Alkylation, Isomerisation And Polymerisation | Chemical Technology - Chemical Engineering PDF Download

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 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 

Penex^TM: Higher octanes, higher product yields more than 120 licensed units

 Par-Isom^TM: 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