Flash Distillation Flashcards
The difference between stage operation (A) and a continuous phase contact operation (B) is that
A. (A) is co-current flow while (B) is counter-current flow
B. (A) yields discreet concentration changes while (B) yields infinitesimal concentration changes
C. (B) yields discreet concentration changes while (A) yields infinitesimal concentration changes
D. an ideal (B) yields equilibrium concentration while (A) does not
B. (A) yields discreet concentration changes while (B) yields infinitesimal concentration changes
One hundred moles per hour of solution containing 80 moles of A, the rest B, is subjected to a simple continuous distillation. D moles of distillate containing 72 moles A is obtained. If A is five times more volatile than B, the concentration of A in the distillate is
A. 0.85
B. 0.80
C. 0.533
D. none of these
A. 0.85
One hundred moles per hour of solution containing 80 moles of A, the rest B, is subjected to a simple continuous distillation. D moles of distillate containing 72 moles A is obtained. The temperature of the solution as distillation progresses at constant operating pressure is
A. increasing
B. decreasing
C. constant
C. constant
If the enthalpy of saturated vapor at 200 °F referred to 32 °F is 1300 BTU/lb while the enthalpy of saturated liquid (Cp = 1) referred to 0 °F is 400 BTU/lb, then the latent heat of vaporization of the component at 200 °F is
A. 900 BTU/lb
B. 932 BTU/lb
C. 868 BTU/lb
D. none of these
B. 932 BTU/lb
Desorption is another term for
A. dephlegmation
B. stripping
C. flash distillation
D. rectification
B. stripping
In a simple batch distillation, the boiling point of the distillate product compared to the residue is
A. the same
B. lower
C. higher
B. lower
When the feed to the rectifying column is a saturated liquid, the feed line is
A. vertical
B. horizontal
C. inclined to the left
D. inclined to the right
A. vertical
The distillation process involves
A. momentum transfer
B. mass transfer
C. heat transfer
D. heat and mass transfer
D. heat and mass transfer
A liquid mixture containing 45% benzene and 55% toluene by weight is to be fed to a fractionating column at a rate of 5000 kg/hr. The feed rate in kg mol/hr is
A. 58.74
B. 58.80
C. 48.80
D. 28.846
A. 58.74
A binary solution, where A is a low boiler, exhibiting a maximum boiling point, is subjected to flash distillation. If the feed has a concentration in A less than the azeotropic point, the concentration of the distillate will be
A. higher in A
B. higher in B
C. same
B. higher in B
The unit operation by which miscible liquids are separated from one another through heat and mass transfer is
A. extraction
B. sedimentation
C. distillation
D. filtration
C. distillation
When the relative volatility of two miscible components is close to 1.00, the components can be separated by
A. simple fractionation
B. batch distillation
C. extractive distillation
D. low pressure distillation
C. extractive distillation
Vacuum distillation is resorted to in order to
A. reduce the number of trays in the column
B. use thinner shell plates for the column
C. avoid high feed and reboiler temperatures
D. obtain more bottom products
A. reduce the number of trays in the column
The degrees of freedom associated with a ternary distillation process, according to the Gibbs’ phase rule, is
A. 2
B. 3
C. 4
D. 5
B. 3
To improve the degree of separation of the more volatile component from the less volatile component through distillation, the chemical engineer may, without changing the other variables,
A. increase the feed temperature
B. reduce the column pressure
C. increase the reboiler temperature
D. increase the column pressure
B. reduce the column pressure
Increasing the operating pressure of the distillation column
A. does not make a difference in components separation
B. makes separation difficult
C. sharpens separation
D. requires less heat in the feed heater
B. makes separation difficult
A reboiler provides heat to the
A. top
B. the intermediate reflux
C. the feed
D. the bottom of the distillation column
D. the bottom of the distillation column
When the molal latent heat of vaporization of the binary system is very much dependent on concentration, the most appropriate method to use to determine the number of ideal stages is
A. Fenske-Underwood Method
B. McCabe-Thiele Method
C. Ponchon-Savarit Method
D. Lewis-Matheson Method
C. Ponchon-Savarit Method
Open steam binary rectification may be applied with success if the less volatile component is
A. water
B. alcohol
C. benzene
D. acetone
A. water
At minimum reflux ratio, the number of plates is
A. minimum
B. infinite
C. maximum
D. between minimum and maximum
B. infinite
In a vacuum distillation column, the vacuum is usually created by a
A. steam ejector
B. vacuum pump
C. compressor
D. centrifugal pump
B. vacuum pump
The relative volatility of the mixture at the azeotropic point where the solution exhibits minimum boiling point is
A. less than 1
B. equal to 1
C. greater than 1
B. equal to 1
The ease or difficulty of separating components by distillation is determined by the
A. relative volatility
B. viscosity
C. mole fraction
D. weight fraction of the components
A. relative volatility
A debutanizer is a
A. heat transfer equipment
B. mass transfer equipment
C. fluid transfer equipment
D. size reduction equipment
B. mass transfer equipment
In distillation, the cooled liquid stream returned to the column to cool a plate or stage is called
A. reboil
B. reflux
C. feed
D. bottoms
B. reflux
A binary mixture of 2 moles benzene and 8 moles toluene will boil at
A. 110 °C
B. 110 °F
C. 105 °C
D. 102 °C
D. 102 °C
McCabe-Thiele method to determine the theoretical number of stages may be applied with acceptable result if
A. the components have different boiling points
B. the system follow Trouton’s Rule
C. the components have high relative volatility
D. heat losses and heat of solution are negligible
B. the system follow Trouton’s Rule
The distribution coefficient of n-hexane at 10 atm abs and 200 °C is
A. 2.6
B. 1.4
C. 0.9
D. none of these
B. 1.4
The theoretical minimum reflux ratio in a distillation column is attained if the column has
A. 1 plate
B. 10 plates
C. 100 plates
D. an infinite number of plates
The theoretical minimum reflux ratio in a distillation column is attained if the column has
A. 1 plate
B. 10 plates
C. 100 plates
D. an infinite number of plates
D. an infinite number of plates
The physical separation of components in a miscible mixture by simultaneous evaporation and condensation is
A. absorption
B. extraction
C. drying
D. distillation
D. distillation
In batch open steam distillation, the solution to be open steam distilled should be
A. miscible in water
B. completely immiscible in water
C. slightly miscible in water
D. containing large non-volatile impurities
B. completely immiscible in water
In a distilling column, the highest pressure will be at
A. the top
B. the feed plate
C. the bottom
D. between the feed plate and the top
C. the bottom
The unit operations by which the lighter components in a multicomponent solution of volatile liquids are separated from the heavier components is called
A. absorption
B. drying
C. distillation
C. distillation
In distillation where there are two components and both components are found in both phases, only one variable such as liquid phase concentration can be changed independently if the pressure is fixed and the temperature and vapor phase concentration will follow. This statement is _______
A. true
B. false
A. true
A heat transfer equipment to convert vapor to liquid is an/a
A. evaporator
B. reboiler
C. condenser
D. still
C. condenser
For a mass transfer to take place, there must be a
A. concentration gradient
B. more than two components involved
C. heat present
D. enthalpy change
A. concentration gradient
A 50% by weight benzene-toluene mixture is fed to a column at 180 °F and 1 atm. The condition of this feed is
A. saturated liquid
B. saturated vapor
C. sub cooled liquid
D. mixture of liquid and vapor
C. sub cooled liquid
A distillation column with a partial condenser is composed of 7 theoretical stages in rectifying section and 8 theoretical stages in the stripping section. If the overall plate efficiency is 60%, then the actual feed plate is the
A. 11th
B. 13th
C. 12th
D. 8th from the top
A. 11th
Using the Antoine’s Equation, the vapor pressure of tetrahydrofuran at 80 °C is estimated to be ______ torr
A. 2000
B. 1518
C. 1173
D. 2562
C. 1173
A distillation column with a partial condenser is composed of 7 theoretical stages in rectifying section and 8 theoretical stages in the stripping section. If the overall plate efficiency is 60%, then the actual number of plates is
A. 24
B. 22
C. 25
D. 15
B. 22
Strictly speaking, the relative volatility of most ideal binary solution is
A. not affected by temperature
B. greatly affected by temperature
C. slightly affected by temperature
D. greatly affected by pressure
C. slightly affected by temperature
For a non-azeotropic solution being distilled, the temperature in the distillation column, from bottom to top
A. increases
B. decreases
C. becomes maximum
D. becomes constant
B. decreases
The primary reason why close steam is used in an open batch steam distillation is to
A. increase the number of degrees of freedom
B. increase the operating temperature
C. supply the heat needed by the vaporizing liquid
D. increase the operating pressure
A. increase the number of degrees of freedom
In a two-component flash distillation process, when the operating pressure is specified, the concentration of the distillate may be improved in the more volatile component if
A. the operating temperature is decreased
B. the operating temperature is increased
C. the amount of distillate is increased
D. none of these
A. the operating temperature is decreased
A distillation column with a partial condenser is composed of 7 theoretical stages in rectifying section and 8 theoretical stages in the stripping section. The overall plate efficiency is 60%. If HETP of the column is 2 ft then the height of an equivalent packed column is
A. 30 ft
B. 43 ft
C. 26 ft
D. none of these
C. 26 ft
The percentage change in the boiling point of 20-mole benzene-toluene solution when the pressure is increased from 1 atm to 2 atm is
A. 10.5% increase
B. 25.5% increase
C. 25.5% decrease
D. none of these
B. 25.5% increase
The recent availability of digital computers resulted in the development of many analytical expressions for the evaluation of K-values. Which of the items below is a source of analytical method for K-values?
A. NRTL
B. Wilson Equation
C. UNIQUAC
D. all of these
D. all of these
The activity coefficient of a component in a non-ideal liquid solution at low pressure is approximated to be equal to
A. one
B. vapor pressure multiplied by the composition in the liquid phase in mole fraction
C. vapor pressure divided by the total pressure
D. none of these
D. none of these
The approximate minimum number of stages for a binary system with relative volatility of 2.35, fractionally distilled to yield compositions of 0.98 in the distillate 0.045 in the bottoms is
A. 4.8
B. 7
C. 8.1
D. 12
C. 8.1
For nearly pure products in a stage operation, the theoretical number of plates may be estimated using the
A. Rayleigh Equation
B. Fenske Equation
C. Tiller-Tour Equation
D. Murphree Equation
C. Tiller-Tour Equation
