TheLittlestGuy

In this article, we will discuss the element carbon and the ways in which it moves around our planet. Carbon is the forth most abundant element in the universe and is the basic building block for all life. Carbon atoms are everywhere. In the stone we walk on, the CO₂ in the air, the backbone of polymers, and most importantly, in all life. Without carbon, there would be no life - no you, no me.

For the purposes of this discussion and most practical purposes, I’m assuming that mass cannot be created or destroyed. Since essentially nothing besides energy is entering or leaving the earth, the combined amount of carbon on the earth is constant. It’s like a bank account. If you don’t deposit or withdraw any money, then your balance remains the same. The same is true of carbon on the earth. If no carbon enters or leaves or is created or destroyed, then the total amount is constant. This called the law of Conservation of Mass. Imagine a log of wood inside of a large metal box filled with air. Weight the entire box and its contents. Now seal the box and cut the log up until it is just a pile of sawdust. Weight the box. Now burn the sawdust inside. Weight the box again. The weight is the same as before. Mass is not being created or destroyed when you cut the log up or burn it. It simply changes form. If you were to uniquely label each atom in the original log, you would still be able to find every atom after the log was burned. The atoms would be arranged differently but they would all be somewhere in the box. For example, a carbon atom from the wood’s cellulose would now be a carbon atom in a molecule of CO₂.

[Click the image above to see how atoms move around during chemical reactions but note that they are not created or destroyed. They can all be accounted for. Image courtesy of chemistryland]

carbon problem

So if the number of carbon atoms on the planet is constant no matter what we do, then why is there suddenly a “carbon problem?” The problem is that we are converting a lot of carbon from one form to another. When we burn fossil fuels we don’t create carbon, we just convert it from a hydrocarbon, which was safely buried under the earth’s surface, to CO₂ in the atmosphere which is a greenhouse gas (a gas that basically traps heat in the earth’s atmosphere).

Plants, on the other hand, take CO₂ from the air and make sugars by a process called photosynthesis. The process converts light energy from the sun into chemical energy, which the plant can use later. If this plant is used as sugar for ethanol production or is decomposed by an animal or bacteria, then these carbon atoms that it took out of the air will be released as CO₂ again. See how this is a cycle? Plants are a sort of carbon converter, meaning that they have the ability to remove carbon from the air and store it for a little while. If the plant (or more commonly little phytoplankton that live on the surface of the ocean) die and are preserved in the right way, then they can be transformed over millions of years into a fossil fuel like crude oil. During the last century or two, humans have been finding and burning a lot of fossil fuels and releasing the stored carbon in order to use the stored energy to do work. We are releasing all that carbon that the original plant removed from the atmosphere millions of years ago. The graph below shows how CO2 levels have increased over the last 200 years since humans started burning a lot of fossil fuels.

[Note how quickly humans have changed things. Volcanic activity accounts for the peaks on the far left. Image courtesy of NASA]

The problem that our world is currently facing is that too much of the earth’s carbon is being converted to the form of CO₂ in the atmosphere. The process of a plant or organism removing CO₂ from the air by photosynthesis and then dying and becoming a fossil fuel takes millions of years (thus fossil fuels are non-renewable). But to dig up that fossil fuel and combust it hardly takes any time at all, especially at the pace we are going at. So we’re basically draining a non-rechargeable battery and dumping CO₂ into the atmosphere several times faster than it could ever be pulled back out. Eventually we’ll be out of this free energy and there will be a lot more CO₂ in the atmosphere than we are used to. The carbon cycle is a delicate balance that can swing too far in one direction or the other, potentially eliminating natural life on the planet.

The picture below is a simple diagram of the carbon cycle. The black labels and numbers shows the amount of carbon stored in various parts of the planet. The deep oceans, for example, are the largest carbon sink, storing 38,100 gigatons of carbon. The purple arrows and numbers show how the carbon is moving around our planet. Humans release about 5.5 gigatons of carbon every year from fossil fuels alone. That’s about 40,300,000,000,000 pounds of CO₂ a year, nearly enough gas to fill 1.8 Billion Goodyear blimps or cover the surface of the earth in CO₂ filled ping-pong balls. As CO₂ concentrations in the atmosphere get higher, the average temperature of the earth rises. As the earth’s temperature rises, the oceans become warmer. Cold water can store more dissolved CO₂ than warmer water so the oceans release even more CO₂ into the atmosphere as they warm up. [Have you ever opened a warm coke before and it made a huge mess all over yourself? That’s because the CO₂ that makes the coke fizzy was less soluble in the coke (mostly sugar water) than if the coke had been cold]

[Units are gigatons of carbon. Image courtesy of NASA]

who cares?

Who cares? You do – you just may not fully realize it yet. Currently, we’re releasing far more CO2 into the atmosphere than is being removed. 1.8 Billion Goodyear blimps filled with anything is a lot. The CO2 in the atmosphere will soon reach high enough levels to do serious permanent damage to the earth and its inhabitant (that includes humans). You wouldn’t give your child or grandchild a warm coke and let them deal with the sticky mess. So why would you give them a messy planet to clean up?

What is crude oil and what is all this talk about it? Crude oil is a dark black or brown slurry of different hydrocarbons, some organics, and trace amounts of metals. Hydrocarbons are highly combustible chains of carbon and hydrogen atoms. Hydrocarbon molecules with different length and configuration have different physical and chemical properties. Learn more about hydrocarbons here (link). Compressed and heated organic materials that have died and sunk to the bottom of the ocean (mostly algae and zooplankton) slowly undergo chemical changes over long periods of time to become crude oil. This process is not fully understood and is relatively complicated. Different time lengths, organic material, and conditions change the properties of the oil that results.

Crude oil is extracted from the ground and then separated into different components according to how big the molecules are. Differences in boiling points (which are highly dependent on hydrocarbon chain length) allow for the separation of different components, called fractions, from one another. The process uses the same ideas that distillation uses. If you want to take liquor that’s 20% alcohol and 80% water and make it stronger you can heat it up so that the alcohol vaporizes while most of the water stays as a liquid. If you can capture this alcohol vapor and condense it back into a liquid, it will be a higher percent alcohol by volume. There’s no chemical reaction here, its just a separation technique. A refinery basically separates crude oil (which has millions of unique molecules of thousands of different lengths) into different fractions. The heaviest fractions, like asphalt, have very long carbon chains and are actually solids while shorted chains (as short as just one carbon atom and four hydrogen atoms) are light and are usually gases like natural gas. In between these two extremes are liquid hydrocarbons which are the main components of gasoline, kerosene, heating oil etc. The picture below shows how crude enters a fractionating column and is separated into light and heavy components by chain lengths.

[Click to enlarge. Image from www.energyinst.org.uk/education/coryton/page7.htm]

Different fractions have different uses. Below is a short list of products that come from crude oil with little alteration:

• Petroleum coke
• Sulfur
• Asphalt
• Waxes
• Lubricants
• Alkenes (olefins, which are polymerized into plastics)
• Fuel oils
• Jet fuel
• Diesel
• Gasoline
• Kerosene
• Aromatics (used in chemical production)
• Lights ends (ethane, propane, butane, pentane and other short chain hydrocarbons)
• Natural gas

why is oil used?

Wikipedia [http://en.wikipedia.org/wiki/Petroleum] says that “Due to its high energy density, easy transportability and relative abundance, it [oil] has become the world’s most important source of energy since the mid-1950s.” I think that sums things up well. Thanks wiki. During the 1970’s oil got a great deal of attention because of the energy crisis caused by inconsistent OPEC exports and alternative sources of energy were researched for a while. When it became apparent that finding clean, abundant, and cheap energy was not going to happen for a while and the energy crisis died down, then the focus went back to oil.

Extracting oil from the earth is a difficult process. The earth is quickly running out of easy-to-access oil. Usually less than 50% of the oil in a reservoir can be extracted by current cost effective techniques, so we’re not even getting all of the oil out of current wells. Some energy companies are trying to find new ways to reach oil in existing wells. Most oil is less dense than water so it floats on top of water (like grease sits on top of water when you add water to a dirty cooking pan). But some oil, called heavy oil, is more dense than water and sits lower in reservoirs. Some energy companies may try to pump a liquid that is even denser than this heavy oil into wells and make the heavy oil rise towards the top of the reservoir. The picture below shows what a typical reservoir looks like. Other types of petroleum resources exist. Oil shale and oil sands are far more abundant on the earth but also much more difficult to extract energy from without high costs and potential environmental damage.

[Image from: techalive.mtu.edu/meec/module19/Page1.htm]

production and consumption

Petroleum fuels 90% of transportation vehicles and provides 40% of the United States’ energy (wiki). The top three oil producing countries are Saudi Arabia, Russia, and the United States but most of the world’s readily accessible reserves are located in the Middle East (Saudi Arabia, Kuwait, Qatar, UAE, and Iraq). Venezuela has large reserves of heavy, sour crude (sour crude has a lot of molecules with sulfur atoms in them while sweet crude does not) and currently has the world’s largest refinery according to maximum capacity in barrels of oil per day. The United States, China, and Japan are the top consumers of Crude supplies, but the USA consumes around 20,588,000 barrels a day of crude oil, almost three times as much as the number two consumer, China.

the trouble with oil

The organic material that is found in crude oil sometimes contain sulfur atoms which if combusted turns into SO₂ and then into H₂SO₄, which causes acid rain. Acid rain kills everything from fish to forests. Soot is also produced when molecules containing sulfur are combusted. In an attempt to reduce emissions and the effects of acid rain, sulfur emissions have some of the tightest governmental regulations in the refining industry. LSD, Low Sulfur Diesel is diesel with a sulfur concentration below 500 ppm – the old standard. Ultra Low Sulfur Diesel (ULSD), the required diesel for new trucks starting in 2007, must have sulfur concentrations below 15 ppm. In a few more years, all highway vehicles will use ULSD by law. Below are the stickers you may have seen on diesel gas pumps.

[Image from: http://www.factsonfuel.org/images/labels.jpg]

While it is a step in the right direction to remove sulfur from petroleum before it is combusted, it’s far from enough. The real problem with oil as an energy source isn’t the sulfur, it’s the carbon. When hydrocarbons are combusted they necessarily release CO₂, which is a greenhouse gas. Climate change, a part of which is global warming, has been directly linked to the increased CO₂ levels in the over the last 100 years.

According to wikipedia, “petroleum’s worth as a portable, dense energy source powering the vast majority of vehicles and as the base of many industrial chemicals makes it one of the world’s most important commodities.” If we want to stop climate change, and eventually have a chance at reversing it, we must stop combusting fossil fuels like crude oil. It’s just that simple. How to replace the energy lost by not burning oil is the challenge. It’s a challenge, but not impossible. We’ll have to work in order to find a suitable solution or our grand childen will pay dearly for our mistakes.