User:Milton Beychok/Sandbox

This needs a lot of work yet 

Gasoline or petrol is derived from petroleum crude oil. Conventional gasoline is mostly a blended mixture of more than 200 different hydrocarbon liquids ranging from those containing 4 carbon atoms to those containing 11 or 12 carbon atoms. It has an initial boiling point at atmospheric pressure of about 35 °C (95 °F) and a final boiling point of about 200 °C (395 °F). Gasoline is used primarily as fuel for the internal combustion engines in automotive vehicles as well in some small airplanes. In Canada and the United States, the word "gasoline" is commonly used and it is often shortened to simply "gas" although it is a liquid rather than a gas. In fact, gasoline-dispensing facilities are referred to as "gas stations".

Most current or former Commonwealth countries use the term "petrol" and dispensing facilities are referred to as "petrol stations". The term "petrogasoline" is also used sometimes. In some European countries and elsewhere, the term "benzin" (or a variant of that word) is used to denote gasoline.

In aviation, "mogas" (short for "motor gasoline") is used to distinguish automotive vehicle fuel from aviation fuel known as "avgas".

Gasoline production from crude oil
Gasoline and other end-products are produced from petroleum crude oil in petroleum refineries. It is very difficult to quantify the amount of gasoline produced by refining a given amount of crude oil for a number of reasons:


 * There are quite literally hundreds of different crude oil sources worldwide and each crude oil has its own unique mixture of thousands of hydrocarbons and other materials.


 * There are also hundreds of crude oil refineries worldwide and each of them is designed to process a specific crude oil or a specific set of crude oils. Furthermore, each refinery has its own unique configuration of petroleum refining processes that produces its own unique set of gasoline blend components.


 * There are a great many different gasoline specifications that have been mandated by various local, state or national governmental agencies.


 * In many geographical areas, the amount of gasoline produced during the summer season (i.e., the season of the greatest demand for automotive gasoline) varies significantly from the amount produced during the winter season.

However, from the data presented in the adjacent image as an average of all the refineries operating in the United States in 2007, refining a barrel of crude oil (i.e., 42 gallons or 159 litres) yielded 19.2 gallons (72.7 litres) of end-product gasoline. That is a volumetric yield of 45.7 percent. The average refinery yield of gasoline in other countries may be different.

From a marketing viewpoint, the most important characteristic of a gasoline is its octane number (discussed  later in this article). Paraffinic hydrocarbons (alkanes) wherein all of the carbon atoms are in a straight chain have the lowest octane numbers. Hydrocarbons with more complicated configurations such as aromatics, olefins and highly branched paraffins have much higher octane numbers. To that end, many of the refining processes used in petroleum refineries are designed to produce hydrocarbons with those more complicated configurations.

Some of the most important refinery process streams that are blended together to obtain the end-product gasolines are:


 * Reformate (produced in a catalytic reformer): has a high content of aromatic hydrocarbons and a very low content of olefinic hydrocarbons (alkenes).
 * Catalytically cracked gasoline (produced in a fluid catalytic cracker): has a high content of olefinic hydrocarbons and a moderate amount of aromatic hydrocarbons.
 * Hydrocrackate (produced in a hydrocracker): has a moderate content of aromatic hydrocarbons.
 * Alkylate (produced in an alkylation unit): has a high content of highly branched paraffinic hydrocarbons such as isooctane.
 * Isomerate (produced in a catalytic isomerization unit): has a high content of the branched isomers of pentane and hexane.

In the United States
There is no "standard" composition or set of specifications for gasoline. In the United States, because of the complex national and individual state and local programs to improve air quality, as well as local refining and marketing decisions, petroleum refiners must supply fuels that meet many different standards. State and local air quality regulations involving gasoline overlap with national regulations and that leads to adjacent or nearby areas having significantly different gasoline specifications. According to a detailed study in 2006, there were at least 18 different gasoline formulations required across the United States in 2002. Since many petroleum refiners in the United States produce three grades of fuel and the specifications for fuel marketed in the summer season vary significantly from the specifications in the winter season, that number may have been greatly understated. In any event, the number of fuel formulations has probably increased quite a bit since 2002. In the United States, the various fuel formulations are often referred to as "boutique fuels".

Some of the major properties and gasoline components focused upon regulation by the various national and state or local programs are:


 * Vapor pressure: The vapor pressure of a gasoline is a measure of its propensity to evaporate. Evaporative emissions of the hydrocarbons in the gasoline lead to the formation of ozone in the atmosphere which reacts with vehicular and industrial emissions of gaseous nitrogen oxides (NOx) to form what is called photochemical smog. Smog is a combination of the words smoke  and fog and traditionally referred to the mixture of smoke and sulfur dioxide that resulted from the burning of coal for heating buildings in places such as London, England. Modern photochemical smog does not come from coal burning but from vehicular and industrial emissions of hydrocarbons and nitrogen oxides. It appears as a brownish haze over large urban areas and is irritating to the eyes and lungs.


 * Nitrogen oxides: Various nitrogen oxides (NOx) are formed during the combustion of gasoline in vehicles and the combustion of other fuels in industrial facilities. NOx is one of the ingredients involved in the atmospheric chemistry that produces photochemical smog and, as such, is a prominent air pollutant. In fact, it is one of the six so-called "criteria air pollutants" that are regulated by National Ambient Air Quality Standards (NAAQS) of the United States. The NOx emitted by vehicular engines using gasoline are largely controlled by the use of on-board devices, called catalytic converters, installed on most modern automobiles and other vehicles. They convert the NOx emissions into gaseous nitrogen and oxygen. They also convert any gaseous carbon monoxide emissions into carbon dioxide as well as converting any unburnt gasoline hydrocarbons into carbon dioxide and water vapor.


 * Toxic metals:
 * Tetra-ethyl lead (TEL) —  In the 1920's, petroleum refining technology was rather primitive and produced gasolines with an octane number of about 40 – 60. But automotive engines were rapidly being improved and required better  gasolines, which led to a search for octane enhancers. That search culminated in 1924 in the development and widespread usage of tetra-ethyl lead (TEL), a colorless, viscous liquid with the chemical formula of (CH3CH2)4Pb. The addition of as little as 0.08 volume percent TEL (i.e., 0.8 ml of TEL per litre or 3 ml/gallon of gasoline) in gasolines resulted in significant octane number increases. For about the next 50 years, TEL was used as the most cost effective way to raise the octane number of gasolines. During that period, petroleum refining technology grew until high-octane gasolines could, in fact, be produced without using TEL. Also, in about the 1940's, it was discovered that the lead being emitted in the exhaust gases from vehicular internal combustion engines was a toxic air pollutant that seriously affected human health. Because of its toxicity and the fact that catalytic converters being installed in vehicles could not tolerate the presence of lead, the U.S. Environmental Protection Agency (U.S. EPA) launched an initiative in 1972 to phase out the use of TEL in the United States and it was completely banned for use in on-road vehicles as of January 1996.  Using TEL in race cars, airplanes, marine engines and farm equipment is still permitted. TEL usage has also been phased out by most nations worldwide. As of 2008, the only nations still allowing extensive use of TEL are the Democratic People's Republic of Korea, Myanamar, and Yeman.
 * Methylcyclopentadienyl manganese tricarbonyl (MMT) —  In Canada, MMT has been used as an octane enhancer in gasoline since 1976. It is also permitted for use as a gasoline octane enhancer in Argentina, Australia, Bulgaria, France, Russia, United States and conditionally in New Zealand. MMT is a yellow liquid with chemical formula of (CH3C5H4)Mn(CO)3. According to the U.S. EPA, ingested manganese is a required element of the diet at very low levels but it is also a neurotoxin and can cause irreversible neurological disease at high levels of inhalation. The U.S. EPA has a concern that the use of MMT in gasoline could increase inhalation manganese exposures.  After completing a 1994 risk evaluation on the use of MMT in gasoline, the U.S. EPA was unable to determine if there is a risk to the public health from exposure to emissions of MMT gasoline. As of now (2009), gasoline in the United States is allowed to contain MMT at a level equivalent to 0.00826 g/L (1/32 g/gallon) of manganese. However, there are still many concerns about the possible adverse health effects from the usage of MMT and less than one percent of the gasoline marketed in the United States contains MMT.


 * Other toxic compounds: Gasoline contains some benzene (C6H6) which is an aromatic compound that is a known human carcinogen. For that reason, the amount of benzene in gasoline is limited by environmental regulations. In general, the combustion of aromatics can lead to the formation of other compounds that have deleterious effects on human health, such as aldehydes, butadiene, and polycylclic aromatic hydrocarbons (PAHs). Therefore, the total amount of aromatics in gasoline is also limited by environmental regulations.


 * Olefins: Photochemical smog is formed by various atmospheric chemistry reactions between nitrogen oxides and waht are called reactive hydrocarbons in the presence of sunlight. In the context of photochemical smog formation, some hydrocarbons are more reactive than others. For example, olefins are very reactive and methane is not reactive to any extent. For that reason, the olefin content of gasolines is limited by environmental regulations.


 * Sulfur: Any sulfur compounds in gasoline will result in combustion exhaust emissions of sulfur dioxide to the atmosphere. Such emissions contribute to the formation of so-called acid rain and they also interfere with the on-board catalytic converters and reduce their efficiency. Therefore, the sulfur content of gasolines is limited by environmental regulations.


 * Oxygen: Oxygen-containing compounds called oxygenates such as ethanol with a chemical formula of C2H5OH or methyl tertiary-butyl ether (MTBE) with a chemical formula of C5H12O.

Octane rating
An important characteristic of gasoline is its octane rating, which is a measure of how resistant gasoline is to the abnormal combustion phenomenon known as pre-detonation (also known as knocking, pinging, spark knock, and other names). Deflagration is the normal type of combustion. Octane rating is measured relative to a mixture of 2,2,4-trimethylpentane (an isomer of octane) and n-heptane. There are a number of different conventions for expressing the octane rating; therefore, the same fuel may be labeled with a different number, depending upon the system used. 

Storage stability
Gasoline is insoluble in water but ethanol and water are mutually soluble. Thus, end-product gasolines containing ethanol will, at certain temperatures and water concentrations, separate into a gasoline phase and an aqueous ethanol phase. For example, the adjacent graph shows that phase separation will occur in a gasoline, at temperatures of 5 to 16 °C (40 to 60 °F), containing 10 volume percent ethanol and as little as 0.40 to 0.50 volume percent water.

Gasolines containing less than 10 volume percent ethanol will experience phase separation more easily, meaning that phase separation will occur at higher temperatures and even lower water contents. Gasolines containing more than 10 volume percent ethanol will experience phase separation less easily meaning that the separation will occur at lower temperatures and higher concentration.

Gasoline stored in fuel tanks and other containers will, in time, undergo oxidative degradation and form sticky resins referred to as gums. Such gums can precipitate out of the gasoline and cause fouling of the various components of internal combustion engines which reduces the performance of the engines and also makes it harder to start them. Relatively small amounts of various anti-oxidation additives are included in end-product gasoline to improve the gasoline stability during storage by inhibiting the formation of gums.

Other additives are also provided in end-product gasolines, such as corrosion inhibitors to protect gasoline storage tanks, freezing point depressants to prevent icing, and color dyes for safety or governmental regulatory requirements.

Possible references



 * Questions and Answers Relating to the Review of the Existing Fuel Quality Regulations, New Zealand Ministry of Economic Development, December 2005.


 * Otto Cycle (About the internal combustion engine four-stroke cycle invented by Nicolaus A. Otto)