A structural design procedure for extended fully thermally coupled distillation columns is proposed and applied to the example quaternary systems of several combinations of relative volatility in order to show the design performance. The procedure gives the optimum structure for a given quaternary separation, and therefore iterative computation encountered in the design using commercial packages is not required. Because of extra degrees of freedom in the design of the columns, various designs can yield the same products for a given specification. The structural design of this study leads to the most efficient design thermodynamically. With the outcome of the structural design, thermodynamic efficiency, arrangement of main and satellite columns, and location of interlinking streams are also examined.