Equipment: To carry out the experiment, I will require the following apparatus and chemicals:
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10 cm3 measuring cylinder 15. Long teat pipette
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Butan-1-ol (7.5cm3) 16. Conc. Hydrochloric acid (10cm3)
- Access to balance 17. Sodium hydrogencarbonate solution, 5%
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50cm3 pear-shaped flask 18. Anhydrous sodium sulphate
- Sodium Bromide (10g) 19. Test tubes (2)
- Tap funnel and stopper 20. Small funnel with cotton wool plug
- Distillation head 21. Glass rod
- Clamp and stand 22. Small beaker
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250cm3 beaker (for water bath) 23. 0-110°C thermometer and holder
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Conc. Sulphuric acid (10cm3) 24. Specimen tube
- Anti-bumping granules
- Reflux condenser
- Guard tube containing soda lime
- Small Bunsen or electric heating mantle
Risk Assessment
Some extra precautions I ill take is to have my apparatus set-up checked with the teacher from time to time.
Carrying out the reaction
7.5 cm3 of butan-1-ol was poured into a 10cm3-measuring cylinder (Our alternative for a batch reactor). After weighing the measuring cylinder and it’s contents we poured it into a 50cm3 pear-shaped flask. Precautions were taken to prevent the highly inflammable and volatile alcohol from catching fire or lost through evaporation. To the alcohol, 10cm3 of concentrated sulphuric acid was added to the tap funnel. We then added the sulphuric acid to the reaction over a period of 5 minutes with cooling by means of a water bath. The apparatus was also swirled at the same time to ensure the acid reacted. This was to prevent the sulphuric acid from reacting to fast as it is an n exothermic reaction. (A high temperature may vaporise quickly the Butan-1-ol, which will decrease the yield.
After the reaction, we removed the top funnel and distillation head from the top of the flask and the cooling bath from around the flask and dried the outside of the flask. We set up the apparatus for reflux added a few anti bumping granules and heated for a period of 45 minutes. Reflux is needed because the reaction needs to go to completion and as with other organic liquids it is often necessary to reflux because heat needs to be applied without losing reactions through evaporation.
Purifying the product
After refluxing, the next step in the experiment was to purify the product. To do this, we sucked of the upper organic layer from the reaction mixture, and transferred it to a small separating funnel. Then we added 10cm3 of concentrated hydrochloric acid to the organic layer in the tap funnel. The mixture was then shaken vigorously in the stoppered funnel releasing pressure from time to time. After the mixture had completely reacted, the organic layer was carefully sucked out. Then the 1-bromobutane was poured into a test-tube. Then we ran it into a tap funnel and 10cm3 of Sodium Hydrogencarbonate was added to the organic solution. Then we shook the contents vigorously and allowed the pressure to escape. When the two layers separated, the lower layer was run into a test-tube. Anhydrous Sodium Sulphate was added to the contents of test-tube to act as a drying agent and remove the last traces of water.
The reason for the multiple layers of products is the fact that there are in fact many reactions taking place at the same time in the flask. The reactions are:
1) Sodium Bromide reacts with sulphuric acid to form hydrogen bromide and sodium hydrogen sulphate.
NaBr + H2SO4 → HBr + NaHSO4
2) Hydrogen Bromide is oxidised to bromine molecules as concentrated sulphuric acid is a very good oxidizing agent. The sulphuric acid reacts to form sulphur dioxide gas.
HBr + H2SO4 → Br2 + 2SO2
3) Hydrogen bromide disassociates and the bromide ion from it attacks the carbon atom with the –OH function group in butan-1- ol and displaces the –OH function group forming a bromo function group and a hydroxide ion, which then associates itself with another H+ ion to form water.
CH3CH2CH2CH2OH + Br → CH3CH2CH2CH2Br + OH-
4) A molecule of sulphuric acid attacks the lone pair on an –OH function group, releasing a molecule of water and a mixture of butoxybutane and but-1-ene is formed, along with the regenerated sulphuric acid.
CH3CH2CH2CH2OH + H2SO4 → CH3CH2 CH = CH2 +H2O + H2SO4
I decide which layer is to be kept from the basis of density; 1-bromobutane has a density of 1.276gcm-3.
Hydrochloric acid is to be added because the acid protonates the butn-1-ol, giving an ionic species that is much more soluble in water than the alcohol itself:
CH3CH2CH2CH2OH + H+ → CH3CH2CH2CH2OH+
Testing the purity of the liquid
We carried out a fractional distillation of the 1-bromobutane and the fraction between 100ºC and 104ºC was collected in a weighed specimen tube and we recorded the mass of 1-bromobutane collected.
Observations
1. When the chemicals were added in the pear-shaped flask, exothermic reaction occurred which produced a lot of heat.
2. During reflux as the reaction progressed, the liquid became less opaque and a trace of yellow colour was seen. The reactants separated into 2 distinct layers which was not obvious before refluxing. The reason for this is because there are a lot of reactions taking place in the same flask.
Diagrams
Simple Distillation
Refluxing
Calculation
CH3CH2CH2CH2OH + HBr →CH3CH2CH2CH2
(Butan-1-ol) (hydrogen) (1-bromobutane) (water)
(bromide)
RMM of Butan-1-ol
12 + 3 + 12 + 2 +12 +2 + 12 + 2 + 16+ 1=74g
RMM of 1-bromobutane
12 + 3 + 12 + 2 + 12 + 2+ 12 + 2 +80=137g
C= 12, H=1, O= 16
C= 48 C= 48
H= 11 H= 9
O = 16 Br= 80
74 137
74g → 137g
1g → 137
74
Therefore 6g → 137 * 6
74
Theoretical yield = 11.12g
Measuring cylinder with butan-1-ol = 25.07 g
Measuring cylinder without butan-1-ol =19.12g
Amount of butan1-ol == 5.95g
Mass of 1- bromobutane= 2.9g
Percentage yield = actual yield * 100
Theoretical yield
= 3.77/11.12 * 100
= 33%
Volume of 1- bromobutane = 2.9cm3
Density= 3.77/2.9= 1.3
Mass = d*v
Mass of butan-1-ol = 0.8*7.5g = 6g
Mass of 1-bromobutane= 1.3*2.9= 3.77g
Benefits of automation
There are many benefits related to automation, like heating tanks instead of a Bunsen burner, which would speed up the heating and any excess heat would be recycled and put back into the heating tank to reduce costs. The main benefits of automation are;
There are many ways in which industrial methods have replaced certain procedures in the laboratory e.g. boiling is replaced by heating tanks that heat the mixture till it reaches it’s optimum temperature. Temperature recording manually by a main reactor with automatic temperature control system. Computer set with a certain quantity needed does accurate measuring of the feedstock and when that quantity is reached, the computer allows no more in; tanks have automatic temperature registers to take accurate readings. The industries contain bulk storage facilities,
The industrial production technique is more advance and produces a higher amount of yield.
1) They speed up processes that would normally take longer in the laboratory.
2. They are often easier to carry out because most are computerised processes.
3. They are often cheaper than original processes because they are carried out at compromise conditions
4. It has reduce the amount of workers because most operations are carried out automatically.
Problems that occurred and how I rectified them
1. When adding the concentrated sulphuric acid to the contents in the pear-shaped flask (batch reactor), the colour change rapidly to a dark brown colour. This was probably because I added to much acid to the mixture at once. To correct this problem, I carried out the procedure again and extended the time I had to add the acid to ten minutes.
2. When adding the concentrated acid to the mixture in the flask, it produced an exothermic reaction which produced a lot of heat. To prevent the reaction from taking place to fast and to avoid the evaporation of the mixture, I placed it in a cold water bath.
3. At the end of the purifying the product, I had to add drying agent to the 1-bromobutane to absorb the remaining water. I had to check this by observing the visibility of the solution until it was clear. After adding a lot of the drying agent, the visibility still wasn’t clear so I stopped and continued with the next step of the experiment.
4. During the separation of the different layers it was impossible to avoid running part of the other layer into the test tube as well.
5. The booklet we were provided with suggested we use a guard tube which contained soda lime when refluxing. This would have absorbed acid fumes or sulphur dioxide gas that might have been given off. There were no guards available which didn’t make the experiment safe. This factor did not affect the yield we obtained.
6. During the purification of the product, releasing the pressure from time to time might have also allowed the escape of the product as it evaporates easily. I limited the time allowed to reduce pressure to about 5 seconds instead of longer.
7. When we carried out the reflux procedure the 1st time, we left our mixture in a beaker covered with cling film. During the 2nd lesson, we found out that the whole substance had evaporated into the atmosphere and had to re-start the experiment.
8. While I was doing step 10, transeferring the bottom layer, (bromobutane layer into a clean test tube). Some of the top layer got transferred with the bromobutane in the test tube as well. From this, I lost some of my percentage yield.
9) When purifying the product, sodium hydrocarbonate solution is added. There was some acid in the funnel that can be marked the build up of gas pressure. To justify this problem, the shakings must be very gentle and released between each shaking.
Evaluation
I have carried out the laboratory procedure of preparing 1-bromobutane. From the experiment, I got a yield of 33% which is quite high considering the amount of problems that occurred and yield that was lost due to evaporation. I also got a boiling point of 96ºC while according to the literature value from “Nuffield Advanced Science Revised Book of Data, by Hendrina Ellis published in 1984, page 106” shows that the actual boiling point is 101.7ºc. This means that the 33% of yield obtained also contains some impurities.
Some of the likely impurities are;
1) During the separation of 1-bromobutane from the butan-1-ol, it is possible that the mixture did not completely separate from another. According to physchem.ox.ac.uk/MSDS/BU/2-butanol.html, the boiling point of butan-1-ol is 98ºC. This means if the solution contained 1-bromobutane, it would have started to distillate before the 1- bromobutane.
2) Water: it was clear the anhydrous sodium sulphate did not dry out the water in the 1-bromobutane completely because it didn’t look completely clear. Since the boiling point of water is 100C this could have started to condense just before the 1- bromobutane into the beaker.
Adaptations that could be made to the experiment
1) During the reactions of the chemicals in the batch reactor, a sand bath could have been used instead of a water bath. The sand spreads the heat uniformly over the base of the flask. This reduces the likelihood of cracking and unwanted side reactions occurring (e.g. excessive oxidation either of bromide ions to bromine or of the alcohol to carbon).
2) Fractional Distillation: is a similar method to simple distillation except that it contains a fractionating column. It is used to separate mixtures of volatile liquids. Since 1-bromobutane is a volatile liquid this would have been a good alternative. The fractionating column will ensure that only the liquid that boils at its boiling point will pass into the condenser. Although this wouldn’t have improved the yield, it certainly would have improved the boiling point and reduced the amount of impurities and the yield.
3) During refluxing, we could have heated the mixture for longer. We heated our mixture for a total period of 30 minutes. The reaction that occurred was an organic reaction which is basically slow because of the need to break down strong covalent bonds. Increasing the reflux period to 45-50 minutes would have ensured the reactions took place completely.
Description of The batch reactor
The batch reactor we used in the laboratory is less efficient compared to the one used in the industries. A lot of heat is lost due to exothermic reactions taking place in the pear shaped flask but the industries the reactions can be controlled automatically. The industries also have bigger batch reactors and carry out reactions on a larger scale (Glass-Lined -2,250 to 23,000 litres).
How a batch reactor works in industries
The reactor control Task controls all of the activities of the reactor. The normal sequence of events is:
- Load raw material into the reactor.
- Cool the reactor contents to the pre-reaction cooling temperature by opening the cooling valve to its maximum cooling position.
- Add the catalyst - This step is controlled by a PID loop which adjusts the catalyst flow. The goal is to add the catalyst as fast as possible without creating a dangerous pressure condition in the reactor. The GAIN of the PID loop is continuously adjusted to match the GAIN of the reaction, i.e., the ratio of energy released to the amount of catalysts added.
- After the proper amount of catalyst has been added, the mixture is cooled to a stabilizing temperature. This cooling is also controlled by a PID loop. The parameters of the loop are set to achieve maximum cooling until the temperature approaches the stabilizing temperature. The parameters are then changed to stabilize the temperature.
- When the temperature is within 1 degree of the setpoint for a period of time, the contents of the reactor are emptied by opening the delivery valve. This Task also responds to an emergency stop switch which restarts the batching process and to an over temperature condition which suspends the addition of catalysts until the temperature returns to a safety level.
AGITATOR CONTROL
This task has the simple function of turning on the agitator motor whenever there is more than 15 pounds of material in the reactor. This Task also causes the agitator motor to stop if the emergency stop switch is tripped or if a motor overload condition occurs. If there is an overload condition, the agitator motor stops and the overload light flashes until the reset switch is pressed. When the reset switch is pressed this Task goes back to normal operations.
OPERATOR INTERFACE
This Task handles all communications with the operator. Information displayed to the operator includes menus of recipe choices, batch statistics, prompts for entering information, and alarm messages. This Task also performs diagnostics analysis and displays troubleshooting information to the operator when alarm situations occur. This Task also receives input from the operator. At the start of each batch the operator enters the recipe type and the number of batches to mix.
ALARM MONITORING
This Task continuously watches for alarm conditions. The three conditions that are continuously monitored are if the reactor temperature is greater than 250 degrees, the agitator motor load is greater than 2700 watts, or the emergency switch is tripped. If any of these conditions are true then this Task puts the other control Tasks into the proper States to handle the condition and waits in an appropriate reset State for the condition to normalize.
APPLICATION SIMULATION
One of the very powerful features of State Logic is the ability to easily simulate the process and test the control software. This task shows a simple example of how this is accomplished.
In addition to the control of the reactor, this program also provides simulation of the analog inputs for temperature and pressure, which would normally be read from sensors on the reactor. The program also sets values in variables which would normally go to the analog outputs. The valve controlling the flow of coolant and the valve controlling the flow of the catalyst are the two values which are stored in variables in this program rather than sent to actual devices.
Bibliography
1) Nuffield Advanced Science Revised Book of Data, by Hendrina Ellis published in 1984,
Websites
1)physchem.ox.ac.uk/MSDS/BU/2-butanol.html,
2) but.htm
