Column Efficiency Of A Distillation Column Biology Essay

The chief aim of this experiment was to happen the figure of theoretical phases and column efficiency of a distillment column with 8 screens trays and a partial reboiler at entire reflux and finite reflux ( with a reflux ratio of 2 ) .

The liquid condensate flowrate were measured and the provender flowrate was found at finite reflux. Samples were taken from the bottom merchandise and the distillation when steady sweetheart was reached inside the column. The densenesss of these samples were found and utilizing graphs, the composing of methyl alcohol was found. The McCabe-Thiele method was so used to happen the figure of theoretical phases for both entire reflux and finite reflux. The column efficiency was so found.

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The consequences showed that the figure of theoretical phases for entire reflux was 2 and for finite reflux was 4. The column efficiency for entire reflux was 25 % and for finite reflux was 50 % . Fenske ‘s equation was besides used to happen the figure of theoretical phase for entire reflux ; this value besides came to 2.

The quantifiable mistakes in this experiment were rather low, with the highest value at 3 % and the lowest at 0.0089 % .

Introduction & A ; aims

Distillation is one of the most widely used procedures for dividing liquid mixtures into several different constituents. Distillation can be carried out utilizing two methods. The first method is boiling the liquid mixture to be separated and to distill the vapor, without allowing any liquid return to the still. There is so no reflux. The 2nd method returns a portion of the condensate to the still under such conditions that the liquid comes in contact with the vapor on the manner to the capacitor. Both methods can be run as a batch or uninterrupted procedure.[ I ]

Distillation is normally the cheapest and best method for dividing liquid mixtures to its constituents except when:

The volatility difference between the constituents is excessively little

The mixture is extremely fouling or highly caustic

A compound is thermally unstable[ two ]

The chief portion of a distillment system is the distillment column. The provender can be input at different locations in the column but must be introduced where the liquid composing is similar to the provender composing. The subdivision above the provender point location is known as the rectification subdivision, the subdivision below the provender point location is known as the denudation subdivision. The liquid merchandise is collected at the underside of the column, whereas the distillation is collected at the top. To increase the pureness of the merchandises there is frequently a reflux. This means the liquid merchandise goes into a reboiler and back into the column. For the distillation, the watercourse goes into a capacitor and is so split into a merchandise watercourse and a watercourse traveling back into the column. This system is known as finite reflux, as the end product watercourse is split into a merchandise and a reflux. A entire reflux system would intend that everything from the top of the column returns as a reflux, hence there is no merchandise.

Inside the column can either make full filled with wadding or contain trays. Packing is normally classed in three ways.

Random or dumped packing – as the name suggests, the wadding is indiscriminately packed such as Raschig rings

Structured or strategically arranged packing – crimped beds of wire mesh or corrugated sheets such as SulzerA® Wire Gauge Packing

Grids – similar to structured wadding but these are open-lattice structured such as Koch High-Capacity FlexigridA®

There are besides three types of trays which are used. Bubble cap tray, sieve trays and valve trays. Bubble cap trays were used chiefly in the 1960 ‘s but are now merely used for particular applications. The most common trays used today are sieve or valve trays. A bubble cap tray is a level perforated home base with chimney-like pipes, known as risers, around the holes. Liquid and foams are trapped on the tray to a deepness at least equal to the riser tallness. This gives rise to the alone belongings of the bubble cap tray to run at low vapor and liquid rates. The sieve tray is a level perforated home base which allows vapor to lift through the holes. The speed of the vapor prevents the liquid from fluxing down the holes ( known as crying ) . If dolorous occurs, the liquid will flux through the holes ensuing in decreased efficiency.

The column we are utilizing in our experiment utilizations sieve trays

The chief aim of this experiment is to:

Determine the figure of theoretical home bases.

Determine the column efficiency for finite reflux for a mixture of Methanol and Water.

Determine the column efficiency for entire reflux for a mixture of Methanol and Water.







L, xN

V, yN+1Mass balances utilizing diagram below

Where F is the provender

B is the bottom merchandise

D is the distillation

V is the vapor flow

L is the liquid flow

ZF, XB and XD are the corresponding mole fractions for the more volatile constituent

ten ( liquid ) and y ( vapor ) are the mole fractions for the more volatile constituent

Overall mass balance

( 1 )

Overall stuff balance

( 2 )

Top of the column overall balance

( 3 )

Top of the column stuff balance

( 4 )

Rearranging equation 4 in footings of yn+1 and utilizing equation 3 gives:

( 5 )

Reflux ratio is given as:

( 6 )

Substituting equation 6 into 4 gives:

( 7 )

Equation 7 is the equation for the operating line for the rectification subdivision. The rectification subdivision can besides be found diagrammatically by pulling a line through the points ; ( XD, XD ) and ( 0, XD/R+1 )

The bottom operating line is given by:

three ( 8 )

Where L ‘ and V ‘ are the liquid and vapor flow in the denudation subdivision

The bottom operating line can besides be found diagrammatically by linking ( XB, XB ) to the intersection of the top operating line and the provender line.

The provender line is given by:


( 9 )


( 10 )

Uniting equations 9 and 10 and replacing the overall stuff balance from equation 2 gives:

( 11 )

If we define the fraction of vapor in the provender as degree Fahrenheit, so V-V’=fF and L-L’=- ( 1-f ) F, therefore:

( 12 )

( 13 )

Equation 13 is the equation for the q-line. Q is defined as the ratio of heat to evaporate 1 mol of provender to the molal latent heat of the provender

( 14 )

Where Q is the flowrate and I» is the latent heat

The full equation for the q-line is:

( 15 )

Where xq and yq are the points of intersection of the rectifying and the denudation operating lines. XF is the mole fraction of the more volatile constituent in the provender.

For the computation of q-line:

( 16 )

Where I» is the latent heat

H is the heat content

Cp is the specific heat capacity

Terbium is the temperature at the boiling point

T is the initial temperature

To obtain the specific heat of a mixture, the undermentioned equation is used

( 17 )

Where ten is the mass fraction of constituents A or B

M is the molecular mass of A or B

To happen the theoretical phases for this column, a McCabe-Thiele method must be used, where the provender line and operating lines must be drawn on a VLE diagram.

For the column efficiency, the undermentioned equation is used

( 18 )

The theoretical figure of phases can besides be calculated utilizing Fenske ‘s Method[ four ]:

( 19 )

Where N is the figure of theoretical phases ( non including the reboiler )

I± is the comparative volatility, which is given by:

( 20 )

Experimental Details & A ; Procedure

Experimental setup

A distillment column with:

– 8 screen home bases

– A 12 liter partial reboiler

– two 5 liters feed armored combat vehicles

– a peristaltic provender pump

– a reflux valve

– a capacitor

– a top merchandise armored combat vehicle

– a bottom merchandise armored combat vehicle

An electrical console and a Personal computer which takes readings at each thermocouple, which are placed on each screen tray

A rotameter to set the chilling H2O flow

4 flasks

A denseness metre

A stop watch

A measurement cylinder

A beaker

A standardization curve to happen the pump dial scene

A graph to happen the composing of methyl alcohol at 20A°C


Methanol is a toxicant if ingested and is reasonably toxic by endovenous paths into the organic structure. It is mildly toxic by inspiration.

Side effects include ocular nervus neuropathy, ocular field alterations, concern, cough and other respiratory effects

It is besides extremely flammable

No bare fire must be brought near methyl alcohol

Latex baseball mitts should be worn when managing anything incorporating methyl alcohol

Lab coats and goggles should be warn at all times

Experimental Procedure

Set the chilling H2O flow to 3 l/min

Bend on the reboiler warmer and set the heat input to 1.5kW

Once the column has filled up with liquid set the heat input of the reboiler down to 0.65kW

Once the column has reached steady province under entire reflux ( the temperatures of the trays should be changeless i.e. consecutive horizontal lines on the computing machine. The temperatures of each tray will be different, but should all be changeless ) take sampled from the top and bottom merchandise watercourses. Label these flasks top ( entire reflux ) and underside ( entire reflux ) severally. Leave these samples to chill to about 20A°C

Allow the column to return to steady province and so find the condensate flowrate by trying the condensate in a measurement cylinder over the length of 1 minute.

Make certain to unclutter the liquid held up in the pipes before taking this measuring

Determine the provender flow F which gives a distillation flow equal to three times the underside flow i.e. D=3B

This can be determined by utilizing the undermentioned equations:

and and

L is known, R is given as 2. Therefore D can be calculated. From D, B can be calculated. Using D and B, F can be calculated

Using the value of F, find the pump dial puting utilizing the standardization curve given

Set the reflux ratio R to 2. And turn on the reflux valve and the provender pump

Open the valve to the bottom merchandise receiving system ( this now becomes a finite reflux )

Once steady province is reached, take sampled from the top and bottom merchandises utilizing the flasks given and label these flasks top ( finite reflux ) and underside ( finite reflux ) severally. Leave them to chill to about 20A°C

Record the provender temperature

Once all the 4 samples in the flasks have reached about 20A°C, use the denseness metre to mensurate their densenesss and temperatures. Use the density/composition graph to happen the mol % composing of methyl alcohol and record the consequences.


Results & A ; Calculations

Measurements found

Temperature ( A°C )

Density ( g/cm3 )

Methanol ( mol % )

Entire reflux









Finite reflux









Table 1 – measurings found

Feed temperature ( terminal ) – 19.2A°C

Feed temperature ( initial ) –


Determination of the provender flowrate F

L was found to be 25ml/min

Roentgen was given as 2

Using the standardization curve, the pump dial puting for the provender was 2.39

Number of theoretical phases

Entire Reflux ( Graph 1 )

The reflux ratio is equal to 0 therfore the operating line is the y=x line on the McCabe Thiele diagram. Ploting points ( xD, xD ) as ( 90.0, 90.0 ) and ( xB, xB ) as ( 21.0, 21.0 ) and ( xF, xF ) as ( 25.0,25.0 )

Looking at the McCabe Thiele diagram ( Graph 1 ) it can be seen that there are 3 theoretical phases. The figure of theoretical phases without the reboiler is 2.

Finite Reflux ( Graph 2 )

Ploting points ( xD, xD ) as ( 92.1, 92.1 ) and ( xB, xB ) as ( 20.5, 20.5 ) and ( xF, xF ) as ( 25.0,25.0 )

The specific heat capacity can be found utilizing equation 17:

For latent heat:

Qs can now be found:

The gradient for the provender line is:

This provender line starts at point ( 25.0, 25.0 )

To happen the top operating line, the Y intercept in equation 7 is needed

So the top operating line runs from ( 92.1, 92.1 ) to ( 0, 30.7 )

Looking at the McCabe Thiele diagram ( Graph 2 ) it can be seen that there are 5 theoretical phases. The figure of theoretical phases without the reboiler is 4.

Column efficiency

Entire reflux

Finite reflux

ciphering figure of theoretical phases utilizing Fenske ‘s equation for entire reflux

First, we need to cipher the comparative volatility utilizing equation 20:

xmeth is the norm between 0.579 and 0.665 at liquid mol % of 20.0 and 30.0. The norm is 0.622

Using equation 21:

( rounded up to whole number )

Harmonizing to Fenske ‘s equation the figure of theoretical phases non including reboiler for the entire reflux is 2.

Entire Reflux

Finite Reflux ( R=2 )

Number of theoretical phases ( without reboiler )



NTS utilizing Fenske ‘s equation

( without reboiler )


Column efficiency ( % )



Table 2 – Consequences

Mistake analysis

Common Sense Footing

Condensate flowrate L

L = V/T

V = 25ml A± 0.5ml

T = 60s A± 0.5s

The maximal mistake is +2.86 %

The minimal mistake is -2.81 %

The mean mistake is A± 2.835 %

Feed flowrate F

L = 25ml/min A± 0.5ml/min

The maximal mistake is +2.00 %

The minimal mistake is -2.00 %

The mean mistake is A± 2.00 %

Combination of mistakes

Feed conditions parameter ( Q )

T = 19.2A°C A± 0.05A°C

Therefore, the uncertainness is:

Therefore the mistake is:

Condensate Flowrate L

Feed Flowrate F

Feed Parameter ( Q )



2.835 %

2.00 %

0.0089 %

Table 3- Mistakes


From the consequences above it can be seen that the column at entire reflux has 2 figure of theoretical phases ( without a reboiler ) while the column with finite reflux has 4. Therefore the column efficiency of the finite reflux is higher, at 50 % , while the entire reflux efficiency is 25 % .

These consequences correlate with anticipations and Fenske ‘s equation ever shows that the figure of theoretical phases for entire reflux is 2. At entire reflux, there is no merchandise and the fluids maintain cycling about and dividing. However, in a finite reflux, a distillation is collected while a fresh provender is added. The ground for the figure of phases being really low is that H2O and methyl alcohol have really different boiling points ; therefore it is reasonably easy to divide a mixture of H2O and methyl alcohol. The ground for the higher efficiency at finite reflux is because the merchandise is collected and a degree or pureness is maintained. It must be noted that the reflux ratio used at finite reflux was 2. At other reflux ratios, the consequences would be different.

Mistakes and Restrictions

Looking at table 3 it can be seen that the mistakes calculated were really little, with the highest mistake at about 3 % . The combination of mistake for the provender parametric quantity ( Q ) is really little with a value of 0.0089 % . This shows that quantifiable mistakes are non the ground for the bulk of the mistake in this experiment.

Mistakes may hold occurred due to the followers:

The column may non hold reached steady province before samples were taken

Using the graphs to find the pump dial puting for the flowrate was non easy to read

The dial for the reflux valve and the chilling H2O flowrate may non hold been set right

When mensurating the flowrate of the liquid flow L, one individual was clocking while another was utilizing the cylinder to roll up the liquid. There may hold been an mistake in the coordination of both people. One individual may non hold closed the valve when it needed to be closed, hence doing more liquid to travel into the cylinder. Giving a somewhat inaccurate flowrate.

Using the graph to find the composing of methyl alcohol from the denseness was hard to read, particularly as the denseness was given to 3 denary topographic points.

The samples were non precisely 20A°C before their composings were read off the graph ( which was based on the sample being 20A°C )

The McCabe-Thiele diagram besides allows for human mistake as the phases may non be wholly accurately drawn


Wait thirster for the column to make steady province

All dials and scenes should be digital so they can be set more accurately

The samples should be cooled to precisely 20A°C before mensurating the denseness

More repetitions of the experiment should be done to guarantee dependability of consequences