Supercritical fluids are very dense fluids, with superior properties when compared to liquids or solvents. The most commonly used of these fluids is CO_2. Unlike solvents, it has a much less harsh impact on the environment.

Pumping high density liquid CO₂ requires supercritical CO₂ pumps, such as the range of high-pressure pumps from Core Separations.

Why is Supercritical CO₂ So Effective?

Once it reaches critical temperature, CO₂ remains a gas-like fluid, combining the solvating power of a liquid with the diffusion properties of a gas. Adding small amounts of fluids or other modifiers can improve its solvating properties.

Applications for supercritical CO2 include

• Supercritical fluid extraction (SFE)
• Supercritical fluid chromatography (SFC)
• Injection moulding and extrusion
• Synthesising polymers in plastic production
• Manufacturing electronic chips
• Producing microparticles
• Cleaning, as a solvent substitute
• Replacing solvents in chemical processes.

But, supercritical CO2 will only be effective if the means of delivering it is effective too.

Supercritical CO₂ pumps must maintain excellent pressure and temperature control, and deliver a consistent CO₂ feed.

Adaptive Pressure Control

Pressure control is a key parameter in supercritical CO2 extraction. The two facets that enable this in a pump are:

• An automatic back pressure regulator, and
• Accurate PID (proportional, integral, derivative) control of this regulator.

Fluctuations can result in changes to density and therefore solubility during extraction. A regulatory solution that offers a superior level of control but is also flexible enables the supercritical pump to achieve +/- 2 bar of a set point.

This system is known as APC (adaptive pressure control). With APC, PID control of the automatic pressure regulator provides accurate, stable and consistent CO₂ extraction.

Thermal Control

Control of heating and cooling is crucial in supercritical CO₂ applications, and this involves precise thermal regulation processes.

Manipulating pressure and temperature are both important in controlling density during extractions, but there tends to be more emphasis on pressure control.

However, maintaining certain temperature ranges is vital, and these can be very broad.

This is especially relevant when performing operations in sub ambient conditions below 31°C, classified as subcritical.

Core Separations has integrated thermal regulation directly into its software, providing internal control of gas temperature, rather than only controlling the external jacket temperature of vessels.

Density and Flow

How you supply CO₂ to an extraction system can have an impact on its efficiency and consistency. The common method is to draw liquid CO₂ from a cylinder using a compression pump.

The disadvantage here is that when the pressure drops, there is a phase change from liquid to gas, causing a significant drop in density.

The best way to manage this is with a flow meter, to monitor incoming CO₂ densities in real-time. This allows for flexibility in controlling pump speeds, in response to varying densities.

And altering density can influence flow. Core Separations pumps achieve this by controlling temperature at different points throughout the process.

Accurate temperature control from Huber Circulators within the pump chill the incoming feed, eliminating any temperature effects on CO₂ density.

The overall effect is a supercritical CO₂ pump that can performs to changing specifications, producing consistent results.

For more information about supercritical pumps from Core Separations, please contact us here at SciMed.

High-Pressure Pumps Features:

• Dual ceramic pistons minimize pressure pulses
• Wide flow rate capability
• Low dead volume pump heads

Scimed – An SFE Journey 2000-2020

Over the last 20 years Scimed has been providing SFE technology into a number of different industries. We have worked with some of the pioneering providers to offer customised solutions from including Waters and Separex which was created by Michel Perrut with Jean-Yves Clavier.

We have continued to develop our in-house capabilities to offer custom solutions which are integrated here in the UK. This has allowed our customers to work even closer with us to create a custom solution to their problems. Liaising with notifying bodies we create high-tech, high pressure assemblies that compile with the current PED safety legislation. All our systems are CE marked by an accredited NoB after vigorous testing.

Scimed offer some of the most advanced and up to date technologies in the field of supercritical fluids offering solutions under a range of pressures exceeding 1000 bar. Working closely with Core Separations based in Dallas  we have expertise in almost every aspect of supercritical processing.

Now in 2021 we are looking to continue pushing the boundaries of the technologies to help our customers innovate.

You can also visit the Core Separation website for more product details by clicking on their logo below: