Analysis of Petroleum Products
The Chemical Analysis Petroleum products, including gasoline, diesel, and jet fuel, have numerous specifications and test methods due to commercial, safety, environmental, quality, and processing considerations. This blog provides an overview of the primary standard test methods for these fuels, as well as typical specification limitations and ranges. Please note that specifications can vary over time, between countries, and for different product classes. The provided numbers are only examples of this variation.
Gasoline and diesel specifications vary from strict limits in markets with advanced emission control and fuel efficiency requirements to weaker limits in areas with minimal or no regulations. The stricter limits enable the use of advanced technologies that improve vehicle and engine efficiency, as well as sophisticated emissions control systems. The weaker limits focus on basic vehicle and engine performance as well as the protection of emissions control systems.
For up-to-date and detailed versions of these test methods, please refer to ASTM and other vendors. Additionally, standard test methods for crude oil properties are also available.
Acidity, Total Acid Number (TAN)
Measures the total amount of acid compounds present in petrochemical samples, expressed in mg of KOH per g of sample. The total acid number (TAN) is an important measure for assessing petroleum products, reflecting the quantity of acidic components in the sample. Because this information helps evaluate the corrosiveness of the product. Additionally, refined petroleum products like engine oil degrade under operating conditions. That can lead to the formation of acidic substances, causing the acid number to rise over time. This increase in the acid number indicates the need to replace the used oil with fresh oil. The significance of measuring the acid number is underscored by various standard procedures, including internal company specifications and national and international standards from organizations such as ASTM, DIN, and ISO.
Total Acid Number (TAN)
Acidic constituents in petroleum products and biodiesel can corrode metals, impair water separation, and also indicate degradation. TAN is crucial for quality control, lubricant formulation, and monitoring degradation. To determine the acid number, take an oil sample and mix it with a solvent solution of toluene, isopropyl alcohol, and water. Then titrate the mixture with alcoholic potassium hydroxide (KOH), and express the result as milligrams of KOH per gram of the sample. Different methods are used to detect the endpoint of the titration. However, the presence of water greater than one percent may affect the acid number of oil; that’s why moisture should be removed from the oil sample.
ASTM D3242: Titration with alcoholic potassium hydroxide, using a color indicator, to determine acidity in aviation turbine fuel.
ASTM D664: Potentiometric titration using a glass electrode and reference electrode to determine acid number in petroleum products.
Chemical Analysis of Petroleum Products: Procedure
Dissolve the sample in a mixture of toluene and isopropyl alcohol containing a small amount of water. The resulting single-phase solution is blanketed by a stream of nitrogen bubbling through it. Titrate with standard alcoholic potassium hydroxide to the endpoint, which indicates the color change (orange in acid and green in base) of the added p-naphtholbenzein solution.
Other Methods
– Alternative test methods: IP 354, ISO 6618, ASTM D974
Typical specifications
– Jet Kerosene: 0.015-0.10 mg KOH/g (by D3242)
– Diesel: 0.08 mg KOH/g (by D664)
However, these specifications are under the given reference number of the ASTM method; these specifications may change for every organization. Because every product manufacturing has its own standard.
Petroleum Products
Although petroleum product analysis involves a combination of physical and chemical tests, it is used to determine the composition and properties for quality control and safety. However, key analyses include elemental composition (C, H, N, S, and O) using techniques like gas chromatography (GC) and mass spectrometry (MS) and molecular characterization using methods like liquid chromatography-mass spectrometry (LC-MS) to identify and quantify different hydrocarbon types, such as alkanes, aromatics, and asphaltics. Physical property tests, like density, viscosity, and flash point, are also crucial for evaluating a product’s usability and safety.
Chemical Composition
Elemental composition: Analyzes the percentage of elements like carbon (93-97%), hydrogen (10-14%), nitrogen (0.1-2%), oxygen (0.05-1.5%), and sulfur (0.5-6%).
Hydrocarbon type: Identifies and quantifies different hydrocarbon groups, such as paraffins (alkanes), naphthenes (cycloalkanes), and aromatics.
Trace components: Detects and quantifies impurities or additives like sulfur compounds, nitrogen compounds, and trace metals.
Biomarkers: Identifies specific molecules from biological sources to provide geochemical information about the petroleum’s origin, age, and also depositional environment.
Analytical techniques of Petroleum Products
Gas Chromatography (GC): Separates components based on volatility and molecular weight. Often used with a detector to identify and quantify compounds in lighter fractions.
Gas Chromatography-Mass Spectrometry (GC-MS): A more powerful technique for analyzing aromatics and other complex components by combining GC separation with the identification capabilities of a mass spectrometer.
Liquid Chromatography-Mass Spectrometry (LC-MS): Used for analyzing heavier, less volatile components like resins and asphaltenes that cannot be analyzed by GC.
Time Domain Nuclear Magnetic Resonance (TD-NMR): Used to determine physical and chemical properties based on magnetic field relaxation times.
Physical property tests of Petroleum Products
Density: Measured using a density meter to check quality and purity.
Viscosity: Measured using a viscometer to evaluate fluidity and usability.
Sulfur content: Analyzed to determine environmental impact and combustion performance.
Water content: Measured with a water analyzer to detect contamination.
Flash point: The lowest temperature at which a liquid can form an ignitable mixture in air, determined with a flash point tester to evaluate safety and performance.
Carbon residue: Measures the amount of carbon residue left after evaporation to assess combustion efficiency and pollution potential.