Lecture 1

Question 1

What is needed to separate chemical mixtures and why?

Answer 1

The separation of a chemical mixture into its components is not a spontaneous process, and therefore requires energy in some form.

Question 2

What are the general steps to separate a chemical mixture?

Answer 2

Okay not to confuse you but listen,

A general first step (before separating the main chemical mixture) is to ensure that the feed is in a single, homogeneous phase. If it is multi-phase (BUT NOT NECESSARILY), it is best to first separate the phases by gravity or centrifugation to reach this homogenous phase and then proceed to the next step of separating each phase mixture.

A schematic of a general separation process is shown in digital notes. The phase state of the feed can be a vapor, liquid, or solid mixture. The products of the separation differ in composition from the feed and may differ in the state of the phase.

Question 3

How is the separation of a chemical mixture accomplished?

Answer 3

The separation is accomplished by inducing the different chemical species in the feed to partition among the different product phases. There are four basic methods for doing this as discussed in the next FC

Question 4

Plan of attack ;)

Answer 4

Okay so now I’m going to mention the 4 basic methods (this is an important chuck of the lecture) then I’m to slightly explain them, and then I will get into examples of each method (ill highlight what was discussed explicitly in the lecture) and I will identify separating agent employed (This is linked back to the definition start gaining intuition)

Question 5

What are the 4 basic separation techniques?

Answer 5

All examples are depicted in digital notes.

1. Phase Creating: The feed to the separator is a single-phase vapor, liquid, or solid. The second phase is Created by the
   transfer of energy to or from the feed by an energy-separating agent (ESA). The ESA can be heat transfer or shaft work by means of compression or by the reduction of pressure through a turbine or across a valve. (As you can see here you CREATED a vapor phase from a liquid phase).
2. Phase addition: The feed to the separator is a single-phase vapor, liquid, or solid. The second added phase is called a
   mass-separating agent (MSA). Certain components in the feed move from the feed phase to the MSA phase. After sufficient time and agitation to approach phase equilibrium, the product phases are separated.
3. Barrier: For example, you can use a barrier like a membrane. The barrier
   allows passage of certain species in the feed while excluding or slowing other species.
4. External force field or gradient: an external force field or gradient is used to preferentially attract certain species in the feed. The force field might be electrical or centrifugal.

Question 6

Quick note

Answer 6

Mentioned operations such as Distillation ,, Liquid-liquid extraction, Absorption, stripping, Membrane separations, and Adsorption are all operations we will dive into detail in the future so take this as a light intro to them.

Question 7

What are the common Separation Operations Based on Phase Creation?

Answer 7

1. Partial condensation or vaporization (highlighted in the lecture): Is used when the feed mixture is a vapor OR a liquid with components that differ widely in volatility. Heat is transferred to or from the feed in
   a heat exchanger followed by phase separation by gravity in a
   vessel
2. Flash vaporization: Partial vaporization of a liquid by reducing the feed pressure with a valve or turbine, followed by phase separation.

*Generally, The liquid product is enriched with respect to the less volatile species, while the vapor product is enriched with respect to the more volatile species

3. Distillation (highlighted in the lecture):: happens when the degree of separation by a single equilibrium stage is inadequate because the volatility differences among key species are insufficiently large. Distillation involves vigorous mixing during contacts between countercurrently flowing liquid and vapour phases, creating multiple equilibria.

Examples of all of these are shown in the digital notes, look at the note under as well but do the next flashcard then look at the “gaining intuition” bit

Question 8

Gaining intuition.

Answer 8

Okay Habibi i want to draw your attention into the fact that the first two Separation Operations Based on Phase Creation only occur when there is a big difference between the volatiles of the compounds, where one equilibrium stage is needed to separate the compounds. In fact these two operations are referred to as single equilibrium stages because the interphase mass transfer of species is so rapid that phase equilibrium is closely approached.

Bas when this is not the case we use distillation which works to create many different Equilbruims to separate these components.

This is also represented in the explanation of the diagram under FC 6.

Question 9

What are the disadvantages of using MSA?

Answer 9

(1) the need for an additional separator to recover the MSA for recycle

(2) the need for MSA makeup

(3) possible product contamination by the MSA

(4) more complex design procedures.

Question 10

What are the common Separation Operations Based on Phase Addition (Two FC because large explanations)?

Answer 10

All of them are shown in digital notes

1. absorption: Used when the feed mixture is a vapour, and it is desired to remove
   the higher molecular weight (heavier) components from the lower molecular weight (lighter) components. The feed gas enters at the bottom of a multistage column and flows up the column countercurrent to the MSA, called an absorbent (meaning in soaks up water well) , which enters at the top of the column. A SUBSEQUENT separation, often distillation, separates the absorbate (Lower MW Gas) from the absorbent(MSA), which is then recycled to the absorber (Vapor).
2. Stripping: The inverse of absorption. A liquid feed mixture is separated, by contacting the feed, which enters at the top of the column, with a gas stripping MSA that enters at the bottom. A SECOND separation operation may be needed if it is necessary to separate the stripping agent (MSA) from the components stripped from the liquid feed (Higher MW) and/or to recycle the stripping agent(MSA) to the stripper (The MSA Feed).

• Simply first one takes high MW gas from the feed and turns them Liquid and the other does the opposite.

The other two are in the next FC since It is long

Question 11

Pt . 2

Answer 11

All of them are shown in digital notes

3. Liquid–liquid extraction (Highlighted and discussed in upcoming weeks): using a solvent as the MSA, when distillation is impractical, e.g., because the feed is temperature-sensitive. A solvent (MSA) selectively dissolves only certain components in the feed. The products are an extract, L’, containing the
   extracted components, and a raffinate, L”, containing the unextracted species. Several countercurrently arranged stages may be necessary. Additional separation operations, often distillation, are needed to
   recover the solvent for recycling.
4. Adsorption: When MSA is a porous solid, in the form of granules, that selectively removes one or more components from a
   vapour or liquid feed mixture. Adsorption separations are often conducted batchwise or semicontinuously in vessels or columns.

Question 12

What are the two different membranes used in membrane separation (Barrier)?

Answer 12

1. Microporous membranes: separation is effected by differing rates of species diffusion through the membrane
   PORES.
2. Nonporous membranes: separation is controlled by differences in solubility in the membrane and rates of species diffusion through the membrane MATERIAL.

Question 13

What are retentate and permeate>

Answer 13

retentate (components that do not pass through the membrane) and
the permeate (components that do pass through the membrane).

Question 14

What are the Common Separation Operations Based on Barriers (membrane separation)?

Answer 14

All of them are shown in digital notes

1. Dialysis: the transport, by a concentration gradient, of small solute molecules through a porous membrane. The molecules unable to pass through the membrane are small, insoluble, non-diffusible particles.
2. Reverse osmosis: the selective transport of a solvent, for example, water, through
   a microporous membrane after the pressure of the feed is increased to a value higher than the osmotic pressure of the solution. Solutes in the solvent do not permeate the membrane
3. gas permeation: Separation of gases through nonporous membranes, using a pressure driving force
4. Pevaporation: Certain species in the liquid feed diffuse through the nonporous membrane, where they are evaporated before exiting as permeate. This method uses low pressures to enhance vaporization and the heat of vaporization must be supplied. It is used to separate azeotropic mixtures and achieves high purities.

Question 15

What are the different forces/gradients used in the External force field or gradient separation?

Answer 15

1. Centrifugation: establishes a pressure
   field that separates mixtures according to their size, shape, and
   density. can also separate large polymer molecules according to molecular
   weight.
2. Thermal diffusion: If a temperature gradient is applied to a homogeneous
   solution. It has been used to enhance the separation of isotopes in permeation
   processes
3. electrophoresis, which exploits the different migration velocities of charged colloidal or suspended species in an electric field. For example. In electrodialysis, cation- and anion-permeable membranes carry a fixed charge that prevents migration of species with like charge

Question 16

Okay, break moment.

Answer 16

We are done with Chapter 1, there is one more diagram in the digital notes that compares the scalability of the different separation techniques and another that summarizes all of what was mentioned. Now we move on to chapter 4 which takes about separations by phase creation and
phase addition in a single equilibrium step (a stage). But today we are looking at the basic principles like Gibs phase rule, zeotropic mixtures and the inverse lever rule.

Question 17

What are the two different thermodynamic equilibriums and which one is generally most focused upon?

Answer 17

Thermodynamic equilibrium includes both
physical (phase) equilibrium and chemical (reaction) equilibrium. This course considers, with few exceptions, only
physical equilibrium. Possible chemical reactions are, in most cases, assumed to be too slow to occur during the interval that
mixtures are being separated. This assumption is not an important limitation because with the exception of ionic reactions in aqueous phases or catalyzed chemical reactions, chemical reaction rates are much slower than mass-transfer rates

Question 18

What exactly is physical (phase) equilibrium? (imp read carefully and gain intuition)

Answer 18

At phase equilibrium, molecules are still moving in both directions across phase boundaries, but no further temperature, pressure, or phase composition CHANGES occur. Thus, the equilibrium is
dynamic rather than static.

Both the temperature and pressure
are equal in each phase, but the phase compositions differ except for azeotropic mixtures (This is crucial to understand when we start to derive the Gibs phase rule). These composition differences allow mixtures to be separated when the phases disengage.

Question 19

What are multiple-phase (multiphasic) equilibrium? And what is important to know about them? (imp)

Answer 19

multiple-phase equilibrium is when two or more phases are in physical (phase) equilibrium.

Now here it is important to note that even though in such systems (just as the one shown in digital notes) not all phases are in contact, but still all phases are in equilibrium. For example, even though in the diagram we see that the n-hexane-rich phase is not in direct contact with the water-rich phase, approximately 0.06 mol% water is present in the n-hexane-rich phase at physical equilibrium. This is important when it comes to considering the degree of freedom in the Gibs phase rule as will be described soon!

Question 20

What is Gibbs’ phase rule? (no derivation yet ;))

Answer 20

Gibbs’ phase rule is the theoretical foundation for phase equilibrium.

Consider an equilibrium system consisting of one or more phases, NP, with one or more chemical components, C. In the absence of chemical reactions; and for negligible gravitational, electrical, magnetic, and surface forces, the intensive thermodynamic variables (those independent of the mass) are: temperature, T; pressure, P; and composition, e.g., in mole fractions. Let NV = the number of variables and NE = the number of independent equations that relate the intensive variables. Then, the number of degrees of freedom for the system is ND = NV − NE, where ND is the number of variables that must be specified so that the remaining variables can be determined from the independent equations.

Considering all of this, the Gibbs’ phase tule can be derived to be:

ND = C − NP + 2

Question 21

What is the derivation of Gibbs’ phase rule

Answer 21

Check written notes

Question 22

What is an example of Gibbs’ phase rule (not that imp just read through it you already know it)

Answer 22

The phase diagram of H₂O (shown in digital notes) represents the boundaries between its vapor, liquid, and solid states in terms of temperature (T) and pressure (P). For a single-phase system (NP = 1), ND = 2, meaning both T and P must be specified to define the state. When two phases coexist (NP = 2), ND = 1, so only one variable (either T or P) can be freely chosen, while the other is determined by the phase boundary, such as the vapor pressure curve (ya3ni two phases can have either the same T or thr same P but not both). If all three phases coexist (NP = 3), ND = 0, meaning both T and P are fixed at a unique triple point where solid, liquid, and vapor exist simultaneously.

Question 23

Break moment again

Answer 23

No we move on to binary systems, we will start first by taking about zeotropic mixtures and azeotropic mixtures then we will talk about the inverse level rule ;)

Question 24

What are the two types of binary mixtures?

Answer 24

1. Zeotropic binary mixture: At equilibrium,
   the vapor and liquid phases of a zeotropic mixture never have the same composition
2. Azeotropic binary mixture: An azeotropic mixture at equilibrium has identical compositions of the vapor and the liquid

Question 25

What is the thermodynamic separation index? + equation

Answer 25

It is the relative volatility of a binary mixture, α(A,B), that is a measure of the degree of difficulty for the separation of a more volatile component from a less volatile component by the three separation operations in Table 1.1 (FC 7): (1) partial vaporization of the mixture when a liquid, (2) partial condensation of the mixture when a vapor, or (3) multistage distillation. For a mixture, αA,B is a function of pressure, temperature, and phase compositions. The equation is shown in written notes, look also at the 'imp think!"

Question 26

What intuition do we gain about the separation index?

Answer 26

Okay so the separation index basically determines what separation technique we will use. 3yani if the boiling points between both volatile compounds are high, which indicates a high separation index, we know that they will be separated easily via one eq stage so we can use an operation such as flash vaporization, but if the boiling points are close, and therefore the index is small, multiple equilibrium stages are needed, which then results in an operation such as distillation. CONNECTIONS PEOPLEEEE!!!!

Question 27

What are the two plots used to describe Experimental vapor–liquid equilibrium (VLE) data and what is each useful for?

Answer 27

The two most useful plots are T–yA–xA and yA–xA plots for isobaric conditions. The T–y–x plot is useful for determining phase states, phase-transition temperatures, phase compositions, and phase amounts for a given pressure. It is the one we encountered most in phys chem. Look at digital notes ;). Constant-pressure y–x plots as shown in digital notes are useful because the vapor-and-liquid compositions are points on the equilibrium curve. Such plots usually include a 45∘ reference line, y = x (explained later on). Generally, they are convenient for determining COMPOSITIONS as a function of mole-percent vaporization by geometric constructions. (this is using the Q-line which we will get to).

Question 28

What are some terminologies needed to know for T–yA–xA? (recap)

Answer 28

supporting Diagram in digital notes. Mixture conditions above the saturated vapor curve correspond to a (superheated vapor). Conditions below the saturated liquid curve correspond to a (subcooled liquid). Two-phase mixtures only exist at conditions on or between the two curves. Temperatures slong the saturated vapor curve are called (dew-point temperature)s, while temperatures along the saturated liquid curve are (bubble-point temperatures).

Question 29

What is the inverse-lever-arm-rule rule and its derivation?

Answer 29

It is a rule applied toT–yA–xA used to calculate the relative molar amounts of the vapor (V) and liquid (L) phases at a point between the dew-point line and the bubble-point line. Quick note before going to derivation, The overall composition of the two phases remain at a mole fraction we started at, y3ani if we heat from a subcooled liquid at x= 0.30 and we reach the in between region to get different composition for the two phases we will still have an overall composition of 0.30. okay go to derivation i hope it is there because micheal didn't upload slides yet and i don't trust my written notes too much

Question 30

How can we determine the composition of a vapour and a liquid using a yA–xA plots at isobaric conditions?

Answer 30

Okay this is a bit confusing but I will try my best to explain it in the written notes

Question 31

What is Raoult's law and modified Raoult’s law?

Answer 31

Raoults law is a law the relates vapor–liquid equilibrium ratio (K-value) to the vapour and liquid composition. If the liquid phase is an ideal solution and the ideal gas law holds we have Raoults normal law: Ki = yi/xi= Psi/P If the liquid phase is a non-ideal solution and the ideal gas law holds then we have modified Raoult’s law: Ki = yi/xi= γiL*Psi/P where γiL is the activity coefficient for component i in the liquid phase. Note that you generally won't have to use modified Raoult’s law (Alhamdulillah)

Question 32

How does an azeotrope form when the liquid phase is an ideal solution and the ideal gas law holds?

Answer 32

When a liquid solution is ideal and Raoult's law applies, azeotropes will only occur when the vapour pressure curves for the two components cross each other in the temperature range between the two boiling points at the system pressure.

Question 33

How does an azeotrope form when the liquid phase is a non-ideal solution and the ideal gas law holds?

Answer 33

When the liquid solution is nonideal and modified Raoult's law applies, the variation of activity coefficients with composition often cause azeotrope formation even when the vapour-pressure curves do not cross. This is similar to polymer and the r(ab) values as shown in digital notes.

Question 34

What are the minimum and maximum boiling points?

Answer 34

The minimum-boiling azeotropes are where, under isobaric conditions, the azeotrope boils at a temperature below the boiling point of either of the two pure components. At the azeotropic composition, both K-values and the relative volatility are 1. Less common are maximum-boiling azeotropes, where the azeotrope boils at a temperature greater than the pure component boiling points

Question 35

One kind of obvious intuition from azeotropes?

Answer 35

is that you need to be careful when making an azeotrope for distillation applications.