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Supercritical Fluids (SFCs) / Supercritical Fluid Extraction

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Published: Thu, 08 Feb 2018


The experimental determination of the yield of pyrethrins from the Chrysanthemum cinerariaefolium flower is usually carried out with Chromatographic Techniques. A lot of methods about this have been reported over the years [Z-M. ChertY.H. Wang (1996)]. These include HPLC [13 -22], GC [22-26] and SFC [B. Wenclawiak, A. Otterbach (2000) methods. Because of the need for only analyzing the pyrethrins (not reporting for the individual six pyrethrins but analyzing for total pyrethrins), GC was selected as a method of choice.

The yield reported from literature usually ranges from 0.91 – 1.30% of the dry weight [Kolak et al., 1999], 0.60 – 0.79% [Bakarić (2005)], 0.75 – 1.04% [Bhat (1995)],

1.80 – 2.50% [Morris et al. (2005), Bhat and Menary, (1984); Fulton, (1999)], 0.50 – 2.0% [Kiriamiti et al. (2003)], and 0.90 – 1.50% [Pandita and Sharma (1990)].

However, Casida and Quistad (1995) in their book: Pyrethrum Flowers: Production, Chemistry, Toxicology and Uses (pp123-193), states that it is possible to obtain pyrethrin yield of 3.0% or even more.

We obtained, with hexane extraction in a water bath at controlled temperatures and vigorous stirring (with three magnetic stirrers at a speed of 30rpm); pyrethrin yields varying from 0.85 – 3.76% of the dry weight. To our knowledge, this is the first time to report of pyrethrins yield above 3% envisaged by Casida and Quistad.

Key words:

Supercritical Fluid Extraction, Supercritical Carbon Dioxide, Pyrethrins, Solvent extraction, Extraction Yield, Gas Chromatography, Pyrethrin concrete, Crude Hexane Extract.


GC Gas Chromatography

HPLC High Performance Liquid Chromatography

SFC Supercritical Fluid Chromatography

SCF Supercritical Fluid

SCFs Supercritical Fluids

SFE Supercritical Fluid Extraction

SC-CO2 Supercritical Carbon Dioxide

SC Supercritical

CO2 Carbon Dioxide

et al et alii (and others)

pp page

% percentage

CHE crude hexane extracts

BC Before Christ

PY pyrethrin

PYI pyrethrin 1

PYII pyrethrin 2

C1 cinerin 1

C2 cinerin 2

J1 Jasmolin 1

J2 Jasmolin 2

P1 pyrethrin 1

P2 Pyrethrin 2

A1 area of pyrethrins 1

A2 area of pyrethrins 2

WHO world health organization


Pc critical pressure

Tc critical Temperature

Cp critical point

Cm centimeters

~ Approximately

oC degree centigrade

MPa mega Pascal

FID flame ionization detector

n-hexane normal hexane

mL milliliters

/min per minute

Soc. Society

Eds editions

Sci. Science

m meters

mm millimeters

tR retention time

k’ Retention factor

R2 Pearson correlation coefficient

LOQ limit of quantification

LOL limit of linearity

LOD limit of detection

BOD beyond limit of detection

IS internal standard

k response factor

f relative response factor

µm micro meters

µL micro liters

rpm revolutions per minute

1.0. CHAPTER 1: Introduction and Literature Review
1.1.0 Supercritical Fluids (SCF)

When a fluid is forced to a pressure and temperature above its critical point (Fig. 1), it becomes a supercritical fluid. Under these conditions, various properties of the fluid are placed between those of a gas and those of a liquid.

The supercritical state of a fluid is thus defined as one whose liquid and gas are indistinguishable from each other, or one in which the fluid is compressible (i.e. behaves as a gas) while having a density similar to a liquid and, therefore, similar solvating power. Their low viscosity and relatively high diffusivity gives them better transport properties than liquids, can diffuses easily through solid materials and hence faster and better extraction yields. The most important properties of a SCF are its density, viscosity, diffusivity, heat capacity and thermal conductivity. Higher densities of SCFs contribute to greater solubilization of compounds, while low viscosities enable Easy penetration into solids and facilitate flow with fewer hindrances. Manipulating the temperature and pressure above the critical points affects the properties of SCFs and enhances their ability to penetrate and extract targeted molecules from the source materials [1]. Since density is directly related to solubility, by altering the extraction pressure, the solvent strength of the fluid can be modified to exhibit desirable transport properties that enhance its adaptability as a solvent for liquid extraction processes. The density of a SCF is closer to that of liquids and its viscosity is comparable with gases, hence high diffusivity and faster dissolution of solute particles (the diffusivity of SCFs is ~10-4 cm2 s-1 while that of liquid solvents is ~10-5 cm2 s-1). This has contributed to the increasing use of SCF as solvents for extraction purposes.

1.2.0 Supercritical Fluid Extraction (SFE)

Supercritical Fluid Extraction (SFE) is a separation technology that uses supercritical fluid as the solvent. Every fluid is characterized by a critical point, which is defined in terms of the critical temperature and critical pressure. Fluids cannot be liquefied above the critical temperature regardless of the pressure applied, but may reach a density close to the liquid state as mentioned earlier.

The consumer and public awareness of the health, environmental and safety issues emanating from organic solvents use in chemical processes and above all, the possibility of contaminating the final products with the solvent are forces to reckon with in recent times. This has driven the chemical industry looking for the best separation technologies to obtain natural compounds from high purity and healthy products that are of excellent quality [2]. The high cost of organic solvents, environmental regulations, and new requirements in the medical fields, for all time purer and highly valuable products have also revitalized the need for the development of new but clean technologies for products processing [3].

1.3.0 Supercritical Carbon Dioxide (SC-CO2)

SFE with Carbon dioxide (CO2), for this and many reasons is most unique and is able to save both time and money while retaining an overall extraction precision and accuracy.

CO2, therefore, compressed to pressures above its critical pressure [4]; isothermally shows effective solubility powers in the region of its critical temperature [5-6].

Though a lot of SCFs can be adapted as solvents, CO2 is by far, the most extensively used due to its non-toxic, inert and non-flammable nature. It is also inexpensive and is generally environmentally accepted substance [7].

Biological products are often thermally labile, lipophilic, and non-volatile and as such required to be kept and processed at around room temperatures. CO2 has a critical temperature of 31oC which makes it particularly an attractive medium for this task. Other fluids show critical temperatures in the vicinity of critical state but are often difficult to handle and to obtain in pure state, may be toxic, explosive or ecologically unsafe. For such logical reasons, SFE using CO2 has emerged as an attractive unit operation for processing biomaterials.

However, its limitations include the difficulty of extracting polar analytes, owing to the non-polar character of CO2, the different recoveries obtained from spiked and natural samples, and the frequent need for clean-up steps after extraction. Poor thermodynamic description of Supercritical (SC) solvent-solute mixtures, high capital cost for its extraction processes and an almost absence of engineering data to facilitate scale-up and design are also the prime factors that limits the use in industrial and commercial scales. For an excellent engineering design requires reliable data on the transport of a given biomaterial into the SC-CO2; such as the thermodynamic properties, fluid-liquid or fluid-solid equilibrium data of the biomaterial in the region of the temperatures and pressures where processing is technically and economically viable. Also, the measurements for the biomaterial plus SC-CO2 mixture in this condition, any mass transfer limitations for the bulk material into the SC solvent and the selectivity for the desired chemical species with the rest of the solubles in the biomaterial is paramount. Nonetheless, SFE with CO2 has great potential in the field of biomaterial processing as evidenced by the many papers published and the communications presented at the recent symposia on Supercritical fluid Technology [8]. CO2 is a good solvent for extracting lipid-soluble compounds and enables a high level of recovery [9]. CO2 is supercritical above 31.10C and 7.38 MPa, which makes it an ideal solvent for extracting thermally sensitive materials such as pyrethrins.

1.4.0 Set-Up and Principle

A Pilot plant equipped with two fractionation cells. (1) CO2 pump; (2) modifier pump; (3) solid samples extraction cell; (4) fractionation cell 1; (5) fractionation cell 2; (6) valve.

A fluid (CO2) is brought to a specific pressure-temperature combination, which allows it to attain supercritical solvent properties for the selective extraction of active ingredients from the sample matrix of a biomaterial (in this case Pyrethrum). The sample is exposed to the SC- CO2 under controlled conditions; time, temperature, and pressure that allow dissolution of the active ingredients (Pyrethrins) from the sample in the SCF. The dissolved active ingredients will then be separated from the supercritical solvent by a significant drop in solution pressure [10]. Several guiding principles can be utilized to effect the extraction of these ingredients, particularly the quantitative extraction. This ideal extraction method would afford total recovery and high purity of the isolated desired ingredients (Pyrethrins). Due to the inherent variability in density, chemical composition etc, many substances that can be extracted by SFE, modification of the extraction conditions; specifically temperatures, pressures, and extraction time, may be necessary to obtain maximum extraction yield.

In addition to being used for total active ingredient (Pyrethrins) quantification, the pressure-temperature-time variables in this case would be manipulated to allow selective extraction of minute quantities of polar or non-polar analyses from the Pyrethrum sample matrices. This will help attain the optimum extraction time for the process.

1.5.0 Pyrethrum

Pyrethrum flowers come from the Chrysanthemum genus. Due to the size, shape, and colour of the petals; and the daisy-like appearance, they are often called “painted daisies” or “painted ladies.” Other names given to it are Buhach, Chrysanthemum Cinerariaefolium, Ofirmotox, Insect Powder, Dalmatian Insect Flowers, and Parexan.

According to Visiani (1842-1852), it was first recorded in Dalmatia [11]. Other writers [Bakarić P. (2005)] believe that the Pharmacist Antun Drobac (1810-1882) from Croatia was the first to prove its insecticidal activity [12].

Yet there are claims that it was first identified to possess insecticide properties in Asia around 1800 or about 300 B.C.[ Jeanne Roberts]; and that the Crushed and powdered plants were used as insecticides by the Chinese as early as 1000 BC.

The Pyrethrum contains about 1-2% pyrethrins by dry weight, but approximately 94% of the total yield is in the seeds of the flower [Casida J.E., Quistad G.B. (1995)] [13].

From literature [14] [Coomber H.E. (1948)], the chemical structures of the active ingredients, pyrethrin I and pyrethrin II was identified in 1924 by a German chemist Herman Staudinger and a Croatian scientist Lavoslav Ružička.

Kenya is the world’s main producer today, producing more than 70% of the global supply [Casida (1973)]. [15-17]

1.6.0 Pyrethrins

Pyrethrins are the natural active ingredients of the chrysanthemum. Pyrethrin I, cinerin I and jasmolin I are esters of the chrysanthemic acid, and cinerin II, pyrethrin II, and jasmolin II are esters of the pyrethric acid. The three chrysanthemic acid esters are referred to as pyrethrins I (PYI), and the pyrethric acid esters as pyrethrins II (PYII) [Essig K., Zhao Z. J. (2001)]. Pyrethrins I, though insoluble in water, are soluble in some hydrocarbons and organic solvents [WHO (1975)].

According to Todd et al. (2003), they are non-volatile at ambient temperatures, non-toxic to mammals and other worm-blooded animals; and highly unstable in light (photodegradable) [Chen and Casida, (1969)], biodegradable [WHO (1975)], but toxic to aquatic animals. They are mainly used for biological crop protection and as domestic insecticides; and are the major formulations of synthetic pyrethroids.

Pyrethrins when used in sufficient amounts are very effective in killing many insects.

Although pyrethrins are soluble in a number of organic solvents such as hexane, acetone, benzene, petroleum ether, methanol, chlorinated hydrocarbons, etc; other considerations as practical, economic and environmental concerns limit the use of many of these solvents. This reduces the options to just a few.

One of the qualities of Hexane in the extraction of pyrethrins is that it can dissolve the active ingredients effectively without dissolving all the other natural contaminants (pigments, waxes, fatty acids, etc), which are present and must be removed. Removing it from the concrete is also possible at lower temperatures, which limits degradation due to prolonged heating. Its low boiling point is also an added quality. Again, it can be recovered for recycling and reduces the weight of the concrete. Above all, it is inexpensive, accessible and environmentally friendly. It is non-toxic, non-corrosive, non-reactive, and non-flammable.

1.7.0 Pyrethrin Extracts

Although pyrethrins are soluble in a number of organic solvents such as hexane, acetone, benzene, petroleum ether, methanol, chlorinated hydrocarbons, etc; other considerations as practical, economic and environmental concerns limit the use of many of these solvents. This reduces the options to just a few.

Normal Hexane (n-hexane) is the solvent for the extractions. One of the qualities of Hexane in the extraction of pyrethrins is that it can dissolve the active ingredients effectively without dissolving all the other natural contaminants (pigments, waxes, fatty acids, etc), which are present and must be removed. Removing it from the concrete is also possible at lower temperatures, which limits degradation due to prolonged heating. Its low boiling point is also an added quality. Again, it can be recovered for recycling and reduces the weight of the concrete. Above all, it is inexpensive, accessible and environmentally friendly. It is non-toxic, non-corrosive, non-reactive, and non-flammable.

The Hexane is heated above ambient temperature, considering its boiling point (pyrethrum is 170 oC – 200 oC) [23] as the upper limit; for efficient extraction but raising the temperature has an effect. It promotes and aids degradation of the active ingredients. The concentration of pyrethrins in the concrete is expected to be 30 ± 10% by weight with contaminants. Organic compounds that have lower molecular weights (ester, ether, etc) are soluble in liquid carbon dioxide. Some constituents of pyrethrum are partially soluble in liquid CO2, while others are not. Fatty acids, alkanes, triterpenols, Water, are those slightly soluble yet inorganic salts, amino acids, sugars, carotenoids, and fruit acids are insoluble [Marc Sims, (1981)]. Pyrethrins are very soluble in liquid CO2 due to the lone ketone and at least one or ester in its molecules. The rest of the molecule is hydrocarbon.

Normally, GC analysis of the Pyrethrin components is difficult because Pyrethrin I and II undergo thermal isomerization to form isopyrethrin I and II at temperatures above 200oC [24-27]. These temperatures can neither be avoided in split or splitless injection systems nor in the elution from capillary columns. This brings about a transition of the isopyrethrins continuously and lead to improper integration of Pyrethrin I and II the peaks.

The use of very short thin film columns combined with an on-column injection system17 will reduce this thermal conversion. Yet even with such columns the capacity and the separation performance will be insufficient. It also means that the natural Pyrethrins will appear together but the overall detection of the total amount of the pyrethrins is therefore feasible.

1.8.0 Properties

Pyrethrum is very important due to these key properties:

1.8.1 Action: It attacks rapidly, the nervous system of the insects providing knockdown and killing effects eventually.

1.8.2 Immunity: In fact, there are beliefs that insects developing resistance to Pyrethrum is not practicable due to the complex nature of its structure

1.8.3. Toxicity: For a long time, it has proven to be safe for humans and other warm blooded animals but some claim it is toxic for cats [PetEducation.com], but toxic to aquatic animals even at as 2 parts per trillion [Bhanoo, Sindya (2010)] Green Inc. Energy, Environment, and the Bottom Line. New York Times, http://greeninc.blogs.nytimes.com

1.8.4 Activity: It has a vast spectrum of activity and can be used against any insect species. This is because of its closely related group of compounds (PYI and PYII).

1.8.5 Repellency and inhibition/jamming: Pyrethrum is also used to repel insects in food and grain during storage and personal protection. Beside this, it is also used to inhibit insect’s biting efficiency [ ] or jam their biting ability

1.8.6 Flushing: It is considered to have the greatest flushing action than any insecticide. It disturbs and flashes out the insects in their hiding outs.

1.8.7 Environment: Pyrethrum is photodegradable and as such is environmentally friendly (half-life of 12 days in soil) [www.ehow.com]. It also decomposes in air and relatively high temperatures and therefore presents no hazards due to persistence [NPTN Fact Sheet]. National pesticide telecommunications network

1.9.0 Pyrethroids

Pyrethroids are man-made (synthetic) but chemically stabilized form of natural pyrethrins. Their structures are adapted and resemble that of pyrethrins and as such have similar activities. They are altered to improve their stability and potency.There are two kinds. Type I include tetramethrin, Allethrin, bioresmethrin, resmethrin and permethrin. Some type II pyrethroids are cyfluthrin, cypermethrin, deltamethrin, fenvalerate, cyphenothrin, and fluvalinate. They are persistent compounds (cypermethrin, permethrin and deltamethrin) and are resistant to degradation by air and light and therefore, are appropriate for use in wide applications, but they have higher significant mammalian toxicities (Morgan, 1989).

1.10.0 Synergist

Despite the potency and safety of pyrethrum, it has few limitations. Some insects are able to recover from the knockdown effect. Again, because it breaks down in air and sunlight, it looses its effectiveness quickly in outdoor use. These are combated by treating pyrethrum extract with a liquid called Synergist. This has the ability to protect the pyrethrum from breaking down in the insect’s system. Small quantities of pyrethrum are mixed with these chemicals to effectively and efficiently control insect populations. The most popular of there are MGK-264 and Piperonyl butoxide.

1.8.0 Experiments
1.8.1. Objective

The purpose of this experiment is to determine, compare the efficiency and provide a method by which pyrethrins are obtained in an appreciably pure and at the same time stable form (yet economical) from pyrethrum flowers by extracting

1) with an organic solvent (n-hexane) in a Soxhlet extraction and finally obtaining the pyrethrins from the concrete using sc.CO2 (proposed method); and

2) Directly with SC.CO2 and finally dissolving the concrete in organic solvents (methanol, petroleum ether and n-hexane) to obtain the pyrethrins (Factory method).

1.8.2. Chemicals

Grounded chrysanthemum cinerariaefolium, Hexane, CO2 SFE grade

1.8.3. Instruments

Soxhlet apparatus, burner, and flask, filter paper

1.8.9. SFE apparatus

A self built apparatus with the following parts will be used: the pump, cylinder, oven, flow valves, pressure gauges, and thermometers.

1.9.0. Normal (Organic) Solvent Extractions
1.9.1. Water bath

Extraction of the pyrethrins from 100g of the grounded pyrethrum flowers with hexane would be conducted in a water bath (YUHUA, DF-101S) in batches at temperatures of 35oC, 40 oC, 45 oC, 50 oC, 60 oC and 70 oC in 3hrs, 4hrs, 5hrs, 6hrs and 7hrs; in a 1000mL round bottomed flask. Agitation would be achieved by stirring vigorously with three big size magnetic stirrers at a speed of 20rpm. The hexane would then be removed with a rotary evapourator (YUHUA, RE-2000B) at a temperature of 25 oC and at a speed of 180rpm; to obtain the pyrethrin concrete (20mL) also called Crude Hexane Extract (CHE).

1.9.2. Chromatographic Conditions

A Gas Chromatogram with flame ionization detection (FID); Agilent…., HP-5 capillary Column, 30mm × 0.25mm id., 0.25um ¬lm thickness would be used. Each run required about 50mins. The instrument would be calibrated with multiple-point standard additions calibration method using the six individual standard samples to be prepared. The peak area of each component in the sample solutions would be fitted within the linear range of the standard. The split/split less injector, in the ratio 20:1, would be kept at 250 â—¦C. Nitrogen would be the carrier gas at a ¬‚ow rate of 1.6µL/min with an injection volume of 0.1µL.

The temperature program would start at 180 oC, kept for 11 minutes, heated at 10â—¦C/ min to 200 â—¦C, kept for 8 minutes; heated to 210 â—¦C at 10 â—¦C/min, kept for 18 minutes, then heated to 245°C at 30°C/min, staying at this temperature for 4 minutes.

1.9.3. SFE Conditions

The carrier gas will be Hexane with a constant flow rate of 2mL/min, pressure would be between 13-25Mpa. The temperature program would be from 35-45oC. Contact time would be within 3hrs to 6hrs.


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2.0. CHAPTER 2: Report on GC analysis and Organic (Normal) Extractions

2.1.0 Objective

The objective of this section of the experiment was to establish standard curves, by gas chromatographic techniques; for pyrethrins 1 (PYI) and pyrethrins 2 (PYII); the two groups of the six essential ingredients (Cinerin 1, Jasmolin 1, Pyrethrin 1; and Cinerin 2, Jasmolin 2, Pyrethrin 2) of the chrysanthemum (with the standard sample provided by the company), and to determine the percentage yields (and global yield) after Hexane (normal) extractions.

2.2.0 Background

In analytical chemistry, the accuracy of quantitative measurements of the constituents of samples, using standard samples of known composition usually requires calibration. It is usually, but not automatically, done with samples and standards dissolved in appropriate solvents. This is due to the ease of preparing and diluting accurately, mixture of standard samples. Several standard solutions are prepared and analysed or measured, a line or curve is drawn (fit) to the data points and the obtained equation is used to translate values from the unknowns into corresponding concentrations. It has the advantage that random errors in the preparation and readings of standard solutions are averaged over many standards. Again, non-linearity can be seen and eliminated by fitting into the linear sensitivity range by dilution.

Yet still, this can be compensated for by using non-linear curve fitting methods.

It is usually, but not limited to a first-order of measured fit signal (area) on the y-axis against concentration on the x-axis. The model equation is:

y (signal) = m (slope) * x (concentration) + c (intercept)…………………… (1)

It is the most common and straightforward method, but its main drawback is that it cannot compensate for non-linearity. A minimum of two data points are needed to construct the curve. The concentration, x of the unknown sample is given by

x = (y-c)/m……………………………………….. (2)

Where y is the measuredsignal, m is the slope and c is the intercept from the curve (straight line fit). The value of c is zero if the curve is forced through the origin: then

x = y/m……………………………………….. (3)

2.3.0 Gas Chromatography

Gas Chromatography (GC) is a means by which separations, quantifications and identifications of analytes of a given solution or mixture is done.

The essentials required for this method are an injection port where samples are placed. There is also a column on where separations of the components are done; a carrier gas whose flow is regulated to carry the samples all along the instrument, and a detector for the identification of analytes as well as a data processor.

By this tool, a sample is brought to the vapour form and a carrier gas sends the sample into a column. The carrier gas should be inert; chemically. The choice is often governed by the type of detector which is used. With a gas-liquid chromatography, the column is normally packed with a solid stationary phase. Once the sample moves along the column, the analytes that interact strongly with the phase spend more time in the stationary and the moving gas phases, hence will require more time to travel along the column.

There are generally two types of columns: packed and capillary (sometimes called open tubular). Packed columns are 1.5 – 10m in length and have about 2 – 4mm internal diameter. Capillary columns are coated with liquid stationary phases or lined with thin layer which adsorb the stationary phase. They are more efficient than packed columns.

After exiting the column the analytes once separated are detected by a detector and their response recorded for analysis.

The time from inje

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