Lecture 3

Question 1

What are supercritical substances?

Answer 1

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.

Question 2

Where are supercritical substances used?

Answer 2

in the pharmaceutics and food industry

Question 3

what can supercritical substances do?

Answer 3

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

Question 4

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

Answer 4

It has increased density like a liquid

Question 5

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

Answer 5

diffusivity and viscosity like a gas

Question 6

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

Answer 6

a mesophase

Question 7

what are supercritical substances good for?

Answer 7

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

Question 8

what are some applications of supercritical substances?

Answer 8

• 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

Question 9

Why is progesterone not taken orally?

Answer 9

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

Question 10

how is a supercritical substance made?

Answer 10

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

Question 11

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

Answer 11

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

Question 12

What is GRAS? and what does it mean?

Answer 12

generally recognised as safe,

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

Question 13

Is supercritical CO2 GRAS?

Answer 13

yes

Question 14

What are the advantages of using supercritical substances?

Answer 14

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

Question 15

What is the phase rule?

Answer 15

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

Question 16

What does the phase rule tell us?

Answer 16

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

Question 17

What is a phase?

Answer 17

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

Question 18

What is a component?

Answer 18

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

Question 19

What is a one component system?

Answer 19

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

we get a degrees of freedom of 1

Question 20

What does a degrees of freedom of 1 mean>?

Answer 20

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

Question 21

What happens in a 2 component system?

Answer 21

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

Question 22

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

Answer 22

three variables:

Temperature, pressure and concentration

Question 23

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

Answer 23

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

Question 24

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

Answer 24

neither component is pure

Question 25

What is a tie line?

Answer 25

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

Question 26

What does the area outside the curve mean?

Answer 26

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

Question 27

What changes depending on where you are inside the curve?

Answer 27

the composition of the phase

Question 28

What does a ratio change mean?

Answer 28

the relative weight of each phase varies along the line

Question 29

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

Answer 29

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

Question 30

What is a eutectic mixture?

Answer 30

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

Question 31

What is on the x axis of this eutectic mixture phase diagram?

Answer 31

different composition of the mixture.

Question 32

How many regions are there?

Answer 32

4 regions.

regions which contain the two phases are comparable to the phenol-water example

Question 33

What is the eutectic point?

Answer 33

the lowest temperature at which a liquid phase can exist

Question 34

What is the number of degrees of freedom of the eutectic point?

Answer 34

0 because we dont have to describe pressure, temperature or concentration as there is only one point