FACULTY OF CHEMICAL ENGINEERING PROCESS ENGINEERING LABORATORY II (CPE554) NAME
:
STUDENT ID.
:
GROUP
: EH2425B
EXPERIMENT TITLE
: LAB 4: DISTILLATION COLUMN
DATE PERFORMED
: 18TH OCTOBER 2016
DATE OF SUBMISSION
: 1ST NOVEMBER 2016
LECTURER’S NAME
: SIR MUHAMAD FITRI BIN OTHMAN
No Title . 1 Abstract/Summary 2 Introduction 3 Aims/Objective 4 Theory 5 Apparatus 6 Methodology/Procedure 7 Results 8 Calculations 9 Discussion 10 Conclusion 11 Recommendation 12 Reference/Appendix Total marks Checked by:
……………………………............ (SIR MUHAMAD FITRI BIN OTHMAN)
CONTENT
Marks 5 5 5 10 5 10 10 10 20 10 5 5 100 Date:
Remarks
1.0 ABSTRACT 2.0 INTRODUCTION 3.0 OBJECTIVES 4.0 THEORY 5.0 APPARATUS AND MATERIALS 6.0 PROCEDURES 7.0 RESULTS 8.0 CALCULATIONS 9.0 DISCUSSIONS 10.0 CONCLUSIONS 11.0 RECOMMENDATIONS 12.0 REFERENCES 13.0 APPENDICES
2 2-3 3 3-6 6 7-8 9-10 11-13 13-14 14-15 15 16 17
1.0 ABSTRACT This experiment is conducted to determine the refractive index of the distillation column for various boil-up rates in batch distillation column, to observe the degree of forming on trays for each power supply, to determine the refractive index of unknown concentration of methylcyclohexane (MCH)/toluene and to plot the curve relating refractive index and percentage of ethanol. Distillation column is used to determine pressure drop for various boilup rates in batch distillation. The degree of foaming on trays for each power increment also can be determined. In order to study the pressure drop of the column, the power was set to 0.5 kW and then 0.75, 1.00, 1.25 and 1.50 kW. For each power, the sample was collected until it reached 90mL and then the procedures were repeated for each increment. The collected samples were tested for its refractive index using refractometer. It is observed that degree of foaming increases when the power was increased. The degree of foaming at 0.5 kW was gentle as opposed to the others, where the foaming starts to become vigorous. Finally, the refractive index for pure MCH and toluene was determined in order to match the mixture obtained from the sample. 2.0 INTRODUCTION 1
Distillation columns are one of the main units used for separation processes in industry. Distillation is a process of separating the component substances from a liquid mixture into two or more products that have different boiling points, by partial vaporization of a liquid mixture and/or by partial condensation of a gas mixture thereby rendering liquid phase richer in less volatile (with higher boiling point) component and the vapor phase is richer in more volatile (with lower boiling point) component. Distillation may result in essentially complete separation (nearly pure components), or it may be a partial separation that increases the concentration of selected components of the mixture. Distillation probably accounts for 90% of all separation processes in the chemical industry, and is also a significant user of energy due to the necessary heating involved. This process is conducted by using the Distillation Column apparatus. The column is consisted of bubble cap trays, reboiler, product and feed tank, reflux splitter, and condenser. Each bubble cap allows vapor to pass upward from the tray below and condense while allowing liquid to pass back. Two heat exchangers are located above the column. The second exchanger acts as a condenser. It condenses the vapor leaving the first exchanger using cooling water. The condensate flows into the reflux tank. Then it can be refluxed back to the top of the column or directed to the product tank. The basic requirement for the separation of components by distillation is that the composition of the vapor be different from the composition of the liquid with which it is in equilibrium at the boiling point of the liquid. Distillation is concerned with solutions where all components are appreciably volatile, such as ammonia-water or ethanol-water solutions, where both components will be in the vapor phase. As a feed enters the column and some fractions may vaporise and rise up the tower. The vapour components will condense and leave the column at different levels as the temperature decreases up the tower. Based on a binary mixture, the more volatile component will come out at the top of the tower, and the less volatile component will leave at the bottom as a liquid. The less volatile component will have a higher boiling point so it will be a liquid in the column. This experiment will investigate the pressure drop over the distillation column for various boil-up rates. 3.0 OBJECTIVES 1) To determine the pressure drops and refractive indexes of the distillation column for various boil-up rates in batch distillation column. 2) To observe the degree of forming on trays for each power supply. 3) To determine the refractive index of unknown concentration of methylcyclohexane (MCH)/toluene. 2
4) To plot the curve relating refractive index and percentage of methylcyclohexane. 4.0 THEORY Distillation is a separation process of a mixture into two or more products that have different boiling points, by partial vaporization of a liquid mixture and/or by partial condensation of a gas mixture thereby rendering liquid phase richer in less volatile (with higher boiling point) component and the vapor phase is richer in more volatile (with lower boiling point) component. Any countercurrent separation device has its own capacity limit. This limit is the known as flooding point and is a result of high vapor velocity. At high vapor velocities, the pressure exerted by the vapor from below balances the gravity head of the liquid, as a result liquid starts building up in the column. This condition is reflected by sudden increase in the pressure drop.
Figure 4.1: Equipment setup The equipment will be set up to operate at total reflux meaning all the formed vapor will after condensation return to the column. The charge of feed mixture can be loaded directly in the 3
reboiler through the filler cap provided without first charging the feed tank. At total reflux there will be no feed or top product or bottom product. Make up 10 L of a mixture of 50 mol % methylcyclohexane and 50 mol% toluene required for this mixture are 50 mol ×98.19 g/ gmol 50 mol × 92.15 g /gmol of MCH : of toluene 0.774 g/ml 0.867 g /ml 6343.0 ml of MCH :5314.3 ml of toluene 1.19 ml of MCH :1.00 ml of toluene
Thus for 10 L of the mixture consist 5.43 L of methylcyclohexane and 4.57 L of toluene.
The total pressure drop across each tray is the sum of that caused by the restriction of the holes in the sieve tray and that caused by passing through the liquid (foam) on the top of the tray. As the velocity of the vapors passing up the column increases, then the overall pressure drop also increases. The velocity is controlled by varying the boil-up rate which is done by varying the power input to the reboiler. Under conditions with no liquid present, the sieve trays will behave like an orifice in that the pressure drop will be proportional to the square of the velocity. Due to the fact that there is a liquid head however, this square relationship does not become apparent until the head of liquid has been overcome and foaming is taking place. In a graph, of pressure drop vs boil-up rate (log/log), at low boil-up rates the pressure drop will remain fairly constant until foaming occurs when the pressure drop would be expected to rise sharply for unit increases in boil-up rate.
For the system methylcyclohexane/toluene, mixture of known concentration can be made up and their refractive indexes measured. The refractometer measures the critical angle of the liquid under thest and each concentration will show a different critical angle. From this the refractive index can be found.
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Figure 4.2: Cross section of Refractometer.
The volumes of constituents to use were calculated as followed: For 25 mol % MCH, 75 mol % toluene; Molecular weight MCH = 98.19 g/gmol Molecular weight toluene = 92.15 g/gmol Density of methylcyclohexane = 0.774 g/ml Density of toluene = 0.867 g/ml V MCH × ρMCH ×100 MW MCH 25= V MCH × ρMCH V tol × ρtol + MW MCH MW tol
25=
100 V tol MW MCH ρ 1+ × × tol V MCH MW tol ρ MCH
5
3=
V tol MW MCH ρ × × tol V MCH MW tol ρMCH
V tol MW tol ρ =3 × × MCH V MCH MW MCH ρtol V tol 92.15 0.774 =3 × × V MCH 98.19 0.867 V tol =2.51V MCH Thus, for 100 ml of mixture required 28.49 ml MCH and 71.51 ml toluene.
5.0 APPARATUS AND MATERIALS Distillation column Model UOP3CC, Refractometer, stopwatch, 100 ml measuring cylinder, dropper, distilled water, methylcyclohexane and toluene.
6.0 PROCEDURES A. Experiment 1: Determining Column Pressure Drop. 1. 2. 3. 4. 5. 6. 7.
The general start-up procedures were performed. All valves on the equipment were ensured to be closed. Valve V10 on the reflux pipe were opened. The boiler was filled with 10 litres of mixture to be distilled. The filler cap on the top of the reboiler was firmly replaced. The power of the control panel was switched on. The temperature selector switch was set to T9, the temperature in the
reboiler. 8. Valve V5 was opened admitting the cooling water to the condenser at a flow rate on F11 of approximately 3 L/min. 9. The power controller for the reboiler heating element on the control panel was turned fully anti-clockwise and the switch turning on the power to the heating element was switched to ‘power on’ position. 10. Another red lamp will illuminate indicating the heating element was on. 6
11. The power controller was turned until a reading of approximately 0.5kW is obtained on the digital wattmeter. 12. The boiler was let to heat for 10 minutes for warm up the contents of the reboiler. 13. After 10 minutes, valve V6 and valve V7 were opened. The pressure drop on the manometer was recorded for top and bottom pressure. 14. The degree of foaming on the trays was observed and recorded in the result table. 15. Valve V3 was opened to collect 90 ml of the sample using measuring cylinder while the collecting time was recorded using stopwatch. Later on, the boil up rate (L/hour) was calculated based on the time taken. 16. The collected sample was later on determined the refractive index using Refractometer. 17. Before that, the refractometer must be calibrated first using distilled water before testing the refractive index of the sample. 18. The experiment was repeated using 0.75, 1.0, 1.25 and 1.5 kW power. 19. The general shut-down procedures were performed.
B. Experiment 2: Determining Mixture Compositions. 1. The refractive index of pure methylcyclohexane and pure toluene were measured. 2. Small quantities of 25 mol %, 50 mol %, and 75 mol % of MCH were made and their refractive indexes were measured. 3. The volume of constituents to use were calculated as followed: For 25 mol % MCH, 75 mol % toluene; Molecular weight MCH = 98.19 g/gmol Molecular weight toluene = 92.15 g/gmol Density of methylcyclohexane = 0.774 g/ml Density of toluene = 0.867 g/ml V MCH × ρMCH ×100 MW MCH 25= V MCH × ρMCH V tol × ρtol + MW MCH MW tol
7
25=
3=
100 V MW MCH ρ 1+ tol × × tol V MCH MW tol ρ MCH
V tol MW MCH ρ × × tol V MCH MW tol ρMCH
V tol MW tol ρ =3 × × MCH V MCH MW MCH ρtol V tol 92.15 0.774 =3 × × V MCH 98.19 0.867 V tol =2.51V MCH Thus, for 100 ml of mixture required 28.49 ml MCH and 71.51 ml toluene.
7.0 RESULTS A. Experiment 1: Determining Column Pressure Drop. Power
Boil-Up Rate
Pressure Drop (cm H2O)
Degree of Foaming
Refractive
(kW)
(L/h)
Top Bottom Overall
on Trays
Index
0.5
4.0602
167
93
74
Gently localised
1.43396
0.75
8.4595
171
92
79
Violent localised
1.43707
1.0
23.1400
203
70
133
1.25
28.1700
220
40
180
1.5
36.8601
235
30
205 8
Foaming gently over whole tray Foaming gently over whole tray Foaming violently
1.45068
1.45345 1.45263
over whole tray Table 7.1
Pressure drop vs Boil Up Rate 250 200 150 Pressure Drop (cmH2O)
100 50 0 0
5
10
15
20
25
30
35
40
Boil Up Rate (L/h)
Graph 7.1
B. Experiment 2: Determining Mixture Compositions. Volume (mL)
Concentration of MCH (%)
Refractive Index
Toluene
Methylcyclohexane
100%
0
100
1.42383
75%
21.875
78.125
1.43716
50%
45.59
54.41
1.45526
25%
71.51
28.49
1.47402
0%
100
0
1.49612
Table 7.2 9
Graph of Refractive Index vs Mole Fraction MCH 1.52 1.5 1.48 1.46 Refractive Index 1.44 1.42 1.4 1.38 0.00
0.20
0.40
0.60
0.80
Mole Fraction Methylcyclohexane
Graph 7.2
8.0 CALCULATIONS Molecular weight methylcyclohexane = 98.19 g/gmol Molecular weight toluene = 92.15 g/gmol Density methylcyclohexane = 0.774 g/mL Density toluene = 0.867 g/mL V MCH × ρMCH ×100 MW MCH 25= V MCH × ρMCH V tol × ρtol + MW MCH MW tol
25=
100 V tol MW MCH ρ 1+ × × tol V MCH MW tol ρ MCH
10
1.00
1.20
3=
V tol MW MCH ρ × × tol V MCH MW tol ρMCH
V tol MW tol ρ =3 × × MCH V MCH MW MCH ρtol V tol 92.15 0.774 =3 × × V MCH 98.19 0.867 V tol =2.51V MCH
For 100 mL of mixture, quantity required :i.
0% methylcyclohexane : 100% toluene VMCH + Vtol = 100mL 0 + Vtol = 100mL VMCH = 0 mL Vtol = 100mL
ii.
25% methylcyclohexane : 75% toluene VMCH + Vtol = 100mL VMCH + 2.51VMCH = 100mL VMCH = (100/3.51) mL VMCH = 28.49 mL Vtol = 71.51 mL
iii.
50% methylcyclohexane : 50% toluene VMCH + Vtol = 100mL
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VMCH + 0.838VMCH = 100mL VMCH = (100/1.838) mL VMCH = 54.41 mL Vtol = 45.59 mL iv.
75% methylcyclohexane : 25% toluene VMCH + Vtol = 100mL VMCH + 0.28VMCH = 100mL VMCH = (100/1.28) mL VMCH = 78.125 mL Vtol = 21.875 mL
v.
100% methylcyclohexane : 0% toluene VMCH + Vtol = 100mL VMCH + 0 = 100mL VMCH = (100/1) mL VMCH = 100 mL Vtol = 0 mL
9.0 DISCUSSIONS
A fractionating column or fractionation column is an essential item used in distillation of liquid mixtures which is to separate the mixture into its component parts, or fractions, based on the differences in volatilities. Continuous distillation, a form of distillation, is an ongoing separation in which a mixture is continuously (without interruption) fed into the process and 12
separated fractions are removed continuously as output streams. Distillation is the separation or partial separation of a liquid feed mixture into components or fractions by selective boiling (or evaporation) and condensation The aims of the experiment A, to determine the pressure drop inside the distillation column and Experiment B to determine the refractive index of MCH for the calibration curve. In the distillation column, the inlet feed has already contained a mixture of toluene and methyl cyclohexane. The mixture will be run through a column of trays. There are two outlet streams which are the rectifying (top) and the stripping (bottom). The distillates which are the high volatile component (HVC) and low volatile component (LVC) can be determined from their boiling point. Methylcyclohexane has a low boiling point which is 101°C, while toluene has a boiling point higher than the methylcyclohexane which is 111°C. Thus, methylcyclohexane is the one whom will be vaporized first and then released up to the rectifying column. In order to determine the pressure drop over the distillation column for various boil-up rates in batch distillation, the graph 7.1 had been plotted. The graph of pressure drops against boil-up rates shown that both the pressure drops and boil-up rates values increased as the power of boiler heater was increased from 0.50 kW to 1.50 kW. Moreover, the degree of foaming on trays recorded changing its pattern with different power supply through our observation. At 0.5 kW, we observed that the degree of foaming on trays was gently localised. Meanwhile at 0.75 kW, the pattern was started to show a violent localized, later on, at 1.00kW, it was started to foam gently over the tray same as at the power 1.25kW. Lastly, at 1.50kW, foaming violently over whole tray. Thus, it shown that, the degree of foaming on the trays will increase as the power supply increase.
The refractive indexes were also obtained using the refractometer for all of the different power intensities. The refractive indexes are shown the increasing pattern from the power of 0.5kW to 1.25kW, but it slightly decreased at power of 1.5kW. This happened maybe due to some technically problem during sampling.
Furthermore, the mixture compositions also can determined by using refractometer. In order to prevent error while reading the value of refractive index by using refractometer, blank calibration is applied first with distilled water. As a result, random error due to contaminated 13
at sample reading can be avoid. In the determination of the compositions of mixture of methylcyclohexane/toluene using refractometer, not only the compositions were collected but also the refractive index. From the graph Refractive index vs. mole fraction of methylcyclohexane (MCH) plotted, we can see that the refractive index values drops as the mole fraction methylcyclohexane increased. It clearly shows the decreasing linearly from 0 mole fraction of MCH until it reached 1.00.
10.0 CONCLUSIONS In conclusion, the objectives of this experiment are to determine the pressure drops and refractive index of the distillation column for various boil-up rates in batch distillation column, to observe the degree of forming on trays for each power supply, to determine the refractive index of unknown concentration of methylcyclohexane (MCH)/toluene and to plot the curve relating refractive index and percentage of methylcyclohexane. The greater the heater powers are used, the higher the boil-up rate. As the boil-up rate is increasing, the time consume to collect the sample is decreasing. Simultaneously, when the temperature of the mixture is increasing, the pressure drop will be increasing.
The
relationship between pressure drop and boil-up rate is shown on the graph plotted which shown the pressure drop increased as the power increased. As for the degree of foaming on trays, the degree of foaming was increased as the power supply increased. Also, the refractive index values are also recorded at all power intensities. In Experiment B, graph 7.2 had shown the relationship between the mixture composition or mole fraction of the methylcyclohexane with their refractive index. From the graphs of Refractive index vs. mole fraction of MCH, the relationship is determined in which the refractive index values decreased as mole fraction of MCH is increased until it reached 100 mol % MCH. In brief, all the objectives of the distillation column experiment are achieved and the experiment is successfully done. 11.0 RECOMMENDATIONS 1) Before starting the experiment A, make sure that all the valves on the equipment are fully closed.
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2) Repeat the important steps several times to obtain accurate date and reduce some errors. 3) Error should be avoided such as the overflowed of the sample from the column into the manometer arms which affected the values of pressure drops significantly and totally violates the theory 4) Make sure that our eye is the same level as the meniscus of water when we take the reading to avoid parallax error. 5) Be careful with the hot liquid while collecting the sample to avoid inflammation to the skin. 6) Do a blank calibration before read exact refractive index to prevent error while reading the refractive index value. 7) Always wear gloves during conducting this experiment to avoid any contact of chemical with bare hand. Toluene and methylcyclohexane are flammable, irritating and toxic. If possible use a fume hood.
12.0 REFERENCES 1) Christie J. G. (2014). Transport Processes & Separation Process Principles (Includes Unit Operations), 4th Edition. Pearson Education Limited, United Kingdom. 2) Laboratory manual, (n.d). Laboratory manual: Distillation column. Faculty of Chemical Engineering and Bioprocess. UiTM Shah Alam. 3) McCabe, W. L. and J. C. Smith (1976). Unit Operations of Chemical Engineering (3rd Edition.). McGraw-Hill, USA. 4) Bravo, Jose L. and James K. Fair. (Jan, 1990). "Distillation Columns." Chemical Engineering Progress. Retrieved from http://www.srsengineering.com/our-products/distillation-columns/how-columns-work/ 5) Sujata N., Betsy S. at. al. (n.d.). Encyclopedia of Chemical Engineering Equipment; Distillation Column. Retrieved from http://encyclopedia.che.engin.umich.edu/Pages/SeparationsChemical/DistillationColu mns/DistillationColumns.html 6) Process Engineering Guide: Laboratory Distillation (n.d.). GBH Enterprises, Ltd. Retrieved from http://www.slideshare.net/GerardBHawkins/laboratory-distillation
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13.0 APPENDICES
Figure 13.1: Distillation Column
Figure 13.2: Sample is taken using measuring cylinder
Figure 13.3: Continuous Distillation Column Model UOP3CC
Figure 13.4: Reading values
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Figure 13.5: Automatic Digital Refractometer
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