Published on EGEE 101: Energy and the Environment (https://www.e-education.psu.edu/egee101)

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Lesson 6: Beyond the Barrel

Overview

You drive up to the station, get gas (gasoline), pay for it (hopefully), and you're on your way. That's generally all the thinking we do about our gasoline supply, except when we're faced with price increases, which then sparks complaining. If you've pumped petrol (gasoline) in Europe, however, your fuel costs will be much greater. We wait until Lesson 8 to think about war/security issues that can also cause drastic price increases. Please watch the following introductory (0:33) video.

Dr. Mathews, happy to be filling up his 1992 Toyota at US gasoline prices rather than the standard British price. The picture was taken summer 2001; it was a very good year for cheap gasoline! What is today's price?
Click for the transcript.

Transcript [Dr. Mathews parked his car at a gas station. He gets out of his car and walks over to the pump. As he is talking he puts the pump into the car's fuel hole, fills the tank, and replaces the pump to its holster.] Dr. Mathews: Today we are going to be talking about how we transform crude oil into the useful products we use. Mainly gasoline, as well as jet fuel, petroleum coke. Even medicines, plastics, and cosmetics. We use an awful lot of things in transforming this. There is a lot of requirements too: it has to be environmentally benign, it needs to be environmentally friendly, and of course, it has to make a profit for the industry, too. [Video ends]

This lesson covers what happens to crude oil between the time it gets pumped out of the ground and the time you use it as gasoline. We will look at the transformation of crude oil to gasoline, and the many other products that you use every day, probably without any knowledge that they came from the same source as gasoline.

Lesson Objectives

Your success in this lesson will be based on your ability to do the following;
  • Articulate how crude oil is transported.
  • Articulate how crude oil is transformed into fuels (refinery operations).
  • Discuss fuel changes for vehicle pollution reduction.
  • Discuss fuel chemistry, identify key chemical species.
  • Discuss SPR issues (security/storage approach etc.)

Wake Up Your Brain

Question: Do you agree that we should export crude oil to other nations?

Yes
No

Click for the answer...

ANSWER:
A few years ago this was a question about importing crude oil. We still import but are now a net exporter (how things change). The prosperity of the nation currently requires crude oil as it still powers transportation. As you will see we now are producing more domestic oil and natural gas production. We also produce alternative fuels as well. Tie that in with efficiency improvements in automobiles and we have more oil than we need. We do still import crude oil from Canada, select areas of the Middle East and other nations.

Crude Quality Issues: Viscosity, S Content, density etc

Crude oil is a highly variant natural resource. The quality ranges are similar to coal and depending on the maturation of the crude the quality can be high or low (younger crude's are of lower quality). One of the first indications of quality is color. The variations in oil color can be dramatic, and very indicative of the quality of that crude. Not all crude oil is black - higher quality oils can be golden or amber in color.

Crude oil samples in various bottles.
These crude oil samples are from New Zealand
Credit: Trans-Orient Oil

All the quality measures here are based on the ability to produce the desired products. In the U.S., about 50% of the oil is converted into gasoline. So an oil that produces a higher % of gasoline "cuts" is more desirable and have a higher quality oil. Take note, we have used much of the higher quality crude oil already! Now we need to use the lower quality oils too and the general trend is to use increasingly lower quality crudes. This quality reduction has an impact on how we refine the crude into the desired products.

Viscosity

Viscosity is the resistance to flow. Do not use the term "Thickness" which is a length measurement. The higher the viscosity the slower the liquid will flow and the lower the quality. We have many techniques for measuring viscosity, some of which are quite high-tech. Here is one of the simplest, utilizing one of the testing devices in one of our petroleum labs over in Hosler. Please watch the following (2:41) video.

The race is on.....which of the crude oils will win this viscosity test?
Click for the transcript.

[Video opens with Dr. Mathews standing with a viscometer.] Dr. Mathews: This is a Saybolt Viscometer. There are an awful large number of ways to measure viscosity. This is perhaps one of the simplest. I am going to pour this into a heated reservoir. [Dr. Mathews pours a beaker of Pennsylvania Crude Oil into the machine.] Dr. Mathews: And do the same with the other crude oil. [Dr. Mathews pours a beaker of Gulf of Mexico crude oil into the machine.] Dr. Mathews: The reason the reservoir is heated is because the temperature is a factor that influences viscosity. And now I am going to do a very simple experiment. What I am going to do is yank these chains and we are going to see how long of a time difference it is between the Pennsylvania crude on the left and the Gulf of Mexico crude on the right, to see how much more viscous the Gulf of Mexico crude is. So here we go. [Dr. Mathews pulls two chains which allow the oil to flow through the machine and starts a timer.] Dr. Mathews: As you can see the Pennsylvania crude oil, the higher quality crude oil, the old deep crude oil, is flowing out very rapidly. There is the same quantity in each reservoir and they are at the same temperature. Whereas the Gulf of Mexico, the blacker of the crude oils, is taking much longer to come out. Again, a very easy determination of the quality of the crude oil is the viscosity. [The Pennsylvania crude oil has finished flowing out of the machine.] Forty-two seconds for the Pennsylvania crude, and we are going to be here for a while for the Gulf of Mexico. [The Jeopardy theme plays as we wait for the Gulf of Mexico crude to finish flowing out. Dr. Mathews shows the stopwatch every once in a while. It ends at three minutes and seventeen seconds.] [Video ends.]

Dr. Mathews

The viscosity process is a measure of quality because the chemical structure of the crude influences its flowability. Longer chain molecules, for example, are harder to flow than short chains because of non-bonding interactions. If you have had any chemistry you will recall ionic (type of bonding in salt crystals) and covalent bonding (the type of bonding between 2 carbon atoms). Those are bonding interactions. There are several non-bonding interactions that occur which attract (and repel) molecules. It is the relative strength of these non-bonding interactions that influence the resistance to flow.

Elemental Composition

For coal, we used the correct terminology, which was ultimate analysis. For crude, that terminology we use is Elemental Analysis. Crude oil is complex, it contains C, H, N, S, O, and metals too. But the bulk of the composition is C and H, the rest being the N, S, O, and metals. S is a good indication of the quality of the crude because as the oil is heated underground the weak S-C bond can break, producing H2S (hydrogen sulfide gas). So, older crudes - higher quality - will have lower S content. Higher S crudes also cost more to process as S is a catalyst poison it has to be removed or the extensive catalysts used in the petrochemical industry would be damaged, as would your catalytic converter. The atomic H/C ratio is also an indicator of quality (why?)

Elemental Composition of Typical Crude
Element Percentage
Carbon 84 - 87%
Hydrogen 11 - 14%
Sulphur 0 - 6%
Nitrogen 0 - 1%
Oxygen 0 - 2%

Chemical Structures

Hydrocarbons are molecules that contain only the elements of carbon and hydrogen. These are the bulk of the crude oil. We find 4 types of chemical structures of hydrocarbon in crude oil:

  • Straight-chain
  • Paraffins
  • Branched-chain paraffins
  • Aromatics Naphthalenes

Please watch the following (:08) video. Paraffin - Straight & Branched

We have seen normal (for example n-heptane [1]) and branched (2,2,4 iso-octane) examples of the paraffins. They all have the same formula: CnH2n+2 (n is the number of carbon atoms). For example, in the cetane molecule above, to determine the molecular weight (Mw) you can count the carbons (x 12 the amu of a carbon atom) and count the hydrogen atoms (x 1 amu) and add the numbers together to obtain the molecular weight. Or you can use the formula:

Cetane has 16 carbon atoms (but if we used decane you would know how many carbons it contained, right?) so C16H(2 x 16)+2 OR C16H34 and the Mw is = (12 x 16) + (1 x 34) = 226 amu (atomic mass units).

The paraffins are the desired contents of the crude oil. Long chains (> 60 carbon atoms are wax) used to be used extensively for the production of candles. Now we use the shorter chains produce gasoline, diesel and jet fuel (and many other products). Note that each molecule might have many structural isomers, for example, a molecule containing 10 carbon atoms has 75 structural isomers. If an isomer is an unfamiliar term to you, I'd suggest looking it up online.

Please watch the following (:09) video. Aromatics

Benzene model

Aromatics are found in both crude oil and coal. In crude oil they are now undesirable because of soot production during combustion.

Soot from a diesel engine.
This is soot from a diesel engine.
Credit: JPM

I took the soot picture above with a scanning electron microscope so we can see the very small (>1 micron) spherical soot particles. These spheres join together to form chains of spheres. To give you some idea of the scale: 80 microns is about the width of human hair. Take note that the aromatics have a much lower H/C ratio than the paraffins. The benzene ring contains double bonds (not shown). Aromatics can exist in complex structures containing many rings. The non-bonding interaction between these rings is strong and so pure compounds of 3 rings are solid at room temperature. The equivalent normal paraffin is a viscous liquid under the same conditions.

Please watch the following (:09) video. Naphthenes

Please watch the following (:09) video. Napthalene.
Example of cyclohexane

These are cyclo-paraffins and the example of cyclohexane above looks like a benzene molecule. There are no double bonds within the ring and so every carbon (in this example) has 2 hydrogen atoms bonded to it. Cyclohexane has an interesting boat or chair configuration. Can you see the differences?

Classification

In a similar manner to coal, as the source rock is buried deeper, the temperature increases with increasing depth. Thus, looking at quality indicators allows for a classification system similar to that of coal rank.

Because "old deep" oil provides the highest quantity of gasoline, it is the higher quality crude oil.

Most graphs you are used to seeing or plotting have just 2 axes. This works fine if you're just comparing 2 components, but as you see below, we're comparing 3 general classifications for crude oil compound types. It is the ratio of these compound types (aromatics, paraffins, and naphthenes) that impacts the quality of the crude (in addition to S content, especially when the S is within the aromatic portion, which makes it much harder to remove during refining). So, to plot 3 items on a single graph we use ternary diagrams like the one you see above. At the three apexes, the composition would either be pure (100%) aromatics, pure naphthenes, or pure paraffins (clockwise from top). Along any of the borderlines of this triangle, you're looking at a mixture of just 2 of these components (aromatics – naphthenes or naphthenenes, paraffins or paraffins - aromatics). At any point within the triangle, the crude contains all three components, in varying degrees.

Graphic of a ternary diagram which illustrates the relative percentage of aromatics, paraffins, and naphthenes in crude oil.
This ternary diagram is used to illustrate the relative percentage of three components in crude oil. The patterned band represents the mixture found in the majority of crude oils.
Credit: EJS

Take the example of 50% aromatics to begin with. To plot this point on the graph, you'd create a drop a horizontal line about halfway between the apex (100 %) and the base of the triangle opposite of that apex (0%), representing 50%. You repeat this process to locate the other %'s of the compound types on the graph, and the point you're after is the convergence of those three lines. Thus, the center of the triangle is: 33%, 33%, and 33% of aromatics, naphthalenes, and paraffins– crude oil that would generally fall into the "old shallow" classification. Here is a dynamic example [2].

Crude Oil Transportation

We move crude oil and the finished products (gasoline for example) via a variety of methods: pipeline, tanker, and the multi-wheeled big (trucking) rigs. We are concerned that the transportation be performed safely, and without spillage.

Trans-alaskan pipeline. The pipes are unning above ground through a field
The Trans-Alaskan pipeline stands on stilts to avoid damaging the permafrost (the oil inside the pipeline is hot-which is how it comes out of the ground) and to allow wildlife safe passage.
Credit: NA

By far the best method of transporting a fluid is by a pipeline. Some of these pipelines are very long, such as the 800-mile Trans-Alaskan pipeline, which carries 17% of the domestic production of crude oil. These pipelines are expensive, however, a cost of $8 billion at 1977 rates! The pipeline is cleaned periodically with "pigs" (which are mechanical devices that can travel inside the pipe to remove any wax buildup from the inside of the wall - other pigs check for corrosion etc.) Perhaps we will build a new pipeline (go and take a quick look at this project: Keystone [3]) to bring an improved (upgraded) tar sand obtained crude oil from Canada all the way to Texas.

Keeping these pipelines functioning properly [4] is no small feat.

Pipeline Audio - Click for text description. This will expand to provide more information.
Dr. Mathews: A very significant concern of having the Tran-Alaskan pipeline is preventing leaks. Alaska is just a very beautiful state and there is a great deal of wildlife there; and of course oil is detrimental to wildlife. Some of the leaks, however, are very hard to avoid. A particular case in early 2002 when a local inhabitant of the area was sitting on his back porch, of course drinking, taking pop shots at the pipe. Put about five or six holes into the Trans-Alaskan pipeline causing a great deal of spillage. Things like this are hard to prevent against. It would be awful difficult to protect 700, 800 miles of pipeline. And so this also factors into security risks. It would be very easy to bomb this section of the pipeline. Preventing the movement of oil, a significant amount of crude oil, from getting from Alaska to Valdez.
 Graphical map of Alaska with the pipeline shown going vertically down the center of the state.
Pipelines are an efficient method of transporting oil over land but for sea crossings, oil tankers are still the method preferred although there are some underwater pipelines.
Credit: ANL

Unfortunately, the pipeline ends in Valdez (because it is a relatively deep port, good for tankers, and is free of ice most of the year). Thus, to get the Alaskan crude oil from the state of Alaska to the markets in the rest of the United States requires tankers to carry the fuel the ocean leg of the journey. Generally, this is to the refinery operations on the West Coast (we in the North East get our crude oil from exotic locations such a Nigeria, Saudi Arabia, Venezuela, etc but also from even more exotic locations such as Warren, or Oil City, etc. in Pennsylvania! In 1989 the Exxon Valdez ran aground leaking 11 million gallons of crude oil. This was the worst spill in US history; it resulted in legislation that addressed the transportation of crude oil into US territorial waters (more on the Oil Pollution Act of 1990, later in the lecture).

  A tanker and workers beneath it (they look like ants next to an SUV).
Following the Exxon Valdez spill tankers operating in US waters need to be double hulled. Notice the workers at the bottom of the tanker.
Credit: CONOCO

The US produces a great quantity of crude oil (but it provides only about 55 % of our needs). Our production is only exceeded by that of Russia and Saudi Arabia (normally we are 2nd). Much of it arrives in the country via tanker. Those tankers operating in US territorial waters now need to be double hulled (by 2015) as a strategy to reduce large oil spills. Remember these tankers can be huge.

There are only a few travel "lanes" for the international trade of crude oil. Much of the transportation is via tanker or via pipelines (The World is not Enough-James Bond Movie, splendid). This has major security implications for the safe delivery of a very valuable commodity. The map below shows the important oil flow bottlenecks.

World map showing the crude oil flow and specific bottle points.
World Crude Oil Flows 2013.
Credit: EIA

It is not just transportation of crude oil, or its products, but storage also. We produce (extract) a lot of oil, and we also store a lot of oil and crude oil products. Safety is a concern around all the flammable liquids. Spills inland can be just a devastating as those affecting the coastline. Regulations also require that the retaining walls, which surround the tank, are sufficient to retain the liquid in the event of a failure.

 A crude oil storage facility.  There are large brown tanks all over the hillside.
A tank farm holding the raw crude oil or finished products.
Credit: EIA
Crude oil tank "sunken" into the depression created by and the retaining wall to prevent spills.
More tanks.
Credit: EPA

What you don't see in the image is that the tanks are in a very large depression in the ground (a bit like an empty swimming pool). Should the tanks break, the oil would be retained in the "swimming pool" by the retaining walls.

Oil products have also been leaking into the ground from the storage of gasoline at gasoline stations. Recall the MTBE issues. When you buy a house one of the things the homeowners have to reveal is if there is a storage tank on the property. It is not good news if there is one, as often they need to be removed. You also accept liability if it does leak at a later date.

Road crashes also leak crude oil products like gasoline. The fire trucks carry long buoyant absorbent socks (similar to booms) to prevent gasoline and diesel spills from further contaminating the waterways.

The influence of any spill on the surrounding wildlife depends on the nature and the size of the spill, as well as the ability of the wildlife to avoid the area. Gasoline, for example, will eventually evaporate; diesel and most of the other fuel oils, however, will not evaporate completely.

 Oil truck which is being pulled out of a ditch by a crain.
An oil spill from a road tanker.
Credit: WA

Oil (and oil products) Spills

Oil will seep to the surface and form tar pits, or on the ocean form a small oil slick. These events are natural and occur every day. However, we move large quantities of crude oil and nearly as much in various products (gasoline, jet fuel, etc.) Some spillage due to transportation is going to occur. When it does there are different approaches to cleaning the spill. It comes down to three general approaches: Contain and remove, disperse with chemicals, or do nothing (it will eventually disperse). There are also "spills" as a result of war (First Gulf War), and from drilling, notable the Gulf of Mexico drilling disaster associated with BP's Deepwater Horizon operation [5]. Here is a good article on the relief well that finally stopped the spill. [6] After reading this page you should know how spills are treated and prevented.

 An oil leak reaching the shore.
Picture of an oil leak reaching the shore. Here the oil comes close to shore, where there is a concentration of wildlife.
Credit: EPA
 An off shore drilling location which has caught fire.
Spills can also occur at the drilling location. The oil business remains a dangerous occupation.
Credit: EPA
Picture of workers putting towels on the oil covered water to absorb the oil.
Here man made absorbents are used to collect the oil then it is off to a landfill or to a combustion site. Natural materials such as feathers are also used (fur tends to be hard to obtain!
Credit: EPA
 A boom which is a floating device used as a baracade to stop an oil spill from spreading.
Here a boom prevents the oil from spreading. Some of the booms are even fire retardant. The skirt below the surface and the floatation parts act as a physical barrier. Not as useful in very rough seas.
Credit: EPA
 A dead duck lying on he sand. He is covered in oil.
Birds die for several reasons: drowning (the feathers absorb so much oil the air is displaced resulting in loss of buoyancy), ingesting oil (from preening to remove it), and from hypothermia.
Credit: EPA
 People standing around an oil spill with brooms.
Cleanup tends to be person power intensive and very expensive. The argument comes down to which is cheaper, cleanup or prevention? That debate depends very much on the value you place on environments.
Credit: EPA
  Boats pulling booms to contain an oil spill.
Here the oil can be seen on the surface with booms being used to contain the spill.
Credit: Photo Source
 workers power washing oil off of the shore and into the water.
The cleanup on the shores of Prince William Sound. High-pressure hoses wash the oil from the beach into the water where it is contained by a boom prior to removal.
Credit: Photo Source
  The storage facility for oil which is sorrounded by large containment walls.
Not only is crude oil stored but so are the products. Containment walls prevent jet fuel, gasoline spills from leaving the storage site should the containment vessel fail.
Credit: EPA
 A single hulled tanker which was ripped open.
Double-hulled tankers might have helped prevent an oil spill in this case. Some collisions will produce spills even from double-hulled tankers. Which is safer, all your eggs in few large baskets or many smaller baskets?
Credit: EPA
 A tanker which was involved in a collision.
Shipping lanes are highly congested in many oil exporting areas, collisions are best avoided, as a tanker may require several miles to stop!
Credit: EPA
 A containment area which is sorrounded by containment walls.
Fire at refineries and at storage sites are dangerous to the nearby residents. Containment walls should stop the fire from spreading.
Credit: EPA
 Enormous billows of smoke from an oil spill that was set on fire to remove the pollution.
The fire will help reduce the water pollution at this location but it will produce lots of air pollution. In remote locations (out to sea) fire might be the only choice.
Credit: EPA
 An oil rigger on the north pole.
Some environments are more sensitive than others. Although there is oil in the North Pole area no country owns the land/ice although many maintain a presence there! (Including us Brits!)
Credit: EPA

 

Distillation Video (Petroleum Refining Basics)

Watch this ten minute video about petroleum refining.

Text Version [7]

Refinery Operations

The role of the refinery is very simple. Make a profit for the shareholders and produce an environmentally responsible product.

The method of making a profit is to carefully follow the supply and demand curve for their products.

Products from a refinery are the obvious: gasoline (46%), diesel, jet fuel, & fuel oil and the less obvious (to some of us): asphalt, coke (for the aluminum, iron, and steel industries), chemicals, plastics, & lubricants (including motor oil).

The demand for these products will be dependent on the weather (fuel oil), economy, driving habits (Americans are driving further, and more in the summer), military conflict (jet fuel, etc during the Gulf war and other conflicts), and other suppliers. The quality that a barrel of crude oil produces will also be dependent on the quality of the crude oil, which can be highly variable.

 A refinery reflected in the water in Tampa Florida
A refinery lit up at night in Tampa, Fl. We only have about 100 refineries in the US. Similar to our lack of new construction with utilities (electricity generation), we have not built any new refineries in years. We are at risk of running out of capacity and having to import finished products such as gasoline (assuming other locations will have excess capacity).
Credit: NETL

Major Refinery Components

Separation

Desalination

The first thing to do is clean up the crude oil and take out the water from the oil. An interesting feature of this water contamination is that it contains salt. This is a very corrosive liquid (salt water) and needs to be removed prior to any other processing steps.

Distillation Tower

Distillation is the heart of the refinery operation. It is the location where the crude oil is separated into many "cuts". Often the distillation tower is very noticeable, as it tends to be one of the taller structures at the refinery. The crude oil is separated into certain "cuts" depending on the volatility of the compounds. This occurs as a continual process: crude oil arrives, is stored and sent for separation via the distillation tower. The cuts are blended, or altered to increase the quality or the quantity of the more desirable products.

A distillation tower
A distillation tower, again with me in the lower bottom right to give you a sense of scale.
Credit: EIA

Crude oil is very complex. Some crude oils will contain over 1,000,000 separate compounds. Different isomers, length molecules, sized molecules will be present. It is very difficult and expensive to separate the compounds into pure cuts, so we don't even try. We are content to separate the molecules into an initial series of cuts.

Do you know what factors influence the desirability of different products [8]?

Refinery Products - Click for text description. This will expand to provide more information.
Dr. Mathews: The role of a refinery is to make money for the share holders. It is a billion dollar operation to build one of these refineries and keep it processing. We only have about a hundred of them in the United States and they have to meet a variety of demands and a multitude of products. Now the market for some of these products are very large, such as gasoline. The market for some other products will be much smaller, for example candle wax. However, what they are going to produce depends very much on the quality of the crude oil that comes in. For example, sulfur-rich crude oil is going to take much more work to clean up. That is why they tend to be a lower quality and cheaper. If you are getting lower quality or less mature crude oils then you are going to get less of a gasoline fraction and perhaps more asphalt cuts or other cuts. So what is the desired products depends much on the quality of your crude oil. Because it is what it is naturally going to give you and how much work you are willing to put in to meet the product demand. The bottom line is you have to make money. If you can make more money by selling gasoline, such as in the summer months when Americans drive the most, then that is what you will do. You will increase your gasoline output. In the winter, when you can probably make more money selling fuel oil because there is a higher a demand for things like home heating, which we have already discussed, then that is what you will do. Instead of producing as much gasoline you are going to produce fuel oil. Or in times of the Gulf War, certain refineries will be producing a great deal of military jet fuel. So depending on the weather, depending on the holidays coming up, and driving seasons, and the demand for air travel, which of course diminished somewhat after September eleventh. These all effect what is the desired product coming out of the refinery. And it is variant, so realize what is coming out in America is not necessarily the same for Europe. For example in Europe, they have a great deal of a number of diesel vehicles, so the demand there for more diesel and less gasoline. So all of these things come into play.

Below is a very simplified view of the distillation process. If you find that this topic keenly interests you, then you should consider the 3 credit, 400-level class our department offers just on this subject alone. The processes and products are explained in more detail below the image! Place your mouse over the green text on the image for more information.

The distillation process at a glance. Place the mouse over the green text on the image for more information.
Credit: EIA

The crude oil is heated before entering the distillation tower. In the tower, the more volatile compounds will turn into gases and flow up the tower, and those compounds that have higher volatilization temperatures will remain behind and get hotter. Thus, the top of the tower will have the lower temperatures and the compounds that have the lower boiling points (temperatures). The bottom of the tower will have the less volatile compounds and have the hotter temperature. To ensure good separation there are lots of stages (also called trays) that the volatile compounds may pass on the way up the tower. When the volatiles are cool enough they will turn back into the liquid form. It is the liquid in the trays that will make up the initial cut. A better quality crude oil will yield more of the lighter cuts than the denser cuts. Unfortunately, even the good quality crude oils will not give a 45% gasoline cut from the crude oil which is what is desired (average for the year), thus other processing steps are required to increase the yield. As always, "How stuff works [9]" provides more good information on this topic.

Vacuum Distillation Towers

Some refineries will also operate a vacuum distillation unit to increase the more useful products from the remnants of the atmospheric distillation tower. By lowering the pressure it becomes easier for certain compounds to enter the vapor stage at lower temperatures.

Chemical Processes

Often the gasoline fraction produced by the initial cut in the distillation tower will not be of sufficient quantity or quality for the market and so chemical processing is required to increase the product yield and to ensure appropriate quality and compliance with environmental regulations (which in turn is dependent on market and country location; California, for example, has more stringent requirements than central Pennsylvania).

Cracking

In the past, the longer chain molecules were highly prized for the production of waxes, and while they're still prized for specialty lubricants, the market is not as large as the gasoline market, so some of the long chain molecules will be "cracked" to produce the smaller molecules that are of appropriate length for gasoline production.

  Example of cracking.
Example of Cracking
Credit: JPM

This cracking can be achieved through high temperatures and high pressures or through combined catalysts and temperatures with high pressures. The "ends" of the molecule require capping hydrogen atoms so to achieve this one fragment forms a carbon to carbon double bond that we chemists call an alkene (we call paraffin alkanes).

Gasoline Quality - Revisited

Gasoline quality is often indicated by the octane number. 2,2,4-trimethylpentane is assigned an octane number of 100 (it contains 8 carbons hence the name "iso" octane, compounds can have octane numbers higher than 100), heptane an octane number of 0. The octane number of gasoline indicates the fuel has the same combustion performance in an engine as a certain blend of 2,2,4-trimethylpentane and heptane (i.e., an octane value of 80 has fuel characteristics similar to a blend of 80% 2,2,4-trimethylpentane and 20% heptane). The higher the octane number the less likely the fuel is to "knock", i.e. buying a higher octane number gasoline indicates a better quality fuel.

Lead (tetraethyl lead to be precise) [10]

Lead Audio - Click for text description. This will expand to provide more information.
Dr. Mathews: Lead, or more specifically tetraethyl lead, was added to gasoline to increase the octane number. It's palely branched molecule has a very high octane number. And so it is useful in helping prevent knocking. The secondary use is that the lead would vaporize in the cylinder, and some of it would go out the exhaust, but some of it would help coat the inside of the cylinders. And so a number of cars took advantage of that and used lead as a natural lubrication. Unfortunately, the lead would leave through the tailpipe and would generally concentrate in the brains of young children. Lead in the air would be breathed in and unfortunately does not exit the body. And so high levels of lead, highly detrimental, and actually reduced brain capacity in small children and young children. And so one of the reasons for getting rid of it was the fact that it is detrimental to your health. We have the same problem in houses built before something like 1974 where another lead compound was added to paint for a couple of reasons. One is the pigments in it, you could get some nice bright whites and also that the bugs would not like to eat it very much because of that lead content. The main reason though that lead was taken out of gasoline was that the lead would have coated any catalyst in the catalytic converter, preventing it from working. So prior to the invention of catalysts, catalytic converters for your vehicle, the lead had to be essentially taken out, or actually not added, to the gasoline.

As you'll recall from Lesson 5, was also used as an octane enhancer but has been banned from most of our gasoline back in 1970.

The quality of the gasoline can be increased by reforming, which is either altering the shape (isomerisation) or altering the composition of the molecules. Essentially, the quality of gasoline can be increased by increasing the branched chain producing higher octane numbers.

API's Refining Crude Oil

Click on the image below to open The American Petroleum Institutes Refining portion of "Adventures in Energy". Go through all of the Refining Oil pages.

View of the API Adventrues in Energy webpage.
All About Petroleum. Click here to learn more [11]
Credit: API

 

Lesson 6 Coverage Map

Mouseover the content for more information. When finished here complete the L06 quiz.

Accessible Version (word document) [12]

Deliverable

After looking at this map, please take the L06 quiz.


Source URL: https://www.e-education.psu.edu/egee101/node/525

Links
[1] http://youtu.be/i3ctRVPVTC4
[2] https://courseware.e-education.psu.edu/courses/egee101/flash/ternary.html
[3] https://www.nrdc.org/stories/what-keystone-pipeline
[4] https://www.e-education.psu.edu/egee101/sites/www.e-education.psu.edu.egee101/files/Lesson05/L05_pipelineLeak.mp3
[5] http://www.bp.com/en/global/corporate/gulf-of-mexico-restoration/deepwater-horizon-accident-and-response.html
[6] http://beyondeconomics.org/2010/07/05/gulf-oil-spill/
[7] https://www.e-education.psu.edu/egee101/node/767
[8] https://www.e-education.psu.edu/egee101/sites/www.e-education.psu.edu.egee101/files/Lesson05/desired_products.mp3
[9] http://science.howstuffworks.com/environmental/energy/oil-refining.htm
[10] https://www.e-education.psu.edu/egee101/sites/www.e-education.psu.edu.egee101/files/Lesson05/lead.mp3
[11] http://www.adventuresinenergy.org/Refining-Oil/index.html
[12] https://www.e-education.psu.edu/egee101/sites/www.e-education.psu.edu.egee101/files/Lesson06/Lesson%206%20Coverage%20Map.docx