SPRING 2019

CL 4003 PETROCHEMICALS AND REFINERY ENGINEERING

Lecture 32

Department of Chemical Engineering

Birla Institute of Technology Mesra, Ranchi1

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Integrated UOP aromatics complex

UOP TATORAY PROCESS

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✓ The Tatoray process provides an ideal way of producing

additional mixed xylenes from low-value toluene and heavy

aromatics.

✓ The incorporation of a Tatoray unit to an aromatics complex

can double the yield of PX from naphtha feedstock.

✓ The two major reactions in the Tatoray process:

disproportionation and transalkylation.

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TATORAY PROCESS

✓ The conversion of toluene alone to an equilibrium mixture of

benzene and xylenes is called disproportionation.

✓ The conversion of a blend of toluene and A9 to xylenes is called

transalkylation.

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TATORAY PROCESS

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Major Tatoray reactions

UOP PAREX PROCESS

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✓ The UOP Parex process is an innovative adsorptive separation

method for the recovery of para-xylene from mixed xylenes.

✓ The term mixed xylenes refers to a mixture of C8 aromatic

isomers that includes ethylbenzene, para-xylene, meta-xylene,

and ortho-xylene.

✓ These isomers boil so closely together that separating them by

conventional distillation is not practical.

✓ The Parex process provides an efficient means of recovering

para-xylene by using a solid zeolitic adsorbent that is selective

for para-xylene. 8

PAREX PROCESS

✓ UOP Parex units are designed to recover more than 97 wt % of

the para-xylene from the feed in a single pass at a product

purity of 99.9 wt % or better.

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PAREX PROCESS

UOP ISOMAR PROCESS

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✓ The UOP Isomar process is used to maximize the recovery of a

particular xylene isomer from a mixture of C8 aromatic

isomers. The Isomar process is most often applied to para-

xylene recovery, but it can be used to maximize the recovery of

ortho-xylene or meta-xylene.

✓ The term mixed xylenes is used to describe a mixture of C8

aromatic isomers para-xylene, ortho-xylene, meta-xylene, and

ethylbenzene (EB).

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ISOMAR PROCESS

✓ In the case of para-xylene recovery, a mixed-xylenes feed is

charged to a UOP Parex unit where the para-xylene isomer is

preferentially extracted at 99.9 wt% purity.

✓ The Parex raffinate is almost entirely depleted of para-xylene

and is sent to the Isomar unit.

✓ The Isomar unit essentially create additional paraxylene from

the remaining ortho and meta isomers. Effluent from the Isomar

unit is then recycled to the Parex unit for recovery of additional

para-xylene.

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ISOMAR PROCESS

✓ The two main categories of xylene isomerization catalysts are

dealkylation (ethyl benzene) catalysts and isomerization

catalysts.

✓ Dealkylation catalyst converts EB to a valuable benzene

coproduct. An EB isomerization catalyst converts EB to

additional xylenes.

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ISOMAR PROCESS

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ISOMAR PROCESS

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Typical Parex-Isomar loop

Pyrolysis gasolines

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✓ Pyrolysis gasoline (PyGas) is a by-product of high temperature

naphtha cracking during ethylene and propylene production.

✓ It is a mixture of highly unsaturated hydrocarbons ranging from

C5s to C12s. PyGas contains considerable amounts of

aromatics, normally 40-80% (benzene, toluene and xylene),

together with paraffins, olefins and diolefins. Composition of the

PyGas produced depends on the feedstock and operating

conditions and varies from plant to plant.

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INTRODUCTION

✓ Ethylene and propylene are produced commercially by steam

cracking of a wide range of hydrocarbon feedstocks.

Consequently, a significant amount of PyGas is produced, as it

is a major by-product of these plants. The production of PyGas

is generally about 20-30% when naphtha is used as a feedstock.

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INTRODUCTION

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Typical compositions of C5-gasoline and aromatic cuts

produced by naphtha steam cracking

Components C5-gasoline C6-200 °C cut C6-C8 cut

Paraffins & Naphthenes 11.8 7.8 9.7

Olefins 5.5 2.4 3.0

Diolefins 18.1 8.7 5.9

Aromatics

Benzene 28.0 35.2 43.7

Toluene 13.9 17.4 21.7

C8 7.2 9.0 11.3

Alkenylbenzene 3.0 3.8 4.7

C9- 12.5 15.7 -

Total aromatics 64.6 81.1 81.4

Sulfur content (ppm) 220 180 150

There are two main routes to utilise the PyGas produced to provide

useful products:

✓ PyGas contains a large quantity of aromatic (BTX) and aliphatic

hydrocarbons and therefore can be used as a gasoline pool due

its high octane number.

✓ The high content of aromatics present in PyGas makes it a good

potential feedstock for aromatics extraction.

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INTRODUCTION

✓ As may be observed from the table, these cuts contain

significant amount of olefins, diolefins and alkenylaromatics,

which make them unsuitable for direct use as a gasoline. These

unstable compounds cause gumming in motors and therefore

must be removed.

✓ During storage, olefins, diolefins and alkenylaromatics present

in gasoline react with absorbed atmospheric oxygen and with

each other, forming resinous, polymeric, and non-volatile

materials with a high molar mass that are commonly called

gum. 21

INTRODUCTION

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INTRODUCTION

✓ When olefins and diolefins are in contact with dissolved oxygen,

reactions can occur which lead to fouling in process units.

✓ Hydroperoxides, the immediate products of reaction of oxygen

and hydrocarbons, undergo reactions leading directly to

insoluble oxidized species, or in parallel reactions, to dissolved

oxidized species which then convert to insolubles.

✓ Oxidation products include species such as peroxides,

aldehydes, acids, and ketones, as well as components with

molecular mass 200-600 g/mol, referred to as gum.

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INTRODUCTION

✓ The nucleation or agglomeration of the insoluble oxidized

products, may occur in the bulk fluid, or on the surface of the

heat exchanger.

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INTRODUCTION

✓ The gum formed in gasoline during storage, leads to formation

of deposits in carburettor, fuel injectors, intake manifold, on

intake ports and intake valves, and in the combustion chamber.

The gums clog fuel metering orifices, result in sticking of intake

valves and form carbon deposits in the combustion chamber.

Deposit formation in fuel system and combustion chamber lead

to loss in fuel efficiency and increase in carbon monoxide and

unburned hydrocarbon emissions.

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INTRODUCTION

✓ The formation of deposits in the combustion chamber increases

the effective engine compression ratio. The combustion chamber

deposits can increase HC and NOx emissions by up to 10 to

15%.

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INTRODUCTION

On account of excessive instability, dienic compounds can not be

eliminated at the same time as olefins and sulfur compounds. Two

successive operations are therefore necessary in this case:

(a) Selective hydrogenation of diolefins, also called

hydrodedienization of first step hydrogenation.

(b) Fairly severe hydrotreating to convert nearly all the sulfur

compounds, but sufficiently selective to avoid significantly

hydrogenating the aromatics; this is hydrodesulfurization, also

called second step hydrogenation.

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Pyrolysis gasoline hydrotreating

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Hydrogenation of pyrolysis gasoline (C5-C9 cut)

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Hydrogenation of pyrolysis gasoline (C6-C8 cut)

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Hydrogenation of pyrolysis C6-C8 cut

Composition cut Crude cut Dedienized

cut

Dedienized &

desulfurized

cut

Diolefins and styrene 10.6 0.3 0

Olefins 3.0 2.4 0

Benzene 43.7 43.7 43.6

Toluene 21.7 21.7 21.5

Xylenes &

ethylbenzene

11.3 11.3 11.3

Total sulfur ppm 150 145 0.5

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