Application note

Supercritical CO2 for fragrant & oil extraction

The French company SFE Process develops and manufactures equipment for automated extraction of natural compounds from raw materials such as plants for end customers typically within food, perfumery, cosmetics and pharmaceutical industries. The use of supercritical CO2 allows low temperature extraction of essential oils, aromas or perfumes from a natural product without denaturing it. 
To improve the accuracy and hence the quality of the extraction equipment, SFE Process contacted Bronkhorst France for their flow meters.

What is supercriticial CO2?

As an effective alternative for volatile organic solvents, supercritical CO2 - carbon dioxide - has proven its worth. We talk about supercritical fluids when there is no distinct between the gaseous and liquid phase of the fluid. In this case, for CO2 , this is at temperatures higher than 31° C and pressures > 73 bars. This is called the 'supercritical' state. This state combines useful liquid properties - being a solvent - and gaseous properties - high diffusivity-, making it a good extracting agent. 

Supercritical CO2 extraction for perfume

SFE Process: "We are completely satisfied with the Bronkhorst flow instruments, and with their service and support."

Application requirements

Control of the supercritical CO2 flow and temperature allows selective and accurate extraction of compounds from the raw material. Without a flow meter, analysis would be based on theoretical flow curves with an accuracy of approx. 20%, which does not allow for repeatable successive extractions in terms of production yield. Knowing the precise mass flow of CO2 passing through the raw material guarantees repeatable yields. So, such a flow meter is needed. Moreover, the extraction process needs to be conducted in an automated way.

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Important topics

  • Accuracy & repeatability
  • Automation/control
  • Versatility - able to monitor temperature and density
  • Service & support

Process solution

The Bronkhorst solution consists of a Coriolis-based mass flow meter - mini CORI-FLOW M15 series - for the SFE Process' industrial equipment, and a mini CORI-FLOW M14 mass flow meter for laboratory equipment. The flow meters are equipped with the Modbus protocol for communication between the flow instruments and the rest of the SFE Process equipment.

The standard industrial equipment developed by SFE Process is used for pressures up to 400 bars and 100°C. In laboratory applications, the pressure can go up to 1000 bars. The mass flow meters are placed in front of the pump that applies the high pressure to the extractor.

Flow scheme supercritical CO2 extraction
Flow scheme

At the start of the supercritical CO2 extraction process, the natural raw material is placed in a container which is put in the extraction part of the equipment. Here, a pump continuously circulates the CO2 in a supercritical state, and selected compounds are dissolved in the supercritical CO2 medium. By playing with temperature and pressure in the extractor, it can be defined which compounds are extracted. After extraction, in the separation part of the equipment the pressure is decreased to separate the (now gaseous) CO2 from the extracted compounds. This CO2 is recovered and can be used for subsequent extraction cycles. During a cycle, several different compounds can be extracted, and they are collected into two or three separate vessels in liquid or solid form.

Solid materials such as flowers or wood are typical raw materials out of which compounds are extracted. Another application is the removal of organic solvents from plastic waste, in order to clean and recycle the plastic.

SFE Process’ extraction equipment allows automatic extraction due to a set of pre-recorded recipes that can be fully parameterised according to the raw materials and the to-be-extracted compounds. By integrating a flow meter, it is possible to accurately measure the CO2 flow and to control this flow continuously to ensure an optimal extraction. The mass of the CO2 flow is measured as important information to analyse the extraction efficiency.

In addition, the flow meter accurately measures the temperature and density of the carbon dioxide. The temperature is measured to make sure that the CO2 is supplied in a liquid state before pumping. If necessary, adjustments can be made by e.g. changing the heat exchanger or pump settings. 

Extraction control and monitoring is extremely accurate and is conducted in real-time. Thus, it is a real quality assurance of production, which saves time and money and which improves the process.

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SFE Process equipment for supercritical CO2 extraction
SFE Process equipment for supercritical CO2 extraction

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