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Petroleum Processing

Summary and Final Tasks

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Summary

Catalytic processes constitute the core of the petroleum refineries to accomplish a number of conversion and finishing tasks. Catalytic cracking has been developed to produce high yields of gasoline with high octane # from high-boiling stocks using catalysts. Compared to thermal cracking, catalytic cracking takes place at lower temperatures and pressures and proceeds through carbocationic active species produced on acidic sites on catalyst surfaces. Fluid Catalytic Cracking (FCC) has become universal refining process because of its high efficiency and feed flexibility. This process involves breaking up long chains of n-alkanes into shorter chains of branched alkanes (isoalkanes), cycloalkanes (naphthenes), and aromatics in high yields. Although the main product from FCC is high-octane number gasoline, it also 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

You should now be able to:

  • distinguish the chemistry of catalytic cracking from the 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 processes differ from those from thermal cracking processes;
  • 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.

Reminder - Complete all of the Lesson 7 tasks!

You have reached the end of Lesson 7! Double-check the to-do list below to make sure you have completed all of the activities listed there before you begin Lesson 8. Please refer to the Course Syllabus for specific time frames and due dates. Specific directions for the assignments below can be found 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: The dry air flow rate to the regenerator is given as 593 SCMM (standard cubic meters per minute). Considering that a significant portion of coke is carbon, calculate the carbon burning rate in the regenerator in kg/min. Remember: (1 kgmole at STP = 22.4 m3).

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

Questions?

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.