How Are Sulphur and Nitrogen Determined?

Sulphur (S) and Nitrogen (N) analysis is one of the most important stages of the fuel production process. Both chemical elements can have a significant impact on manufacturing efficiency, finished product quality and resale price. For this reason, most refineries have stringent chemical analysis procedures in place.

Why analysis matters

Compromised catalyst performance is one of the biggest concerns associated with high sulphur content. This is because trace amounts of sulphur can contaminate feedstocks and compromise the important process catalysts used in chemical and petroleum refining. Sulphur has a particularly damaging effect on metal catalysts such as nickel, which is used in hydrocarbon steam reforming.

Excess sulphur in LPG can increase SOx emissions and fast-track corrosion in engine and exhaust systems. Oxidisation occurs when process catalysts are contaminated with feedstocks containing sulphur-bearing materials, another reason why sulphur analysis is a top priority for refineries.

Nitrogen-containing compounds can also compromise the efficacy of catalysts and make the refining process complex and more energy-intensive. This includes even the most elementary nitrogen-containing compounds such as amines and pyridines, which can neutralise acidic catalysts. In some scenarios, high levels of nitrogen may require expensive pre-treatment stages.

Without a good understanding of nitrogen content, refiners risk “red tars” forming as a result of autoxidation. High nitrogen levels can corrode specialised equipment such as atmospheric distillation units (ADUs), as well as jeopardise thermal stability and reduce the performance and resale value of finished products.

Monitoring S & N levels

So how does the industry analyse and regulate the levels of sulphur and nitrogen found in feedstocks and finished fuels? Below we explore some of the most common methods used to determine S and N content.

Complying with industry test methods

Surveyors, refineries and QC labs must all comply with a variety of test methods when testing for sulphur and nitrogen. These include ASTM D5453, described by ASTM International as the “Standard Test Method for Determination of Total Sulphur in Light Hydrocarbons, Spark Ignition Engine Fuel, Diesel Engine Fuel, and Engine Oil by Ultraviolet Fluorescence.” Other commonly used methods include ASTMD4629 used to determine the total nitrogen present in liquid hydrocarbons and ASTM D6667, the “Standard Test Method for Determination of Total Volatile Sulphur in Gaseous Hydrocarbons and Liquefied Petroleum Gases by Ultraviolet Fluorescence.”

Precision, accuracy and robustness are all critical factors to consider when analysing sulphur and nitrogen content. Sebastian Sanchez, Product Manager at Dutch-based company TE Instruments, explores the innovative methods and analytical instruments being used to calculate chemical elements in ‘Strengthen your Lab Performance: Learn about new developments on sulphur and nitrogen determination.’