Organic Chemistry Biofuels Activity Worksheet

On Line Activity: Biofuels – Analysis

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Calculations

1. Calculate the volume of ethanol collected in all four distillations. Follow these steps:

  1. Convert the measured density of the distillate from each fraction to % ethanol by volume (concentration). Use the conversion chart in https://handymath.com/cgibin/ethanolwater3.cgi?submit=Entry

 

  1. Calculate the volume of ethanol collected in each fraction. Multiply the distillate volume in each fraction by the concentration of ethanol in each fraction.
  2. What is the total volume of ethanol collected? Sum the volume of ethanol collected in each fraction.
  3. The total volume of ethanol collected = the % recovery of ethanol because you started with 100 mL of fermentation broth (x/100 *100) = x%

 

Data for distillation of fermented apple juice

Total volume of fermentation broth: 256.32 mL

Volume for distillation: 100.00 mL

Volume of pot residue: 61.3 mL

Time for distillation: 35 min

Sugar content per serving size = 43 g glucose per 296 mL of juice

Fraction

Temp (° C)

Distillate

volume (mL)

Density of Distillate (g/mL)

Concentration (% EtOH by Volume)

Volume of EtOH (mL)

1

76

1.99

0.806

 

 

2

79-92

3.80

0.891

 

 

3

92-94

3.96

0.902

 

 

4

94-95

3.51

0.972

 

 

5

95-96

3.74

0.974

 

 

6

96-97

3.81

0.990

 

 

7

97-98

3.11

0.990

 

 

8

98

2.00

0.997

 

 

 

Total Volume of Ethanol =

 

% Recovery of Ethanol =

 

Data for distillation of fermented grape juice

Total volume of fermentation broth: 249.88 mL

Volume for distillation: 100.00 mL

Volume of pot residue: 72.0 mL

Time for distillation: 40 min

Sugar content per serving size = 40 g glucose per 240 mL of juice

Fraction

Temp (° C)

Distillate

volume (mL)

Density (g/mL)

Concentration (% EtOH by Volume)

Volume of EtOH (mL)

1

78

1.32

0.809

 

 

2

78

1.70

0.852

 

 

3

86

1.32

0.870

 

 

4

87

1.36

0.872

 

 

5

88

1.29

0.890

 

 

6

90

0.71

0.890

 

 

7

90

1.80

0.905

 

 

8

91

1.20

0.920

 

 

9

92

1.31

0.921

 

 

10

92

1.44

0.960

 

 

11

94

2.74

0.974

 

 

12

94

1.74

0.980

 

 

13

95

1.73

0.980

 

 

14

95

1.70

0.990

 

 

15

96

1.47

0.990

 

 

16

97

1.045

1.000

 

 

 

Total Volume of Ethanol =

 

% Recovery of Ethanol =

 

 

Data for distillation of fermented potato starch

Total volume of fermentation broth: 219.52 mL

Volume for distillation: 100.00 mL

Volume of pot residue: 73.2 mL

Time for distillation: 40 min

Sugar content per serving size = potato starch is pure glucose in starch form. 50 g glucose in 50 g of starch

Fraction

Temp (° C)

Distillate

volume (mL)

Density (g/mL)

Concentration (% EtOH by Volume)

Volume of EtOH (mL)

1

78

1.98

0.809

 

 

2

78-80

2.15

0.852

 

 

3

80-87

2.30

0.872

 

 

4

87

2.13

0.895

 

 

5

87

1.85

0.922

 

 

6

87-89

1.59

0.948

 

 

7

89

3.20

0.957

 

 

8

89-93

1.87

0.987

 

 

9

95

2.97

0.987

 

 

10

95

2.56

1.000

 

 

 

Total Volume of Ethanol =

 

% Recovery of Ethanol =

Data for distillation of fermented corn mash

Total volume of fermentation broth: 209.36 mL

Volume for distillation: 100.00 mL

Volume of pot residue: 68.5 mL

Time for distillation: 34 min

Sugar content per serving size = 16 g glucose per 90 g corn

Fraction

Temp (° C)

Distillate

volume (mL)

Density (g/mL)

Concentration (% EtOH by Volume)

Volume of EtOH (mL)

1

79-92

1.345

0.867

 

 

2

92

1.232

0.910

 

 

3

92

1.204

0.940

 

 

4

92

1.469

0.950

 

 

5

92

1.368

0.955

 

 

6

92

1.236

0.960

 

 

7

92-94

1.295

0.980

 

 

8

94

1.430

0.982

 

 

9

94-95

1.310

0.989

 

 

10

95

1.109

0.990

 

 

11

95

1.424

0.991

 

 

12

95

1.369

0.992

 

 

13

95

1.498

0.996

 

 

14

95

1.435

0.997

 

 

15

95

1.192

0.997

 

 

16

95

1.045

0.998

 

 

17

95

1.287

0.998

 

 

18

95

1.414

0.999

 

 

19

95

1.411

1.000

 

 

 

Total Volume of Ethanol =

 

% Recovery of Ethanol =

 

 

 

 

 

 

 

  1. Calculate the volume of ethanol produced per gram of starting material (corn, starch, or juice) (mL/g). The amounts of starting material are as follows: 100.0 g of corn, 50.0 grams of potato starch, 100.0 mL of juice. The density of Welch’s apple juice is 1.05 g/mL and Welch’s grape juice is 1.06 g/mL.

 

Example Calculation: There was 220 mL of total fermentation broth (100 mL was taken for distillation) collected and the group calculated a percent recovery of 6.1% ethanol. Take the volume of ethanol that would have been produced had all of the fermentation broth been distilled and divide it by the grams of starting material (mass of corn, potato starch, juice):

 

220 𝑚𝐿 𝑥 6.1% = 13.42 𝑚𝐿 𝑒𝑡ℎ𝑎𝑛𝑜𝑙

13.42 𝑚𝐿 𝑒𝑡ℎ𝑎𝑛𝑜𝑙

= 0.13 𝑚𝐿/𝑔

100 𝑔 𝑐𝑜𝑟𝑛

 

  1. Add the volume of distillate collected in all fractions and the remaining residue in the round bottom flask. How does this compare to the original volume? If any was lost, calculate the percent volume lost in the distillation process.

 

Example Calculation: Let’s say the total volume collected in the fractions was 7.1 mL and the total volume remaining in the distillation flask was 90.5 mL (volume distilled was 100 mL). The percent loss can be calculated by:

% 𝐿𝑜𝑠𝑠 = word image 858 𝑥 100 = 2.4%

 

 

  1. Calculate the theoretical yield (in mL) of ethanol that can be produced in each fermentation. You will need to consider how much of the carbohydrate source was used, how much sugar/carbohydrate is contained in each source, and the chemical equation for the fermentation of sugar/glucose into ethanol. Assume that all available more complex carbohydrates, such as starch, were converted into glucose via the acid hydrolysis pre-fermentation step. After calculating the theoretical yield for all four carbohydrate sources, calculate the percent yield of each.

 

word image 2474

 

  1. Calculate the energy supplied by the heating mantle to the distilling flask and compare to the energy released when the ethanol is combusted. Which is greater? Is this procedure commercially viable? Assume the power of the heating mantle is 130 Watts and Power=Energy/time (watts = J/s). How long did it take you to complete the distillation (in seconds)? Assume that ethanol generates 27.3 kJ/g of material.

 

Carbohydrate Source

Time to

Complete

Distillation

Apple Juice

35 min

Grape Juice

40 min

Potato Starch

40 min

Corn

34 min

 

  1. Consider a hectare of land; calculate the amount of ethanol that could be obtained per year with each crop: apples or grapes, potatoes, corn and grass. Note: 1 hectare = 2.47 acre

 

Grass (Example): Assume an average quarterly harvest of 3.5 tons of grass per acre (yields will be greater in the summer and less in the fall. Assume 2.0 g of grass yields approximately 0.65 mL of ethanol or 0.33 mL/g.

 

𝑌𝑒𝑎𝑟𝑙𝑦 ℎ𝑎𝑟𝑣𝑒𝑠𝑡 𝑜𝑓 𝑔𝑟𝑎𝑠𝑠 𝑖𝑛 𝑘𝑔 𝑝𝑒𝑟 ℎ𝑒𝑐𝑡𝑎𝑟𝑒 𝑜𝑓 𝑙𝑎𝑛𝑑:

 

3.5 𝑡𝑜𝑛𝑠 𝑔𝑟𝑎𝑠𝑠 4 𝑞𝑢𝑎𝑟𝑡𝑒𝑟 2.47 𝑎𝑐𝑟𝑒 907 𝑘𝑔 31364 𝑘𝑔 𝑔𝑟𝑎𝑠𝑠

𝑥 𝑥 𝑥 =

1 𝑎𝑐𝑟𝑒 • 𝑞𝑢𝑎𝑟𝑡𝑒𝑟 1 𝑦𝑒𝑎𝑟 1 ℎ𝑒𝑐𝑡𝑎𝑟𝑒 1 𝑡𝑜𝑛 ℎ𝑒𝑐𝑡𝑎𝑟𝑒 • 𝑦𝑒𝑎𝑟

 

𝐴𝑝𝑝𝑟𝑜𝑥𝑖𝑚𝑎𝑡𝑒 𝑌𝑖𝑒𝑙𝑑 𝑜𝑓 𝐸𝑡ℎ𝑎𝑛𝑜𝑙 𝑖𝑛 𝐿𝑖𝑡𝑒𝑟𝑠 𝑝𝑒𝑟 ℎ𝑒𝑐𝑡𝑎𝑟𝑒 𝑜𝑓 𝑙𝑎𝑛𝑑 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟:

1000 𝑔 0.65 𝑚𝐿 𝑒𝑡ℎ𝑎𝑛𝑜𝑙 1 𝐿 10193 𝐿 𝑒𝑡ℎ𝑎𝑛𝑜𝑙

31,364 𝑘𝑔 𝑔𝑟𝑎𝑠𝑠 𝑥 𝑥 𝑥 =

2.0 𝑔 𝑔𝑟𝑎𝑠𝑠 1000 𝑚𝐿 ℎ𝑒𝑐𝑡𝑎𝑟𝑒 • 𝑦𝑒𝑎𝑟

1

 

𝑘𝑔

 

 

Corn: A typical corn crop is 158 bushels per acre, about 45 pounds of corn per bushel. Use the amount of ethanol (in mL/g) that was produced from corn in our experiment.

 

Apples: A typical orchard can produce 450 bushels per acre, 42 pounds per bushel of apples. Apples are approximately 90% juice. Use the amount of ethanol (in mL/g) that was produced from apple juice in our experiment.

 

Grapes: A typical vineyard can produce 4 tons of grapes per acre. Grapes are approximately 90% juice. Use the amount of ethanol (in mL/g) that was produced from grape juice in our experiment.

 

Potatoes: Assume 300 bushels per acre with 60 pounds of potatoes per bushel. Potato starch accounts for approximately 10% of the mass (the rest is mostly water). Use the amount of ethanol (in mL/g) that was produced from potato starch in our experiment.

 

  1. Calculate the heat of combustion in kJ/L for 1.0 L of ethanol and 1.0 L of octane. The density of ethanol is 0.789 g/mL and the density of octane is 0.703 g/mL. What does your answer imply about the fuel mileage for ethanol versus octane (the primary hydrocarbon in gasoline).

 

DHf (kJ/mol)

C2H5OH (l) -277.7

C8H18 (l) -250.0

O2 (g) 0

CO2 (g) -393.5

H2O (l) -285.8

 

C8H18 (l) + 25/2 O2 (g)

C2H5OH (l) + 3O2 (g)

 

8CO2 (g) + 9H2O (l)

2CO2 (g) + 3H2O (l)

 

∆𝐻 𝐶𝑜𝑚𝑏𝑢𝑠𝑡𝑖𝑜𝑛 = (∆𝐻 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠) − (∆𝐻 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠)

  1. Short Essay Question: Compare and contrast all five glucose sources. Consider the relative amounts of ethanol produced per gram of material, and the amount of material and resources needed to produce each crop.

 

  1. Did the student’s data provided to you ever measure a density of any fraction that corresponded to a percent ethanol of higher than 95.6% (azeotrope)? What do you think can explain this data?

 

  1. Include a graph prepared of percent ethanol versus fraction number for each distillation of a carbohydrate source. Do the graph’s make sense?

 

 

 

 

 

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