1. Module 5

1.21. Page 2

Module 5 Lesson 5

Module 5—Hydrocarbons and the Petroleum Industry

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Crude oil is a complex mixture of hydrocarbons. There are different types of crude oil. Read pages 386–387 in the textbook to learn more about the different types of crude oil, the property that determines the grade of crude oil, and the refining process.

 

Try This


Refining and other processes, like dewaxing, make use of the different boiling points of molecules within oil.

 

View the presentation “Fractional Distillation” to test your understanding of the principles and processes involved in oil refining. As you move your mouse over the possible answers in each question, a pop-up window will appear allowing you to self-score and to see where you chose incorrectly.

 

Only complete steps 1–10 at this time. You will complete the other steps later in this lesson.

 

Self-Check


SC 1. Complete “Practice” questions 1–6 on page 388 of the textbook.

 

Check your work.
Self-Check Answers

 

Contact your teacher if your answers vary significantly from the answers provided here.

 

SC 1.


Practice 1.


Both a fractionation tower and a laboratory-scale distillation apparatus use a heat source to boil off components of a mixture. Both employ a vertical column to more efficiently separate and collect the fractions obtained by condensing them.

 

In a fractionation tower, the mixture is continuously fed in, and the fractions condense simultaneously at various levels in the tower. In the lab-scale process, a mixture is placed in the flask and the components are distilled and condensed one at a time.

 

Practice 2.

  1. Crude oil is heated in the absence of air in the fractionation tower because, at such a high temperature, the oxygen in the air would cause the crude oil to burn.

  2. C5H12(l) + heat → C5H12(g)
    C8H18(l) + heat → C8H18(g)

  3. C5H12(g) → C5H12(l) + heat
    C8H18(g) → C8H18(l) + heat

  4. Octane has a higher boiling point than pentane because octane's London forces are stronger, mainly due to octane's greater number of electrons (66 e- versus 42 e-).

  5. Pentane rises higher in the tower than octane.

Practice 3.


The fractions used for cracking stock are kerosene, fuel oil, gas oil, and greases. Cracking changes products that are in less demand into products that are in greater demand. Cracking also results in products that give a greater monetary return to the refinery.

 

Practice 4.


Approximately 95% of petroleum is used as fuel. The major fuel produced is gasoline.

 

Practice 5.

  1. Straight-run gasoline contains hydrocarbons with five to 12 carbon atoms, which is more than the lighter fractions but less than the heavier fractions.

  2. C5H12(g) + 8 O2(g) → 5 CO2(g) + 6 H2O(g)
    2 C8H18(g) + 25 O2(g) → 16 CO2(g) + 18 H2O(g)

    It is assumed the fuel is vapourized before burning in the cylinder.

Practice 6.

  1. The hydrocarbons are all similar nonpolar molecules, so they are mutually soluble.

  2. Water molecules are very unlike hydrocarbons in that water is a highly polar hydrogen-bonded substance. There is little tendency for the crude oil solution to dissolve any water.

 

Read

 

Earlier in this module you learned that cracking is the process by which larger hydrocarbons are broken into smaller hydrocarbons. Cracking is one of the main processes used to modify molecules in crude oil into more desirable forms.

 

As you learned in the previous section, 95% of crude oil is used to produce fuels for heating or transportation. These fuels are a mixture of many hydrocarbons ranging in size from five to 12 carbons each. Read pages 389–391 in the textbook to learn more about the chemical processes and different types of cracking involved in refining oil.

 

Try This


Open the presentation “Fractional Distillation” again. Use steps 11–15 to test your understanding of chemical processes in cracking and reforming, and of alkylation used in refining oils. Select the “i” shown on each page to view simulations of the processes described.

 

Self-Check

 

SC 2. Complete “Practice” questions 8–15 on pages 391–392 of the textbook.

 

Check your work.
Self-Check Answers

 

Contact your teacher if your answers vary significantly from the answers provided here.

 

SC 2.

 

Practice 8.


If only physical means were used to refine oil, there would be too much of the heavier fractions produced, and the supply of products such as gas oil and greases would exceed the demand. Also, straight-run gasoline is of lower quality than gasoline containing compounds produced by reforming and alkylation.

 

Practice 9.

  1. CH3-(CH2)16-CH3 → CH3-(CH2)6-CH3 + CH3-(CH2)7-CH3 + C
  2. CH3-(CH2)8-CH3 → CH3-(CH2)3-CH3 + CH3-(CH2)2-CH3 + C
  3. CH3-(CH2)14-CH3 → CH3-(CH2)7-CH3 + CH3-(CH2)4-CH3 + C

Practice 10.


Hydrocracking is carried out on heavier fractions, whereas catalytic reforming is done on lighter fractions. The processes complement each other because both improve the quality of the gasoline produced at the refinery.

 

Practice 11.


Alkylation increases the amount of branching within the molecules. Catalytic reforming provides an increase in the amount of aromatic molecules in the gasoline.

 

Practice 12.

  1. CH3-(CH2)4-CH3 + H2 → CH3-CH3 + CH3-CH2- CH2-CH3
  2. CH3-CH(CH3)-CH2-CH2-CH3 + H2 → CH3-CH2-CH3 + CH3-CH2-CH3
  3. CH3-C(CH3)2-CH2-CH3 + H2 → CH3-CH3 + CH3-CH(CH3)-CH3

Practice 13.

  1. propane + pentane → 2,2,4-trimethylpentane + hydrogen

  2. CH3-(CH2)6-CH3 → CH3(C6H4)CH3 + 4 H2
  1. pentane → ethylcyclopropane + hydrogen

You may have discovered that it is not obvious that C3H5(C2H5) is a cyclic compound.

  1. CH3-(CH2)8-CH3 → CH3-CH(CH3)-CH(C2H5)-CH2-CH2-CH2-CH3

Practice 14.

  1. Benzene has the molecular formula C6H6, which gives an H:C ratio of 1:1. Even with alkyl groups attached, the ratio remains close to 1:1.

  2. Alkanes, alkenes, and large alkynes have a ratio close to 2:1.

  3. In hydrocracking, as aromatics are converted to aliphatic compounds, hydrogen is added but no carbon is removed. As a result, the H:C ratio must increase. For aromatics, the ratio increases from approximately 1:1 to approximately 2:1.

Practice 15.

 

Hydrocracking produces a product with a higher H:C ratio than catalytic cracking and does not produce coke (carbon), an undesirable by-product.

 

 

Read


Oil sand is a natural resource that is receiving a great deal of attention. Read page 395 in the textbook to learn more about oil sand and the extraction of the hydrocarbons, called bitumen, from oil sand.