Alternative Forms of Energy : Part II
I had previously written a blog entitled What Will be Powering Our Cars in the Future? and since them some people have asked me to produce/write a second blog expanding the on the ideas presented in the first blog. In this particular blog I will discuss in more detail certain aspects presented the previous blog as well as presenting new information like the pros and cons on the use of Ethanol based fuels.
I would like to note before the discussion begins that I am a physicists and not a chemist, but I do play a bad chemist here at allpar. Therefore I have asked for the help from jstwe314 (a member here at allpar) who has a degree in physics but has worked as a chemist for many years. jstwe314 has added a lot (and I mean a lot) of information here on the actual chemistry behind certain reactions that I will be discussing. And I would also like to personally thank jstwe314 for all of his insight into this particular field.
This blog will be broken down into five sections; the chemistry behind the reactions of certain hydrocarbons, the pros and cons on the use of Ethanol, the facts about the use of hydrogen as a source of fuel, the physics behind particular alternative forms of energy, and why all of this is not the final answer for energy independence.
_______The Chemistry behind the Reactions of certain Hydrocarbons_______
In order for us to understand why there is a need for alternative sources of energy or how they actually work, let us first describe to you some basic principles of gasoline. For starters here are some notes about Gasoline.
Gasoline is is made up almost entirely of hydrocarbons, which are molecules made up of carbon and hydrogen. Hydrocarbons present in gasoline usually have between 6 and 12 carbon atoms in each molecule. A good average is probably octane, which has eight carbon atoms and 18 hydrogen atoms and is written C8H18. (Note: sugars are hydrocarbons with oxygen….interesting)
When a hydrocarbon is burned (that is, reacted with oxygen), it forms carbon dioxide (CO2) and water (H2O). For our “average” gasoline of C8H18, the reaction is 2 molecules of octane reacting with 25 molecules of oxygen (O2) to form 18 molecules of water (18*H20) and 16 molecules of carbon dioxide (16*CO2).
Of course, this reaction only occurs completely in an ideal world. In the real world, there is usually not quite enough oxygen available or fast enough inside your car’s engine to allow the reaction to occur completely, so there is also some carbon monoxide (CO) formed as well.
In addition, since the oxygen is provided by bringing air into the engine, and since air consists mostly of nitrogen, some oxides of nitrogen (NO#) are formed as well. Finally, some of the trace elements in the gasoline (such as sulfur) can react to form small amounts of other pollutants, such as SO2 or sulfur dioxide.
In summary gasoline is a mixture of:
- Natural or straight run gasoline, that is, distillate in the temperature range 40-205 degrees Celsius, C5-C10 and cycloalkanes, like cyclohexane C6H12.
- Reformate, that is, n-alkanes and maybe olefins rearranged to branched alkanes, methyl- and ethyl- groups on straight chain alkanes.
- Aromatics, like benzene, C6H6.
- Oxygenates and octane boosters like MTBE (methyl tertiarybutyl ether) and ethanol.
- Proprietary additives and detergents for corrosion control and fuel system.
- Anti-oxidants, metal deactivators, deposit modifiers, surfactants, freezing point depressants, and corrosion inhibitors.
- There are over 500 different hydrocarbons present in gasoline.
Question: How is the heat produced in combusting hydrocarbon fuels apportioned between the carbon and the hydrogen present in the fuel?
Answer: It all depends on the fuel. Let us look at different types of fuels or hydrocarbons.
For a gasoline (say C7H16) fueled vehicle 39% of the power comes from the hydrogen, and 61% from the carbon. Gasoline averages 2.3 hydrogen atoms per carbon atom.
For a diesel (say C12H26) fueled vehicle 38% of the power comes from the hydrogen, and 62% from the carbon. Diesel fuel averages 2.2 hydrogen atoms per carbon atom.
How are these percentages actually calculated? ***Note*** for the purposes of this website, we have answered this question (percentages) assuming it is an accounting problem. Take these values with a grain of salt.
A procedure to calculate the heat released in combustion of an alkane hydrocarbon is to multiply the number of carbon atoms per molecule by 100.7 kcal/mol and multiply the number of hydrogen atoms per molecule by 28.4 kcal/mol and add.
Sample Calculations:
1. Natural gas, methane, CH4: 100.7 + 4(28.4) = 100.7 (energy from the carbon atom) + 113.6 (energy from the hydrogen atoms)= 214 kcal/mol in total from methane.
Percent heat from hydrogen = 113.6/214 = 53%
2. Propane, C3H8: 3(100.7) + 8(28.4) = 529 kcal/mol
Here is a table with the above examples plus more; H. of C. = Heat of Combustion.
|
# Carbon Atoms |
# Hydrogen Atoms |
Name |
H. of C. (kcal/mol) |
H. of C. (BTU/gal) |
% of Heat from Hydrogen |
|
1 |
4 |
Methane |
213 |
121,459 |
52 |
|
3 |
8 |
Propane |
530 |
84,448 |
43 |
|
8 |
18 |
Octane |
1318 |
114,194 |
39 |
|
12 |
42 |
Dodecane |
1947 |
125,881 |
38 |
For a NGV like the Honda GX, 53% of the power comes from the hydrogen in the natural gas, and 47% from the carbon. So the GX could, just barely, be called a MHFV (mostly hydrogen fueled vehicle). Natural gas is mainly methane (CH4) and there are 4 hydrogen atoms per carbon atom, the largest ratio for any hydrocarbon fuel.
Summary:
- For more information on the chemical makeup of gasoline, please visit this website.
- Gasoline may be plentiful today, but I think that we can all agree that fossil fuels will not be around forever. For reasons backing up this statement, see my previous blog.
- We as a society should focus our attention for finding new sources of oil and natural gas as well as finding new alternative sources of energy because of the previous statement.
- A very hot topic as of late is the use of Ethanol to help run our automobiles. I will continue with the current topic of this blog and discuss possible pros and cons of Ethanol in the next section.
_______The Pros and Cons on the Use of Ethanol_______
The Facts:
Ethanol consists of hydrocarbons with the addition of oxygen or C2H5OH. Ethanol is also commonly known as ethyl alcohol, alcohol, or grain spirit. Ethanol is a clean-burning alcohol produced by bacteria that ferment the sugars in corn and cornstalks as well as other products.
Pros:
- Since ethanol is an alcohol based product, it does not produce hydrocarbons when being burned or during evaporation. This is great since hydrocarbons contribute to the formation of ground level ozone or O3 (a greenhouse gas).
- Aldehyde emissions from the combustion of ethanol blends are slightly higher than when burning gasoline. An aldehyde is a compound containing a carbonyl group with at least one hydrogen attached to it. R-C=O where R may be some hydrocarbon or hydrogen atoms. However, The Royal Society of Canada termed the possibility of negative health effects caused by aldehyde emissions from the use of ethanol blends as being “remote”.
- By adding ethanol, which contains oxygen, combustion in the engine is more complete and CO is reduced. Research shows that reductions may reach as high as 30% depending on the type and age of the automobile, the emission
system used, and the atmospheric conditions. Ethanol blends dramatically reduce emissions of hydrocarbons, a major contributor to the depletion of the ozone layer. - High-level ethanol blends reduce nitrogen oxide emissions by up to 20%.
- High-level ethanol blends can reduce emissions of Volatile Organic Compounds (VOCs) by 30% or more (VOCs are major sources of ground-level ozone formation).
- As an octane enhancer, ethanol can cut emissions of cancer-causing benzene and butadiene by more than 50%.
- Sulphur dioxide and Particulate Matter (PM) emissions are significantly decreased with ethanol. (Note: Sulphur is found only in gasoline and not from Ethanol itself.)
- Ethanol has a pleasant smell.
Cons:
- 1.5 gallons of ethanol has the energy of 1 gallon of gasoline. (Conventional Gasoline = 5.253 MBtu/Barrel and Fuel Ethanol = 3.539 MBtu/Barrel where M = million)
- It takes 3 units of input energy to make 4 units of ethanol energy. Therefore, a gallon of ethanol replaces only 2/3 of a gallon of gas, and making it requires the fossil energy in about 1/2 a gallon of gas. In summary one must make 6 gallons of ethanol to save the fossil energy in one gallon of gas. This is expensive using US corn but much cheaper with Brazilian sugar cane or beets.
- With 15,000 square miles of land devoted to ethanol, we reduce our energy dependence by just over 1/4 of 1%.
- To achieve independence would require 50% more land than in the US counting Alaska.
- Ethanol production or the production of corn is not good for the soil; corn uses more nitrogen fertilizer than other crops, which pollutes our waterways.
- There are other cons related to the refining processes that I am exactly not familiar with.
_______The Facts about the use of Hydrogen as a Source of Fuel_______
I am not going to go into stating whether or not we as a society should place our energy (not a pun) into using or not using Ethanol as a temporary replacement for gasoline. But I will continue the blog by talking about a possible next generation of fuel, which of course would be hydrogen, another very current hot topic.
I am also just going to give you some facts about hydrogen like; what it actually is, where it comes from, and how we will begin to use it.
- Hydrogen must be stored at extremely low temperatures and high pressure. A container capable of withstanding these specifications is larger and more expensive than a standard typical gas tank. Hydrogen storage could be viewed as a problem by consumers.
- The heat or energy would be obtained from the combination of two hydrogen atoms with one oxygen atom or 4H + O2 -> 2H2O. The formation of water is in a lower energy state relative to the atoms in an unbounded state therefore this reaction is exothermic and energy is released.
- Ideally if this could be utilized, using hydrogen as a fuel, this would be a true renewable source of energy. Hydrogen stored in the car would react with oxygen from the air creating water or H2O. The water would be released into the environment for us to use again at a later date.
- Today, hydrogen is mostly extracted from natural gas, making it a fossil fuel product. The mining of the gas and the hydrogen extraction process are not pollution free, even if fuel cell powered cars
essentially are.
- In order for the hydrogen to be truly “renewable” or “green,” it would have to be produced from water by electrolysis. Electrolysis requires a large amount of electricity, though, so the source of the electricity would also need to be renewable and clean if the whole process is to be.
- We must put the same amount of energy into gathering hydrogen as we will get out of it when we use it. Therefore the entire process has a net efficiency is 0%.
- The reader should then ask the question: If we have to burn or use fossil fuels to make hydrogen, what have we really gained?
_______The Physics behind Alternative Forms of Energy_______
Turbines:
The majority of electricity today is produced by burning coal or oil to heat up water. The water is converted into high temperature and high pressure steam through different stages of boiling and super heating within the confines of the boiler tubes. This high pressure, high temperature steam then passes through a main steam pipe to the turbine. A turbine is a rotary engine that extracts energy from fluid flow. It converts mechanical energy from fluid flow, and for more information on a turbine find it under Wind and Hydro-electric power.
As we discussed in the previous section, we learned that if we were to obtain hydrogen from water, we must then use electrolysis to extract the hydrogen. This means that we must burn fossil fuels in order to obtain hydrogen from the renewable source of water. One way for us to get around the use of fossil fuels, in this instance, is to find or use other alternative sources of renewable electricity. Examples of these include wind, hydro-electric, and solar power.
Wind and Hydro-electric Power:
Uses Faraday’s law which states that electricity (or moving charges) is produced when the field of a magnetic field is changing in time.
A turbine has magnets connected to its moving parts and as a windmill spins its blades or water moves through a damn, this causes the magnets to move. The magnets move around some copper wires, say, which generates electricity in the wires.
Solar Power:
Uses the photo-electric effect that was first discovered by Einstein (he won his Noble prize for this)
A photon hits the metal which releases an electron, the electron moves producing current thus electricity. This is a completely free, natural, and renewable source of energy. Drawbacks include: a bad efficiency of current solar panels, the cost in constructing solar panels, the need for huge land areas of solar panels to generate enough energy for them to be productive.
Follow the links provided for more information on the the physics behind each idea presented and Click here for more information on different types of Energy Sources
_______Why all of this is not the Final Answer for Energy Independence_______
Unfortunately the world is not just black and white….there are a lot of shades of grey. For all of the positive benefits of Ethanol there are equally huge drawbacks in my opinion.
Hydrogen gas also has its drawbacks in its current form, the fact that we must use natural gas or methane in order for us to gather hydrogen. If hydrogen is to be obtained from water then a massive amount of electricity must be used. Currently, electricity is produced from fossil fuels. It is like a never ending deadly cycle. We as a society cannot seem to end the cycle of using fossil fuels to run our cars, cool or heat our homes, surf on the internet to listen to some lunatic talk about energy. It is like there is no end to the cycle or we are just not smart enough to find a break.
The only way I see it, if we want to reduce our dependency on fossil fuels is the use of Nuclear power. I am not going to discuss the pros and cons of Nuclear power, we all know what they are; cheap power, wonderful efficiency, harmful by-products with no place to store them, etc.
The other way for us to break the cycle is for us to fund more research into fusion reactors. Unlike Nuclear (or fission) reactors the by-products of fusion are not harmful, 4 hydrogen atoms are smashed together to get one helium atom. This technology has been used in bombs (the H-bomb) which have a great destructive power with more output energy relative to the older nuclear (or fission) bombs. The current problem for us is that we are unable to gather and use the output energy. Hopefully current researchers and engineers will be able to solve this among other problems with this particular form of energy.