C₅/C₆ Isomerization

Once-through C₅/C₆ isomerization

The scheme of once-through C₅/C₆ Isomerization is based on a permutable reactors design; that is, either reactor can be used in the lead or lag position or it can be operated independently during catalyst servicing. This insures an ultra-high on-stream service.

De-isopentanizer (DIP)

To improve the octane boosting effect of the isomerization process, a deisopentanizer column can be integrated upstream of the isomerization unit. The advantages of this scheme are the following:

• having a new separate base with a high MON to be blended into the gasoline pool: isopentane
• sending a low isopentane-containing feed to the isomerization unit, so that the net isopentane production is larger

A further step to increase the octane pool is to split the reformate into two cuts. A light reformate is thus obtained including C₅ and C₆ components. This cut can be isomerized after separating the isopentane. This can be achieved by blending the light reformate with the straight run light naphtha and processing them simultaneously.

Isomerization with De-isohexanizer (DIH)

For still higher RON isomerate, a deisohexanizer can be added downstream from the reaction section. The higher octane and more volatile iso-hexanes (dimethylbutanes) are removed by distillation together with the C₅’s. The distillate is combined with the de-isohexanizer bottom to become the final isomerate product. A side-stream from the bottom half of the column, concentrated in lower octane species such as methylpentanes (MPs) and the unconverted n-hexane, is recycled to the reactor.

De-pentanizer (DP)

To reach a higher RON, a Depentanizer can be implemented between the Stabilizer and the DIH, allowing to recycle the unconverted nC₅ back to the DIP. This overall improvement of the C₅ conversion leads to an increase of the isomerate RON.

Ipsorb™

The Ipsorb™ scheme is shown to recycle the normal paraffins for their complete conversion.

This process uses a deisopentanizer (DIP) to separate the isopentane from the reactor feed. A small amount of hydrogen (H2) is also added to the reactor feed. The isomerization reaction proceeds at moderate temperature, producing an equilibrium mixture of normal isoparaffins. The catalyst has a long service life. The reactor products are separated into isomerate product and normal paraffins in the Ipsorb™ molecular sieve separaction section, which features a novel vapor phase PSA technique. This enables the product to consist entirely of branched isomers.

Hexorb™

Ultimately, to go beyond the 90 RON threshold, substantial conversion of the methyl pentanes is required. This can be achieved with full conversion of normal paraffins by integrating the Hexorb™ separation process with the reaction section. This process combines a cyclic molecular sieve adsorption system with a downstream de-isohexanizer that splits raw isomerate from the molecular sieve section into an isomerate overhead stream rich in isopentane and dimethylbutanes and poor in the lower octane methylpentanes (MPs) from two streams containing heavier components.