Question 3 (a) With the aid of examples, explain why absorption is one of the important unit operations in the process industry. [5 marks] (b) State the assumptions made when deriving the Kremser equation and starting from first principles work out the Kremser equation that gives the number of stages for the case when the absorption factor is equal to one. [5 marks] (c) A gas mixture of composition shown in Table Q3 is to be treated at 37C and 34 bar in an already existing absorption column with 8 theoretical stages. The oil stream used to purify the gas mixture is assumed pure. Under these conditions the methane is not absorbed since it is the carrier gas. It is desired that 95% of the propane is absorbed in the oil. The Henry's constants in bar are shown in Table Q3. Assume a dilute system. Table Q3 Component Molar fraction in the feed Henry's constant (bar) Methane (carrier gas) 0.88 Ethane 0.05 Propane 0.05 n-Butane 0.02 47 17 6 i. How many moles of solvent must be used per gas mole, when 95% of the propane must be absorbed? [5 marks] ii. Calculate the absorption factors for all components in the mixture. [3 marks] iii. Estimate the recoveries of ethane and n-butane. [2 marks] iv. What are the molar compositions of the treated gas and the liquid streams? [5 marks] RELEVANT EQUATIONS: Ln YN-Y-A YN-Yo YN+1--1 L A = N = mG YN+-Yo Ln(A) -1 where symbols have their usual meaning.