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Chemistry Of Petroleum 4: Treatment Of Hydrocarbons
To introduce how petroleum fractions are chemically treated within the refinery process to supply useful materials.
This lesson is the fourth in a series of lessons about the chemistry of petroleum which can be intended for upper-level chemistry students in the 11th and 12th grades. Try to be an experienced chemistry teacher to teach these lessons. The goal of these lessons is to introduce high-school students to using oil as an energy source in today’s high-tech world. In the Chemistry of Petroleum 1: What are Hydrocarbons students will explore hydrocarbons, the molecular basis of petroleum, and learn to differentiate between organic and inorganic compounds.
In the Chemistry of Petroleum 3: Distillation of Hydrocarbons, students will probably be introduced to the distillation processes by which petroleum is refined to produce useful petroleum fractions.
This particular lesson is a continuation of lesson 3, which taken together complete the crude oil refining process. Lesson 3 concludes with the crude oil being separated into petroleum fractions, based on the relative boiling points of the hydrocarbons in the unique crude oil. In this lesson, students explore how those petroleum fractions are treated chemically to provide useful fuels that are familiar to them, such as diesel, jet fuel, and gasoline.
As students explore the interactive, they may be overwhelmed with the quantity of terminology and reactions related to the treatment process. Students do not need to know or memorize the main points of those reactions; rather, they should achieve a general understanding that a series of chemical reactions are important in producing the fuels which are used on an everyday basis.
As in lesson 3, this activity provides a chance to clarify the common misconception that crude oil is composed of individual molecules of diesel, kerosene, and the other refined products. By the top of these lessons, students should understand that there is no such thing as a single molecule generally known as diesel, or kerosene, or light gases, with a particular chemical formula, like H2O. Fuel oils, like diesel, are a mixture of different molecules that share similar properties. The two main properties shared in a petroleum fraction are the variety of carbons in a molecule and the boiling point.
Begin by asking students: “We all know that petroleum is used to make gasoline. But what other products are made from petroleum ” Ask students to brainstorm in groups, each group generating a listing of at least ten items that they have seen or used in the past 24 hours which might be petroleum products. An inventory of items could be found at: A few Products Made from Petroleum.
As student groups share their product items, generate a class list. Point out that these items and lots of more are all made with fuels derived from crude oil or petroleum. Ask students:
– How do you think our use of petroleum products has changed over time
– Given the high customer demand and the fact that crude oil is a limited resource, how do you think refineries take advantage of out of the crude oil they have
Review with students the primary stages of crude oil refinement and treatment by making a flowchart. In the beginning of the flowchart, write the words “crude oil.” At the tip of the flowchart, place the list of products generated by the scholars. Begin to fill in the flowchart by asking students what happens to crude oil once it’s located within the earth. Next steps should include extraction and taking the crude oil to a petroleum refinery. Once on the refinery, the crude oil undergoes the distillation process. The outcomes of distillation are petroleum fractions. Ask students, “Describe what has happened to the hydrocarbons in the distillation process.”
Now students should review the Oil Refining: A more in-depth Look interactive by watching the introductory video and going through the distillation process. The movie has an accompanying script which you can print out. The narrator speaks rapidly, so it is a good suggestion to read the script after watching the movie the primary time. After reading the script, students can watch the movie a second time, which is able to facilitate understanding.
– What chemical property was used to separate the hydrocarbons within the distillation process
Go through the seven fractions, emphasizing that the fractions are composed of a mixture of hydrocarbons, and will not be composed of a single molecule. For example, kerosene is a mixture of hydrocarbon molecules from the unique crude oil that contain between 10-16 carbons. This means that there are hydrocarbons in the kerosene fraction that contain 10 carbons and others that contain 11, and so on through 16.
Point out that through the distillation process, the hydrocarbons have not been altered or modified in any way; they have simply been separated by size using the chemical property of boiling point differences. It is a physical change. On the flowchart after distillation and before the students’ list of everyday products and oils, crude oil last trading day write the word “treatment.” Define for students that treatment is the series of chemical reactions and technologies to switch the distilled fractions to make useful and marketable oils.
Allow students to explore the treatment section of the interactive on their own using the Treatment of Hydrocarbons student crude oil last trading day esheet. Students can answer the questions using the Treatment of Hydrocarbons student sheet. Answers are available on the Treatment of Hydrocarbons teacher sheet. Review the questions together as a category. Through discussion and review of the guiding questions, explain that there are three different treatment processes, generally. These are:
1. Removing impurities in the hydrocarbons, corresponding to metals and sulfur
2. Breaking down large, heavy hydrocarbons
3. Reshaping or building hydrocarbons from smaller ones
The goal of those processes is to make useful products, corresponding to diesel, gasoline, jet fuel, and asphalt. In the end, these final products are not individual molecules, but blends of treated hydrocarbons of assorted lengths and structures.
Go through examples of every of the three processes. Begin with the first process (Removing impurities in the hydrocarbons) by asking students:
– What are the 2 processes that are used to remove sulfur
Tell students that the final idea behind hydrotreating is to add hydrogen gas at high pressure and temperature to the petroleum fractions. The oil and hydrogen then enter a reactor loaded with a catalyst.
– What’s a catalyst
In hydrotreating, a metal surface is usually used as a catalyst. These metals include palladium, nickel, platinum, cobalt, and iron. Draw a general reaction formula for students to understand hydrotreating.
S + H2 (g) → H2S (g)
(Catalyst, heat, and pressure)
If possible, project the treatment page of the interactive for the category. Click on one of the fuels and then on the hydrotreating box to show students an example of one of the kinds of reactions that happen in the hydrotreating unit. Solid sulfur is converted to hydrogen sulfide gas, which is then removed.
S8 (s) + 8H2 (g) → 8H2S (g)
(Catalyst, heat, and pressure)
Tell students that the hydrotreating process also removes nitrogen compounds, which if not removed, would react with the oxygen within the air and produce nitric acid (HNO3).
Begin describing an example of the second process (Breaking down large, heavy hydrocarbons) by asking students:
– Do large hydrocarbons have high or low boiling points Why
Write the formula for docosane on the board: C22H46, and tell students that this large hydrocarbon is found in the gas oil fraction after distillation. The gas oil fraction is composed of a mixture of hydrocarbons with 20–70 carbons. If possible, project the treatment page of the interactive in front of the classroom and click on the red circle next to “gas oil.” Then click on the throbbing yellow circle in the gas oil pipe to display the chemical structure of docosane. Ask students:
– What’s the primary treatment process for the gas oil fraction
Tell students that cracking processes break down heavy hydrocarbons (you might want to use the term large hydrocarbon molecules) into lighter products (smaller hydrocarbon molecules). Several types of cracking processes are used. Give attention to catalytic cracking, telling students that this process uses high heat and a catalyst to break larger molecules into smaller, more useful ones. Draw the next reaction to point out students how catalytic cracking works:
C22H46 + heat + catalyst → C12H26 + C6H12 + C4H8
The catalyst used is often silica or alumina. Within the above reaction, docosane is converted to dodecane, cyclohexane, and butene. The smaller hexane and butene could be combined with other smaller compounds to make gasoline stock. The larger dodecane is a component of diesel stock, which can be utilized to fuel ships and factories.
Describe an example of the third process (Reshaping or building hydrocarbons from smaller ones) by clicking the red circle next to “light naphtha” on the treatment page of the interactive. Doing so will show two treatment processes: hydrotreating and isomerization. Ask students:
– Are the hydrocarbons in light naphtha large or small relatively
Tell students that light naphtha is a mixture of mostly pentane and hexane. Have students draw the chemical structures of pentane and hexane. If possible, provide models of every structure. Ask students:
– What is an isomer
Write the next reaction on the board:
C5H12 → C5H12
Tell students that this is the reaction for pentane to isopentane. Ask students to draw the chemical structure of isopentane. Using the model for pentane, remove the fifth carbon from the chain and move it to the second carbon. This new structure is isopentane (also called methylbutane or 2-methylbutane), which has the same chemical formula as straight-chained pentane. Tell students that this isomerization is important within the petroleum treatment process because isomers improve the standard of gasoline versus the straight-chained molecules. In reality, isomers improve the octane rating for gasoline.
Have students work in groups to decide on one of the top products of the crude oil distillation and treatment process: diesel, kerosene, gasoline, jet fuel, or asphalt. Ask each group to develop a presentation that discusses how their final product is formed. As they are doing this exercise, they need to ensure to categorise each step as a physical or chemical change. Their information should draw upon all aspects of the interactive, including the movie. Their presentations should begin with the tiny sea plants living millions of years ago and move through the means of forming kerogen, and ultimately petroleum. Remind students to incorporate drilling before moving into the distillation and treatment process. Students should include a flow chart in their presentations. Encourage students to make use of different methods of displaying their information. For instance, students may choose to present a storyboard, comic book, PowerPoint, essay, or a brief film. Assess students based on their holistic understanding of how useful gas oils are made from crude oil through a series of important chemical processes.
Have students explore what octane ratings for gasoline signify concerning the product. There are quite a few misconceptions that students may have. After a lesson, encourage students to survey their parents, teachers, and other drivers about what they know about octane ratings of gasoline. You and your students can review Discovering the Science of Petrol to learn more about octane.