FSC 432
Petroleum Processing

Lesson 5 Overview

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Overview

Video: FSC 432 Lesson 5 (3:29)

Lesson 5 Overview
Click here for transcript of Lesson 5 Overview.

Hello. In lesson five, we will pick up the second part of the separation processes. Remember in lesson four, we've talked about distillation as perhaps the most significant separation process.

In this lesson, we will start with the light ends unit. You know that the light ends unit process the lightest fraction of crude oil. We call it the overhead from the distillation column. It ends up as LPG. That is propylene and butane, and the naphtha fractions that are very important for producing gasoline.

Now, since this is the lightest fraction of crude oil, it's simpler in its molecular makeup, so we can begin actually to see individual compounds. So we can use analytical data, like vapor liquid equilibrium, and we could use analytics expressions, equations like Fenske equations to make calculations about the separation of these components, like propane from butane and so forth.

Now, distillation is, of course, one and most important separation process, but there are other processes that would use other physical properties like the solvent power of compounds, of chemicals. Now, one such technique is called solvent extraction. We could use solvent extraction to fraction the residue that comes from distillation rather than this atmospheric or vacuum distillation residue. It is more common to have the vacuum distillation residue that goes into the solvent fractionation processes.

One important solvent technique is deasphalting, which is done to remove asphalt, the stuff that you put on the road for pavement, and the function, the principal objective of deasphalting is not to make asphalt, really. It is a byproduct, but it to remove asphalt so what remains after removing the asphalt from the residue could be used for producing more fuels and other more relevant products in downstream processing in a petroleum refinery.

Here you'll see a sample of asphalt that is produced by the deasphalting process by rejecting it from the crude oil using the anti-solvent behavior for anti-solvent phenomenon in the deasphalting process. You can see this is pure asphalt. You need to mix that with aggregates to pave the roads so the bottom of the barrel is solid form here.

Another solvent extraction process is called dewaxing. That removes wax. This is the candle wax, the paraffin wax that we know. Again, the purpose here is not to make candle wax but to remove wax from this heavy fraction of crude oil so that what is left over is a good base stock to make lubricating oils or engine oils.

Overview

This section will continue to discuss the separation processes that are carried out on the distillate products obtained from the atmospheric and vacuum distillation units, and the residue from the vacuum distillation unit, as introduced in Section 4. Light Ends Unit (LEU) fractionates the lightest fraction of crude oil obtained as overhead distillate from the atmospheric column in a series of distillation towers to produce LPG as a refinery product and straight-run light, and heavy naphtha for further processing in finishing and conversion units to produce gasoline streams for the blending pool (Section 3). Vacuum distillation residue (VDR) can be fractionated using solvent extraction (deasphalting) to produce an insoluble (asphalt) and a soluble fraction, deasphalted oil (DAO). DAO can be further processed by freezing point separation in a suitable solvent to separate wax. The remaining dewaxed oil is used as base stock for producing lubricating oil. Heavy vacuum gas oil (HVGO) can also be used as a feedstock for dewaxing.

Learning Outcomes

By the end of this lesson, you should be able to:

  • analyze the vapor-liquid equilibrium and evaluate the application of Fenske Equation to distillation in Light Ends Unit;
  • describe the principles of solvent fractionation as a separation technique;
  • place the Deasphalting Process in the refinery and interpret the significance of this process for refining;
  • interpret the gradient solubility model that explains the solution of asphaltenes in resin and oil fractions and analyze the structure of asphaltenes;
  • analyze the process parameters for deasphalting and assess the anti-solvent effect;
  • evaluate the unit operations of deasphalting and assemble the process flow diagram;
  • explain the purpose of dewaxing and examine the physical and chemical dewaxing processes.

What is due for Lesson 5?

This lesson will take us one week to complete. Please refer to the Course Syllabus for specific time frames and due dates. Specific directions for the assignments below can be found on the Assignments page within this lesson.

Lesson 5 Checklist
Readings J. H. Gary and G. E. Handwerk, Mark J. Kaiser, Chapter 15 (Lubricating Oil Feedstocks)
Assignments Exam 1 will cover the material in Lessons 1-5. Exam 1 is found in the Exam 1 Module.

Exercise 4:
  1. Use of Fenske Equation to evaluate the performance of a distillation column
  2. Qualitative evaluation of process parameters to estimate product yields from deasphalting

Questions?

If you have any questions, please post them to our Help Discussion Forum (not email), located in Canvas. I will check that discussion forum daily to respond. While you are there, feel free to post your own responses if you, too, are able to help out a classmate.