Question

Give the industrial preparation of ethanol.

Answer 1

Ethanol is manufactured industrially on a large scale by the following two primary methods:

1. Hydration of Ethene (Petrochemical Method)

Ethene obtained from petroleum cracking is reacted with steam in the presence of a phosphoric acid catalyst (H₃PO₄) at high temperature and pressure.

\[ \text{CH}_2=\text{CH}_2 + \text{H}_2\text{O} \xrightarrow[\text{High Temp / Pressure}]{\text{H}_3\text{PO}_4} \text{CH}_3\text{CH}_2\text{OH} \]

2. Fermentation of Sugars/Molasses (Biological Method)

Molasses (rich in sucrose) is diluted with water and fermented using yeast at around 303 K in the absence of air. Yeast provides enzymes (invertase and zymase) to drive the conversion:

Inversion of Sucrose:

\[ \text{C}_{12}\text{H}_{22}\text{O}_{11} + \text{H}_2\text{O} \xrightarrow{\text{Invertase}} \text{C}_6\text{H}_{12}\text{O}_6 \text{ (Glucose)} + \text{C}_6\text{H}_{12}\text{O}_6 \text{ (Fructose)} \]

Conversion to Ethanol:

\[ \text{C}_6\text{H}_{12}\text{O}_6 \xrightarrow{\text{Zymase}} 2\text{CH}_3\text{CH}_2\text{OH} + 2\text{CO}_2 \]