The CO2 extraction method is a popular extraction technique used to produce high-quality botanical extracts, such as essential oils, terpenes, and other flavor and fragrance compounds. There are two main types of CO2 extraction methods: subcritical and supercritical. While these methods have similarities in terms of the use of CO2 as a solvent for extraction, they also have some notable differences that impact the outcome of the extraction process.
Subcritical CO2 Extraction
Subcritical CO2 extraction, also known as low-pressure or mild extraction, is performed at temperatures and pressures below the critical point of CO2 (31°C, 73.8 PSI). Subcritical CO2 extraction can be used for delicate and heat-sensitive compounds, such as terpenes, that may be damaged or destroyed by more intense extraction methods. Subcritical CO2 extraction also produces extracts that are more selective and nuanced than supercritical CO2 extraction methods. This is because subcritical CO2 extraction utilizes lower pressures and temperatures, resulting in a slower process that encourages selectivity by targeting select temperature and pressure points to extract desired compounds. Typically the particles of the starting material will be less finely ground and less fully dissolved in carbon dioxide.
Subcritical CO2 extraction is often referred to as “the gentlest” method of extraction, as it produces high-quality extracts with minimal damage to the starting material. During the subcritical CO2 extraction process, the CO2 releases the target compounds from the plant material, and the compound-mixture is collected at a much lower pressure in a separate container. One challenge of subcritical CO2 extraction is that it can be a slower process, and therefore, production can be limited depending on the size of the extraction equipment.
Supercritical CO2 Extraction
Supercritical CO2 extraction, also known as high-pressure extraction, is performed at higher temperatures and pressures than subcritical CO2 extraction, typically around 60°C and 3000 PSI. Supercritical CO2 extraction is a faster and more efficient method of extraction, making it a popular choice for larger commercial operations. Supercritical CO2 extraction is ideal for extracting a broad spectrum of chemical constituents including both non-polar and polar compounds due to its tuning functionality. Pressure and temperature can be increased and decreased to extract oils of varying polarity so that extracts can be collected mid-run.
During the supercritical CO2 extraction process, CO2 behaves both as a gas and liquid, as high pressure compresses the gas, increasing the density of the gas and allowing it to flow through the plant material (solid). The pressure is released downstream where the plant-based oil and CO2 gas are separated, and the oil is collected. The attractive feature of supercritical CO2 extraction is its speed and higher volume of extract yield. However, supercritical CO2 extraction can often yield an extract with more impurities if not done correctly, as the higher pressure and temperature parameters can cause undesirable constituents to be extracted along with the desired compounds.
Comparison of Subcritical and Supercritical CO2 Extraction
While the differences between the subcritical and supercritical CO2 extraction process are significant, they both offer unique advantages and disadvantages that should be considered depending on the desired outcome of the extraction process. Some of the main differences between these methods include:
- Pressure and Temperature: Subcritical CO2 extraction is performed at temperatures and pressures below the critical point of CO2, while supercritical CO2 extraction is performed at higher temperatures and pressures above the critical point of CO2.
- The selectivity of the process: Subcritical CO2 Extraction is selective, slower, and very nuanced, whereas supercritical CO2 extraction gives faster, broad-range extraction, but can extract undesirable constituents.
- Yield: Supercritical CO2 extraction usually yields a larger amount of extract than subcritical CO2 extraction does, yet the yield may not be as selective, nuanced or high quality as sub-critical CO2 extraction.
- Speed: Supercritical CO2 extraction can be a faster process than subcritical CO2 extraction, primarily used for batch processing larger volumes.
- Cost-effectiveness: Subcritical CO2 extraction can be less cost-effective than supercritical CO2 extraction due to the need for slower processing, lower volume batches and more in-depth concentration work.
While both subcritical and supercritical CO2 extraction processes use CO2 as a solvent for extraction, they are distinct processes with advantages and disadvantages that should be considered depending on the desired outcome and properties of the starting material. Subcritical CO2 extraction is a slower, gentler process that produces highly selective, nuanced, and high-quality extracts, whereas supercritical CO2 extraction is a faster, broader range, high volume process that may result in a lower quality extract with contaminants. While it has tempting benefits of speed, volume and broad extraction of constituents, it may not be the optimization choice when quality and selectivity are key. Ultimately, choosing the right extraction method depends on the nature of the desired extract, the nature of the starting material, and the unique requirements of the application.