The Process of Fermentation of Sugar and Distillation in Ethanol and Carbon Dioxide

Objective

The objective of this lab is to transform sugar by yeast into ethanol and carbon dioxide using fermentation of sugar and distillation (To separate ethanol from fermentation mixture). Another purpose that took place in this lab was to introduce “green” principles of chemistry.

Theory

^The first step in the fermentation of disaccharides (such as sucrose or maltose) is a simple hydrolysis to monosaccharides (hexoses like glucose and fructose). These are then converted to their 6-phosphate esters, which are then turned into fructose 1,6-diphosphate. Lastly, the fructose 1,6-diphosphate is converted to phosphate esters of the trioses such as dihydroxyacetone (a ketotriose) and glyceraldehyde (an aldotriose). This substance oxidizes into phosphoglyceric acids, which lead to pyruvic acid. This acid loses carbon dioxide to form acetaldehyde, which is reduced to ethanol.

After fermentation has been completed, fractional distillation produces an ethanol-water azeotrope, with a boiling point of 78.15 degrees Celsius. The azeotrope has 95.6% alcohol by weight (97.2% by volume). To obtain anhydrous ethanol, water is removed from the azeotrope by distillation with benzene to furnish the pure product, which has a boiling point of 78.37 degrees Celsius.

*Higher alcohols (C3-C5) called fusel oils are obtained in small amounts by fractionation of the fermented liquor. These alcohols do not come from the sugars. They arise from enzyme action on amino acids, which are derived from the raw materials used and from yeast cells. The alcohols are all primary, mainly n-propyl, isobutyl, isopentyl (3-methyl-1-butanol, and optically active 2-methyl-1-butanol).

^Also the Mechanism

*Also the Side Reaction

Main Reaction

Side Reaction

Higher alcohols (C3-C5) called fusel oils are obtained in small amounts by fractionation of the fermented liquor. These alcohols do not come from the sugars. They arise from enzyme action on amino acids, which are derived from the raw materials used and from yeast cells. The alcohols are all primary, mainly n-propyl, isobutyl, isopentyl (3-methyl-1-butanol, and optically active 2-methyl-1-butanol).

Mechanism

The first step in the fermentation of disaccharides (such as sucrose or maltose) is a simple hydrolysis to monosaccharides (hexoses like glucose and fructose). These are then converted to their 6-phosphate esters, which are then turned into fructose 1,6-diphosphate. Lastly, the fructose 1,6-diphosphate is converted to phosphate esters of the trioses such as dihydroxyacetone (a ketotriose) and glyceraldehyde (an aldotriose). This substance oxidizes into phosphoglyceric acids, which lead to pyruvic acid. This acid loses carbon dioxide to form acetaldehyde, which is reduced to ethanol.

Observations

• The solution in the round bottom flask smelled really bad.
• The ethanol took a long time to boil.
• Fraction A was burning for a long time and the flame was strong and high
• Fraction B burned for a while as well.
• Fraction C burned as well, but it did not burn as well as A and B

Conclusion

The objective of this lab to transform sugar by yeast into ethanol and carbon dioxide using fermentation of sugar and distillation (To separate ethanol from fermentation mixture) was successful. The percent yield was found to be 55.39%. Because Fraction B was found to have the closest density to that of ethanol, the yield from that fraction (12.23 g) was used as the actual yield.

Two possible explanations for the low %yield could be that the week of fermentation was not long enough for all of the sucrose to hydrolyze into monosaccharides. Also, there was a side reaction that produced fusel oils, again resulting in a low %yield.

The density was a little high and again this could be due to the production of fusel oils which has a higher density than ethanol (by about .04 to .06 g/mL more).