Why Do We Need Effective Testing Methods in the Petrochemical Industry?

Petrochemicals are ubiquitous in modern-day society – from the fuels that we use in our cars and planes to the production of chemical feedstocks for use in plastics, paints, cosmetics and beyond.¹

These petrochemicals are derived from crude oil using various separation and refinement processes, and because these products are so widely used in consumer sectors, there needs to be a high degree of safety testing involved in monitoring their production.

“The process that starts with the extraction of crude oil from the ground (usually by drilling) and ends when the crude oil has been transformed into fuel for vehicles (i.e., gasoline), as well as other commercially available oils and waxes,” explained Prof. Mindy Levine, Department of Chemical Sciences, Ariel University. 

Effective chemical analysis in the petrochemical industry is crucial to achieving a safe production process and favorable product outcome.

The need for petrochemical testing

Petrochemicals are frequently used in highly regulated industries, for example, specialist plastic products used in the medical sector. Consequently, these petrochemical products need to be thoroughly tested to ensure that they are safe for use.

Testing to evaluate the exact chemical composition of crude products is also key, as this helps to prevent any problems occurring downstream due to impurities. Such impurities will react differently during the refinement process, potentially clogging pipes, corroding processing equipment and contaminating catalysts during the extraction and production stages.² This danger is especially true for sulfur impurities, which can poison or deactivate the precious metal catalysts that are used during the petrochemical refinement process, resulting in lost productivity. If trace sulfur is present, then the sulfur will react with the metals, forming metal-sulfur complexes on the surface of the catalyst that degrades catalytic performance.³

Chemically, crude oil is very complex. As a natural resource, the composition of the oil and the number of trace elements present can vary greatly between different reservoirs or oil fields.

While most of these molecules present in crude oil are hydrocarbon chains ranging from 1 to over 100 carbon atoms in length, there are other chemical constituents in the oil, such as oxygen, nitrogen, and halogen elements, that may also be present and must be monitored in order to prevent fouling and contamination of the process equipment.⁴

Each stage of the petrochemical process involves a chemical or physical transformation. Levine elaborates: “It is important to conduct petrochemical analysis before and after each transformation: before the transformation, to ensure that there are no undesired components that will interfere with the efficacy of the transformation, and after the transformation, to ensure that the transformation has been successful and that no residual contaminants are left for the subsequent stage.”

Throughout the various stages of petrochemical processing, analytical methods are deployed to ensure that products are pure, free from contamination, meet regulatory requirements and are fit for purpose. The testing of the products at different stages also ensures that the process parameters are fully optimized and capable of producing high quality products.

Figure 1: A variety of consumer products are derived from petrochemicals. Credit: Technology Networks, adapted from Petrochemical Analysis.

Gas chromatography for petrochemical analysis

Gas chromatography (GC) is a very versatile technique that is employed extensively within the petrochemical industry to detect trace amounts of contaminants within petrochemical samples.

In brief, gas chromatography is an analytical technique wherein a sample is dissolved into a volatile solvent and vaporized. The vaporized molecules are transported through the apparatus via a mobile phase ― an inert, oxygen-free carrier gas ― to a heated chromatographic column, known as the stationary phase. As the carrier gas carries the vaporized sample through the column, the molecules in the sample are separated out based on the differences in boiling point/vapor pressure, as well as their strength of interaction with the stationary phase. This causes the different molecules to separate, after which they can be analyzed by a detector of the technician’s choice.

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There are many detectors available for gas chromatographs that enable the precise analysis of different chemical constituents. Gas chromatography mass spectrometry (GC-MS) combines GC with a mass spectrometer, which measures the mass-to-charge ratio (m/z) of charged particles. This enables the precise determination of molecular weights and chemical structures of molecules and fragments in a sample. In petrochemical analysis, such a method can be used to separate out and characterize hydrocarbon fractions in petroleum.

Beyond this, there are a number of other detectors, including catalytic combustion detector (CCD), discharge ionization detector (DID), electron capture detector (ECD), flame photometric detector (FPD), helium ionization detector (HID), infrared detector (IRD), mass spectrometer (MS), photo-ionization detector (PID), pulsed discharge ionization detector (PDD), thermionic ionization detector (TID) that are used to analyze different chemical constituents.

Gas chromatography–sulfur chemiluminescence detection (GC–SCD) is also used within the petrochemicals sector to quantify the concentration of sulfur containing molecules, such as mercaptans, hydrogen sulfide, benzothiophenes and thiophenes, in hydrocarbon samples. This technique is highly sensitive to these sulfur compounds, which can disrupt the refinement process if left undetected.

Modern-day GC approaches may also use multiple detectors simultaneously, allowing for a broader range of chemical species to be determined in a single sample run.⁵

One GC technique that was specifically designed for the petrochemical industry back in the 1990’s and is now widely used in the sector is two-dimensional gas chromatography (GC-GC). This method uses two chromatographic columns to enhance separation and improve the resolution of the peaks when working with petroleum samples.

GC-GC was first used to separate oxygenated hydrocarbons in combustion products but is now used to separate the so-called PIONA hydrocarbons –  paraffins, isoparaffins, olefins, naphthenes and aromatics – to ensure that naphtha products are of a high and standard quality. The concentration of PIONA compounds in naphtha can vary based on the region the crude oil comes from and so should be carefully monitored.⁶ GC-GC is also used to deduce the octane number and combustion performance of different fuels, as well as for determining the composition of hydrocarbon oil spills.

Gas chromatography is the most prominent chromatography technique used in petrochemical analysis, but liquid chromatography techniques – such as liquid chromatography mass spectrometry (LC-MS) and high-performance liquid chromatography (HPLC) –  are also used to tackle the heavier petrochemical products that have higher boiling points.⁷ This is due to the higher boiling point making it more difficult to vaporize and analyze with GC.

Trace elemental analysis for the petrochemical industry

Inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES) are another two analytical techniques that are widely used in the petrochemical industry to detect trace elements during the extraction and refining of crude oil.

In both methods, plasma is created through ionizing the sample being analyzed. The resulting ions can then be sent to a suitable ion detector for quantification.

“ICP-OES uses a high temperature plasma matrix to generate element-specific atomic emission spectra and determine the atomic composition of a sample. ICP-MS uses the same high temperature matrix as ICP-OES), but the detection of the sample is done using mass spectrometry to determine the mass of the sample and all sample fragments,” explained Levine.

ICP-MS and ICP-OES are frequently used to detect trace elements of iron, vanadium, nickel, and arsenic and other metallic species in complex petrochemical samples, as well as being utilized in the analysis of naphtha products, bitumen products and other fuels.⁸

Trace elemental analysis is important at all stages of petrochemical processing.

“It [trace elemental analysis] is the only method available to detect minute quantities of contaminating elements. Such minute quantities can have a significant effect on various stages of the process, and if undetected, can render the entire refining process ineffective,” noted Levine.

For example, vanadium and iron can cause damage to refinery furnaces; volatile organometallic compounds can contaminate distillates and damage equipment; and lead, arsenic and iron can contaminate the catalysts used in processing. Kerosene products are also highly prone to metallic contamination originating from the original crude oil sample, the pipework it passes through and the tanks it is stored in. All these issues can impact both the combustion performance and the safety of any equipment petrochemical products may be used in.

While both ICP methods are used in the petrochemical industry, there are some differences in how the two techniques perform and what their limits are. ICP-MS tends to have lower detection limits than ICP-OES (parts per trillion compared to parts per billion) and covers a wider range of relevant analytes. The advantage of ICP-OES lies with its ability to analyze both metal and non-metal species with a good resolution.⁹ However, the overall resolution in ICP-MS is superior and can analyze a greater variety of relevant trace elements.¹⁰

Additionally, ICP-OES specifically is often used to analyze petrochemical-based lubricants. Lubricant wear in mechanical machines manifests in the form of metal particles breaking off into the lubricant. The lubricant then becomes contaminated with solid particles that cause further breakdown of the metal components as the overall lubricity is reduced, leading to a cycle where more wear and degradation occurs over time through the lubricant becoming more contaminated. ICP-OES is used in lubricant analysis because it can simultaneously analyze all metals, as well as non-metals, simultaneously.⁹

ICP-OES also boasts a much higher throughput and a faster analysis time than ICP-MS, with the technique able to analyze many samples per hour―around 48 to 60 samples per hour depending on the specific instrument used. Additionally, ICP-OES systems are typically cheaper to buy, run and maintain than ICP-MS instruments. For some smaller analytical laboratories, this could be an important factor when considering what petroleum and petrochemical analysis services they are able to offer.

Other approaches to petrochemical analysis

Alongside ICP-MS, ICP-OES and the various chromatography-based methods used for petrochemical analysis, there are also many other techniques that are also frequently employed in the industry. This includes nuclear magnetic resonance (NMR), which is used analyze petrochemical reservoir samples; X-ray fluorescence (XRF) spectroscopy for the detection of trace amounts of sulfur and metals; and infrared (IR) spectroscopy, which is used in the processing stages to detect if any samples have become contaminated with metal additives due to machinery wear.

Petrochemical testing is a vital process within the petrochemical industry and its adjacent end-user sectors. Proper analysis ensures that robust and optimized processes are in place at all stages of production, while checking that these final products are safe-to-use and of a high quality. Collectively, the analytical techniques deployed by petrochemical analysts are crucial in supporting a chemical sector that, at its core, is responsible for the handling of chemically complex and potentially volatile compounds, and enduring that they are safe for consumer use.