Yellow Gold and Green Highways:
Recycled Oil as a Solution to the Nation’s Fuel Crisis
Karen L. Johansen
Pace University School of Law
White Plains, NY 10603
LAW 802: Dr. David Rahni
Spring 2004
Abstract
Both gasoline and diesel fuel pose serious risks to the environment and human health, are becoming increasingly more expensive, and promote reliance on foreign oil-producing nations. In addition, the limited supply of crude oil is projected to run out before the twenty-first century is halfway through. Producing fuel from vegetable oil is environmentally sustainable, far less polluting, more economical, and much healthier for humans. The most polluting activity the average person engages in is driving a personal vehicle. Because diesel fuel is chemically similar to vegetable oil, diesel engines can be successfully run on a vegetable oil fuel known as “biodiesel” in its pure form or mixed with diesel fuel, and they can also be run on straight vegetable oil. With little to no vehicle modification, drivers of diesel vehicles can drastically reduce their contribution to air pollution while protecting their health, the environment, and their wallets.
Introduction
Oil has long been referred to as ‘black gold’ because of its source of wealth and seemingly limitless applications. After some thought, it seems that every facet of the life to which we have grown accustomed is cripplingly dependent on some form of oil. Think of all the things that operate because of methane, butane, propane, gasoline, kerosene, diesel fuel, home heating oil, motor oil, grease, asphalt, tar and wax. All these products originate in crude oil. Many cannot imagine a world without even one of these products. However, if the current consumption rate of 24,000,000,000 barrels per year remains constant, the oil supply would run out around 2040. Consumption rarely remains constant; in fact, it increases about two percent per year, and that rate is also increasing. With that in mind, it has been estimated that between 2010 and 2025, all fossil oil products will be too expensive for the average Western consumer (1).
Blind ignorance will not help, although it seems to be that path that most people have chosen. Not only have people not embraced the notion of conservation, but also many are going in the opposite direction, which is evident on every outing. The number of trucks, minivans and SUVs has increased over the years, both in popularity and in sheer size. Oil and gas is big business; there has certainly been no major push from the automobile industry to encourage smaller, more fuel-efficient vehicles. There has been limited introduction of hybrid and alternative fuel vehicles, but nothing of any real significance when balanced with the number of Chevrolet Suburbans and the new GMC XUVs leaving the dealerships.
Everyone agrees that something must be done; but what, and by whom? Everyone agrees that change is necessary, but few are willing to step up and give up some of the comforts of modern life. However, unless we want the next generation to tell their grandchildren how they walked to school, uphill both ways, in all types of weather, and had no lights and no heat when they arrived, a concerted effort to manage our limited resources and develop sustainable technologies must be a priority of utmost importance.
Although government can be woefully slow at effecting significant, meaningful change, individual consumers have the ability, and some would say, the duty, to take actions at the personal level. One such way is to limit usage of petroleum products.
Theoretical Analysis
Hydrocarbons and Fractional Distillation
Crude oil, or petroleum, is the unprocessed oil that comes out of the ground. It is a fossil fuel, made from naturally decaying plants and animals over millions of years. Crude oil contains hydrocarbons, which are molecules made up of hydrogen and carbon in varying shapes and sizes. These molecules can form in chains, branches and rings, in many combinations. Hydrocarbons contain a lot of energy and can take on many different forms. For these two reasons, hydrocarbons have become an essential part of our society. To make the hydrogen carbons useful, however, the crude oil must be processed in a way that separates and sorts the hydrocarbons into similar groups (2).
The process by which hydrocarbons are sorted is called fractional distillation (see Figure 1). The theory behind this process is that longer hydrocarbon chains have progressively higher boiling points as their length increases. In a distillation column, crude oil is heated and different chain lengths are separated by their vaporization temperatures. The more carbons a chain possesses, the higher that chain’s boiling point. For example, petroleum gas, such as methane (CH4), propane (C3H8) and butane (C4H10), have one to four carbon atoms per molecule and a boiling point of less than 40 degrees Celsius. Gasoline, used for fuel, has between five and twelve carbon atoms, is normally in a liquid state at room temperature, and has a boiling range of 40 to 205 degrees Celsius. Diesel fuel, also normally a liquid at room temperature, contains between twelve and twenty-two carbon atoms, and has a boiling range of 250 to 350 degrees Celsius. The longest chains are found in the residuals, such as coke, asphalt, tar, and waxes. These complex molecules contain more than seventy carbon atoms and boil at 600 degrees Celsius and higher. The molecules with more carbon atoms generally contain more potential energy than smaller molecules. For example, diesel fuel, with twelve to twenty-two carbons, generally contains more energy than gasoline fuel with five to twelve carbons (3).
Figure 1: Fractional Distillation (3)
Fractional distillation involves several steps. First, the crude oil is heated, frequently with high-pressure steam at temperatures near 600 degrees Celsius (3). The oil boils, forming a vapor. The vapor then enters the bottom of a tall column filled with trays. Each tray contains many holes to allow vapor to pass through. The column is hottest at the bottom and coolest at the top. When the vapor rises through the column, it cools. As the vapor reaches a point in the column where the column’s temperature equals the vapor’s boiling point, it condenses into liquid form. The liquid is collected on the trays, at which point the fractions are passed to condensers and then to storage tanks, or are sent for further processing (4). The whole process resembles a vertical labyrinth.
Often, there is an overabundance of fractions that boil at higher temperatures, and not enough gasoline to meet the demand. The larger molecules can be broken down into smaller molecules, including gasoline, through a process called cracking. This happens when the larger molecules are heated in the absence of air (2). In Figure 1, a cracking unit has been installed to break down molecules with sixteen to thirty-six carbon atoms into molecules with eight carbon atoms. These smaller molecules are then used in the production of gasoline.
Figure 2: Energy increases with molecule size (5)
Formula / Energy(kJ/mol) / Structure / Formula / Energy
(kJ/mol) / Structure
CH4
Methane / 0.00 / / C6H14
Hexane / 14.53 /
C2H6
Ethane / 3.41 / / C7H16
Heptane / 17.24 /
C3H8
Propane / 6.27 / / C8H18
Octane / 19.96 /
C4H10
Butane / 9.09 / / C9H20
Nonane / 22.68 /
C5H12
Pentane / 11.81 / / C10H22
Decane / 25.39 /
Diesel fuel is heavier than gasoline because it contains more carbon atoms in longer chains. Diesel fuel takes less refining, which is why it is usually cheaper than gasoline. Diesel fuel also has a higher energy density. Generally, larger molecules contain more energy than smaller molecules (see Figure 2). One gallon of diesel fuel contains 147,000 BTU, while one gallon of gasoline contains only 125,000 BTU (6). BTU stands for British Thermal Units. One BTU is “the amount of energy required to increase the temperature of 1 pound of water by 1 degree Fahrenheit, at normal atmospheric pressure. Energy consumption is expressed in Btu to allow for consumption comparisons among fuels that are measured in different units.” For example, one kilowatt hour, or kWh, is the energy needed to use a 100-watt light bulb for ten hours) is a unit of energy (7). One kWh of electricity is equivalent to 3,412 BTU (8).
Gasoline and Diesel Engines
Although the inner workings of vehicle engines are becoming more and more complex, the basics behind gasoline and diesel engines are relatively simple. Gasoline engines are internal combustion engines. They take a small amount of high-energy fuel and ignite it, releasing energy in the form of expanding gas. This energy is used to propel a vehicle. Most cars use a four-stroke combustion cycle (See Figure 3). During the intake stroke, the intake valve opens, and the piston moves down to allow in a cylinder of air and gasoline. In the compression stroke, the piston moves back up to compress the fuel and air. When the compression is complete, the spark plug ignites the gasoline, which explodes, and forces the piston back down. This is the combustion stroke. Finally, the exhaust valve opens and the exhaust leaves the cylinder and goes out the tailpipe. This is the exhaust stroke. This cycle repeats over and over to continue to propel the vehicle. When a driver quickly accelerates, this process speeds up (9).
Figure 3: Internal Combustion (Gasoline) Engine (9)
In a perfect system, internal combustion engines would produce only pure carbon dioxide and water. However, this is not a reality for several reasons. Carbon monoxide is formed when combustion is incomplete. Not enough oxygen is available fast enough to react completely with all of the carbon. Nitrogen is the most prevalent gas in the earth’s atmosphere, comprising approximately 78 percent by volume. Oxygen comprises nearly 21 percent by volume. Thus, there is nearly four times as much nitrogen as oxygen by volume (10). Because of this fact, and the high temperature and pressure in the cylinder, nitrogen and oxygen combine, resulting in nitrogen oxides. Impurities in the gasoline, such as sulfur, can result in the release of sulfur oxides. Additionally, unburned hydrocarbons are released as a result of incomplete combustion (11).
Diesel engines, created in 1895 by Rudolf Diesel of Germany, work differently from internal combustion engines. Diesel engines also use four steps (See Figure 4). First, air enters the chamber. A piston compresses the air to increase its temperature and pressure. Fuel is then injected into the chamber. The heat of the compressed air ignites the fuel, releasing the energy that propels the vehicle. Finally, the exhaust leaves the chamber and the vehicle and the process repeats (6).
Figure 4: Diesel Engine (12)
Diesel engines produce pollutants similarly to gasoline engines. Because diesel fuel has traditionally been less refined, it is a “dirtier” fuel and releases much more soot than gasoline engines. This is not an inherent characteristic of diesel engines; rather, it is the manufacturing of the engines and the fuel itself (13).
There are several main differences between gasoline and diesel engines. Gasoline engines intake a mixture of air and gasoline, compress it, and ignite it with a spark plug. Diesel engines take in just air, and then inject the fuel into the compressed air. Diesel engines have a higher compression ratio than gasoline engines, potentially leading to better efficiency. Gasoline engines use either a carburetor, through which air and fuel mixes before entering the cylinder, or fuel injection, through which fuel is injected just before the intake stroke. Diesel engines use direct injection, whereby the fuel is injected directly into the cylinder (6). Because there is a smaller risk of pre-ignition in diesel engines than gasoline engines, diesels have the potential to run on a wide variety of fuels.
The combustion phase in an internal combustion engine is possible because of the relatively low flash point of gasoline fuel compared to its autoignition point. Flash point is the temperature at which a fuel and air mixture becomes ignitable (14). The higher a fuel’s flash point, the safer it is to store and handle (15). Autoignition point is the temperature at which a substance self-ignites, or spontaneously combusts. Gasoline has a low flash point, below 45 degrees Celsius, so that it will ignite from the spark generated by the sparkplug, but a high autoignition point, 246 degrees Celsius, so that it does not ignite too soon on its own in the engine. Diesel engines are high-combustion engines; air is compressed until its temperature exceeds diesel fuel’s autoignition point, then the fuel is injected, where it self-ignites. Because there is no ignition source in diesel engines, diesel fuel must have a high flash point, over 45 degrees Celsius, and a low autoignition temperature, 210 degrees Celsius (14). Were someone to put diesel fuel in an internal combustion engine, the spark from the spark plug would not raise the fuel above its flash point, and it would not combust. Therefore, diesel fuel is not suitable for a gasoline engine. Conversely, were someone to put gasoline in a diesel engine, the gasoline would not self-ignite, and without a spark, would not combust. For the opposite reason, gasoline is not suitable for a diesel engine.
Gasoline and diesel fuel are mainly comprised of hydrocarbons, but commercial formulas also contain additives such as benzene, toluene, ethylbenzene, and xylene, known as BTEX, and ethanol, methanol, methyl tert-butyl ether, or MTBE. These chemicals are added to improve engine and fuel efficiency (16). However, they have been found to cause cancer and neurological impairment, and have often caused environmental pollution that outweighs its intended benefits (17). A full discussion of these fuel additives is beyond the scope of this paper.
Vegetable Oil as an Alternative Fuel
With a basic understanding of gasoline and diesel engines, it is now appropriate to examine the methods by which a growing number of people are utilizing a more sustainable and cost effective fuel source in their diesel vehicles – vegetable oil.[1] There are three ways to use vegetable oil in a diesel engine; biodiesel, vegetable oil/kerosene mixture, and straight vegetable oil. Each will be discussed in turn.
Biodiesel is a bit of a misnomer, since it contains no petroleum products. Rather, it is a fuel made from 80-90 percent vegetable oil, 10-20 percent alcohol, and less than two percent catalyst. Biodiesel can be used in all diesel engines on its own or mixed with diesel fuel. Using biodiesel requires no vehicle modifications. Pure biodiesel is known as B100. A common mixture is 20 percent biodiesel and 80 percent diesel, known as B20. Both B100 and B20 are commercially manufactured, albeit on a limited scale. Biodiesel can also be made at home, with proper precautions (18). This will be discussed below, after a brief introduction of the basic chemistry involved.
As discussed above, hydrocarbons contain hydrogen and carbon atoms. Alkanes are one type of hydrocarbon. They can be represented by the general formula CnH2n+2. All of the molecules in Figure 2 are alkanes. Note that all of the names end with –ane. All alkanes have certain chemical properties in common. They are less dense than water; when combined, alkanes float at the surface. Alkanes are non-polar molecules. This means that they do not have separate centers of positive and negative charge (as does a magnet) (2). Alkanes dissolve low-polarity molecules, such as fats, oils and waxes. One of the most important properties of alkanes is their ability to burn and produce a great quantity of heat. For this reason, they are excellent fuels. Both gasoline and diesel fuel contain light liquid alkanes (2).
When one hydrogen atom is removed from an alkane, the molecule becomes an alkyl. Functional groups, or groups of atoms that have characteristic chemical and physical properties, attach to alkyl groups. The alkyl then takes on the characteristics of the functional group. The simplest example is methane. (See Figure 5). The formula for methane is CH4. This follows the alkane formula; n=1, 2n+2=4. There is one carbon atom and four hydrogen atoms. Methane, minus one hydrogen atom, becomes methyl. Methyl is an alkyl. Methyl combined with an alcohol group, OH (oxygen-hydrogen), becomes methanol, an alcohol. Methanol is also known as wood alcohol.
Figure 5: Methane, Methyl, and Methanol (19)
Esters are compounds made from a carboxylic acid and an alcohol. The general formula for esters is alkyl+COO+alkyl. Carboxylic acids are a functional group, like alcohols. The general formula for carboxylic acids is alkyl+COOH. Vegetable oils are esters of glycerin and carboxylic acids (2).
Biodiesel is made through a process called transesterification. This literally means changing an ester into a different ester. Through transesterification, vegetable oil is turned into vegetable methyl ester by removing the glycerin molecule from the chain of esters. Glycerin, an alcohol, is what makes vegetable oil thick and sticky. By removing the glycerin, the oil becomes less viscous. To pull out the glycerin, a catalyst, or a substance that starts a reaction, is needed (18).
To make biodiesel, methanol, an alcohol, is mixed with sodium hydroxide (NaOH) or potassium hydroxide (KOH), the catalyst, to create sodium methoxide or potassium methoxide. This is then mixed with the vegetable oil. (See Figure 6). The mixture must then be set aside for eight hours while the glycerin separates. After eight hours, the glycerin can be drained and used as soap if NaOH was used, or as fertilizer if KOH was used. What remains is biodiesel, which can be used in a diesel engine (18).