Cracking is used to convert long alkanes into shorter, more useful hydrocarbons. The process is known as catalytic cracking because it only happens in the presence of a. In this video, we look at how cracking is used to convert long chain hydrocarbons into shorter chain hydrocarbons. The source of the large hydrocarbon molecules is often the naphtha fraction or the gas oil fraction from the fractional distillation of crude oil petroleum. The four general classes of hydrocarbons are alkanes, alkenes, alkynes and aromatics. Use of a catalyst in the cracking reaction increases the yield of highquality products under much less severe operating conditions than in thermal cracking.
The rate of cracking and the end products are strongly dependent on the temperature and presence of catalysts. To solve this supplyanddemand problem, we use a process called catalytic cracking to break the long chain hydrocarbons into shorter, more useful, hydrocarbons. These different carbon chain lengths cause boiling points to vary between different carbon molecules. Furthermore, it should be treated in order to obtain highly effective end products. Why would an oil company want to crack hydrocarbons answers. This process is necessary to cover the increased industrial demand for highgrade fuels, due to the fact that crude oil is not as abundant as necessary. Simply put, hydrocarbon cracking is the process of breaking a long chain of hydrocarbons into short ones. The longchain hydrocarbon alkane molecules are passed over a catalyst either silica or aluminium oxide heated to about 600700 c. Cracking hydrocarbons learn chemistrythe mixture of gaseous shortchain hydrocarbons produced is collected. Catalytic cracking in which a catalyst is employed and which produces high yields of branched and cyclic alkanes. Reforming is described as the processing of straightchain hydrocarbons into branchedchain alkanes and cyclic hydrocarbons for efficien gcse. Thermal cracking gives mixtures of products containing high proportions of hydrocarbons with double bonds alkenes.
Catalysts used in the cracking of crude oil are usually hydrated aluminum silicates. Hydrocarbons and crude oil gcse chemistry combined science. After fractional distillation at atmospheric pressure and a rectification of the previously formed residues in vacuum, a cracking of long chain hydrocarbons is performed. In thermal cracking, high temperatures typically in the range of 450c to 750c and pressures up to about 70 atmospheres are used to break the large hydrocarbons into smaller ones. Cracking is the breakdown of a large alkane into smaller, more useful alkenes. Difference between fractional distillation and cracking. Catalytic cracking long chain hydrocarbon molecules can be broken down into smaller, more useful molecules using a catalyst. Chemistry, multiple choice help asap yahoo answers. Steam cracking plants figures 1 and 2 use a variety of feedstocks, for example.
The first two groups are the most commonly known as they are used to obtain regular petrol or natural gas and in the production of plastic respectively. Jan 24, 2011 can crack long chain hydroarbons such as bitumen not that useful into smaller, more useful hydrocarbons such as petrol, diesel and kerosene. The spread approximates the profit margin that an oil refinery can expect to make by cracking the long chain hydrocarbons of crude oil into useful shorter chain petroleum products. One area of uops expertise is fluid catalytic cracking that breaks long chain hydrocarbons from crude oil into shorter compounds. Oct 14, 2011 fluid catalytic cracking produces a high yield of gasoline and lpg, while hydrocracking is a major source of jet fuel, diesel, naphtha, and lpg. For this reason, we tend to break up the longer chains into lots of smaller chains. Several complex reactions are involved, but the principal mechanism by which long chain hydrocarbons are cracked into lighter products can be explained by the carbonium ion theory. As a result, the smaller fractions are in high demand. Give a reason why longchain alkanes are often cracked. Producing ethanol using crude oil is a completely different process. Such long chain hydrocarbons are cracked to produce alkanes and alkenes which.
Useless, long chain compounds are converted into more useful shorter chain compounds. Nov 14, 2017 in this video, we look at how cracking is used to convert long chain hydrocarbons into shorter chain hydrocarbons. Cracking, in petroleum refining, the process by which heavy hydrocarbon molecules are broken up into lighter molecules by means of heat and usually pressure. Crack spread is a term used on the oil industry and futures trading for the differential between the price of crude oil and petroleum products extracted from it. Since crude oil is a mixture of different components, it should be processed to obtain a better product that has no impurities. Longchain definition and meaning collins english dictionary. Cracking breaks long alkanes hydrocarbons with only single bonds into shorter alkanes and short alkenes hydrocarbons with one or more double bonds. As shorter chain molecules are more flammable and burn with a cleaner flame these are in higher demand.
Short chain hydrocarbons are more flammable and make very good and useful fuels. The more carbons there are in a molecule, the higher the boiling point. Mar 23, 2016 learn complete crude oil refining process from distillation to cracking. The ethene comes from cracking long chain hydrocarbons found in crude oil. First, crack the vapour of liquid paraffin by passing it over a heated catalyst to produce. Cracking hydrocarbons in liquid paraffin with a catalyst. 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. Cracking hydrocarbons learn chemistrythe mixture of gaseous short chain. Thermal cracking is a type of chemical reaction that uses heat to break down long chain molecules into smaller, more reactive, and therefore potentially more useful, molecules. 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. Cracking breaks longchain hydrocarbons into short chain hydrocarbons which are more useful. Cracking is the breakdown of long chain alkanes into smaller hydrocarbons, usually by heating. Cracking hydrocarbons in liquid paraffin with a catalyst resource. Hydrocarbons definition, classes and chain lengths capedcom.
Cracking oil fractions reaction conditions products equations. Learn complete crude oil refining process from distillation to cracking. Crude oil is a mixture of hydrocarbons with different carbon chain lengths. Many of the substances with longer molecules produced from the fractional distillation of crude oil are cracked.
Select three advantages of cracking from the list below. The different carbon chain lengths in different alkanes also serve different purposes in everyday societies. Petrol and other fuels are produced from it using fractional distillation. Wont run out of crude oil as quickly because it can be changed into useful forms. In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or longchain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carboncarbon bonds in the precursors. Notice the long starting hydrocarbon is saturated no double bonds, some of the products are unsaturated.
In the school laboratory, you may have carried out cracking for yourself using liquid paraffin and broken pot. Bunsen valves see diagram below can be made by attaching a 3 cm long. Jun 15, 2016 to solve this supplyanddemand problem, we use a process called catalytic cracking to break the long chain hydrocarbons into shorter, more useful, hydrocarbons. In general, shorter chain hydrocarbons are more useful than longer chains. Its a process in which long chain hydrocarbons are cracked into shorter, more useful chains. Cracking converts longer alkane hydrocarbon molecules into smaller alkane. The majority of the use we get out of crude oil is as fuel. Cracking chemistry mccook, illinois national historic chemical landmarks j. The most common reaction for alkanes is the cleavage of a carbonto carbon. Catalytic cracking an overview sciencedirect topics. Cracking hydrocarbon can be defined as a process which breaks down the long chain of hydrocarbons into the smaller hydrocarbon. Cluster models neglect the longrange structure and may not reveal subtle.
Carbon chain lengths process of fractional distillation. Asked in chemistry, elements and compounds, hydrocarbons. Cracking and alkenes crude oil, hydrocarbons and alkanes aqa. Catalytic cracking involves taking a heavy oil and heating it to a high temperature in the presence of a catalyst. Shove a pipe into it and remove a very heavy sludge like thick pastey oil from the ground. Sep 11, 2017 crude oil is a major source of hydrocarbons that is used to produce fuels. Alkenes are used for other compounds and can be used to make polymers. This cracking requires high temperatures and a catalyst of phosphoric acid in order to work.
Hydrocarbon cracking is the process whereby large and heavy hydrocarbon molecules long chain hydrocarbons are broken down up into simpler and smaller bits as light hydrocarbons short chain hydrocarbons by the breaking a carboncarbon bonds in cracking stock. The mixture of gaseous shortchain hydrocarbons produced is collected and. In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or longchain hydrocarbons are broken. In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carboncarbon bonds in the precursors. Alkenes are reactive molecules that are used to make plastics and other chemicals.
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 long chained, higherboiling hydrocarbons into shorterchained, lowerboiling hydrocarbons. See how crude oil is converted in useful different fractions and how long chain hydrocarbons are converted in branched. Crude oil is a major source of hydrocarbons that is used to produce fuels. The petroleum fractions with shorter carbon chains such as petrol. Making crude oil usefulfractional distillation and cracking.
Gcse crude oil revise the thermal cracking reaction. During cracking, the long molecules break apart, forming smaller alkanes and alkenes. Cracking is the process in which higher hydrocarbons are broken down and converted into lower hydrocarbons. Its only natural that we use long chain hydrocarbons in cracking we want the. An alternative way of cracking longchain hydrocarbons is to mix the vapour with steam at a very high temperature. Only its full of crap and also from lying around there for millions of years under high pressure and emense heat its full of long chain hydrocarbons chains of hydrogen and carbon. Cracking why is crude oil important as a source of new materials. Generally, the rate of cracking and the final products. Crude oil is a mixture mostly of alkanes, both unbranched and branched. North sea oil rig or similar dig a hole under water. Cracking and alkenes crude oil, hydrocarbons and alkanes. Fractional distillation and cracking are two such methods.669 1441 635 687 1247 1496 91 1230 1370 320 142 1155 779 31 665 1271 1500 607 233 1419 497 767 676 265 549 1308 847 886 1239 1002 842 57 566 326