Sodium

From Wikipedia, the free encyclopedia

Sodium,  ₁₁Na

Spectral lines of sodium
General properties
Name, symbol	sodium, Na
Pronunciation	/ˈsoʊdiəm/ SOH-dee-əm
Appearance	silvery white metallic
Sodium in the periodic table
Li ↑ Na ↓ K neon ← sodium → magnesium
Atomic number	11
Standard atomic weight (±)	22.98976928(2)[1]
Element category	alkali metal
Group, block	group 1 (alkali metals), s-block
Period	period 3
Electron configuration	[Ne] 3s1
per shell	2, 8, 1
Physical properties
Phase	solid
Melting point	370.944 K ​(97.794 °C, ​208.029 °F)
Boiling point	1156.090 K ​(882.940 °C, ​1621.292 °F)
Density near r.t.	0.968 g·cm−3
when liquid, at m.p.	0.927 g·cm−3
Critical point	2573 K, 35 MPa (extrapolated)
Heat of fusion	2.60 kJ·mol−1
Heat of vaporization	97.42 kJ·mol−1
Molar heat capacity	28.230 J·mol−1·K−1
vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 554 617 697 802 946 1153
Atomic properties
Oxidation states	1, −1 ​(a strongly basic oxide)
Electronegativity	Pauling scale: 0.93
Ionization energies	1st: 495.8 kJ·mol−1 2nd: 4562 kJ·mol−1 3rd: 6910.3 kJ·mol−1 (more)
Atomic radius	empirical: 186 pm
Covalent radius	166±9 pm
Van der Waals radius	227 pm
Miscellanea
Crystal structure	​body-centered cubic (bcc)
Speed of sound thin rod	3200 m·s−1 (at 20 °C)
Thermal expansion	71 µm·m−1·K−1 (at 25 °C)
Thermal conductivity	142 W·m−1·K−1
Electrical resistivity	47.7 nΩ·m (at 20 °C)
Magnetic ordering	paramagnetic[2]
Young's modulus	10 GPa
Shear modulus	3.3 GPa
Bulk modulus	6.3 GPa
Mohs hardness	0.5
Brinell hardness	0.69 MPa
CAS Registry Number	7440-23-5
History
Discovery and first isolation	Humphry Davy (1807)
Most stable isotopes
Main article: Isotopes of sodium
iso NA half-life DM DE (MeV) DP 22Na trace 2.602 y β+→γ 0.5454 22Ne* 1.27453(2)[3] 22Ne ε→γ – 22Ne* 1.27453(2) 22Ne β+ 1.8200 22Ne 23Na 100% 23Na is stable with 12 neutrons
* = excited state

Sodium /ˈsoʊdiəm/^[4] is a chemical element with symbol Na (from Latin: natrium) and atomic number 11. It is a soft, silver-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is ²³Na. The free metal does not occur in nature, but instead must be prepared from its compounds; it was first isolated by Humphry Davy in 1807 by the electrolysis of sodium hydroxide. Sodium is the sixth most abundant element in the Earth's crust, and exists in numerous minerals such as feldspars, sodalite and rock salt (NaCl). Many salts of sodium are highly water-soluble, and their sodium ions have been leached by the action of water so that sodium and chlorine (Cl) are the most common dissolved elements by weight in the Earth's bodies of oceanic water.

Many sodium compounds are useful, such as sodium hydroxide (lye) for soap-making, and sodium chloride for use as a de-icing agent and a nutrient (edible salt). Sodium is an essential element for all animals and some plants. In animals, sodium ions are used against potassium ions to build up charges on cell membranes, allowing transmission of nerve impulses when the charge is dissipated. The consequent need of animals for sodium causes it to be classified as a dietary inorganic macro-mineral nutrient.

§Characteristics

§Physical

Sodium at standard temperature and pressure is a soft silvery metal, that oxidizes to grayish white unless immersed in oil or inert gas. Sodium can be readily cut with a knife, and is a good conductor of electricity. These properties change dramatically at elevated pressures: at 1.5 Mbar, the color changes from silvery metallic to black; at 1.9 Mbar the material becomes transparent, with a red color; and at 3 Mbar sodium is a clear and transparent solid. All of these high-pressure allotropes are insulators and electrides.^[5]

When sodium or its compounds are introduced into a flame, they turn it yellow,^[6] because the excited 3s electrons of sodium emit a photon when they fall from 3p to 3s; the wavelength of this photon corresponds to the D line at 589.3 nm. Spin-orbit interactions involving the electron in the 3p orbital split the D line into two; hyperfine structures involving both orbitals cause many more lines.^[7]

§Chemical

Emission spectrum for sodium, showing the D line.

A positive flame test for sodium has a bright yellow color.

When freshly cut, sodium has a bright, silvery luster. If exposed to air, the surface rapidly tarnishes, darkening at first and then forming a white coating of sodium hydroxide and sodium carbonate.

Sodium is generally less reactive than potassium and more reactive than lithium.^[8] Like all the alkali metals, it reacts exothermically with water, to the point that sufficiently large pieces melt to a sphere and may explode; this reaction produces caustic soda (sodium hydroxide) and flammable hydrogen gas. When burned in dry air, it mainly forms sodium peroxide as well as some sodium oxide. In moist air, sodium hydroxide results.^[9] Sodium metal is highly reducing, with the reduction of sodium ions requiring −2.71 volts.^[10] Hence, the extraction of sodium metal from its compounds (such as with sodium chloride) uses a significant amount of energy.^[9] However, potassium and lithium have even more negative potentials.^[11]

§Isotopes

20 isotopes of sodium are known, but only ²³Na is stable. Two radioactive, cosmogenic isotopes are the byproduct of cosmic ray spallation: ²²Na with a half-life of 2.6 years and ²⁴Na with a half-life of 15 hours; all other isotopes have a half-life of less than one minute.^[12] Two nuclear isomers have been discovered, the longer-lived one being ^24mNa with a half-life of around 20.2 microseconds. Acute neutron radiation, such as from a nuclear criticality accident, converts some of the stable ²³Na in human blood to ²⁴Na; by measuring the concentration of ²⁴Na in relation to ²³Na, the neutron radiation dosage of the victim can be calculated.^[13]

§Occurrence

²³Na is created in the carbon-burning process in stars by fusing two carbon atoms together; this requires temperatures above 600 megakelvins and a star of at least three solar masses.^[14] The Earth's crust contains 2.6% sodium by weight, making it the sixth most abundant element on Earth.^[15] Because of its high reactivity, it is never found as a pure element. It is found in many different
minerals, some very soluble, such as halite and natron, others much less soluble such as amphibole, and zeolite. The insolubility of certain sodium minerals such as cryolite and feldspar arises from their polymeric anions, which in the case of feldspar is a polysilicate. In the interstellar medium, sodium is identified by the D spectral line; though it has a high vaporization temperature, its abundance allowed it to be detected by Mariner 10 in Mercury's atmosphere.^[16]

§Compounds

Structure of sodium chloride, showing octahedral coordination around Na⁺ and Cl⁻ centres. This framework disintegrates upon dissolution in water and reassembles upon evaporation.

Sodium compounds are of immense commercial importance, being particularly central to industries producing glass, paper, soap, and textiles.^[17] The sodium compounds that are the most important include table salt (NaCl), soda ash (Na₂CO₃), baking soda (NaHCO₃), caustic soda (NaOH), sodium nitrate (NaNO₃), di- and tri-sodium phosphates, sodium thiosulfate (Na₂S₂O₃·5H₂O), and borax (Na₂B₄O₇·10H₂O).^[18] In its compounds, sodium is usually ionically bonded to water and anions, and is viewed as a hard Lewis acid.^[19]

Two equivalent images of the chemical structure of sodium stearate, a typical soap.

Most soaps are sodium salts of fatty acids. Sodium soaps are harder (higher melting) soaps than potassium soaps.^[18] Sodium chloride is extensively used for anti-icing and de-icing and as a preservative; sodium bicarbonate is mainly used for cooking. Along with potassium, many important medicines have sodium added to improve their bioavailability; although in most cases potassium is the better ion, sodium is selected for its lower price and atomic weight.^[20]Sodium hydride is used as a base for various reactions (such as the aldol reaction) in organic chemistry, and as a reducing agent in inorganic chemistry.^[21]

§Aqueous solutions

Sodium tends to form water-soluble compounds, such as halides, sulfates, nitrates, carboxylates and carbonates. The main aqueous species are the aquo complexes [Na(H₂O)_n]⁺, where n = 4–6.^[22] The high affinity of sodium for oxygen-based ligands is the basis of crown ethers; macrolide antibiotics, which interfere with Na⁺ transport in the infecting organism, are functionally related and more complex.^{[citation needed]}

Direct precipitation of sodium salts from aqueous solutions is rare, because sodium salts typically have a high affinity for water; an exception is sodium bismuthate (NaBiO₃).^[23] Because of this, sodium salts are usually isolated as solids by evaporation or by precipitation with an organic solvent, such as ethanol; for example, only 0.35 g/L of sodium chloride will dissolve in ethanol.^[24] Crown ethers, like 15-crown-5, may be used as a phase-transfer catalyst.^[25]

Sodium content in bulk may be determined by treating with a large excess of uranyl zinc acetate; the hexahydrate (UO₂)₂ZnNa(CH₃CO₂)·6H₂O precipitates and can be weighed. Caesium and rubidium do not interfere with this reaction, but potassium and lithium do.^[26] Lower concentrations of sodium may be determined by atomic absorption spectrophotometry^[27] or by potentiometry using ion-selective electrodes.^[28]

§Electrides and sodides

Like the other alkali metals, sodium dissolves in ammonia and some amines to give deeply colored solutions; evaporation of these solutions leaves a shiny film of metallic sodium. The solutions contain the coordination complex (Na(NH₃)₆)⁺, whose positive charge is counterbalanced by electrons as anions; cryptands permit the isolation of these complexes as crystalline solids. Cryptands, like crown ethers and other ionophores, have a high affinity for the sodium ion; derivatives of the alkalide Na⁻ are obtainable^[29] by the addition of cryptands to solutions of sodium in ammonia via disproportionation.^[30]

§Organosodium compounds

The structure of the complex of sodium (Na⁺, shown in yellow) and the antibiotic monensin-A.

Many organosodium compounds have been prepared. Because of the high polarity of the C-Na bonds, they behave like sources of carbanions (salts with organic anions). Some well known derivatives include sodium cyclopentadienide (NaC₅H₅) and trityl sodium ((C₆H₅)₃CNa).^[31]

§History

Salt has been an important commodity in human activities, as shown by the English word salary, which derives from salarium, the wafers of salt sometimes given to Roman soldiers along with their other wages. In medieval Europe, a compound of sodium with the Latin name of sodanum was used as a headache remedy. The name sodium is thought to originate from the Arabic suda (صداع), meaning headache, as the headache-alleviating properties of sodium carbonate or soda were well known in early times.^[32] The chemical abbreviation for sodium was first published by Jöns Jakob Berzelius in his system of atomic symbols,^[33] and is a contraction of the element's New Latin name natrium, which refers to the Egyptian natron,^[32] a natural mineral salt primarily made of hydrated sodium carbonate. Natron historically had several important industrial and household uses, later eclipsed by other sodium compounds. Although sodium, sometimes called soda, had long been recognised in compounds, the metal itself was not isolated until 1807 by Sir Humphry Davy through the electrolysis of sodium hydroxide.^[34][35]

Sodium imparts an intense yellow color to flames. As early as 1860, Kirchhoff and Bunsen noted the high sensitivity of a sodium flame test, and stated in Annalen der Physik und Chemie:^[36]

“

In a corner of our 60 m3 room farthest away from the apparatus, we exploded 3 mg. of sodium chlorate with milk sugar while observing the nonluminous flame before the slit. After a while, it glowed a bright yellow and showed a strong sodium line that disappeared only after 10 minutes. From the weight of the sodium salt and the volume of air in the room, we easily calculate that one part by weight of air could not contain more than 1/20 millionth weight of sodium.

”

§Commercial production

Enjoying rather specialized applications, only about 100,000 tonnes of metallic sodium are produced annually.^[17] Metallic sodium was first produced commercially in 1855 by carbothermal reduction of sodium carbonate at 1100 °C,^{[citation needed]} in what is known as the Deville process:^[37][38][39]

Na₂CO₃ + 2 C → 2 Na + 3 CO

A related process based on the reduction of sodium hydroxide was developed in 1886.^[37]

Sodium is now produced commercially through the electrolysis of molten sodium chloride, based on a process patented in 1924.^[40][41] This is done in a Downs cell in which the NaCl is mixed with calcium chloride to lower the melting point below 700 °C. As calcium is less electropositive than sodium, no calcium will be deposited at the cathode. This method is less expensive than the previous Castner process of electrolyzing sodium hydroxide.

Reagent-grade sodium in tonne quantities sold for about US$3.30/kg in 2009; lower purity metal sells for considerably less.^{[citation needed]} The market for sodium is volatile due to the difficulty in its storage and shipping; it must be stored under a dry inert gas atmosphere or anhydrous mineral oil to prevent the formation of a surface layer of sodium oxide or sodium superoxide. These oxides can react violently in the presence of organic materials. Smaller quantities of sodium cost far more, in the range of US$165/kg; the high cost is partially due to the expense of shipping hazardous material.^[42]

§Applications

Though metallic sodium has some important uses, the major applications of sodium use is in its many compounds; millions of tons of the chloride, hydroxide, and carbonate are produced annually.

§Free element

Metallic sodium is mainly used for the production of sodium borohydride, sodium azide, indigo, and triphenylphosphine. Previous uses were for the making of tetraethyllead and titanium metal; because applications for these chemicals were discontinued, the production of sodium declined after 1970.^[17] Sodium is also used as an alloying metal, an anti-scaling agent,^[43] and as a reducing agent for metals when other materials are ineffective. Note the free element is not used as a scaling agent, ions in the water are exchanged for sodium ions. Sodium vapor lamps are often used for street lighting in cities and give colours ranging from yellow-orange to peach as the pressure increases.^[44] By itself or with potassium, sodium is a desiccant; it gives an intense blue colouration with benzophenone when the desiccate is dry.^[45] In organic synthesis, sodium is used in various reactions such as the Birch reduction, and the sodium fusion test is conducted to qualitatively analyse compounds.^[46] Lasers emitting light at the D line, utilising sodium, are used to create artificial laser guide stars that assist in the adaptive optics for land-based visible light telescopes.^{[citation needed]}

§Heat transfer

NaK phase diagram, showing the melting point of sodium as a function of potassium concentration. NaK with 77% potassium is eutectic and has the lowest melting point of the NaK alloys at −12.6 °C.^[47]

Liquid sodium is used as a heat transfer fluid in some fast reactors,^[48] due to its high thermal conductivity and low neutron absorption cross section, which is required to achieve a high neutron flux; the high boiling point allows the reactor to operate at ambient pressure. Drawbacks of using sodium include its opacity, which hinders visual maintenance, and its explosive properties. Radioactive sodium-24 may be formed by neutron activation during operation, posing a slight radiation hazard; the radioactivity stops within a few days after removal from the reactor. If a reactor needs to be frequently shut down, NaK is used; due to it being liquid at room temperature, cooling pipes do not freeze. In this case, the pyrophoricity of potassium means extra precautions against leaks need to be taken. Another heat transfer application is in high-performance internal combustion engines with poppet valves, where valve stems partially filled with sodium are used as a heat pipe to cool the valves.

§Biological role

In humans, sodium is an essential nutrient that regulates blood volume, blood pressure, osmotic equilibrium and pH; the minimum physiological requirement for sodium is 500 milligrams per day.^[49] Sodium chloride is the principal source of sodium in the diet, and is used as seasoning and preservative, such as for pickling and jerky; most of it comes from processed foods.^[50] The UL for sodium is 2.3 grams per day,^[51] the threshold which could lead to hypertension when exceeded,^[52] but on average people in the United States consume 3.4 grams per day.^[53] Hypertension causes 7.6 million premature deaths worldwide each year.^[54] (Note that salt contains about 39.3% sodium^[55]—the rest being chlorine and other trace chemicals; thus the UL of 2.3g sodium would be about 5.9g, or 2.7ml of salt—about half a US teaspoon^[56])
The renin-angiotensin system regulates the amount of fluids and sodium in the body. Reduction of blood pressure and sodium concentration in the kidney result in the production of renin, which in turn produces aldosterone and angiotensin, retaining sodium in the urine. Because of the increase in sodium concentration, the production of renin decreases, and the sodium concentration returns to normal.^[57] Sodium is also important in neuron function and osmoregulation between cells and the extracellular fluid, their distribution mediated in all animals by Na⁺/K⁺-ATPase;^[58] hence, sodium is the most prominent cation in extracellular fluid.^[59]

Unusually low or high sodium levels in humans are recognized in medicine as hyponatremia and hypernatremia. These conditions may be caused by genetic factors, physical factors associated with ageing or illnesses involving vomiting or diarrhea.^[60]

In C4 plants, sodium is a micronutrient that aids in metabolism, specifically in regeneration of phosphoenolpyruvate and synthesis of chlorophyll.^[61] In others, it substitutes for potassium in several roles, such as maintaining turgor pressure and aiding in the opening and closing of stomata.^[62] Excess sodium in the soil limits the uptake of water due to decreased water potential, which may result in wilting; similar concentrations in the cytoplasm can lead to enzyme inhibition, which in turn causes necrosis and chlorosis.^[63] To avoid these problems, plants developed mechanisms that limit sodium uptake by roots, store them in cell vacuoles, and control them over long distances;^[64] excess sodium may also be stored in old plant tissue, limiting the damage to new growth.

§Precautions

Care is required in handling elemental sodium, as it generates flammable hydrogen and caustic sodium hydroxide upon contact with water; powdered sodium may spontaneously explode in the presence of an oxidizer.^{[citation needed]} Excess sodium can be safely removed by hydrolysis in a ventilated cabinet; this is typically done by sequential treatment with isopropanol, ethanol and water. Isopropanol reacts very slowly, generating the corresponding alkoxide and hydrogen.^[65] Fire extinguishers based on water accelerate sodium fires; those based on carbon dioxide and bromochlorodifluoromethane lose their effectiveness when they dissipate. An effective extinguishing agent is Met-L-X, which comprises approximately 5% Saran in sodium chloride together with flow agents; it is most commonly hand-applied with a scoop. Other materials include Lith+, which has graphite powder and an organophosphate flame retardant, and dry sand.

Diesel fuel

From Wikipedia, the free encyclopedia

Diesel fuel /ˈdiːzəl/ in general is any liquid fuel used in diesel engines, whose fuel ignition takes place, without spark, as a result of compression of the inlet air mixture and then injection of fuel. (Glow plugs help achieve high temperatures for combustion during engine startup in cold weather.) Diesel engines have found broad use as a result of higher thermodynamic and thus fuel efficiencies. This is particularly noted where diesel engines are run at part-load; as their air supply is not throttled as in a petrol engine, their efficiency still remains high.

The most common type of diesel fuel is a specific fractional distillate of petroleum fuel oil, but alternatives that are not derived from petroleum, such as biodiesel, biomass to liquid (BTL) or gas to liquid (GTL) diesel, are increasingly being developed and adopted. To distinguish these types, petroleum-derived diesel is increasingly called petrodiesel.^[1] Ultra-low-sulfur diesel (ULSD) is a standard for defining diesel fuel with substantially lowered sulfur contents. As of 2006, almost all of the petroleum-based diesel fuel available in UK, Europe and North America is of a ULSD type. In the UK, diesel fuel for on-road use is commonly abbreviated DERV, standing for diesel-engined road vehicle, which carries a tax premium over equivalent fuel for non-road use (see Taxation).^[2] In Australia diesel fuel is also known as 'distillate'.^[3]

Origins

Diesel fuel originated from experiments conducted by German scientist and inventor Rudolf Diesel for his compression-ignition engine he invented in 1892. Diesel originally designed his engine to use coal dust as fuel,^[4] and experimented with other fuels including vegetable oils^[5] such as peanut oil, which was used to power the engines which he exhibited at the 1900 Paris Exposition and the 1911 World's Fair in Paris.^[6]

Types

Diesel fuel is produced from various sources, the most common being petroleum. Other sources include biomass, animal fats, biogas, natural gas, and coal.

Petroleum diesel

A modern diesel dispenser

Petroleum diesel, also called petrodiesel,^[7] or fossil diesel is the most common type of diesel fuel. It is produced from the fractional distillation of crude oil between 200 °C (392 °F) and 350 °C (662 °F) at atmospheric pressure, resulting in a mixture of carbon chains that typically contain between 8 and 21 carbon atoms per molecule.^[8]

Synthetic diesel

Synthetic diesel can be produced from any carbonaceous material, including biomass, biogas, natural gas, coal and many others. The raw material is gasified into synthesis gas, which after purification is converted by the Fischer–Tropsch process to a synthetic diesel.^[9]
The process is typically referred to as biomass-to-liquid (BTL), gas-to-liquid (GTL) or coal-to-liquid (CTL), depending on the raw material used.

Paraffinic synthetic diesel generally has a near-zero content of sulfur and very low aromatics content, reducing unregulated emissions of toxic hydrocarbons, nitrous oxides and particulate matter (PM).^[10]

Biodiesel

Biodiesel made from soybean oil

Fatty-acid methyl ester (FAME), more widely known as biodiesel, is obtained from vegetable oil or animal fats (biolipids) which have been transesterified with methanol. It can be produced from many types of oils, the most common being rapeseed oil (rapeseed methyl ester, RME) in Europe and soybean oil (soy methyl ester, SME) in the USA. Methanol can also be replaced with ethanol for the transesterification process, which results in the production of ethyl esters. The transesterification processes use catalysts, such as sodium or potassium hydroxide, to convert vegetable oil and methanol into FAME and the undesirable byproducts glycerine and water, which will need to be removed from the fuel along with methanol traces. FAME can be used pure (B100) in engines where the manufacturer approves such use, but it is more often used as a mix with diesel, BXX where XX is the biodiesel content in percent.^[11][12]

FAME as a fuel is regulated under DIN EN 14214^[13] and ASTM D6751.^[14]

FAME has a lower energy content than diesel due to its oxygen content, and as a result, performance and fuel consumption can be affected. It also can have higher levels of NOx emissions, possibly even exceeding the legal limit. FAME also has lower oxidation stability than diesel, and it offers favorable conditions for bacterial growth, so applications which have a low fuel turnover should not use FAME.^[15] The loss in power when using pure biodiesel is 5 to 7%.^[12]

Fuel equipment manufacturers (FIE) have raised several concerns regarding FAME fuels: free methanol, dissolved and free water, free glycerin, mono and diglycerides, free fatty acids, total solid impurity levels, alkaline metal compounds in solution and oxidation and thermal stability. They have also identified FAME as being the cause of the following problems: corrosion of fuel injection components, low-pressure fuel system blockage, increased dilution and polymerization of engine sump oil, pump seizures due to high fuel viscosity at low temperature, increased injection pressure, elastomeric seal failures and fuel injector spray blockage.^[16]

Unsaturated fatty acids are the source for the lower oxidation stability; they react with oxygen and form peroxides and result in degradation byproducts, which can cause sludge and lacquer in the fuel system.^[17]

As FAME contains low levels of sulfur, the emissions of sulfur oxides and sulfates, major components of acid rain, are low. Use of biodiesel also results in reductions of unburned hydrocarbons, carbon monoxide (CO), and particulate matter. CO emissions using biodiesel are substantially reduced, on the order of 50% compared to most petrodiesel fuels. The exhaust emissions of particulate matter from biodiesel have been found to be 30 percent lower than overall particulate matter emissions from petrodiesel. The exhaust emissions of total hydrocarbons (a contributing factor in the localized formation of smog and ozone) are up to 93 percent lower for biodiesel than diesel fuel.

Biodiesel also may reduce health risks associated with petroleum diesel. Biodiesel emissions showed decreased levels of polycyclic aromatic hydrocarbon (PAH) and nitrited PAH compounds, which have been identified as potential cancer-causing compounds. In recent testing, PAH compounds were reduced by 75 to 85 percent, except for benz(a)anthracene, which was reduced by roughly 50 percent. Targeted nPAH compounds were also reduced dramatically with biodiesel fuel, with 2-nitrofluorene and 1-nitropyrene reduced by 90 percent, and the rest of the nPAH compounds reduced to only trace levels.^[18]

Hydrogenated oils and fats

This category of diesel fuels involves converting the triglycerides in vegetable oil and animal fats into alkanes by refining and hydrogenation, such as H-Bio. The produced fuel has many properties that are similar to synthetic diesel, and are free from the many disadvantages of FAME.

DME

Dimethyl ether, DME, is a synthetic, gaseous diesel fuel that results in clean combustion with very little soot and reduced NOx emissions.^[19]

Storage

In the US, diesel is recommended to be stored in a yellow container to differentiate it from kerosene and gasoline, which are typically kept in blue and red containers, respectively.^[20] In the UK, diesel is normally stored in a black container, to differentiate it from unleaded petrol (which is commonly stored in a green container) and leaded petrol (which is stored in a red container).^[21]

Measurements and pricing

Cetane number

The principal measure of diesel fuel quality is its cetane number. A cetane number is a measure of the delay of ignition of a diesel fuel.^[22] A higher cetane number indicates that the fuel ignites more readily when sprayed into hot compressed air.^[22] European (EN 590 standard) road diesel has a minimum cetane number of 51. Fuels with higher cetane numbers, normally "premium" diesel fuels with additional cleaning agents and some synthetic content, are available in some markets.

Fuel value and price

As of 2010, the density of petroleum diesel is about 0.832 kg/L (6.943 lb/US gal), about 11.6% more than ethanol-free petrol (gasoline), which has a density of about 0.745 kg/L (6.217 lb/US gal). About 86.1% of the fuel mass is carbon, and when burned, it offers a net heating value of 43.1 MJ/kg as opposed to 43.2 MJ/kg for gasoline. However, due to the higher density, diesel offers a higher volumetric energy density at 35.86 MJ/L (128,700 BTU/US gal) vs. 32.18 MJ/L (115,500 BTU/US gal) for gasoline, some 11% higher, which should be considered when comparing the fuel efficiency by volume. The CO₂ emissions from diesel are 73.25 g/MJ, just slightly lower than for gasoline at 73.38 g/MJ.^[23] Diesel is generally simpler to refine from petroleum than gasoline, and contains hydrocarbons having a boiling point in the range of 180–360 °C (360–680 °F). The price of diesel traditionally rises during colder months as demand for heating oil rises, which is refined in much the same way. Because of recent changes in fuel quality regulations, additional refining is required to remove sulfur, which contributes to a sometimes higher cost. In many parts of the United States and throughout the United Kingdom and Australia,^[24] diesel may be priced higher than petrol.^[25] Reasons for higher-priced diesel include the shutdown of some refineries in the Gulf of Mexico, diversion of mass refining capacity to gasoline production, and a recent transfer to ultra-low-sulfur diesel (ULSD), which causes infrastructural complications.^[26] In Sweden, a diesel fuel designated as MK-1 (class 1 environmental diesel) is also being sold; this is a ULSD that also has a lower aromatics content, with a limit of 5%.^[27] This fuel is slightly more expensive to produce than regular ULSD.

Taxation

Diesel fuel is very similar to heating oil, which is used in central heating. In Europe, the United States, and Canada, taxes on diesel fuel are higher than on heating oil due to the fuel tax, and in those areas, heating oil is marked with fuel dyes and trace chemicals to prevent and detect tax fraud.
"Untaxed" diesel (sometimes called "off-road diesel") is available in some countries for use primarily in agricultural applications, such as fuel for tractors, recreational and utility vehicles or other noncommercial vehicles that do not use public roads. This fuel may have sulfur levels that exceed the limits for road use in some countries (e.g. US).

This untaxed diesel is dyed red for identification,^[28] and using this untaxed diesel fuel for a typically taxed purpose (such as driving use), the user can be fined (e.g. US$10,000 in the US). In the United Kingdom, Belgium and the Netherlands, it is known as red diesel (or gas oil), and is also used in agricultural vehicles, home heating tanks, refrigeration units on vans/trucks which contain perishable items such as food and medicine and for marine craft. Diesel fuel, or marked gas oil is dyed green in the Republic of Ireland and Norway. The term "diesel-engined road vehicle" (DERV) is used in the UK as a synonym for unmarked road diesel fuel. In India, taxes on diesel fuel are lower than on petrol, as the majority of the transportation for grain and other essential commodities across the country runs on diesel.

Taxes on biodiesel in the U.S. vary between states; some states (Texas, for example) have no tax on biodiesel and a reduced tax on biodiesel blends equivalent to the amount of biodiesel in the blend, so that B20 fuel is taxed 20% less than pure petrodiesel.^[29] Other states, such as North Carolina, tax biodiesel (in any blended configuration) the same as petrodiesel, although they have introduced new incentives to producers and users of all biofuels.^[30]

Uses

Diesel fuel is widely used in most types of transportation. The gasoline-powered passenger automobile is the major exception.

Unlike gasoline and liquefied petroleum gas engines, diesel engines do not use high-voltage spark ignition (spark plugs). An engine running on diesel compresses the air inside the cylinder to high pressures and temperatures (compression ratios from 14:1 to 18:1 are common in current diesel engines); the engine generally injects the diesel fuel directly into the cylinder, starting a few degrees before top dead center (TDC) and continuing during the combustion event. The high temperatures inside the cylinder cause the diesel fuel to react with the oxygen in the mix (burn or oxidize), heating and expanding the burning mixture to convert the thermal/pressure difference into mechanical work, i.e., to move the piston. Engines have glow plugs to help start the engine by preheating the cylinders to a minimum operating temperature. Diesel engines are lean burn engines,^[31] burning the fuel in more air than is required for the chemical reaction. They thus use less fuel than rich burn spark ignition engines which use a stoichiometric air-fuel ratio (just enough air to react with the fuel). As Professor Harvey of the University of Toronto notes, "due to the absence of throttling [constant amount of air admitted, per unit fuel, with no user-determined variation], the high compression ratio and lean fuel mixture, diesel engines are substantially more efficient than spark-ignited engines", generally; Harvey cites the side-by-side comparisons of Schipper et al. and the estimates of >20% lower fuel use and (given difference in differences in energy content between fuel types) >15% lower energy use.^[32] Gas turbine and some other types of internal combustion engines, and external combustion engine, both can also be designed to take diesel fuel.^{[citation needed]}

The viscosity requirement of diesel fuel is usually specified at 40 °C.^[22] A disadvantage of diesel as a vehicle fuel in cold climates, is that its viscosity increases as the temperature decreases, changing it into a gel (see Compression Ignition – Gelling) that cannot flow in fuel systems. Special low-temperature diesel contains additives to keep it liquid at lower temperatures, but starting a diesel engine in very cold weather may still pose considerable difficulties. Another disadvantage of diesel engines compared to petrol/gasoline engines is the possibility of runaway failure. Since diesel engines do not need spark ignition, they can run as long as diesel fuel is supplied. Fuel is typically supplied via a fuel pump. If the pump breaks down in an "open" position, the supply of fuel will be unrestricted, and the engine will run away and risk terminal failure.^[33]

With turbocharged engines, the oil seals on the turbocharger may fail, allowing lubricating oil into the combustion chamber, where it is burned like regular diesel fuel. In vehicles or installations that use diesel engines and also bottled gas, a gas leak into the engine room could also provide fuel for a runaway, via the engine air intake.^[34]

Railroad

Diesel displaced coal and fuel oil for steam-powered vehicles in the latter half of the 20th century, and is now used almost exclusively for the combustion engines of self-powered rail vehicles (locomotives and railcars).^[35][36]

Aircraft

The first diesel-powered flight of a fixed-wing aircraft took place on the evening of 18 September 1928, at the Packard Proving Grounds near Utica, Michigan. With Captain Lionel M. Woolson and Walter Lees at the controls the first "official" test flight was taken the next morning, flying a Stinson SM1B (X7654), powered by a Packard DR-980 9-cylinder diesel radial engine, designed by Woolson. Charles Lindbergh flew the same aircraft and in 1929, it was flown 621 miles (999 km) nonstop from Detroit to Langley Field, near Norfolk, Virginia. In 1931, Walter Lees and Fredrick Brossy set the nonstop flight record flying a Bellanca powered by a Packard diesel for 84 hours and 32 minutes. X7654 is now owned by Greg Herrick and is at the Golden Wings Flying Museum near Minneapolis, Minnesota.
Diesel engines for airships were developed in both Germany and the United Kingdom by Daimler-Benz and Beardmore produced the Daimler-Benz DB 602 and Beardmore Typhoon respectively. The LZ 129 Hindenburg rigid airship was powered by four Daimler-Benz DB 602 16-cylinder diesel engines, each with 1,200 hp (890 kW) available in bursts and 850 horsepower (630 kW) available for cruising.^[37] The Beardmore Typhoon powered the ill-fated R101 airship, built for the Empire airship programme in 1931.

With a production run of at least 900 engines, the most-produced aviation diesel engine in history was probably the Junkers Jumo 205. Similar developments from the Junkers Motorenwerke and licence-built versions of the Jumo 204 and Jumo 205, boosted German diesel aero-engine production to at least 1000 examples, the vast majority of which were liquid-cooled, opposed-piston, two-stroke engines.

In the Soviet Union significant progress towards practical diesel aero-engines was made by the TsIAM (Tsentral'nyy Institut Aviatsionnovo Motorostroyeniya - central institute of aviation motors) and particularly by A.D. Charomskiy, who nursed the Charomskiy ACh-30 into production and limited operational use.^[38]

Military vehicles

Armored fighting vehicles use diesel because of its lower flammability risks and the engines' higher provision of torque and lower likelihood of stalling.^[39][40]

Cars

Diesel-powered cars generally have a better fuel economy than equivalent gasoline engines and produce less greenhouse gas emission.^[41] Their greater economy is due to the higher energy per-litre content of diesel fuel and the intrinsic efficiency of the diesel engine.^[42] While petrodiesel's higher density results in higher greenhouse gas emissions per litre compared to gasoline,^[43] the 20–40% better fuel economy achieved by modern diesel-engined automobiles offsets the higher per-litre emissions of greenhouse gases, and a diesel-powered vehicle emits 10–20 percent less greenhouse gas than comparable gasoline vehicles.^[44][45][46] Biodiesel-powered diesel engines offer substantially improved emission reductions compared to petrodiesel or gasoline-powered engines, while retaining most of the fuel economy advantages over conventional gasoline-powered automobiles.^[44] However, the increased compression ratios mean there are increased emissions of oxides of nitrogen (NO_x) from diesel engines.^[47] This is compounded by biological nitrogen in biodiesel to make NO_x emissions the main drawback of diesel versus gasoline engines.^[47]

Other uses

Poor quality (high sulfur) diesel fuel has been used as an extraction agent for liquid–liquid extraction of palladium from nitric acid mixtures.^[48] Such use has been proposed as a means of separating the fission product palladium from PUREX raffinate which comes from used nuclear fuel.^[48] In this system of solvent extraction, the hydrocarbons of the diesel act as the diluent while the dialkyl sulfides act as the extractant.^[48] This extraction operates by a solvation mechanism.^[48] So far, neither a pilot plant nor full scale plant has been constructed to recover palladium, rhodium or ruthenium from nuclear wastes created by the use of nuclear fuel.^[49]

Diesel fuel is also often used as the main ingredient in oil-base mud drilling fluid.^[50] The advantage of using diesel is its low cost and that it delivers excellent results when drilling a wide variety of difficult strata including shale, salt and gypsum formations.^[50] Diesel-oil mud is typically mixed with up to 40% brine water.^[51] Due to health, safety and environmental concerns, Diesel-oil mud is often replaced with vegetable, mineral, or synthetic food-grade oil-base drilling fluids, although diesel-oil mud is still in widespread use in certain regions.^[52]

During development of Rocket engines in Germany during World War II J-2 Diesel fuel was used as the fuel component in several engines including the BMW 109-718.^[53] J-2 diesel fuel was also used as a fuel for gas turbine engines.^[53]

Chemical analysis

Chemical composition

Diesel does not mix with water.

Petroleum-derived diesel is composed of about 75% saturated hydrocarbons (primarily paraffins including n, iso, and cycloparaffins), and 25% aromatic hydrocarbons (including naphthalenes and alkylbenzenes).^[54] The average chemical formula for common diesel fuel is C₁₂H₂₃, ranging approximately from C₁₀H₂₀ to C₁₅H₂₈.^[55]

Chemical properties

Most diesel fuels freeze at common winter temperatures, while the temperatures greatly vary.^[56] Petrodiesel typically freezes around temperatures of −8.1 °C (17.5 °F), whereas biodiesel freezes between temperatures of 2º to 15 °C (35º to 60 °F).^[56] The viscosity of diesel noticeably increases as the temperature decreases, changing it into a gel at temperatures of −19 °C (−2.2 °F) to −15 °C (5 °F), that cannot flow in fuel systems. Conventional diesel fuels vaporise at temperatures between 149 °C and 371 °C.^[22]
Conventional diesel flash points vary between 52 and 96 °C, which makes it safer than petrol and unsuitable for spark-ignition engines.^[57] Unlike petrol, the flash point of a diesel fuel has no relation to its performance in an engine nor to its auto ignition qualities.^[22]

Hazards

Reduction of sulfur emissions

In the past, diesel fuel contained higher quantities of sulfur. European emission standards and preferential taxation have forced oil refineries to dramatically reduce the level of sulfur in diesel fuels. In th European Union the sulphur content has dramatically reduced during the last 20 years. Automotive dieselfuel is covered in the European Union by standard EN 590 In the 1990s specifications allowed a content of 2000ppm max of sulphur, reduced to a limit of 350pmm by the beginning of the 21st century with the introduction of Euro3 specifications. The limit was lowered with the introduction of Euro 4 by 2006 to 50ppm (ULSD, Ultra Low Sulphur Diesel). The standard currently in force in European Europe for Diesel Fuel is the Euro 5, with a maximum content of 10 ppm.^{[citation needed]}

emission standard	at latest	sulphur content	cetane number
Euro 1	1. January 1993	max. 2000 ppm	min. 49
Euro 2	1. January 1996	max. 500 ppm	min. 49
Euro 3	1. January 2001	max. 350 ppm	min. 51
Euro 4	1. January 2006	max. 50 ppm	min. 51
Euro 5	1. January 2009	max. 10 ppm	min. 51

In the United States, more stringent emission standards have been adopted with the transition to ULSD starting in 2006, and becoming mandatory on June 1, 2010 (see also diesel exhaust). U.S. diesel fuel typically also has a lower cetane number (a measure of ignition quality) than European diesel, resulting in worse cold weather performance and some increase in emissions.^[58]

Environment hazards of sulfur

High levels of sulfur in diesel are harmful for the environment because they prevent the use of catalytic diesel particulate filters to control diesel particulate emissions, as well as more advanced technologies, such as nitrogen oxide (NO_x) adsorbers (still under development), to reduce emissions. Moreover, sulfur in the fuel is oxidized during combustion, producing sulfur dioxide and sulfur trioxide, that in presence of water rapidly convert to sulfuric acid, one of the chemical processes that results in acid rain. However, the process for lowering sulfur also reduces the lubricity of the fuel, meaning that additives must be put into the fuel to help lubricate engines. Biodiesel and biodiesel/petrodiesel blends, with their higher lubricity levels, are increasingly being utilized as an alternative. The U.S. annual consumption of diesel fuel in 2006 was about 190 billion litres (42 billion imperial gallons or 50 billion US gallons).^[59]

Algae, microbes, and water contamination

There has been much discussion and misunderstanding of algae in diesel fuel. Algae need light to live and grow. As there is no sunlight in a closed fuel tank, no algae can survive, but some microbes can survive and feed on the diesel fuel.^[60]

These microbes form a colony that lives at the interface of fuel and water. They grow quite fast in warmer temperatures. They can even grow in cold weather when fuel tank heaters are installed. Parts of the colony can break off and clog the fuel lines and fuel filters.^[61]

Water in fuel can damage a fuel injection pump, some diesel fuel filters also trap water.

Road hazard

Petrodiesel spilled on a roadway poses a hazard to vehicles, due to its high evaporation temperature. After the light fractions have evaporated, a greasy slick is left on the road which can destabilize moving vehicles. Diesel spills severely reduce tire grip and traction, and have been implicated in many accidents. The loss of traction is similar to that encountered on black ice. Diesel slicks are especially dangerous for two-wheeled vehicles such as motorcycles.