Alkylation, Isomerisation And Polymerisation Chemical Engineering Notes | EduRev

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Chemical Engineering : Alkylation, Isomerisation And Polymerisation Chemical Engineering Notes | EduRev

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Alkylation, Isomerisation And Polymerisation 

Alkylation

Alkylation process commercialized in 1938, since then there has been tremendous growth in the process. In US and Europe about alkylate is about 11-12 percent and 6 percent in the gasoline pool respectively. Alkylate is a key component in reformulated gasoline. Alkylation processes are becoming important due to growing demand for high octane gasoline and requirement of low RVP, low sulphur, low toxics. Alkylate is an ideal blend stock to meet these requirement. 

The process of alkylation different iso-parraffins using olefins were developed during thirties using aluminium chloride catalyst, however, later catalyst was replaced by HF and sulfuric acid. Although butylenes alkylation is one of the most commonly used process, however, alkylation of amylenes obtained from C5 fraction of FCC can be another route to increase the availability of alkylate. Alkylation of C5 cut from FCC can significantly reduce RVP of finished gasoline pool.

C5 alkylate: Amylene alkylation has two fold advantage: It increase the volume of alkylate available while decreasing Reid vapor pressure and olefinic content of gasoline blend stocks The process of HF alkylation produces high octane blend stock for iso-parraffin (mainly iso butane) and olefin (propylene, butylene and amylenes) in the process of HF catalyst to meet all the criteria of reformulated gasoline. Replacing high risk toxic liquid acids, such as hydrofluoric acid (HF) and sulphuric acid with solid acid catalysts is challenging goal iso-parraffin alkylation technology.

Process

 The reaction involved in aliphatic alkylation consists of conversion of iso-butane and butylenes to iso-octanes using HF catalyst. Commonly alkylation process used are mention in Table M-VI 7.1.

Alkylation, Isomerisation And Polymerisation Chemical Engineering Notes | EduRev

The side reaction results in increased iso-butane consumption increased acid consumption increased acid soluble formation, equipment handling and for the corrosion problem. Figure MVI 7.1 gives the details of iso-parraffin alkylation mechanism  

Some of the other side reaction is the formation of paraffin, which boils above and below the desired product. Impurities in the feed acid and normal operating practices all can contribute to additional side reactions. Comparison of Alkyclean Technology with Modern Sulphuric Acid and Hydrofluoric Acid Technologies is shown in Table M-VI 7.2.

The key factors to be controlled in alkylation process are:

  • Maintaining proper composition of reaction mixture which include isobutene olefins and the HF acid  
  • Maintaining the proper reaction environment which includes adequate contacting, controlled temperature, and freedom from surges.
  • Making a proper separation of the reactor effluent into its various components

Table M-VI 7.1: Common Alkylation Processes 

 

Process

Description

CONOCO            Phillips

process (ReVA Process)

Alkylation of propylene, butylenes, pentenes and isobutane to high quality motor fuel using HF catalyst

Stratco INC

Alkylation of propylene, butylenes and amylenes with isobutane using strong sulfuric acid to produce high octane branched chain hydrocarbons using effluent refrigeration alkylation process

UOP HF Alkylation

Process

Alkylation of isobutane with light olefins (propylene, butylenes and amylenes to produce branched chain parafinic fuel) using hydrofluoric acid catalyst. More than 100 commercial process

UOP AlkyleneTM

UOP Alkylene process is based on solid catalyst(HAL-100) for alkylation of light olefins and isobutane to form a complex mixture of isoalkanes which are                                     highly branched

trimethylpentanes(TMP) that have high octane blend values of approximately100

Exxon Alkylation

Alkylation of propylene, butylenes and penrylene with isobutene in the presence of sulphuric acid catalyst using autorefrigeration. Products: a low sensitivity, highly iso, low RVP, high octane gasoline blend stock paraffinic

AlkylClean solid Acid alkylation technology ( ABBLumus global)

The alkylation process uses a robust zeolite solid acid catalyst formulation coupled with a novel reactor processing scheme to yield a high quality alkylate product. The catalyst contains no halogen

 
Table M-VI 7.2: Comparison of Alkyclean Technology with Modern Sulphuric Acid and Hydrofluoric Acid Technologies   

Parameter

Modern sulphuric

acid technology

Modern hydrofluoric acid technology

Alkyclean

Base condition

C4 feedstock

C4=feedstock

C4=feedstock

Product RON

95

95

95

Product MON

Base

Base or better

Base or better

Alkylate yield

Base

BASE

90% of base

Total installed cost

Base

85% OF BASE

50% of base

Total installed cost,

including

OSBL(regeneration, facilities, and /or safety installations)

Base

Less

None

ASO yield

Base

Less

None

Equipment maintenance

High

High

Much lower

Corrosion problems

Yes

Yes

Higher

reliability and on stream

factor

Base

Base

Match fcc or better/shorter

Safety

Unit specific safety

precautions as well as transport precautions

unit specific

precautions

C safety precautions required that extend throughout refinery

very specific

No special

precautions

other than those

for any refinery

process unit

Catalyst

H2SO4

HF

Zeolite

Environmental

Significant waste

streams generated

Significant waste

streams generated

No emissions to

air, water, or

ground

 
 
 
Alkylation, Isomerisation And Polymerisation Chemical Engineering Notes | EduRev

Figure M-VI 7.1: Iso-paraffin Alkylation Mechanism 

Isomerisation 

Petroleum fractions contain significant amounts of n-alkanes and the isomerisation of alkanes into corresponding branched isomers is one of the important process in refining . The highly branched paraffins with 7-10 carbon atoms would be the best to fulfill the recent requirements of the reformulated gasoline . The production of paraffin bases high – octane gasoline blend stock, such as isomers from isomerisation of light and mid cut naphtha might be a key technology for gasoline supply to cope with future gasoline regulation 

Light naphtha and paraffin isomerisation recognizes emerging technologies in order to boost octane in light gasoline fractions. Recent pricing trends show isomerisation could be a significant contributor to octane pool which will offset the loss from gasoline desulfurisation and aromatic reduction. Isomerate as % of gasoline used is USA 8percent, Western Europe 16percent.

Isomerisation involves

  • Isomerisation of Light paraffins
  • Isomerisation of C5-C6paraffins
  • Isomerisation of n-butane

Isomerisation of C5-C6 paraffins: Allow low octane number paraffins 5 and 6 carbon atoms into higher octane number paraffins

n-pentanen-isopentane: n-hexane to 2-methyl pentane, 3 methyl pentane (low octane 75)

2,2 dimethyl butane, 2,3 dimethyl butane

Isomerisation of n-Butane; to produce isobutene feed for alkylation or as source of isobutene dehydrogenation to manufacture MTBE

Isomerisation Catalyst

Two types of isomerization catalyst, zeolite and chlorinated alumina, has been used. Zeolite catalyst requires higher temperatures and provide lower octane boost while chlorinated alumina’s results in highest octane, however, it has higher sensitivity to feed stock impurities requiring strict feed pretreatment to eliminate oxygen, water, sulphur and nitrogen is containing compounds.

  • Zeolite  
  • Chlorinated alumina

 Zeolite catalyst requires higher temperatures and provide lower octane boost Chlorinated alumina’s results highest octane, however, it has higher sensitivity to feed stock impurities requiring strict feed pretreatment to eliminate oxygen, water , sulphur and nitrogen containing compounds

Isomerisation of Light Naphtha

 C5/C6 feed either from straight run crude distillation or from catalytic reforming. Table M-VI 7.3 gives details of isomerization of light paraffins catalyst.

 Reformate: separated in lighter mostly benzene and heavier containing C7

 Catalyst: Zeolite or Pt on Chlorinated alumina Operating Condition: 

Operating Condition: 

                                    Pt on chlorinated    Pt on zeolite
                                        alumina

Temperature oC            120-180                  250-270
Pressure                         20-30                     15-30
Space velocity h-1            1-2                        1-2
H2 /HC ratio                     0.1-2                     2-4
Product RON                 83-84                      78-80

Once Through Process  

Recycle Process: Unconverted n-paraffins and any single branched isomers from double branched isomers

Recycling with Distillation: Deisohexaniser

Recycling with Adsorption: Adsorption on Molecular sieve: n-paraffins are adsorbed and separated by desorption

Table M-VI 7.3: Isomerisation of Light Paraffins Catalyst 

 

Isomerisation Catalyst

 

1st generation

Friedel and Crafts AlCl3 catalysts, exhibit very high activity at low temp980-100oC

2nd generation

Metal/ support bifunctional catalyst essentially Pt/alumina sensitivity to poisons are less acute, however, require higher temperature (350-550oC.

rd            •

3 generation

Metal/support bifunctional catalysts with increased acidity by halogenation of the alumina support. Sensitive to poisons and need pretreatment, Corrosion problem. High activity at low temperature9120oC-to 160oC

4th generation

Bifunctional zeolite catalysts, very resistant to catalyst poison and feed does not need pretreatment

 

Isomerisation of n-butane 

To produce isobutene feed for alkylation or as source of isobutene dehydrogenation to manufacture MTBE

UOP Butamar Process:

Catalyst: Pt/chlorintated Al2O3

Operating Condition: Temperature: 180-220 oC,

 Pressure: 15-20 bar

Soacevel: 2h-1 

H2/HC: 0.5 to 2 

UOP isomerisation Technologies: 

Some of the UOP Light paraffin isomerisation technology are 

PenexTMHigher octanes, higher product yields more than 120 licensed units

 Par-IsomTM: UOP introduced par-ISOM TM in 1996 using zeolite chloride sulfate of zirconium catalyst. It is chracterised by lower equipment cost, multiple catalyst approach. Some advantage of Penex process Maximum octane bbls, high octane, best long-term profitability higher investment cost. It can handle undesired feedstocks including feed and process high benzene content feeds. It has wide range of operation. Penex once through Penex plus TM for extra high benzene levels DIH, DIP/DIH, MDEX TM

Penex:Para-ISOM process with PI-242 catalyst: Best LPG production , good octane, rapid payback, low investment cost

Polymerisation 

Polymerization processes have received considerable interest in petroleum refining because of the higher requirement of reformulated gasoline and phasing of MTBE. The process may be attractive in two main areas .

  • Upgrading of C2 and C Temperature: 150-200oC, Pressure: 30-50bar, space velocity 0.3-0.5 m3/h per m3 cuts from catalytic cracking for oligmerization ethylene & propylene to olefinic gasoline.
  • Producing high quality middle quality  
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