Paraffin

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.

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.[1]

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 Ireland, Britain 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 the Latin parum (= barely) + affinis with the meaning here of "lacking affinity", or "lacking reactivity".[2] This is because alkanes, being non-polar and lacking in functional groups, are very unreactive.

Contents

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 47 °C and 64 °C ( 117°F to 147°F), and having a density of around 0.9 g/cm3.[3] It is insoluble in water, but soluble in ether, benzene, and certain esters. Paraffin is unaffected by most common chemical reagents, but burns readily.

Pure paraffin wax is an excellent electrical insulator, with an electrical resistivity of between 1013 and 1017 ohm metre.[4] 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.[5][6]

Paraffin wax (C25H52) 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 per kelvin) and a heat of fusion of 200–220 J g−1.[7] This property is exploited in modified drywall for home building material: it 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.[8] Paraffin wax phase change cooling coupled with retractable radiators was used to cool the electronics of the Lunar Rover.[9] Wax expands considerably when it melts and this allows its use in thermostats for industrial, domestic and, particularly, automobile purposes.[10][11]

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.

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.[3] Liquid paraffin (medicinal) 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.[12] 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.

Uses

Gaseous

Liquids

Paraffin wax

References

  1. ↑ Britannica (1911)
  2. ↑ "Paraffin, n". Oxford English Dictionary. Oxford, England: Oxford University Press. March 2009. 
  3. ↑ 3.0 3.1 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. 
  4. ↑ "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. 
  5. ↑ "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. 
  6. ↑ Rhodes, Richard (1986). The Making of the Atomic Bomb. New York: Simon and Schuster. pp. 163. ISBN 0-671-44133-7. 
  7. ↑ "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. 
  8. ↑ "Micronal PCM SmartBoard". http://www.micronal.de/portal/basf/ien/dt.jsp?setCursor=1_290798. 
  9. ↑ Dean, W. G.; Karu, Z. S. (February 1993). "Space Station thermal storage/refrigeration system research and development". Lockheed Missiles and Space Co. Report. NASA. http://adsabs.harvard.edu/abs/1993lock.rept.....D. Retrieved 28 November 2008. 
  10. ↑ Wax-pellet thermostat United States Patent 4948043
  11. ↑ 11.0 11.1 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. 
  12. ↑ "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. 
  13. ↑ "Dyed saddle leather—German pull up finish". Walsall, England: J & E Sedgwick. http://www.je-sedgwick.co.uk/jes/mib/d/dyed+saddle+leather+german+pull+up+finish/pid/7723339/. Retrieved 14 April 2010. "applying specially formulated mineral oils to the open grain of the leather" 
  14. ↑ Staff (Fall 2004). "Rocket motor uses common household product for fuel". OASIS Ocean Air Space Industry Site (Stennis Space Center Pearlington, MS: NASA) 1 (3): 6. http://www.nasa.gov/centers/stennis/pdf/69281main_fall.pdf. Retrieved 28 November 2008. 
  15. ↑ [1]
  16. ↑ 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. 

See also