Simple

1
Simple Fractional Distillation

• Experiment Simple Fractional Distillation
• Evaluation of the relative effectiveness of
  Simple Fractional Distillation to separate
  mixtures of organic compounds based on
  differences in Boiling Point
• Note This experiment is combined with theGC
  Distillates experiment next week, i.e., 1 report.
• Text References
• Slayden - p. 41- 44
• Pavia - Tech 3.1 - 3.8 p. 583 - 591
• Pavia - Tech 6.1 - 6.3 p. 612 - 615
• Pavia - Tech 13.1, 13.4 p. 723 - 724 729 - 731
• Pavia - Tech 14.1 - 14.3 p. 733 - 740
• Pavia - Tech 15.1 - 15.6 p. 744 - 755

2
Simple Fractional Distillation

• Overview
• The Simple Fractional Distillation experiment
  (this week) is combined with the GC Distillates
  experiment next week
• A mixture (unknown mole ) of Ethyl Acetate and
  Butyl Acetate will be subjected to both a Simple
  Distillation and a Fractional Distillation (uses
  a Vigreux Fractionation Column)
• Each distillation will result in three (3) vials
  of distillate representing 3 temperature ranges
  0-95oC 95-105oC and 105-130oC
• Volume recovery of total distillate as well as
  volume recovery of the distillate fractions will
  be computed
• Fractions 1 2 will be combined mathematically
  and assumed to be Ethyl Acetate
• Fraction 3 will be assumed to be Butyl Acetate

3
Simple Fractional Distillation

• Overview
• From the Volumes and respective Densities, the
  mass, moles, mole fraction, and mole will be
  computed.
• In the GC Distillates experiment, two (2)
  additional sets of Mole values will be computed
  for the original unknown mixture and each of the
  6 distillate vials collected in week 1
• Gas Chromatography (Peak Areas by Triangulation
  and Mole corrected for non-linear Thermal
  Conductivity Response).
• Refractive Index (Determination of Mole from a
  Regression Curve relating Refractive Index of
  known mixtures of Ethyl Butyl Acetate to the
  measured Refractive Index values of the
  distillate fractions).
• Report Use of volume recoveries and mole to
  evaluate the relative effectiveness of Simple
  Fractional Distillation to separate mixtures of
  organic compounds based on differences in Boiling
  Point

4
Simple Fractional Distillation

• Vapor Pressure / Boiling Point
• According to Kinetic Theory, the molecules in a
  liquid are in a constant state of Thermal Motion
  and some of these molecules are moving fast
  enough to escape from the liquid forming a vapor
  above the liquid. This vapor exerts a pressure on
  the surface of the liquid, i.e., Vapor Pressure
• Vapor Pressure The pressure of the vapor
  coexisting with a confined liquid or solid, i.e.,
  the pressure in an evacuated container containing
  a liquid at constant temperature after the liquid
  and escaping molecules near the surface of the
  liquid the vapor - reach equilibrium
• The Vapor Pressure of a liquid increases,
  generally exponentially, with temperature
• Boiling Point As a liquid is heated, the vapor
  pressure of the liquid increases to the point at
  which it just equals the applied pressure -
  usually atmospheric pressure. The liquid now
  begins to bubble (boil)

5
Simple Fractional Distillation

• Vapor Pressure / Boiling Point (Cont)
• Different liquid compounds or mixtures of liquids
  have different vapor pressures at a given
  temperature.
• Liquids with high vapor pressures (Volatile
  compounds) require relatively little energy
  (heat) to increase the vapor pressure to match
  the applied (atmospheric) pressure, and thus,
  boil, i.e. they have low boiling points.
• Liquids with low vapor pressures require
  considerably more energy to increase the vapor
  pressure to the point where it matches the
  applied pressure, thus, they have relatively high
  boiling points.
• The individual compounds in a mixture each exert
  its own pressure partial pressure.
• The sum of the partial pressures equals to the
  total vapor pressure of the solution

6
Simple Fractional Distillation

• Raoults Law
• In a solution of two miscible liquids (A B) the
  partial pressure of component A (PA) in the
  solution equals the partial pressure of pure A
  (PAo) times its mole fraction (NA)
• Partial Pressure of A in solution PA
  (PAo) x (NA)
• Partial Pressure of B in solution PB
  (PBo) x (NB)
• When the total pressure (sum of the partial
  pressures) is equal to or greater than the
  applied pressure, normally Atmospheric Pressure
  (760 mm Hg), the solution boils
• Ptotal PA PB PAo NA PBo NB
• If the sum of the two partial pressures of the
  two compounds in a mixture is less than the
  applied pressure, the mixture will not boil. The
  solution must be heated until the combined vapor
  pressure equals the applied pressure

7
Simple Fractional Distillation

• Raoults Law (Cont)
• Example
• Consider a solution at 100 oC where NA 0.5 and
  NB 0.5
• What is the Partial Pressure of A in the solution
  if the Vapor Pressure of Pure A at 100 oC is 1020
  mm Hg?
• Ans PA PoANA (1020) (0.5) 510 mm Hg
• What is the Partial Pressure of B in the solution
  if the Vapor Pressure of Pure B at 100 oC is 500
  mm Hg?
• Ans PB PoBNB (500) (0.5) 250 mm Hg
• Would the solution boil at atmospheric pressure
  (760 mm Hg)?
• Ans Yes Ptotal PA PB (510 250)
  760 mm Hg
• What is the composition of the Vapor at the
  Boiling Point?
• Ans The mole fraction of each would be
• NA (vapor) PA / Ptotal 510/760 0.67
• NB (Vapor) PB / Ptotal 250/760 0.33

8
Simple Fractional Distillation

• Distillation
• Process of vaporizing a liquid, condensing the
  vapor, and collecting the condensate in another
  container
• Uses of Distillation
• Separating liquids with different boiling points
• Purifying a liquid.
• Distillation Methods
• Simple
• Vacuum (at reduced pressure)
• Fractional
• Steam

9
Simple Fractional Distillation

• Distillation (Cont)
• Pure Substance
• Temperature remains constant during distillation
  process so long as both vapor and liquid are
  present
• Miscible Liquid Mixture
• Temperature increases throughout process because
  composition of vapor changes continuously.
• Composition of vapor in equilibrium with the
  heated liquid is different from the composition
  of the liquid

10
Simple Fractional Distillation

• Simple Distillation
• Single Vaporization / Condensation cycle of a
  mixture that produces a distillate that is always
  impure at any temperature range between the range
  of boiling points of the components
• Therefore, it is impossible to completely
  separate the components in a mixture with Simple
  Distillation
• Relatively pure substances can be obtained from a
  mixture with Simple Distillation if the boiling
  points of the components differ by a large amount
  (100oC)
• If a small increment of the initial distillate is
  separated and redistilled and this process is
  repeated many times, effectively producing
  multiple sequential Vaporization/ Condensation
  Cycles, an increasingly pure solution can be
  attained. This would be a very tedious process
  involving a large number of distillations

11
Simple Fractional Distillation

• Fractional Distillation
• Accomplishes the same thing as Multiple Simple
  Sequential Vaporization / Condensation Cycles, by
  inserting a Fractionating Column (a Vigreux
  Column) between the Distillation Flask and the
  Distillation Head.
• The Fractionating Column, of which there are many
  types containing a variety of packing materials,
  subjects the mixture to many Vaporization/Condensa
  tion Cycles as the material moves up the column
  toward the Distillation Head, which is attached
  to the Condenser.
• With each cycle within the column, the
  composition of the vapor is progressively
  enriched in the lower boiling liquid.
• This process continues until most of the lower
  boiling compound is removed from the original
  mixture and condensed in the receiving flask

12
Simple Fractional Distillation

• Fractional Distillation (Cont)
• When the lower boiling liquid is effectively
  removed from the original mixture, the
  temperature rises and a second fraction
  containing some of both compounds is produced.
• As the temperature approaches the boiling point
  of the higher boiling point compound, the
  distillate condensing into the third receiving
  flask is increasingly pure in the higher boiling
  point compound

13
Simple Fractional Distillation

• Fractional Distillation (Cont)

As the distillation proceeds, the composition of
the liquid and the vapor are continuously
changing The Horizontal and Vertical Lines
represent the processes that occur during a
fractional distillation. Each Horizontal Line
(L3V3, L2,V2), etc., represents both the
vaporization step of a given vaporization/condensa
tion step and the composition of the vapor in
equilibrium with the liquid at a given
temperature. Examples At 53oC with a liquid
composition of 80 A and 20 B (L4V4 on the
diagram), the vapor would have 95 A and 5 B
when equilibrium has been established between the
liquid and the vapor. At 63oC with a 50/50 liquid
mixture of AB (L3V3 on the diagram), the vapor
would have a composition of 80 A 20 B at
equilibrium.

14
Simple Fractional Distillation

• Column Efficiency - How pure can you get!!
• A common measure of the efficiency of a
  Fractionation Column is given by its number of
  Theoretical Plates
• One Theoretical Plate is equivalent to a Simple
  Distillation, i.e., one Vaporization /
  Condensation Cycle
• The smaller the boiling point difference, the
  greater the number of theoretical plates a
  fractionating column must have to achieve
  separation of mixtures

Boiling Point Number of Difference
Theoretical Plates 108 1 54 3 20 10
7 30 4 50 2 100
15
Simple Fractional Distillation

• Distillation Equipment Setup
• Note Equipment used in distillation experiment
  is expensive
• Use care to avoid breakage
• ASK BEFORE YOU ACT!!
• Equipment
• Heating Block (or sand bath) Heating Plate
• 50 mL round bottom Distilling Flask (with boiling
  chip)
• Distillation Head
• Thermometer Thermometer Adapter
• Vigreux Fractionation Column (second group only)
• Aluminum foil for Vigreux Column
• Water Jacket Condenser (with rubber tubing for
  water)
• Receiving containers 10 mL graduated cylinder
  3 labeled vials
  with sealing caps

16
Simple Fractional Distillation

• Distillation Equipment Setup (Cont)
• Use 2 ring stands to support apparatus.
• Attach clamp to Ring Stand the Condenser
• Attach clamp to other Ring Stand Distillation
  Head.
• Use Blue Plastic Clamp to secure Water Jacket
  Condenser to neck of Distillation Head.
• Use Blue Plastic Clamp to secure Distillation
  Head (or Vigreaux Column) to Distillation Flask.
• Insert thermometer through adapter so that the
  bulb is positioned ¼ inch below opening to the
  Condenser.
• NOTE Wrap the Distillation Head, Vigreux Column,
  and Distillation Flask in Aluminum foil
  to improve heat insulation

17
Simple Fractional Distillation

• Typical Distillation Setup

18
Simple Fractional Distillation

• Elements of The Experiment
• Two Distillations
• Simple Distillation
• Fractional Distillation with Vigreux Column
• Work in groups of 4 (2 groups of 2 each)
• First group - Simple Distillation
• Second group - Fractional Distillation
• Each group of 4 will share data, but reports will
  be written independently.
• Each report must contain all of the raw data from
  the group, i.e., from both distillations

19
Simple Fractional Distillation

• Elements of The Experiment (Cont)
• Simple and Fractional distillations
• Note Can be setup as a single (1) procedure
• Note In Procedure Description make note of
  addition of the Vigreux column used in the
  Fractional Distillation.
• Total Volume recovered (simple fractional)
• Percent volume recovered
• Total Volume in temperature range 0 95
  oC
• Total Volume in temperature range 95 105 oC
• Total Volume in temperature range 105 130 oC
• Mass of compounds (from volume and density)
• Moles Mole of Increments

20
Simple Fractional Distillation

• Data Collection
• Place 20 mL of mixture in 50 mL round bottom
  flask
• Set Hot Plate setting to about 5
• Use 10 mL graduated cylinder to collect
  distillate
• Collect distillate in 5 degree increments
  recording the incremental volume collected in the
  5 degree interval
• Note 1st increment is from 0oC 65oC
• Continue to collect incremental volumes in 5
  degree increments, until temperature reaches 95oC
• Transfer the total volume collected in the
  graduated cylinder up to 95oC to the first
  labeled vial
• Continue to collect distillate in 5 degree
  increments from 95oC to 105oC
• Transfer the total volume collected between95oC
  - 105oC into the second labeled vial

21
Simple Fractional Distillation

• Data Collection (Cont)
• Increase temperature setting of Hot Plate.
• Continue to collect 5 degree volume increments in
  the graduated cylinder until 1 mL remains in the
  flask
• Note DO NOT DISTILL TO DRYNESS
• Turn off heat.
• Allow liquid in Distillation Head Vigreux
  column to cool and drain into the Distillation
  Flask (Pot Residue)
• Transfer the Pot Residue to the graduated
  cylinder
• Determine the volume of Pot Residue
• Transfer the contents of the graduated cylinder
  to the third labeled vial

22
Simple Fractional Distillation

• Data Collection (Cont)
• Suggested Table Template For Distillation Data

Incremental Volumes For each 5 oC temperature
interval, record the volume of distillate
collected in that temperature range. Cumulative
Volumes for the 0 95 oC, 95 105 oC, and the
105 - 130 oC fractions, can be computed by
summing the incremental volumes for each
fraction. Pot Residue Pot Residue is the volume
of undistilled sample remaining in the
Distillation Flask after the Hot Plate is turned
off. Allow the apparatus to cool down then
transfer the remaining liquid in the Distillation
Flask to the Graduated Cylinder. The Pot Residue
becomes part of the final increment of Distillate.
Vial 1
Vial 2
Vial 3
23
Simple Fractional Distillation

• Results
• NOTE The following data analysis scheme is to be
  applied to both the Simple and Fractional data
• Keep the distillates collected in the three vials
  for the next experiment - Gas Chromatography of
  Distillates
• First Vial - All the distillate up to 95oC
• (Mainly Ethyl Acetate B.P. - 77.1oC)
• Second Vial - All the distillate collected
  between95-105oC
• Third Vial - All distillate above 105oC
• (Mainly Butyl Acetate B.P. 126.1oC)

24
Simple Fractional Distillation

• Results (Cont)
• Calculate the Recovery of the distillate
• (Total Final Volume / Initial Volume) x 100
• Use Excel to plot a bar chart of temperature
  increments on the x-axis and volume increments on
  the y-axis
• Note First increment is 0 65oC
• Draw perpendicular lines to the 95 110 degree
  marks on the x-axis.
• Calculate the total volume to the left of the95
  oC line
• Calculate the total volume in the zone between95
  105 oC
• Calculate the total volume to the right of
  the105 oC line

25
Simple Fractional Distillation

• Example BarChart

1st Increment
3rd Increment
2ndIncrement
26
Simple Fractional Distillation

• Results (Cont)
• Calculate volume percent composition of each
  fraction.
• Vol 1st fraction Vol 1st fraction / Total
  Vol Rcvd x 100
• Vol 2nd fraction Vol 2nd fraction / Total Vol
  Rcvd x 100
• Vol 3rd fraction Vol 3rd fraction / Total
  Vol Rcvd x 100

27
Simple Fractional Distillation

• Compute Mass and Moles of fractions from fraction
  volumes, densities, molecular weights.
• Combine Fractions 1 2 and assume it is Ethyl
  Acetate
• Assume Fraction 3 is Butyl Acetate
• Compute Mole Fraction Percent (See Next Slide)

28
Simple Fractional Distillation

• Results (Cont)
• Mole Fraction Mole Percent

29
Simple Fractional Distillation

• Mixture Example (1000 mL ? 60 / 40 by Volume)
• Ethyl Acetate (600 mL) Den 0.895 g/mL
• Mol Wgt 88.11
  g/mole
• Butyl Acetate (400 mL) Den 0.882 g/mL
• Mol Wgt 116.16 g/mole
• Compute moles from volume, density, molecular
  weight
• Mole Fraction
• Ethyl Acetate 6.095 / 9.132 0.667 x
  100 66.7
• Butyl Acetate 3.037 / 9.132 0.333 x
  100 33.3

30
Simple Fractional Distillation

• The Report (Combined with GC Distillates Report)
• Only one (1) procedure is required for the
  Distillation Equipment setup, simple
  distillation, fractional distillation. Use one
  table to report results.
• The Description for each procedure involving a
  computation must include the computational logic
  behind the equation used and the equation setup
  with suitable definition of the variables.
• The Summary section restates the results in
  paragraph form.
• For comparison purposes each Simple result
  should be paired with its equivalent Fractional
  result.
• For example The total volume recovered for the
  Simple Distillation was 17.6 ml (88.0), while
  the total volume recovered from the Fractional
  Distillation was 18.3 mL (91.5)

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Simple Fractional Distillation

• The Report (Cont)
• The Conclusion section should address the
  following comparisons of Simple (S) vs.
  Fractional Distillation (F)
• Volume Recovery
• Mole values for Vial 1 (S vs F) Vial 2 (S vs
  F) and Vial 3 (S vs F)
• Significance of any volumes collected in the 2nd
  Vial relative to the overall Efficiency of
  Separation between Simple Fractional
  Distillation