Description / Application
Creosote is the portion of chemical products obtained by the distillation of a tar that remains heavier than water, notably useful for its anti-septic and preservative properties. It is produced in some quantities from the burning of wood and coal in blast furnaces and fireplaces; commonly found inside chimney flues when the wood or coal burns incompletely, producing soot and tarry smoke, and is the compound responsible for the preservation and the flavour of meat in the process of smoking.
The two main types in industrial production are wood-tar creosote and coal-tar creosote. The coal-tar variety, having stronger and more toxic properties, has chiefly been used as a preservative for wood, while the wood-tar variety has been used for meat preservation, wood treatment, and for medicinal purposes as an expectorant, anti-septic, astringent, anaesthetic and laxative, though these have mostly been replaced by newer medicines. Coal-tar creosote had also, in the past, been used as an escharotic to burn malignant skin tissue and in dentistry to prevent necrosis but no longer is used that way because of its toxic, carcinogenic properties and because better and safer treatments are now available. Varieties of creosote have also been made from both petroleum and oil shale called oil-tar creosote, when derived from the oil tar, and water-gas-tar creosote when derived from the water gas tar. Creosote also has been made from pre-coal formations such as lignite, yielding lignite-tar creosote and peat, yielding peat-tar creosote.
Creosotes are commercially valuable and, therefore, are produced industrially on a large scale, either for direct use or as raw material for the production or extraction of various chemicals. There are several other names for such fluids, but most are not trustworthy, being regional, applying to only some variants, or to other fluids as well. For example, the term pitch oil can refer to either creosote-like fluids or kerosene.
For some part of their history, wood-tar creosote and coal-tar creosote were suggested to be the same substance — only in different purities — accounting for their common name; the two were determined only later to be chemically different substances. All types of creosote are composed of phenol derivatives and share some quantity of simple phenols, but these are not the only active element of any creosote. For its useful effect, wood-tar creosote relies on the presence of methyl ethers of phenol, and coal-tar creosote on the presence of naphthalenes and anthracenes; otherwise either would dissolve in water.
Wood-tar creosote is a colourless to yellowish greasy liquid with a smoky odour, produces a sooty flame when burned, and has a burned taste. It is buoyant, with a specific gravity of 1.037 to 1.087, retains fluidity at a very low temperature, and boils at 205-225°C. When transparent, it is in its purest form. Dissolution in water requires up to 200 times the amount of water as the base creosote. The creosote is a combination of plant phenolics: primarily guaiacol and creosol (4-methylguaiacol), which will typically constitute 50% of the oil; second in prevalence, cresol and xylenol; the rest being a combination of monophenols and polyphenols.
The simple phenols are not the only valued element in wood-tar creosote; on their own they coagulate albumin, the water-soluble proteins contained in meat, so serve as a preserving agent, but also cause disintegration. Most of the phenols in the creosote are methoxy derivatives — they contain the methoxy group linked to the benzene nucleus (O–CH3). The level of high methyl derivates created from the action of heat on wood (also apparent in the methyl alcohol produced through distillation) make wood-tar creosote substantially different from coal-tar creosote. Guaiacol is a methyl ether of pyrocatechin, while creosol is a methyl ether of methyl-pyrocatechin, the next homolog of pyrocatechin. Methyl ethers differ from simple phenols in being less soluble in water, and less caustic and poisonous. This allows meat to successfully be preserved without disintegration, and allows creosote to be used as a medical treatment.
Because wood-tar creosote is used for its guaiacol and creosol content, it is generally derived from beechwood rather than other woods, since it distills with a higher proportion of those chemicals to other phenolics. The creosote can be obtained by distilling the wood tar and treating the fraction heavier than water with a Sodium Hydroxide solution. The alkaline solution is then separated from the insoluble oily layer, boiled in contact with air to reduce impurities, and decomposed by diluted sulphuric acid. This produces a crude creosote, which is purified by re-solution in alkali and re-precipitation with acid and then redistilled with the fraction passing over between 200° and 225° constituting the purified creosote.
When ferric chloride is added to a dilute solution, it will turn green; a characteristic of ortho-oxy derivatives of benzene. It dissolves in sulphuric acid to a red liquid, which slowly changes to purple-violet. Shaken with hydrochloric acid in the absence of air, it becomes red, the color changing in the presence of air to dark brown or black.
In preparation of food by smoking, guaiacol contributes mainly to the smoky taste, while the dimethyl ether of pyrogallol, syringol, is the main chemical responsible for the smoky aroma.
Coal-tar creosote is greenish-brown liquid, with different degrees of darkness, viscosity, and fluorescence depending on how its made. When freshly made, the creosote is a yellow oil with a greenish cast and highly fluorescent; the fluorescence increased by exposure to air and light. After settling, the oil is dark green by reflected light and dark red by transmitted light. To the naked eye, it will generally appear brown. The creosote (often called “creosote oil”) consists almost wholly of aromatic hydrocarbons, with some amount of bases and acids and other neutral oils. The flash point is 70–75°C and burning point is 90–100°C, and when burned it releases a greenish smoke. The smell largely depends on the naptha content in the creosote; if there is a high amount, it will have a naptha-like smell; otherwise it will smell more of tar.
In the process of coal-tar distillation, the distillate is collected into four fractions; the “light oil”, which remains lighter than water, the “middle oil” which passes over when the light oil is removed; the “heavy oil”, which sinks; and the “anthracene oil”, which when cold is mostly solid and greasy, of a buttery consistence. Creosote refers to the portion of Coal Tar which distills as “heavy oil”, typically between 230–270°C, also called “dead oil”; it sinks into water but still is fairly liquid. Carbolic acid is produced in the second fraction of distillation and is often distilled into what is referred to as “carbolic oil”.
Commercial creosote will contain substances from six groups. The two groups occur in the greatest amounts and are the products of the distillation process — the “tar acids“, which distill below 205°C and consist mainly of phenols, cresols, and xylenols, including carbolic acid — and aromatic hydrocarbons, which divide into naphthalenes, which distill approximately between 205° and 255°C, and constituents of an anthracene nature, which distill above 255°C. The quantity of each varies based on the quality of tar and temperatures used, but generally, the tar acids won’t exceed 5%, the naphthalenes will make up 15 to 50%, and the anthracenes will make up 45% to 70%. The hydrocarbons are mainly aromatic; derivatives of benzene and related cyclic compounds such as naphthalene, anthracene, phenanthrene, acenapthene, and fluorine. Creosotes from vertical-retort and low temperature tars contain, in addition, some paraffinic and olefinic hydrocarbons. The tar-acid content also depends on the source of the tar — it may be less than 3% in creosote from coke-oven tar and as high as 32% in creosote from vertical retort tar. All of these have anti-septic properties. The tar acids are the strongest anti-septics but have the highest degree of solubility in water and are the most volatile; so, like with wood-tar creosote, phenols are not the most valued component, as by themselves they would lend to being poor preservatives. In addition, creosote will contain several products naturally occurring in coal — nitrogen-containing heterocycles, such as acridines, carbazoles, and quinolines, referred to as the “tar bases” and generally make up about 3% of the creosote — sulfur-containing heterocycles, generally benzothiophenes — and oxygen-containing heterocycles, dibenzofurans. Lastly, creosote will contain a small number of aromatic amines produced by the other substances during the distillation process and likely resulting from a combination of thermolysis and hydrogenation. The tar bases are often extracted by washing the creosote with aqueous mineral acid, although they’re also suggested to have anti-septic ability similar to the tar acids.
Commercially used creosote is often treated to extract the carbolic acid, naphthalene, or anthracene content. The carbolic acid or naphthalene is generally extracted to be used in other commercial products. American produced creosote oils typically will have low amounts of anthracene and high amounts of naphthalene, because when forcing the distillate at a temperature that produces anthracene the soft pitch will be ruined and only the hard pitch will remain; this ruins it for use in roofing purposes, and only leaves a product which isn’t commercially useful.
Coal-tar creosote is the most widely used wood treatment today; both industrially, processed into wood using pressure methods such as “full-cell process” or “empty-cell process”, and more commonly applied to wood through brushing. In addition to toxicity to fungi, insects, and marine borers, it serves as a natural water repellent. Its commonly used to preserve and waterproof cross ties, pilings, telephone poles, power line poles, marine pilings, and fence posts. Although suitable for use in preserving the structural timbers of buildings, it is not generally used that way because it is difficult to apply.
Due to its carcinogenic character, the European Union has regulated the quality of creosote for the EU market and requires that the sale of creosote be limited to professional users. The United States Environmental Protection Agency regulates the use of coal tar creosote as a wood preservative under the provisions of the Federal Insecticide, Fungicide, and Rodenticide Act. Creosote is considered a restricted-use pesticide and is only available to licensed pesticide applicators.
Shipment / Storage
Creosoted Cargo such as piles, telephone poles and railway cross ties preferably to be stowed on deck. The smell of creosote can hardly ever be removed from the decks and it will affect other cargoes. Do not place the containers with creosoted cargo nearby odour sensitive cargo.
In order to preserve wood railway sleepers against weather and the attacks of insects, they are usually impregnated with creosote — a Coal Tar product. Creosote in any form is a very objectionable cargo owing to the very strong and pungent smells which it throws off. Fine or edible goods, dry or wet, should not be stowed in or near to a compartment carrying creosoted timber and the greatest possible care should be observed in removing all traces of creosote or its fumes (after the creosoted goods are landed) before loading grain or any other cargo liable to taint or damage. Cases have occurred, where vessels have been declared unseaworthy because of the presence of these fumes, and large claims for damage to subsequent cargoes have been paid. Sleepers are made from various classes of timber: pitchpine, oak and jarrah wood principally. Iron and concrete sleepers are extensively used; usually nested for shipment.
Creosote is colourless and inflammable with a highly pungent smell. Often shipped in second-hand drums which are prone to leak. A very undesirable cargo, and should only be received on a vessel carrying fine and clean cargo if fumes cannot come into contact with cargo, ships’ stores, or find their way into living quarters. It should be handled and stowed very carefully to avoid leakage, and the greatest care should be taken to remove all traces of creosote stains and smells after discharge before shipping the next cargo.
ISO containers should be lined (floors, and well up the walls) with impervious material (e.g. plastic). Preferably not in containers subsequently to be used for foodstuffs or fine goods. In any case never in insulated or refrigerated containers. Fumes/spillage will almost certainly damage the fabric of container tilts (open sided, open topped containers).When carried in bulk, the oil must be carried in completely self contained tanks to avoid contamination of the creosote. In bulk it is normally carried at a temperature of between 32.2 and 37.8 C° throughout the voyage.
Toxic by inhalation of fumes, skin and eye irritant. Use may be restricted.
See IMDG Code and applicable MSDS sheets.