What are the application advantages of supercritical fluid technology in the field of fine chemical separation and purification?

The application advantages of supercritical fluid technology (mainly composed of supercritical CO ₂, with a critical temperature of 31.1 ℃ and a critical pressure of 7.38MPa) in the field of fine chemical separation and purification stem from its unique physical and chemical properties of both gas diffusion and liquid solubility, which are reflected in the following aspects:

1、 High separation efficiency and strong selectivity

Accurately regulate solubility to achieve targeted separation

The solubility of supercritical fluids exhibits a "continuously adjustable" characteristic with temperature and pressure changes (increasing pressure enhances solubility; increasing temperature enhances solubility for low polarity substances). For example:

Separation of active ingredients from natural products (such as monoterpenes and sesquiterpenes in plant essential oils): By adjusting the pressure (8-20MPa) and temperature (35-60 ℃), the target components can be selectively dissolved (such as low molecular weight monoterpenes being preferentially dissolved at a pressure of 8MPa and high molecular weight sesquiterpenes being dissolved at a pressure of 15MPa), with a separation purity of over 95%, much higher than traditional solvent extraction (purity typically 70% -80%).

High diffusion coefficient and fast mass transfer rate

The diffusion coefficient of supercritical fluid (10 ⁻⁷ -10 ⁻⁸ m ²/s) is 10-100 times that of liquid, and the viscosity (0.01-0.1mPa · s) is only 1/10-1/100 of liquid. It can quickly penetrate into solid materials (such as porous adsorbents and plant cells), shortening the equilibrium time. For example:

Extracting caffeine from tea leaves using supercritical CO ₂ extraction only takes 2-3 hours, while traditional ethanol extraction takes 6-8 hours and increases the extraction rate by 10% -15%.

2、 Green and environmentally friendly, reducing pollution

The solvent is non-toxic and harmless, with no residual risk

Supercritical CO ₂ is widely recognized as a "green solvent":

Chemical inertness (does not react with most organic compounds), non toxicity (LD ₅₀>5000mg/kg), non flammability, avoiding toxic residues and flammable and explosive risks of traditional organic solvents (such as benzene and chloroform), especially suitable for fields with strict purity requirements such as food additives and pharmaceutical intermediates (such as extracting vitamin E, solvent residue can be controlled below 1ppm, far below the EU standard of 50ppm).

After extraction is completed, CO ₂ can be gasified and separated from the product by reducing pressure (to atmospheric pressure), without the need for distillation and dissolution, eliminating energy consumption and pollution in the solvent recovery process from the source.

Environmentally friendly, reducing emissions of three wastes

CO ₂ can be recycled (recovery rate>95%), and there is no discharge of wastewater or waste solvents throughout the entire process;

Compared to traditional distillation (high energy consumption) and adsorption separation (requiring frequent solvent regeneration), the energy consumption of supercritical fluid separation is reduced by 30% -60% (such as separating unsaturated fatty acids in oil, which consumes only one-third of molecular distillation).

3、 Mild operating conditions to protect thermosensitive components

Low temperature operation to avoid component degradation

The critical temperature of supercritical CO ₂ (31.1 ℃) is close to room temperature and is suitable for separating thermosensitive substances (such as enzymes, peptides, volatile aroma components):

Purification of probiotics (such as lactic acid bacteria): Traditional freeze-drying methods can easily lead to bacterial inactivation (survival rate<50%), while supercritical CO ₂ removal of water from fermentation broth can achieve a bacterial survival rate of over 90% and retain metabolic activity under conditions of 35 ℃ and 10MPa.

Extracting natural pigments (such as carotenoids and anthocyanins): Avoiding the oxidative degradation of pigments caused by traditional thermal extraction (60-80 ℃), the retention rate of pigments after supercritical extraction is greater than 90%, and the color stability is improved by 2-3 times.

Low shear force, protecting structural integrity

The flow state of supercritical fluids is mild and causes minimal structural damage to polymer materials such as proteins and polymers. For example:

Separation of collagen peptides: Traditional acid dissolution method is prone to peptide chain breakage, while supercritical CO ₂ extraction (with a small amount of ethanol) can remove impurities under mild conditions. The molecular weight distribution of peptide segments is more concentrated (3000-5000Da), and the biological activity (such as cell proliferation rate) is increased by 40% compared to traditional methods.

4、 Simple process, easy to scale and integrate

Short process, capable of continuous operation

Supercritical fluid separation is typically a "one-step" operation (integrated extraction separation) that does not require multi-stage extraction or complex post-processing. For example:

Separation of EPA and DHA from fish oil: Through a supercritical CO ₂ extraction column, omega-3 fatty acid ethyl esters with a purity greater than 90% can be directly obtained at a pressure of 12-18 MPa and a temperature of 40-50 ℃, while traditional methanol ethanol fractional crystallization requires 3-4 steps, which is a long process and consumes a large amount of solvent.

Easy to integrate with other technologies and expand application scenarios

Combined with membrane separation (supercritical fluid membrane coupling technology): By utilizing the high permeability of supercritical fluid to enhance the mass transfer efficiency of the membrane, the flux for separating antibiotic fermentation broth is increased by 2-3 times compared to traditional membrane filtration, and the membrane fouling rate is reduced by 50%.

Combined with chromatographic technology (supercritical fluid chromatography SFC): As an alternative technology to HPLC, SFC uses CO ₂ as the mobile phase, with fast separation speed (reducing analysis time by 30% -50%) and high column efficiency. It has been widely used for drug impurity detection (such as detecting isomer impurities below 0.1% in raw materials).

5、 Widely applicable in various fields, suitable for the needs of fine chemical industry

Pharmaceutical field: Purification of antibiotics (such as desalination and decolorization of penicillin G), extraction of active ingredients from traditional Chinese medicine (such as increasing the purity of artemisinin from 15% of crude extract to 99%);

Food industry: Removing trans fatty acids from oils and fats (removal rate>90%), extracting fragrances (such as preserving the aroma components of rose essential oil more completely);

Materials field: Purification of polymer monomers (such as polymerization inhibitors in methyl methacrylate, with a purity of 99.99%), preparation of ultrafine powders (particle size distribution can be controlled within 1-10 μ m).

In summary, supercritical fluid technology, with its advantages of "green, mild, and controllable", can meet the requirements of high-purity and high activity products in fine chemical separation and purification, as well as conform to the industry trend of low-carbon and environmental protection. Especially in the separation of heat sensitive, easily oxidizable, and high value-added substances, it has demonstrated irreplaceable application value and is one of the core technologies of "green separation" in the field of fine chemical engineering.