Catalytic isomerization Back

Action Rearrange
Method Catalytic
Purpose Convert straight chain to branch
Feedstock n-Butane, n-Pentane, n-Hexane


Product(s) goes to

Gas plant

The isomerization units convert normal paraffins (such as n-butane, n-pentane and n-hexane) into their respective iso-paraffins. Some of the normal paraffins of light SR naphtha have a low octane number. These are converted to high-octane isomers. In isomerization, like in catalytic reforming, hydrocarbon molecules are rearranged, but unlike catalytic reforming, isomerization just converts n-paraffins to iso-paraffins.

The two important isomerization units are butane (C4) and pentane/hexane (C5/ C6) units.

C4 isomerization unit:

A refinery that has an alkylation unit probably does not have enough iso-butane (iC4) to blend with propylene and butylene. If the refinery has a hydrocracker, it may have excess iso-butane to blend with gasoline. Without a hydrocracker, but with a catalytic cracker and alkylation unit, a refinery may have to supply the iC4. Refineries usually have two choices here – buy it or make a butane isomerization (BI) unit.

A butane isomerization unit produces feedstock for alkylation. The process involves highly active aluminum chloride or hydrogen chloride catalyst at low temperatures to isomerize n-butane.

C5/C6 isomerization unit:

A refinery that has problems meeting gasoline octane targets and has a lot of SR gasoline around needs a C5/C6 isomerization unit. Imagine that n-pentane with octane number 62 can be converted to iso-pentane with octane number 92 and n-hexane with a very low octane number of 25 can be converted to iso-hexane with octane number 75.

Pentane/hexane isomerization is used to increase the octane number by converting n-pentane and n-hexane into their relevant iso-versions. In a typical pentane/hexane isomerization unit, dried and desulfurized feedstock is mixed with a small amount of organic chloride and recycled hydrogen, and heated to reactor temperature. It is then passed over a catalyst in the first reactor, where benzene and olefins are hydrogenated. The feed goes to the isomerization reactor, where the paraffins are catalytically isomerized to iso-paraffins, cooled and passed through a separator.

DMA 35 Ex Petrol

The DMA 35 portable density meter measures the density, SG and °API of samples on-site within seconds. The intrinsically safe instrument (ATEX-marking II 2 G Ex ib IIC T4) has a special housing, resistant to petroleum samples. It is therefore perfectly suitable for measuring petroleum samples in hazardous areas. The integrated RFID interface enables quick sample identification (e.g. tank number) before measurement. Measured results can be stored and printed or exported to a PC wirelessly via IrDA later on. The instrument fully complies with the ASTM D7777 standard.

0.001 g/cm3

Repeatability s. d.:
0.0005 g/cm3

Measuring range:
0 g/cm3 to 3 g/cm3

Minimum sample volume:
2 mL

Benefits of DMA 35 Ex Petrol at Catalytic isomerization

The DMA 35 Ex Petrol portable density meter measures the API gravity, API SG or API density (calculated from true density) of the different liquid final products and byproducts resulting from catalytic izomerization (product group B: refined products) directly at the sampling location for quick identification.  It automatically displays the measured value, already compensated to your reference temperature of choice.