SAM HIGGINBOTTOM INSTITUTE OF AGRICULTURE, TECHNOLOGY AND SCIENCE

FOOD PROCESSING ENGINEERING DEPARTMENT

Paper presentation by

KAMILU ABUBAKAR MAIGALURA13MTAEPF019

andMUSTAPHA MUHAMMAD NASIRU

13MTAEPF018

APFE 806: ADVANCED FOOD TECHNOLOGY

SUPERCRITICAL GAS EXTRACTION

Introduction

Discovery of supercritical fluids (SCF) Supercritical fluid extraction (SFE) Supercritical fluid chromatography (SFC) Column chromatography (CC) Gas chromatography (GC) High-performance liquid chromatography

(HPLC).

Cont. (Introduction)

The technology of (SCFS) and (SFE)

Improve recovery Increase reproducibility Decrease the use of halogenated solvents Fast Efficiency Quantitative and free of contamination

Historical Background of Supercritical Fluids

The first reporter was Baron Cagniad de la Tour in 1822.

Hany and Hogarth in 1979. studied the solubilities of

Cobalt (II) Chloride, Potassium Bromide, and Potassium

iodide in supercritical ethanol Tc = 243 oC, Pc = 63 atm).

They found that the concentrations of the metal chlorides

in supercritical ethanol were much higher than their

vapour pressures. They also found that increasing the

pressure caused solutes to dissolve and decreasing the

pressure caused the dissolved materials precipitate as

“snow”.

Cont. (Historical background)

In 1936 Wilson, Keith and Haylett devised a propane

deasphalting process for refining lubricating oils.

Solexol process was developed for the purification and

separation of vegetable and fish oils.

Zosel patent In 1970, reported the decaffeination of

green coffee with CO2. This process was accomplished by

soaking the beans in water and then immersing them in

supercritical CO2. The presence of water was essential for

efficient extraction of the caffeine from the bean.

Cont. (Historical background)

Since 1980, there has been rapid development of supercritical fluid

extraction of:

Hops (Hubert and Vitzthum 1980)

Cholesterol from butter (Krukonis 1988)

Perfumes and flavours from natural products (Adasoglu et al

1983)

Residual solvents and monomers from polymers (Krukonis 1985)

Unsaturated fatty acids from fish oils (Krukonis 1988).

SCF technology has become an interdisciplinary field shared by chemical

engineer, chemists, food scientists, agronomists, biotechnology and environmental

control and in many areas.

Definition

A supercritical fluid is the phase of a material at critical temperature and critical

pressure of a material.

Critical temperature is the temperature at which a gas cannot become liquid as

long as there is no extra pressure.

Critical pressure is the minimum amount of pressure to liquefy a gas at its

critical temperature.

Supercritical fluids combine useful properties of gas and liquid phases.

it takes the shape of the container.

The motions of the molecules are quite similar to gas molecules.

In order to understand the definition of SF better, a simple phase diagram can be used. The figure below displays an ideal phase diagram.

1. Here we can see the separate phases of carbon dioxide. The meniscus is easily observed.

2. With an increase in temperature the meniscus begins to diminish.

3. Increasing the temperature further causes the gas and liquid densities to become more similar. The meniscus is less easily observed but still exists.

4. Once the critical temperature and pressure have been reached, the two distinct phases of liquid and gas are no longer visible. The meniscus can no longer be seen. One homogenous phase called the "supercritical fluid" phase occurs.

1

2

3

4

Tc Pc

Properties of Supercritical Fluids

Supercritical Fluid shares some common properties with both gases and

liquids. These properties are:

Density

Viscosity

Diffusivity

Table 1: Order of density, viscosity and diffusivity of gases, liquids and supercritical

fluids.  Properties Liquid Supercritical fluid Gas Density (kg/m3) 1 000 200 – 800

1Viscosity (mPas) 0.5 –1.0 0.05 – 0.1

0.01Diffusivity (cm2/s) 10-5 10-4 – 10-3 0.1

Table 2: Critical points for typical solvents

Solvent Tc (oC) Pc (Bar) ρc (g/ml)

Ammonia 132.5 113.5 0.24

Benzene 289.0 48.9 0.30

n-Butane 152.0 38.0 0.23

Carbon dioxide 31.1 73.8 0.45

Chlorotrifluoromethane 28.8 39.5 0.58

Dichlorodifluoromethane I 11.7 39.9 0.56

Ethane 32.2 48.9 0.20

Ethanol 243.4 63.8 0.28

Ethylene 9.3 50.4 0.22

Isopropanol 235.3 47.6 0.27

Methanol 240.5 79.9 0.27

Nitrous oxide 36.5 72.3 0.46

n-Propane 96.8 42.6 0.22

Propylene 91.9 46.2 0.23

Toluene 318.6 41.1 0.29

Water 374.2 221.2 0.34

Advantages of working with SFC

The physical properties of supercritical fluids between liquids and gases enable the SFC technique to combine with the best aspects of HPLC and GC, as lower viscosity of supercritical fluids makes SFC a faster method than HPLC. Lower viscosity leads to high flow speed for the mobile phase.

Thanks to the critical pressure of supercritical fluids, some fragile materials that are sensitive to high temperature can be analyzed through SFC.

High pressure conditions provide a chance to work with lower temperature than normally needed. Hence, the temperature-sensitive components can be analyzed via SFC.

In addition, the diffusion of the components flowing through a supercritical fluid is higher than observed in HPLC due to the higher diffusivity of supercritical fluids over traditional liquids mobile phases. This results in better distribution into the mobile phase and better separation.

Applications of SFC 

The applications of SFC range from food to environmental to pharmaceutical

industries. In this manner, pesticides, herbicides, polymers, explosives and fossil

fuels are all classes of compounds that can be analyzed. SFC can be used to

analyze a wide variety of drug compounds such as antibiotics, prostaglandins,

steroids, taxol, vitamins, barbiturates, non-steroidal anti-inflammatory agents,

etc. Chiral separations can be performed for many pharmaceutical compounds.

SFC is dominantly used for non-polar compounds because of the low efficiency

of carbon dioxide, which is the most common supercritical fluid mobile phase,

for dissolving polar solutes. SFC is used in the petroleum industry for the

determination of total aromatic content analysis as well as other hydrocarbon

separations.

Application of SFC in Food Processing  

Food processing is the most widely investigated industrial application of

supercritical fluid technology. Carbon dioxide is a particularly suitable solvent for

food processing applications, because its moderate critical temperature (Tc = 31.1

°C), and critical pressure (Pc = 73.8 bar) enables the extraction of thermally labile

food compounds. Additionally, it is non-toxic, odourless, environmentally

acceptable (does not damage the ozone layer, and does not produce smoke), and

relatively inexpensive, and does not have photochemical reaction. Compared with

conventional solvents such as hexane, carbon dioxide does not leave any harmful

solvent residue after extraction. The food material to be extracted is often solid,

and therefore semi-batch extraction is frequently used. A schematic picture of a

semi-batch supercritical fluid extraction system is presented in Figure 2.

Figure 2: Operating principle of a semi-batch supercritical fluid extraction system.

Extraction of supercritical fluids

The unique physical properties of supercritical fluids, having values for density,

diffusivity and viscosity values between liquids and gases, enables supercritical

fluid extraction to be used for the extraction processes which cannot be done by

liquids due to their high density and low diffusivity and by gases due to their

inadequate density in order to extract and carry the components out.

Complicated mixtures containing many components should be subject to an

extraction process before they are separated via chromatography. An ideal

extraction procedure should be fast, simple, and inexpensive. In addition,

sample loss or decomposition should not be experienced at the end of the

extraction. Following extraction, there should be a quantitative collection of

each component.

The higher diffusivity and lower viscosity of supercritical fluids, as compared to

regular extraction liquids, help the components to be extracted faster than other

techniques. Thus, an extraction process can take just 10-60 minutes with SFE,

while it would take hours or even days with classical methods. The dissolving

efficiency of a supercritical fluid can be altered by temperature and pressure. In

contrast, liquids are not affected by temperature and pressure changes as much.

Therefore, SFE has the potential to be optimized to provide a better dissolving

capacity. In classical methods, heating is required to get rid of the extraction liquid.

However, this step causes the temperature-sensitive materials to decompose. For

SFE, when the critical pressure is removed, a supercritical fluid transforms to gas

phase. Because supercritical fluid solvents are chemically inert, harmless and

inexpensive; they can be released to atmosphere without leaving any waste.

Through this, extracted components can be obtained much more easily and sample

loss is minimized.

Cont. (Extraction of SCF)

Instrumentation for SFE

 

The necessary apparatus for a SFE setup is simple. Figure 3 depicts the basic

elements of a SFE instrument, which is composed of a reservoir of supercritical

fluid, a pressure tuning injection unit, two pumps (to take the components in the

mobile phase in and to send them out of the extraction cell), and a collection

chamber.Figure 3: Scheme of an idealized supercritical fluid extraction instrument.

There are two principle modes to run the instrument:

 

Static extraction.

Dynamic extraction.

In dynamic extraction, the second pump sending the materials out to the

collection chamber is always open during the extraction process. Thus, the

mobile phase reaches the extraction cell and extracts components in order to take

them out consistently.

In the static extraction experiment, there are two distinct steps in the process:

Step 1. The mobile phase fills the extraction cell and interacts with the sample.

Step 2. The second pump is opened and the extracted substances are taken out at

once.

Extraction modes

Off-line extraction.

On-line extraction.

Off-line extraction is done by taking the mobile phase out with the extracted

components and directing them towards the collection chamber. At this point,

supercritical fluid phase is evaporated and released to atmosphere and the

components are captured in a solution or a convenient adsorption surface. Then

the extracted fragments are processed and prepared for a separation method. This

extra manipulation step between extractor and chromatography instrument can

cause errors.

Cont. (Extraction methods)

The on-line method is more sensitive because it directly transfers all extracted

materials to a separation unit, mostly a chromatography instrument, without

taking them out of the mobile phase. In this extraction/detection type, there is no

extra sample preparation after extraction for separation process. This minimizes

the errors coming from manipulation steps. Additionally, sample loss does not

occur and sensitivity increases.

Applications of SFE

SFE can be applied to a broad range of materials such as:

Polymers,

Oils and lipids,

Carbohydrates,

Pesticides,

Organic pollutants,

Volatile toxins,

Polyaromatic hydrocarbons,

Biomolecules,

Foods,

Flavours,

Pharmaceutical metabolites,

Explosives, and

Organometallics, etc.

Cont. (Applications of SFE)

Common Industrial Applications include:

The pharmaceutical and biochemical industry,

The polymer industry,

Industrial synthesis and extraction,

Natural product chemistry, and

the food industry.

Application in Food Analyses:

caffeine, peroxides, oils, acids, cholesterol, etc. are extracted from samples such

as coffee, olive oil, lemon, cereals, wheat, potatoes and dog feed.

Cont. (Applications of SFE)

Examples of Materials Analyzed in Environmental Applications:

Oils And Fats,

Pesticides,

Alkanes,

Organic Pollutants,

Volatile Toxins,

Herbicides,

Nicotine,

Phenanthrene,

Fatty Acids,

Aromatic Surfactants in samples from clay to petroleum waste, from soil to river

sediments.

Conclusion 

The technology of supercritical fluid extraction (SFE) using supercritical

fluids (SCFs) is an alternative to conventional liquid extraction due to its use

of environmentally compatible fluids, oxygen free environment, shorter

extraction times, etc. Among SCFs, because of being mostly used due to its

many advantages, supercritical CO2 (SCCO2) is the reagent used to extract

plenty of materials. The special properties of SCFs bring certain advantages

to chemical separation techniques. Several applications have been fully

developed and commercialized. Some of them are food and flavouring,

pharmaceutical industry, environmental protection for volatile and lipid

soluble compounds, extraction of high-value oils, isolation of lipids soluble

compounds, extraction of high-value natural aromas, recovery of aromas

from fruits, meat, and fish, etc.

Thank you!