PURPOSE: To prepare pure water from by-product water when producing a mixture of aromatic hydrocarbons, by cooling and condensing the outlet gas of reaction equipment for synthesis of the mixture of aromatic hydrocarbons from methanol and recovering the pure water from the condensate.
CONSTITUTION: Methanol is fed to reaction equipment 1 to synthesize the mixture of aromatic hydrocarbons, the formed high-temperature reaction gas is fed to a cooler 2 to be condensed, and the resulting condensate is fed to a separator 3 to be separated into water, the mixture of aromatic hydrocarbons and gas. Alkali from a line 7 is fed to the water to neutralize it. The neutralized water is led to an evaporating tower or flash tower 4, and unreacted methanol leaving the top of the tower 4 is recycled to the reaction equipment 1. The tower bottom liquid is fed to a distillation tower or flash tower 8 to recover the pure water from the top.