Petrochemical feed stocks

Presented by:

Sarah Al-HoutyOhoud Al-Mutairy

Dlal Al-MoullaHessah Al-Ameer

Introduction

The basic petrochemical manufactured by :

1- Aromatics ( Benzene , toluene , xylene ,and ethyl benzene ) 2- Un saturates (Olefins ,Diolefins ) 3 – Saturates (Paraffin and cyclo paraffin )

Uses of Petrochemical: 1- Plastic production 2- Synthetic fibers 3- Rubber (SBR ) 4-Solvents 5- Polymers

Aromatics Production *Aromatics are obtained mainly from the catalytic reforming of heavy naphtha .

* Solvent liquid – liquid extraction method used to separate aromatics from anther hydrocarbons .

* Finally the aromatics are separated to produce ( Benzene , toluene , xylene which separated to m- o -p –xylenes , and ethyl benzene )

Solvent extraction of Aromatics :The points important for solvent

selection : 1- Good thermal stability . 2- Raid phase separation .3-Non corrosively . 4 - High capacity ( Solubility of Aromatic ) . 5- High selectivity for aromatics versus

non aromatics.

Solvent extraction of Aromatics :

There are Two major solvent that used to extract aromatics :

1 -Sulfolane .

2 -Ethylene glycol .

Comparison of Solvent Systems For Aromatics

Recovery

Extractive splitter

Extract recovery column

Extraction equipment

2-101.5Wash water wt%

1.442Relative Volatility

33S/L

Tetra-ethylene

Sulofane

General L-L extraction flow sheet

Solvent extraction of Aromatics :

Aromatics Separation :* Benzene and Toluene can be recovered from the extract product stream of the extraction unit by distillation.

* The separation by distillation become more difficult Because the boiling points of C8 aromatics are so close together.

* Solution: by using a combination of distillation and crystallization or adsorption.

o-Xylene

m-Xylene

p-Xylene

Ethyl benzene

Toluene

Benzene

aromatics

291.1

282.4

281

277.1

231.2

176.2

Fo

Boiling point

144.4

139.1

138.4

136.2

110.6

80.1

Co

Sequence of Aromatics recovery operation :

For a good desired separation efficiency the reflux ratio must be high. Disadvantage: it needs more energy so the cost will be higher.

Solution : Alkylation Benzene with ethylene to produce ethyl Benzene.

Processing sequence to produce C8 aromatics :

Benzene :

*The primary source of benzene is from the reforming unit, but substantial amount of benzene are also produced by hydrodealkylation of toluene

*Process flow for a hydrodealkylation unit (HAD):

1-Feed can be to toluene or admixture of to toluene and xylenes.

2-The feed is heated to 1175 f (630 c) at 600psig (4140kpa).

3-The feed charged to an open non catalytic reactor (L/D= reflux ration < 20) where thermal dealkylation of to toluene and xylenes take place during residence time of 25-30 seconds.

4-The hydrogenation step in the dealkylation reaction is highly exothermic [Q 22,000 Btu/lb-mol]So the temperature is controlled by injection of quench hydrogen at several point along the reactor.

Results :

-The hydealkylation reaction results in the conversion of benzene.

-Also small amount of polymer is formed, primarily diphenyl.

-To prevent catastrophic corrosion of the furnace tubes small amount of hydrogen sulfide is added.

-To minimize polymerformation.

Un saturate Production :

*Steam cracking of gas oil naphthas is most important process for producing a wide range of unsaturated hydrocarbons for petrochemical use.

1 -alkane (single bond) dehydrogenation(-H2) alkene (double bond)

Come from 1-ethylene.

LBG or flue gas 2-propalene.

( C2, C3, C4 )3-Butadiene.

2 -Steam – cracking : is the thermal cracking and reforming of hydrocarbons with steam at :

a- low pressure. b- High temperature.

c- Very short residence times (generally < seconds).

Process of Un saturated

- The hydrocarbon is mixed with steam in the steam/ hydrocarbon weight ratio of (0.2 to 0.8) and fed into a steam – cracking furnance.

- The residence times in the cracking Zone range from (0.3 to 0.8) seconds

- There is a coil with : outlet temperature between 1400 and 1500F , and out let pressure in the rang 10 to 20 psig .

- The coil outlet steam is quickly quenched to about 600F to stop the cracking and polymerization reactions, by transfer –line heat exchanger with a low – pressure drop .

-The quenched furnace outlet stream is sent a primary fractionators where it is separated into:a- gas steam.b- Liquid steams according to boiling point range.

-The gases are separated into to individual component as desired by compression and high – pressure fractionation .

- Paraffin obtained from the dewaxing of lubricating oil base stocks are frequently steam – creaked to produce a wide range of linear olefins.

Steam –Cracking Condition :

8-1060-80C3 conversion wt%

0.12-0.150.3-0.9Steam /HC

15-3045Pressure psig

1100-12001100-1650Coil outlet temp F

Wax Naphtha

*If we use wax stream it must be de oiled before being used as a stream –cracker feed stock.

*By choosing feed stock with an initial boiling point greater thane the end point of the desired product it will :

a) Increase the yield of the desired olefins.

b) Makes it possible to separate the product olefins from the feed paraffines by distillation

*Results: atypical product stream conditions above 80% mono olefins with only a small percentage less than 11 carbon.

*Linear mono olefins: it is also produced by several catalyst processes:_The overall process consists of:

a) Vapor- phase catalytic dehydrogenation unit b) Followed by an extraction unit.

-The linear olefins will extract from paraffin hydrocarbons by adsorption on a bed of solid adsorbent material

-They use a hydrocarbon as desorbed, it boiling at lower temperature thane olefin product

So the separation of olefin product from adsorbent will be easy.

-Then the adsorbant hydrocarbon is recycled in the extraction section.

*The results:-The olefin product contains about 96 wt% linear olefins of which about 98%are mono-olefins.

Saturated Paraffin’s

1-Normal paraffin’s:

They are recovered from petroleum fractions by vapor phase adsorption on molecular sieves.

2-Cycloparaffin’s:

They are prepared by hydrogenation of the corresponding aromatic compounds.

Normal paraffin’s:

It uses molecular sieves which are materials containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids.

Molecular sieves are often utilized in the petroleum industry.

5 Å pore diameter sieves are

used.

1-The adsorption takes place in vapor phase at pressure of (5-10 psig) and temperature of (300-350oC).

2-AMMONIA is used as a adsorbent.

3-The sieves loses its capacity because of contamination , so it is regenerated by controlled burn-off.

N-paraffin recovery by adsorption :

Cyclo paraffin’s

*Example(1): Cyclohexane is prepared by hydrogenation of benzene.

*The hydrogenation of benzene is carried out on:

*Platinum.

*Raney Nickel supported on alumina or silica alumina.

*The hydrogenation reaction is highly exothermic.

*The reaction temperature is controlled by recycling and injecting the cyclohexane to

the reactor.

*Example (2):Tetralin and Decalin are prepared by hydrogenation

of Naphthalene.

*The same as hydrogenation of cyclohexane .

*The catalyst is Cobalt-molybdenum.

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