How Diester Base Oil Prevents Carbon Deposits in Screw Air Compressors

Air compressor oil is the "lifeblood" of the compressor, while coking is the silent killer of its efficient operation. Once coking occurs inside a screw air compressor, it can lead to insufficient air delivery and reduced efficiency at best, or rotor lock-up at worst-importantly increasing maintenance costs and causing production downtime. How do diester base oils solve the coking challenge in screw air compressors? This article analyzes their advantages, including high-temperature oxidation resistance and low carbon residue, to show how they prevent carbon deposits at the source and safeguard long-term equipment operation.

What is a Diester Base Oil?
A diester base oil is a type of synthetic ester base oil belonging to API Group V (other synthetic oils). It is produced through the esterification reaction between a dicarboxylic acid and a monohydric alcohol (or a dihydric alcohol and a monocarboxylic acid). Each molecule contains two ester linkages (-COO-), hence the name "diester." Typical examples include dioctyl adipate (DOA) and dioctyl sebacate (DOS), both of which are common industrial diester base oils.

Chorus offers diester base oils specifically designed for air compressors, featuring flash points reaching 200–230°C and pour points down to -70°C.
In addition, Chorus supplies a wide range of synthetic ester base oils suitable for various severe operating conditions-such as high-temperature chain oils, gear oils, and engine oils. Welcome to contact us for customised solutions and the latest quotations.

Why Do Screw Air Compressors Develop Coking and Carbon Deposits?

Under the harsh operating conditions of screw compressors, mineral-based specialty oils inevitably undergo oxidation, leading to coking and carbon deposits:

①High temperature is the primary driver: The oxidation rate doubles for every 10°C rise in temperature, and the mixture of oil mist and hot gas heats up rapidly.

②High oxygen partial pressure: High oxygen concentrations accelerate oxidation.

③Synergistic catalysis by condensed water and metals: This considerably aggravates the oxidation process.

Carbon residue causes wear in the compression chamber, exhaust valve failure, and localized overheating, leading to mechanical failures or even fires and explosions (statistically, 40% of air compressor fires and explosions are caused by this), posing a severe threat to equipment and personnel safety. Therefore, to ensure safe compressor operation and reduce failures, it is essential to improve oil oxidation stability and reduce carbon residue. Synthetic compressor oils were developed precisely to meet these demanding requirements, with diesters representing an important category among synthetic ester base oils.

How Diester Base Oils Solve the Coking Problem in Screw Air Compressors

1. Excellent Thermal-Oxidative Stability & Low Carbon Residue: They exhibit strong thermal stability within the 150–180°C range, while screw compressor discharge temperatures typically reach 80–110°C. The polar ester linkages (-COO-) in diester molecules provide natural detergency, keeping early oxidation products dissolved or colloidally dispersed to prevent them from depositing, resulting in low carbon residue.

2. Low High-Temperature Volatility & Low Oil Consumption: In high-temperature environments, evaporation loss is minimal and oil consumption is lower than that of mineral oils. This reduces the costs associated with stocking backup oil and disposing of waste oil, while extending service intervals and lowering overall costs.

3. Superior Lubrication Performance: Diesters feature strong polarity, allowing diester-based fluids to form a highly effective protective lubricating film on metal surfaces. This prevents wear on heavy-duty components under both high-temperature operating conditions and low-temperature start-ups.

4. Outstanding Low-Temperature Performance: With pour points dropping as low as -50°C to -70°C-a level unattainable by mineral oils-they deliver exceptional low-temperature fluidity. They are suitable for cold regions or low-temperature operating conditions while maintaining stable operation in high-temperature environments, offering a broad operating temperature range.

5. Environmentally Friendly & High Biodegradability: Diesters achieve a biodegradation rate of over 80% within 30 days. They are environmentally friendly and align with current international environmental protection standards.

The application of diesters in screw air compressors effectively solves the coking problem. In practical applications, they need to be blended with air compressor oil additive packages to enhance the oil's anti-wear, anti-rust, and anti-corrosion performance. Chorus can supply a wide range of additive packages to help improve oil performance. Welcome to contact us for the latest quotations.