Method of and an apparatus for separating a liquid mixture

A method of separating a liquid mixture wherein the liquid mixture is heated; the heated liquid mixture is supplied to a pervaporation membrane module to separate a permeable component of the liquid; a portion of non-permeated liquid is circulated through a circulation pipe into a liquid mixture feeding pipe before a heater, and the remaining portion of the non-permeated liquid is extracted to the outside of the system, and wherein the temperature of the liquid in the liquid mixture feeding pipe in which the non-permeated liquid has been mixed with the liquid mixture or in the circulation pipe for the non-permeated liquid, is measured, and when the measured temperature is out of a predetermined range, new supply of the liquid mixture and/or extraction of the non-permeated liquid is stopped.