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What are supercritical substances?

something which i above the critical temperature, within the supercritical region of a phase diagram.

These substances do not really behave as a liquid or a gas, but a bit of both.


Where are supercritical substances used?

in the pharmaceutics and food industry


what can supercritical substances do?

they can permeate solid substances if there are any holes or pores


What sort of properties of a liquid does a supercritical substance have?

It has increased density like a liquid


what sort of properties of a gas does a supercritical substance have?

diffusivity and viscosity like a gas


if supercritical substances are not really regarded as a state of matter, what are they commonly referred to as?

a mesophase


what are supercritical substances good for?

dissolving stuff, due to its high density and abilitiy to soludise


what are some applications of supercritical substances?

- can penetrate into coffee beans to remove the caffeine. The high diffusivity of the supercritical substance can solidify the caffeine when you pull it out in its dissolved state

good for diffusing and mass transport e.g. the transdermal delivery of progesterone.

supercritical fluid can be used to turn progesterone into a more soluble form, then it can increase the permeation and help it move into the skin to be used


Why is progesterone not taken orally?

most of it is digested and not absorbed.

it can be administered topically but these dont dissolve so cant really be absorbed into the body


how is a supercritical substance made?

not easily, as not everything can become a supercritical fluid.
The temperature and pressure values required vary depending on the compound.

We need to adjust temperature and pressure to be in the supercritical region of the phase diagram for that particular substance in order to convert it into a supercritical fluid


Why is carbon dioxide one of the most attractive compounds to use?

only requires a pressure of 73.8bar and a temperature of 31.1 degrees C which is easy to achieve and control

lots of other drugs tend to degrade at higher temperatures


What is GRAS? and what does it mean?

generally recognised as safe,

substances which the FDA have approved as safe, so dont have to undergo extra regulatory things


Is supercritical CO2 GRAS?



What are the advantages of using supercritical substances?

can be used for extraction processes which can take nicotine out of tobacco, flavour extraction, drug synthesis.

useful for thermolabile products (those that thermally decompose easily)

good for dissolving stuff and doesnt require harsh conditions


What is the phase rule?

A formula: F = C-P=2
where F = degrees of freedom
C = component
P = phase


What does the phase rule tell us?

it gives us the number of degrees of freedom which is the least number of independent variables that must be fixed to describe the system completely


What is a phase?

a homogenous physically distint portion of a system that is separated from other portions of the system by boundaries.

e.g. theboundary between air and the solid table.
e.g. if you mix oil and water, they are both liquid but will separate into 2 layers or phases


What is a component?

the chemical species.
It is a distinct species present in the system.

E.g. in a glass of ice and water, both are the same component (same species) even though they exist in 2 phases


What is a one component system?

glass with ice in it. even though there are 2 phases.

we get a degrees of freedom of 1


What does a degrees of freedom of 1 mean>?

we only need to describe ONE axis to know what the substance is on a phase diagram
e.g. if you describe the temperature alone its enough to know exactly where/what it is

whereas if the system was just water the degrees of freedom would be 2 so we would need to describe 2 things to find out exactly what it is


What happens in a 2 component system?

the maximum degrees of freedom = 3
we would need a 3-dimensional grpha OR we could keep one variable constant and still have a 2D graph.
e.g. keep temperature or pressure constant


In the case of two partially miscible liquids, how many variables are there?

three variables:
Temperature, pressure and concentration


What happens if we increase the concentration of one of the liquids (phenol) in the other liquid (water) while keeping temperature constant at 50degrees?

The liquid will remain in a single phase (miscible) until a point (e.g. 11% of phenol in water) where it wil lsplit into 2 phases


What is the purity of the liquids when they are in two phases?

neither component is pure


What is a tie line?

A line drawn on the phase diagram which represents the same composition of liquids throughout but in different ratio


What does the area outside the curve mean?

All systems outside the curve only have one phase i.e. they are homogenous


What changes depending on where you are inside the curve?

the composition of the phase


What does a ratio change mean?

the relative weight of each phase varies along the line


How do you work out the weight ratio on a tie line?

Measure the length of the point to each end,
Ratio should be DC/BD where B is on the left, C is on the right and D is the point of which weight ratio you are trying to find


What is a eutectic mixture?

a 2 component system containing liquid and solid phases
These will be simplified to be completely miscible liquids and completely immiscible solids

e.g. salol-thymol in the solid phase does not mix, but if you heat it up, everything dissolves so liquid salol and liquid thymol do mix