Flow control in catalysis at high pressure

September 26, 2017 Yann Le-Guenniou

In this blog, I would like to share an application of our flow instrumentation at one of our customers in which we needed to deal with high temperature and high pressure. This customer – an energy research organisation - investigates a catalysed chemical reaction of a mixture of hydrocarbon compounds.

Catalysts are being used to accelerate a chemical reaction without actually being consumed. So a small amount of catalyst is sufficient to obtain a large amount of reaction products.

Solid catalysts are often small, highly porous particles, with a large internal surface area in a small volume. This internal surface contains active sites on which the reaction takes place. Gaseous or liquid chemicals diffuse into the pores of these particles, and react at the catalytically active sites to reaction products that diffuse out of the particle. Often, these reactions occur at extreme process conditions.

What were the application requirements?

A simple and reliable solution had to be found to inject a liquid flow at a high pressure. This injection has to take place at 30 to 60 bars, and needs to result in a stable flow without pulsation. Furthermore, the liquid flow needs to be controlled accurately, and during the process it has to be known how much liquid actually has been injected.

catalysis at high pressure
Catalysis at high pressure

Which solution did the customer choose?

The solution comprises a Coriolis mass flow meter that controls a HPLC piston pump at the inlet side of the reactor and an independently operating back pressure controller at the outlet side. The tested Coriolis mass flow meter (mini CORI-FLOW ML120) has proven to be a very stable and accurate mass flow meter. The WADose HPLC pump gives a very stable flow without pulsation. The combination of an HPLC pump and mass flow meter works as a mass flow controller. The control valve of the Coriolis mas flow meter is not necessary, as the pump is used as an actuator.

The pump can handle a liquid viscosity of max. 40 mPa.s at the upstream side. The maximum operating temperature is 70 °C. The temperature of the furnace that contains the reactor tube with small catalyst particles is much higher. The pressure at the reactor tube outlet has to remain at a high value. Beyond the outlet there is a cold trap for water or oil condensation, a back pressure controller with control valve that can handle pressure differences up to 400 bars and an exhaust to atmospheric pressure.

The pressure controller can handle gas and liquid in a very stable controlled flow. Especially at very small flow rates, this pressure controller has a much better control performance than a mechanical pressure reducer. The exhaust is used to remove gas that has been produced at the reaction.
The pump has three control modes:

  1. pressure
  2. volumetric (only the speed of the piston is controlled)
  3. and mass flow
The latter is a special feature that can be offered, and is convenient from a chemist’s point of view. As the flow can be controlled directly, the exact number of moles injected to the process is known. Control and monitoring occurs via the digital interface. The mass flow measure and setpoint, density, temperature and counter value are visible via this single digital interface.

Wadose pump with mini cori-flow
Wadose pump with mini CORI-FLOW

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