Flow control for isomerization

Improving reliability and productivity of your process


An isomerization process can be used to improve the octane numbers of light straight-run naphtha. Efficient and reliable valve operations provide the means for significant yield improvements and energy savings in an isomerization process. Valmet offers a wide selection of reliable valves for isomerization applications.


Reliable and field-proven dryer performance



Meet noise, emission and fire safety regulations set by local authorities


Reach plant uptime targets with on-line diagnostic capabilities

Process overview

An isomerisation process can be used to improve the octane numbers of light straight-run naphtha. In isomerisation, the atoms of a molecule remain the same but are rearranged producing an isomer. Isomerisation processes also saturate benzene into cyclohexane by hydrogenation as benzene concentration in gasoline is legislated due to environmental concerns.

Using a simpler once-through process, research octane numbers (RON) can be improved from 70 to about 80-84. When also utilising recycling of the unconverted hexane, octane numbers can further be improved to around 87-93.

The pentane/hexane and hydrogen feed usually enter the process through dryers which are used to ensure that the feed is free of oxygen sources that could decrease catalyst activity. If a catalyst type is used that can tolerate water, dryers may not be necessary.

After mixing with make-up hydrogen, the feed is heat-exchanged against the reactor effluent. It then enters a charge heater (or heat exchanger) before entering the reactors. The reactors are kept at a temperature of about 100-200 °C (200-400 °F) as the equilibrium of the isomerisation reaction is pushed towards the isomers at lower temperatures. The relatively low temperature slows down the reaction rate, requiring the use of a catalyst to make the reaction proceed at a reasonable rate. In order to maintain high catalyst activity, some catalysts require the addition of small amounts of organic chlorides. Hydrogen quenches are used to maintain reactor temperature and catalyst activity.

Some cracking also occurs in the reactors, and the light gas formed is removed in the stabilisation column. The remaining part exits the stabiliser through the bottom. This stream then enters a deisohexaniser where the unconverted hexane is separated and recycled. 

Isomerization process
Isomerization process

Isomerization applications

Efficient and reliable valve operations provide the means for significant yield improvements and energy savings in an isomerization process. Product yield can be optimised with efficient reactor quench control. Energy efficiency is improved by substantially minimizing the amount of heating fluid utilised to preheat the feed to the isomerization process. Valmet provides valves for different izomerization applications – from feed and regenerant control and dryer switching valves, hydrogen quench control, reactor inlet shut-off, column heat and product control and column overhead vapour control. You can learn more from the application report below. 

Neles™ solution for feed control

Neles globe valve with an intelligent ND valve controller provide excellent control reliability and accuracy for the application.

  • Best possible control accuracy, ensuring that the feed ratio is kept at the right amount
  • Long lasting tightness, as the valve utilises metal seats
  • Minimise leaks, as the rugged one piece body structure eliminates potential leak paths
  • Different inherently characterised trims, available as equal percentage, linear and quick open
  • Process variability reduced with the intelligent ND valve controller

Neles™ solution for dryer switching

Neles ball valves with a SwitchGuard™ (SG) intelligent on/off valve controller.

  • Particle build-up prevention, as the seat and ball are in continuous contact effectively wiping the seat surface with every cycle
  • A high cycle design, which makes it perfect for high cycling applications such as dryer switching
  • Durable two-way tightness as standard with live-loaded metal seats
  • Field proven design, as the Neles ball valves have been widely used in drying applications
  • Configure to meet process demands – SG gives the possibility to set the on-off valve stroking times and profiles according to the process needs

Neles™ solution for hydrogen quench

Neles globe valves ensure efficient and reliable reactor quenching.

  • Optimise hydrogen consumption, as reliable control reduces variability
  • Use more efficient catalysts, as more active catalysts require control that is quick to respond
  • Wide rangeability, ensuring that the reactor temperature can be kept constant with varying feed composition
  • Interchangeable trim parts making it possible to easily change flow characteristics
  • Detect problems in advance with the ND intelligent valve controller

Solution for reactor inlet shut-off

Neles™ ball valve with a ValvGuard™ (VG) intelligent safety solenoid ensures that the valve will be operational when needed.

  • Long life time, due to robust design
  • Anti-blowout valve shaft, ensuring the safety of personnel and equipment
  • High torque piston actuator, designed to overcome static friction
  • Partial stroke test, which can be performed by the VG9000 either automatically or manually to ensure that the valve is working properly
  • Compliance up to SIL 3 by third party certifications
  • HART & Foundation fieldbus communication compatibility
  • Advanced diagnostics capability of the VG9000, increasing safety and allowing plant safety targets to be reached more economically

Neles™ solution for column control

Neles globe valve provides a robust and economical solution for these applications. In case extreme rangeability is required, Neles segment valves are the valve of choice for the application. To ensure the best possible control accuracy and reliability, these valves may be equipped with the Neles ND intelligent valve controller.

Neles™ solution for overhead vapour

With close to equal percentage characteristics and superior tightness, Neles triple eccentric disc valve is an economical and reliable choice for large size control applications.

  • Triple eccentric design, reducing wear and producing tight shut-off
  • No resilient parts exposed to the medium, extending the life time of the valve
  • Mechanically induced disc to seat contact, meaning that the seal does not rely on assistance from differential pressure
  • Easy and stable column operation, since free movement of the disc ensures minimal seat friction
  • Low emissions as a result of utilising rotary design and a reliable stem packing