In this movingbed process, highboiling petroleum feedstock is introduced into the reactor. I know cracking is usually used to crack alkanes to get smaller hydrocarbons as they are easier to ignite and alkenesas they have more industrial uses. There are a few things you will need to know about their physical properties in an exam. In english language, it seems only logical to say cyclic alkanes are alkanes, but id like to point out that, according to the iupac, alkanes are acyclic branched or unbranched hydrocarbons, and so, technically, it cannot be. Petroleum is converted to useful products such as gasoline in three steps. The increasing boiling points of the alkane homologous series can be. Reforming is a process involving different types of reactions with a goal of converting straight chain alkanes into branched hydrocarbons and aromatic compounds. There are several types of hydrocarbons formed in this reaction and the products include. Why do long hydrocarbons have higher boiling points. Cracking, in petroleum refining, the process by which heavy hydrocarbon.
The current theory explaining catalytical cracking is based on ion theory assuming a carbocation intermediate. This is lesson 6 of a 6 lesson unit on hydrocarbons. Cracking is used to convert long alkanes into shorter, more useful hydrocarbons. This section of revision science covers getting hydrocarbons from oil. Feb 27, 2016 we look at how larger alkane molecules are cracked. 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. The process converts lowoctane linear hydrocarbons paraffins into branched alkanes. Alkanes alkanes are saturated hydrocarbons contain single.
Alkanes are virtually insoluble in water, but dissolve in organic solvents. 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. Cracking is defined as a process, wherein complex organic molecules namely long chain hydrocarbons or kerogens are broken down into smaller molecules namely light hydrocarbons. 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. Covers thermal and catalytic cracking, ppt file, application questions, answers and an assessed homework activity with mark scheme. 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.
Model the industrial process of cracking larger hydrocarbons to produce smaller alkanes that can be converted into petrol. 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. Cracking of hydrocarbons is illustrated in the below diagram. Making crude oil usefulfractional distillation and cracking. This is a process where straight chain alkanes are turned into branched alkanes and cyclic alkanes are turned into aromatic compounds. As chemistry aqa cracking alkanes teaching resources. Some of these alkanes have the molecular formula of c5h12 and c10h22. Straightchain alkanes, prone to preignition or knocking. The heavy naphtha has an initial boiling point of about 140 to 150 c and a. Other articles where catalytic reforming is discussed. Cracking meaning types of cracking organic chemistry. Explain why the straight chain isomer of c 10 h22 has a higher boiling point than. Cracking hydrocarbons in liquid paraffin with a catalyst.
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. Difference between catalytic cracking and catalytic reforming. Thermocracking is used to break down high molecular mass alkanes into low molecular mass alkanes as well as alkenes using heat and a catalyst. But i really doubt about cracking of benzene as lot of energy is required to destroy the. Cracking and alkenes crude oil, hydrocarbons and alkanes. What follows applies equally to alkanes and cycloalkanes. The cracking products, such as ethene, propene, buta1,3diene and c 4 alkenes, are used to make many important chemicals. Cracking converts large alkane molecules into smaller, more useful, alkane and alkene molecules.
How does it work why is crude oil both important and useless. Naphtha reforming in catalytic reforming, as in thermal reforming, a naphthatype material serves as the feedstock, but the reactions are carried out in the presence of hydrogen, which inhibits the formation of unstable unsaturated compounds that polymerize into higher boiling materials. Cc bonds of larger alkanes are broken producing smaller alkanes suitable for gasoline. The fractionating tower, shown below, shows the temperature gradient which separates the fractions according to their boiling points. It is caused by the breaking of carboncarbon bonds. Reforming is generally used to turn smaller straight chain alkanes into branched or cyclic hydrocarbons of the same size. Catalytic reforming is a chemical process used to convert petroleum refinery naphthas distilled from crude oil typically having low octane ratings into highoctane liquid products called reformates, which are premium blending stocks for highoctane gasoline. 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. First, crack the vapour of liquid paraffin by passing it over a heated catalyst to produce and collect a mixture of gaseous shortchain hydrocarbons. Petrol is a mixture of compounds and so boils over a range of temperatures around 0. Igcse alkanes alkenes 5 cracking alkanes exercise youtube. Modern living is built on crude oil this hub explains how crude oil is changed into the things we use everyday, from petrol to plastic.
What are the economic reasons for cracking alkanes. Reforming an alkane or a cycloalkane means that the amount of carbon atoms stays the same, but the structure does not. The current version explicitly states that alkanes can be cyclic. The alkanes are the most complex of the organic molecules. It also produces high proportions of branched alkanes and aromatic hydrocarbons like benzene. Oct 05, 2011 this feature is not available right now. An alkene is a hydrocarbon that contains a carboncarbon double bond.
May 27, 2009 cracking, isomerisation and reforming are usually used to make smaller branched alkanes from the longchained alkanes. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Cracking always yields low boiling alkenes as the byproducts. 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. Basically, the above reactions are representative only for thermal cracking, i. Catalytic reforming is a chemical process used to convert petroleum refinery naphthas distilled. The slightly higher boiling points for the cycloalkanes are presumably because the molecules can get closer together because the ring structure makes them tidier and less wriggly. Boiling points increase with increasing chain length because of the increasing strength of the intermolecular forces.
Larger hydrocarbon molecules can be broken down into. Reforming reforming reactions are reactions where a straight chain alkane is converted into a branched alkane or cycloalkane to increase the octane number in petrol. Cracking is the name given to breaking up large hydrocarbon molecules into smaller and more useful bits. For the love of physics walter lewin may 16, 2011 duration. How do oil companies use cracking isomerisation and reforming. The alkenes can then undergo polymerisation to make polymers such as plastics while the shorter alkanes are typically used for fuel. 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. Nov 27, 2015 year 12 lesson graded outstanding to teach cracking. Small branched alkanes can not pack as closely together, so they have weak. This is achieved by using high pressures and temperatures without a catalyst, or lower temperatures and pressures in the presence of a catalyst. Catalytic cracking and coking of cycloalkane1octene. The process converts lowoctane linear hydrocarbons paraffins into branched. Many of the substances with longer molecules produced from the fractional distillation of crude oil are cracked.
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. Thermal cracking is achieved at higher temperatures aided by catalysts in catalytic cracking. The purpose of cracking is to produce high demand hydrocarbons. The word zeolite comes from the greek word zein, which means to boil, because. The reaction sequence below shows the production of heptane, c 7h16, from fractional distillation of crude oil, followed by cracking, reforming and isomerisation. Cracking is conducted at high temperatures, by two processes. Thermal cracking is a process in which hydrocarbons present in crude oil are subject to high heat and temperature to break the molecular bonds and breaking down longchained, higher boiling hydrocarbons into shorterchained, lower boiling hydrocarbons. The alkane is brought into contact with the catalyst at a temperature of about 500c and moderately low pressures. Cracking why is crude oil important as a source of new. The products of cracking include alkanes and alkenes, members of a different homologous series. The fractions can then be refined further by cracking, reforming and isomerisation. Cracking, isomerisation and reforming are usually used to make smaller branched alkanes from the longchained alkanes. The reaction sequence below shows the production of heptane, c7h16, from fractional distillation of crude oil, followed by cracking, reforming and isomerisation.
Relative reactivities of alkanes in catalytic cracking reactions. Water vapor and catalyst, mostly aluminosilicates e. The powerpoint includes theory, experiment, and activities to be completed. 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 same principle can be applied to any homologous series. We look at how larger alkane molecules are cracked. The process of breaking higher hydrocarbons with high boiling points into a variety of lower hydrocarbons that are more volatile low. Cracking hydrocarbons in liquid paraffin with a catalyst resource. In chemistry, it is a process of breaking down large alkane into simpler alkenes and alkanes.
The catalytic cracking of high molecular weight hydrocarbons to more. Then test the mixture for unsaturation with bromine water. The process forms a higher proportion of branched and cyclic hydrocarbons than thermal cracking see also reforming and isomerisation below. Journal of catalysis 126, 600609 1990 relative reactivities of alkanes in catalytic cracking reactions yury v. The products of cracking can be any alkanes or alkenes as long as the equation is balanced and the chemicals produced make sense for example, methene does not exist scientists control the type of products formed by controlling the pressure, temperature, amount of reactants and so on and so forth of the reaction. Cracking is a process in which cc bonds of larger alkanes are broken producing smaller alkanes suitable for gasoline. A singleevent microkinetic model semk is applied to model initial coking rates during the catalytic cracking of cycloalkane1 octene mixtures at 693753 k and cycloalkane and 1octene. Cracking cracking is the breaking down of an unsaturated hydrocarbon into smaller hydrocarbons. Model the industrial process of cracking larger hydrocarbons to produce.
As the chains increase in length the intermolecular forces increase, which increases the boiling point. Reforming is a similar process to catalytic cracking that is used in. Petrol and other fuels are produced from it using fractional distillation. The use of thermal cracking units to convert gas oils into naphtha dates from before. Relative reactivities of alkanes in catalytic cracking. Fluid catalytic cracking, introduced in 1942, is the process most frequently used. These unsaturated hydrocarbons are called petrochemicals, that form a variety of useful compounds such as, polyethylene etc. The reaction sequence below shows the production of heptane, c 7h16, from fractional. As you can see in the video opposite, cracking needs a catalyst and a high temperature. The mechanism of catalytic cracking has not been fully resolved. Pdf chemical mechanisms of catalytic cracking over solid. For hydrocarbons of similar molecular mass, branched alkanes have lower boiling. In english language, it seems only logical to say cyclic alkanes are alkanes, but id like to point out that, according to the iupac, alkanes are acyclic branched or unbranched hydrocarbons, and so, technically, it cannot be cyclic at all.
The rate of catalyst greatly depends upon the factors such as the presence of catalyst and temperature. Dec 30, 2017 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. Both these reactions result in the formation of chemicals that improve the performance of fuels as well as enable more exotic compounds to be made. Catalytic cracking an overview sciencedirect topics.
Alevel chemistryocrchains, energy and resourcesbasic. This is being formed either by removal of a hydride ion or by addition of a proton. Year 12 lesson graded outstanding to teach cracking. Explain the variation in boiling points of the alkanes shown. This allows the alkane mixture in crude oil to be separated by fractional distillation. Main difference catalytic cracking vs catalytic reforming. 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. There is huge demand for shorter chain fractions, whereas longer chain fractions are not as useful and are of lower. Thermal cracking is a process in which hydrocarbons present in crude oil are subject to high heat. How do oil companies use cracking isomerisation and. As the relative molecular mass, or number of carbon atoms in an alkane increases, so does its boiling or melting point. In this movingbed process, high boiling petroleum feedstock is introduced into the reactor.
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. Graded with a video link and mark schemes for everything. Catalytic cracking and catalytic reforming are two processes used in the conversion of crude oil into useful products. In petroleum refining, this process is used in the production of petrol, diesel, and gasoline. 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.
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