How to prepare the matrix for supercritical CO2 extraction?

Supercritical CO2 extraction is a method of separating valuable compounds from plant matrices with high efficiency and selectivity. Supercritical fluids are highly compressed gases which at a certain specific temperature and pressure behave halfway between a gas and a liquid. Once reached the supercritical state, the extraction solvent density increases with the increase of the pressure, in turn enhancing the solubility of the extracted materials.

The process of supercritical CO2 extraction can be divided into two steps:

1. The plant material is solubilized with the solvent at the supercritical state.
2. The extracted compounds are then recovered from the solvent to produce the end product.

It is crucial to prepare the plant matrix thoroughly to achieve optimal results during extraction. The matrix should be prepared before being placed in the baskets. Even more important is to remove as much water as possible from the matrix for two main reasons. If you’re interested in learning why it is essential to remove water from the matrix, keep reading!

As mentioned above, it is crucial to prepare the plant matrix to achieve the best results. This means removing water. Here are the reasons why, in the supercritical CO2 extraction process, it is necessary to eliminate water to prepare the matrix effectively.

1. Water (which is polar) is incompatible with supercritical CO2 (which is non-polar). Water therefore has the opposite polarity compared to SC-CO2 and is completely insoluble in it, but can be expelled from the matrix by simple mechanical action, uselessly absorbing kinetic energy and lengthening the process times. Make sure you have dried the matrix very well, leaving a quantity of water less than 10% by weight, optimally around 7%, otherwise you will waste energy and money extracting the water (it costs much less to use a dryer!).
2. Grinding the matrix is very important because it increases the exchange surface and facilitates extraction. However, we must not exaggerate. Grain size values greater than 2 mm or less than 0.5 mm do not very often give satisfactory results. When the particle size of the matrix is too large, the difficulty coefficient of the extraction may be too large and the process efficiency too low. When the grain size of the matrix is too small we are dealing with dust. Powders easily suffer from the channeling effect. Wormholes form in the matrix and most of the CO2 will pass into these channels without extracting anything. Furthermore, dust tends to clog the filters, which will require frequent cleaning. Dusts < 0.4 mm must be absolutely avoided as they can pass through the filters and clog the high pressure circuit, block the valves, break the basket filters. Typically, the milled matrix should contain less than 10% particle sizes smaller than 0.4 mm.