When ethanol is heated with excess conc. $\mathrm{H}{}_2\mathrm{SO}{}_4$ at 443 K, the main product is

With excess acid at about 443 K ($170{}^{\circ }\mathrm{C}$), ethanol is dehydrated to ethene. Ethoxyethane is the product at the lower temperature of about 413 K with excess alcohol.