The 4 Main Indicators of Synthetic Base Oil

Acid value

The definition is simple, the milligrams of KOH are consumed for titrating every 1g of sample. The meaning of acid value is the milligrams of potassium hydroxide required to neutralize the free fatty acids in 1 gram of ester base oil.

In the chemical reaction production process of ester oil, it is often necessary to add excessive fatty acids to complete the reaction, and the excess acid needs to be carefully removed during the post-treatment process. Acid value becomes an important indicator of ester oils.

We hope that ester base oils do not contain residual free fatty acids during the production process, so we require the acid value to be as low as possible. Therefore, the acid value is a reflection of the process accuracy of production control.

When evaluating the performance of base oil, the hydrolysis characteristics of ester base oil are a key point. If the acid value is too high, it means that it is easy to hydrolyze and accelerate the decline of ester oil. At the same time, excessive free acid can cause corrosion and oxidation problems. Therefore, the lower the acid value, the better.
 

Saponification value

Saponification value refers to the value at which oil turns into soap. Definition: The number of milligrams of KOH required to saponify 1g of oil sample under specified conditions. Comparing saponification value and acid value, acid value is usually used to treat the epidermis, while saponification value means the interior, so saponification value is far more important than acid value. Saponification is equivalent to breaking down the composition into acids and alcohols, and then weakening the acid. So the determination process of saponification value usually uses heating to destroy its original structure, allowing the saponification reaction to proceed.

If an ester oil has a fixed carbonyl number, such as a trimethylolpropane ester with three carbonyl groups, the significance of saponification value comes out. Firstly, it can evaluate the length of fatty acids, which is the carbon number. If the molecular weight of fatty acids is large, the smaller the molar ratio of 1g of oil sample, the less milligrams of KOH required, which means the lower the saponification value. On the contrary, the smaller the molecular weight, the lower the carbon number, and the higher the saponification value. Secondly, saturation and branching can be evaluated based on molecular weight.

So, what is the standard for saponification value? Due to different applications, sometimes it needs to be higher and sometimes it needs to be lower. For cutting fluids, the saponification value mainly reflects the overall content of fatty acids or fatty esters in the cutting fluid, because only the higher the content, the greater the amount of alkali needed in the future. Therefore, some people also say that the higher the saponification value, the better the lubrication.

Iodine value

Definition: The number of grams of iodine that can be absorbed by 100g of ester base oil. The higher the iodine value, the higher the content or degree of unsaturated fatty acids in the ester.

If the iodine value of oleic acid (1 double bond) is lower than that of linoleic acid (2 double bonds), this parameter can describe the degree of unsaturated fatty acids in the finished ester. Therefore, whether it is a free unsaturated acid or an ester, it will affect the iodine value. Sulfonate value is mainly used to determine the key parameters of oil properties, such as if the iodine value is greater than 130, it can be determined that the oil is dry.

Sometimes people have heard of bromine value, especially in the field of PAO. Bromine value, like iodine value, is an indicator of the degree of unsaturation in organic compounds. Due to the difference in molecular weight, bromine value=iodine value X0.632. In addition to this difference, the main target of bromine value is petroleum hydrocarbons, as bromine is more powerful and has fewer side reactions.

Hydroxyl value

The hydroxyl value commonly used in industry refers to the milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl group in 1g of the sample, expressed in mgKOH/g.

Hydroxyl value refers to the number of - OH groups in the product, and like acid value, it is an important focus in controlling production engineering. Acid value mainly monitors the reaction material acid, while hydroxyl value monitors the reaction material alcohol. For finished products, the lower the hydroxyl value, the better.
active esterification reaction between hydroxyl groups in the sample and excess anhydride to produce esters. After the excess anhydride is hydrolyzed into acid, it is titrated with an alkaline standard solution. Therefore, many factors affect the measurement of hydroxyl value. In many base oils of metalworking fluids, the hydroxyl value is a crucial performance parameter that affects the viscosity and emulsification of the base oil.