What is the suitable pressure for distillation separation of methanol and isopropanol?

Brief description of process flow: the crude methanol from methanol synthesis section, with the temperature of 40℃ and the pressure of 0.4MPa, passes through the crude methanol buffer tank (F4050 1) and is preheated to about 70℃ by the crude methanol preheater (C405 10), and then enters the pre-rectification tower (E4050 1).

In order to neutralize crude methanol, NaOH aqueous solution with the concentration of 1-5% (wt%) was added to the precolumn by alkali pump (J40506A, B). .