Distillations columns are used to separate light boiling components from heavier

Question

Distillations columns are used to separate light boiling components from heavier boiling components, and makeup over 95% of the separation systems for the chemical process industries. A commonly used distillation column is a propylene-propane splitter. The overhead product from this column is used as a feedstock for the production of polypropylene, which is the largest quantity of plastic produced worldwide. Figure below shows a diagram of a propylene-propane splitter (C_3 refers to propane and C_3^= refers to propylene). The steam is used to provide energy, and is not involved in the process material balance). Assume that the composition and flow rates listed on this diagram came from process measurements. Determine if the overall material balance is satisfied for this system. Evaluate the component material balances as well. What can you conclude?

Explanation / Answer

From the overall Material balance

Entering flow rate = 106,000 lb/hr

This must be equal to two leaving streams ( 74000 lb/hr as well as 34000 lb/hr)

But the sum is 74000+34000= 108000 lb/hr, Hencee the oveall balanace is not satisfied.

Let the top product flow rate be D and bottoms product be B

106000 = D+B ,   B= 106000-D (1)

Writing C3 balance

106000*0.3 = D*0.3/100 + B*0.9    from 1, 31800 = D*0.3/100 + (106000-D)*0.9

31800 = D*0.3/100 +95400- D*0.9

D*0.9-D*0.3/100 = 95400-31800

D*(0.9-0.003)= 63600

D*0.897= 63600

D = 70903 lb/hr

D= 106000-70903=35907 lb/hr

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