FSC 432
Petroleum Processing

Lesson 7 Overview



Video: FSC 432 Lesson 7 (5:00)

Click here for transcript of Lesson 7 Overview

Now this a painting in our EMS museum collections from the MS Museum collections. This is a very early refinery, I would think. You can see the oil wells here, and they're refined. The oil is refined right at the site, which is essentially distillation. You can see this must be the distillation tower. You can see the furnace here with the chimney to heat the crude to the required temperatures. And then collect the fractions.

At the time, it was kerosene, obviously, for lighting. And then, later on, maybe light gasoline. See the storage tank, maybe for the gasses and so forth. So in the last lesson, we've talked about thermal cracking processes to make more of the lighter stuff, essentially. Like distillates, or gasoline from the crude oil, by breaking chemical bonds. And we mentioned that pretty soon, the thermal cracking processes could not meet the demand for quality.

And what has changed in the meantime, when we have now close to the Second World War era, where the motors-- now engines-- have higher compression ratios, and they would require higher octane number gasoline. That means they would need gasoline that would not ignite spontaneously with pressure. And it is pressurized with air. That's essentially what the octane number measures, it's anti-knocking property.

So most catalytic processes, catalytic conversion processes, were developed right before and during the Second World War, mainly for making higher quality, higher performance fuels and in higher yields, in higher quantities. So introducing the catalyst to crack, to crude oil, into gasoline boiling range is not done just to increase the rate of cracking, or has anything to do with kinetics, really. That's what catalysts typically do.

In this case, introduction of the catalyst changes the whole chemistry of cracking. Now we've talked about having neutral, reactive species free of radicals and thermal cracking processes. In catalytic cracking, the reactive species are ions. Or cations, actually, cargo cations that are produced on catalyst surfaces. So we need an acid catalyst-- typically aluminum, silica or zeolites-- in order to create these cationic species.

Why do we need that? Because carbo cations go through isomerization reactions very fast. That means we will have now an opportunity to make branched alkanes or isoparaffins because of this isomerization of the ions as opposed to non-isomerization of the free radicals. Isomerization in free radicals is very, very slow. So it doesn't happen.

So pretty much all gasoline production in the US is done through catalytic means. Fluid catalytic cracking is really the most popular processes. It is the heart of a refinery in the United States, FCC process that generates high octane gasoline. It's a very flexible process. It could use a range of feed stocks in the gas oil, boiling range all the way up to light vacuum gas oil.

For heavier materials, something like heavy vacuum gas oil or vacuum distillation residue, we need to introduce hydrogen so that we could convert these heavy fractions without rejecting larger quantities, or very large quantities, of carbon. Then we get into a hydro cracking processes.

So in this lesson we will go over the historical development of catalytic cracking processes, ending up of course with FCC-- which is universally used and accepted now-- and talk about the hydra cracking processes, some of the conditions that are necessary for treating those very heavy ends of crude oil into upgraded products without rejected carbon, so in higher yields.

Credit: Dutton Institute © Penn State is licensed under CC BY-NC-SA 4.0


Catalytic conversion processes became important in petroleum refining after the Second World War. Catalytic cracking has been developed to produce high yields of gasoline with high octane # from high-boiling stocks using catalysts. As different from thermal cracking, catalytic cracking.

  • uses a catalyst;
  • takes place at lower temperature and lower pressure;
  • is more selective and flexible.

One particular catalytic cracking process, Fluid Catalytic Cracking (FCC), has captured universal acceptance in the refining industry because of its feed flexibility, ability to modify product yields through minor changes in the process operating conditions. FCC is used to produce high-octane gasoline mainly from straight-run atmospheric gas oil and light vacuum gas oil (LVGO) [1]. This process involves breaking up long chains of n-alkanes into shorter chains of branched alkanes (isoalkanes), cycloalkanes (naphthenes), and aromatics by using acidic catalysts. In addition to high-octane gasoline, catalytic cracking produces LPG, cycle oils, and olefin-rich light hydrocarbons (C3, C4). The olefins are used as petrochemical feedstocks, or as reactants in alkylation and polymerization reactions, to produce higher molecular weight branched alkanes and olefins to contribute to the high-octane gasoline pool.

Hydrocracking processes have been introduced for upgrading heavier crude oil fractions such as heavy vacuum gas oil (HVGO) and vacuum distillation residue VDR. The heaviest fractions of crude oil, HVGO and VDR, may not be easily processed by FCC because of potential problems with excessive coking on the catalysts. For upgrading these high-boiling and aromatic-rich feedstocks, hydrogen is introduced in the hydrocracking process, along with bi-functional catalysts systems, to keep coking under control while upgrading the heavy fractions to light and middle distillates.

Learning Outcomes

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

  • distinguish the chemistry of catalytic cracking from chemistry of thermal cracking and illustrate the formation of carbocations and IUPAC terminology for classification of carbocations;
  • categorize the formation of different carbocations on active sites of cracking catalysts and assess the classification of acid sites (Lewis vs Bronsted) on catalyst surfaces;
  • compare, with examples, how the product yields and composition obtained from catalytic differ from those from thermal cracking;
  • analyze the thermodynamics of carbocation formation and evaluate how ionic chain reactions produce hydrocarbons with high octane numbers;
  • appraise the historical evolution of catalytic cracking processes and formulate the driving forces that have shaped this evolution in reactor design and catalyst development;
  • locate the hydrocracking process and hydroprocessing in the refinery flow diagram, illustrate hydrocracking processes and evaluate different process objectives.

What is due for Lesson 7?

This lesson will take us less than 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 7 tasks
Readings J. H. Gary, G. E. Handwerk, Mark J. Kaiser, Chapters 7 (Catalytic Hydrocracking) and Chapter 8 (Hydroprocessing and Resid Processing)
Assignments Exercise 6

Quiz 3. Will cover material in Lessons 6 and 7. Check the Syllabus, or Course Calendar for Quiz 3 schedule.


If you have any questions, please post them to our Help Discussion (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.