Back to Library

(AI-Powered Suggestions)

Related Topics

A topic from the subject of Distillation in Chemistry.

  • 1 year ago
  • 6 min read

Vacuum Distillation in Petroleum Refining

Introduction

Vacuum distillation is a specialized distillation technique used in petroleum refining to separate high-boiling point components that cannot be vaporized under atmospheric pressure. By reducing the pressure within the distillation column, the boiling points of the components are lowered, allowing for their effective separation.

Basic Concepts

Vapor pressure: The pressure exerted by a vapor when in equilibrium with its liquid phase at a given temperature.

Boiling point: The temperature at which the vapor pressure of a liquid equals the external pressure.

Vacuum: A space with a pressure below atmospheric pressure, typically achieved using vacuum pumps.

Equipment and Techniques

Vacuum distillation column: A vertical column equipped with trays or packing to promote contact between the vapor and liquid phases.

Vacuum pumps: Create and maintain a reduced pressure within the column.

Feed preheater: Heats the crude oil to a temperature appropriate for vaporization.

Condenser: Cools and condenses the vaporized components.

Types of Processes

Batch distillation: A single charge of crude oil is processed in a vacuum column.

Continuous distillation: Crude oil is continuously fed into the column while distillates and residues are removed.

Data Analysis

Vapor pressure curves: Plot the vapor pressure of each component as a function of temperature.

Boiling point determination: Extrapolate the vapor pressure curves to atmospheric pressure to determine the boiling points at ambient conditions.

Distillation profiles: Plot the boiling range distribution of the distillates to optimize the separation process.

Applications

Production of heavy oil cuts: Vacuum distillation allows for the separation of heavy vacuum gas oil (VGO), heavy vacuum distillate (HVD), and vacuum residue.

Lubricant base oil production: Neutral oils and base stocks for lubricants are extracted from VGO through further processing.

Asphalt production: Vacuum residue is used as a feedstock for asphalt production.

Conclusion

Vacuum distillation is a key process in petroleum refining, enabling the efficient separation of high-boiling point components. By understanding the basic concepts, equipment, and techniques involved, engineers can optimize the process to meet specific product requirements for fuel, lubricant, and asphalt production.

Vacuum Distillation in Petroleum Refining
Overview

Vacuum distillation is a crucial separation process in petroleum refining, used to separate high-boiling components from crude oil. This process is essential for producing valuable products from the heavier fractions of crude oil that would otherwise be difficult to process.

Key Points
  • Purpose: To separate heavy fractions from crude oil into various products, such as vacuum gas oil (VGO) and residuum (bottom of the column). VGO is further processed into fuels and lubricants.
  • Process:
    1. Crude oil (or a pre-fractionated stream like atmospheric residue) is preheated to a high temperature.
    2. The heated crude oil enters a vacuum distillation column operating under reduced pressure (typically below 10 mmHg). This significantly lowers the boiling points of the components.
    3. The reduced pressure allows the heavier components to vaporize and rise through the column.
    4. The column contains trays or packing that provide surface area for vapor-liquid contact and efficient separation based on boiling point.
    5. Different fractions are drawn off at various points along the column according to their boiling points.
    6. Non-volatile components remain at the bottom of the column as residuum.
  • Advantages:
    • Minimizes thermal cracking of heavy fractions, preventing the formation of undesirable byproducts.
    • Produces higher quality products with improved thermal stability and reduced sulfur content.
    • Allows for the processing of heavier crude oils which would otherwise be too difficult to refine with atmospheric distillation alone.
  • Challenges:
    • High energy consumption due to vacuum requirements and the need for preheating.
    • Potential for coking and fouling of equipment due to the high temperatures and presence of heavy components. Regular maintenance and cleaning are required.
    • Complex operation and control due to the many variables involved (pressure, temperature, feed rate, etc.).
Main Concepts

Vapor Pressure: Under vacuum, the boiling point of the feedstock is significantly reduced. This allows heavier components, which would decompose at atmospheric pressure, to vaporize at lower temperatures, thus preventing cracking.

Fractionation: Different components in the feedstock have different vapor pressures and boiling points. This difference allows for their separation based on boiling ranges within the vacuum distillation column.

Equipment: Vacuum distillation columns are designed to handle high temperatures, low pressures, and large volumes of feedstock. They incorporate features like a vacuum system (steam ejectors or vacuum pumps), efficient trays or packing, and effective heat exchangers.

Vacuum Distillation in Petroleum Refining

Experiment: Fractional Distillation of Crude Oil under Reduced Pressure

Materials

  • Vacuum distillation apparatus (including a round-bottom flask, heating mantle, fractionating column, condenser, vacuum adapter, and receiving flask)
  • Crude oil sample (a small quantity)
  • Thermometer (capable of measuring temperatures up to at least 400°C)
  • Vacuum pump and pressure gauge
  • Heating mantle or hot plate with stirring capabilities
  • Ice bath for the condenser
  • Appropriate collection vessels for the distillate fractions
  • Safety goggles and gloves

Procedure

  1. Assemble the vacuum distillation apparatus carefully, ensuring all connections are airtight. The fractionating column is crucial for effective separation.
  2. Add a small amount of crude oil (approximately 50-100 mL) to the round-bottom flask. Avoid overfilling.
  3. Securely attach the flask to the heating mantle and the condenser to the vacuum adapter.
  4. Connect the vacuum pump to the vacuum adapter. Ensure the system is properly sealed to maintain vacuum.
  5. Start the vacuum pump and gradually reduce the pressure inside the apparatus to the desired level (typically below atmospheric pressure; monitor the pressure gauge carefully).
  6. Slowly increase the heat applied to the heating mantle, monitoring the temperature of the vapor using the thermometer. The heating rate should be controlled to avoid bumping and to allow for efficient fractionation.
  7. As the crude oil heats, different fractions will begin to vaporize and condense in the fractionating column and condenser at different temperatures. Collect these fractions in separate receiving flasks.
  8. Continue the distillation until the desired fractions have been collected or the residue in the flask becomes very viscous.
  9. Once the distillation is complete, carefully turn off the heating mantle and allow the apparatus to cool before disconnecting any components. Release the vacuum slowly.
  10. Record the temperature ranges at which each fraction was collected, as well as the volume of each fraction collected.

Key Procedures and Considerations

  • Maintaining a controlled vacuum is critical for preventing bumping and achieving efficient separation at lower temperatures.
  • Careful control of the heating rate is essential to prevent the rapid boiling and splashing of the crude oil.
  • The use of a fractionating column increases the efficiency of separation by providing more surface area for condensation and revaporization.
  • Proper safety precautions (goggles, gloves) must be observed throughout the experiment.
  • The collected distillates may require further analysis (e.g., gas chromatography) to fully characterize their composition.

Significance

Vacuum distillation is a crucial process in petroleum refining because it allows for the separation of high-boiling-point components of crude oil that would decompose at atmospheric pressure. This process yields valuable products like lubricating oils, waxes, and asphalt, which would not be easily obtained through atmospheric distillation. The lower temperatures used under vacuum also increase the efficiency and safety of the refining process, resulting in higher quality products and reduced energy consumption.

Share on: