Process designs for fractional crystallization from solution

A systematic procedure is presented for the identification of alternative process designs for fractional crystallization from solution. We seek designs that involve low rates of recycle, evaporation, and dilution. Only a limited number of general process designs need be analyzed if the crystallizations are operated at hot and cold points of multiple saturation and if the salts are ordered so that the relative composition is greater at the cold point of multiple saturation than at the hot point of multiple saturation. Multiple component systems with sufficiently temperature-dependent equilibria are examined which form (1) anhydrous and hydrated single salts; (2) anhydrous and hydrated, congruently soluble multiple salts; and (3) anhydrous and hydrated, incongruently soluble, multiple salts. Further, we show that systems that form solid solutions and systems that do not have sufficiently temperature-dependent equilibrium can be considered as simple extensions of the general principles