Short Path Distillation 3t4b66
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BKF3751-Chemical Engineering Laboratory II
1.0
Introduction
1.1
Introduction (Literature review and theory) Short path distillation is a distillation technique that involves the distillate travelling a
short distance, often only a few centimeters, and is normally done at reduced pressure. The vapor stream travels a "short path" directly to the condenser which is located within the evaporator chamber. Since the vapor stream is immediated condensed, the short path distillation process precludes the vapor from forming vapor pressure. This allows ultimate pressures of 0.001 mbar to be attained. Short residence time and low evaporation temperature will cause a minimum thermal stress to the distilled product. This also allows heat sensitive materials to undergo purification at much lower temperatures preventing degradation. A short path ensures that little compound is lost on the sides of the apparatus. Typical applications are high molecular organic compounds particularly from the fields of chemistry, pharmaceutical and food industry. Short-Path Distillation is a continuous separation process working under vacuum conditions. Evaporation takes place from a heated wiped film. Caused by the pressure drop between the place of vaporization and the vacuum system the operating pressure in typical wiped film evaporators with external condenser is limited to some millibars. The considerably lower pressure in the Short Path Evaporator is obtained by the short distance for the vapors on their way from the evaporator surface to the condenser. In addition, the cross section area of flow is equal to the evaporator surface, so that there is only a minor pressure drop between evaporator and condense. Separation processes can essentially be termed as mass transfer processes. The classification can be based on the means of separation, mechanical or chemical. The choice of separation depends on the pros and cons of each. Mechanical separations are usually favored if possible due to the lower cost of the operations as compared to chemical separations. Systems that cannot be separated by purely mechanical means (e.g. crude oil), chemical separation is the remaining solution. The mixture at hand could exist as a combination of any two or more states: solid-solid, solid-liquid, solid-gas, liquid-liquid, liquid-gas, gas-gas, solid-liquid-gas mixture. Separation of components from a liquid mixture via distillation depends on the differences in boiling points of the individual components. Also, depending on the 1
BKF3751-Chemical Engineering Laboratory II
concentrations of the components present, the liquid mixture will have different boiling point characteristics. Therefore, distillation processes depends on the vapor pressure characteristics of liquid mixtures. The vapor pressure of a liquid at a particular temperature is the equilibrium pressure exerted by molecules leaving and entering the liquid surface. Here are some important points regarding vapor pressure: energy input raises vapor pressure, vapor pressure is related to boiling, a liquid is said to ‘boil’ when its vapor pressure equals the surrounding pressure, the ease with which a liquid boils depends on its volatility liquids with high vapor pressures (volatile liquids) will boil at lower temperatures, the vapor pressure and hence the boiling point of a liquid mixture depends on the relative amounts of the components in the mixture, distillation occurs because of the differences in the volatility of the components in the liquid mixture. The Separation efficiency denotes by: Separation efficiency =
X 100
Mechanical stirring a determining factors for the distillation efficiency, mechanical stirring ensures a complete mixing and a better heat transfer rate between the hot oil jackets and the feed. The higher degree of stirring increasing the heat transfer rate subsequently bringing the higher distillation effect. Temperature of the evaporator is another important variable in optimizing the distillation efficiency where the optimum temperature should have to be selected to supply enough heat for the water to be condensed. The distillation efficiency will be increased by increasing of temperature. However, excessive of heat can result in degradation of product. Feed rate control is crucial in distillation process, as the residence time in the evaporator determine the efficiency of heat transfer. If the feeding rate is high then the residence time of feed in evaporator decrease may causing the feed to be not well heated. Hence the feed will be ing through without any separation happen.
2
BKF3751-Chemical Engineering Laboratory II
1.2
Objectives 1. To introduce the short path distillation principles using continuous system. 2. To observe the effects of stirrer speed and temperature on the efficiency of separation, e.g ethylene glycol-water.
3
BKF3751-Chemical Engineering Laboratory II
2.0
Methodology
2.1
Equipment/Apparatus/Material 1. Short Path Distillation Unit 2. Ethylene glycol – water mixture
2.2 1.
Procedures The ethylene glycol is mixed with water in a ratio of 7:3 at total of 1 litre in a beaker. Then the mixture is stirred homogeneously.
2.
All valves are initially checked closed except the valves HV02, HV04, HV05, HV11 and HV12. The cold trap is ensured to be filled with dry ice.
3.
Valve HV-01 is removed and the feeding funnel V-100 is filled with the homogeneous mixture.
4.
The main power supply at the control is switched ON.
5.
The computer and the software program are turned ON.
6.
The thermostat is set at 70°C, Chiller at 12°C and vacuum pump pressure at 100mbar. The pressure throughout the experiment is manually mantained. [To adjust vacuum pump pressure, manually adjust valve, V14. To adjust the desired flow rate, adjust the opening valve HV03. To adjust the desired stirrer speed, adjust it from the software].
7.
Valve HV-13 is opened to allow for some of the hot bath to circulate through the heating jacket of the feeding funnel to pre-heat the feed in the funnel. NOTE: Valve HV13 must be close before switching off the thermostat, B-400.
8.
Once the chiller temperature and thermostat temperature have reach the set points, the experiment is started.
9.
Every set of experiment is run for 10 minutes. After 10 mins, the volume of distillate is recorded down from V-104 and volume of concentrate from V-105-107.
10. The experiment is repeated with different operating parameters as shown in the table in result and discussion.
4
BKF3751-Chemical Engineering Laboratory II
SAMPLING PROCEDURE 1.
For every batch of experiment, HV03 is kept opened at each sampling to ensure the flowrate is constant throughout experiment. To do this, the vacuum pump is switched off, while HV07, HV08 and HV09 are opened to let the condensate and distillate to flow into V-104 to V-107 respectively.
2.
After all the liquid are flows into each vessel, HV07, HV08 and HV09 are closed. The next experiment is continued by switching on the vacuum pump again.
3.
The collected distillate and condensate can then be used for futher testing.
4.
The feed flowrate is calculated by dividing the total volume of sample collected to the total time taken.
5
BKF3751-Chemical Engineering Laboratory II
3.0
Result and Discussion
3.1
Result
3.1.1 Effect of stirrer speed Vacuum Pressure, PT-200
100mbar
Evaporator Temperature, TT-100
70oC
Feed Flow Rate
13ml/min
Time
10min
EG-Water Ratio
7:3
Time Start
Stirrer Speed (rpm) 50 100 200 220
0920 0930 0940 0950
Distillate Volume (ml) 23 19 16 15
Concentrate Volume (ml) 87 90 97 100
Separation Efficiency (%) 66.92 69.23 74.62 76.92
Concentrate Volume (ml) 100 50 42 40 38
Separation Efficiency (%) 76.92 38.46 32.31 30.77 29.23
3.1.2 Effect of evaporator temperature Feed Flow Rate
13ml/min
Stirrer Speed, M-500
220rpm
Vacuum Pressure
100mbar
Time
10min
EG-Water Ratio
7:3
Time Start
Temperature (oC)
0950 1000 1010 1020 1030
70 72 74 76 80
Distillate Volume (ml) 15 15 13 12 11
6
BKF3751-Chemical Engineering Laboratory II
3.2
Discussion
The graph of stirrer speed against separation efficiency and evaporator temperature against separation efficiency are as below:
Graph of Stirrer Speed against Separation Efficiency 78
Separation Efficiency (%)
76 74 72 70 68 66 0
50
100
150
200
250
Stirrer Speed (rpm)
Graph 1: Graph of Stirrer Speed against Separation Efficiency
Graph of Evaporator Temperature against Separation Efficiency 90
Separation Efficiency (%)
80 70 60 50 40 30 20 10 0 68
70
72
74
76
78
80
82
Evaporator Temperature (oC)
Graph 2: Graph of Evaporator Temperature against Separation Efficiency 7
BKF3751-Chemical Engineering Laboratory II
Under same temperature, when stirrer speed increase, distillate volume decrease and concentrate volume increase and thus separation efficiencies increase. However, distillate volume and concentrate volume are both decrease when evaporator temperature increase and stirrer speed is constant. Thus, the separation efficiencies decrease. The separation efficiency at different operating conditions is calculated using the following formula: Efficiency
ConcentrateVolume x100 % Feed Volume
Short path distillation also called molecular distillation. It offers the advantage of distillation at considerably reduced pressure and thus reduced evaporation temperature with economical distillation rates. As the distance for the vapors between evaporator and condenser is extremely short and thus it is no pressure drop. So the obtainable vacuum is not limited. Short path distillation can be applied whenever all other distillation methods lead to thermal product damage, or rough vacuum require extremely high temperature. As mentioned, short path distillation is applied whenever heat-sensitive substance have to be distilled for purification, typical applications are particularly from the field of chemistry, pharmaceuticals, plastic industry, cosmetics industry and food industry. Typical examples of such heat-sensitive products are synthetic vitamins, paraffin waxes, derivatives of alkaloid, e.g. Quinine and THC, acrylates, plasticizer, fragrance, and essential oils such as ginger oil, pepper oil, fish oil and others.
8
BKF3751-Chemical Engineering Laboratory II
4.0
Conclusion and Recommendations
From the experiment, it can be concluded that as the stirrer’s speed increases, the volume of pure ethylene glycol increases, while the volume distillate of pure water decreases. On the other hand, as the temperature increases, the distillation of pure water increases, while the condensate of ethylene glycol decreases. Therefore, an increase of stirrer speed in short path distillation, improves the separation efficiency of the homogenous mixture. The maximum separation efficiency achieved is 76.92% at stirrer speed of 220rpm. To ensure constant feed flow rate, HV03 should not be closed at each sampling. Instead, switch off the vacuum pump, open HV07, HV08 and HV09 to let the condensate and distillate to flow into V104 to V107 respectively.
9
BKF3751-Chemical Engineering Laboratory II
5.0
Reference
Retrieved 29 July, 2010 from http://www.bayertechnology.com/en/products/reaction-and-polymertechnology/stirring-technology/our-service.html
Retrieved 29 July, 2010 from http://lorien.ncl.ac.uk/ming/distil/distildes.htm Retrieved 29 July, 2010 from http://www.avta-us.com/basics.html Retrieved 29 July, 2010 from http://www.chemtechservicesinc.com/short-path-distillation.html
10
BKF3751-Chemical Engineering Laboratory II
6.0
Appendix
11
1.0
Introduction
1.1
Introduction (Literature review and theory) Short path distillation is a distillation technique that involves the distillate travelling a
short distance, often only a few centimeters, and is normally done at reduced pressure. The vapor stream travels a "short path" directly to the condenser which is located within the evaporator chamber. Since the vapor stream is immediated condensed, the short path distillation process precludes the vapor from forming vapor pressure. This allows ultimate pressures of 0.001 mbar to be attained. Short residence time and low evaporation temperature will cause a minimum thermal stress to the distilled product. This also allows heat sensitive materials to undergo purification at much lower temperatures preventing degradation. A short path ensures that little compound is lost on the sides of the apparatus. Typical applications are high molecular organic compounds particularly from the fields of chemistry, pharmaceutical and food industry. Short-Path Distillation is a continuous separation process working under vacuum conditions. Evaporation takes place from a heated wiped film. Caused by the pressure drop between the place of vaporization and the vacuum system the operating pressure in typical wiped film evaporators with external condenser is limited to some millibars. The considerably lower pressure in the Short Path Evaporator is obtained by the short distance for the vapors on their way from the evaporator surface to the condenser. In addition, the cross section area of flow is equal to the evaporator surface, so that there is only a minor pressure drop between evaporator and condense. Separation processes can essentially be termed as mass transfer processes. The classification can be based on the means of separation, mechanical or chemical. The choice of separation depends on the pros and cons of each. Mechanical separations are usually favored if possible due to the lower cost of the operations as compared to chemical separations. Systems that cannot be separated by purely mechanical means (e.g. crude oil), chemical separation is the remaining solution. The mixture at hand could exist as a combination of any two or more states: solid-solid, solid-liquid, solid-gas, liquid-liquid, liquid-gas, gas-gas, solid-liquid-gas mixture. Separation of components from a liquid mixture via distillation depends on the differences in boiling points of the individual components. Also, depending on the 1
BKF3751-Chemical Engineering Laboratory II
concentrations of the components present, the liquid mixture will have different boiling point characteristics. Therefore, distillation processes depends on the vapor pressure characteristics of liquid mixtures. The vapor pressure of a liquid at a particular temperature is the equilibrium pressure exerted by molecules leaving and entering the liquid surface. Here are some important points regarding vapor pressure: energy input raises vapor pressure, vapor pressure is related to boiling, a liquid is said to ‘boil’ when its vapor pressure equals the surrounding pressure, the ease with which a liquid boils depends on its volatility liquids with high vapor pressures (volatile liquids) will boil at lower temperatures, the vapor pressure and hence the boiling point of a liquid mixture depends on the relative amounts of the components in the mixture, distillation occurs because of the differences in the volatility of the components in the liquid mixture. The Separation efficiency denotes by: Separation efficiency =
X 100
Mechanical stirring a determining factors for the distillation efficiency, mechanical stirring ensures a complete mixing and a better heat transfer rate between the hot oil jackets and the feed. The higher degree of stirring increasing the heat transfer rate subsequently bringing the higher distillation effect. Temperature of the evaporator is another important variable in optimizing the distillation efficiency where the optimum temperature should have to be selected to supply enough heat for the water to be condensed. The distillation efficiency will be increased by increasing of temperature. However, excessive of heat can result in degradation of product. Feed rate control is crucial in distillation process, as the residence time in the evaporator determine the efficiency of heat transfer. If the feeding rate is high then the residence time of feed in evaporator decrease may causing the feed to be not well heated. Hence the feed will be ing through without any separation happen.
2
BKF3751-Chemical Engineering Laboratory II
1.2
Objectives 1. To introduce the short path distillation principles using continuous system. 2. To observe the effects of stirrer speed and temperature on the efficiency of separation, e.g ethylene glycol-water.
3
BKF3751-Chemical Engineering Laboratory II
2.0
Methodology
2.1
Equipment/Apparatus/Material 1. Short Path Distillation Unit 2. Ethylene glycol – water mixture
2.2 1.
Procedures The ethylene glycol is mixed with water in a ratio of 7:3 at total of 1 litre in a beaker. Then the mixture is stirred homogeneously.
2.
All valves are initially checked closed except the valves HV02, HV04, HV05, HV11 and HV12. The cold trap is ensured to be filled with dry ice.
3.
Valve HV-01 is removed and the feeding funnel V-100 is filled with the homogeneous mixture.
4.
The main power supply at the control is switched ON.
5.
The computer and the software program are turned ON.
6.
The thermostat is set at 70°C, Chiller at 12°C and vacuum pump pressure at 100mbar. The pressure throughout the experiment is manually mantained. [To adjust vacuum pump pressure, manually adjust valve, V14. To adjust the desired flow rate, adjust the opening valve HV03. To adjust the desired stirrer speed, adjust it from the software].
7.
Valve HV-13 is opened to allow for some of the hot bath to circulate through the heating jacket of the feeding funnel to pre-heat the feed in the funnel. NOTE: Valve HV13 must be close before switching off the thermostat, B-400.
8.
Once the chiller temperature and thermostat temperature have reach the set points, the experiment is started.
9.
Every set of experiment is run for 10 minutes. After 10 mins, the volume of distillate is recorded down from V-104 and volume of concentrate from V-105-107.
10. The experiment is repeated with different operating parameters as shown in the table in result and discussion.
4
BKF3751-Chemical Engineering Laboratory II
SAMPLING PROCEDURE 1.
For every batch of experiment, HV03 is kept opened at each sampling to ensure the flowrate is constant throughout experiment. To do this, the vacuum pump is switched off, while HV07, HV08 and HV09 are opened to let the condensate and distillate to flow into V-104 to V-107 respectively.
2.
After all the liquid are flows into each vessel, HV07, HV08 and HV09 are closed. The next experiment is continued by switching on the vacuum pump again.
3.
The collected distillate and condensate can then be used for futher testing.
4.
The feed flowrate is calculated by dividing the total volume of sample collected to the total time taken.
5
BKF3751-Chemical Engineering Laboratory II
3.0
Result and Discussion
3.1
Result
3.1.1 Effect of stirrer speed Vacuum Pressure, PT-200
100mbar
Evaporator Temperature, TT-100
70oC
Feed Flow Rate
13ml/min
Time
10min
EG-Water Ratio
7:3
Time Start
Stirrer Speed (rpm) 50 100 200 220
0920 0930 0940 0950
Distillate Volume (ml) 23 19 16 15
Concentrate Volume (ml) 87 90 97 100
Separation Efficiency (%) 66.92 69.23 74.62 76.92
Concentrate Volume (ml) 100 50 42 40 38
Separation Efficiency (%) 76.92 38.46 32.31 30.77 29.23
3.1.2 Effect of evaporator temperature Feed Flow Rate
13ml/min
Stirrer Speed, M-500
220rpm
Vacuum Pressure
100mbar
Time
10min
EG-Water Ratio
7:3
Time Start
Temperature (oC)
0950 1000 1010 1020 1030
70 72 74 76 80
Distillate Volume (ml) 15 15 13 12 11
6
BKF3751-Chemical Engineering Laboratory II
3.2
Discussion
The graph of stirrer speed against separation efficiency and evaporator temperature against separation efficiency are as below:
Graph of Stirrer Speed against Separation Efficiency 78
Separation Efficiency (%)
76 74 72 70 68 66 0
50
100
150
200
250
Stirrer Speed (rpm)
Graph 1: Graph of Stirrer Speed against Separation Efficiency
Graph of Evaporator Temperature against Separation Efficiency 90
Separation Efficiency (%)
80 70 60 50 40 30 20 10 0 68
70
72
74
76
78
80
82
Evaporator Temperature (oC)
Graph 2: Graph of Evaporator Temperature against Separation Efficiency 7
BKF3751-Chemical Engineering Laboratory II
Under same temperature, when stirrer speed increase, distillate volume decrease and concentrate volume increase and thus separation efficiencies increase. However, distillate volume and concentrate volume are both decrease when evaporator temperature increase and stirrer speed is constant. Thus, the separation efficiencies decrease. The separation efficiency at different operating conditions is calculated using the following formula: Efficiency
ConcentrateVolume x100 % Feed Volume
Short path distillation also called molecular distillation. It offers the advantage of distillation at considerably reduced pressure and thus reduced evaporation temperature with economical distillation rates. As the distance for the vapors between evaporator and condenser is extremely short and thus it is no pressure drop. So the obtainable vacuum is not limited. Short path distillation can be applied whenever all other distillation methods lead to thermal product damage, or rough vacuum require extremely high temperature. As mentioned, short path distillation is applied whenever heat-sensitive substance have to be distilled for purification, typical applications are particularly from the field of chemistry, pharmaceuticals, plastic industry, cosmetics industry and food industry. Typical examples of such heat-sensitive products are synthetic vitamins, paraffin waxes, derivatives of alkaloid, e.g. Quinine and THC, acrylates, plasticizer, fragrance, and essential oils such as ginger oil, pepper oil, fish oil and others.
8
BKF3751-Chemical Engineering Laboratory II
4.0
Conclusion and Recommendations
From the experiment, it can be concluded that as the stirrer’s speed increases, the volume of pure ethylene glycol increases, while the volume distillate of pure water decreases. On the other hand, as the temperature increases, the distillation of pure water increases, while the condensate of ethylene glycol decreases. Therefore, an increase of stirrer speed in short path distillation, improves the separation efficiency of the homogenous mixture. The maximum separation efficiency achieved is 76.92% at stirrer speed of 220rpm. To ensure constant feed flow rate, HV03 should not be closed at each sampling. Instead, switch off the vacuum pump, open HV07, HV08 and HV09 to let the condensate and distillate to flow into V104 to V107 respectively.
9
BKF3751-Chemical Engineering Laboratory II
5.0
Reference
Retrieved 29 July, 2010 from http://www.bayertechnology.com/en/products/reaction-and-polymertechnology/stirring-technology/our-service.html
Retrieved 29 July, 2010 from http://lorien.ncl.ac.uk/ming/distil/distildes.htm Retrieved 29 July, 2010 from http://www.avta-us.com/basics.html Retrieved 29 July, 2010 from http://www.chemtechservicesinc.com/short-path-distillation.html
10
BKF3751-Chemical Engineering Laboratory II
6.0
Appendix
11
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