Does the refining method of base oil affect the quality of lubricants?
author: Leila
2024-09-25
How important is the selection of base oil in the process of selecting lubricants?
Undoubtedly, base oil must be considered in the process of selecting lubricants, and the quality of base oil is closely related to the refining method. Lubricants are divided into mineral oil and synthetic oil, mineral oil accounts for the majority, and base oil largely determines the performance and grade of lubricants. To understand why the quality of base oil varies, let's briefly talk about different refining methods here.
1. Acid/clay refining
This process involves treating crude oil with sulfuric acid or oleum to fractionate, which increases the concentration and viscosity index, but deepens the color of the oil and makes the oil more susceptible to aging. At present, this refining method is limited to the production of certain white oils and sulfonates, or the reprocessing of waste oil. This process has been largely replaced by more advanced refining methods because a large amount of acid mud is produced during the processing. It is difficult to treat these acid muds, and the treatment process is harmful to the environment.
2. Solvent refining
This term refers to the use of wet extraction to remove aromatics and other unwanted components from fractionated oil. Common extractants include phenol, furfural, and sulfur dioxide. Furfural is widely used in the refining of paraffin oil. The oil refined by this process is neutral oil, and there is also an extract rich in aromatic substances. This extract is a valuable process oil and fuel oil.
After solvent extraction, the neutral oil is dewaxed and fluid polished. Dewaxing improves low-temperature fluidity, and fluid polishing improves color and stability. The quality of the base oil ultimately depends on the strictness of the temperature and pressure control in the fluid polishing process. After completing all these processes, additives can be added. This process may have solvent residues.
3. Catalytic hydrogenation refining
Also called hydrotreating, this process is to react the fractionated oil with hydrogen under the action of a catalyst, heating and pressurizing (420 degrees Celsius, pressure 3000psi). With this process, more than 90% of aromatic substances are converted into hydrocarbons, and the loss of raw materials is relatively small. Therefore, this process is favored by many base oil and lubricant manufacturers, and the grade is higher than the previous two.
The principles used in all hydrorefining processes are very similar. The crude oil fraction is preheated to between 150 and 420 degrees Celsius, mixed with hydrogen (or gas with high hydrogen content), and passed through a fixed bed reactor. The reaction rate of hydrogen and oil is regulated with the participation of a catalyst.
The base oil produced by hydrorefining is higher in purity, but they also have some problems. The oil produced by the hydrorefining method cannot be mixed well with certain additives because the additives will precipitate from the solution. In other words, for some chemicals, the solubility of the hydrotreated base oil is poor, so the dissolution of the additives is seriously affected.
In addition, in the case of a high degree of hydrorefining, the base oil contains almost no aromatic compounds, and the additive formula in these oils must add sealing expansion agents. The base oil refined by solvent is just the opposite. Some aromatic compounds are retained, which are natural sealing expansion agents themselves.
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