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Publication Title | Assessing Technical Feasibility of Supercritical Extraction Processes of Naturally

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Assessing Technical Feasibility of Supercritical Extraction Processes of Naturally


Typical Example of Solubility Parameters Determination

Case Study #1 – Extraction of Peppermint Oil from Raw Peppermint Leaves

The primary goal of a laboratory SFE and Phase Monitor unit testing is to assess technical feasibility of a potential supercritical fluid extraction application. Experimental work begins using a supercritical fluid extraction bench top laboratory unit. The bench scale laboratory extraction unit typically has 10ml to 4 liter sample vessel capacity. Product samples and data from the feasibility testing are used to assess product quality, and to research the following process variables: 1) Preparation of feedstock 2) Extractor conditions 3) Separator conditions. The extract product is analyzed to determine how changes in these parameters change extract yield, concentration, and quality. Phase equilibrium experiments should be carried out to determine the preliminary processing conditions in which the compound of interest solubilizes and precipitates from the supercritical fluid. This information can then be utilized to give a “starting point” to the extraction and separator processing conditions and insight to a commercial scale supercritical fluid extraction system. If the results from preliminary testing is encouraging, process development protocol is followed by proceeding to the next step. Examples demonstrating the use of both laboratory SFE and supercritical fluid phase equilibrium instrument will be shown in this poster.

Once the appropriate solubility parameters are obtained for a material at a given temperature, pressure, and co-solvent condition with the Phase Monitor, these data can then applied to give a “starting point” to the development of the true processing parameters in a supercritical fluid extraction unit. Pictured below are some typical cloud point data for the solubility of poly(styrene-co-acronitrile) and poly(methyl methacrylate). When the supercritical fluid and sample is clear, the sample is soluble, when there is a “cloud point” of the supercritical fluid and sample there is no (or minimal) solubility.

The traditional isolation method for peppermint oil is by steam distillation. SFT developed a process to extract peppermint oil using supercritical fluids. Interestingly enough, the true peppermint “taste” that you are familiar is actually a combination of the pure peppermint oil isolated and the partial thermal decomposition products of the pure peppermint oil. The taste of “pure” peppermint oil is very different from that of the traditional steam distillation method. After determination of the general solubility parameters of peppermint oil in the SFT-Phase Monitor a matrix of extraction conditions were explored. The SFE conditions were optimized to obtain the highest yield, best quality, and purest fraction.

Solubility Experiments – Phase Monitor

Fraction 3: Dark Wax w/Some Peppermint Oil: 250 Bar, 400 degrees Celsius, Yield of 3.0%

The yield and quality of pure peppermint oil was greater with supercritical fluids than that of traditional steam

Direct, visual observation of materials under actual supercritical conditions is an important first step in the development and refinement of supercritical fluid extraction processes. A specially designed phase equilibrium view cell or “Phase Monitor” is used to observe the dissolution, melting, precipitation, swelling and crystallization of compounds at a wide range of pressures and temperatures. Observations of materials are performed in the supercritical region, under precisely controlled conditions. The Phase Monitor simplifies the determination of critical point for binary, tertiary or complex mixtures. Through a better understanding of phase behavior as a function of temperature, pressure, co- solvent, and sample concentration, a significant time and cost savings for supercritical process development is realized.

distillation and there was no thermal decomposition of the oil noted, giving a much purer fraction.

Variable-Volume Equilibrium View Cell Design

Saw Palmetto is a type of palm tree that grows in parts of the southeastern United States. The berry of the saw palmetto plant contains a compound that may reduce the symptoms of benign prostatic hyperplasia (BPH), a noncancerous enlargement of the prostate gland. From the 1870s until 1950, saw palmetto was commonly used to treat prostate and other urinary problems. In the United States, saw palmetto is available as a dietary supplement. There are currently 8 supercritical fluid extraction facilities worldwide processing Saw Palmetto. The experimental path again began with a typical parametric investigation of extraction conditions on Phase Monitor and Lab SFE Unit. The data was compared to that obtained on pilot scale extraction below. Saw Palmetto extracted by the traditional method (solvent) currently costs at $35-45/kg. Supercritical fluid processing cost ~ $0.80-$1.60/lb.

Main components include a Variable-Volume Equilibrium View Cell, Pressure Generator, Light Source and Color CCD Video Camera, sample mixing, and optional Video Monitor Display Panel Module, PC Video Capture Software, and Co- Solvent Addition Module. Experiments can be Performed from a Few Hundred psi to 10,000 psi (689 Bar, 69 mPa) and from ambient temperature to 150o degrees Celsius.

Supercritical Fluid Extraction Development Unit

Occurring Materials Using Benchtop Laboratory Equipment

Validation of Solubility Measurements

The accuracy of the SFT-Phase Monitor as an experimental method was validated by comparing the experimentally determined critical point for pure CO2 with the literature values. The gradual phase transition of carbon dioxide from a single phase supercritical state through the critical point to a two phase subcritical state is pictured below. (The view cell shown here has a glass tube sample holder inserted in the cell).

CO2 Storage

Kenneth J. James, Ph.D.,* Supercritical Fluid Technologies, Inc.,

A typical SFE Extractor is comprised of a High Pressure Carbon Dioxide Pump, Fluid Preheater, Co- Solvent Addition Module, Extraction Sample Cell, Heated Micrometering Valve, Atmospheric (or Pressurized) Collection/Separator Vessel(s) and Flow Meter. Feedstock is placed in the High Pressure Extraction Vessel and Carbon Dioxide Flows Through Extraction Vessel into the Micrometering Valve. The Micrometering Valve depressurizes the supercritical fluid (to the gas state) and the analyte of interest precipitate in the collection vessel.

Temp (C) 80

Pressure (psig) Liquid 3150 5120 8000 9540

Solvent/Feed Ratio

10 30.55 18.33 18.33 18.33

Yield (1% ) ND 14.46 15.13 15.07 15.27

Comparison of Lab Scale and Pilot Plant Results

Key processing parameters of the raw material to achieve the desired quality and yield are now detailed in the SFE unit.


Liquid 3160 5200 7600 9540

10 27.5 18.33 18.33 18.33

ND 15.86 15.27 15.6 15.13

18.33 15.07

Preparation of Feedstock: Grating, Grinding (cryogrinding), Flaking, Pelletizing, Drying, and Wetting Extractor Conditions: Pressure, Temperature, Preheater settings, Solvent Selection, Co-solvent

18.33 15.27

Selection (Concentration), Flow Rate, Vessel Aspect Ratio, and Solvent/Feed Ratio


Separator Conditions: Pressure, Temperature, Adsorbent Separation, Membrane Separation, Filter Separation, Centrifugal Separation, Fractional Separation

Fraction 1: Peppermint Oil: Pressure 88 Bar, 60 degrees Celsius, 8-10 liters/minute expanded carbon dioxide gas. Yield of 2.0% Peppermint Oil (Pure Peppermint Fraction).

Fraction 2: Peppermint Oil with some Waxes: 150 Bar, 200 degrees Celsius, 8-10 Liters/Minute. Yield of 2.5% Peppermint Oil w/Waxes.

Case Study #2 - Saw Palmetto Extraction Data to Determine Larger Scale Extractor Operation Conditions


Liquid 3040 5040 7500 9640

10 27.5 18.33 18.33 18.33

ND 15.6 15.13 14.86 13.33

Saw Palmetto Extraction Data to Determine Extractor Operation Conditions on a Lab Scale Unit

240 x Scale-Up of Laboratory SFE

Entrainer System



Extract Product


Recycle System

Pressure Temp (C)

Pilot Plant SF-Ratio Yield (%) (%)

5100 60 8000 80 9500 80

18.33 15.13

20.0 14.8 20.0 16.0 10.0 16.0


Saw Palmetto Process Scale Unit

Conclusions: The laboratory scale Phase Equilibrium Monitor and SFE Unit are useful for process development, determining extraction/separation operating conditions. The Variable-Volume Equilibrium View Cell apparatus is an accurate and quick method for obtaining solubility data (especially with multi-component mixtures). The laboratory scale SFE Unit is remarkably accurate for determining extraction rate data for preliminary economic analysis of a Commercial-Scale application. The data obtained matches up well with much larger scale processing units.

CO2 Make-Up

Lab-Scale SF-Ratio Yield


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