Petroleum Products Overview

I. Purpose

1. Understanding Oil Product Classifications: Gain a basic understanding of how oil products are classified and a brief overview of their production processes.
2. Interpreting Inspection Reports: Learn how to read inspection reports and assess the quality of oil products based on the data provided.

II. Introduction to Oil Product Knowledge

1. Definition of Petroleum

   Crude oil is the unprocessed oil extracted from underground. Petroleum is a viscous, flammable liquid mineral oil, mostly black, brown, or green in color, with some being yellow. Generally, petroleum is lighter than water, with a density of (0.77–0.98) g/cm³. It is a complex mixture composed of various hydrocarbons.

   Petroleum products are a general term for various commodities produced directly using petroleum or a portion of petroleum as raw materials.

2. Petroleum Products

   (1) Composition: The main elements in petroleum are carbon and hydrogen, with small amounts of oxygen (O), nitrogen (N), sulfur (S), phosphorus (P), and trace elements like chlorine (Cl), iodine (I), arsenic (As), silicon (Si), sodium (Na), potassium (K), etc., all existing in compound forms. Petroleum is not a single compound but a mixture composed of hundreds or even thousands of compounds. Therefore, during distillation, the distillates are generally continuous.

   • A. Hydrocarbon Organic Compounds: This includes alkanes, cycloalkanes, and aromatic hydrocarbons.
   • B. Non-Hydrocarbon Organic Compounds: These are derivatives of hydrocarbons containing elements like oxygen, sulfur, and nitrogen in addition to carbon and hydrogen. Although their elemental content is minimal (usually about 10%–15% of the total petroleum), their impact on petroleum processing and product quality is significant and cannot be ignored. Most need to be removed during processing. If appropriately treated, they can also produce some useful chemical products.
   • C. Inorganic Compounds: Petroleum also contains small amounts of inorganic substances, mainly water, chlorides of sodium, calcium, and magnesium; sulfates and carbonates; as well as small amounts of sludge, rust, etc. Their hazards include increasing the viscosity of crude oil, increasing energy consumption during storage and transportation, accelerating equipment corrosion and wear, promoting scaling and coking, and affecting the activity of deep processing catalysts. Therefore, crude oil must undergo physical and chemical treatments before transportation and processing to remove these harmful inorganic substances as much as possible.

   (2) Classification by Component Weight: Petroleum products can be divided into liquefied petroleum gas, gasoline, kerosene, diesel, lubricating oil, asphalt, etc., based on the weight of their components. For example:

   • Liquefied Petroleum Gas (LPG): Mainly composed of C₂–C₄ hydrocarbons (gaseous at room temperature and pressure).
   • Gasoline Fraction: Distillates boiling between 35–200°C.
   • Kerosene Fraction: Distillates boiling between 175–300°C.
   • Diesel Fraction: Distillates boiling between 200–350°C.

   (3) Classification Standards: Petroleum products are classified according to ISO/DIS 8681-1985 “Petroleum Products and Lubricants—Method of Classification and Designation of Types.” Categories are indicated by the first letter of the English name representing the product’s main feature. For example:

   • Fuel (F): Fuel
   • Solvents and Chemical Raw Materials (S): Solvent
   • Lubricants and Related Products (L): Lubricant

   (4) Grading of Petroleum Products:

   • A. Gasoline: Graded by research octane number (RON). For example, “90 gasoline” means the RON is not less than (equal to or greater than) 90. Understanding the grading method can help solve certain problems. For instance, although GB17930-1999 “Unleaded Gasoline for Motor Vehicles” only specifies standards for 90, 93, and 95-grade gasoline, we can deduce that 97-grade gasoline should have an RON not less than 97 based on the definition.
   • B. Diesel: Graded by pour point into seven grades: No. 10, No. 5, No. 0, No. –10, No. –20, No. –35, and No. –50 diesel.
   • C. Fuel Oil: Classified based on operating conditions and burner types into No. 1, No. 2, No. 4 Light, No. 4, No. 5 Light, No. 5 Heavy, No. 6, and No. 7.
   • D. Engine Oils (Gasoline and Diesel):
     • Type Codes: For example, gasoline engine oils SC, SD, SE, SF; diesel engine oils CC, CD; dual-purpose oils SD/CC, SF/CD.
     • Viscosity Grades: Single-grade oils like 30, 40, 50; multi-grade oils like 15W/40.
     • A complete engine oil designation should include the above information, e.g., “SF 15W/40 gasoline engine oil.”

III. Introduction to Professional Terminology of Oil Products

1. What is the Distillation Range of Petroleum Products? What is the Significance of Measuring the Distillation Range?

   Pure compounds have specific boiling points, but petroleum and its products are complex mixtures mainly composed of various hydrocarbons and a small amount of hydrocarbon derivatives. Their boiling points exhibit a wide range, forming a multi-component mixture with continuous boiling points. Therefore, petroleum products do not have a definite boiling point but are usually represented by their boiling point range or distillation range.

   When petroleum products are heated, the components with smaller molecular weights and lower boiling points evaporate first. As the temperature rises, components with larger molecular weights and higher boiling points gradually evaporate until all high-boiling-point substances have evaporated. The temperature range from the initial boiling point (the temperature when the first drop of condensate appears) to the final boiling point (the highest temperature when distillation ends) is called the distillation range. Measuring the distillation range involves heating a certain volume or weight of oil under specified conditions, then recording the corresponding temperatures at various distillation volumes or the distillation volumes at specific temperatures.

   Significance of Measuring the Distillation Range:

   • A. Determining Fraction Composition: It’s foundational data for plant design and assessing the composition of petroleum fractions.
   • B. Process Control: Used as a basis for controlling product quality and process parameters in refining and petrochemical production.
   • C. Evaluating Evaporation and Usage Performance: It’s an important index for evaluating the evaporation characteristics and determining the performance of oil products.

   Example: In GB17930-1999 “Unleaded Gasoline for Motor Vehicles,” distillation temperatures at various percentages are key indicators of vehicle performance:

   • (1) 10% Distillation Temperature and Starting Performance: Indicates the content of light fractions in the fuel. The lower the 10% distillation temperature, the easier the engine starts, with shorter starting times and less fuel consumption. However, too many light components can cause vapor lock.
   • (2) 50% Distillation Temperature and Acceleration Performance: Reflects the average volatility and acceleration performance of the fuel. A lower temperature shortens the warm-up time for the engine to reach normal operating conditions and makes shifting easier. If the 50% temperature is too low, the fuel’s calorific value decreases, reducing engine power.
   • (3) 90% Distillation Temperature and Combustion Safety: Indicates the content of heavy components in the fuel, relating to the completeness of fuel evaporation and combustion. A higher 90% distillation temperature means more heavy components, making complete combustion difficult. Generally, a lower 90% distillation temperature is preferable.
   • (4) Final Boiling Point: Represents the boiling point of the heaviest fraction in the fuel. A higher final boiling point may dilute lubricating oil and increase mechanical wear. Incomplete combustion can also lead to carbon deposits in the cylinder or clogging of fuel lines.
2. Density

   Density is the simplest and most commonly used physical property index for petroleum and its products. It refers to the mass contained per unit volume at a specified temperature, denoted by the symbol ρ and measured in kg/m³.

   • (1) Standard Density: Since density varies with temperature (oil expands when heated, reducing its density), densities measured at higher temperatures are lower than those at lower temperatures. For comparison, oil densities are usually expressed at a specified temperature. According to China’s GB standard, the standard density is the density of petroleum and its products at 20°C, measured in g/cm³.
   • (2) Apparent Density: The density reading observed using a densitometer at a certain temperature, denoted by ρₜ, measured in g/cm³.

   Significance of Measuring Density:

   • A. Quantity Conversion: Knowing the fuel volume and measuring its density allows for the calculation of its mass.
   • B. Preliminary Product Identification: Density can help initially determine the oil product type.

     Typical densities:

     • Gasoline: ρ = (0.7–0.76) g/cm³
     • Aviation Kerosene: ρ = (0.77–0.84) g/cm³
     • Diesel: ρ = (0.81–0.84) g/cm³
     • Heavy Oil: ρ = (0.91–0.97) g/cm³
     • Lubricating Oil: ρ = (0.87–0.89) g/cm³
   • C. Assessing Quality and Composition Changes: Density can approximately evaluate changes in oil product quality and chemical composition. Especially during production and storage, if the oil density significantly increases or decreases, it may indicate mixing with heavier or lighter oils.
3. Viscosity

   Viscosity is one of the main usage indicators of petroleum products, especially crucial for classifying and grading various lubricating oils, assessing quality, and determining their applications. In the process of oil flow and transportation, viscosity plays an important role in factors like pressure drop, making it an indispensable physical constant in calculations and design.

   Significance of Measuring Viscosity:

   • (1) Some lubricating oil standards grade products based on kinematic viscosity values, such as refrigerating machine oils and machinery oils, which are classified by their kinematic viscosity at 40°C.
   • (2) Viscosity is an important quality indicator for lubricating oils. Selecting an oil with the correct viscosity ensures stable and reliable engine operation. As viscosity increases, engine power decreases, and fuel consumption increases. Excessive viscosity can cause starting difficulties, while too low viscosity reduces the oil film’s supporting capacity, failing to maintain a continuous lubricating layer between friction surfaces, increasing wear.
   • (3) Viscosity is an important parameter for the storage and transportation of lubricating and fuel oils. Increased viscosity due to lower temperatures can raise pump pressure and make pipeline transportation difficult.
   • (4) Viscosity is a crucial property of diesel fuel. The viscosity of oil products generally increases with heavier fractions, affecting atomization and combustion in internal combustion engines. Excessive viscosity leads to larger and uneven oil droplets from injectors, poor atomization, insufficient mixing with air, and incomplete combustion. Diesel fuel also lubricates the plunger pump; too low viscosity affects pump lubrication, increasing plunger wear. Therefore, according to GB252-2000, the kinematic viscosity of No. 0 and No. 10 diesel is (3–8) mm²/s.
4. Hazards of Water Content in Oil Products
   • (1) Water in light fuel oils raises the freezing point and worsens low-temperature flow performance. For example, in aviation fuel during high-altitude flights, ice formation can block fuel lines, interrupting fuel supply.
   • (2) Water in lubricating oils can freeze into ice particles in winter, blocking oil pipelines and filters. Freezing in certain engine parts can increase wear.
   • (3) Water in electrical oils reduces dielectric performance due to its presence, potentially causing short circuits and even equipment damage.
   • (4) Gasoline can easily contain water during production and storage, especially at the bottom of large storage tanks. If a vehicle’s engine stalls or vibrates severely after refueling, it may be due to water-contaminated gasoline. Water in gasoline can cause rust on the inner walls of metal fuel tanks. Rust particles can adhere to the fuel pump filter, increasing the resistance to fuel suction, leading to insufficient fuel supply to the engine, decreased power, and eventual pump failure.
5. Definition of Mechanical Impurities

   Mechanical impurities refer to all impurities present in oil products that are insoluble in specified solvents. These include sediments or suspended substances insoluble in solvents like gasoline, benzene, or ethanol-ether (4:1 mixture), ethanol-benzene (1:4 mixture), etc. These impurities mainly include sand, dust, fibers, rust, and metal shavings.

   Significance of Measuring Mechanical Impurities:

   For fuel oils, mechanical impurities reduce equipment efficiency, cause component wear, or even halt normal operation. For example, mechanical impurities in gasoline can clog filters, reduce fuel supply, or interrupt it entirely. In diesel fuel, mechanical impurities can block fuel lines, exacerbate wear of precision parts in fuel pumps and injectors, degrade fuel atomization quality, and reduce fuel supply. Mechanical impurities may also cause fuel pump plungers and injector needles to seize, fuel outlet valves to close improperly, or injector nozzles to clog.

6. Measuring Low-Temperature Flow Properties of Oil Products

   Since various oil products may be used at low temperatures, the flow properties of liquid oil products (engine fuels and lubricating oils) at low temperatures become important indicators for evaluating usage performance and determining storage and transportation conditions. Indicators such as cloud point, crystallization point, freezing point, cold filter plugging point, pour point, and congealing point have been established to evaluate low-temperature performance. The variety of indicators is due to different purposes and varying test methods and standards adopted by countries or regions.

   Pour Point: The lowest temperature at which the cooled test sample can still flow under specified conditions, expressed in °C.

   Congealing Point: The highest temperature at which the test sample stops flowing under specified cooling conditions, expressed in °C.

   The congealing point of pure substances is constant, but it decreases in substances containing impurities. For petroleum products, the congealing point is related not only to the content of impurity substances (not mechanical impurities) but also mainly to the weight of fractions and especially to chemical composition. Generally, lighter fractions have lower congealing points, while heavier fractions have higher congealing points. In heavy oil products, the wax content plays a decisive role in the congealing point—the more wax, the higher the congealing point.

7. Ash Content

   Ash is the inorganic residue remaining after eliminating the carbon residue from oil products under specified conditions, expressed as a mass percentage. It represents the incombustible material left after igniting the oil sample according to specified conditions.

8. Flash Point

   The flash point is the lowest temperature at which the vapor emitted by an oil under specified conditions forms a mixture with air that can momentarily flash upon contact with a flame, expressed in °C.

   Depending on the nature and usage conditions of petroleum products and the testing conditions, different methods are used, broadly divided into two types. Generally, light petroleum products with high volatility are tested using the closed cup method.

   Significance of Measuring Flash Point:

   • (1) Assessing Fraction Composition: The flash point can determine the lightness or heaviness of fraction composition. Generally, higher vapor pressure and lighter fraction composition result in lower flash points, and vice versa.
   • (2) Evaluating Fire Hazards: The flash point helps assess the fire risk of oil products. The lower the flash point, the more flammable the fuel, and the greater the fire hazard. Liquids with flash points below 45°C are called flammable liquids, while those above 45°C are called combustible liquids.
9. Sulfur Element

   Sulfur is one of the common elements found in petroleum. The sulfur content in crude oil varies greatly, from a few ten-thousandths to several percent.

   Hazards of Sulfur in Petroleum Processing and Product Application:

   • (1) Corrosion: Sulfur corrodes petroleum processing equipment and containers. High sulfur content can cause significant damage to aluminum alloy engine cylinders.
   • (2) Odor and Discoloration: Many sulfur compounds, especially mercaptans, have intense and peculiar odors.
   • (3) Environmental Pollution: Burning sulfur-containing oils produces SO₂, polluting the environment.
10. Corrosiveness of Petroleum Products

    The corrosiveness refers to the oil product’s ability to corrode metal materials.

    Oil-induced equipment or mechanical corrosion can be due to many factors, mainly the presence of small amounts of sulfur and its compounds, water-soluble acids and bases, organic acids, certain additives, etc., which react chemically or electrochemically with metal materials.

11. Octane Number

    The octane number is a conventional value used to indicate the anti-knock performance of spark-ignition engine fuels (the ability of gasoline to resist knocking during combustion). It is determined through specified engine tests by comparing with standard fuels and is expressed as the volume percentage of iso-octane (2,2,4-trimethylpentane) in the standard fuel that has the same anti-knock performance as the test fuel.

    Significance:

    The octane number is the most important quality indicator for automotive gasoline, reflecting a country’s refining industry level and vehicle design standards. Generally, a variable compression ratio single-cylinder test engine, known as an octane rating engine, is used to evaluate gasoline’s octane number. Standard fuels are blended from two hydrocarbons with significantly different anti-knock properties: iso-octane (octane number set at 100) and n-heptane (octane number set at 0). By blending these in different volume ratios, standard fuels with octane numbers from 0 to 100 are obtained.

    • (1) Motor Octane Number (MON): Represents the anti-knock performance of gasoline when the engine operates at 900 r/min. The test is conducted at higher mixture temperatures (typically heated to 149°C). The MON reflects the anti-knock performance of gasoline during high-speed, heavy-load, or long-distance driving.
    • (2) Research Octane Number (RON): Represents the anti-knock performance when the engine operates at 600 r/min. The test is conducted at lower mixture temperatures (usually without heating). RON reflects the anti-knock performance of gasoline during low-speed driving with frequent acceleration. The U.S. and Western European countries mainly use RON. Premium gasoline typically has an RON of 96–100, while regular gasoline ranges from 90–95.

    Using gasoline with an octane number lower than required can lead to insufficient anti-knock performance, causing incomplete combustion, engine knocking (commonly known as “pinging”), reduced power, and increased fuel consumption. Using low-grade gasoline in high-compression engines can also increase carbon deposits in cylinders and injectors, raising failure rates and maintenance frequency. Incomplete combustion deteriorates exhaust emissions, worsening atmospheric pollution.

    Anti-Knock Additives: Substances added to gasoline to improve its anti-knock performance, commonly alkyl lead compounds like tetraethyl lead and tetramethyl lead. Due to their high toxicity and environmental hazards from vehicle emissions, the addition of lead to gasoline is now restricted to achieve unleaded gasoline. Currently, the ASTM-CFR test engine is widely used in China for determining gasoline octane numbers.

12. Significance of Measuring Diesel Cetane Number

    The cetane number represents a diesel fuel’s ignition performance in an engine. Since diesel engines are compression-ignition engines without other ignition devices, it’s crucial that diesel fuel injected into the cylinder mixes with compressed air and ignites rapidly under high temperature and pressure conditions. Generally, a higher cetane number means shorter ignition delay, lower autoignition temperature, better combustion performance, and significant practical value in enhancing engine power. However, the cetane number is not the higher the better. To ensure uniform combustion without unnecessarily increasing fuel consumption, a cetane number between 40–50 is usually sufficient for light diesel.

IV. Sampling of Petroleum Products

Sampling methods for liquid petroleum products are specified in GB/T4756-1984; solid and semi-solid petroleum products in SH 0229-92; and liquefied petroleum gas in SH0233-92. Below is a brief introduction to common sampling methods for liquid petroleum products.

1. Tank Sampling
   • Top Sample: At 1/6 of the depth.
   • Middle Sample: At 1/2 of the depth.
   • Bottom Sample: At 5/6 of the depth (or near the outlet liquid surface).
   • Composite Sample: Mix equal proportions of top, middle, and bottom samples (if consistent).
2. Tank Car Sampling
   • At 1/2 of the depth.
3. Precautions
   • (1) All sampling equipment must be rinsed once with the oil to be sampled.
   • (2) For diesel and gasoline, especially gasoline with very low flash points, seal the container promptly after sampling.
   • (3) When temporarily storing samples, keep them indoors away from open flames and direct sunlight.

V. Reports

1. Determining Legitimate Inspection Agencies

   The establishment qualifications of testing institutions are explicitly stipulated by the state. According to Article 19 of the “Product Quality Law of the People’s Republic of China,” product quality inspection institutions must have corresponding testing conditions and capabilities. After passing assessments by product quality supervision departments of the people’s government at or above the provincial level or their authorized departments, they can undertake product quality inspection work. Article 22 of the “Measurement Law of the People’s Republic of China” stipulates that product quality inspection institutions providing public data must pass assessments of their measurement verification, testing capabilities, and reliability by the measurement administrative departments of the people’s governments at or above the provincial level.

2. How to Identify the Authenticity of Inspection Agencies

   When identifying the authenticity of an inspection agency, pay attention to the following points:

   • (1) Check whether the inspection unit has a “Certificate of Measurement Accreditation” from the provincial Quality and Technical Supervision Bureau.
   • (2) Verify if the testing instruments have a “Measurement Qualification Certificate” attached by metrological verification departments and whether they are within the valid period.
   • (3) Look for marks such as “CMA” (China Metrology Accreditation) or “CAL” (Authorization Mark of Provincial or Higher Quality Supervision Departments) on the report.

VI. Test Method Standards (GB, SY, SH)

Petroleum product test methods are mostly conditional test methods. To ensure these conditions serve an authoritative role and have legal binding force during arbitration and appraisal, a series of analytical method standards (i.e., test method standards) need to be formulated. Test method standards are divided into five categories according to technical levels.

• (1) International Standards: Formulated through cooperation and consultation between countries with common interests, recognized by most countries as advanced standards applicable internationally, such as ISO standards.
• (2) Regional Standards: Used within groups formed by several countries or regions, such as standards formulated and used by the European Community.
• (3) National Standards: Generally issued by designated national agencies, such as GB (China), ANSI (USA), BS (UK), JIS (Japan), DIN (Germany), etc.
• (4) Industry Standards: Issued by relevant industries, such as HG for standards by the Ministry of Chemical Industry of the People’s Republic of China, SH for standards by the China Petrochemical Corporation. The ASTM standards by the American Society for Testing and Materials and the IP standards by the Institute of Petroleum are renowned professional standards globally and are targets for standardization of analysis methods in various countries.
• (5) Enterprise Standards: Standards formulated by enterprises.

Petroleum product test methods belong to method standards in technical standards. The letters (Chinese Pinyin) in the numbering indicate the standard level, the middle numbers are the standard number, and the last two digits represent the year of approval. For example:

• GB254-87: National Standard No. 254 of the People’s Republic of China, approved in 1987.
• SH0112-92: Industry Standard No. 112 of the China Petrochemical Corporation, approved in 1992.
• RQB230-81: Enterprise Standard No. 230 of Refinery No. 2, established in 1981.

Petroleum Product Standards refer to the main indicators that specify the quality specifications of petroleum and petroleum products according to their performance and usage requirements. In China, the following standards are mainly implemented:

• Mandatory National Standards (GB)
• Recommended National Standards (GB/T)
• Petroleum and Petrochemical Industry Standards (SH)
• Enterprise Standards
• For foreign-related matters, standards are implemented as agreed upon.