CHEM10003 E3 Extracting chemicals from nature PDF

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2020 CHEM10003 Experiment 3...

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Kelvin Ton

Experiment 3: Extracting chemicals from nature Aim To isolate caffeine from commercially available ground coffee using Soxhlet extraction and high pressure/temperature extraction with a coffee espresso machine, and to evaluate and compare the extraction techniques used to isolate caffeine with respect to yield, cost and environmental impact Experimental Method Refer to First Year Chemistry Laboratory Manual, University of Melbourne 2020, page 46-55 Results Method A – Soxhlet extraction: The product appeared to be in the form of a white crystalline sheet at the bottom of the beaker. Trial

1

2

3

m(coffee)

1.00g

1.02g

1.03g

m(Beaker + Boiling Chips)

34.609g

31.113g

35.472g

m(Beaker + Boiling Chips + caffeine)

34.652g

31.159g

35.516g

m(caffeine)

0.043g

0.046g

0.044g

Average Caffeine Yield = 0.0443g Average Coffee Mass = 1.017g %yield =

0.0443 1.017

x 100 = 4.36%

Method B – Coffee Machine Extraction: The product appeared to be in the form of a white crystalline sheet at the bottom of the beaker, however it had a slightly brown taint. Trial Total m(coffee) Total v(coffee collected) v(coffee extract) m(beaker + boiling chips) m(beaker + boiling chips + caffeine) m(caffeine)

1 15.16g 44.0g 10.00ml 34.237g 34.245g 0.008g

2 15.16g 44.0g 10.00ml 33.672g 33.681g 0.009g

3 15.16g 44.0g 10.00ml 35.298g 35.312g 0.014g

Kelvin Ton

Average Caffeine Mass per Extract = 0.0103g Caffeine Mass from Total Volume = %yield =

0.0453 15.16

44.0 10.00

x 0.0103 = 0.0453g

x 100 = 0.30%

Rf values Sample Method A Distance travelled by spot 2.55cm from spotting position Rf value 2.55/4.90=0.520

Method B 2.60cm

Control group 2.50cm

2.60/4.90=0.531

2.50/4.90=0.510

Questions Question 1: i)

ii)

Compounds that may be dissolved in the lower brown NaOH layer is tannic acid, as well as chlorogenic acids as the bottom layer is comprised of molecules that are water soluble as they are polar. There is intramolecular ionic bonding between the molecules due to the NaOH being pronated and the caffeine molecules being de-pronated. However, the intermolecular bonding which is present is hydrogen bonding between the H attached to O in water, and with the other molecules such as the chlorogenic acids.

Question 2: The colour of the coffee extract in method B is much darker than the extract obtained in method A. This can be attributed to the fact that the solvent used was water instead of acetone, and the coffee machine has a higher pressure and temperature. Water can only be a solute for polar molecules, whereas acetone can dissolve both non-polar and polar molecules as it is less polar than water.

Question 3: i)

ii)

The compound extracted as caffeine is identified by comparing the Rf values of both method A and B, and because they were almost identical to the control group, the compound extracted in both methods are identical, being caffeine The purity of the extract is identified by the number of spots displayed by the TLC by each spotting pattern. A pure extract of the sample will only produce one spot

Kelvin Ton

iii)

per each spotting pattern, whereas an impure extract will produce one or more spots. The caffeine obtained in Method B was discoloured and the TLC did not show this – a limitation of TLC all compounds must be able to absorb UV light to produce spots, and only aromatic compounds absorb UV light. This explains the slightly discoloured single dot observed in method B, which could be explained by a little contamination of the sample.

Discussion In this experiment, method A (4.36%) achieved a higher percentage yield of caffeine than method B (0.30%). There were many discrepancies between the two methods, one being that there were 15 cycles of the Soxhlet extraction and only 1 cycle in the expresso machine. Further, the TLC’s main limitation of only being able to see compounds that absorb UV light may have affected the result – the discolouration of a spot in method B may mean that the sample was contaminated. In method B, when the 10.00mL of coffee extract was measured, it was slightly above the 10mL mark, and still had bubbles at the top of the liquid, therefore reducing the precision of the measurement and being a limitation. There may have been other mistakes or systematic errors that were not taken into account that could have affected the results.

Conclusion In conclusion, method A had a greater percentage yield than method B. Through the TLC, it was also determined that both extracts (A and B) were pure samples, however there were limitations with TLC.

Kelvin Ton

Executive Summary The chemical laboratory was asked to compare the cost, yield and environmental impact for the large-scale extraction of caffeine from coffee beans. Method A resulted in a higher percentage yield (4.36%) of caffeine and was carried out by extracting caffeine through Soxhlet extraction. Method B resulted in a lower percentage yield (0.30%) and was completed using a coffee espresso machine at high pressures and temperatures. For cost for 1kg Caffeine production Coffee: 1329 30500 = 1/ 30500 1329 Let C=22.950kg Cost = 22.950 x 15 =$344.24

Coffee: 37900 =334.51kg 1153 25000/1133 = C Let C = 22.065 Let F = 4.4 (trials) Cost = $5017.65

Acetone: 25 x C = 573.74L Cost = $24097.07 NaOH: 20 x C = 459.00L Cost = $917.98 Ethyl Acetate: 15 x C = 344.24L Cost = $13769.75 MgSO4: 3.2 x C =73.439kg Cost = $7343.87 Soxhlet: 25 x C x 30 = $17212.19

Water: 44 x C = 970.87L Cost = $1941.75 NaOH: 15 x F x C = 1456.3L Cost = $2912.62 Ethyl Acetate: 15 x F x C = 1456.3L Cost = $58252.43 MgSO4: 3.2 x F x C = 310.68kg Cost = $31067.96 Heat + Pressure: 44 x C = 970.87L Cost = $38834.95 Disposal: Disposal: MgSO4 + NaOH + coffee – caffeine =554.38L Coffee – caffeine + NaOH + MgSO4 =2100.5L Cost = $1385.95 Cost = $5251.25 Method A total cost for 1kg = $65071.05 Method B total cost for 1kg = $143278.61 The environmental impacts of Method A were slightly better than Method B even though it used acetone, which is a volatile and flammable liquid. This is because method B has a greater amount of waste, containing sodium hydroxide, a corrosive chemical. Therefore, it is recommended that the company implement method A over method B since it is more cost efficient, thus a greater yield of caffeine. The method fails to take into account the cost of labour and does not really involve the time taken to produce the outcome. Further, the method of producing this on a large-scale has not been considered....