Petroleum solvents (nefras, white spirit)

Petroleum solvents (nefras) are straight-run gasoline or kerosene fractions of low-sulfur crude oils, as well as dearomatised products of catalytic reforming, used for dissolving and extracting organic compounds. They are transparent oily liquids with a characteristic petroleum odour that are highly flammable and require safety precautions during handling. Petroleum solvents occupy a key place in the paint and coatings, rubber, oil extraction, wood chemical and other industries, and their range includes dozens of grades differing in hydrocarbon composition, boiling ranges and aromatic content.

Chemical Nature and Classification Principles

Chemically, petroleum solvents are mixtures of hydrocarbons of various classes — paraffinic (alkanes), isoparaffinic (isoalkanes), naphthenic (cycloalkanes) and aromatic (arenes). The ratio of these groups determines the dissolving power, volatility, toxicity and other performance characteristics of the product.

Depending on the predominant hydrocarbon composition, petroleum solvents are classified into groups. Group P combines paraffinic solvents containing more than 50% by mass of normal alkanes. Group I includes isoparaffinic solvents with an isoalkane content of more than 50%. Group N is represented by naphthenic solvents in which cycloalkanes account for more than 50%. Group A combines aromatic solvents with an arene content of more than 50%, and group C — mixed solvents in which the content of each hydrocarbon group does not exceed 50%.

Additionally, within groups P, I, N and C, subgroups are distinguished depending on the aromatic hydrocarbon content. Subgroup 0 corresponds to an arene content of less than 0.1%, subgroup 1 — from 0.1 to 0.5%, subgroup 2 — more than 0.5 to 2.5%, subgroup 3 — more than 2.5 to 5.0%, subgroup 4 — more than 5.0 to 25.0%, subgroup 5 — more than 25.0 to 50.0%. This detail allows the solvent to be precisely matched to a specific technological task, whether it is degreasing, extraction or dilution of paint and coating materials.

The designation of a petroleum solvent includes the group name, subgroup number and boiling limits written through a slash. For example, the petroleum ether fraction is designated as nefras-P4-30/80, straight-run gasoline for the rubber industry — as nefras-C3-80/120, white spirit substitute — as nefras-C4-155/200, heptane solvent — as nefras-C3-94/99, and petroleum aromatic solvent — as nefras-A-150/330.

White Spirit as a Key Representative

White spirit (nefras-C4-155/200) is one of the most in-demand petroleum solvents and is a high-boiling gasoline fraction. Chemically, it is a mixture of aliphatic hydrocarbon fractions from C7 to C12. In international practice, white spirit is also known as Stoddard solvent, mineral spirit and turpentine substitute.

Requirements for white spirit in Russia and CIS countries are regulated by GOST 3134-78. According to the standard, the density at 20 °C must not exceed 0.790 g/cm³. The fractional composition is characterised by an initial boiling point not higher than 160 °C, with 10% of the product distilling at a temperature not higher than 170 °C and 90% not higher than 195 °C. At least 98% of the product must distil up to 200 °C, and the residue in the flask must not exceed 2.0%. The flash point in a closed cup is not lower than 33 °C. Volatility by xylene is in the range of 3.0–4.5, and the aniline point is not higher than 65.0 °C. The mass fraction of aromatic hydrocarbons does not exceed 16%, and the mass fraction of total sulfur — 0.025%. The product must pass the copper strip test, confirming the absence of corrosive-active compounds.

White spirit belongs to hazard class 3 in terms of impact on the human body. It is highly flammable, and its vapours form explosive mixtures with air. When working with white spirit, personal protective equipment must be used, effective ventilation must be provided and fire safety measures must be observed.

Nefras-C 50/170 as a Technical Solvent

A separate group of petroleum solvents consists of products intended for technical purposes. Nefras-C 50/170 is a transparent oily liquid with a characteristic petroleum product odour and belongs to toxicity class 4. Requirements for this product are established by GOST 8505-80. Nefras-C 50/170 finds application in various industries where dissolution or extraction of organic compounds is required, as well as a base for technical compositions.

Production Technology

The production of petroleum solvents is inextricably linked to petroleum refining processes. The main sources of feedstock are straight-run gasoline and kerosene fractions of low-sulfur crude oils, as well as catalytic reforming products which, after dearomatisation, acquire the necessary properties. The technological process includes fractionation of petroleum feedstock to isolate narrow fractions with specified boiling ranges, hydrotreating to remove sulfur compounds and, if necessary, dearomatisation to reduce the content of aromatic hydrocarbons.

The quality of petroleum solvents is assessed by a set of indicators: fractional composition, density, flash point, aromatic hydrocarbon and sulfur content, aniline point and volatility. These characteristics determine the behaviour of the solvent in the technological process — evaporation rate, dissolving power with respect to film-formers, safety and compatibility with other formulation components.

Applications

Paint and coatings industry remains the largest consumer of petroleum solvents. White spirit and other group C grades are used to dilute oil paints, enamels, varnishes, primers, drying oils and bitumen materials. Solvents provide the required viscosity of the paint material, uniformity of application and quality of the formed coating. In the production of drying oils and oil paints, petroleum solvents perform the function of a technological medium that allows the consistency and drying time to be regulated.

Rubber industry uses nefras to dissolve rubbers and prepare rubber adhesives, as well as to degrease surfaces before bonding. Grades with certain boiling limits ensure the stability of adhesive compositions and the required evaporation rate.

Oil extraction industry uses petroleum solvents to extract vegetable oils from seeds and cake. In this process, high dissolving power, low toxicity and composition stability are important, since the solvent is repeatedly returned to the cycle.

Wood chemical industry uses nefras to extract resins and other valuable components from wood raw materials.

Production of household insecticides and household chemicals is also based on the use of petroleum solvents, which act as a carrier for active substances and ensure the convenience of application of finished forms.

Metalworking and degreasing is another important application area. Petroleum solvents effectively remove oils, fats and other contaminants from the surface of metal parts before painting, assembly or coating.

Other directions include the production of printing inks, photocopier toners, wood preservatives, bitumen and asphalt products, as well as use as solvents in chemical synthesis and laboratory practice.

Safety and Storage

Petroleum solvents are classified as flammable liquids, which requires strict compliance with fire safety rules. Storage is carried out in hermetically sealed containers, in well-ventilated areas, away from heat sources and open flames. When working with solvents, personal protective equipment must be used, including rubber gloves, protective goggles and protective clothing. Solvent vapours can cause irritation of the respiratory tract, dizziness and drowsiness, so premises must be equipped with effective ventilation. On contact with skin, solvents degrease and dry it, which can lead to dermatitis, so prolonged contact must be avoided.

Organising supplies of petroleum solvents, including selecting the grade for a specific technology, logistics and financial support, requires an individual approach taking into account requirements for fractional composition, aromatic hydrocarbon content and transportation conditions. Petroleum solvents are transported in specialised tank cars, barrels and cans in compliance with the requirements for the transport of flammable liquids.