Simple and Differential Distillation Experiment Procedure

AIM: Differential distillation, distillation process, distillation calculation, obtain distillation data for binary mixture.

OBJECTIVES: To compare experimentally (F/W) values to that of calculated from Rayleigh’s equation.

PRINCIPLE/THEORY:

If an infinite number of successive flash vaporization of liquid is carried out with a number of decimally small portions of liquid each time, then the net result would be equivalent to a simple distillation of differential distillation. In practice, the method can be approximated to a batch of liquid containing charged to a kettle or still fitted with some of the heating devices such as a steam jacket. The charge is boiled slowly and the vapours are withdrawn rapidly as they form through a condenser where they are liquefied and the condensate is collected in the reservoir. The first portion of the distillate will be richest in more volatile substance and as distillation proceeds, the vaporized product becomes lean. 

Rayleigh’s equation which can explain this phenomenon by EQUATION

Modified Rayleigh’s equation
Log (Fx_F /Wx_w) = a  log [F (1-x_F) /W (1-x_w )] 
a = Öa_W a_F
Where F is total number of moles of the feed, W is the numbers moles of residue XF and XW are mole fractions of more volatile substance in feed, and residue, which relates the number of moles of ‘A’ remaining in the residue Wxw to that of ‘B’ remaining W (1- Xw). These expressions are most likely to be valid for an ideal mixture, for which ‘a’ is most nearly constant.

EQUIPMENT USED:

• Simple distillation column
• Mantle heater
• 250 ml beakers-2
• 50 ml beaker-1
• Specific gravity bottle (25 ml)
• Thermometer

MATERIAL USED: Methanol –water.

EXPERIMENTAL PROCEDURE:

1. Measure exactly 300 ml using a measuring jar and transfer this 300 ml of feed into a beaker. In case of feed in the bottle is less than 300 ml make up with pure methanol.
2. Set aside 50 ml of the feed for measurement of specific gravity. Find specific gravity.
3. The balance 250 ml is transferred into round bottom flask of the setup.

4. Assemble the glass setup carefully. i.e. connect the condenser, thermal well etc. Place a thermometer in the thermal well of the still.
5. Start the condenser water supply. Ensure a rich flow of water through the condenser.
6. Check all the connections and then slowly heat the feed by using mantle heater.
7. When vapour is produced, it will condense in the condenser and collected in a 250 ml beaker.
8. This procedure is continued up to half the volume of feed is vaporized and condensed.
9. The volume of feed in the beaker is reduced to half the volume stop the heating process while supplying water to the condenser about 15 minutes. 

10. Make sure that no vapours are produced to shut the water supply.
11. Cool the residue, the specific gravity, or R.I for the residue and distillate are found.
12. The volume of the distillate and residue are also measured accurately using a measuring jar.
13. A calibration chart is prepared for (specific gravity or R .I) to the mole fraction of methanol in the solution.

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OBSERVATIONS:

Volume of feed = _____________ ml .
Room temperature = _____________ `C .
Distillate temperature =_______________`C.
Barometric pressure =728 mmHg .
Volume of distillate = _____________ml.
Volume of residue =______________ml.
Temperature of the first bubble starts at =_________`C.
Temperature at the end of distillation = ______________`C.
Specific gravity of the feed =_________
Specific gravity of the distillate =________
Specific gravity of the residue =_________

S.G.sample= (Wt of S.G. Bottle + Sample ) – (Wt of the empty S.G Bottle)/{(Wt of the S.G bottle + Distillate water )-(Wt of empty S.G Bottle )}

Temperature-Vapor pressure data:
Get the temperature –vapor pressure data for both methanol and water from Perry’s handbook.
Selection of upper and lower limits of temperatures.
First temperature----- Boiling point of more volatile component (here it is methanol ) corresponding to site barometric pressure (728 mmHg).
Last temperature ----boiling point of less volatile component (here it is water ) corresponding to site barometric pressure (728 mmHg).
Any number of temperature between the above two may be selected for filling up table 1

DATA ANALYSIS:

plot the graph between S.G Vs mole fraction X.
Get the temperature – vapor pressure data of water, methanol from Perry’s handbook.
Then plot the graph between vapor pressure of methanol Vs T and Vapor pressure of water Vs Tin the same graph.
Calculation X, Y* data for the methanol-water system at Pt =728 mmHg using Raoult’s law.( α are also computed).
NOTE: refer example problem (1) in distillation chapter of R.E Treybal (mass transfer book ).
Plot X Vs Y* (Take equal scale on both axes).
from graph 1, find X f ,X d ,Xw .
Calculate moles of feed, distillate & residue using the values of Xf, Xd and Xw obtained from step6.
compute ln (F/W) ( i.e. experimental value ).
Plot the graph between 1/(Y*-X) Vs X. This graph was plotted using data available in step 4. The area under this curve between the limits Xf & Xw gives the RHS of Rayleigh ‘s equation. This gives ln (F/W) (theoretical value).

Graphs to be plotted:
For a methanol-water system,
Specific gravity Vs mole fraction X.
Plot Y* Vs X.
Vapor pressure Vs Temperature of both methanol and water.
1/(Y*-X) Vs X (report area under the curve between the limits Xf and Xw ).
RESULTS:

ln(F/W) experiment =
ln(F/W) rayleigh’s equation =

DATA TABLES:

Preparation of calibration chart:

S.No	A volume of  methanol	Volume of        water	Specific   gravity	Mole fraction of methanol
1	30	0
2	25	5
3	20	10
4	15	15
5	10	20
6	5	25
7	0	30

Table 1:

S.No	Temperature	PA(mmHg) (methanol)	PB (mmHg)    (water)	XA = (Pt-PA) / (PA- PB)	Y A= PA.XA/Pt

Table 2:

S.No	X	Y*	1/(Y *-X)	α =(PA/ PB)

Rayleigh equation

Unveiling the Rayleigh Equation: A Comprehensive Guide

Discovered by Lord Rayleigh in 1885, this equation has found widespread applications in diverse fields, from seismology and geophysics to materials science and non-destructive testing. This comprehensive guide aims to provide a deep understanding of the Rayleigh Equation, its underlying principles, and its practical uses.

Rayleigh Wave Calculator

Shear Modulus (G):

Density (ρ):

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Frequency (f) - for Wavelength/Wave Number:

Rayleigh Wave Velocity (vR):

Wavelength (λ):

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Material Database

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Rayleigh equation for separation of chemicals:

For the batch distillation process where a fixed quantity of feed is charged to the distillation column and the separation of volatile products is done by supplying heat through the still or reboiler. As the boiling point of the liquid is reached a portion of the liquid starts to vaporize to the top of the column and is directed to the condenser, the vapor leaving the column is always in equilibrium with the liquid in the bottom of the column, thus a material balance equation is produced by Rayleigh called Rayleigh Equation which provides standard equilibrium data. For research and calculation of process conditions, this data is used to generate design equations. To determine the composition change with time Rayleigh equation is used and can be derived as:

Consider a liquid mixture of ‘Ao’ moles fed to the batch column. Let ‘A’ moles of liquid remain in the bottom of the column. At a given instant of time let y and x be the composition of vapor and liquid.

Material Balance:
Total moles of component B left in the vessel: xA
Let dA be the amount of liquid vaporized than the mole of component B varies is: ydA or dAB
: dAB = Adx+xdA






By integration to the limits of initial and final concentrations, we produce a Rayleigh Equations:

simple distillation experiment is used to calculate the vapor-liquid equilibrium data of various liquid mixtures by applying the above Rayleigh Equation

Rayleigh Equation Calculator (Batch Distillation)

Initial Moles in Still Pot (Wi): Final Moles in Still Pot (Wf): Initial Mole Fraction of More Volatile Component (Xi): Relative Volatility (α):

This calculator provides a practical tool for understanding and applying the Rayleigh equation in batch distillation with a combination of the analytical solution and Newton-Raphson method providing a fast and accurate result.