Hello everybody. Now, let us study another emerging technology
in food processing that is Supercritical Fluid Extraction. This topic will also be taken in two parts. In the Part 1 today, we will discuss about
the principles of the process and technological aspects including the systems available for
supercritical fluid extraction. In the part two, we will study the application
of this technology in food processing. There is a great demand and in fact need is
felt for the development of green technology. Particularly in the food processing from the
ancient time and time immemorial these extraction and isolation of natural products from various
sources has been done by using large amount of organic solvent or these processes generate
accordingly large amount of organic waste. These industrial solvents which are generally
used traditionally for the extraction processes, many of them are hazardous to human health
and increasing concern about the environment pollution and the other such factors or undesirable
effects of these organic solvents. Let us feel the need of green chemistry. Also, the structure regulations in the use
of industrial solvents have increased the demand of green technology like supercritical
fluid extraction. Supercritical fluid extraction method uses
clean, safe, inexpensive, non-flammable, non-toxic and environment friendly solvents. Also, the energy costs are lower in this process
when compared to that of the traditional solvent extraction processes. So, the first thing comes in our mind what
is supercritical fluid extraction though what is this process about. So, this process that is supercritical fluid
extraction is the process of separating one component from another using a supercritical
fluid as the extraction solvent, ok. As you can see here in this flow diagram that
the material from which the component to be extracted is placed in some vessel, where
the supercritical fluid is introduced in the vessel under certain conditions, all right. At under these conditions the fluid supercritical
fluid extracts those materials or those components from those materials. And then finally, it is separated using appropriate
methods that is the extracted materials is obtained in the collection vessel. This aspect, in further we will elaborate
little in more detail when we study, when we discuss the technological aspects of the
process. So, similarly what is now, supercritical fluid,
supercritical extraction, the supercritical fluid; so, what is supercritical fluid? And in this regard, you can see in this where
there is a concept there is a critical point, there is critical point is the highest temperature
and pressure above which a material can exist in vapour liquid equilibrium, ok. You can see in this diagram phase diagram
that is this is the triple point this line, that is this x axis is the temperature and
y axis is the pressure. So, may be above this temperature and pressure
on this line the material is solid, but if the temperature and pressure is increased
beyond this, so in on this line the solid material may get converted into liquid. Further increase in the pressure and temperature
that is when the critical point curve, if you increase the temperature and pressure
beyond the critical point then this liquid will be converted into some sort of its state
nature and this is supercritical region, it becomes a supercritical fluid and as I told
you that the material exists in a equilibrium between vapour and liquid. So, supercritical fluid is single homogeneous
fluid formed at the temperature and pressure above critical point. These have the properties intermediate to
liquid and gas like they have the properties of liquid as far as their weight etcetera
is concerned, they are heavy like liquid, but they have the penetration power of the
gas, ok. For the production of the supercritical fluid
either the material temperature can be increased above that region or the material pressure
can be brought to the desired level either by compressing or by some other methods. So, important thing is that it has to come
that is like in this case above this, ok. That is the critical temperature and pressure
is to be maintained. In this slide I have tried to show you that
a comparison between the physical properties of gas, liquid and supercritical fluid. The physical important physical properties
like density, dynamic viscosity, kinematic viscosity, thermal conductivity, diffusion
coefficient and surface tension. And as I told you that they the supercritical
fluid like you can see in the data that this is for the supercritical fluid. So, and the values if you compare that they
have the properties intermediate to those of the liquid and the gaseous state. And accordingly sometime this is SCF are also
known as or called as compressible liquid or dense gases. They have higher solvent power and this high
solvent power of these supercritical fluids is mainly due to their liquid like density
that is their density is much higher, that is 100 to 1000 times greater than gases. And they have excellent transport properties. And this excellent transport property is owing
to the gas like viscosity it is 10 to 100 times less than the liquid, and diffusivity
is also better and they in fact the gas like viscosity diffusivity together with the zero
surface tension. This contributes to the transport properties
of these gases and rather they improve the transport they have the excellent transport
properties. So, different supercritical fluids and their
critical pressure and temperature above which they become super they come in supercritical
stage is shown in this table. You can see the data. But the two supercritical that is which is
indicated by red is worth seeing that is the carbon dioxide it has a critical temperature
304.1 degree Kelvin and critical pressure 73.8 bar. So, the in fact the temperature requirement
is less here and the water has a critical temperature 643 sorry 647.3 degree Kelvin
and 221.2 bar pressure. So, the most commonly supercritical fluid
used in the food industry is the carbon dioxide. Its properties that it has the properties
like it is inert, it is inexpensive, easily available, odourless and tasteless, environment
friendly. There is no solvent residue in the food after
the extraction, it is suitable for thermoliable natural products, low energy inputs, good
solvent for non-polar substances. So, these are the good desirable characteristics
of the supercritical carbon dioxide which make it as a very good solvent for making
or for use in food processing industry. Water you can see you can compare the data
it becomes another good equally good solvent but the here in this (Refer Time: 11:45) just
the data only of carbon dioxide and water has been shown. So, the critical temperature you can see in
the degree Celsius in this figure the water has 31.1 degree Celsius and this pressure
73 point, means that is the carbon dioxide above a temperature of 31.1 degree Celsius
and the pressure of 73.8 bar, it will behave like a supercritical fluid and its critical
volume at this stage become 73.9 litre per kmol. Whereas, the water which is again as far as
its properties are concerned, it may be also considered as a good solvent, it is inert
and other characteristics are there but here you see that both the temperature and pressure
required to bring it in supercritical stage are comparatively very high. The temperature in fact is 374 degree Celsius
and the pressure accordingly is 221 bar and under these condition its critical volume
is also less that is 57.1. So, it in fact from the practical application
point of view the use of water as a supercritical fluid rather becomes impractical or infeasible
that is why it is not used and the carbon dioxide its temperature and pressure it can
be easily achieved and it can be easily converted into. And this is the pictorial that is the diagram
how the state changes when the liquid carbon dioxide is converted into by increasing the
temperature and pressure is brought in to the supercritical fluid. So, its nature or state is shown here in this. So, let us before we come to the process application
technological, let us briefly understand the properties of the supercritical fluid. How these properties are actually they different
from the normal supercritical or normal carbon dioxide and liquid carbon dioxide? Because that becomes an important consideration
in the extraction processes and designing extraction process or parameters and optimising
the conditions and so on, ok. So, as I told you that is these supercritical
fluids they behave as a dense gas occupying all available volume as a single phase, but
they cannot be condensed as liquid by increasing the pressure. The densities of the supercritical fluids
depend on temperature and pressure varying in the range of may be 400 to 700 kg per cubic
metre and which is significantly lower than the density of the liquid, ok. Liquid you can say normally that is they have
the density of 1000 kg per cubic metre. So, this significantly lower density of the
supercritical carbon dioxide is an important advantage in the extraction processes. Also, the transport properties of the supercritical
fluids are those between the liquid and gases. Viscosity of supercritical carbon dioxide
is about 0.5 mPa per second milli Pascal per second and which is significantly lower than
the viscosity of the hexane. Even the molecular diffusivity of supercritical
fluid carbon dioxide at 40 degree Celsius is about one order of magnitude higher than
that of the diffusivity in the liquid state, and in fact viscosity and diffusivity their
multiplication are constant. So, this provides a good; so, makes that is
these properties are particularly transport property density, viscosity, etcetera it makes
it useful in the supercritical. So, that is the favourable transport properties;
that is are desirable in extraction operations like low viscosities facilitate the penetration
of supercritical fluid into the particulate beds. And it reduce the power requirement in transferring
the fluids through the system. Higher diffusivity increases the mass transfer,
and approaches to the equilibrium. Means you see it results in that is the higher
diffusivity of the SCF gives higher extraction efficiency in the processes. And the phase equilibria between the SCF and
food component that is the equilibrium between SCF solvent and food component to be extracted
are required for quantitative analysis of the extraction processes. That is how, when, under which conditions,
what are the various factors, which influence and how the phase equilibria can be maintained
between this and because this is also important as far as the extraction yield and extraction
efficiency of the process is concerned. Another important property as I told you the
solubility that is the solvent power of the supercritical fluid depends on its structure,
its polarity, as well as its density. Initial stages of SCF extraction are governed
by the distribution coefficient of the solute between the dense phase and the sample matrix. Therefore, it is controlled by the solubility. So, solubility parameters of a dense gas can
be estimated by these equations, where rho by rho liquid is the ratio of the density
of the dense gas to that of the liquid at its boiling point and the Pc obviously, is
the critical temperature. So, from this one can get the solubility parameter
of the dense gas from these equations. And the equilibrium because this is again
important equilibrium is expressed by the solubility of the component at a given temperature
and pressure. And this is usually determined by the experimental
methods that is for particular product, for particular depending upon the material characteristics
etcetera. What are the parameters, pressure temperature
another things what are required so that should be experimentally determined. But, as far as the SCF CO 2 is concerned and
its usefulness in food processing operations, the following that is the rule which I have
listed here they apply. And what are those? There is three major points that is the number
one solubility of low molecular weight and low polarity organic compounds like carbohydrates,
alcohols, carboxylic acid, esters, aldehyde etcetera is very high in SCF CO 2. Means there is a complete miscibility. On the other hand, the other important rule
which governs the process is the macromolecules and highly polar molecules. Like sugar, starch, proteins, salt etcetera
are not soluble. So, means there is these material that is
which I have shown in the first that is they can be easily extracted and they are completely
miscible, but the other macromolecules this cannot be so, and the food this components
macro molecules remain intact in the food but other bio actives or smaller components
and low polar component, low molecular weight components can be easily extracted. Also, the solubility of some insoluble components
of course, can be increased by the addition of some Co-solvents or entrainers such as
ethanol, acetone etcetera. For like for example, the solubility of beta
carotene is increased to a great extent by using a mixture of carbon dioxide, that is
supercritical carbon dioxide and ethyl acetate, like ethyl acetate here is used as a CO-solvent. So, the co-solvent that have seen in the last
slide that is they have important effect sometime they improve the efficiency of the process,
they increase the extractability of a particular compound. So, accordingly the co-solvents or entrainer
actually, they are normally that is those which are use they are organic substances
which have volatility intermediate to supercritical fluid solvent and the solute to be extracted. And generally it is added in small concentration
may be 1 to 5 molecular percentage right and a small amount of co-solvent increases the
ability of a supercritical carbon dioxide to dissolve polar compound without significantly
changing its density and compressibility. That is its soluble solubilisation power extractability
is improved but other characteristics are not disturbed. The co-solvent mixed with SCF solvent is supercritical
that is the important thing that is it mixture has also to come under the supercritical state. That is means that is the may be that is individually
solvent and co-solvent may be having different critical pressure and temperature to come
into the supercritical state, but here mind it when the co-solvent is mixed with the SCF. So, may be there may be certain change in
the temperature. So, there it should be it will be supercritical
state at the mixture when the mixture or pressure is above the mixture critical pressure and
the temperature is above its mixture critical temperature. And the common type of co-solvents used or
entrainers used are methanol, ethanol, acetone, and propanols etcetera. So, in this slide again that is this is or
this data are taken from the literature. So, different co-solvents, their characteristics,
like what is the critical temperature, critical pressure, molecular mass, dielectric constant,
polarity index etcetera all those things that are given here in this table. And they become useful consideration from
this it becomes easy to select a proper co-solvent which is suitable for extraction of a particular
material in a particular process. Now, we come towards the another equipment
part and its process part of the things like in a supercritical fluid extraction system
that is what are the different components, ok. We can see here in this figure that is number
1, that is the system should have one carbon dioxide supply source all right that CO 2
or a SCF source means there is there either in the carbon dioxide cylinder or some other
that is you should have a carbon dioxide source. And then a chiller unit. Then a co-solvent or modifier pump of course,
it is optional that is if required in the process it may not be completely necessary,
ok. Then a pump is needed to pressurize the gas,
and an oven containing the extraction vessel that is where the actually material is put
all right that is the vessel extraction vessel. So, in this the material and carbon dioxide
come in contact then a restrictor that is to maintain high pressure in the extraction
line and then finally, the separator it come to through a separator all right, and then
which normally works under a lower pressure and finally, there is a material is collected,
the restrictor material is collected. So, it has some extract collection collecting
vessel. And accordingly as in case of any other system
there is the necessary instrumentation for controlling and maintaining the pressure,
temperature, there is flow and other things are obviously, they are provided even controller,
indicators and etcetera accessories. So, regarding operating principle of the supercritical
fluid extractor, it can operate in static mode, dynamic mode or in a combination mode. The process can be made batch or continuous. In the static mode there is the supercritical
fluid is circulated in the extraction vessel for a certain period of time after which it
is passed through followed. So, it is released through the restrictor
to the trapping vessel whereas, in the dynamic mode of extraction there is a continuous flow
of SCF, that is the SCF is allowed to flow continuously through the sample in the extraction
vessel and go out to the restrictor to the trapping vessel. And sometime also there are combination systems
that is where conduction of static extraction for sometime followed by a dynamic extraction. So, combination is the mixture of a combination
or both static as well as dynamic. So, all these types of systems are available
and the systems are batch operation or continuous operation (Refer Time: 27:02). So, this it is a that is a just process flowchart
for any that is the general supercritical fluid extraction process. So, in here there is the fluid the introduction
in the extraction vessel that is by appropriate assembly, appropriate process, for the large
scale process one should have obviously, with a conveying equipment, and feeding equipment
and controller etcetera. So, thing is there the first the extraction
vessel has to be fed with the material from which that extraction is to be done. Then, before the pressurization, before bringing
that is operating fluid then obviously, there is here in this extraction vessel the material
is brought to in contact with the supercritical fluid under required conditions of the pressure
and temperature. So, before pressurizing the system is allowed
to reach the pre-set operating parameters and these operating parameters may be experimental
trial and other all methods that is depending upon what are the components one wants to
extract. So, it is set and then the supercritical fluid
is cooled in the chiller to ensure liquid feed to the pump. And then after that this chilled carbon dioxide
is discharged into the pressure vessel and adjustment of the pressure is done to the
desired level. So, simultaneous discharge of co-solvent through
the pump at the predetermined flow rate is done in the system, where the co-solvents
are used and then the conduction of the extraction operation it may be is allowed either in the
dynamic mode or in the combination mode or in the static mode, allowed in the batch system
which may batch system may include one set of the extraction unit whereas, the continuous
system may have the combination of different set of extraction unit either in parallel
or in series. So, finally, after this it is allowed that
is a particular time, definite time then it is the last step is the isolation of the dissolved
solute by precipitation and by adsorption or by any other appropriate method and then
followed by release or recovery of the supercritical fluid. So, that is the there is the process operation
of the method. The supercritical fluid technology has many
advantages like it is a very good green process, it results in the replacement of organic solvent
with environment friendly and non-toxic solvent, it reduces the risk of the solvent residue
because the in the organic solvent, most of the material fluids is a that is the solvent
residue always remain particular in residual cake in the other things that remains a problem. So, no such type of problem is here in this
case. It is a rapid process, it is suitable for
the extraction and purification of low volatile component, ok. Even suitable for thermo labile natural products. So, both low volatile as well as highly volatile
thermo sensitive products etcetera they can be extracted easily with and even the extracted
product that is their quality can be improved. Complete and easy recovery of solvent from
the extract or the raffinate both is possible and it is very efficient, and the process
can be made continuous. It has low handling cost, selectively extract
target compounds, and is a versatile set of technology. And this is in fact one of the very emerging
technology and novel technology for food processing application, for getting that is the value
added products from the food materials. And this aspects that is the its application
in the food processing industry etcetera we will take up in the second part of this lecture. Thank you.
