Crystallization from solution costs

The above-mentioned advantages of the melt crystallization processes concerning the temperature level of the product component do not exist if the comparison is made to the crystallization from solutions, because the product is crystallized in solution at temperatures lower than its melting point. However, the solvent has to be separated (evaporated), usually in larger amounts, and is often to be treated as impurity. Hence, melt crystallization does not need any additional substance compared to extraction or solution crystallization. Therefore, no wastewater will be produced and no other chemical (solvent) has to be reprocessed. The capital and energy costs for solvent recycling can represent a major portion of a product isolation process utilizing solution crystallization. 

U.S. 6,649,754 (to Merck) describes a process for making mannitol by hydrogenation of a mixture of glucose and fructose. U.S. 3,632,656 (to Atlas Chemical) describes recovery of mannitol from a mixture with sorbitol by crystallization from aqueous solution. U.S. 4,456,774 (to Union Carbide) describes an adsorptive separation of mannitol from sorbitol. U.S. 6,235,947 (to Takeda Chemical Industries) describes a process for recrystallizing mannitol to improve the crystal morphology and hence make a more compressible product that can be used in making tablets. Estimate the cost of production of Mannitol by the Merck route and determine which separation is most economical. What is the additional cost of making the recrystallized product via the Takeda route ... 

Salting-out crystalli tion operates through the addition of a nonsolvent to the magma ia a crystallizer. The selection of the nonsolvent is based on the effect of the solvent on solubiHty, cost, properties that affect handling, iateraction with product requirements, and ease of recovery. The effect of a dding a nonsolvent can be quite complex as it iacreases the volume required for a given residence time and may produce a highly nonideal mixture of solvent, nonsolvent, and solute from which the solvent is difficult to separate. 

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