Application and Production of Ashless Dispersants?

I. How are Ashless Dispersants Used?

Currently, succinimide, based on polyamines, is the mainstream dispersant, accounting for over 80% of total dispersant usage. This chemical structure easily forms micelles in lubricating oil, ensuring strong solubilization of initial liquid oxidation products and excellent colloidal dispersion of solid particles such as carbon deposits and soot. It effectively ensures the low-temperature dispersion function of internal combustion engine oils, particularly effectively addressing the low-temperature sludge problem in gasoline engine oils. When gasoline engine oils with added dispersants are changed after prolonged operation, sludge in the crankcase is reduced. It also improves the dispersion and solubilization of soot and lubricating oil oxidation products generated at high temperatures. Especially when combined with metal detergents, it has a synergistic effect, improving lubricating oil quality while reducing the amount of additives required. Due to these advantages, ashless succinimide dispersants have experienced rapid development and application.

Because the main functions of dispersants in oils are dispersion and solubilization, in modern passenger car engine oils, an addition of 1-10% can effectively control the smoke point of passenger car diesel engine oils. Railway locomotive oils require good alkalinity and high dispersibility, also necessitating the addition of dispersants. For medium-speed cylindrical piston engine oils, a smaller addition of 2-4% is preferred to achieve the dispersing function. Traditionally, marine cylinder oils do not contain dispersants, but laboratory studies have found that adding dispersants can not only improve the detergency and dispersibility of marine cylinder oils but also significantly reduce the amount of highly alkaline additives required, lowering costs. Therefore, they are increasingly being used in the production of marine cylinder oils. Two-stroke gasoline engine oils involve the mixing and combustion of lubricating oil and fuel oil. Excessive metal detergents and antioxidants can easily lead to wear and ring adhesion. Using special dispersants or a combination of detergents can prevent these phenomena. It should also be noted that succinimidyl dispersants, due to their low-molecular-weight polyisobutylene alkyl groups, can increase low-temperature viscosity if added in excess, causing inconvenience in the formulation of multi-grade oils. Adding polymerizable dispersants (viscosity index improvers) to replace part of the dispersant can improve low-temperature performance while providing satisfactory low-temperature dispersibility.

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