Introduction

The determination of carbon, hydrogen, and especially nitrogen is useful for determining the complex nature of sample types covered by this test method. The CHN results can be used to estimate the processing and refining potentials and yields in the petrochemical industry.

The concentration of nitrogen is a measure of the presence of nitrogen-containing additives. Knowledge of its concentration can be used to predict performance. Some petroleum products also contain naturally occurring nitrogen. Knowledge of hydrogen content in samples is helpful in addressing their performance characteristics. Hydrogen to carbon ratio is useful for assessing the performance of upgrading processes.

Method Reference

ASTM D5291-26 Standard Test Method for Instrumental Determination of Carbon, Hydrogen, and Nitrogen in Petroleum Products and Lubricants

Principle

From the combustion product gas stream, oxides of sulfur are removed with calcium oxide in the secondary combustion zone. A portion of the remaining mixed gases is carried by helium gas over a hot copper train to remove oxygen, and reduce NO_x to N₂, over carbon dioxide absorber to remove CO₂, and over magnesium perchlorate to remove H₂O. The remaining elemental nitrogen is measured by the thermal conductivity cell. Simultaneously, but separately from the nitrogen measurement, the carbon and hydrogen selective infrared cells measure the CO₂ and H₂O levels.

Sample Preparation

Reference Materials

EDTA, or other suitable reference materials.

Note: ASTM D5291 requires the use of pure compounds for calibration.

Carrier and Combustion Gases

Helium gas: high purity (99.999 %)

Oxygen gas: high purity (99.999%)

Additional Reagents (as Specified by the Instrument Manufacturer)

Magnesium Perchlorate

Quartz Wool

Copper Turnings

Coated Calcium Oxide (Furnace Reagent)

Nitrogen Catalyst

Magnesium Oxide (for Liquid Samples)

Experimental Requirements

The absorbent used in this test is magnesium oxide (MgO). A typical amount is 200 mg. If a relatively large oil sample is used, increase the amount of absorbent accordingly to ensure complete absorption of the liquid sample.

Quickly encapsulate the sample and record its mass.

Use a pipette or another reliable sampling tool and draw the sample quickly. When loading, dispense the sample onto the magnesium oxide. Avoid sample adhesion to the wall of the tin-foil cup.

Refer to the instrument manual for details.

Instrument and Basic Parameters

SDCHN636 Carbon, Hydrogen and Nitrogen Analyzer

Method Parameters

The following are typical settings.

Combustion tube: 950 °C Desulfurization tube: 900 °C Reduction tube: 700 °C

Procedure

Weigh about 50 mg of a homogeneous test specimen taken according to Practice D4057 or D4177, into a tin-foil cup. Crimp the tin-foil cup closed with forceps.

a. Weigh the solid samples in tin-foil cup.

b. Weigh the liquid samples in tin-foil cup and saturate with an absorbent (magnesium oxide, MgO) within a tin-foil cup. Quickly fold and seal the cup tightly, then encapsulate it with a second tin-foil cup. These precautions slow combustion to prevent flashback with light samples or to ensure complete combustion.

2. To start the analysis sequence, run five blank tin-foil cup followed by eight calibration standards.

3. Store all the results in the instrument memory and recall the best calibration values. Enter these results and the known calibrant concentrations into the microprocessor to generate a calibration curve.

4. Combust the encapsulated sample as for the calibrant. Depending on the sample matrix, adjust the oxygen flow rate and combustion time to overcome incomplete combustion.

Typical Results

Summary

The repeatability of these test procedures for measuring carbon, hydrogen, and nitrogen was determined in four petroleum-based samples. The results show that for the four samples analyzed in parallel, the carbon ranges were 0.08%, 0.44%, and 0.67%; the hydrogen ranges were 0.01%, 0.01%, and 0.12%; and the nitrogen ranges were 0.01%, 0.05%, and 0.07%. All observed ranges were within the repeatability limits calculated according to ASTM D5291-26, Standard Test Method for Instrumental Determination of Carbon, Hydrogen, and Nitrogen in Petroleum Products and Lubricants (Method A), confirming that the determination with SDCHN636 Carbon, Hydrogen and Nitrogen Analyzer meets the precision criteria specified in the standard.

For more information about the Sundy SDCHN636 Carbon, Hydrogen and Nitrogen Analyzer, please contact us by phone or email.

Phone: +86-731-88112150

Email: sales@sundytech.com