A 100 mole mixture of ethanol and water containing 50 moles of ethanol is separa

Question

A 100 mole mixture of ethanol and water containing 50 moles of ethanol is separated by batch distillation method. Case 1) 25 moles are evaporated by heating the mixture slowly in 10 hours at a constant boil-up rate (or evaporation rate). Case 2) 25 moles are evaporated in 1 hour by heating the mixture at a higher but constant boil-up rate. Case 3) The 100 mole mixture is divided into 5 batches, each containing 20 moles. Each batch is heated for 10 hours to produce 5 moles of vapor (total vapor from all five batches = 25 moles). Identify the following as TRUE or FALSE: a) The average distillate composition in case (2) will be smaller than in case (1). b) The temperature of the liquid residue left in the reboiler will be greater in case (2) compared to case (1). c) The vapor composition in case (3) will be smaller than in case (1).

Explanation / Answer

case 2 it is evaporated at higher temperature so distillate will contain more water when compared to case 1 where water is evaporated at lower temperature. so composition of ethanol will be less in case (2) when compared to case (1)

a) True

temperature of residue will also be high as it being heated at higher temperature than case 1)

b) True

Vapour composition will be equal in both case 3 and case 1

c) False

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