Cracking, in petroleum refining, the process by which heavy hydrocarbon molecules are broken up into lighter molecules by means of heat and usually pressure. Thermal cracking heats the naphtha fraction with steam at a high temperature about 800c and high pressure. You therefore need to employ high reaction temperatures and catalysts to effect the decomposition efficiently. The principal reactions in catalytic reforming include dehydrogenation of naphthenes to aromatics with significant quantity of hydrogen as byproduct and cracking isomerization of nparaffins into iparaffins. Cracking is the breakdown of a large alkane into smaller, more useful alkenes. In reforming or aromatisation, cyclic and acyclic alkanes containing six to. Cracking is the name given to breaking up large hydrocarbon molecules into smaller and more useful bits. It is found that plasma cracking of hydrocarbons is an effective method for instant hydrogen production, at room temperature and atmospheric pressure, which is just suitable for onboard applications. 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.
Crude natural gas may contain in addition to methane ca. Petrol and other fuels are produced from it using fractional distillation. Cracking, in petroleum refining, the process by which heavy hydrocarbon molecules are broken up into lighter molecules by means of heat and usually pressure and sometimes catalysts. Reforming takes straight chain hydrocarbons in the c 6 to c 8 range from the gasoline or naphtha fractions and rearranges them into compounds containing benzene rings. Basically, the above reactions are representative only for thermal cracking, i. Cracking is the most important process for the commercial production of gasoline and diesel fuel. The process of cracking, increases the relative amounts of the lower hydrocarbons. The cracking and reforming of crude oil fractions presentation.
Cracking does involve breaking a strong cc bond in the alkane to produce smaller molecules. Covers physical properties, london forces, petroleum fractional distillation, cracking, reforming, combustion, and catalytic converters. Light alkanes co2 reforming to synthesis gas over ni based. As chemistry aqa cracking alkanes teaching resources. Cracking and reforming reactions are quite varied in their products e. The process converts lowoctane linear hydrocarbons paraffins into branched alkanes. Since only small amounts of unsaturated hydrocarbons are formed during this process, catalytic cracking is being used for the production of gasoline. Cracking and alkenes cracking is a reaction in which larger saturated hydrocarbon molecules are broken down into smaller, more useful hydrocarbon molecules, some of which are unsaturated. An alkene is a hydrocarbon that contains a carboncarbon double bond. Reforming is generally used to turn smaller straight chain alkanes into branched or cyclic hydrocarbons of the same size. Modern highpressure thermal cracking operates at absolute pressures of about 7,000 kpa. Year 12 lesson graded outstanding to teach cracking. Steak cracking involves heating alkanes from the naphtha and kerosene fractions c 6 c 16 to 900c without a catalyst and using steam as a diluent to reduce coking.
Hydrogen is produced as a byproduct of the reactions. Cracking the hydrocarbons in paraffin to form shorter alkanes and alkenes can be done as a class practical. Alevel chemistryocrchains, energy and resourcesbasic. Feb 27, 2016 we look at how larger alkane molecules are cracked. In the reforming process, multiple chemical processes take place, they include. The blend of sophisticated straight chain, branched, and aromatic hydrocarbons is precise dependent on the temp etc. In chemistry, it is a process of breaking down large alkane into simpler alkenes and alkanes.
Covers thermal and catalytic cracking, ppt file, application questions, answers and an assessed homework activity with mark scheme. In order to convert it into syngas via reforming reactions without prior separation in view of a gas to liquid gtl process, an overall understanding of both ch 4 and higher alkanes dry reforming mechanisms is required for developing catalysts with a. 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 the process of breaking longer chained alkanes down into smaller.
Cracking, isomerisation and reforming are usually used to make smaller branched alkanes from the longchained alkanes. The principal product from catalytic reforming is called reformate, consisting of c 4 to c 10 hydrocarbons. The process of breaking higher hydrocarbons with high boiling points into a variety of lower hydrocarbons that are more volatile low boiling, is called cracking or pyrolysis. Cracking hydrocarbons on a microscale resource rsc education. Dehydrogenization of cyclohexanes to aromatic hydrocarbons. This forms a mixture of straightchain alkanes and alkenes mainly ethene with a small proportion of branched and cyclic hydrocarbons. Learn vocabulary, terms, and more with flashcards, games, and other study tools. For example, hexane can be cracked to form butane and. Many of the substances with longer molecules produced from the fractional distillation of crude oil are cracked. Small branched alkanes can not pack as closely together, so they have weak.
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. The products of cracking include alkanes and alkenes, members of a different homologous series. It also produces high proportions of branched alkanes and aromatic hydrocarbons like benzene. Main difference catalytic cracking vs catalytic reforming. Thermal you heat large hydrocarbons at high temperatures sometimes high pressures as well until they break apart.
Catalytic reforming is the process of converting 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. Reforming is a similar process to catalytic cracking that is used in addition to cracking to turn straight chain alkanes into branched and cyclic. For example, a higher hydrocarbon c 1 0 h 2 2 splits according to the reaction. In thermal cracking, high temperatures typically in the range of 450 c to 750 c and pressures up to about 70 atmospheres are used to break the large hydrocarbons into smaller ones. Catalytic cracking and catalytic reforming are two processes used in the conversion of crude oil into useful products. The mechanism of catalytic cracking has not been fully resolved.
Reforming or aromatisation aromatisation involves reactions of the type, dehydrogenation, cyclisation, and isomerisation. It will lead you to information on reforming and isomerisation as well as a repeat. Cracking is used to convert long alkanes into shorter, more useful hydrocarbons. Cracking hydrocarbons in liquid paraffin with a catalyst. Reforming is the process of increasing the amount of cycloalkanes and hydrocarbons containing benzene rings, to improve octane number. 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. In petroleum refining, this process is used in the production of petrol, diesel, and gasoline. The process is frequently applied to lowquality gasoline stocks to improve their combustion characteristics. Reforming is described as the processing of straightchain hydrocarbons into branchedchain alkanes and cyclic hydrocarbons for efficien gcse. Hydrogen is recycled through the mixture to reduce coking. Modification of alkanes by cracking, isomerisation and reforming. Cracking meaning types of cracking organic chemistry. Graded with a video link and mark schemes for everything.
Cracking is conducted at high temperatures, by two processes. The cracking products, such as ethene, propene, buta1,3diene and c 4 alkenes, are used to make many important chemicals. Isomerism, cracking and reforming flashcards quizlet. Reforming is a processing technique in which the molecular structure of a hydrocarbon is rearranged to alter its properties. Catalytic cracking has been in use since the 1930s. Learn the basics about the cracking of hydrocarbons and why it is done. Thermal cracking gives mixtures of products containing high proportions of hydrocarbons with double bonds alkenes. For the love of physics walter lewin may 16, 2011 duration.
We look at how larger alkane molecules are cracked. Opposite to cracking, reforming is used to create larger molecules of hydrocarbons from smaller ones. Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful hydrocarbon molecules two types of cracking are heat thermal and catalytic the cracked products maybe smaller alkanes, alkenes and hydrogen molecules. You can change one fraction into another by one of three methods. Thermal reforming alters the properties of lowgrade naphthas by converting the molecules into those of higher octane number by exposing the materials. The cracking of hydrocarbons into hydrogen by the action of dielectric barrier discharge plasma is studied. 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. A look at the three processes used by the petrochemical industry to get the most from crude oil fractions. The alkane is brought into contact with the catalyst at a temperature of about 500c and moderately low pressures. Cracking and alkenes crude oil, hydrocarbons and alkanes. However, safety concerns by many teachers and availability of equipment in some schools mean that this key and interesting experiment is often done as a demonstration. Thermal reforming alters the properties of lowgrade. Crude oil cracking reforming and isomerisation youtube.
This is achieved by using high pressures and temperatures without a catalyst, or lower temperatures and. The reforming process takes place in temperature conditions of 500 to 530 degree celsius and 2 to 25 kgcm 2 pressure rating under an influence of a catalyst. The current theory explaining catalytical cracking is based on ion theory assuming a carbocation intermediate. For example, hexane, c 6 h 14, loses hydrogen and turns into benzene. Chemical processing how oil refining works howstuffworks. At fuse school, teachers and animators come together to make fun. Cracking of hydrocarbons is illustrated in the below diagram. This page describes what cracking is, and the differences between catalytic cracking and thermal cracking used in the petrochemical industry. 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. A brief description of the difference between thermal and catalytic cracking of. Difference between catalytic cracking and catalytic reforming. These unsaturated hydrocarbons are called petrochemicals, that form a variety of useful compounds such as, polyethylene etc. 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. In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby.
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. The most commonly used catalysts for catalytic reforming are platinum or rhenium on a silica base. Cracking takes large hydrocarbons and breaks them into smaller ones. Alkanes alkanes are saturated hydrocarbons contain single. Cracking always yields low boiling alkenes as the byproducts. Cracking and alkenes crude oil, hydrocarbons and alkanes aqa. The most commonly used catalyst for catalytic cracking is zeolite. Cracking and reforming effectively increase the gasoline yield from 19% to 47%. 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. Hydrocarbons can be broken down cracked to produce smaller, more useful molecules.
This is achieved by using high pressures and temperatures without a catalyst, or lower temperatures and pressures in the presence of a catalyst. An overall process of disproportionation can be observed, where light, hydrogenrich products are formed at the expense of heavier molecules which condense and are depleted of hydrogen. Petrol containing a high proportion of straight chain alkanes tends to ignite in. Hydrogen production through plasma cracking of hydrocarbons. 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.
78 480 74 272 471 1500 748 429 6 749 1172 846 206 654 760 639 63 952 673 345 213 966 1521 993 1081 1350 487 349 1344 307 339 239 810 759 1412 91 733 431 521 82 882 152 142 294 662 370 698 193 1018 673