Petroleum naphtha

Petroleum naphtha is an intermediate hydrocarbon liquid stream derived from the refining of crude oil. It is most usually desulfurized and then catalytically reformed, which re-arranges or re-structures the hydrocarbon molecules in the naphtha as well as breaking some of the molecules into smaller molecules to produce a high-octane component of gasoline (or petrol).

There are quite literally hundreds of different petroleum crude oil sources worldwide and each crude oil has its own unique composition or assay. There are also hundreds petroleum refineries worldwide and each of them are designed to process either a specific crude oil or specific types of crude oils. That means that it is virtually impossible to provide a definitive, single definition of the word naphtha since each each refinery produces its own naphthas with their own unique initial and final boiling points and other physical and compositional characteristics. In other words, naphtha is a generic term rather than a specific term.

In addition, naphthas may be also be produced from coal tar, shale deposits, tar sands such as in Canada, the destructive distillation of wood and coal gasification or biomass gasification to produce a syngas followed by the Fischer-Tropsch process to convert the syngas into liquid hydrocarbon products. For that reason, this article is entitled Petroleum naphtha and deals only with naphthas produced by the proccessing of crude oil in petroleum refineries.

The major source of petroleum naptha in a petroleum refinery

The first unit process in a petroleum refinery is the crude oil distillation unit. The overhead liquid distillate from that unit is called virgin or straight-run naphtha and that distillate is the largest source of naphtha in most petroleum refineries. The naphtha is a mixture of very many different hydrocarbon compounds. It has an initial boiling point of about 35 °C and a final boiling point of about 200 °C, and it contains paraffin, naphthene (cyclic paraffins) and aromatic hydrocarbons ranging from those containing 4 carbon atoms to those containing about 10 or 11 carbon atoms.

The virgin naphtha is often further distilled to produce a light naphtha containing most (but not all) of the hydrocarbons with 6 or less carbon atoms and a heavy naphtha containing most (but not all) of the hydrocarbons with more than 6 carbon atoms. The heavy naphtha has an initial boiling point of about 140 to 150 °C and a final boiling point of about 190 to 205 °C.

It is the virgin heavy naphtha that is usually processed in a catalytic reformer because the light naphtha has molecules with 6 or less carbon atoms which, when reformed, tend to crack into butane and lower molecular weight hydrocarbons which are not useful as high-octane gasoline blending components. Also, the molecules with 6 carbon atoms tend to form aromatics which is undesirable because governmental environmental regulations in a number of countries limit the amount of aromatics (most particularly benzene) that gasoline may contain.

Types of virgin naphthas

The table just below lists some fairly 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:

Typical Heavy Naphthas

Crude oil name $\Rightarrow$ Location $\Rightarrow$	Barrow Island Australia	Mutineer-Exeter Australia	CPC Blend Kazakhstan	Draugen North Sea
Initial boiling point, °C	149	140	149	150
Final boiling point, °C	204	190	204	180
Paraffins, liquid volume %	46	62	57	38
Naphthenes, liquid volume %	42	32	27	45
Aromatics, liquid volume %	12	6	16	17

Cracked naphthas

Some refinery naphthas also contain some olefinic hydrocarbons, such as naphthas derived from the fluid catalytic cracking, visbreakers and coking processes used in many refineries. Those olefin-containing naphthas are often referred to as cracked naphthas.

In some (but not all) petroleum refineries, the cracked naphthas are desulfurized and catalytically reformed (as are the virgin naphthas) to produce additional high-octane gasoline components.

Other uses

Some petroleum refineries also produce a small amount of specialty naphthas for use as solvents, paint removers, cigarette lighter fuel, portable camping stove fuel and lantern fuel. Those specialty naphthas are subjected to various purification processes. Sometimes the specialty naphthas are called white oil or white gas.

On a much larger scale, petroleum naphtha is also used in the petrochemical industry as feedstock to steam reformers for the production of hydrogen, ethylene and other olefins.