Understanding Detergent Additives in Engine Oils: An Overview
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Contents
What is Detergent for Internal Combustion Engine Oils?
Performance Comparison of Main Detergents
Types of detergents for Lubricants.
Alkyl phenates and sulfurized alkyl phenates
What is Detergent for Internal Combustion Engine Oils?
Detergent (for Internal Combustion Engine Oils) is a chemical that can clean engine parts and keep engine parts clean, and help suspend undesirable solid particles in engine oil. Detergent has four functions: acid neutralization, detergence, dispersion, and solubilization.
In engine oil formulations, most detergents use alkaline metal soaps to neutralize organic or inorganic acids generated during oxidation or combustion.
Detergents are generally combined with dispersants and ZDDP and are mainly used in internal combustion engine oils.
- In 1943, the United States discovered that diesel engine oil added with organic carboxylic acid metal soaps, such as oil-soluble fatty acids or naphthenic acids could solve the problem of increased carbon deposits in piston ring grooves, people call it detergent because this type of oil-soluble metal soap has the cleaning ability similar as a water-soluble soap.
- The research on detergents started with metal soaps, and became popular with fatty acids and naphthenic acid soaps. Due to most of the fatty acid metal salts and naphthenic acid metal salts are also oxidation catalysts to lubricant oil, they were replaced by sulfonates, phenates, and phosphates with the development of the lubricant industry.
- In modern lubricant additives, the most popular detergents include Sulfonates, Sulfurized Alkylphenates, Phosphonotthiolate, Alkylsalicylates and Naphthenates. The five types of detergents are initially applied with neutral salts.
- In the late 1940s and early 1950s, with the increase of high-power supercharged diesel engines and the increase of sulfur-containing fuels, as well as more understanding of the neutralization of detergents, people began to develop base detergents and over-base detergents.
- In the late 1950s, detergent products with a base value of 250 mg KOH/g were developed.
- At present, the amount of high base number of products takes the majority of modern lubricant additives, and the base value can reach up to 400~500mgKOH/g. More than 75% of detergents are used in gasoline engine oil and diesel engine oil. The detergent dosage in automobile engine oil can reach 3%~15%, and the content in marine engine oil will be even higher. Marine cylinder oils (TBN 100) contain up to 30% additives, most of these additives are detergents.
Functions of Detergents
Acid Neutralization Ability
Most detergents have a base value, and some have a high base value, which is called a Total Base Number (TBN), and TBN represents the ability to neutralize acids. Different metal salts have different acid-neutralization abilities.
Alkaline sulfonate and phosphate detergents are strong acid-strong alkali salts, and only the over-alkaline part of the detergent, that is, carbonate and hydroxide, can neutralize Acid ability, while neutral sulfonates and phosphates are soaps and have no ability to neutralize acids. However, basic carboxylates, salicylates, and phenates are strong base-weak acid salts, making them Lewis bases. Not only the over-alkaline part has the neutralizing ability, but also the soap has the ability to neutralize the acid.
High base value detergents are generally a combination of carbonates (CaCO3, BaCO3, MgCO3, Na2CO3, Li2CO3, etc.) and metal hydroxides [Ca(OH)2, Ba(OH)2, Mg (OH)2, NaOH, LiOH] and other superparticle state colloids are dispersed in neutral metal-based detergents.
Overbased detergents with high alkali reserves can continuously neutralize the oxidation-derived acids of lubricating oil and fuel oil, preventing them from further oxidative condensation, and thereby reducing the resinous deposits in the engine. At the same time, it can also neutralize the sulfur oxide generated after the combustion of sulfur-containing fuels, preventing it from sulfonating lubricating oil;
It can also neutralize the carboxylic acid, sulfuric acid, nitric acid, etc. produced after gasoline combustion, and prevent them from further acting on hydrocarbons.
Due to the neutralization of these inorganic acids and organic acids, the corrosion of these acidic substances on the metal parts of the engine is prevented, which is especially important for diesel engine oils and marine oils that use high-sulfur fuels.
Detergence Ability
The detergent is in the form of micelles in the oil and it has strong adsorption on the undesirable resinous film and carbon deposits. It can wash off the resinous film and carbon deposit adhering to the piston and disperse them in the oil.
In general, the stronger the dispersing properties, the stronger the properties.
Dispersion
The detergent can absorb the small solid particles such as colloid and carbon particles that have been generated and disperse them in the oil, preventing them from agglomerating to form large particles that adhere to the cylinder or settle into sludge.
Solubilization
Solubilization is the phenomenon that liquid solutes that are originally insoluble in oil are dissolved due to the addition of a small amount of surfactant.
Detergents are some surfactants, often dispersed in oil as micelles, which can dissolve oxygen-containing compounds containing hydroxyl and carbonyl groups, nitro-containing compounds, sludge, soot, and water. These substances are the intermediates for forming the paint film. They are solubilized into the center of the micelles and surrounded by the additive molecules forming the micelles, thereby preventing further oxidation and condensation, and reducing the formation of paint films and carbon deposits. Indeed, the solubilization of the deposit precursors by detergents, i.e. the ability to make these highly reactive functional groups less active, thereby preventing their transformation into deposits, is much less solubilizing than ashless dispersants many.
Basically, the detergent consists of the Lipophilic Group, Polar Group, and Hydrophilic Group. As the following table:
| ITEM | Lipophilic Group | Polar Group | Hydrophilic Group | Molecular Structure |
| Sulfonate | Alkylaryl | Sulfonic acid group | Ca, Mg, Ba, Na |  |
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| Alkylphenols and Sulfurized Alkylphenates | Alkylaryl | Phenolic hydroxyl | Ca, Ba |  |
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| Alkyl salicylates | Alkylaryl | Salicylate | Ca, Mg, Ba |  |
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| Thiophosphate | Polyisobutylene n=17-20 |
phosphorothioate or phosphoric acid | Ca, Ba |  |
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The detergent and dispersion performance of the main detergents and dispersants
| Lubricant Additives | Solubilization Ability | Dispersion Ability | Detergence Ability | |||||
| Solid /% | Pyruvate/(mmol/kg) | organic acid decomposition products/% | asphalt/% | carbon black /% | Prevent carbon black adsorption /% | clean the adsorbed carbon black /% | Prevent carbon black adsorption under electric field/% | |
| Calcium alkyl salicylate | 0-3 | 37 | -- | 30-60 | 10 | 10 | 2-4 | 90-100 |
| Alkyl phenate | 3.6 | 32 | 30-70 | 30-50 | 20-30 | -- | 3 | 90 |
| Barium thiophosphate | -- | 346 | -- | -- | 40 | -- | -- | 90 |
| Calcium alkyl phenol sulfide | -- | 24 | -- | -- | 38 | -- | -- | 50 |
| Magnesium sulfonate | -- | -- | 70 | -- | 90 | -- | -- | 20 |
| Calcium sulfonate | 6-10 | 20 | 60-100 | 70-90 | 100 | 34 | 6 | 10 |
| Succinimide | 8-20 | 360 | -- | 80-100 | 100 | 85 | 53 | 0 |
Performance Comparison of Main Detergents
| ITEM | Dispersion | Acid neutralization | Solubilization | Antirust | Antioxidation |
| Neutral, Base sulfonate | middle | middle | middle | yes | no |
| High Base sulfonates | middle | high | middle | yes | no |
| Neutral, Base Phenate | low | middle | low | no | yes |
| High Base Alkyl Phenate | low | high | low | no | yes |
| Alkylsalicylate | low | middle | low | no | yes |
| Thiophosphate | middle | middle | middle | no | yes |
Types of detergents for Lubricants.
According to the source of raw materials, sulfonate detergents can be divided into:
- Petroleum Sulfonate;
- Synthetic Sulfonate.
According to the base number, sulfonates are divided into:
- Neutral Sulfonate;
- Middle Base Number Sulfonate;
- High Base Number Sulfonate;
- Super High Base Number Sulfonate.
According to the type of metal:
- Calcium Sulfonate;
- Magnesium Sulfonate;
- Sodium Sulfonate;
- and Lithium Sulfonate.
Sulfonate
Calcium Sulfonate is the most used sulfonate detergent.
Because of the low ash content of Magnesium Sulfonate, it meets the requirements of low ash lubricating oil and has good rust resistance. It is mostly used in high-grade gasoline engine oil, and it is relatively easy to pass the MS Ⅱ D rust test.
Since barium salt is a heavy metal and is toxic, its application is less and less, and Barium Sulfonate is almost completely eliminated as a lubricating oil detergent. But Barium Sulfonate has excellent anti-rust performance on various metals and is suitable for use as an Anti-rust Additive.
The over-based calcium sulfonate is formed by dispersing the excess base in the micelles in the form of calcium carbonate (CaCO3,) to form an over-based sulfonate. The ratio of calcium salt (m) dispersed as calcium carbonate to calcium salt of sulfonate (n) exceeds 30:1.
Neutral or low base sulfonates have a better dispersing effect on soot and other substances, while over based sulfonates have better neutralization ability and high temperature detergency.
Sulfonate can be firmly adsorbed on the surface of the iron metal to form an impermeable protective film, which ensures its good antirust performance.
Compared with salicylate and phenate, sulfonate is better than salicylate and phenate in terms of solubilization and dispersion, but under harsh high temperature conditions, the neutralization speed and detergency are worse than salicylate and phenate.
In particular, all sulfonate additives have poor anti-oxidation and anti-corrosion properties, and high-basic value sulfonate additives even promote oxidation.
In order to make up for the lack of anti-oxidation, in addition to compounding different high and low base sulfonates in modern engine oils, it is more important to use sulfonates in combination with sulfurized alkyl salts, dispersants, and anti-oxidants and anti-corrosion additives.
Generally, sulfonate has good high-temperature detergency, strong neutralization ability, good rust resistance, and some dispersibility. Its raw material is easy to obtain and the price is cheap. It can be compounded with other additives to prepare various internal combustion engine oils. It is also used for Marine cylinder and engine oils.
Alkyl phenates and sulfurized alkyl phenates
Alkylphenplte detergent is one of the engine oil detergents that appeared in the late 1930s. From the beginning, this type of additive was quickly made into various derivatives, such as sulfurized alkylphenate, formaldehyde condensation alkylphenate, Amine formaldehyde condensation alkyl phenate.
Since the 1950s, with the development of various high-power diesel engines and the application of high-sulfur fuels, in order to effectively solve the problems of increased carbon deposits on pistons and corrosion & wear of cylinder liners, alkylphenol detergents have gradually developed towards high base products with TBN 200~250.
The most commonly used alkylphenol salts are calcium salts and magnesium salts, and the most commonly used ones are calcium salts.
However, the performance of pure alkyl phenate is poor, and it is difficult to metalize to produce high-basic products, so Sulfurized Salt Alkyl Phenate and alkyl phenate appear almost at the same time and become the most widely used in the world today. It has a wide range of species, and its consumption is second only to sulfonates, and alkaline phenates account for one-third of the lubricant detergent additive market.
According to the base number, sulfurized alkyl phenates include:
- Low base sulfurized alkyl phenate (TBN100);
- Medium base sulfurized alkyl phenate (TBN150);
- High base sulfurized Alkyphenate (TBN250);
- Super-high base sulfurized alkyl phenate calcium (TBN300).
Characteristics of sulfurized phenate:
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Sulfurized alkylphenate is easy to dissociate in the oil medium, so it has a particularly good neutralization ability and excellent anti-oxidation and anti-corrosion properties.
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Sulfurized alkylphenate has particularly good high-temperature detergency, and is particularly effective in suppressing carbon deposits in the top ring groove of supercharged diesel engine oil. It is one of the indispensable additives for supercharged diesel engine oil;
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Sulfurized alkylphenate is widely used in various grades of internal combustion engine oil due to its good alkali retention and water separation ability, and is still one of the main additives of marine lubricating oil.
The difference between Phenate Detergents and Sulfonate Detergents:
Both high-base sulfonate & high base alkyl phenate has good acid neutralization ability.
High-base sulfonate may reduce the antioxidant performance in Lubricants. But high-base alkyl phenate has antioxidant properties.
Sulfurized alkylphenate is compounded with other detergents, dispersants, and ZDDP, and is widely used in various internal combustion engine oils, especially in supercharged diesel engine oils to reduce carbon deposits. It maintains good alkalinity and is well used in marine cylinder oil, so it has been developed on a large scale in Western countries and has become one of the most important lubricant additives at present.
Alkyl salicylate
Alkyl salicylate is an aromatic carboxylate containing hydroxyl, which is not the same type as alkyl phenols, but it has similar characteristics to alkyl phenols from the point of view of its chemical structure and its performance. Because salicylate uses CO2, carboxyl groups are introduced into the benzene ring of the alkylphenol salt, and the metal is transferred from the hydroxyl group position to the carboxyl group position.
The molecular polarity of the alkylphenol is strengthened and its purity at high temperature is greatly improved. However, its antioxidant and antiseptic properties are not as good as those of alkylphenol sulfide.
As early as 1930, people used salicylate as a multi-effect additive and then developed salicylate-containing metal. The patent was published in the early 1940s, the industrial production and practical application began in the 1950s, and it began to be a normal salt and gradually developed in the direction of alkaline salt, and its base value also has a low base value, medium base value, and high base value products, the highest base value of calcium salt is 280mgKOH/g, and magnesium salt can reach 350mgKOH/g.
Metal types are calcium salt, barium salt, zinc salt, and magnesium salt, calcium salt is used more.
At present, China can produce 3 series of alkyl calcium salicylate products with low base value, medium base value, and high base value, among which the output of high base alkyl calcium salicylate products is larger.
The product properties of calcium alkylsalicylate with different base numbers are different.
- The low-base alkylsalicylate has a low ash content, which has a better concordant effect with sulfide alkylphenol with a high base number and can be used to prepare low ash internal combustion engine oil.
- High-base alkyl salicylate has a high base value, strong neutralization ability, and good water separation, and can be used to modulate Marine diesel engine oil.
- High base value alkyl magnesium salicylate salt has low ash content, good anti-wear performance, a certain anti-rust ability, and can be used to prepare gasoline oil.
In short, the high base value alkyl salicylate has good detergency, strong acid neutralization ability, stability at high temperatures, and certain anti-oxidation and anti-corrosion performance, and it is suitable for various steam and diesel engine oils combined with other oil additives. Compared with sulfide alkyl phenol salts, it has more detergency performance, but less anti-oxygen and anti-corrosion. Due to the complex production process, the cost of the product is more expensive, and its low-temperature dispersion is relatively poor, the application range is not as common as sulfide alkyl phenol salts in the world, only Shell, Japan OSCA, and some Russian companies have this product.
