continious distillation

ChE 492Chemical Engineering Laboratory

CONTINUOUS DISTILLATION

EXPERIMENT NO. 6 DATE: 09/09/03 DUE DATE: 16/09/03

NAME: ABHISHEK KUMAR SINHA ROLL NO. Y0013 ASHOK KUMAR Y0077

INSTRUCTOR: Dr. D P RaoTA NAME: M Shankar Rao

DEPARTMENT OF CHEMICAL ENGINEERINGI.I.T KANPUR

OBJECTIVE1. To observe the operation of continuous distillation in a sieve plate column.2. To determine the number of theoretical plates at total reflux.3. To observe the difference between efficiencies of distillation column at total and

optimum reflux conditions. 4. To obtain an overall heat balance.

THEORYDistillation is a way of separating the components of a solution which depends on the distribution of substances between two phases (gas & liquid) when both components are volatile.Heat acts as an external agent for creating the new phase. Under Total Reflux the following relations hold goodL = V, in both the enriching & stripping sections (1)y = x for all trays (2)hence, the operating line of McCabe Thiele diagram coincides with the y = x line.For the column being operated at some other Reflux ratio R, the quality is given by

Slope of the q line is given by

Slope of the enriching section operating line

It passes through y = x = xd

Slope of the stripping section operating line

It passes through the intersection of the enriching section operating line & the q line.

Some Important TermsTotal Reflux: This is mainly used during the start up of distillation column. In this case the following relations hold good:L = V, in both enriching and stripping sections.y = x, at all trays.Minimum Reflux ratio: This is a theoretical concept. It is the value of reflux ratio when there are infinite numbers of stages in the distillation column. Graphically the minimum reflux ratio is obtained as 2.2The optimum value for reflux ratio is generally taken as 1.2 times the minimum reflux ratio.Column efficiency for total reflux,

EXPERIMENTAL SETUP

Figure 1 Experimental Setup for Continuous Distillation

The experimental set up consists of the following equipments:1) Reboiler2) Variac3) Heating mantle4) Metering Pump5) Reflux Drum6) Thermometers

MeteringPump

FEED

Meteringpump

Water outlet

Water inlet Distillate

Refluxuxxxx

Distillation Column(Sieve Plate)

Thermometer

Reflux drum

Reboilerer

Thermometer

Heating Mantle

S.S. Jack

Sample collector

Variac

The feed is fed to the distillation column using a metering pump. It consists of equal volume fractions of ethanol and water. The liquid in the reboiler is heated using a heating mantle. Both the distillation column and the reboiler are properly insulated so as to reduce the heat loss from the system. A part of the distillated is again sent to the column using a metering pump. The rest of it is collected in a separate drum. Water at room temperature is used as a fluid for cooling the vapors. Constant supply of feed and water are ensured so as to carry out distillation at steady state.

SPECIFICATIONSNumber of Actual Theoretical Stages = 12Feed Position from above = 6Amount of Feed Taken = 2.5 10-3 m3.Composition of Feed Solution = 50% by volumeRefractive Index of Feed Solution = 1.348.Mole Fraction of Ethanol in feed = 0.24Cooling Water Flow Rate = 49.33 10-6 m3/sInlet Temperature of cooling Water = 306 KOutlet Temperature of Cooling Water = 307 KHeat Input by Heater = 450 W

OBSERVATIONS

TABLE 1 Correspondence of volume % to mole % for Ethanol-Water Mixture.

SN Vol% of Ethanol Mol% of Ethanol1 0 0.002 10 0.033 20 0.074 30 0.125 40 0.176 50 0.247 60 0.328 70 0.429 80 0.55

10 90 0.7411 100 1.00

TABLE 2 Refractive Indices of Distillates and Bottoms for Total Reflux

SN t, s RIB RID TB (K) TD (K)1 0 1.3460 1.360 359 3462 5 1.3465 1.359 359 3463 10 1.3460 1.360 359 3464 15 1.3462 1.358 359 346

TABLE 3 Refractive Indices of Distillates and Bottoms for R = 2.76


TABLE 4 Refractive Indices of Distillates and Bottoms for R = 4.82


RESULTS AND DISCUSSIONCALIBRATION CURVEThe calibration curve between refractive index and Volume % of ethanol, used for calculations is as follows:

where, Molecular Weight of Ethanol, MWEthanol = 0.046 kg/mol Molecular Weight of Water, MWWater = 0.018 kg/mol Density of Ethanol, Ethanol = 789 kg/m3

Density of Water, Water = 1000 kg/m3

TABLE 5 Calibration of a Refractrometer

SN Vol% of Ethanol Mol% of Ethanol RI1 0 0.00 1.3302 10 0.03 1.3333 20 0.07 1.3374 30 0.12 1.3405 40 0.17 1.3436 50 0.24 1.3487 60 0.32 1.3518 70 0.42 1.3539 80 0.55 1.355

10 90 0.74 1.35811 100 1.00 1.363

y = -0.0364x2 + 0.0659x + 1.3318

1.325

1.330

1.335

1.340

1.345

1.350

1.355

1.360

1.365

0.0 0.2 0.4 0.6 0.8 1.0Mol% of Ethanol, x

Ref

lect

ive

Inde

x, R

I

FIGURE 2 Calibration Curve for Refractrometer

EQULIBRIUM DATA FOR ETHANOL WATER SYSTEM

From Gibbs Phase Rule, to completely specify the properties of two component system we have to fix two parameters. Pressure is 1 atm and by specifying different temperature we can generate equilibrium curve.By using NRTL equation with the help of Aspen Plus we generated

TABLE 6 Equilibrium Data for Ethanol Water System

T, K x y373.17 0.00 0.00363.17 0.05 0.34359.15 0.11 0.45357.09 0.16 0.51355.87 0.21 0.55354.43 0.32 0.59353.93 0.37 0.61352.72 0.53 0.67352.08 0.63 0.72351.82 0.68 0.74351.60 0.74 0.78351.34 0.84 0.85351.30 0.89 0.89351.34 0.95 0.94351.46 1.00 1.00

FIGURE 3 T-xy curve for Ethanol Water Mixture at 1 atm by NRTL Equation of State

FIGURE 4 y-x curve for Ethanol Water Mixture at 1 atm by NRTL Equation of State

TOTAL REFLUXShown below Table for total reflux (R= ). Since this is total reflux case so xB and xD

will not change, and hence Refractive Index of boiler and distillate sample remain constant.

TABLE 7 Table for Total Reflux (R= )SN t, s SG TOP RIB xD xB TB (K) TD (K)1 0 1.3460 1.331 0.6989 0.03 372.15 3462 5 1.3465 1.330 0.6405 0.02667 372.15 3463 10 1.3460 1.360 0.6989 0.2484 359 3464 15 1.3462 1.358 0.5927 0.2527 359 346

GRAPHICAL CALCULATION OF NUMBER OF STAGES

350

355

360

365

370

375

0.0 0.2 0.4 0.6 0.8 1.0Mole Fraction of Ethanol in Liquid and Vapor Phase, x,y

Temperature T, K

x y

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0

Mole Fraction of Ethanol in Liquid, x

Mole Fraction of Ethanol in Vapor, y

Graphical calculation for number of stages is done by McCabe-Thiele method and corresponding stage efficiency is calculated by using the formula given in the theory.

FIGURE 5 Plot for calculating number of stages by McCabe-Thiele Method.

Number of stages =1.553

=12.94%

REFLUX RATIO, R = 2.7647

Reflux ratio is calculated by varying the amount of distillate.Total volume collected coming out from condenser =6.4mlVolume of liquid collected in same time interval =1.7ml

=2.7647

TABLE 8 Table for Reflux Ratio, R=2.7647

SN t, s RIB RID xD xB TB (K) TD (K)1 0 1.3510 1.360 0.6989 0.3648 359 3462 5 1.3500 1.362 0.7816 0.3396 359 3463 10 1.3490 1.363 0.8605 0.3155 359 3464 15 1.3492 1.363 0.8605 0.3202 359 346

GRAPHICAL CALCULATION OF NUMBER OF STAGES

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1

Mole fraction of Ethanol in Liquid, x

Mole fraction of Ethanol in Vapor, y

Graphical calculation for number of stages is done by McCabe-Thiele method and corresponding stage efficiency is calculated by using the formula given in the theory for stage efficiency.

Graphical calculation for number of stages is done by McCabe-Thiele method and corresponding stage efficiency is calculated by using the formula given in the theory for stage efficiency.

Since this is not the case of total reflux, composition of top and bottom changes. Hence number of tray calculation and efficiency is done for the corresponding time at which sample is collected.

FIGURE 6 Plot for calculating number of stages by McCabe-Thiele Method for R =2.7647 at t = 0 min

From Figure 6, At t = 0, Number of stages =1.558

=12.98%

From Figure 7, At t =5 min, Number of stages = 4.25

= 35.4%


=56.08%

00.10.20.30.40.50.60.70.80.9

1

0 0.2 0.4 0.6 0.8 1Mole fraction of Ethanol in Liquid, x


FIGURE 7 Plot for calculating number of stages by McCabe-Thiele Method for R=2.7647 at t = 5 min

FIGURE 8 Plot for calculating number of stages by McCabe-Thiele Method for R = 2.7647 at t = 10 min

From Figure 9, At t =15 min, Number of stages =5.5

= 45.83%

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1



0

0.1

0.2

0.3

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0.9

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0 0.2 0.4 0.6 0.8 1



FIGURE 9 Plot for calculating number of stages by McCabe-Thiele Method for R=2.7647 at t=15 min

REFLUX RATIO = 4.8182Reflux ratio is calculated by varying the amount of distillate.Total volume collected coming out from condenser =6.4mlVolume of liquid collected in same time interval =1.1l

= 4.8182

TABLE 9 Table for Reflux Ratio (R=4.8182)

SN t, s RIB RID xD xB TB (K) TD (K)1 0 1.3490 1.362 0.8762 0.3155 359 3462 5 1.3492 1.3625 0.8762 0.3202 359 3463 10 1.3515 1.361 0.7575 0.3778 359 3464 15 1.3517 1.363 0.9052 0.3831 359 346

GRAPHICAL CALCULATION OF NUMBER OF STAGES Graphical calculation for number of stages is done by McCabe-Thiele method and corresponding stage efficiency is calculated by using the formula given in the theory for stage efficiency.Since this is not the case of total reflux, composition of top and bottom changes. Hence number of tray calculation and efficiency is done for the corresponding time at which sample is collected.

00.1

0.20.3

0.40.5

0.60.7

0.80.9

1



FIGURE 10 Plot for calculating number of stages by McCabe-Thiele Method for R=2.7647 at t=0 min


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1



0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1




FIGRUE 13 Plot for calculating number of stages by McCabe-Thiele Method for R = 2.7647 at t = 15 min


= 45.74%

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

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0 0.2 0.4 0.6 0.8 1



From Figure 11, At t =5 min, Number of stages =9.15

=76.25%

From Figure 12, At t = 10 min, Number of stages =2.1

=17.5%

From Figure 13, At t = 15 min, Number of stages =5.36

= 44.47%

HEAT LOSS CALCULATION

Where, W = Mass Flow Rate of Water = (49.33 10-6 m3/s) 1000 kg/m3 = 49.33 10-3 kg/s CP, Water = 4186 J/kg T = 1 K QReboiler = 575 WHeat Loss = 450-206.495

=243.5W

CONCLUSIONS

1) It is clear from the above calculations and the graphs plotted that the total reflux condition gives the minimum number of stages to operate a distillation column but at the same time the efficiency obtained is very low.

2) The efficiency of the distillation column obtained at the optimum reflux condition is higher i.e. 76.25% than that obtained at the total reflux condition (i.e. 12.94%).

3) The heat loss incurred is about 243.5W.

NOTATIONS Relative volatility

Hin, Hout Inlet and Outlet Enthalpy. WN Theoretical Number of Trays.Qcondenser Condenser Duty. WQReboiler Reboiler Duty. WRI Refractive IndexRID Refractive Index of DistillateRIB Refractive Index of BottomsS1 Initial Batch Charge. molS2 Residue in kettle at the end. molxD Product concentration, mole fraction.

xB Final still concentration, mole fraction.

REFERENCES1. Fenske, “Ind. Eng. Chem“, 24, 482, (1932).

2. Smoker and Rose, Trans. Am. Inst. Chem. Engrs. 36, 285 (1940). 3. Winkle, M.V, “Distillation”, McGraw Hill Book Co., New York, (1967)

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continious distillation