CaCO3 precipitate is made by reacting CaO with an aqueous solution of Na2CO3, the by-product being NaOH. After decanting, slurry leaving the precipitation tank is 5% w/w CaCO3, 0.1% NaOH, and the balance water. 100 000 kg hr–1 of slurry is fed to a two-stage counter-current continuous washing system to be washed by 200 000 kg hr–1 of fresh water. Underflow from each unit contains 20% w/w solids. Calculate fraction of NaOH recovered and mass percentage NaOH of dried product. Would adding a third stage be worthwhile?

a process consists of two distillation columns. the composition of the feed to the first column is 30 mol% benzene, 30 mol% toluene, and 40 mol% xylene. the top stream of the first column does not contain xylene. the benzene content of the dome stream from the first column is 55 mol %. the bottoms stream from the second column has a flow of 100 mol/h and contains 15 mol% toluene and no benzene; while the top stream of the second column contains 50 mol % benzene. the upper stream flow of the first tower is twice the upper stream flow of the second tower. determine the molar flux of the fresh feed stream and the overhead stream leaving the first column.