This is the first book on non-equilibrium thermodynamics. It covers a gap that has been left by the treatment of separation processes using classical thermodynamics. Because separation phenomena are dynamic processes, classical thermodynamics may not describe the true phenomena occurring in a particular separation media; rather a flux of entropy will bring the system out of the classical equilibrium and, as a consequence, different rules should apply - non-equilibrium thermodynamics. This book offers a different look at the theory of separation.