传质与分离 习题

Midterm Examination for Mass Transfer and Separation Processes

Name_____________ Student No._______________ Class______________ Score________

1. Fill in the blanks or choose the correct answer

(1)For a binary mixture, when the mol fraction of liquid phase is x=0.6, the bubble point is t1, the mol fraction of the corresponding equilibrium vapor phase is y=0.7, dew point is t2. The relation between t1 and t2 is then .

A. t1 = t2; B. t1 < t2; C. t1 > t2; D. uncertain

(2)The basic principles of azeotropic and extractive distillation are .

(3)In designing a distillation column, for certain F，xF，xD ,xB, if parameter of thermal condition of feed is changed from q=1 to q=0, and the reflux ratio and vapor flow rate of stripping section are kept constant, the required theoretical plates will（ ）.

A increase； B decrease； C not change； D be uncertain

(4)The mol fraction of a binary mixture of more volatile component is XF=0.5. After flash distillation, the ratio of the quantities of vapor and liquid is 1:1. If the relative volatility is 2, the mol fraction of more volatile component in the vapor phase is , and the mol fraction of more volatile component in the liquid phase is .

(5)For rectification and stripping in a column type equipment, the operating line must lie the equilibrium line because . For absorption, the operating line must lie the equilibrium line because .

(6)The reason for ??AfHTLs?3~5 is to ensure the separation of

.

(7)HETP is referred to .

(8)In the total reflux operation of a distillation column, the slope of the operating line in x-y diagram is（ ）.

A 0； B 0.5； C 1； D ∞.

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(9)The conditions required for constant molal overflow are .

(10) In the operation of a plate column, if temperature of reboiler and column pressure decreases, the possible reason is .

2.Questions

(1) Is it the only way that the minimum reflux ratio must be found by drawing the operating line that is tangent to the equilibrium curve for abnormal equilibrium curve?

(2)In a plate column with dowm-comer, when Hd??(HT?hW), liquid flooding will happen. Explain the meanings of Hd,?,HT,hW, and give measures for avoiding flooding.

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3.An 1 atm continuous distillation column with reflux is used for the separation of a mixture of benzene and toluene. The feed is 60 mole percent benzene, and the feed rate is F=100Kmol/h, the moles of liquid to stripping section of column per mole of feed is 0.5, the reflux ratio is 1.5 times the minimum reflux ratio. The required mole fraction in overhead product is 0.95, in bottom product is 0.05. the relative volatility between benzene and toluene is 2.5. Calculate （1）Flow rates of overhead product and bottoms product. （2）Minimum reflux ratio.

（3）Operating line equation of rectifying section. （4）Operating line equation of stripping section.

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4.A distillation column is used for the separation of a binary mixture with relative volatility equal to 2. The vapor flow rate to a certain plate is 100kmol/h with mole fraction yA=0.3, and liquid flow rate to the plate is 100kmol/h with mole fraction xA=0.4. Assume the molal latent heat of component A and B is the same as each other, and heat losses equal to zero. The liquid phase Murphree efficiency of the plate is 0.5. What are the compositions of vapor and liquid phases leaving the plate?

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