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A benzene/toluene liquid mixture consisting of 31 mole% benzene is fed to a reboiler, where 1250 KW of heat is provided causing the mixture to partially vaporize. The vapor output has a flowrate of 80 kmol/hr and consists of 40 mole% benzene. The liquid output has a flowrate of 100 kmol/hr. The two output streams are in equilibrium and exit the reboiler at 130 oC. Determine the temperature of the feed stream. Neglect the effect of pressure and consider the following additional data:
Cp(g) | Cp(l) | delta H (vap) kJ/mol |
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@ BP | |||||||||||
Benzene | 82.44 | 134.8 | 30.77 | ||||||||
Toluene | 103.7 | 155.96 | 38.06 | ||||||||
Cp(g) | Cp(l) | delta H (vap) kJ/mol |
BP | ||||||||
@ BP | |||||||||||
Benzene | 82.44 | 134.8 | 30.77 | 80.1 | |||||||
Toluene | 103.7 | 155.96 | 38.06 | 110.6 | |||||||
Mass Balance, | gas Out | 80 mol/hr | Q (BP to 130 deg C) | Q (T to BP deg C) | |||||||
Benzene (40%) |
32 | mol/hr | 131904 | =32*134.8*(80-T) | |||||||
Toluene | 48 | 99552 | =48*155.96*(110-T) | ||||||||
Input = (Gas + Liq Outlet) |
180 mol/hr | Reboiler | 231456 | = Q (gas) Total | |||||||
Benzene (31 %) |
55.8 | ||||||||||
Toluene | 124.2 | ||||||||||
Liq out | 100 mol/hr | ||||||||||
Benzene | 23.8 | ||||||||||
Toluene | 76.2 | ||||||||||
Heat required for vaporisation | |||||||||||
= [gas moles Benzene x H (vap)] + [gas moles Toluene x H (vap)] | |||||||||||
= | 2811.52 | kJ | |||||||||
1250 kW in 1 hr is provided | |||||||||||
= 3600 x 1250 | kJ | ||||||||||
= | 4500000 | kJ | |||||||||
By heat balance,
(temperatures in K) Heat for the gas moles to go from temp T to respective boiling points + Heat of vaporisation and then the heat for the gas moles to go from their Boiling points to 130 deg C |
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=> [32*134.8*(353-T)] + [48*155.96*(393-T)] + 380784 + 2811.52 = 4500000 | |||||||||||
=> [4313.6* (353-T)] + [7486*(393-T)] = 4116404.48 | |||||||||||
=> 1522700 + 2941998 - 11800 T = 4116404.48 | |||||||||||
=> T = 29.51 deg C | |||||||||||