Topic: Octane number. Cracking and reforming.

Target group

High school / technical school student

Core curriculum

New core curriculum:

High school and technical high school. Chemistry – basic level:

XIII. Hydrocarbons. Pupil:

9) explains the concept of octane number (LO) and gives ways to increase gasoline LO; translates to what is cracking and reforming and justifies the need to conduct these processes in industry.

High school and technical high school. Chemistry – extended level:

XIII. Hydrocarbons. Pupil:

14) explains the concept of octane number (LO) and provides ways to increase gasoline LO; translates to what is cracking and reforming and justifies the need to conduct these processes in industry.

Old core curriculum:

High school and technical high school. Chemistry – basic level:

XIII. Hydrocarbons. Pupil:

9) explains the concept of octane number (LO) and gives ways to increase the gasoline LO; explains what cracking and reforming is and justifies the necessity of conducting these processes in industry.

General aim of education

The student interprets ON and discusses ways of obtaining gasoline.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• which means ON;

• the concept of octane number;

• ways to increase the octane number;

• practical meanings of the octane number;

• for what purpose and how it is possible to improve the quality of fuel;

• define the concept of cracking and reforming;

• explain what cracking and reforming is practically about;

• justify the necessity of cracking and reforming in industry.

Methods/techniques

• expository

  • talk.

• exposing

  • film.

• activating

  • thought experiment.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in pairs;

• collective activity.

Teaching aids

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers.

Lesson plan overview

Introduction

1. The teacher hands out Methodology Guide or green, yellow and red sheets of paper to the students to be used during the work based on a traffic light technique. He presents the aims of the lesson in the student's language on a multimedia presentation and discusses the criteria of success (aims of the lesson and success criteria can be send to students via e‑mail or posted on Facebook, so that students will be able to manage their portfolio).

2. The teacher together with the students determines the topic – based on the previously presented lesson aims – and then writes it on the interactive whiteboard/blackboard. Students write the topic in the notebook.

3. Health and safety – before starting the experiments, students familiarise themselves with the safety data sheets of the substances that will be used during the lesson. The teacher points out the need to be careful when working with them.

Realization

1. In order to remind you of the previous lesson, the teacher asks the pupils questions, eg. In the range of temperatures during petroleum distillation gasoline is obtained, how they are divided, how many carbon atoms there are hydrocarbons. It reminds you which hydrocarbons are called saturated and unsaturated.

2. The teacher recommends students to prepare an observation journal in abstract. He informs that they will watch the movie „Testing the properties of gasoline and engine oil”. Before this happens, they are to formulate a research question and hypotheses and note them in the indicated place. After the screening, they set together observations, then conclusions, and write them down as well.

3. In reference to the film, the teacher asks the students the question: „Why gasoline can not be extinguished with water?” - there is a discussion.

4. The teacher explains the concept of cracking and discusses the conditions under which this process is carried out. Then, he writes the equation of reactions on the octadecane cracked total formulas with the possibility of obtaining alkanes and alkenes. He also displays on the multimedia board the tetradecane cracking reaction equation. To preserve the students' ability to write equations, the teacher asks the volunteers for an array and recommends writing the heptadekan and nonadekanu cracking.

5. The lecturer explains the concept of octane number. He explains the principle of its determination for gasoline, e.g. ON = 98, ON = 95. He also mentions the cetane number for diesel oil.

6. The teacher discusses ways of increasing the gasoline's ON: adding anti‑knock agents (he discusses examples of anti‑knock agents) and reforming (he explains what this process consists in). Explains the rules for naming branched hydrocarbons on the example of hexane isomers.

7. The teacher uses the text of the abstract for individual work or in pairs, according to the following steps: 1) a sketchy review of the text, 2) asking questions, 3) accurate reading, 4) a summary of individual parts of the text, 5) repeating the content or reading the entire text.

8. At the end of the lesson, the teacher asks students to do an interactive exercise - individual work.

Summary

1. The student indicated by the teacher sums up the lesson, telling what he has learned and what skills he/she has been practicing.

Homework

1. Make at home a note from the lesson using the sketchnoting method.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Octane number. Cracking and reforming.

Cars with a combustion engine are powered by petrol and the ones with compression‑ignition (diesel) engine are powered by gas oil. What are the properties of these two types of fuels?

The quantity of petrol obtained directly as a result of fractional distillation of crude oil is not sufficient to meet the demand for this fuel. That it why it is produced in the processing of hard coal or synthesis gas, or in cracking from the highest fractions obtained during fractional distillation of crude oil. Cracking (crack means break, burst) is a process that involves breakdown of long carbon chains into shorter ones. If cracking of long chains takes place under appropriate pressure (4–6 MPa) and temperature (740‑810 K), without air access, we are dealing with thermal cracking. If molecules with shorter chains are formed as a result of heating (at temp. of about 720 K), under the influence of elevated pressure and in the presence of a catalyst (for example AlClIndeks dolny 3₃, CrIndeks dolny 2₂OIndeks dolny 3₃, aluminosilicates), we are dealing with catalytic cracking. Catalyst makes it possible to decrease temperature and pressure needed during this process. Alkanes and alkenes with shorter carbon chain are formed as a result of cracking of alkanes, for example:

Petrol obtained in the fractional distillation of crude oil is a mixture of hydrocarbons with simple carbon chains, which burns explosively, which is why it cannot be used as a fuel in vehicles. The octane number (ON) is the most significant parameter determining the quality of petrol. It reflects capacity of combustion in a cylinder of combustion engine without detonating (igniting). A mixture of petrol and air ignited by a sparking plug should burn evenly and not too quickly, because too rapid combustion causes uneven engine operation and its premature wear. Patrol of ON = 98 burns like a mixture consisting of 98% of isooctane and 2% of n‑heptane (n‑alkanes have the lowest octane numbers).

The octane number of petrol can be increased using the so‑called antidetonators, which are chemical anti‑knock agents. Iodine and aniline were one of the first of such agents. Employees of General Motors were testing 33,000 different chemical substances within 7 years and in 1922 they discovered and patented the anti‑knock effect of tetraethyllead – a compound with the following formula: Pb(CIndeks dolny 2₂HIndeks dolny 5₅)Indeks dolny 4₄. This substance turned out to be cheap and very effective because ON of petrol was increased from 60 to 96 if merely 0.15 g of this reagent was added to 1 dmIndeks górny 3³ of petrol. However, it was soon realised that highly toxic lead compounds are released into the atmosphere with exhaust gases, posing a threat to people and natural environment. Nowadays, lead‑free petrols are used with antidetonators, mainly ethers, such as methyl tert‑butyl ether (MTBE) and ethyl tert‑butyl ether (ETBE) or alcohols (for example methanol and ethanol).

Reforming is another process used to increase the octane number of petrol. It consists in changing the components of gasoline at high temperature and in presence of catalysis, as a result of which branched and cyclic hydrocarbons (including aromatic ones) are formed. When these hydrocarbons are added to fuel, they increase its octane number. Reforming leads to: isomerization (production of hydrocarbons with the same composition but different structure), cyclization (conversion of chain hydrocarbons into ring hydrocarbons) and aromatization (transformation of chain hydrocarbons into ring hydrocarbons with a specific structure; those who will have extended chemistry curriculum will learn more about these hydrocarbons).

• Petrol is obtained in the fractional distillation of crude oil and needs to be modified before it can become a motor fuel.

• Octane number is a parameter that measures resistance of petrol to knocking.

• Antidetonators are anti‑knock agents, which increase the octane number of petrol.

• Cracking is a method for obtaining petrol from heavier fractions of crude oil distillation.

• Reforming is a methods for obtaining high‑octane components of petrol (branched and ring hydrocarbons) from simple hydrocarbon.