A method of supplying a mixture of three or more components being crude 2-ethylhexanol to a distillation column assembly, and assorting and distilling 2-ethylhexanol having a purity of 99 wt%, the distillation column assembly comprising: a dividing wall column that has one inflow point, three outflow points and an internal dividing wall and a typical distillation column that has only two inflow points and two outflow points are sequentially connected to each other; and streams of the two outflow points of the DWC are introduced into the two inflow points of the typical distillation column, wherein the dividing wall column is divided into six zones as follows; a column top zone refers to an upper area of a main column with no dividing wall, an upper supply zone refers to a sub-area whose one face is partitioned by the dividing wall and which is located above an inflow material (raw material) stream, an upper outflow zone refers to a sub-area whose one face is partitioned by the dividing wall and which is located above an outflow material stream, a lower supply zone refers to a sub-area whose one face is partitioned by the dividing wall and which is located below the inflow material stream, a lower outflow zone refers to a sub-area whose one face is partitioned by the dividing wall and which is located below the outflow material stream, and a column bottom zone refers to a lower area of a main column with no dividing wall, wherein, in the case of a direct sequence, the DWC and the typical distillation column are arranged in that, when operated, two streams introduced from the DWC into the typical distillation column are an intermediate boiling-point stream and a high boiling-point stream, respectively, or in the case of an indirect sequence, the the DWC and the typical distillation column are arranged in that, when operated, two streams introduced from the DWC into the typical distillation column are the intermediate boiling-point stream and a low boiling-point stream, respectively. a dividing wall column that has one inflow point, three outflow points and an internal dividing wall and a typical distillation column that has only two inflow points and two outflow points are sequentially connected to each other; and streams of the two outflow points of the DWC are introduced into the two inflow points of the typical distillation column, wherein the dividing wall column is divided into six zones as follows; a column top zone refers to an upper area of a main column with no dividing wall, an upper supply zone refers to a sub-area whose one face is partitioned by the dividing wall and which is located above an inflow material (raw material) stream, an upper outflow zone refers to a sub-area whose one face is partitioned by the dividing wall and which is located above an outflow material stream, a lower supply zone refers to a sub-area whose one face is partitioned by the dividing wall and which is located below the inflow material stream, a lower outflow zone refers to a sub-area whose one face is partitioned by the dividing wall and which is located below the outflow material stream, and a column bottom zone refers to a lower area of a main column with no dividing wall, wherein, in the case of a direct sequence, the DWC and the typical distillation column are arranged in that, when operated, two streams introduced from the DWC into the typical distillation column are an intermediate boiling-point stream and a high boiling-point stream, respectively, or in the case of an indirect sequence, the the DWC and the typical distillation column are arranged in that, when operated, two streams introduced from the DWC into the typical distillation column are the intermediate boiling-point stream and a low boiling-point stream, respectively.