18 Questions
What is the primary purpose of using a flash or equilibrium distillation process?
To rapidly vaporize a liquid mixture
What is the relationship between the feed pressure and the pressure inside the flash drum?
The feed pressure must be below the critical pressure of the mixture
Which of the following is NOT a key factor to consider in the design of a flash distillation process?
Viscosity of the feed mixture
How does the temperature of the feed entering the flash drum compare to the boiling point of the feed at the drum pressure?
The feed temperature is higher than the boiling point at the drum pressure
What is the purpose of pressurizing and heating the feed before it enters the flash drum?
To increase the amount of the feed that vaporizes in the drum
What is the primary purpose of the liquid-vapor separation that occurs in the flash drum?
To produce two streams with different compositions
What is the key characteristic of an azeotropic mixture?
One component is more volatile than the other only at a particular concentration range
In the example given, if the feed mixture is subjected to flash distillation at 1 atm, what fraction of the feed must be vaporized to obtain a vapor composition of 75 mol% A?
$\frac{2}{3}$
What type of azeotrope is formed when the boiling point of the mixture is higher than the boiling points of the individual components?
Homogeneous maximum boiling azeotrope
Which type of azeotrope involves a liquid-liquid equilibrium region in the phase diagram?
Homogeneous minimum boiling azeotrope in a system with miscibility gap
In a flash distillation process, what is the primary factor that determines the vapor and liquid compositions leaving the separator?
The vaporized fraction of the feed
What is the purpose of increasing the separator pressure in a flash distillation process?
To decrease the vaporized fraction of the feed
In an equilibrium distillation process, what does the McCabe-Thiele diagram show?
X vs. Y diagram
In a vapor-liquid equilibrium (VLE) diagram, what does the slope of the operating line represent?
Pressure
Which type of mixtures consist of one component that is more volatile than the other throughout the concentration range?
Non-azeotropic mixtures
What does a material balance equation represent in flash distillation?
Mass conservation
In flash distillation, what does the balance equation 0 = 1 + 3 represent?
Material balance between feed and products
What is the primary focus of the phase equilibrium data for Benzene-Toluene?
Vapor-liquid distribution at equilibrium
Study Notes
Flash or Equilibrium Distillation
- Flash distillation is a special operation within distillation where a liquid mixture is heated up and fed into a distillation equipment with a constant flow rate.
- The system is called "flash" distillation because the vaporization is extremely rapid after the feed enters the drum.
- Key factors to consider:
- Pressure and temperature of the flash drum
- The pressures must be chosen so that at the feed pressure, the feed is below its boiling point and remains liquid.
- Size of the drum
- Liquid and vapor compositions and flowrates
- Pressure, temperature, and flowrate of the feed entering the drum
- At the pressure of the flash drum, the feed is above its boiling point and some of it vaporizes.
- Drum pressure must be below the critical pressure for the mixture so that a liquid phase can exist.
Azeotropic Mixtures
- Azeotropic mixtures consist of one component that is more volatile than the other only at a particular concentration range.
- Examples: Ethyl acetate – Ethanol, Chloroform - Acetone
- Types of azeotropic mixtures:
- Homogeneous minimum boiling azeotrope
- Homogeneous minimum boiling azeotrope in a system with miscibility gap
- Homogeneous maximum boiling azeotrope
- Homogeneous maximum boiling azeotrope in a system with miscibility gap
- Double azeotrope
- Heterogeneous azeotrope
Material Balance and Vapor-Liquid Equilibrium
- Overall material balance equation: 0 = 1 + 3
- More volatile component balance equation: 0(- = 1( + 3'
- Vapor-Liquid Equilibrium (VLE) Diagram or XY or YX Diagram describes the distribution of a chemical species between the vapor phase and a liquid phase.
- Phase equilibrium data can be represented using diagrams such as McCabe-Thiele diagram, which shows both the y vs.x diagram and operating lines.
Types of Feed Material
- Based on the phase diagrams, two types of mixtures can be classified:
- Non-azeotropic mixtures: mixtures that consist of one component that is more volatile than the other in the entire concentration range (Example: Benzene – Toluene)
- Azeotropic mixtures: mixtures that consist of one component that is more volatile than the other only at a particular concentration range.
Explore the concept of flash or equilibrium distillation, a special operation within distillation where a liquid mixture is heated up and fed into a distillation equipment with constant flowrate. Learn about the rapid vaporization process that occurs in flash distillation.
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