Naphtha

Naphtha is a flammable liquid hydrocarbon mixture composed primarily of low-molecular-weight aliphatic and aromatic hydrocarbons. It is most commonly obtained as a fraction of crude oil during petroleum refining, though it can also be produced from natural gas condensates, petroleum distillates, and through the fractional distillation of coal tar and peat. The term is historically broad and context-dependent, having been used to describe a range of petroleum-related liquids across different periods, industries, and regions. In Australia, naphtha is commonly known as Shellite, reflecting its use as a light petroleum solvent and fuel.

Etymology and Linguistic Origins

The word naphtha originates from Latin, via Ancient Greek, and is ultimately derived from the Middle Persian word naft, meaning “wet” or “petroleum”. This term itself is thought to have been assimilated from the Akkadian language, where napṭum referred to petroleum or bitumen. Cognates of the word persist across many Semitic and Indo-European languages, including Arabic (naft), Syriac (naft), and Hebrew, all signifying petroleum or crude oil. These linguistic connections reflect the long-standing human familiarity with naturally occurring hydrocarbons, particularly in the Near East.

Naphtha in Antiquity

In antiquity, naphtha referred broadly to naturally occurring petroleum substances, especially those that were highly flammable. Ancient texts describe materials consistent with light petroleum fractions that could ignite easily when exposed to heat or sunlight. In the Second Book of Maccabees, a substance called Nephthar is described as igniting spontaneously under sunlight, suggesting a volatile hydrocarbon mixture. Similarly, the Mishnah mentions naphtha as one of the oils generally permitted for use in lamps, though preferences varied among scholars.
Ancient Greek sources used the term to denote petroleum, pitch, or resinous materials. Such substances were reportedly employed in incendiary devices, including those used by Roman engineers. These early applications highlight the remarkable combustibility of light petroleum fractions long before the development of modern refining techniques.

Historical Development in the Modern Period

From the nineteenth century onwards, the meaning of naphtha became more closely associated with specific petroleum-derived solvents and fuels. Solvent naphtha came to denote products rich in aromatic hydrocarbons such as xylene and trimethylbenzenes, obtained through petroleum distillation. These substances found widespread industrial use as solvents, degreasers, and cleaning agents.
One notable historical application was in laundry soaps, where mineral spirits derived from naphtha served as active cleaning agents. Over time, concerns regarding carcinogenicity and health risks led to the removal of certain naphtha components from consumer products. During this period, the term petroleum naphtha was commonly used to describe a colourless, gasoline-like liquid, while coal tar naphtha referred to darker, aromatic-rich mixtures obtained from coal tar.

Petroleum Usage and Global Terminology

In older English usage, naphtha was sometimes synonymous with crude oil, though this meaning is now obsolete. However, many modern languages retain related terms with varying meanings. In several Eastern European and Baltic languages, words derived from nafta denote crude oil or diesel fuel. In Russian, neft refers to crude oil, while nafta may denote lighter petroleum fractions. In parts of South America, particularly Argentina, Uruguay, and Paraguay, nafta is commonly used to mean petrol. These variations underscore the term’s semantic flexibility and regional specificity.

Classification and Types

Efforts to categorise naphtha more precisely have led to several classification schemes. One common distinction is between light naphtha and heavy naphtha, based primarily on boiling point ranges. Light naphtha typically consists of hydrocarbons with five to six carbon atoms per molecule, while heavy naphtha contains hydrocarbons with six to ten carbon atoms.
Another approach considers hydrocarbon structure, differentiating paraffinic, naphthenic, and aromatic naphthas. In practice, petroleum naphtha often contains a mixture of light and heavy components and may constitute approximately 15–30% of crude oil by weight. Because these definitions overlap and vary by industry, the term remains broad and context-dependent.

Industrial and Commercial Uses

Naphtha has a wide range of industrial applications due to its volatility, solvency, and combustibility.
One significant use is in the dilution of heavy crude oil. Heavy crude is highly viscous and cannot be easily transported by pipeline. Naphtha acts as an efficient diluent, reducing viscosity and enabling transport. After processing, the naphtha can often be recovered and reused, making it economically advantageous. The importance of such diluents has increased as global oil production has shifted towards heavier crude reserves.

Fuel Applications

Light naphtha has long been used as a fuel in specialised contexts. It is the primary component of lighter fluid for wick-based cigarette lighters and is commonly used in camping stoves and lanterns under the name white gas. Its low boiling point allows for easy ignition, and it is often preferred over kerosene because it leaves fewer residues and is less prone to clogging fuel systems.
Historically, naphtha was also used as a fuel in certain marine engines known as naphtha launches, particularly where steam engines were impractical or restricted by safety regulations. As an internal combustion engine fuel, however, petroleum naphtha has limited use due to its low octane rating and reduced efficiency compared with petrol. It can operate unmodified diesel engines but produces noisier combustion and longer ignition delays.

Role in the Plastics and Petrochemical Industry

Naphtha is a critical feedstock in the petrochemical industry, particularly in the production of plastics. Through processes such as steam cracking, naphtha is converted into basic olefins, including ethylene and propylene, which serve as the building blocks for a vast array of polymers, synthetic fibres, and chemical products. In this context, naphtha plays a central role in modern industrial chemistry and materials science.

Health and Safety Considerations

Naphtha poses several health and safety risks due to its chemical properties. It is highly flammable and forms explosive vapour–air mixtures. Safety data sheets commonly list hazards including skin and respiratory irritation, central nervous system effects, and potential carcinogenicity, depending on composition.
Occupational exposure may occur through inhalation, ingestion, or skin contact. Regulatory bodies have established exposure limits to mitigate health risks. In high concentrations, naphtha vapours can be immediately dangerous to life or health, necessitating strict controls in industrial settings.