3.5. Liquid benzene and liquid n-hexane are blended to form a stream flowing at
ID: 717725 • Letter: 3
Question
3.5. Liquid benzene and liquid n-hexane are blended to form a stream flowing at a rate of 1700 lbm/h. An on-line densitometer (an instrument used to determine density) indicates that the stream has a density of 0.810 g/mL. Using specific gravities from Table B.1, estimate the mass and volumetric feed rates of the two hydrocarbons to the mixing vessel (in U.S. customary units). State at least two assumptions required to obtain the estimate from the recommended data. 3.22. A mixture of methanol and propyl acetate contains 25.0 wt% methanol. (a) Using a single dimensional equation, determine the g-moles of methanol in 200.0 kg of the mixture. (b) The flow rate of propyl acetate in the mixture is to be 100.0 lb-mole/h. What must the mixture flow rate be in lbm/h? 3.25. A mixture is 10.0 mole% methyl alcohol, 75.0 mole% methyl acetate (CIO), and 15.0 mole% acetic acid. Calculate the mass fractions of each compound. What is the average molecular weight of the mixture? What would be the mass (kg) of a sample containing 25.0 kmol of methyl acetate?Explanation / Answer
3.5)
The specific gravity of n-hexane = 0.659
The specific gravity of benzene = 0.88
Density of benzene = specific gravity * density of water
= 0.88 * 62.43 = 54.9 lb m/ ft^3
Density of n-hexane = 0.659 * 62.43
= 41.1 lb m / ft^3
The volumetric flow rate = 1700 lmb/h * ft3 / 0.810 * 62.43 lbm = 33.6 ft3/h
Mass of benzene mB = QB ft3/h * 54.9lbm/ft3
= 54.9 QB
Mass of n-haxane mH = QH ft3/hh * 42.3 lmb/ft3
= 42.3 QH
Now mB+ mH = 54.9QB + 42.3 QH =1700 ---------- (1)
Q = QB + QH
QB + QH = 33.6
Or QH = 33.6 - QB ---------- (2)
Now using equation (2) in (1), we get
54.9 QB +42.3 (33.6- QB) =1700
54.9 QB + 1421.28 - 42.3 QB =1700
12.6 QB = 278.72
QB = 22.1 ft3/h
Using Equation (2) , we get
QH = 33.6- 22.1 = 11.5 ft3/h
The mass of benzene and n-hexane from the values of QB and QH,
mB = 54.9 * QB
= 54.6 * 22.1
= 1213.29 lbm
mH = 42.3 * QH
= 42.3 * 11.5
= 486.45 lbm
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