Demulsification properties of oil

The demulsification properties describe the ability of lubricants to separate water and prevent the formation of emulsions. In various plants and production facilities, contact of the lubricant with water cannot be prevented. The lubricant must therefore be able to separate the water in order to guarantee the lubricating properties. Otherwise, the oil may age faster and the lubricating film may break off.

The demulsibility decreases with increasing aromatic and MTBE¹ content in the presence of surface-active substances. The addition of additives such as demulsifiers counteracts the formation of emulsions. This reduces the surface tension of the water droplets in the oil, so that they form larger droplets and can be separated more easily.

¹ Methyl tert-butyl ether

The test procedure for determining the demulsification properties of oil is set by the ISO 6614 or ASTM D1401 standard. For this, 40 ml of oil and 40 ml of distilled water are placed in a measuring cylinder and heated to a certain temperature. The contents of the measuring cylinder are then mixed by a stirrer for five minutes. An emulsion of oil and water is formed, which is left to settle. Water and oil slowly separate from each other, the water collects as the lower phase and the oil rises to the top. The emulsion remains in the middle. At intervals of five minutes each, the volumes of water, oil and the emulsion phase in between are measured. The measurement of the phases is continued until one hour has passed or the emulsion phase is less than or equal to 3 ml. The faster the emulsion diminishes, the better are the demulsification properties of the oil.

Wherever water can get into a machine or a production process, lubricants with good demulsifying properties are needed. These are required, for example, in hydraulic systems, turbines or guideways. A quick separation of oil and water is often desirable. However, exceptions can occur. In the case of hydraulic oils of class HLP-D, it is necessary, among other things, that the lubricant binds the finest water droplets and keeps them in suspension.