liquid phase

adsorption using a series of horizontallysituated chambers that are isolated from oneanother.

IFP’s EluxylProcess

Adsorption process is used for separation.

Hybrid Process(IFP & Chevron)

This process combines the best feature ofadsorption and crystallisation.

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The parex process has four major streams that are

distributed to the adsorbent chamber by rotary

valve. These streams include:

• Feed in: Mixed xylene.

• Dilute extract out: p-xylene product diluted with

desorbent.

• Dilute raffinate out: ethyl benzene, m-xylene, and o-

xylene diluted with desorbent.

• Desorbent in: recycle desorbent from the

fractionation column.

At any time, only four of the bed lines are active, carrying the net

streams into and out of the adsorbent chamber. The rotary valve

periodically switches the position of the liquid feed and

withdrawals points as the composition profile moves down the

chamber

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1

2

3

4

5

6

7

8

9

10

11

12

R a f f i n

a t e

Extract

D e s o r b e n t

F e e d

I

IV

II

III

Rotary

Valve

Extract

Column

Raffinat

e

column

Desorbent

Feed from

xylene unit

Light

End

Column

Light ends

p-xylene

Raffinate

D e s o r b e n t P u r i f i c a t i o n

Heavy ends

Desorbent

recycle

Pump

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Aromatic Conversion Processes

• Hydrodealkylation

• Isomerisation

•Dismutation and Trans alkylation

• Disproportionation (Vapor or liquid

phase)

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Disproportionation

• Transfer of the alkyl group between two

similar molecule producing a lower anda higher homologue is

disproportionation.

• Trimethyl benzene to tolueneXylene

• Propylene Ethylene + ButeneCH3

CH3

CH3

+2

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Dealkylation

C

H

3

CH3

O2

+CO2 + H2

+CO2 + H2Steam

+ H2 + CH4

Detachment of alkyl group Toluene Benzene + Xylene

Methyl

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Cyclar Process •

Cyclar process selectively converts liquefied petroleumgas to high value benzene, toluene and xylene.

•First commercial scale plant has been in case of therefineries of British Petroleum located at Gragemouth,

Scotland

•Special features of Cyclar process are: • Inexpensive and plentiful LPG.

• Requires minimal feed pretreatment and productpurification equipments.

• Simplicity in process.

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• BP’s Cyclar process is a real break through to

aromatics and dependence on naphtha forreforming or cracking is reduced.

• The selectivity of aromatics is said to be high at

65% with hydrogen as a valuable co-product

which are around 6%.

• In the process for conversion of LPG to

petroleum grade aromatics, LPG is continuously

converted to aromatics in four radial flowreactors arranged in vertical stack using zeolite

catalyst with a non-metal.

The BP-UOP Cyclar Process

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• In the aromatization reaction, bifunctional

catalyst mainly ZSM-5 type catalyst is usedwith non noble metal promoter like Zn, Ga,etc.

• Acidic nature of the catalyst is produced by

zeolite.• Aromatization is a complex reaction, which

involves – Dehydrogenation,

– Oligomerisation, – Cyclisation,

– Dealkylation

– Alkylation

The BP-UOP Cyclar Process

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Reactions in Cyclar Process

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UOP-BP Cyclar Process for LPG aromatization

Stripper

Stripperoff gas

C6+

Aromaticproduct

Gasrecoverystation

Boostercompressor

Hydrogen

Net fuelgas

Charge and Interheaters

Fresh Feed

Recycle to Reactor

FromReactor

LPSeparator

CatalystRegeneration

Stacked reactors

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Cyclar Aromatic Product Distribution

Toluene

43 %

C9+ Aromat ics9%

Xylenes

21%

Benzene

27 %

Benzene

22 %

Xylenes

25 %

C9+ Aromati cs

9%

Toluene

44 %

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Dearomatising of Naphtha • Dearomatising of naphtha is another option for

production of aromatics from naphtha rich inaromatics.

• The process step involves includes

– Feed preparation,

– Extraction of aromatics

– Extractive stripping – Raffinate washing

– Solvent recovery

– Clay treatment,

–Fractionation to produce pure benzene andtoluene

• Feed preparation involves separation of 65-110 oCcut from C5 -140 oC naphtha in a series of twofractionators.

•E i f i i d b i l h l

Documents

Aromatics 2010