Paraffin

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For the fuel called "paraffin" in the United Kingdom and South Africa, see Kerosene. For medical uses, see Liquid paraffin (medicinal).
File:Paraffin.jpg
Paraffin wax
Molecular weight distributions of produced oil and its wax deposit.

In chemistry, paraffin is a term that can be used synonymously with "alkane", indicating hydrocarbons with the general formula CnH2n+2. Paraffin wax refers to a mixture of alkanes that falls within the 20 ≤ n ≤ 40 range; they are found in the solid state at room temperature and begin to enter the liquid phase past approximately 37 °C (99 °F).[1]

The simplest paraffin molecule is that of methane, CH4, a gas at room temperature. Heavier members of the series, such as octane, C8H18, and mineral oil appear as liquids at room temperature. The solid forms of paraffin, called paraffin wax, are from the heaviest molecules from C20H42 to C40H82. Paraffin wax was identified by Carl Reichenbach in 1830.[2]

Paraffin, or paraffin hydrocarbon, is also the technical name for an alkane in general, but in most cases it refers specifically to a linear, or normal alkane — whereas branched, or isoalkanes are also called isoparaffins. It is distinct from the fuel known in the United Kingdom, Ireland and South Africa as paraffin oil or just paraffin, which is called kerosene in most of the U.S., Canada, Australia and New Zealand.

The name is derived from Latin parum ("barely") + affinis, meaning "lacking affinity" or "lacking reactivity" indicating paraffin's unreactive nature [3])

Paraffin wax

Paraffin wax (or simply "paraffin", but see alternative name for kerosene, above) is mostly found as a white, odorless, tasteless, waxy solid, with a typical melting point between about 46 and 68 °C (115 and 154 °F),[4] and having a density of around 0.9 g/cm3.[5] It is insoluble in water, but soluble in ether, benzene, and certain esters. Paraffin is unaffected by most common chemical reagents but burns readily.[6]

Pure paraffin wax is an excellent electrical insulator, with an electrical resistivity of between 1013 and 1017 ohm metre.[7] This is better than nearly all other materials except some plastics (notably Teflon). It is an effective neutron moderator and was used in James Chadwick's 1932 experiments to identify the neutron.[8][9]

Paraffin wax is an excellent material to store heat, having a specific heat capacity of 2.14–2.9 J g−1 K−1 (joule per gram kelvin) and a heat of fusion of 200–220 J g−1.[10] This property is exploited in modified drywall for home building material: a certain type (with the right melting point) of wax is infused in the drywall during manufacture so that, when installed, it melts during the day, absorbing heat, and solidifies again at night, releasing the heat.[11] Paraffin wax phase change cooling coupled with retractable radiators was used to cool the electronics of the Lunar Rover.[12] Wax expands considerably when it melts and this allows its use in wax thermostatic element thermostats for industrial, domestic and, particularly, automobile purposes.[13][14]

In industrial applications, it is often useful to modify the crystal properties of the paraffin wax, typically by adding branching to the existing carbon backbone chain. The modification is usually done with additives, such as EVA copolymers, microcrystalline wax, or forms of polyethylene. The branched properties result in a modified paraffin with a higher viscosity, smaller crystalline structure, and modified functional properties. Pure paraffin wax is rarely used for carving original models for casting metal and other materials in the lost wax process, as it is relatively brittle at room temperature and presents the risks of chipping and breakage when worked. Soft and pliable waxes, like beeswax, may be preferred for such sculpture, but "investment casting waxes," often paraffin-based, are expressly formulated for the purpose.[citation needed]

Mineral oil

Main article: Mineral oil

Liquid paraffin, or mineral oil, is a mixture of heavier alkanes, and has a number of names, including nujol, adepsine oil, alboline, glymol, medicinal paraffin, or saxol. It has a density of around 0.8 g/cm3.[5] Medicinal liquid paraffin is used to aid bowel movement in persons suffering chronic constipation; it passes through the gastrointestinal tract without itself being taken into the body, but it limits the amount of water removed from the stool. In the food industry, where it may be called "wax", it can be used as a lubricant in mechanical mixing, applied to baking tins to ensure that loaves are easily released when cooked and as a coating for fruit or other items requiring a "shiny" appearance for sale.[15]

It is often used in infrared spectroscopy, as it has a relatively uncomplicated IR spectrum. When the sample to be tested is made into a mull (a very thick paste), liquid paraffin is added so it can be spread on the transparent (to infrared) mounting plates to be tested. Mineral oil has also seen widespread use in biotechnology for preventing the evaporation of small volumes of liquid during heating. Polymerase chain reaction samples may need to be overlaid with a layer of mineral oil to prevent evaporation[16] during the high heat (95 °C) required to denature DNA.

Uses

Gaseous

  • Fuels

Liquids

Paraffin wax

  • Candle-making
  • Coatings for waxed paper or cloth
  • Food-grade paraffin wax:
    • Shiny coating used in candy-making; although edible, it is nondigestible, passing right through the body without being broken down
    • Coating for many kinds of hard cheese, like Edam cheese
    • Sealant for jars, cans, and bottles
    • Chewing gum additive
  • Investment casting
  • Anti-caking agent, moisture repellent, and dustbinding coatings for fertilizers
  • Agent for preparation of specimens for histology
  • Bullet lubricant – with other ingredients, such as olive oil and beeswax
  • Phlegmatizing agent, commonly used to stabilise/desensitize high explosives such as RDX
  • Crayons
  • Solid propellant for hybrid rocket motors[18]
  • Component of surfwax, used for grip on surfboards in surfing
  • Component of glide wax, used on skis and snowboards
  • Friction-reducer, for use on handrails and cement ledges, commonly used in skateboarding
  • Ink. Used as the basis for solid ink different color blocks of wax for thermal printers. The wax is melted and then sprayed on the paper producing images with a shiny surface
  • Microwax[19]: food additive, a glazing agent with E number E905
  • Forensics aid: the nitrate test uses paraffin wax to detect nitrates and nitrites on the hand of a shooting suspect
  • Antiozonant agents: blends of paraffin and micro waxes are used in rubber compounds to prevent cracking of the rubber; the admixture of wax migrates to the surface of the product and forms a protective layer. The layer can also act as a release agent, helping the product separate from its mould.[20]
  • Mechanical thermostats and actuators, as an expansion medium for activating such devices[14]
  • "Potting" guitar pickups, which reduces microphonic feedback caused from the subtle movements of the pole pieces
  • "Potting" of local oscillator coils to prevent microphonic frequency modulation in low end FM radios.
  • Wax baths for beauty and therapy purposes
  • Thickening agent in many Paintballs, as used by Crayola
  • An effective, although comedogenic, moisturiser in toiletries and cosmetics such as Vaseline
  • Prevents oxidation on the surface of polished steel and iron[21]

See also

References

Notes
  1. ↑ Script error
  2. ↑ Britannica (1911)
  3. ↑ Script error
  4. ↑ Script error This can vary widely, even outside the quoted range, according to such factors as oil content and crystalline structure.
  5. ↑ 5.0 5.1 Kaye, George William Clarkson; Laby,Thomas Howell. "Mechanical properties of materials". Kaye and Laby Tables of Physical and Chemical Constants. National Physical Laboratory. http://www.kayelaby.npl.co.uk/general_physics/2_2/2_2_1.html. Retrieved 2008-03-06.
  6. ↑ Script error
  7. ↑ "Electrical insulating materials". Kaye and Laby Tables of Physical and Chemical Constants. National Physical Laboratory. 1995. http://www.kayelaby.npl.co.uk/general_physics/2_6/2_6_3.html. Retrieved 2007-04-23.
  8. ↑ "Attenuation of fast neutrons: neutron moderation and diffusion". Kaye and Laby Tables of Physical and Chemical Constants. National Physical Laboratory. http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_3.html. Retrieved 2007-04-23.
  9. ↑ Script error
  10. ↑ "Specific Heat Capacity". Diracdelta.co.uk Science and Engineering Encyclopedia. Dirac Delta Consultants Ltd, Warwick, England. http://www.diracdelta.co.uk/science/source/s/p/specific%20heat%20capacity/source.html. Retrieved 2007-08-18.
  11. ↑ "Micronal PCM SmartBoard". http://www.micronal.de/portal/basf/ien/dt.jsp?setCursor=1_290798.
  12. ↑ Script error
  13. ↑ Wax-pellet thermostat United States Patent 4948043
  14. ↑ 14.0 14.1 Bodén, Roger. "Paraffin Microactuator". Materials Science Sensors and Actuators. University of Uppsala. http://hermes.material.uu.se/~klas/Paraffin_lab_eng.pdf. Retrieved 2007-04-23.
  15. ↑ "Mineral Oil (Food Grade)". WHO Food Additives Series 10. Food and Agriculture Organization of the United Nations; World Health Organization. 1976. http://www.inchem.org/documents/jecfa/jecmono/v10je08.htm. Retrieved 2007-08-21.
  16. ↑ Script error
  17. ↑ "Dyed saddle leather—German pull up finish". Walsall, England: J & E Sedgwick. http://www.je-sedgwick.co.uk/products/saddle-leather/dyed-saddle-leather-german-pull-up-finish/. Retrieved 14 April 2010. "applying specially formulated mineral oils to the open grain of the leather"
  18. ↑ Script error
  19. ↑ http://www.microcrystallinewax.net
  20. ↑ Freund, etc., (1982:272)
  21. ↑ Dick, William B. "Encyclopedia Of Practical Receipts And Processes". http://chestofbooks.com/reference/Encyclopedia-Of-Practical-Receipts-And-Processes/Steel-Part-6.html. Retrieved 2008-04-27.


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