Sorting Plastic Waste
Multicomponent distillation 1) Mass balances
The feed flowrate is 350 kmols hr-1 and the feed composition is known: 48 mol% propene, 50 mol% propane and 2 mol% butane. The distillate stream composition: 99.9 mol% propene and 0.1 mol% propane. The bottom product stream contains 0.5 mol% propene but the mole fractions of propane and butane are unknown. Therefore, mass balances are carried out around the distillate column.
Overall mass balance: F=D+B
Component mass balance for propene: xFF=yDD+xBB
0.48×350=0.999×F-B+0.005B, B=182.75 kmols hr-1
D=F-B=350-182.75=167.25 kmols hr-1
Component mass balance for propane: xFF=yDD+xBB,
0.5×350=0.001×167.25+xB×182.75
xB=0.5×350-0.001×167.25182.75=0.9567
Component mass balance for butane: xFF=yDD+xBB,
0.02×350=xB×182.75, xB=0.0383 Thus, the mole fractions of propane and butane in the bottom stream are xB=0.9567, xB=0.0383.
The light key will be propene and the heavy key will be propane.
2) Calculation of the bubble point of the feed, distillate and bottom product
Assumptions:
* the system pressure is taken as the atmospheric pressure 101325 Pa * the system is treated as an ideal system
The bubble point temperatures of the feed, distillate and bottom product have been calculated by solving the following equation. The equation is solved by trial and error until the sum of partial pressures exerted by each component equals the system pressure. xpropenePpropenesat+xpropanePpropanesat+xbutanePbutanesat=101325 The vapour pressure of each component is calculated using the relationships below:
Propene: lnPsat=57.263-3382.4T-5.7707lnT+1.0431×10-5T2
Propane: lnPsat=59.078-3492.6T-6.0669lnT+1.0919×10-5T2
Butane: lnPsat=66.343-4363.2T-7.046lnT+9.4509×10-6T2
The feed bubble point was calculated TF=228.6 K
The corresponding vapour pressures of the feed components:
Ppropenesat=116275 Pa, Ppropanesat=90505 Pa, Pbutanesat=13018 Pa
The same calculations were repeated for the distillate
The feed flowrate is 350 kmols hr-1 and the feed composition is known: 48 mol% propene, 50 mol% propane and 2 mol% butane. The distillate stream composition: 99.9 mol% propene and 0.1 mol% propane. The bottom product stream contains 0.5 mol% propene but the mole fractions of propane and butane are unknown. Therefore, mass balances are carried out around the distillate column.
Overall mass balance: F=D+B
Component mass balance for propene: xFF=yDD+xBB
0.48×350=0.999×F-B+0.005B, B=182.75 kmols hr-1
D=F-B=350-182.75=167.25 kmols hr-1
Component mass balance for propane: xFF=yDD+xBB,
0.5×350=0.001×167.25+xB×182.75
xB=0.5×350-0.001×167.25182.75=0.9567
Component mass balance for butane: xFF=yDD+xBB,
0.02×350=xB×182.75, xB=0.0383 Thus, the mole fractions of propane and butane in the bottom stream are xB=0.9567, xB=0.0383.
The light key will be propene and the heavy key will be propane.
2) Calculation of the bubble point of the feed, distillate and bottom product
Assumptions:
* the system pressure is taken as the atmospheric pressure 101325 Pa * the system is treated as an ideal system
The bubble point temperatures of the feed, distillate and bottom product have been calculated by solving the following equation. The equation is solved by trial and error until the sum of partial pressures exerted by each component equals the system pressure. xpropenePpropenesat+xpropanePpropanesat+xbutanePbutanesat=101325 The vapour pressure of each component is calculated using the relationships below:
Propene: lnPsat=57.263-3382.4T-5.7707lnT+1.0431×10-5T2
Propane: lnPsat=59.078-3492.6T-6.0669lnT+1.0919×10-5T2
Butane: lnPsat=66.343-4363.2T-7.046lnT+9.4509×10-6T2
The feed bubble point was calculated TF=228.6 K
The corresponding vapour pressures of the feed components:
Ppropenesat=116275 Pa, Ppropanesat=90505 Pa, Pbutanesat=13018 Pa
The same calculations were repeated for the distillate