What is ASTM D5236? Understanding this Standard for Vacuum Distillation

When refining heavy hydrocarbon mixtures, overheating can cause thermal cracking and inaccurate yields. That’s where ASTM D5236 comes in. What is ASTM D5236? 

Understanding the standard for vacuum distillation is key for refineries and labs separating crude oils, petroleum distillates, and synthetic mixtures without damaging heat-sensitive samples.

ASTM D5236, or the vacuum potstill method, distills heavy hydrocarbons with initial boiling points greater than 150°C. Refineries rely on ASTM D5236 for gas oil, lubricating oil range fractions, and final boiling points, but errors can be costly. This blog breaks down its test method details, compares it to other recommended distillation methods, and highlights its role in refining heavy crude oils.

Key Takeaways

• Precise and High-Quality equipment are key to avoiding costly miscalculations for refineries.
• Refineries that execute ASTM D5236 correctly optimize yields, improve efficiency, and stay ahead of regulatory requirements, through reliable distillate fractions.

ASTM D5236: The Science Behind the Standard

ASTM D5236 is a standard test method for distillation of heavy hydrocarbons using a vacuum potstill method. 

Operating under vacuum prevents thermal cracking and preserves fraction qualities in gas oil and lubricating oil range products.

ASTM D5236 reduces pressure to keep heat-sensitive samples stable while separating components. A low-pressure drop entrainment separator prevents contamination by ensuring only vapors enter the distillation column. This allows higher cut temperatures of above 400C AET, compared to similar methods such as ASTM D2892.

Key Parameters:

• Temperature range: Handles initial boiling points from 150°C to a maximum achievable atmospheric equivalent temperature of 565°C or more.
• Atmospheric equivalent temperature (AET): Converts temperature at vacuum conditions to comparable atmospheric boiling points.
• Vacuum potstill setup: Uses a pressure drop entrainment separator, vapor temperature sensor, and distillation column for precise separation.
• Fraction collection: Produces distillate fractions like gas oil, lubricating oil range, and residues.

How ASTM D5236 Works: Step-by-Step Breakdown

ASTM D5236 requires precision-built equipment to maintain standardized quality. Below is a breakdown of the setup, process, and common challenges.

The vacuum potstill setup

The setup consists of several key components, each playing a crucial role in achieving accurate fraction qualities obtained from the process.

• Reboiler: Holds the sample and provides controlled heating.
• Distillation column: facilitates separation of components
• Entrainment separators: Prevent liquid carryover, ensuring only vapors pass through the system.
• Vacuum pump : Lowers atmospheric pressure to reduce the required temperature for distillation.
• Vapor temperature sensor: Measures the observed vapor temperature, which is essential for calculating atmospheric equivalent temperature AET.
• Flask temperature sensor: Measures the observed flask temperature, which is essential for monitoring and controlling the heating rate..
• Pressure sensor: Measures the observed system pressure, which is essential.
  Temperature and Pressure sensors: Measures the observed vapor temperature, flask temperature, and system pressure,which are essential for calculating atmospheric equivalent temperature AET and recording key data points used in the control of the system during the test.

The distillation process

Once the system is set up, the test begins with sample preparation. ASTM D5236 follows a complex procedure involving multiple steps to produce standardized quality distillates.

1. Sample preparation and loading: The method requires dry, well-mixed samples to prevent inconsistencies. If excess water is present, dehydration may be necessary to avoid disruptions during distillation.
2. Initial boiling point determination (>150°C): The sample is heated at a controlled rate until vapors begin to form. The initial boiling points are recorded, and the increasing boiling point of the mixture is recorded as a function of the volume that has been distilled.
3. Fraction collection and analysis: Vapors condense into separate fractions based on various boiling ranges of interest. Each fraction’s final boiling point is recorded, and the mass and volume are measured
4. Data recording and interpretation: The results generate standard distillation curves, helping refineries predict product yields and optimize refining conditions. 

Common challenges in ASTM D5236

While ASTM D5236 is a reliable test method for distillation, execution errors can lead to inaccurate results, affecting the fraction qualities obtained and overall refinery performance.

Inaccuracies due to poor sample handling: Contaminated or improperly prepared samples can significantly impact the separation process. Inconsistent mixing, residual moisture, or external impurities can distort fraction qualities and affect the reliability of the data collected.

Proper calibration of temperature sensors is essential. A misaligned vapor temperature sensor can lead to incorrect observed vapor temperature readings, which can affect the calculation of atmospheric equivalent temperature (AET).

Even slight calibration errors can disrupt the accuracy of standard distillation curves, leading to incorrect assessments of boiling ranges and product yields.

ASTM D5236 vs. Other Distillation Methods: What Sets It Apart?

D5236 vs. D2892 (True boiling point distillation)

ASTM D2892 starts at atmospheric pressures, and is ideal for lighter fractions with final boiling points below 400°C atmospheric equivalent temperature (AET), using distillation packing to improve separation. ASTM D5236 does not use packing but instead includes a low-pressure drop entrainment separator to allow operation at deep vacuum. This makes ASTM D5236 more suitable for the distillation of heavy hydrocarbon samples.

D5236 vs. ASTM D1160 (Vacuum distillation of petroleum products)

ASTM D1160 is used to generate boiling point curve data, while ASTM D2892 and D5236 are used in the construction of distillate fractions. 

Why ASTM D5236 is crucial for refinery optimization

Accurate standard distillation curves improve vacuum unit performance Proper execution of ASTM D5236 avoids process inefficiencies and unnecessary modifications caused by faulty data. 

By following the correct equipment performance criteria, refineries can optimize yields and maintain standardized quality across distillate fractions.

Industry Applications: Where ASTM D5236 Makes an Impact

Small errors can lead to inaccurate yield predictions, and product inconsistencies. Using a vacuum potstill method, ASTM D5236 helps industries refine crude oils, petroleum distillates, and synthetic mixtures while maintaining accuracy and efficiency.

Refineries & crude assay labs

Refineries need reliable data on distillate fractions to optimize processing and maximize product recovery. ASTM D5236 provides clear insights into vacuum gas oil (VGO), lubricating oil range, and asphalt yields, allowing refineries to:

• Improve crude oil assessments by identifying the true yield potential of heavy hydrocarbon mixtures vacuum
• Avoid overestimating product recovery, which can disrupt operations and lead to costly adjustments
• Enhance vacuum unit performance by using accurate standard distillation curves for better process control

Petrochemical research & development

In research labs, understanding the behavior of distillate fractions is key to developing high-performance products. ASTM D5236 supports:

• Refining synthetic blends and lubricants by analyzing separation patterns under controlled conditions
• Evaluating heat tolerance and stability of feedstocks to determine their suitability for advanced refining and formulation

Quality control & compliance

Accurate testing is critical for meeting industry standards. ASTM D5236 allows quality control teams to:

• Ensure product consistency by verifying that distillate fractions meet the required specifications
• Validate vacuum distillation unit efficiency by comparing actual yields to expected values
• Maintain compliance with internationally recognized principles and avoid setbacks prior to production or distribution

The Cost of Poor ASTM D5236 Execution

Errors in ASTM D5236 testing affect refinery efficiency, profitability, and compliance. Miscalculations in distillation conditions, poor equipment performance, and inaccurate data interpretation can lead to worse yields, inefficient processing, and regulatory setbacks.

A properly generated boiling point curve is essential for refining operations.

Miscalculations in the highest atmospheric equivalent temperature (AET) or test execution can lead to vacuum unit inefficiencies, incorrect gas oil and lubricating oil range recovery estimates, and disruptions when transitioning from lighter to heavier fractions. 

Compared to other methods like ASTM D1160, D5236 delivers boiling data that more accurately reflects real distillation behavior.

Lost profitability due to poor data interpretation

Miscalculations in ASTM D5236 can significantly impact refinery profitability. A 3-6% lower vacuum gas oil (VGO) yield on whole crude compared to design expectations can result in tens to hundreds of millions of dollars in lost revenue annually. 

Inaccurate assessments of heavy crude oils lead to unnecessary process modifications and underperformance of vacuum distillation units. 

Optimize Your ASTM D5236 Vacuum Distillation with PDS

Precision in ASTM D5236 vacuum distillation is key to refining heavy hydrocarbon mixtures efficiently. Performance Distillation Solutions (PDS) offers fully automated, computer-controlled systems that have highly customizable settings for sample-specific needs, as well as fraction collection, and highly accurate boiling point determination.

Our DIST D-5236 CC and DIST D-5236 HV models provide automatic vacuum reduction, dead volume elimination, and stable fraction discharge for accurate, repeatable results. The high vacuum option reaches 0.006 mmHg, allowing higher atmospheric equivalent temperature (AET) values and precise weight vs. temperature data.

PDS systems exceed ASTM D5236 standards, improving efficiency and maximizing distillate fraction yields. Call us today to upgrade your vacuum distillation process.

Conclusion

Refineries rely on ASTM D5236 to separate heavy hydrocarbon mixtures and optimize vacuum distillation conditions. Accurate boiling point curves and reliable distillate fractions maximize gas oil and lubricating oil range recovery, while errors in temperature response time, calibration, or sample handling can lead to costly miscalculations.

Accurate distillation data is the foundation of efficient refining. With strict regulatory limitations prior to production and the need for standardized quality, every test method for distillation must be executed with precision. The right expertise and equipment keep refineries competitive and profitable.