General Names:
Alkyl benzene bottom sulfonates
Dialkyl benzene sulfonates
Heavy alkylate sulfonates
Overbased sulfonates or overbasified sulfonates
Petrolum sulfonates
Sulfonates
Synthetic petroleum sulfonates
Synthetic long-chain alkyl benzenes sulfonates
Petro-sulfonates
Oil-soluble Sulfonates
Sulfonated Petroleum Oils
Examples:
Calcium petroleum sulfonate
Sodium salt of dialkyl (C10-C14) benzene sulfonate
Barium dinonylnaphthalene sulfonate
Description
Petroleum sulfonates are derived from sulfonating petroleum distillates, typically involving the reaction of sulfuric acid or sulfur trioxide with petroleum fractions. These compounds are characterized by a sulfonate group (-SO3H) attached to an aromatic hydrocarbon, which can vary in molecular weight and structure. A group of sulfonates whose common characteristic is their molecular weight and oil solubility. The molecular weight is higher than that of the normal detergent sulfates and sulfonates making the acids and salts generally insoluble in water but soluble in mineral oil. The various types of sulfonates are characterized by different molecular weight, the particular salt and the alkalinity. These products originated as a by-product in the refining of petroleum and were thus referred to as petroleum sulfonates.
Petroleum sulfonates are sulfonated extracts from lubricating oil fractions. The products are sulfonates of fused ring compounds and there are usually two fractions, the green acids which are water soluble and the mahogany acids which are water insoluble but soluble in mineral and natural oils. However, due to shortages of the natural sulfonates, plus certain disadvantages, chemical manufacturers have attempted to find synthetic replacements for these natural petroleum sulfonates. Such products have become known as synthetic petroleum sulfonates.
Synthesis
The synthesis of petroleum sulfonates involves several steps:
Feedstock Selection: Suitable petroleum fractions or alkylbenzene are chosen based on desired properties.
Sulfonation: The feedstock is reacted with sulfuric acid or sulfur trioxide to introduce sulfonic acid groups.
Neutralization: The resulting sulfonic acids are neutralized with a base (e.g., sodium hydroxide or calcium hydroxide) to form sulfonate salts.
Purification: The product is purified to remove unreacted materials and by-products.
Synthetic petroleum sulfonates are sulfonated alkyl and dialkyl derivatives of benzene, xylene, or naphthalene and are offered by suppliers as a substitute for the petroleum sulfonates, the main types available are:
- Alkyl benzene bottom sulfonates:
These are the sulfonates of the residues from the distillation of the alkylation of benzene to make detergent alkylate. The composition of such residues is a mixture of dialkyl (averaging C12) benzene and diphenyl alkane (the alkane having an average of C12 and the phenyl groups being at both ends of the alkyl chain). On sulfonation, the diphenyl alkane gives a very water-soluble sulfonate which is washed out in the processing. Thus the sulfonate is principally dialkyl benzene sulfonate with the length of the alkyl group dependent upon the distribution of chain length used in the alkylation reaction.
- Dialkyl benzene sulfonates:
The crude alkyl benzene bottoms can be fractionated and the dialkyl benzene separated and then sulfonated. The products are similar to the sulfonates above.
- Synthetic long-chain alkyl benzenes:
The long alkyl chain is synthetically produced at C20-C26 and then reacted with benzene.
- Synthetic long-chain alkyl xylenes:
The alkyl chain is similar to that in (3) but is generally shorter to obtain oil solubility.
- Synthetic dialkyl (normally C9) naphthalenes:
Oil solubility can be achieved at a lower alkyl chain length when naphthalene is the nucleus for sulfonation.
The products are all made by conventional sulfonation reagents, either oleum or sulfur trioxide. Oleum has been the major reagent used in batch reactors but the production is difficult in removing the unreacted acid or sodium sulfate. After neutralization, the product becomes water insoluble and washing can give considerable problems in emulsification. In recent years considerable efforts have been made to sulfonate the various alkylates using continuous sulfur trioxide reactors which have been designed to manufacture water-soluble detergent sulfonates. This method has the advantage of reducing problems of unreacted acid but the high viscosity of the starting alkylates (much higher than conventional dodecyl benzene) can give severe oxidation, poor conversions and considerable sludge formation.
All products are normally produced and sold as 40-60% solutions in a mineral oil. The sodium, calcium and barium salts are the most common although zinc and magnesium salts are available for special applications.
The natural petroleum sulfonates are chemically very ill-defined and subject to variability in some functional uses. This is not easily detected using chemical tests. All the synthetic petroleum sulfonates (groups (1)-(5) in the description above) do not exactly replace the natural products and each group has its specific properties.
General properties
Surface Activity
They act as surfactants, reducing surface tension and improving the wetting and emulsifying properties. Emulsifying mineral oil in water; also they can form microemulsions.
Solubility
Soluble in mineral oil particularly mineral oil which is predominantly paraffinic with low aromatic content, making them suitable for oil-based formulations. Excellent dispersing agents for insoluble dispersions in mineral oils.
Chemical properties:
In general have the properties of sulfonates, i.e. stable to acid/alkali and good heat stability; overbasified salts will combat acidic conditions, e.g. automotive crank case oils.
Thermal Stability
They exhibit good thermal stability, maintaining their properties at elevated temperatures.
Detergency
They are effective detergents, helping to remove contaminants and deposits.
Corrosion Inhibition
They can inhibit corrosion, protecting metal surfaces in various environments by the ability to replace water on a metallic surface and adhere to that surface to give a degree of protection against rust.
Biodegradability
Depending on the specific formulation, some petroleum sulfonates can be biodegradable.
Applications
Automotive and Industrial Lubricants
Engine Oils: Petroleum sulfonates are used as detergents and dispersants in engine oils, keeping the engine clean by preventing the formation of sludge and deposits.
Greases: They enhance the performance of greases, providing improved lubrication and protection under extreme conditions.
Metal working
petroleum sulfonates are used in cutting oils and coolants. They provide lubrication, cooling, and corrosion protection during machining and metal forming processes.
Oil in water emulsifying agents (sodium salts) for mineral oil in producing soluble cutting oils; they also give some degree of rust protection; they are usually used in admixture with other surfactants with emulsifying properties; degreasing of metal surfaces is possible using petroleum sulfonates modified with fatty acid soaps and coupling agents to make emulsion or emulsifiable cleaners.
Rust inhibitors
Petroleum sulfonates are used as rust inhibitors in various applications, including automotive, industrial, and marine environments. They form a protective barrier on metal surfaces, preventing corrosion.
Calcium or barium salts for temporary metal protection; the higher equivalent weight sulphonates ( > 500) are the most efficient.
Fuel oils and petrol
Petroleum sulfonates are used as additives in fuels to improve their properties. They help to prevent deposit formation and corrosion in fuel systems.
Pigment dispersants
Dispersing aids for pigments in organic solvents.
Oilfield Chemicals
Enhanced Oil Recovery (EOR):
petroleum sulfonates are used in surfactant flooding, a method of enhanced oil recovery. They reduce the interfacial tension between oil and water, allowing more oil to be extracted from reservoirs.
Drilling Fluids:
They act as emulsifiers and dispersants in drilling fluids, enhancing the stability and performance of the fluids under high-temperature and high-pressure conditions. crude oil de-emulsifiers; emulsifier for microemulsions in enhanced oil recovery (tertiary recovery).
Mining
Petroleum sulfonates function as promoters or collectors and lower molecular weight products act as frothing agents; main ores processed with sulfonates are iron and silica sand.
Textiles
Petroleum sulfonates are used in textile wet processing as wetting agents and emulsifiers, improving the efficiency of dyeing and finishing processes. The type of formulations used in metalworking are used in textile processing oils to give fiber-metal and fiber-fiber lubrication.
Emulsifiers
In the formulation of emulsions, petroleum sulfonates act as emulsifiers, stabilizing oil-water mixtures. They are used in the production of paints, coatings, and agricultural products. They act as dispersants in paints and coatings, improving the distribution of pigments and enhancing the stability of the formulations.
Detergents and Cleaners
Due to their excellent surface-active properties, petroleum sulfonates are used in industrial and household detergents and cleaners. They help to emulsify oils and remove dirt and grime. They are too employed as De-emulsifiers to separate water-in-oil emulsions in various cleaning processes.
Disadvantages
Cost
The production and refinement process can be costly, leading to higher prices compared to other surfactants.
Compatibility Issues
They may not be compatible with certain additives and materials, limiting their use in specific formulations.
Staining
Petroleum sulfonates can cause staining on fabrics and surfaces, which may be undesirable in some applications.
Foaming
In some applications, excessive foaming can be an issue, requiring the use of anti-foaming agents.
Environmental Concerns
Petroleum sulfonates can be environmentally harmful due to their non-biodegradable nature and potential to accumulate in ecosystems.
Toxicity
Certain formulations can be toxic to aquatic life, necessitating careful handling, disposal and pose health risks to humans upon prolonged exposure.
Specification
Molecular Weight
The molecular weight of petroleum sulfonates can range from low to high, depending on the degree of sulfonation and the nature of the petroleum feedstock.
High molecular weight material gives good rust preventive properties while lower molecular weight material gives good emulsifying properties. If both emulsifying and rust-preventative properties are required, the molecular weight distribution must be carefully controlled.
Sulfonation Degree
The degree of sulfonation determines the surfactant properties and can be tailored to specific applications.
Sulfonate Content
The sulfonate content, usually expressed as a percentage, indicates the amount of active sulfonate groups in the product (50-60%)
Viscosity
can affect the handling and application of petroleum sulfonates, with different grades available for various needs.
Solubility
The solubility in water and oil is a key factor in determining the application of petroleum sulfonates.
Equivalent weight
equals molecular weight for monovalent salts, e.g. sodium, but equal to half the molecular weight for the divalent salts, e.g. calcium. The equivalent weight of the sulfonic acid before neutralization is nearly always in the range 400-600.
Total base number, 0-400 mg KOH/g
Acid number, 0.1-1 % (as sulfuric acid)
Metal content (calcium and barium), 2-3% normal salts, 8-13% overbased
Inorganic salts (sodium sulfate), 0.1-1 %
Inorganic chloride content should be very low ( < 100 ppm) for rust inhibitors.
Water, 0.5-5%
pH: The pH of the product is important for stability and compatibility with other ingredients, and typically ranges from 7 to 10, depending on the neutralizing agent used.
Color: The color of petroleum sulfonates can range from light yellow to dark brown, influenced by the refining process and the presence of impurities.
References
- Schmitt, T. M. (2001). Analysis of Surfactants. CRC Press.
- Rosen, M. J., & Kunjappu, J. T. (2012). Surfactants and Interfacial Phenomena. John Wiley & Sons.
- Myers, D. (2020). Surfactant Science and Technology. John Wiley & Sons.
- Zoller, U. (2004). Handbook of Detergents, Part B: Environmental Impact. CRC Press.
- Mulligan, C. N. (2005). Environmental applications for biosurfactants. Environmental Pollution, 133(2), 183-198.
- Hussain, S. M., & Saleem, M. (2018). Advances in Petroleum Sulfonates: A Review of Their Synthesis and Applications. Journal of Petroleum Science and Engineering, 170, 406-419.
- Smith, R. G., & Doolittle, D. H. (1983). Petroleum Sulfonates in Enhanced Oil Recovery. Journal of Petroleum Technology, 35(5), 919-928.
- McCutcheon, J. A. (1997). Detergents and Emulsifiers. Allured Publishing Corporation.
- American Petroleum Institute. (2020). Petroleum Additives: Technical Data Book.
- Kirk-Othmer Encyclopedia of Chemical Technology (2007). John Wiley & Sons, Inc
