Ethanol is prepared industrially by

Hydration of ethene

$\begin{array}{l}{\mathrm{CH}}_2={\mathrm{CH}}_2+\stackrel{+}{\mathrm{H}}\mathrm{HS}{\overline{\mathrm{O}}}_4\to {\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{HSO}}_4\\ {\mathrm{CH}}_3-{\mathrm{CH}}_2\mathrm{HS}{\mathrm{O}}_4\underset{\text{Boil}}{\overset{{\mathrm{H}}_2\mathrm{O}}{\to }}{\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{OH}+{\mathrm{H}}_2{\mathrm{SO}}_4\end{array}$

Fermentation of sugars :

$\begin{array}{l}{\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}+{\mathrm{H}}_2\mathrm{O}\stackrel{\text{Invertase}}{\to }\underset{\text{Glucose}}{{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6}+\underset{\text{Fructose}}{{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6}\\ \underset{\text{Glucose or Fructose}}{{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6}\stackrel{\text{Zymase}}{\to }2{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}+2{\mathrm{CO}}_2\end{array}$