Nov-2020

Isomalk-2: a low-temperature, non-chlorinated light naphtha isomerisation process (ERTC)

Isomalk-2 is a low-temperature isomerisation technology that has been commercially proven in grassroots projects, revamps of semi-regenerative reforming units, and replacement of other isomerisation technologies.

Zhepeng Liu
Sulzer GTC Technology

Article Summary

This flexible process utilises a robust platinum-containing mixed oxide SI-2 catalyst that works effectively at the low temperatures of 120-140°C (250-285°F), while delivering great stability against the influence of catalytic poisons. Isomalk-2 is a competitive alternative to the most commonly used light naphtha isomerisation processes: chlorinated aluminum oxide and sulphated zirconium oxide catalysts, applicable for simple replacement of these catalyst types. This technology has been commercialised in all possible modes of configuration. By applying the full recycle configuration, an isomerate with a 93 RON value has been achieved in a world-scale reference unit.

Process Overview
Isomalk-2 offers refiners a cost-effective isomerisation option that consistently demonstrates reliable performance with all standard process configurations, including:

- Once-through isomerisation
- Once-through with pre-feed deisopentaniser
- Recycle of low-octane pentanes and hexanes
- Full recycle of all non-branched paraffins and pre-feed deisopentaniser.

Each scheme generates high yield and octane results. The following examples are for a light straight run (LSR) process stream, but may also be applied to a condensate stream or some LSR/condensate combinations.

Once-through Isomerisation
In a once-through isomerisation process scheme, the LSR is mixed with hydrogen. The mixture is then heated and enters a first reactor where benzene saturation and partial isomerisation take place.

The product mixture exits the first reactor, is cooled and then fed to a second reactor to complete the isomerisation reaction at chemical equilibrium. The product mixture from the second reactor is cooled and fed to a separator, where the mixture is separated from the recycled hydrogen gas. Recycled hydrogen is combined with make-up hydrogen and fed through the recycled gas dryers for blending with feed. No hydrocarbon feed drying step is required.

Unstabilised isomerate from the separator is heated and fed to the stabiliser. The stabiliser’s overhead vapours are cooled and fed to a reflux drum. Liquid hydrocarbons from the reflux drum are returned to the stabiliser as reflux, while uncondensed light hydrocarbons are separated and sent to the off-gas system. The bottom product or isomerate is cooled and sent to gasoline blending.

Prefractionation with Recycle of Low-Octane Pentanes and Hexanes
The scheme utilises all the mentioned above methods: prefractionation, isomerisation, and postfractionation. The prefractionation step consists of deisopentanisation of the feed and/or C7+ separation. The postfractionation step consists of separating the high-octane portion of the C5-C6 isomerate and recycling the low-octane n-pentane and hexanes stream. These recycle schemes are optimally designed using dividing wall column technology (GT-DWC).
 
Process development
The improvement of the technology and the introduction of the SI-2B catalyst have made it possible to discontinue hydrogen gas recycling and implement the process with once-through hydrogen supply. This reduces costs for grassroots unit construction, as well as allowing drop-in replacement of the chlorinated catalyst at existing units, thus eliminating reagents supply and wastes generation.

Summary
In summary, the SI-2 catalyst provides high conversion rates and a close approach to thermal equilibrium at low temperatures. Key to the technology is that the SI-2 catalyst exhibits superior activity alongside stability, simplicity, and safety in operation. Features of the Isomalk-2 technology include:

-    Process capability to produce 81-93 RON
-    Low operating costs
-    Regenerable catalyst with superior tolerance to process impurities and water
-    No chloride addition or caustic treatment needed; no wastes produced
-    Mass yield >98%, volume yield up to 100%
-    Up to 6-12 year cycle between regenerations
-    Guaranteed service life of SI-2 catalyst 10+ years
-    Reduced hydrogen consumption.

This short article originally appeared in the 2020 ERTC Newspaper, produced by PTQ / DigitalRefining.

You can view the digital issue here - https://online.flippingbook.com/view/1029582