Methyl Ethyl Ketone from Butyl Alcohol

5. ENERGY BALANCE

Basis:- 1 Hr. Operation
ENERGY BALANCES ACROSS THE FEED PREHEATING EQUIPMENT:The heating of cold 2-butanol feed is to be completed in three stages in order to avoid large heat losses. The cold feed is first preheated to its boiling point using steam as heating medium and then vaporized in a thermosyphon reboiler utilizing the heat contained in the reaction products. The vapor, which has entrained liquid is removed from the knock out drum, and then heated to reaction temperature using flue gas.

COLD FEED PREHEATER:Total feed = 23412.14+2605.77 kg = 26017.91 kg 26017.91 kg per hour of 2-butanol is to be preheated from 250C it boiling point 107.50C. Heat load on preheater, Q = 26017.91 x 1.497(380.5 – 288)

= 3.603 x 106 KJ The heating medium is used is dry saturated steam at 420K Steam requirement = 3.603 x 106 2123.4 = 1696.8 kg/hr 2-BUTANOL VAPORIZER:2-butanol feed is vaporized at 107.50C using reaction products. Heat load on vaporizer is , Q = M x λ = 26017.91 x 557.43 kj = 14.5032 x 106 kj/hr Average Cp of reaction products = 2.3 KJ / Kg 0k 14.5032 x 106 = 26017.91 x 2.304 (642 – T)

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T = 400 K

FIRST SUPER HEATER:2-butanol vapors is to be heat4ed from 380.5 k to 573k . using flue gas which enters at 673 k & cools to 423k. Cp = 2.038 kj/kg k. Heat load on super heater, Q = M x Cp x (T2 – T1) = 26017.91 x 2.038 (573 – 380.5) Q = 10.207 x 106 kj/hr Mass flow rate of flue gas = 10.2072 x 106 1.2 x ( 673-423) = 3.4024 x 104 kg/hr

SECOND SUPER HEATER:It raises the temperature of vapor from 573 to 773 k . using flue gas which enters at 873k abd cools to 623k Cp = 2.674 kj/kg k Heat load on super heater Q = M x Cp x (T2 – T1) = 26017.91 x 2.674 (773 – 573) = 13.9144 x 106 kj/hr Flue gas requirement, 13.9144 x 106 1.195 x (873- 623) = 4.6575 x 103 kg/hr =

ENERGY BALANCE ACROSS THE REACTOR:The feed enters the reactor at 773k and leaves at 663k. The conversion obtained in the reactor is 89.1%. The heat balance includes two terms i.e , sensible heat change due to cooling of reaction mixture and heat consume due to reaction. Q = M x Cp x(T2 – T1) + M x ∆H Mean Cp = 2.68 kj/kg k

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∆H = 73900 kj/kgmol Total 2-butanol feed = 23412.14 + 2579.71 kg = 25991.85 kg/hr = 351.24 kmol/hr

Q = 26017.91 x 2.68 x (663- 773) + 351.24 x .891 x 73900 = 15.457 x 106 It is assume that a flue gas is available at 800k & leaving 750k. Cp = 1.195 kj/kg k Flue gas requirement, 15.457 x 106 1.195 x (800-750) = 25.869 x 104 kg/hr =

ENERGY BALANCE ACROSS THE CONDENSER :The vapor enters condenser at 1270C (400k) at 1 bar pressure. Liquid and the vapor leaving the condenser is in equilibrium. At the more mole fraction x = 0.88 of the condensate we get both liquid and vapor temperature from the T- x- y diagram and temperature are 299.6 k. = liquid temperature., 335.7 k = vapor temperature We take cooling water enters at 240C and leaving at 420C CpH2 = 14650 J/ kg k Cpalcohol = 1760 J/ kg k CpMEK = 1664 J/ kg k Cpmix = 0.867 x 1664 + 0.1089 x 1760 + 0.0241 x 14650 = 1987.42 J/kg. Heat loss to reduction in vapor temperature from 400k to 335.7k Q1= 26017.91 x 1.98742 (400- 335.7) = 3.325 x 106 kj/ hr Heat loss due to condensation Q2 = 2591.34 x 689.19 + 18931.44 x 486.11 = 10.989 x 106 kj/hr Heat loss due to further cooling of a part of vapor is Q3 = 21522.78 x 1.987 x (335.7 – 299.6)

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= 1.544 x 106 kj/hr Total heat lost = Q = Q1 + Q2 + Q3 = (3.325 + 10.989 + 1.544) x 106 kj/hr = 15.858 x 106 kj/hr Mass flow of cooling water = 15.858 x 106 4.187 x (42- 24) = 2.104 x 105 kg / hr

ENERGY BALANCE ACROSS THE ABSORBER :Heat of condensation of MEK = 3707.072 x 443.14 = 1.643 x 106 kj/hr

Heat of condensation of alcohol is = 233.488 x 560 = 0.1308 x 106 kj/hr Heat of solution = (3707.072 + 233.488) x 0.35 = 0.001379 x 106 kj/hr

Heat loss in cooling gasses from 62.7 to 270C = (74.98 x 1.47 + 8.392 x 1.53 + 624.723 x 14.65) (62.7 – 27) = 0.3311 x 106 kj/hr Total heat released = 2.1063 x 106 kj/hr Heat removed by water vapor = (204.045 x 2437.9) = 0.49744 x 106 kj/hr Heat gained by irrigating liquor a) Water: 31980.6816 x 4.186 (T – 300) b) MEK: 3707.072 x 2.299 x ( T-300 ) c) Alcohol: 233.488 x 2.429 x (T- 300 ) Total heat gained = 0.49744 x 106 + 0.142961 x 106 (T300)kj/hr Heat released = heat gained => 2.1063 x 106 = 0.49744x 106 + 0.14296 x 106 (T – 300)

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=>

T = 311.25 k

ENERGY BALANCE ACROSS THE EXTRACTION COLUMN:It is assume that the extraction process is isothermal. All that streams come at 270C and leaves at 270C.

ENERGY BALANCE ACROSS THE SOLVENT RECOVERY & UNIT:Feed is not saturated liquid it is sub-cool liquid. Saturation temperature is 930C From x-y diagram we get Rm = 0.38. R= 2Rm = 0.76 Feed: Alcohol = 233.48 = 3.155 kmol /hr 74 MEK = 3577.639 = 49.689 kmol/hr 72 TCE = 14992.191 = 112.3kmol/hr 133.5 Water = 26.3613 = 1.465 kmol /hr 18 Total = 166.609 kmol /hr Mole fraction of MEK XMEK = 49.689 = 0.2982 166.609 Feed temperature = 270C F . HF =3.155 x170.058 (27- 0) + 49.689x165.726 x 27+112.3 x148.56x27 + 1.465x75.36 x27 F . HF = 0.69025 x 106 kj/hr

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Distillate:Alcohol = 233.488 = 3.1552 kmol /hr 74 MEK = (3577.639 – 21.3454 ) = 49.39 kmol/hr 72 Water = (26.3613 –25.9195) = 0.0246 kmol /hr 18 TCE = 2.5098 = 0.0188 kmol/hr 133.5 Total = 52.5886 kmol/hr D = 52.5886 kmol/hr Mole fraction of MEK, XMEK = 49.39 = 0.94 52.5886 from T-x-y diagram distillate temperature = 80.40C Cp MEK = 170 kj/kmol k Cp alcohol = 228 kj/kmol k Cp water = 75.37 kj/mol k Cp TCE = 148.56 kj/mol k D. HD = [3.1552 x 228 + 49.39 x 170 + 0.4421 x 75.37 + 0.0188x 148.56] (80.4) = 0.7358 x 106 kj/hr Residue: MEK = 21.2454 kg = 0.2965 kmol/hr TCE = 15199.421 kmol = 113.85 kmol /hr 133.5 Water = 25.9195 = 1.4399 kmol /hr 18 Total = 115.5864 kmol/hr 0.2965 = 0.0026 115.5864 From T-x-y diagram the temoerature obtained . T = 1120C = 385k (residue) Cp MEK = 175 kj/mol k Cp alcohol = 260 kj/kmol k Cp water = 75.37 kj/kmol k XMEK =

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Cp TCE = 148.56 kj/kmol k

W. Hw = [ 0.2965 x 175 + 113.85 x 148.56 + 1.4399 x 75.37] x (112) = 1.9123 x 106 kj/hr

Condenser :VHv =D.HD + L. HL + Qc. VHv = (D + L ) . HL +Qc Qc = V x (Hv - HL) Qc = V x λ V = (1 + R ) x D D = 52.5886 kmole/hr V = ( 1 + 0.76 )x 52.5886 = 92.556 kmole/hr. Vxλ = 92.556 x 3.18445 x104 = 2.9474 x106 kj/hr Qc = 2.9474 x 106 kj/hr Cooling water requirement = 2.9474 x 106 4.187 x (42 –24) = 3.911x 104 kg/hr

Reboiler:Overall heat balance F. HF + QB = Qc + D . HD + WHw QB = Qc + D . HD + WHw - F. HF QB = DHD = WHw + Qc - FHF QB = 0.7358 x 106 +1.9123 x 106 + 2.9474 x 106 – 0.69025 x 106 QB = 4.90525 x 106 kj/hr Steam is available at 3.302 bar steam temperature = 410 k

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Steam requirement is = 4.90525 x 106 2153.4 = 2277.91 kg/hr One cooler is attached to cool the residue. Residue enters the cooler at 1120C and leaves at 270C So, cooling water requirement = 1.451299 x106 4.187 (42- 24) = 1.92567 x 104 kg/hr One more heat exchanger is used to raise the temperature of the mixed liquor of condensate and the distillate from the solvent recovery column to 820C 2591.3424 x 170.058 + 18931.435 x 165.726 (26.6) 74 72 + 212.9726 x 260 + 3367.511 x 175 + 2.5098 x 148.56 74 72 133.5 + QB = 2804.315 x 260 + 22298.946 x 165.726 + 2.5098 x 148.56 (82) 74 72 133.5 QB = 2.981 x 106 KJ/hr Steam is available at 3.302 bar, steam temperature = 410 K. Steam requirement = 2.981 x 106 2153.4 = 1384.32 Kg/hr

ENERGY BALANCE ACROSS THE DISTILLATION COLUMN:Condenser: Qc = V x λ Qc= V x λ = 541.261 x 3.1 x 107 + 5.4673 x 4.5 x 107 = 17.025 x 106 So, mass flow rate of cooling water = 17.025 x 106

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4.187 x (42-24) = 2.25899 x 106 kg/hr Reboiler: QB = DHD + WHw + Qc - FHF FHF = 2804.315 x 260 + 22298.946 x 165.726 + 2.5098 x 148.56 (82) 74 72 133.5 = 5.01696 x106 kj/hr DHD= 225.0 x 228 + 22275.0 x 170 74 72 =4.2896 x 106 kj/hr (80.5)

WHw = 2579.7131 x 260 + 23.9731 x 175 + 2.0846 x 148.65 74 72 133.5 = 0.97632 x106 kj/hr QB = 17.274 kj/hr Steam available at = 3.302 bar. Steam temperature = 410 k Steam requirement = 17.274 x 106 2153.4 = 8021.733 kg/hr.

x (107)

Distillate & the residue both has to be cooled Heat load to cool the distillate from 80.5 to 30 0C = 225 x 228 + 22275 x 170 30) 74 72 = 2.69099 x 106 kj/hr. = 2.69099 x 106 4.187 x (42- 24) =3.57056 x 104 kg/hr

(80.5 –

So, cooling water requirement,

Recycle 2-butanol is 107 to 270C

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Heat load = 2579.7131 x 260 + 239731 x 175 + 2.0846 x 148.65 74 72 133.5 = 0.72996 x 106 kj/hr Cooling water requirement = 0.72996 x 106 4.187 x (42 –24) = 9685.52 kg/hr.

(107- 27)

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