Petroleum naphtha is an intermediate hydrocarbon liquid stream derived from therefining ofcrude oil[1][2][3] withCAS-no 64742-48-9.[4] It is most usuallydesulfurized and thencatalytically reformed, which rearranges or restructures thehydrocarbonmolecules in the naphtha as well as breaking some of the molecules into smaller molecules to produce a high-octane component ofgasoline (orpetrol).
There are hundreds of different petroleum crude oil sources worldwide and each crude oil has its own unique composition orassay. There are also hundreds of petroleum refineries worldwide and each of them is designed to process either a specific crude oil or specific types of crude oils. Naphtha is a general term as each refinery produces its own naphthas with their own unique initial and final boiling points and other physical and compositional characteristics.
Naphthas may also be produced from other material such ascoal tar,shale deposits,tar sands, and thedestructive distillation of wood.[5][6]
The first unit operation (after being desalinated) in a petroleum refinery is thecrude oil distillation unit. The overhead liquid distillate from that unit is calledvirgin orstraight-run naphtha and that distillate is the largest source of naphtha in most petroleum refineries. The naphtha is a mixture of many different hydrocarbon compounds. It has an initialboiling point (IBP) of about 35 °C and a final boiling point (FBP) of about 200 °C, and it containsparaffins,naphthenes (cyclic paraffins) andaromatic hydrocarbons ranging from those containing 4carbonatoms to those containing about 10 or 11 carbon atoms.
The virgin naphtha is often furtherdistilled into two streams:[7]
The virgin heavy naphtha is usually processed in a catalytic reformer, because the light naphtha has molecules with six or fewer carbon atoms—which, when reformed, tend to crack into butane and lower molecular weight hydrocarbons that are not useful as high-octane gasoline blending components. Also, the molecules with six carbon atoms tend to form aromatics, which is undesirable because the environmental regulations of a number of countries limit the amount of aromatics (most particularlybenzene) in gasoline.[8][9][10]
The table below lists some typical virgin heavy naphthas, available for catalytic reforming, derived from various crude oils. It can be seen that they differ significantly in their content of paraffins, naphthenes and aromatics:
| Crude oil name Location | Barrow Island Australia[11] | Mutineer-Exeter Australia[12] | CPC Blend Kazakhstan[13] | Draugen North Sea[14] |
|---|---|---|---|---|
| Initial boiling point, °C | 150 | 140 | 149 | 150 |
| Final boiling point, °C | 200 | 190 | 204 | 180 |
| Paraffins, liquid volume % | 46 | 62 | 57 | 38 |
| Naphthenes, liquid volume % | 42 | 32 | 27 | 45 |
| Aromatics, liquid volume % | 12 | 6 | 16 | 17 |
Some refinery naphthas also contain someolefinic (alkene-containing) hydrocarbons,[15] such as naphthas derived from thefluid catalytic cracking,visbreakers andcoking processes used in many refineries. Those olefin-containing naphthas are often referred to ascracked naphthas.[16]
In some petroleum refineries, the cracked naphthas are desulfurized and catalytically reformed (as are the virgin naphthas) to produce additional high-octane gasoline components.
Some petroleum refineries also produce small amounts of specialty naphthas for use as solvents,[17] cleaning fluids and dry-cleaning agents, paint and varnish diluents,asphalt diluents, rubber industry solvents, recycling products, andcigarette-lighter, portable-camping-stove and lantern fuels. Those specialty naphthas are subjected to various purification processes which adjusts chemical characteristics to suit specific needs.[18]
On a much larger scale, petroleum naphtha is also used in thepetrochemicals industry as feedstock tosteam reformers andsteam crackers for the production ofhydrogen,[19]ethylene, and other olefins.[20]
People can be exposed to petroleum naphtha in the workplace by breathing it, swallowing it, skin contact, and eye contact. TheOccupational Safety and Health Administration (OSHA) set the legal limit (permissible exposure limit) for petroleum naphtha exposure in the workplace as 500 ppm (2000 mg/m3) over an 8-hour workday. TheNational Institute for Occupational Safety and Health (NIOSH) has set arecommended exposure limit (REL) of 350 mg/m3 over an 8-hour workday and 1800 mg/m3 over 15 minutes. At levels of 1100 ppm, 10% of the lower explosive limit, petroleum naphtha isimmediately dangerous to life and health.[21]