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Higher alkane

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Higher alkanes are often defined as alkanes having nine or more carbon atoms. Nonane is the lightest alkane to have a flash point above 25 °C, and so not to be classified as dangerously flammable.

The scientific literature uses the term higher alkanes arbitrarily: sometimes literally as “alkanes with a higher number of carbon atoms”, sometimes according to a definition. For instance, other than based on nonane, one definition distinguishes the higher alkanes as the n-alkanes that are solid under natural conditions.

Uses

Alkanes from nonane to, for instance, hexadecane (an alkane with sixteen carbon atoms) are liquids of higher viscosity, less and less suitable for use in gasoline. They form instead the major part of diesel and aviation fuel. Diesel fuels are characterised by their cetane number, cetane being an old name for hexadecane. However the higher melting points of these alkanes can cause problems at low temperatures and in polar regions, where the fuel becomes too thick to flow correctly.

Alkanes from hexadecane upwards form the most important components of fuel oil and lubricating oil. In latter function they work at the same time as anti-corrosive agents, as their hydrophobic nature means that water cannot reach the metal surface. Many solid alkanes find use as paraffin wax, for example in candles. This should not be confused however with true wax, which consists primarily of esters.

Alkanes with a chain length of approximately 35 or more carbon atoms are found in bitumen, used for example in road surfacing. However, the higher alkanes have little value and are usually split into lower alkanes by cracking.

Properties

The properties listed here refer to the straight-chain alkanes (or: n-alkanes).

Nonane to hexadecane

This group of n-alkanes is generally liquid under natural conditions.

   Nonane   Decane   Undecane   Dodecane   Tridecane   Tetradecane   Pentadecane   Hexadecane 
Formula C9H20 C10H22 C11H24 C12H26 C13H28 C14H30 C15H32 C16H34
CAS number [111-84-2] [124-18-5] [1120-21-4] [112-40-3] [629-50-5] [629-59-4] [629-62-9] [544-76-3]
Molar mass (g/mol) 128.26 142.29 156.31 170.34 184.37 198.39 212.42 226.45
Melting point (°C) −53 −30 −26 −9.6 −5 5.5 9.9 18
Boiling point (°C) 151 174 196 216.2 234 253 268–270 287
Density (g/ml) 0.718 0.73 0.74 0.75   0.763 0.769 0.773
Viscosity (cP at 20 °C) 0.711 0.92   1.35   2.18   3.34
Flash point (°C) 31 46 60 71 102 99 132 135
Autoignition
temperature (°C) 		205 210   205   235   201
Explosive limits 0.9–2.9% 0.8–2.6%         0.45–6.5%  

Heptadecane to Tetracosane

From this group on, the n-alkanes are generally solid under natural conditions.

   Heptadecane   Octadecane   Nonadecane   Icosane   Henicosane   Docosane   Tricosane   Tetracosane 
Formula C17H36 C18H38 C19H40 C20H42 C21H44 C22H46 C23H48 C24H50
CAS number [629-78-7] [593-45-3] [629-92-5] [112-95-8] [629-94-7] [629-97-0] [638-67-5] [646-31-1]
Molar mass (g/mol) 240.47 254.50 268.53 282.55 296.58 310.61 324.63 338.66
Melting point (°C) 21 28–30 32–34 36.7 40.5 42 48–50 52
Boiling point (°C) 302 317 330 342.7 356.5 224 at 2 kPa 380 391.3
Density (g/ml) 0.777 0.777     0.792   0.797  
Flash point (°C) 148 165 168          

Pentacosane to Triacontane

   Pentacosane   Hexacosane   Heptacosane   Octacosane   Nonacosane   Triacontane 
Formula C25H52 C26H54 C27H56 C28H58 C29H60 C30H62
CAS number [629-99-2] [630-01-3] [593-49-7] [630-02-4] [630-03-5] [638-68-6]
Molar mass (g/mol) 352.69 366.71 380.74 394.77 408.80 422.82
Melting point (°C) 54 56.4 59.5 64.5 63.7 65.8
Boiling point (°C) 401.9 412.2 422 431.6 440.8 449.7
Density (g/ml) 0.801 0.778 0.780 0.807 0.808 0.810

Hentriacontane to hexatriacontane

   Hentriacontane   Dotriacontane   Tritriacontane   Tetratriacontane   Pentatriacontane   Hexatriacontane 
Formula C31H64 C32H66 C33H68 C34H70 C35H72 C36H74
CAS number [630-04-6] [544-85-4] [630-05-7] [14167-59-0] [630-07-9] [630-06-8]
Molar mass (g/mol) 436.85 450.88 464.90 478.93 492.96 506.98
Melting point (°C) 67.9 69 70–72 72.6 75 74–76
Boiling point (°C) 458 467   285.4 at 0.4 kPa 490 265 at 130 Pa
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