The goal of this process is to produce antiknocking compounds which can be used as engine fuels. Alkanes and alkenes building and cracking formulae. Branched alkanes differ from continuouschain alkanes in that carbon chains substitute for a. Chapter 2 alkanes organic chemistry chm 207 chapter 2 alkanes structure nomenclature subtopics physical properties reactions free radical substitution. The resulting hydrocarbon mirrors its monomers in structure, but is of greater molecular. The zeolites used in catalytic cracking are chosen to give high percentages of hydrocarbons with between 5 and 10 carbon atoms particularly useful for petrol gasoline. In organic chemistry, an alkane, or paraffin a historical name that also has other meanings, is an acyclic saturated hydrocarbon. The cracking and reforming of crude oil fractions presentation free download as powerpoint presentation. Catalytic cracking processes have evolved over the years, and are an exemplary display of che. As the comments have mentioned, it probably begins by the protonation of butene impurities. They consist of the elements carbon and hydrogen, and all the bonds between the carbon atoms are single bonds. Petrol and other fuels are produced from it using fractional distillation.
In industry the fractions obtained from the fractional distillation of crude oil are heated at high pressure in the presence of a catalyst to produce shorter chain alkanes and alkenes. We look at how larger alkane molecules are cracked. Cracking does involve breaking a strong cc bond in the alkane to produce smaller molecules. Petroleum is converted to useful products such as gasoline in three steps.
When the chain is broken, each carbon gains an electron from the covalent bond, forming free radicals then forming alkanes and alkenes useful for polymers. During the cracking process decane which has 10 carbon atoms can be cracked into pentane, ethane and which alkene. This allowed direct determination of adsorption thermodynamics and intrinsic rate parameters. Alkanes formula, definition, structure, properties, videos. Molecular and detailed isotopic structures of petroleum. Cracking is a very important process used in the petrochemical industry to break down the large hydrocarbons intro smaller hydrocarbons, which burns more easily as fuel. Cracking is essentially the thermal decomposition of hydrocarbons such as alkanes into molecules of smaller carbon number, namely lower alkanes as chemical feedstock for other processes and alkenes for polymer production. The cracking products, such as ethene, propene, buta1,3diene and c 4 alkenes, are used to make many important chemicals. Now, sadly, not all alkanes simple organic compounds are straightchain alkanes. Free flashcards to help memorize facts about alkanes fractional distillation, cracking and combustion other activities to help include hangman, crossword, word scramble, games, matching, quizes, and tests. Cycloalkanes are named as per linear alkanes with respect to the number of carbon atoms e. Since only small amounts of unsaturated hydrocarbons are formed during this process, catalytic cracking is being used for.
Reforming involves the breaking of straight chain alkanes into branched alkanes. Ca11eiii petroleum composition, fractional distillation and major products, cracking and reforming. Alkane is solid, liquid or gas at room temperature depends on the size of its molecules. This forms a mixture of straightchain alkanes and alkenes mainly ethene with a small proportion of branched and cyclic hydrocarbons. This involves sending a stream of the hydrocarbon over the heated catalyst and, like cracking, this must be done in the absence of oxygen to prevent the hydrocarbon from. The alkane is brought into contact with the catalyst at a temperature of about. Cracking is one of the most important reactions in the petroleum industry. Recall from chapter 1 introduction to chemistry that distillation separates compounds on the basis of their relative volatility, which is usually inversely proportional to their boiling points.
Reforming is a similar process to catalytic cracking that is used in. By how much does the combination of cracking and reforming. Kinetic studies of alkane hydroisomerization over solid. Chapter 4alkanes and cycloalkanesquestions flashcards. Cracking hydrocarbons in liquid paraffin with a catalyst.
Ca11eii alkanes uses importance as fuels, as starting materials for synthesis. Nov 27, 2015 year 12 lesson graded outstanding to teach cracking. Is the process of breaking a hydrocarbon chain under very high temp and very high pressure. Molecular and structural formulas the alkanes comprise a series of compounds that are composed of carbon and hydrogen atoms with single covalent bonds. Hydrocarbons in the naphtha stream have roughly the same number of carbon atoms as those in gasoline, but their structure is generally more complex. Simple cyclic alkanes often have a prefix cyclo to distinguish them from linear or branched alkanes.
Jun 30, 2015 crude petroleum refining straight chain alkanes of different sizes cracking isomerization reforming smaller alkanes branched alkanes aromatics petroleum products daily consumption of petroleum in the united states is over 17 million barrels which amounts to close to one billion tons per year. The mechanism of catalytic cracking has not been fully resolved. In reforming or aromatisation, cyclic and acyclic alkanes containing six to eight carbon atoms are heated at about 670 k in the presence of palladium, platinum or nickel as catalyst. Others such as branched and cyclic alkanes are added to the gasoline fraction obtained from the distillation of crude oil to enhance the octane rating. This is a gross oversimplification, and is written to satisfy the needs of one of the uk a level exam boards aqa. Reforming is generally used to turn smaller straight chain alkanes into branched or cyclic hydrocarbons of the same size. Alkanes and alkenes free download as powerpoint presentation. First, crack the vapour of liquid paraffin by passing it over a heated catalyst to produce and collect a mixture of gaseous shortchain hydrocarbons.
In this process straight chain alkanes are converted to cycloalkanes and then to aromatic hydrocarbons. Cracking is used to convert large hydrocarbon molecules into smaller molecules. Steam cracking which produces high yields of alkenes. For example, an alkane with eight carbon atoms has the molecular formula c 8 h 2.
The main reactions that occur in reforming are isomerization and aromatization. Learn vocabulary, terms, and more with flashcards, games, and other study tools. A resource to encourage students to think about the general and molecular formulae of organic compounds, focussing on alkanes and alkenes in particular. These shorter chains are often branched, which gives them a higher octane number. Cracking is conducted at high temperatures, by two processes. The combustion of alkanes, including incomplete combustion. Hydrogen production from simple alkanes and oxygenated. The purpose of catalytic cracking is to produce gasoline from. The simplest alkane, methane, has one carbon atom and a molecular formula of ch 4. A random quiz of practice questions on the structure and naming of alkanes nomenclature. Reforming reforming is a similar process to catalytic cracking that is used in addition to cracking to turn straight chain alkanes into branched and cyclic alkanes.
The catalytic cracking of high molecular weight hydrocarbons to more. Alevel chemistryocrchains, energy and resourcesbasic. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which all the carboncarbon bonds are single. As the chains increase in length the intermolecular forces increase, which increases the boiling point. Included are several structural formula equation examples of cracking alkanes into alkenes, lower alkanes and hydrogen. The hydrocarbons that has carbon carbon single bond. Compared to thermal cracking, catalytic cracking occurs at lower temperatures and pressures, is more selective and flexible, and incorporates a catalyst. Apr 27, 20 cracking alkanes by chemical reactions, mechanisms, organic spectroscopy. For example, in a simple firstorder model for the cracking of linear alkanes, and ignoring hd content, the structure of the molecules can be represented as character or number sequences or bitstrings, with 10010 corresponding to the sequence of c and 12 c atoms mentioned previously. Chemistry 5070 o level chapter 25 power point notes. Cracking is the process of breaking longer chained alkanes down into smaller alkanes and alkenes, sometimes for polymer manufacture, and sometimes to improve octane number. The detailed isotopic structure of the source initially modeled as long alkanes, the intermediates, and the product molecules is followed as a function of the level of conversion due to cracking reactions.
Quiz on naming alkanes practice questions on alkane nomenclature for aqa as chemistry, aqa advanced a level chemistry, edexcel as chemistry, edexcel advanced a level chemistry, ocr as chemistry a, ocr advanced a level chemistry a, ocr salters as. Cracking also helps to solve the supply and demand problem. Many of the substances with longer molecules produced from the fractional distillation of crude oil are cracked. Catalytic cracking in which a catalyst is employed and which produces high yields of branched and cyclic alkanes. The reaction sequence below shows the production of heptane, c 7h16, from fractional distillation of crude oil, followed by cracking, reforming and isomerisation. Using this formula, we can write a molecular formula for any alkane with a given number of carbon atoms. The current theory explaining catalytical cracking is based on ion theory assuming a carbocation intermediate. Pdf chemical mechanisms of catalytic cracking over solid. Simply put, hydrocarbon cracking is the process of breaking a longchain of hydrocarbons into short ones. Cracking reforming turns straight chain alkanes into branched and cyclic. To explain the principles of cracking and reforming and the purposes of these. It will lead you to information on reforming and isomerisation as well as a.
Chemical mechanisms of catalytic cracking over solid acidic catalysts. Different types of reactions with a goal of converting straight chain alkanes into branched hydrocarbons and aromatic compounds. Ca11ei alkanes sources and properties industrial preparations and other sources, cracking of large alkane molecules. Igcse alkanes alkenes 5 cracking alkanes exercise youtube. Cracking and alkenes crude oil, hydrocarbons and alkanes aqa. Cracking crack means break, burst is a process that involves breakdown of long carbon chains into shorter ones. In alkylation, low molecular weight compounds, such as propylene and butylene, are mixed in the presence of a catalyst such as hydrofluoric acid or sulfuric acid a byproduct from removing impurities from many oil products. Catalytic cracking has been in use since the 1930s. The mechanism for butane is shown here, instead of a general n alkane initiation.
Steam cracking plants figures 1 and 2 use a variety of feedstocks, for example. Organic nitrogen and nh 3 are poisons to the acidic cracking catalyst and in this lineup the levels can be kept low, which is a requirement if the cracking catalyst is based on amorphous silicaalumina asa the standard before zeolitic hydrocracking catalysts became more common in the 1970s 93. The reaction between alkanes and chlorine or bromine. Graded with a video link and mark schemes for everything. Cracking is the name given to breaking up large hydrocarbon molecules into smaller and more useful bits. Cracking is a process by which bonds of larger alkanes are broken, producing smaller alkanes. Given this scheme, all alkanes generated in a cracking. The alkane is brought into contact with the catalyst at a temperature of about 500c and moderately low pressures. Thermal reforming alters the properties of lowgrade naphthas by converting. Cracking is used to convert long alkanes into shorter, more useful hydrocarbons. Catalytic cracking an overview sciencedirect topics. Sep 06, 2015 reforming reforming is a similar process to catalytic cracking that is used in addition to cracking to turn straight chain alkanes into branched and cyclic alkanes.
Reforming chemistry britannica encyclopedia britannica. This is achieved by using high pressures and temperatures without a catalyst, or lower temperatures and pressures in the presence of a catalyst. Heating of alkanes in the absence of air leads to carboncarbon bond. What is difference between reforming and cracking answers.
Catalytic reforming is the conversion of low octane naphtha into highoctane reformate products. Reforming, in chemistry, processing technique by which the molecular structure of a hydrocarbon is rearranged to alter its properties. The main difference between catalytic cracking and catalytic reforming is that catalytic cracking gives cracked products whereas catalytic reforming gives reformate products. What is used to indicate the presence of a ring in the structure of an alkane.
What are the differences between reforming and cracking in. Feb 27, 2016 we look at how larger alkane molecules are cracked. A random quiz of practice questions on the structure and. The transformation of longchain hydrocarbons with low octane numbers into branched, cyclic or aromatic compounds with high octane ratings is called catalytic reforming.
If molecules change structure without the number of carbon atoms decreasing, e. In addition, class members name 5 branchedchain alkanes and draw the structures for 3. Cocracking of highdensity polyethylene hdpe and vacuum. Cracking fractional distillation gcse chemistry single science. An introduction to the alkanes including cycloalkanes and their physical properties.
Alkanes alkanes are saturated hydrocarbons contain single. Back to previous page naming alkanes notes repeat quiz. Model the industrial process of cracking larger hydrocarbons to produce smaller alkanes that can be converted into petrol. The first thermal cracking process for breaking up large nonvolatile hydrocarbons into gasoline came into. This involves sending a stream of the hydrocarbon over the heated catalyst and, like cracking, this must be done in the absence of oxygen to prevent the hydrocarbon from combusting. An isomer of butane draw a branched isomer of butane 2. Steak cracking involves heating alkanes from the naphtha and kerosene fractions c 6c 16 to 900c without a catalyst and using steam as a diluent to reduce coking.
Hydrocarbons are compounds made up of carbon and hydrogen and these hydorcarbons form important fuels like petroleum,diesel etc. Sep 27, 2017 therefore, both these reactions are very useful in increasing the octane number of the fuel that is obtained from the refinery. Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful hydrocarbon molecules. Difference between catalytic cracking and catalytic reforming. The process is frequently applied to lowquality gasoline stocks to improve their combustion characteristics. Start studying chapter 4 alkanes and cycloalkanesquestions. Commonly, this is done using a process called alkylation. These alkanes vaporize easily in the engines combustion chamber, without forming droplets and are less prone to premature ignition, which affects the engines operation. Covers thermal and catalytic cracking, ppt file, application questions, answers and an assessed homework activity with mark scheme. The results show that the zeolite confinement mediates enthalpyentropy trade. Isomerization involves heating up straight chained alkanes in the presence of suitable catalysts, so that the chains break. Catalytic cracking is the breakdown of large hydrocarbon compounds into small hydrocarbon molecules with the use of moderate temperatures and pressures in the presence of catalysts.
Reforming an alkane or a cycloalkane means that the amount of carbon atoms stays the same, but the structure does not. Platinum seems to be the best catalyst and so the process is sometimes called platforming. Cracking and alkenes crude oil, hydrocarbons and alkanes. Quiz on naming alkanes practice questions on alkane nomenclature for aqa as chemistry, aqa advanced a level chemistry, edexcel as chemistry, edexcel advanced a. This process effectively converts more of the crude oil into compounds suitable for use as gasoline. Cracking of alkanes cracking is a form of thermal decomposition, which breaks long chain hydrocarbons, many of which are not very useful, into shorter molecules by heating them. An ir operando study article in chemistry a european journal 2421 february 2018 with 38 reads.
However, the cocracking of dissolved plastics has attracted more attention, as the prior stage of pyrolysis is not required. If cracking of long chains takes place under appropriate pressure 46 mpa and temperature 740. Cracking can be achieved at high temperature thermal cracking or with the aid of catalysts catalytic cracking. Cracking of alkanes craking refers to the process where cc bonds in long chain alkanes molecules are broken, producing smaller molecules of alkanes and alkenes. Impact of zeolite structure on entropicenthalpic contributions to alkane monomolecular cracking.
Most reactions of organic compounds take place at or adjacent to a functional group. The cracking and reforming of crude oil fractions presentation. A brief description of the difference between thermal and catalytic cracking of alkanes. Cracking alkanes chemical reactions, mechanisms, organic. It really isnt that rough of a subject if you put the time in. The slideshow describes the process of catalytic cracking. Cracking is the breakdown of a large alkane into smaller, more useful alkenes.
Cracking involves breaking up large alkanes which have too many carbons for petrol into shorter chains that can be used in petrol. As chemistry aqa cracking alkanes teaching resources. Since all alkanes are similar in structure and properties, they are called a homologous series. In order to establish a baseline of behavior against which these reactions may be ranked, we need to investigate the reactivity of compounds lacking any functional groups. Cracking, isomerisation and reforming are usually used to make smaller branched alkanes from the longchained alkanes. Chapter 2alkanes organic chemistry chm 207 chapter 2. Mar 16, 2014 a short organic chemistry lecture on alkanes covering isomerism, formulas and nomenclature. Basically, the above reactions are representative only for thermal cracking, i. In fact, there are several versions of thermal cracking designed to produc. The principle of homology allows us to write a general formula for alkanes. When the chains join together again, they are more likely to be branched. Chemical processing how oil refining works howstuffworks.
The branched chain alkanes in the 6 to 10 carbon atom range are preferred as car fuel. Scribd is the worlds largest social reading and publishing site. A brief look at cracking alkanes in the oil industry. It provides an opportunity to practise drawing displayed structural formulae. Catalytic reforming is the conversion of low octane naphtha. Alkanes with at least 4 carbon atoms can form branched forms.