1. 1 of 2 CDB1064/CEB1043 A new chemical plant utilizes crude glycerol (G), a by-product of biodiesel production to produce propylene glycol (PG). The crude glycerol solution can not directly be fed into the reactor because it still contains salts (S) that poison the catalyst in the reactor. The crude glycerol solution (F1) firstly undergoes purification process to remove salts in a liquid-liquid extraction unit (Unit 1). The solution is contacted with 95 wt% of ethanol (E) solution (F2) to include precipitation of the salts. The ethanol stream exits from this unit (F3) dissolved all saits, which is further treated in the microfiltration unit (Unit 2). In Unit 2, the salts precipitate is separated as wet cake stream (F4), while the filtrate (F5) is recycled back to Unit 1. The purified glycerol solution (F6) from Unit 1 is sent to a catalytic reactor (Unit 3). where it reacts with pure hydrogen gas (H) as stream F7. In Unit 3. most glycerol is converted into propylene glycol and other by-products of methanol (M), acetol (A) and ethylene glycol (EG), exit as stream F8 The stream exits from Unit 3 undergoes a series of purifications. Firstly, all unreacted hydrogen is separated from other liquid in liquid/gas separator unit (Unit 4). The hydrogen gas exiting from Unit 4 is recycled back as stream F9 to Unit 3. The liquid stream (F10) from Unit 4 is then sent to the first distillation unit (Unit 5). Unit 5 separates all water (W), all methanol and all acetol as the bottom product (F11). The top product (F12) is sent to the second distillation unit (Unit 6) that separates all unreacted glycerol as bottom product (F13). Overhead product (F14) of Unit 6 is sent to another distillation column (Unit 7) that separates the propylene glycol from the ethylene glycol. The propylene glycol is taken off as the top product (F16) with a purity of 99.7 wt% and the bottom stream (F15) comprises of pure ethylene glycol a. The ethanol solution fed through Stream F2 in the above chemical plant is fed at molar flow rate of 1000 kg/min. Convert the mass flow rate into molar flowrate (in kmolh). [4 marks] 2 CDB1064/CEB1043 b. The molar compositions of water (HO) methanol (CH3OH) and acetol (C.HO2) in stream F11 are 45, 40 and 15 mol%, respectively. Calculate mass composition of each species (in %). The atomic weights for OC and Hare 16, 12 and 1, respectively [4 marks c. Draw the block diagram for the process. Show clearly the unit operations according to the given unit codes and all the streams (with stream number and all species in each streams). [7 marks) d. Compose a flowchart of the reactor unit and write all material balance equations using elemental balance method. The molecular formula for glycerol, hydrogen propylene glycol, ethylene glycol, methanol, acetol and water are CsHiOs. Ha. C.H.O., CsH:O. CH,OH, CH.O. and H.O. respectively. You are not required to solve the balances. 15 marks) 3 3
