Naphtha
From Wikipedia, the free encyclopedia
Naphtha (not to be confused with Naphthalene) is a group of various volatile flammable liquid hydrocarbon mixtures used primarily as feedstocks in refineries for the catalytic reforming process and in the petrochemical industry for the production of olefins in steam crackers. It is also used in solvent applications in the chemical industry.
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[edit] Production of naphtha in refineries and uses
Naphtha is obtained from petroleum refineries as a small percentage (around 4%) of the distillation of crude oil. It is an intermediate between the lighter gasoline and the heavier benzine. Naphtha has a specific gravity of about 0.7. The generic name naphtha describes a range of different refinery cuts used in the different applications. To further complicate the matter similar naphtha types are often referred to by different names.
The different naphthas are distinguished by:
- density (kg/m3 or specific gravity)
- PONA, PIONA or PIANO analysis, which measures (usually in volume percent but can also be in weight percent):
- Paraffin content (volume percent)
- Isoparaffin content (only in a PIONA analysis)
- Olefins content (volume percent)
- Naphthenes content (volume percent)
- Aromatics content (volume percent)
[edit] Paraffinic naphthas
Generally speaking, less dense ("lighter") naphthas will have a higher paraffin content. These are therefore also referred to as paraffinic naphtha. The main application for these naphthas is as a feedstock in the petrochemical production of olefins. This is also the reason they are sometimes referred to as "light distillate feedstock" or LDF (these naphtha types can also be called "straight run gasoline"/SRG or "light virgin naphtha"/LVN).
When used as feedstock in petrochemical steam crackers, the naphtha is heated in the presence of water vapour and the absence of oxygen or air until the hydrocarbon molecules fall apart. The primary products of the cracking process are olefins (ethylene / ethene, propylene / propene and butadiene) and aromatics (benzene and toluene). These are used as feedstocks for derivative units that produce plastics (polyethylene and polypropylene for example), synthetic fiber precursors (acrylonitrile), industrial chemicals (glycols for instance).
[edit] Heavy naphthas
The "heavier" or rather denser types are usually richer in naphthenes and aromatics and therefore also referred to as N&A's. These can also be used in the petrochemical industry but more often are used as a feedstock for refinery catalytic reformers where they convert the lower octane naphtha to a higher octane product called reformate. Alternative names for these types are Straight Run Benzene (SRB) or Heavy Virgin Naphtha (HVN).
[edit] Other applications / descriptions
Naphthas are also used in other applications such as
- (as an unprocessed component - in contrast to reforming above) in the production of petrol/motor gasoline.
- as industrial solvents and cleaning fluids
- as an oil painting medium
- as the sole ingredient in the home cleaning fluid Energine
- as an ingredient in shoe polish
- as an ingredient in some lighter fluids for wick type lighters such as Zippo lighters.
- as an adulterant to petrol
- as a fuel for portable stoves and lanterns, sold in North America as white gas or Coleman fuel.
- historically, as a probable ingredient in Greek fire (together with grease, oil, sulfur, and naturally occurring saltpeter from the desert)
[edit] Examples
Shellite (Australia), also known as white gas (North America), white spirit or Coleman fuel, is a water white liquid with a hydrocarbon odour. Shellite has a flashpoint less than -30 degrees Celsius, and a boiling point of 47 degrees Celsius. The composition of shellite is 95% paraffins and naphthenes, less than 5% aromatic hydrocarbons and less than 0.5% benzene. It is highly flammable and due to its low flashpoint is used in many low pressure camping stoves. Shellite is also a fast drying solvent used for cleaning metal, hard plastic and painted surfaces.
[edit] Etymology
The origin of the word Naphtha is unclear. It is an Ancient Greek word which was used to refer to any sort of petroleum or pitch. The Greeks themselves borrowed the word from the Old Persian words nafata, naft or neft, which were used to describe bubbling oil. Naphtha may also have been derived from the name of the Vedic Hindu and Avestic god Apam Napat, a form of Agni, or fire god.
Naphtha is the root of the words naphthalene and napalm, which is derived from naptha by mixing under controlled conditions with aluminium salts of palmitic acid (a type of soap).
