Using NIR Spectroscopy in Petrochemical Refineries

Petrochemical refinement is a complex, multi-step process involving many hundreds of chemical species. While global growth for the use of oil in transport fuels is slowing, demand for the chemicals produced from crude oil refinement is not,1 with many countries investing as much as $100 billion into their petrochemical industries in response.2

Image Credit: Avigator Fortuner/

Many refineries are looking for ways to capitalize on this ‘crude-to-chemical’ movement as a way of remaining competitive as part of the changing market. Part of this involves focusing the refinement process on the production of high-value compounds, such as middleweight hydrocarbon compounds like naphtha. The other is improving efficiencies and yields at the many stages of the refinement process.

The challenge for this is to find techniques capable of handling the chemical complexity of the crude oil mixtures that can provide quantitative and qualitative information on the chemical species of interest. Such screening is also essential for producing products consistent with international standards and regulations.

Online Analysis with NIR Spectroscopy

One of the best techniques for rapid screening and analysis of hydrocarbon-based mixtures is near-infrared (NIR) spectroscopy. Many petrochemical compounds absorb NIR light very strongly and each chemical has a unique absorption pattern of energies and intensities that are known as a spectral fingerprint. With calibration, NIR spectroscopy can also be used for the quantification of chemical species as the intensity of the observed signals is proportional to the concentration of the chemical present.

With developments in NIR instruments, such as Guided Wave’s NIR-O Process Analyzer3, it is possible to integrate these devices into many different areas of the refinery for automated, online analysis of mixtures. Guided Wave’s NIR-O instrument with the optical multiplexer has been designed so that a single instrument can monitor up to 12 different sample points, giving excellent process coverage. This can be used as part of feedback systems for online optimization of processing or for final product analysis, such as the determination of Fuel Octane Numbers.

Another crucial application of NIR spectroscopy, that the NIR-O instrument is well-suited for, is the monitoring of benzene levels during the refinement processing. Recent EPA legislation states that refiners must take steps to reduce the production of benzene and similar air toxics, such as 1,3-butadiene and naphthalene. Average annual benzene levels must be below 0.62 volume percent.4

By combining NIR spectroscopy with 3rd party chemometric software packages such as Unscrambler, PLS-Toolbox, and Pirouette, Guided Wave offers a complete online solution for the measurement of benzene in gasoline that is consistent with the accuracy of much slower laboratory-based methods that rely on offline sampling. Along with ease-of-use, this represents a significant time and cost savings through the use of an in-situ probe that can monitor process compositional changes in real-time.5

LPG Processing and Quality Control

Another key area that can benefit from the rapid analysis capabilities of Guided Wave’s NIR-O device, is Liquified Petroleum Gas, LPG, processing. In refineries, NIR spectroscopy is widely used for LPG process monitoring6 but less so for composition analysis, which is typically performed via offline measurements using gas chromatography (GC).

Guided Wave has recently shown that by installation of a single NIR-O spectrometer, with sampling points covering the main fractionator units and de-propanizer and de-ethanizer streams, one device can be used to replace more costly and complex to maintain GC instruments.7 Using automated data analysis, the NIR analyzer system could successfully be used to assess the purity of butane and propane produced as well as optimize the speed and quality control of the refinement process itself. As LPG processing often involves a mixture of gaseous and liquid samples, it was also possible to identify the phase of the detected compounds, to include only measurements of the LPG improving the robustness and reliability of the measurement.

Opting for NIR sensing over offline GC analysis results in a significant reduction in capital expenditures for new projects since multiple streams can be monitored simultaneously with a single device. The analyzer is easy to install as long thermally stable fiber optic cables can be used to reach sampling points with no loss of signal quality and can even be used to look at other properties of monitored fuels beyond just chemical composition.

NIR-O Process Analyzer

The NIR-O Process Analyzer

The NIR-O process analyzer can be multiplexed with up to 12 different sample points, essential for use in refineries where there are numerous processing streams. Guided Wave’s patented state of the art sample interfaces, such as the Gold Transmission SST Probe, can withstand the harshest process conditions while still providing unsurpassed optical transmission. Data monitoring of all process streams can be used to boost process optimization with live feedback in all areas of the plant, with a significant positive impact on the refinery profitability, and additional sampling points can be added over time if required.  

The work by Guided Wave demonstrates that NIR technologies can easily compete with conventional GC analysis methods for compositional analysis, with the added advantage of cost and time savings and options for online process monitoring.

The NIR-O Process Analyzer makes use of dual-beam optics and built-in diagnostics to achieve excellent reliability and very high signal-to-noise ratios for optimum sensitivity in measurements. The wavelength accuracy is NIST traceable and the outstanding optical performance allows it to differentiate even the most similar hydrocarbon species, be it liquids, gases or thin films.

  1. BP Energy Outlook – BP, (2020),, accessed 21st October 2020
  2. Why the future of oil is in chemicals, not fuels – A. H. Tullo, (2019), accessed 21st October 2020
  3. NIR-O Analyser – Guided Wave, (2020),, accessed 21st October 2020
  4. United States Environmental Protection Agency (2007),, accessed 21st October 2020
  5. Benzene in Gasoline – Guided Wave (2020), , accessed 21st October 2020
  6. Alcalà, M., Blanco, M., Menezes, J. C., Felizardo, P. M., Garrido, A., Pérez, D., … Romañach, R. J. (2012). Near-Infrared Spectroscopy in Laboratory and Process Analysis. Encyclopedia of Analytical Chemistry.
  7. Foulk, S. J., Mistry, S., Todd, T. R., Peters, N. and Wang, D., (2020), A Novel Configuration for Near-Infrared Analysis of LPG Composition and Quality Control in a Refinery Setting, accessed 21st October 2020


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