Dioxane from water is to be removed by extraction using an organic solvent. The amount of water to be processed is 100 kg/second, with dioxane concentration of 1,500 ppm (parts per million by mole fraction). At the conditions specified, partition coefficient (KD ) for dioxane is 100. The solvent is completely immiscible with water and fresh solvent doesnt contain dioxane.

Answer the following questions:

a) Calculate (i) the extraction factor (E) for a single stage extraction unit when solvent flow rate is 4 kg/second; (ii) the dioxane concentration in water when a single stage extraction unit with an extraction factor of 2 is used for dioxane removal

b) Calculate the minimum solvent flow rate in order to reduce the dioxane concentration in water by 90% if a two-stage, countercurrent extraction cascade is used to perform the separation

c) Your boss asks you to remove as much dioxane as possible using an existing two-stage, crosscurrent extractor with a total solvent flow rate of 4 kg/second. Explain how you would distribute the solvent in the two extraction stages in order to achieve the optimum extraction efficiency, also justify your answer.