%n average, crude oils are made of the following elements or compounds( Carbon - *+ Hydrogen - + Sulfur - to /hydrogen sulfide, sulfides, disulfides, elemental sulfur0 Nitrogen - less than /basic compounds with amine groups0 Oxygen - less than /found in organic compounds such as carbon dio"ide, phenols, ketones, carbo"ylic acids0 etals - less than /nickel, iron, vanadium, copper, arsenic0 • • •
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Salts - less than /sodium chloride, magnesium chloride, calcium chloride0
$rude %il Crude oil is the term for &unprocessed& oil, the stuff that comes out of the ground. It is also known as petroleum. $rude oil is a fossil fuel, meaning that it was made naturally from decaying plants and animals living in ancient seas millions of years ago -- anywhere you find crude oil was once a sea bed. Crude oils vary in color , from clear to tar-black, and in viscosity , from water to almost solid.
$rude oils are such a useful starting point for so many different substances because they contain hydrocarbons. ydrocarbons are molecules that contain hydrogen and carbon and come in various lengths and structures, from straight chains to branching chains to rings. here are two things that make hydrocarbons e"citing to chemists( •
ydrocarbons contain a lot of energy. )any of the things derived from
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crude oil like gasoline, diesel fuel, paraffin wa" and so on take advantage of this energy. ydrocarbons can take on many different forms. he smallest hydrocarbon is methane /$+0, which is a gas that is a lighter than air. 1onger chains with 2 or more carbons are li3uids. 4ery long chains are solids like wa" or tar. By chemically cross-linking hydrocarbon chains you can get everything from synthetic rubber to nylon to the plastic in tupperware. ydrocarbon chains are very versatile#
he major classes of hydrocarbons in crude oils include( •
!araffins general formula( CnH"n#" /n is a whole number, usually from to 560 straight- or branched-chain molecules can be gasses or li3uids at room temperature depending upon the molecule e"amples( methane, ethane, propane, butane, isobutane, pentane, he"ane $romatics general formula( C%H& ' ( /7 is a longer, straight molecule that connects to the ben8ene ring0 ringed structures with one or more rings rings contain si" carbon atoms, with alternating double and single bonds between the carbons typically li3uids e"amples( ben8ene, napthalene Napthenes or Cycloalkanes general formula( CnH"n /n is a whole number usually from to 560 ringed structures with one or more rings rings contain only single bonds between the carbon atoms typically li3uids at room temperature e"amples( cyclohe"ane, methyl cyclopentane %ther hydrocarbons $lkenes general formula( CnH"n /n is a whole number, usually from to 560 linear or branched chain molecules containing one carboncarbon double-bond can be li3uid or gas e"amples( ethylene, butene, isobutene )ienes and $lkynes general formula( CnH"n'" /n is a whole number, usually from to 560 linear or branched chain molecules containing two carboncarbon double-bonds can be li3uid or gas
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e"amples( acetylene, butadienes
9ow that we know what's in crude oil, let's see what we can make from it.
:rom $rude %il he problem with crude oil is that it contains hundreds of different types of hydrocarbons all mi"ed together. 7ou have to separate the different types of hydrocarbons to have anything useful. :ortunately there is an easy way to separate things, and this is what oil refining is all about.
*he oil refining process starts with a fractional distillation column+
;ifferent hydrocarbon chain lengths all have progressively higher boiling points, so they can all be separated by distillation. his is what happens in an oil refinery - in one part of the process, crude oil is heated and the different chains are pulled out by their vapori8ation temperatures.
!etroleum gas - used for heating, cooking, making plastics small alkanes / to + carbon atoms0 commonly known by the names methane, ethane, propane, butane boiling range = less than 6+ degrees :ahrenheit > +6 degrees $elsius often li3uified under pressure to create 1?@ /li3uified petroleum gas0
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Naphtha or ,igroin - intermediate that will be further processed to make gasoline mi" of 2 to carbon atom alkanes boiling range = +6 to 55 degrees :ahrenheit > 6 to 66 degrees $elsius -asoline - motor fuel li3uid mi" of alkanes and cycloalkanes /2 to 5 carbon atoms0 boiling range = 6+ to C25 degrees :ahrenheit > +6 to 562 degrees $elsius .erosene - fuel for jet engines and tractorsD starting material for making other products li3uid mi" of alkanes /6 to * carbons0 and aromatics boiling range = 26 to C degrees :ahrenheit > C2 to 52 degrees $elsius -as oil or )iesel distillate - used for diesel fuel and heating oilD starting material for making other products li3uid alkanes containing 5 or more carbon atoms boiling range = +*5 to 5 degrees :ahrenheit > 526 to 26 degrees $elsius ,ubricating oil - used for motor oil, grease, other lubricants li3uid long chain /56 to 26 carbon atoms0 alkanes, cycloalkanes, aromatics boiling range = 2C5 to C66 degrees :ahrenheit > 66 to C6 degrees $elsius Heavy gas or /uel oil - used for industrial fuelD starting material for making other products li3uid long chain /56 to C6 carbon atoms0 alkanes, cycloalkanes, aromatics boiling range = C66 to 5 degrees :ahrenheit > C6 to 66 degrees $elsius Residuals - coke, asphalt, tar, wa"esD starting material for making other products solid multiple-ringed compounds with C6 or more carbon atoms boiling range = greater than 5 degrees :ahrenheit > 66 degrees $elsius
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7ou may have noticed that all of these products have different si8es and boiling ranges. $hemists take advantage of these properties when refining oil. 1ook at the ne"t section to find out the details of this fascinating process.
he Eefining ?rocess As mentioned previously, a barrel of crude oil has a mi"ture of all sorts of hydrocarbons in it. %il refining separates everything into useful substances. $hemists use the following steps( . he oldest and most common way to separate things into various components /called fractions0, is to do it using the differences in boiling temperature. his process is called fractional distillation . 7ou basically heat crude oil up, let it vapori8e and then condense the vapor. 5. 9ewer techni3ues use Chemical processing on some of the fractions to make others, in a process called conversion. $hemical processing, for e"ample, can break longer chains into shorter ones. his allows a refinery to turn diesel fuel into gasoline depending on the demand for gasoline. . Eefineries must treat the fractions to remove impurities. +. Eefineries combine the various fractions /processed, unprocessed0 into mi"tures to make desired products. :or e"ample, different mi"tures of chains can create gasolines with different octane ratings.
Photo courtesy Phillips Petroleum Company
An oil refinery
he products are stored on-site until they can be delivered to various markets such as gas stations, airports and chemical plants. In addition to making the oilbased products, refineries must also treat the wastes involved in the processes to minimi8e air and water pollution. In the ne"t section, we will look at how we separate crude oil into its components.
:ractional ;istillation
he various components of crude oil have different si8es, weights and boiling temperaturesD so, the first step is to separate these components. Because they have different boiling temperatures, they can be separated easily by a process called fractional distillation. he steps of fractional distillation are as follows( Photo courtesy Phillips Petroleum Company
Distillation columns in an oil refinery
. 7ou heat the mi"ture of two or more substances /li3uids0 with different boiling points to a high temperature. eating is usually done with high pressure steam to temperatures of about 5 degrees :ahrenheit > 66 degrees $elsius. 5. he mi"ture boils, forming vapor /gases0D most substances go into the vapor phase. . he vapor enters the bottom of a long column / fractional distillation column0 that is filled with trays or plates. he trays have many holes or bubble caps /like a loosened cap on a soda bottle0 in them to allow the vapor to pass through. he trays increase the contact time between the vapor and the li3uids in the column. he trays help to collect li3uids that form at various heights in the column. here is a temperature difference across the column /hot at the bottom, cool at the top0. +. he vapor rises in the column. 2. As the vapor rises through the trays in the column, it cools. . Fhen a substance in the vapor reaches a height where the temperature of the column is e3ual to that substance's boiling point, it will condense to form a li3uid. /he substance with the lowest boiling point will condense at the highest point in the columnD substances with higher boiling points will condense lower in the column.0. C. he trays collect the various li3uid fractions. *. he collected li3uid fractions may( pass to condensers, which cool them further, and then go to storage tanks go to other areas for further chemical processing •
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:ractional distillation is useful for separating a mi"ture of substances with narrow differences in boiling points, and is the most important step in the refining process.
*he oil refining process starts with a fractional distillation column+ On the right0 you can see several chemical processors that are described in the next section+
4ery few of the components come out of the fractional distillation column ready for market. )any of them must be chemically processed to make other fractions. :or e"ample, only +6 of distilled crude oil is gasolineD however, gasoline is one of the major products made by oil companies. Eather than continually distilling large 3uantities of crude oil, oil companies chemically process some other fractions from the distillation column to make gasolineD this processing increases the yield of gasoline from each barrel of crude oil. In the ne"t section, we'll look at how we chemically process one fraction into another.
$hemical ?rocessing 7ou can change one fraction into another by one of three methods( • • •
breaking large hydrocarbons into smaller pieces / cracking0 combining smaller pieces to make larger ones / unification0 rearranging various pieces to make desired hydrocarbons / alteration0
$racking $racking takes large hydrocarbons and breaks them into smaller ones.
Cracking breaks large chains into smaller chains+
here are several types of cracking( •
*hermal - you heat large hydrocarbons at high temperatures /sometimes high pressures as well0 until they break apart. steam - high temperature steam /266 degrees :ahrenheit > * degrees $elsius0 is used to break ethane, butane and naptha into ethylene and ben8ene, which are used to manufacture chemicals. visbreaking - residual from the distillation tower is heated /66 degrees :ahrenheit > +*5 degrees $elsius0, cooled with gas oil and rapidly burned /flashed0 in a distillation tower. his process reduces the viscosity of heavy weight oils and produces tar. coking - residual from the distillation tower is heated to temperatures above 66 degrees :ahrenheit > +*5 degrees $elsius until it cracks into heavy oil, gasoline and naptha. Fhen the process is done, a heavy, almost pure carbon residue is left / coke0D the coke is cleaned from the cokers and sold.
Photo courtesy Phillips Petroleum Company
Catalysts used in catalytic cracking or reforming
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Catalytic - uses a catalyst to speed up the cracking reaction. $atalysts include 8eolite, aluminum hydrosilicate, bau"ite and silica-alumina. fluid catalytic cracking - a hot, fluid catalyst /666 degrees :ahrenheit > 2* degrees $elsius0 cracks heavy gas oil into diesel oils and gasoline. hydrocracking - similar to fluid catalytic cracking, but uses a different catalyst, lower temperatures, higher pressure, and hydrogen gas. It takes heavy oil and cracks it into gasoline and kerosene /jet fuel0.
After various hydrocarbons are cracked into smaller hydrocarbons, the products go through another fractional distillation column to separate them.
Gnification Hometimes, you need to combine smaller hydrocarbons to make larger ones -this process is called unification. he major unification process is called catalytic reforming and uses a catalyst /platinum, platinum-rhenium mi"0 to
combine low weight naptha into aromatics, which are used in making chemicals and in blending gasoline. A significant by-product of this reaction is hydrogen gas, which is then either used for hydrocracking or sold.
$ reformer combines chains+
Alteration Hometimes, the structures of molecules in one fraction are rearranged to produce another. $ommonly, this is done using a process called alkylation. In alkylation, low molecular weight compounds, such as propylene and butylene, are mi"ed in the presence of a catalyst such as hydrofluoric acid or sulfuric acid /a by-product from removing impurities from many oil products0. he products of alkylation are high octane hydrocarbons , which are used in gasoline blends to reduce knocking.
Rearranging chains+
9ow that we have seen how various fractions are changed, we will discuss the
