Revised January 1997
 
DISTILLATION EXPERIMENT
 With the glass, six-inch, six-plate laboratory column, please determine the effect of reflux ratio on column and plate distillation efficiencies for the binary system acetic acid-water.  Smith and Kelm (1951) describe the column; other characteristics of the column and its auxiliaries appear in Table I.  This column is typically operated under simulated continuous conditions by continuously returning the overhead product to the reboiler. Make sure that the reflux ratios that you employ are all greater than 2.
 The composition of acetic acid-water samples from the column may be determined by measuring the refractive index of the mixture with an Abbe refractometer.  Instructions for the operation of the refractometer are attached.  You should construct your own calibration curve for acetic acid-water as this will vary with the temperature of the refractometer.  You can compare your calibration curve with data available in the CRC Handbook of Chemistry and Physics. The composition in the reboiler and separator before startup is of the order of 60 to 70% acetic acid by weight.
 When you have determined that the column is operating under steady-state conditions (how will you do this?), take vapor and liquid samples from each tray and liquid samples from both the condenser and reboiler/separator.  Record utility usage for later use in a system energy balance.
 Vapor-liquid equilibrium data for this system, reported previously in two compilations (Chu, et al., 1950; Chu, et al., 1956) and by Brusset, et al. (1968) appear to be inconsistent or in error.  Consequently, we shall rely on basic thermodynamic functions reported recently (Freeman and Wilson, 1985a; 1985b) to predict the equilibrium vapor and liquid compositions.  The attached write-up entitled “Vapor-Liquid Equilibrium and the Acetic Acid/Water System” by T. Przybycien summarizes the applicable equations adapted from Freeman and Wilson's work.
 Column efficiency at each operating condition will be assessed by three different methods in conjunction with a McCabe-Thiele analysis.  For the first method, use a standard McCabe-Thiele operating line.  However, because the heats of vaporization of acetic acid and water are significantly different, the assumptions involved with this operating line are violated.  Fisher (1963) has suggested an alternative expression for the operating line based on a rough tray-by-tray energy balance that relaxes some of the assumptions inherent in the McCabe-Thiele operating line.  Use the Fisher operating line for the second method.  Finally, since you will be sampling the liquid and vapor from each tray, you may construct an experimental operating line based on the measured compositions of the pasing streams.  Compare and discuss the efficeincies determined by these three methods.
 In addition, for each operating condition, determine the vapor and liquid tray efficiencies.  A description of this calculation is given by Henley and Seader (1981).
Expectations
Interim Discussion.  Please come prepared to discuss acetic acid-water VLE behavior and calculations as well as binary distillation equipment operation and analysis techniques calculations.  Please bring your data sheets and a calculated x-y diagram for the acetic acid-water system using the VLE information given in the attached write up.  This will be a graded activity.
Final Report.  Table II provides a guide to the report format and contents.  At our Interim Discussion session, we will discuss report details further.  Table III gives a listing of the grading criteria I will be using for this experiment.
 
Literature Cited

Brussett, Henry, Kayser, Louis and Hacquel, Jean, "Presentation d'un nouvel ebulliometre a recyclage," Chem. Ind., Genie Chim., 99, 220-223 (1968).

Chu, J.C., Getty, R.L., Brennecke, L.F., and Paul, R., DISTILLATION EQUILIBRIUM DATA, Reinhold, New York, 1950, pp. 210 (data only).

Chu, J.C., Wang, S.L., Levy, S.L., and Paul, R., VAPOR-LIQUID EQUILIBRIUM DATA, Edwards, Ann Arbor, Mich., 1956, pp. 550-556.

Fisher, G.T., "Modification of the McCabe-Thiele Method for Systems of Unequal Heats of Vaporization," Ind. Eng. Chem. Process Design Develop., 2, 284-288 (1963).*

Freeman, J.R. and Wilson, G.M., "High Temperature PVT Properties of Acetic Acid/Water Mixtures," AIChE Symposium Series, 81 (244), 1-13 (1985a).

IBID., 14-15 (1985b).

Henley, E.J. and Seader, J.D., EQUILIBRIUM-STAGE SEPARATION OPERATIONS IN CHEMICAL ENGINEERING, Wiley and Sons, New York, 1981, pp. 335-336.

Smith, J.C. and Kelm, E.F., "All-Glass Bubble-Cap Column," Chem. Eng., 58(2), 155-157 (Feb. 1951).
 
TABLE I

Characteristics of Laboratory Distillation Column

Column: Smith, J.C. and E.F. Kelm, Chem. Eng., 58(2), 155-157 (Feb. 1951)

Column inside diameter = 6 in.
Number of Plates = 6
Plate thickness = 1 in.
Plate spacing, excluding thickness = 8 1/4 in.
Caps per plate = 1
Cap diameter = 3 1/2 in.
Cap height = 2 1/2 in.
Number of slots per cap = 28
Width of slots = 1/8 in.
Height of slots = 1/2 in.
Inside diameter of riser = 1 1/2 in.
Height of riser above plate = 1 in.
Static liquid seal = 1 1/4 in.
Inside diameter of downcomer = 1/2 in.
Height of downcomer above plate = 1 3/4 in.

Condenser: Q.V.F. Limited, catalog "Glass for Industry", pp. 7, 11

Type: HE 4/5
Material: Corning type 7740 borosilicate glass
Heat transfer area: 5 square feet
Free cross sectional area: 4.68 square inches
Pipe equivalent to free cross sectional area: 2 inches
Maximum recommended water pressure across coils: 30 psi
Overall height: 30 inches
Outside diameter: 4 inches
Weight, empty: 10 pounds
Weight, coils filled with water: 12.5 pounds
Cooling water pressure drop:

 Cooling water through Pressure drop,
 coil, pounds/hour       psi

 0 0
 1000 3
 2000 7
 3000 16
 3800 30

 
TABLE I
(Concluded)

Heat transfer characteristics:  the heat transferred can be considered on average as 75 BTU/(hr.) (sq. ft.) (°F), although the figure may vary from 10 to 120 according to conditions of use.  The following information indicates typical working conditions:

 Coolant rate: 3,300 pounds/hour
 Coolant inlet temperature: 20°C
 Steam condensed: 40 pounds/hour

Reboiler: Q.V.F. Limited, catalog "Glass for Industry," pp. 27, 51

 Type: HEB 6/5
 Material: Corning type 7740 borosilicate glass
 Heat transfer area: 5 square feet
 Free cross sectional area: 8 square inches
 Pipe equivalent to free cross sectional area: 3.187 inches
 Maximum recommended steam working pressure in coil: 50 psi
 Overall height: 18 inches
 Outside diameter at top: 6 inches
 Nozzle outside diameter: 1 inch
 Weight, empty: 10 pounds
 Heat transfer characteristics:

Steam pressure psig Water evaporated,pound/hour* Calc. overall coefficientBTU/(hr) (sq ft) (°F)
10 10 75
20 18 75
50 35 75

 * Based on evaporation from 100°C at atmospheric pressure.

Separator: Pfaudler Company, DWG E371-0918

 Type: vertical
 Material 316 L stainless steel
 Dimensions: 16 in ID x 20 in x 12 gauge
 Capacity: 20 gallons approximately

 
 TABLE II
Distillation Lab Report Requirements

I. Calculations
 A. Refractive Index Calibration Curve for water/acetic acid system
 B. VLE Calculations for water-acetic acid system: xy diagram
C. Column Efficiency Analysis for each reflux ratio, using:
1. standard McCabe-Thiele operating line
2. Fisher-corrected McCabe Thiele operating line
3. experimental operating line
D. Plate Efficiency Analysis for each reflux ratio
E. Error Analysis: propagate error through efficiency calculations

II. Report Format (must be prepared via a word processor)
A. Abstract: what was studied and what results were obtained
B. Table of Contents
C. Introduction: present a brief overview of distillation processes, describe the experiment and experimental aims, include a theoretical section which presents the basic equations which will be employed in this report. (note: the thermodynamic equations given in the attachment are not required in this section, however, a brief overview of the approach should be described).
D. Apparatus and Procedure: include an apparatus section which presents a schematic diagram for the experimental apparatus using standard piping and equipment symbols, also include a detailed procedures section which describes the various procedures employed in the experiment.
E. Results and Discussion: present all experimental results including the RI calibration plot and the efficiencies obtained using the various approaches. Also include a discussion of the impact of operating conditions on results as well as the effects of uncertainties in the measurements.
F. Conclusions: summarize the salient results, include recommendations for improving column performance and and the experiment in general.
G. References
H. Figures (no hand drawn material - use plotting and drawing softeware packages)
I. Appendices
1. Sample Calculations, including error analysis (may be neatly hand-written)
2. Raw Experimental Data: yellow pages from lab notebook
3. Source Code listing for VLE program

III. Covering Memo: who did what (Group Leader's responsibility)
 
TABLE III

Distillation Lab Report Final Evaluation Criteria (sample)

I.  Calculations,  Section Grade: ___________
 A.  Computation of sample mole fractions
 B.  Vapor-liquid equilibrium calculations for acetic acid-water system
 C.  Total reflux analysis
  1.  column efficiency (McCabe-Thiele, Fisher, and data operating line)
  2.  tray efficiency
 D.  Finite reflux analysis
  1.  column efficiency (McCabe-Thiele, Fisher, and data operating line)
  2.  tray efficiency
 E.  Error analysis

II.  Report Writeup, Section Grade:___________
A. Covering memo
B. Abstract
C. Table of Contents
D. Introduction
E. Apparatus and Procedure
F. Results and Discussion
G. Conclusions
H. References
I. Figures and Tables
J. Appendixes
1. Sample calculations
2. Raw data

III.  Distillation Laboratory Grade

section grade overall weight
interim report (attached)  20%
final report, I. calculations  40%
final report, II. writeup  40%
distillation lab overall grade  100%
 

 
Additional Information: Directions for Use and Care of the Abbe Refractometer
 
DISTILLATION LAB - INTERIM DISCUSSION GRADING SHEET

Date: _________ Exp. Date: _________ Group No.: _____ M   T   W   R

Group Members:

name attendance(y/n) participation level(good/fair/poor) designated group leader
 
 
 
 

Performance:
Real VLE: calculations and the water/acetic acid system, including xy diagram.
 
 
 
 
 
 
 
 

Binary distillation: column operation and analysis.
 
 
 
 
 
 
 
 

Interim Discussion Grade: _________________
 

Final Report Due Date:  _________________ (2 weeks after interim discussion)
 

Instructor Signature: ___________________________________________