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Simple & Fractional Distillation

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

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Simple & Fractional Distillation

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  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 • Determination of Mole % from Distillate Volume Data, Gas Chromatography, and Refractive Index • Text References • Slayden p. 39-41, 43-46, 47 • Pavia - Tech 14.1 - 14.3; p. 719 – 729 (Simple Distillation) • Pavia - Tech 15.1 - 15.6; p. 729 – 740 (Fractional distillation) • Pavia - Tech 22.1 ­ 22.12; p. 817 – 836 (Gas Chromatography) • Pavia - Tech 24; p. 845 – 850 (Refractive Index)

  2. Simple & Fractional Distillation • Overview • A mixture of Ethyl Acetate and Butyl Acetate (unknown mole %) will be subjected to both a Simple Distillation and a Fractional Distillation (using a Vigreux Fractionation Column) • Each distillation will result in three (3) vials (fractions) 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 (con’t) • From the volumes and respective densities, the mass, moles, mole fraction, and mole % will be computed. • Gas Chromatograms of the 6 distillate vials (3 from Simple Distillation & 3 from Fractional Distillation) plus the original unfractionated mixture will be obtained • Mole % of the components in each fraction will be computed based on the relationship between peak area (readjusted for non-linear thermal response) and mole content • If directed by instructor, Mole % values will also be determined from a standard Regression Curve relating Refractive Index of known mixtures of Ethyl & Butyl Acetate to the measured Refractive Index values of the distillate fractions • Distillation results and mole % values will be used to evaluate the relative effectiveness of component separation by Simple Distillation vs Fractional Distillation

  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 • Boiling Point The normal boiling point (also called the atmospheric boiling point or the atmospheric pressure boiling point) of a liquid is the temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure. At that temperature, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and allow bubbles of vapor to form inside the bulk of the liquid The standard boiling point is now (as of 1982) defined by IUPAC as the temperature at which boiling occurs under a pressure of 1 bar 1 bar = 105 Pascals = 0.98692 atmospheres (atm) = 14.5038 psi (pounds per square inch) = 29.53 in Hg (inches of mercury) = 750.06 mm

  6. Simple & Fractional Distillation • Distillation / Boiling Point Measurement Note: The temperature range you obtain for your boiling point may be inaccurate for three (3) reasons 1. The atmospheric pressure in the lab may not be: 1 bar (0.98692 atm) 2. The thermometers used in the lab may not reflect the actual temperature 3. The thermal inefficiency of the glassware used for the boiling point determination may result in a lower than expected measured value by as much as 2 – 5oC You should take this potential temperature differential into account when you compare your measured results with the list of possible unknowns in lab manual tables

  7. Simple & Fractional Distillation • Vapor Pressure / Boiling Point (Con’t) • 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

  8. Simple & Fractional Distillation • Raoult’s 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

  9. Simple & Fractional Distillation • Raoult’s Law (Con’t) • 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

  10. 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

  11. Simple & Fractional Distillation • Distillation (Con’t) • 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

  12. Simple & Fractional Distillation • Simple Distillation • SingleVaporization / 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

  13. Simple & Fractional Distillation • Fractional Distillation • Accomplishes the same thing as Multiple Simple SequentialVaporization / 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/Condensation 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

  14. Simple & Fractional Distillation • Fractional Distillation (Con’t) • 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

  15. Simple & Fractional Distillation Fractional Distillation (Con’t) 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/condensation 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 A&B (L3V3 on the diagram), the vapor would have a composition of 80% A & 20% B at equilibrium.

  16. 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

  17. 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 & Distillation Head • Water Jacket Condenser (with rubber tubing for water) • Receiving containers – 2 10 mL graduated cylinders & 6 labeled vials with sealing caps

  18. Simple & Fractional Distillation • Distillation Equipment Setup (Con’t) • 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

  19. Simple & Fractional Distillation Typical Distillation Setup

  20. 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

  21. Simple & Fractional Distillation • Elements of The Experiment (Con’t) • 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 • Construct Barchart of incremental volumes (y-axes) vs temperature ranges (x-axes) • For both Simple Distillation & Fractional Distillation: • Determine Total volume recovered • Compute Percent volume recovered • Total Volume in temperature ranges 0 – 95 oC; 95 – 105 oC; 105 – 130 oC • Compute % volume recovered in each fraction

  22. Simple & Fractional Distillation • Combine the volumes from the 1st & 2nd fractions and refer to it as “Fraction A” • Assume the combined 1st & 2nd fractions (fraction A) is Ethyl Acetate and the 3rd fraction (fraction B) is Butyl Acetate • Determine the mass of each compound in fraction A and in fraction B from their respective volumes and density • Compute the Moles of each compound in fraction A and fraction B • Determine the total moles in each fraction • Compute mole fraction • Compute mole %

  23. Simple & Fractional Distillation • Data Collection • Place 20 mL of mixture in a 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

  24. Simple & Fractional Distillation • Data Collection (Con’t) • 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

  25. Simple & Fractional Distillation • Data Collection (Con’t) 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

  26. Simple & Fractional Distillation • Results NOTE: The following data analysis scheme is to be applied separately to both the Simple and Fractional data • First Vial - All the distillate up to 95oC (Mainly Ethyl Acetate – B.P. - 77.1oC) • Second Vial - All the distillate collected between 95-105oC • Third Vial - All distillate above 105oC (Mainly Butyl Acetate – B.P. 126.1oC)

  27. Simple & Fractional Distillation • Results (Con’t) • Calculate the total volume of distillate recovered • 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

  28. Simple & Fractional Distillation • Example BarChart 1stFraction 2ndFraction 3rd Fraction

  29. Simple & Fractional Distillation • Results (Con’t) • Calculate the total volume to the left of the95 oC line (1st fraction)Calculate the total volume in the zone between95 & 105 oC (2nd fraction)Calculate the total volume to the right of the105 oC line (3rd fraction) • Calculate volume percent composition of each of the three (3) fractions • 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

  30. Simple & Fractional Distillation • Compute Masses of Ethyl & Butyl Acetate • Combine Fractions 1 & 2 and assume it is Ethyl Acetate • Assume Fraction 3 is Butyl Acetate • Compute the Mass of Ethyl Acetate and Butyl Acetate from the Volumes and Densities of the two new fractions • Compute the Moles of compound in each fraction • Compute the Total Moles in the two fractions

  31. Simple & Fractional Distillation • Results (Con’t) • Compute the Mole Fraction of each fraction • Compute the Mole % of each fraction

  32. Simple & Fractional Distillation • Example calculations • 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%

  33. Simple & Fractional Distillation • Mole Percent of Distillates by Gas Chromatography • Refer to Website notes on the Gas Chromatography of Acetates Experiment • Refer to Gas Chromatogram of the Equimolar Mixture • Use the TRx/Tri thermal response correction factor for the Ethyl Acetate & Butyl Acetate peaks to adjust the distillate fraction peak areas • Obtain a Gas Chromatogram of the Standard Mixture (“A” or “B”), whichever you used in the Simple & Fractional Distillation experiment • Obtain Gas Chromatograms of each of the 3 vials you collected from the Simple Distillation and each of the 3 vials collected from the Fractional Distillation

  34. Simple & Fractional Distillation • Mole Percent of Distillates by Gas Chromatography (con’t) • Compute the Peak Areas using Triangulation method Note: There are two peaks on each Chromatogram • Adjust the peak areas for non-linear thermal response • NOTE: Use TRs/Tri correction factor from the equimolar mixture used in the GC Acetates experiment • Compute adjusted areas by multiplying measured areas from distillate fraction chromatograms the by the equimolar mixture TRs/Tri correction factor • Compute total area for peaks on each chromatogram • Compute the Mole Fraction • Compute Mole Percent

  35. Simple & Fractional Distillation • Mole Percent by Refractive Index Note: Add to Experiment only if directed by Instructor • Obtain temperature corrected Refractive Index values for the Unknown mixture (A or B) and the 6 simple & fractional distillation vials • Use MS Excel to create a standard regression curve from the known Refractive Index (y-axis) and Mole % Ethyl Acetate (x-axis) values in the table below Solutions of Known Mole % and Refractive Index

  36. Simple & Fractional Distillation • Mole % by Refractive Index (con’t) • Open MS Excel • From previous slide enter “Mole % Ethyl Acetate” values into column A of spread sheet • Enter “Corrected Ref. Index” values into column B • Select data in columns “A” & “B” • Select “Format Cells” from Task Bar • Select “Number” and “4” decimal places • Select “Insert” from Task Bar • Select “Scatter Plot” (2 clicks) to plot the data

  37. Simple & Fractional Distillation • Mole % by Refractive Index (con’t) • Add a trend (regression) line and regression equation to the plot • Click on a data point in the plot • Select “Add a Trend Line” • Select • “Linear” • “Display Equation on Chart” • “Display R-Square value on Chart” • Select and move Regression Equation to upper left corner

  38. Simple & Fractional Distillation • Mole % by Refractive Index (con’t) • Select “Axis Titles” • Select “Horizontal Axis Title” • Select “Title Below Axis” • Enter text - “Mole % Ethyl Acetate” • Select “Chart Title” • Select “Above Chart” • Enter text - “Refractive Index(corr) vs. Mole % Ethyl Acetate” • Select and move chart labels as appropriate

  39. Simple & Fractional Distillation • Mole % by Refractive Index

  40. Simple & Fractional Distillation • Mole % Analysis by Refractive Index (con’t) • The Mole % values of the unknown mixtures are determined either: • Directly from the Regression Curve by selecting the mole % value relative to its equivalent Refractive Index value • Computed from the regression equation • Rearrange the equation as follows to compute your Mole % values y = - 0.00022 x + 1.3949 x (Mole %) = (1.3949 – y (Measured R.I.) / 0.00022 Ex. Measured R.I. 1.3850 X = (1.3949 - 1.3850) / 0.00022 X = 45% Ethyl Acetate (55% Butyl Acetate)

  41. Report Preparation • The Report (Combined with GC Distillates Report) • Scan Chromatograms and insert files into 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

  42. Report Preparation The Report (Con’t) • Each procedure that produces data includes both Simple Distillation results and Fractional Distillation results • 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%) • Create separate procedures for the computation of mass, moles, mole fraction, mole %

  43. Report Preparation • Analysis & Conclusion Section • Discuss the effectiveness of component separation by Simple & Fractional Distillation based on: • Analysis of the bar chart of the incremental & fractional volumes, including the significance of the amounts in the 2nd fraction (95oC – 105oC) • Mole % values from the computed mass (from volume and density) of the fractional volumes • Mole % from peak areas obtained from Gas Chromatography • Compare the results for the original undistilled A or B mixture and the distillate fractions • Mole % from Refractive Index

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