Filtration in crude oil refining

Filtration analysis of refined petroleum products is vital in downstream oil processing. In this blog, discover how dedicated filtration tests and chromatography ensure petroleum products meet government standards for stability and composition.

Petroleum products, such as gasoline and diesel, power economies worldwide and are essential for modern life. But how do refineries make sure their products meet the strict international standards they work towards?

Here we explore various filtration tests performed on refined petroleum products, and discover how the unique properties of membrane filters enable petroleum engineers to assess product characteristics including quality, acceptable storage duration and temperatures.

The refining process

In the final stage of the petroleum processing workflow, oil facilities send processed crude oil to refineries, where petroleum engineers transform it into the final products using fractional distillation. The oil is first heated, then separated into different chemical fractions based on their boiling points. These fractions condense at different heights along the column, so engineers can collect them easily for further processing.

We can divide up the fractions into three types: heavy, middle, and light distillates.

Those with the highest boiling points are the heavy distillates, which include fuel oil used for generating electricity, as well as bitumen, which is used in road construction and in waterproofing products. Middle distillates include diesel fuel, as well as products used to heat homes, such as kerosine. Lighter fractions include naphtha and refinery gases, which go on to form products such as the liquified petroleum gas (LPG) used in cooking equipment and as a more environmentally friendly alternative to Chlorofluorocarbons (CFC’s) in refrigerators.

Filtration analysis and storage of fuels

Fuels generated by refineries often need to be stored for long periods of time before they are used, which can affect their quality. Long term storage means fuels can be exposed to oxygen, resulting in the formation of solid particulates in the fuel. These particulates are often small enough to pass through engine filters and can clog up fuel injectors, leading to engine failure.

To make sure that fuels are suitable for long term storage, engineers perform filtration tests. In the oxidation test outlined in The American Society for Testing and Materials (ASTM D2274) standard, an engineer places samples of a fuel in a test tube, places them into sealed ovens with either pressurized air or oxygen and heats them for 16 hours.

The fuel is then cooled and passed through a filter with a small, defined pore size, such as Whatman™ ME 27 0.8 µm membrane filters. The difference between the weight of filters before and after the experiment helps in calculating the oxygen stability of the fuel.

Testing fuels for use in low temperatures

Gasoline and diesel vehicles play a vital role in sustaining settlements in mountainous or northernly regions with colder climates, delivering food and goods year-round. However, petroleum products and biodiesels used in combustion engines tend to form waxy paraffin crystals. If the temperature drops too low, these crystals can plug fuel system filters and lead to serious machine operation problems.

To assess the wax-forming characteristics of a fuel, engineers measure its cloud point: the temperature at which paraffin crystals begins to separate from the fuel.

The cloud point test outlined in ASTM D5771 is an optical detection stepped cooling method that involves cooling the fuel sample and measuring the amount of light scattering caused by wax formation.

However, cooling the samples can lead to water leaving the solution and forming a general haze that can interfere with the optical readings. To obtain accurate results, the sample of oil should be free of water, which analysts can achieve using cellulose membranes, such as Whatman™ Grade 1 Qualitative Filter Papers.

Filtration in advanced analyses of petroleum distillates

Gasoline is one of the most important and widely used products generated at oil refineries, and governments worldwide have issued extensive regulations on its accepted chemical composition. Many of these regulations aim to improve air quality by ensuring gasoline contains only low levels of chemicals such as napthenes, a group that contains compound harmful to human health and the environment such as benzene or toluene.

The analysts perform measurements of bulk hydrocarbon groups and individual compounds including paraffins, isoparaffins, olefins, napthenes and aromatics (known as ‘PIONA’ analysis). This analysis is essential before gasoline can be exported to different countries, with exports needing to comply with standards in ASTM D5134, D6729, D6730 and D6733.

Petroleum engineers at testing labs use gas chromatography (GC) with vacuum ultraviolet absorption (GC-VUV) for PIONA analysis, in a method outlined in ASTM D8071. When performing GC-VUV, scientists pre-filter the fuel samples using 0.45 µm filters, such as Whatman™ brand Mini-UniPrep™ G2 Syringeless Filters. Pre-filtration

• prevents particulates blocking GC injection syringes
• decreases the build-up of involatile residues at the inlet
• helps ensure efficient analysis of gasoline composition

Petroleum engineers might also use high performance liquid chromatography (HPLC) to measure the level of specific aromatic compounds in distillates like jet fuels. Filtering fuel samples and mobile phases through regenerated cellulose filters, such as SPARTAN™ HPLC Syringe filters, helps make sure the chromatography columns remain free of particulate contaminants.

Using membrane filters to protect chromatography equipment extends the life of expensive equipment and supports reliable test results.

Summary

Filtration tests on petroleum products help engineers assess whether a batch of fuel meets international regulations on chemical composition, helps to minimize the effect of fuel combustion on the environment, and are critical for the safety of end users.

The defined pore sizes of membrane filters and their compatibility with organic solvents make them well suited for analysis of petroleum products, and these tests make up an important stage of downstream processing.

For more information on any of the specific applications of membrane filters mentioned in this blog, or for any other questions relating to filtration analysis, please contact our scientific support team.

To learn more about filtration analysis, visit our Lab Filtration Knowledge Center which has a range of informative articles and videos on membrane filtration, as well as tools to assist in filter selection.