Back-pressure regulation for catalyst research

Catalysts are substances that allow chemical reactions to proceed at lower temperatures. Even though, many chemical reactions that involve catalysts still occur under extreme conditions. For example, Fischer-Tropsch reactions, where a gaseous mixture of carbon monoxide and hydrogen is converted into (liquid) hydrocarbons at high temperature and pressure over a solid catalyst.

In catalytic research, high temperatures and pressures are needed to prevent condensation of the chemical compounds, in order to analyse the chemical composition of the exhaust coming from a reactor. To find out under which process conditions a catalyst will perform optimally for a specific chemical reaction, a large pressure range has to be investigated. To this end, a Bronkhorst pressure controller is used to pressurize an Equilibar dome-load back pressure regulator.

Process solution

A combination of a Bronkhorst EL-PRESS Process Pressure Controller (PPC) with two integrated high pressure solenoid control valves in a forward and back pressure control loop and a dome-loaded back pressure regulator is used to regulate the back pressure of a catalyst research reactor.

In the dome-loaded back pressure regulator, a flexible dome-shaped membrane separates a reference chamber from a process chamber. The EL-PRESS Process Pressure Controller (PPC) determines the pressure in the reference chamber, which in turn controls the pressure in the process chamber - which is directly connected to the catalyst research reactor. A pressure sensor measures the reference pressure based on a setpoint, and the PID controller will decide whether the inlet valve should open to increase the process pressure, or the relief valve to decrease this pressure. The internal PID controller will guarantee a smooth pressure change. Set at the right pressure, the dome-loaded back pressure regulator will keep the desired process pressure.

Typical catalytic processes occur at pressures ranging from several tens of bars to a few hundred bars. Nitrogen from a gas cylinder can be used to pressurise the reference side of the dome. As 200 bar is the maximum gas pressure in such a cylinder only the difference between this pressure and the process pressure can be used to control the latter. Hence, the PID controller and the small dead band will help to sparingly use the pressure difference and to reduce the consumption of high pressure gas. The valves used in this unit are capable of handling a pressure difference of 200 bar.