History and Future Development of Lubricating Oil Additives

From the late 1930s to the mid-1940s, metal detergents such as phenolates, sulfonates, and salicylates emerged. In the 1950s, high-alkalinity metal detergents were developed, solving problems such as increased piston deposits and cylinder liner wear caused by the combustion of high-sulfur fuels in high-power turbocharged diesel engines and marine diesel engines. Subsequently, low, medium, high, and ultra-high alkalinity phenolates, sulfonates, and salicylates were developed to meet the needs of blending various oils. Entering the 1990s, due to the development of smaller, higher-power, and higher-speed engines, traditional metal detergents could no longer meet the requirements. Furthermore, stringent environmental regulations restricted the use of previously toxic, high-ash, sulfur-, phosphorus-, and chlorine-containing additives. Therefore, various countries have been developing and researching new types of metal detergents, such as magnesium salts and overly alkaline detergents.

Currently, my country's total production capacity for low, medium, and high-alkalinity petroleum sulfonate calcium products is 40,000 tons/year; the production capacity for low, medium, and high-alkalinity synthetic sulfonate calcium products is 150,000 tons/year; and the production capacity for medium and high-alkalinity sulfurized alkylphenol calcium products is 100,000 tons/year. The production capacity for calcium salicylate products is 60,000 tons/year, and the production capacity for low, medium, and high-alkalinity naphthenate calcium products is 5,000 tons/year. Compared with foreign calcium and magnesium salt metal detergents, my country's sulfonate products have fewer varieties, lower quality, longer production cycles, and poorer color, failing to meet the needs of lubricating oils. The performance of medium and high-alkalinity sulfurized alkylphenol calcium products is comparable to similar foreign products, but there is still a significant gap in color and viscosity. Calcium salicylate products are mainly medium-alkalinity products, with limited product variety, dark color, high solvent loss, and long reaction cycles. However, modified alkyl salicylate salts and high-alkalinity alkyl salicylate calcium are superior to their foreign counterparts. The main function of ashless dispersants is to control the formation of sludge in gasoline engine lubricating oil, control the deposition of diesel engine lubricating oil, and neutralize acids in combustion products.

In the early 1950s, due to the unsatisfactory effect of metal detergents in inhibiting the formation of low-temperature sludge, DuPont developed polymeric ashless dispersants in 1955. However, their poor thermal stability resulted in unsatisfactory effects on improving low-temperature sludge. In the 1960s, non-polymeric succinimidyl ashless dispersants were developed. Currently, succinimidyl-based ashless dispersants have become the mainstream, accounting for over 80% of their usage. Research and development of dispersants in my country started relatively late. In 1985, dispersants accounted for 0.1% of the total amount of additives, rising to 16.49% in 1994. The variety of dispersants has evolved from bis- and poly-coated succinimidyl ashless dispersants in the 1980s to the current mono-, bis-, poly-coated, high molecular weight succinimidyl ashless dispersants and polyisobutylene succinate-type dispersants. Currently, the production of ashless succinimide dispersants still primarily relies on chlorination processes, with less than 5% of manufacturers employing the less environmentally polluting thermal addition process. Furthermore, the variety of succinimide products is limited, and they tend to be dark in color and high in viscosity. In recent years, China has successively developed new types of ashless dispersants, including high molecular weight ashless dispersants, ester-based ashless dispersants, dianhydride-based ashless dispersants, polyamide-based ashless dispersants, and ultra-high alkali alkyl salicylate calcium (magnesium) dispersants, with some products already in industrial production. These products have created conditions for the development of next-generation composite agents.

The research and development direction for ashless dispersants focuses on better control of sludge and paint film, excellent soot dispersion capabilities, improved low-temperature performance, low low-temperature viscosity, good compatibility with other additives, good water resistance, and biodegradability.

The current status and development trend of viscosity modifiers and pour point depressants: Viscosity modifiers and pour point depressants are a class of lubricating oil additives with large usage, early development, and still widely used. The overall usage of pour point depressants is relatively small, and the variety of types has not changed significantly. In the 1950s, polymethyl methacrylate (PMA) and polyisobutylene (PIB) were used abroad to improve the viscosity-temperature properties of oils. In the late 1960s and early 1970s, ethylene-propylene copolymer (OCP) and styrene-diene copolymer were developed, with OCP being industrialized and accounting for over 60% of sales. Exxon is a representative of OCP development, and its series of products are used in various oils. Because dispersant VII can reduce the amount of ashless dispersant used, avoiding the viscosity increase caused by increasing the amount of ashless dispersant to solve the problem of low-temperature oils, dispersant VII has been extensively studied in recent years. In addition, research on multifunctional VII with dispersibility, antioxidant properties, and anti-wear properties has also attracted the attention of major international companies.

my country has made rapid progress in the research and development of viscosity index improvers. Currently, polyisobutylene, polymethyl methacrylate, and ethylene-propylene copolymer are in production and application. The domestic usage of VII is comparable to that abroad, but the variety is unbalanced, with polyisobutylene accounting for over 80% of usage. Polyisobutylene (POI) exhibits poor shear stability and low-temperature performance, limiting its application in formulating low-viscosity multi-grade oils. In recent years, with the phasing out of low-grade oil crystals, the use of OCPs (Optically Oxide Polymers) has gradually increased, and their varieties are becoming increasingly diversified. As engine regulations become more stringent, the requirements for oil-soluble polymers used in engine lubricants are also rising. Developing environmentally friendly, biodegradable polymers with strong thickening ability, good shear stability, and without compromising detergency is the future development direction for viscosity index improvers.

Current Status and Development Trends of Antioxidant and Anticorrosion Agent Technology: Antioxidants and anticorrosion agents are among the main additives in lubricating oils, primarily including phenolic antioxidants, amine antioxidants, sulfur-phosphorus antioxidants, and other types of antioxidants. With the development of automobiles towards higher speeds and higher loads, higher requirements are placed on the antioxidant properties of oils. Simultaneously, traditional mineral oils, having lost natural antioxidants during refining, necessitate the addition of more antioxidants. Among traditional antioxidants, T501 has a large sales volume, but its low operating temperature and high volatility mean it is only suitable for lubricating oils below 100℃. To improve high-temperature performance, high-molecular-weight phenolic antioxidants, such as bisphenol antioxidants, S-bisphenol antioxidants, and phenolic ester antioxidants, are widely used in internal combustion engine lubricants, especially phenolic ester antioxidants, which show significant effects in high-grade oils (CF4, CI4).

Amine antioxidants are more expensive, but offer good high-temperature antioxidant properties. However, they tend to precipitate and have potential toxicity, which once limited their use. After early N-phenyl-a-naphthylamine and its derivatives were phased out due to their proven carcinogenicity, claims about the high toxicity of amine antioxidants decreased, and their use in some fields has surpassed that of phenolic antioxidants. ZDDP series antioxidants possess multiple properties such as antioxidant, anti-wear, and anti-corrosion, and are one of the main additives in internal combustion engine lubricants. Because their phosphorus content can easily poison the catalyst in catalytic converters, the current approach is to add copper-containing auxiliary antioxidants, creating favorable conditions for the development of low-phosphorus internal combustion engine lubricants. With increasingly stringent environmental protection and raw material requirements, there is a growing need to develop multifunctional, low-ash or ashless high-temperature antioxidants.