Carbon Residue Tests: Couradson and Ramsbottom Methods engineering chemistry notes

Carbon Residue Determination in Lubricating Oils

Introduction

Lubricating oils often contain carbon in combined form. When subjected to high temperatures, oils decompose and leave behind carbonaceous deposits known as carbon residue. Measuring carbon residue indicates the tendency of oil to form deposits on engine parts such as piston rings and valves, affecting performance and longevity.

Methods of Carbon Residue Measurement

There are two standard methods:

1. Couradson Method: Suitable for heavy residual oils, crude oils, and non-volatile stocks.
2. Ramsbottom Method: Applicable for more fluid petroleum products.

Couradson Method

Apparatus

Consists of a silica crucible (65–85 mL) placed inside a skidmore iron crucible with a close-fitting lid having a small horizontal opening. The crucible assembly is covered by a larger hood and heated by a Meker burner. The setup is shown in the diagram below:

Procedure

1. Weigh a known amount of oil sample into the silica crucible.
2. Place the silica crucible inside the skidmore iron crucible and cover with the lid.
3. Place the assembly inside the larger hood fitted loosely to the iron hood.
4. Heat with Meker burner at prescribed rate until all volatile matter vaporizes and burns completely (usually 30 minutes).
5. Remove and cool the crucible in a desiccator.
6. Weigh the residue to calculate carbon residue percentage.

Carbon Residue (%) = (Weight of residue in crucible ÷ Weight of original oil sample) × 100

Ramsbottom Method

Apparatus

This method uses a glass bulb with a capillary tube inlet for the oil sample, which is inserted into an electrically heated furnace maintained around 550°C, as illustrated below:

Procedure

1. Weigh a small amount of the oil.
2. Inject oil into the glass bulb via the capillary tube using a syringe.
3. Place the bulb in the hot furnace at 550°C.
4. Heat until volatile content escapes through the capillary, and the remaining residue undergoes cracking and possible coke formation.
5. Cool the bulb in a desiccator.
6. Weigh the residue to calculate carbon residue percentage.

Carbon Residue (%) = (Weight of residue in bulb ÷ Weight of original oil sample) × 100

Significance of Carbon Residue Tests

• Higher carbon residue values indicate higher tendency to form deposits, which adversely affects engine performance.
• Important for assessing heavy oils, base stocks, and used oils' condition.
• Helps in classifying petroleum products for suitability in various engine and machine applications.

Exam Tips

• Know the difference between Couradson and Ramsbottom methods with applications.
• Memorize the apparatus set-up and procedure steps.
• Understand the significance of carbon residue in engine deposits and lubricant quality.
• Practice the formula for % carbon residue calculation.