Raman Spectroscopy Aids In Setting New Standards

Online Editor

How Raman spectroscopy is delivering reliable results in oil, gas and petrochem laboratories

Most large refineries, petrochemical plants and even large storage terminal complexes have an internal testing laboratory to manage the analysis of crude oil, distillates, petroleum feedstock, fuel additives and refined products. If this option is not available, operators can send samples to external, third-party labs for on-demand analysis. The analytical data is critical for operators to make informed decisions regarding product quality, infrastructure protection, regulatory compliance, and other key factors that ultimately impact profitability.

To conduct tests, laboratories rely on various analytical tools and testing methodologies such as chromatography (gas, liquid, ion), spectroscopy (UV/Vis, FTIR), scanning electron microscopy, calorimetry, titration, and other established techniques.

Many laboratories are now counting solid-state Raman spectroscopy as an essential analytical tool to determine the composition and concentration of components in refined petroleum fuels, aromatics, petrochemicals, liquid petroleum gas (LPG), natural gas, lubricants, additives, feedstocks, intermediaries and other related hydrocarbon products.

Raman Spectroscopy

Raman spectroscopy is a laser-based optical analysis technique used to measure composition through the vibrational properties of molecules. Samples are collected using a 785nm excitation laser and a contact probe that produces a unique spectral fingerprint that identifies the chemical composition and molecular structure of an oil or gas. The distribution of the spectral peaks describes the molecule’s composition, while the signal intensity correlates linearly with concentration.

Since its discovery in the 1920s, Raman spectroscopy has revolutionized process analysis with its non-destructive mode of operation and capability to measure sample composition. However, the broader adoption of this technique is the result of advancements in the stability and portability of solid-state Raman systems and technological improvements in lasers, optics, and detectors that have made the technique faster and more accessible.

“Raman spectroscopy is a well-established technique that compliments everything else in the testing lab,” says Chris Peres of USA-based MarqMetrix, a company that specialises in compositional analysis using Raman spectroscopy and has pioneered advancements in Raman for use in the energy sector. “Although its use in oil and gas analysis is relatively new, it has already proven to be a highly accurate, efficient, and usable compositional measurement tool.”

According to Peres, one promising application example for Raman in internal labs is to speed custody transfer at refineries, storage facilities, storage tanks and pipelines.

Octane tests such as research octane number (RON) or motor octane number (MON) measure gasoline characteristics related to engine knocking. RON is determined by using test methods specified by ASTM D2699 and MON as specified by ASTM D2700. To derive the octane rating, both tests involve increasing the compression ratio of a single-cylinder, four-stroke cycle engine until it starts to knock.

The fuel engine test can take several hours, however, delaying custody transfer. Although Raman testing does not replace fuel engine testing, ASTM D8340 establishes an approach to ensure a degree of confidence in analyser-predicted values in relation to the primary fuel engine testing. ASTM D8340 further stipulates that gasoline can be released based on those values.

“With Raman, one lab technician can run multiple analysis in seconds, including octane, vapour pressure and API gravity. These values can be derived on a single instrument without requiring a dedicated specialist in the testing methodology,” explains Peres.

“For example, at an eight bay refinery rack, the tanker trucks often have to wait while the lab runs a two to three hour octane test to certify the RON and MON before loading can commence,” continues Peres. “With a quick scan using a Raman analyzer, the gasoline could be released while the fuel engine testing is finalised, the product certified, and the documentation filled out.”

The same would apply to other transactions as gasoline is loaded onto barges and ships, offloaded into shore tanks, or distributed through pipelines.

Solid-State Raman

Today’s solid-state Raman systems, such as the MarqMetrix All-In-One, have very few moving parts and are ideal for continuous process monitoring and routine lab analysis. As a result, these systems can be placed at any point of measurement, including inline, atline, or offline.

MarqMetrix has engineered the All-in-One to produce identical and repeatable results from unit to unit in a package 80% smaller than previous Raman instruments. Each device is nearly an exact copy, so common mathematical models can be applied across systems to produce consistent results.

The system works with a wide array of contact probes suitable for oil and gas applications that can be changed in seconds without the need for recalibration. The immersion optic ball lens probes, that are widely used throughout the industry, enable users to achieve reproducible measurements of samples better than 1% accuracy.

“The All-in-One can be used on any components that require Raman analysis, which provides labs with tremendous flexibility in what is measured and how it is operated,” says Peres.

Although the Raman equipment can be used to identify the components within approximately 15 minutes of unboxing, quantifying the concentrations of each component first requires creating a predictive model. For general laboratory use, MarqMetrix offers a library of pre-developed models that covers most common applications.

“For refined fuel, for example, we have built models for jet fuel and diesel gasoline that come with the unit,” explains Peres. “The models are expanded to include additional properties and values, as needed.”

Accurate measurement is more essential than ever in the oil and gas industry. Understanding the chemical composition of raw materials and the consistency of processed products is key to manage processes, reduce risks, and maximise outcomes.

With the advancements in applying Raman spectroscopy systems to sample measurement, laboratories now have a reliable and economical tool that produces accurate, fast results and complements existing testing methodologies.