Using Near-Infrared Spectroscopy (NIRS) for Quality Control and Screening in the Petrochemical Industry

Introduction to the Petrochemical and Refining Industry

From small private wells producing around 100 barrels a day to the large bore wells producing more than 40 times that volume, gas and oil and for fuel are produced in nearly every corner of the globe. Many parts of the refining process are quite similar despite this great variation in size.

Image Credit: Metrohm Middle East FZC

Chemicals derived from natural gas or petroleum, so-called ‘petrochemicals,’ are a vital part of the contemporary chemical industry.

It was around the early 1940s, during the second world war, that the field of petrochemistry became more popular. There was a growing demand for synthetic products at that time which was a great driving force for the development of petrochemical products.

Oil refining aims to supply a defined range of products according to agreed specifications. To separate crude oil into different fractions based on their chemical properties, simple refineries utilize a distillation column, as seen in Figure 1, and the relative quantities are directly dependent on the crude oil employed.

Figure 1. Illustration of a fractionating distillation column used for the purposes of refining crude oil into several desirable end products. Image Credit: Metrohm Middle East FZC

So, it is necessary to gather a variety of crudes that can be blended into a suitable feedstock to create the required quantity and quality of end products. Near-infrared (NIR) spectroscopy is a method that is particularly suited for making the quality control of these end products more cost-effective and efficient for manufacturers.

In addition, NIRS is recognized and accepted by ASTM as an alternative approach to other methods. Dedicated ASTM techniques for method validation, method development and result validation are outlined later in this article.

Below is a short overview of NIR spectroscopy followed by application examples for the petrochemical and refinery industry to learn how refineries and petrochemical producers alike can benefit from NIRS.

A Brief Overview of NIR Technology

The interaction between matter and light is a well-known process. Light employed in spectroscopic techniques is usually described by the wavelength or in wavenumbers in many cases, not by the applied energy.

A NIR spectrometer like the Metrohm NIRS DS2500 Petro Analyzer measures this light-matter interaction to produce spectra like those seen in Figure 2. NIRS is particularly sensitive to the presence of certain functional groups, such as -OH, -CH, -NH and -SH.

Figure 2. Diesel spectra resulting from the interaction of NIR light with the respective samples. Image Credit: Metrohm Middle East FZC

So, NIR spectroscopy is an ideal technique to quantify different QC parameters such as cetane index, water content (moisture), flash point, RON/MON (research and motor octane numbers) and cold filter plugging point (CFPP), to name a few.

In addition, the interaction is also dependent upon the matrix of the sample itself, which also enables the identification of rheological and physical parameters such as viscosity and density.

This technique is suitable for quick multiparameter analysis as all of this information is contained in a single spectrum. Liquid samples like oils are secured within an appropriate container or vial, as seen in Figure 3, then placed as-is on the smart vial holder.

Figure 3. Liquid sample placement for NIR spectra measurement on the smart vial holder from Metrohm. Image Credit: Metrohm Middle East FZC

The measuring mode is referred to as transmission, which is usually an appropriate procedure for analyzing liquids.

As seen in Figure 4, for transmission measurement, the NIR light will travel through the sample while being absorbed and any unabsorbed NIR light passes to the detector. The measurement is completed and the results are displayed in under 60 seconds.

Figure 4. A. Measurements of liquids are typically done with disposable vials. B. The NIRS measurement mode is known as transmission, where light travels through the sample while being absorbed (from left to right in the illustration). Image Credit: Metrohm Middle East FZC

The procedure to gather NIR spectra already highlights two major benefits of NIR spectroscopy compared to other analytical methods: simplicity regarding sample measurement and speed:

• No sample preparation is needed – measure samples as-is.
• Non-destructive – after analysis precious samples can be reused.
• Fast method with results in under a minute.
• Low cost per sample – no solvents or chemicals required.
• Simple to operate – inexperienced users are immediately successful.
• Environmentally friendly method – no waste produced.

Where Can NIRS be Used in the Refining Process?

The refining process can be divided into three different segments:

• Upstream
• Midstream
• Downstream

Upstream is the process of converting crude oil into intermediate products. Refineries are typically very large complexes with numerous hazardous explosive areas. So, operators are reluctant to transport samples from the different processes to the laboratory.

Even the process of gathering samples for analysis at external QC laboratories is laborious and certified transport services and significant paperwork can be required. In most instances, inline measurements are preferred for these reasons. Process NIRS analyzers are usually used to perform these types of measurements.

Figure 5. Flowchart of how crude oil becomes gasoline at the local gas station, and where NIRS can perform quality checks during the process. Image Credit: Metrohm Middle East FZC

When it is received or supplied, fuel is constantly checked for quality, and further to this, many terminals also test fuel quality before offloading the trucks. The total time for receiving and offloading fuel into a storage tank is around 30 minutes, so a quick analysis method like NIRS is very beneficial.

The regulatory agencies need measurement of many of the same quality parameters as in the production of gasoline and diesel downstream at fuel depots and gas stations; this can also be performed with NIRS.

There is a huge benefit if the analysis can be performed on-site by utilizing fresh samples and without the hassle of having to transport them to testing laboratories.

Mobile NIRS Fuel Testing Using the Metrohm NIRS XDS Rapidliquid Analyzer

A number of countries have successfully implemented XDS-RLA, where they enjoy the advantages of having instantaneous on-site results for diesel and gasoline testing. The calibrations developed on the XDS-RLA are easily transferable to the DS2500 Petro Analyzer.

Trained analysts are not needed for the DS2500 Petro Analyzer, and the calibrations do not require constant maintenance, so it is an ideal way to monitor different fuels at service stations, etc.

Figure 6. Examples of mobile fuel testing with the Metrohm DS2500 Petro Analyzer. Image Credit: Metrohm Middle East FZC 

NIRS as an ASTM Compliant Tool for QC

Method Development

ASTM E1655: Standard Practices for Infrared Multivariate Quantitative Analysis

These practices supply a guide for the multivariate calibration of infrared spectrometers employed in establishing the chemical or physical characteristics of materials. These practices are applicable to analyses performed in the near infrared (NIR) spectral region (roughly 780 to 2500 nm) to the mid infrared (MIR) spectral region (roughly 4000 to 400 cm^-1).

Multivariate Analysis of Petroleum Products

ASTM D8321: Standard Practice for Development and Validation of Multivariate Analyses for Use in Predicting Properties of Petroleum Products, Liquid Fuels and Lubricants based on Spectroscopic Measurements

This practice provides a guide for the multivariate calibration of Raman spectrometers and infrared (IR) spectrophotometers utilized in establishing the chemical, physical and performance properties of liquid fuels, including biofuels, petroleum products and lubricants.

This practice applies to analyses performed in the near infrared (NIR) spectral region (around 780 nm to 2500 nm) through the mid infrared (MIR) spectral region (around 4000 cm^-1 to 40 cm^-1).

Method Validation

ASTM D6122: Standard Practice for Validation of the Performance of Multivariate Online, At-Line, Field and Laboratory Infrared Spectrophotometer and Raman Spectrometer Based Analyzer Systems

This practice covers requirements for the validation of measurements made by the field, laboratory or process (online or at-line) infrared (near- or mid-infrared analyzers), or both, and Raman analyzers, utilized in the calculation of chemical, physical or quality parameters (that is, properties) of liquid petroleum products and fuels.

Results Validation

ASTM D8340: Standard Practice for Performance-Based Qualification of Spectroscopic Analyzer Systems

This practice covers requirements for determining performance-based qualification of vibrational spectroscopic analyzer systems intended to be employed to predict the test result of a material that would be produced by a Primary Test Method (PTM) if the same material is tested by the PTM.

To determine their physical, chemical and tribological properties, typical NIRS applications and parameters for the petrochemical and refinery industry

Petrochemicals are subject to standardized test methods.

When producing petrochemicals, laboratory testing is a crucial step in the research, development and quality control. The test parameters in Table 1 are vital for measuring in the petrochemical and refinery industry.

Table 1. Examples for use of NIRS for selected petrochemical QC parameters. Source: Metrohm Middle East FZC

Metrohm Middle East FZC (MME) based out of Sharjah, UAE is the Regional Support Centre for Metrohm AG (Switzerland) which is responsible for sales, service and calibration of lab & process analytical instruments from the following countries –

UAE, KSA, Kuwait, Bahrain, Oman, Qatar, Egypt, Jordan, Lebanon, Iraq, Bangladesh, Pakistan, Sri Lanka, Ethiopia, Ghana, Sudan, Syria, Yemen, Somalia, Iran, Cyprus, Malta, Eritrea, Djibouti & Afghanistan.

This information has been sourced, reviewed and adapted from materials provided by Metrohm Middle East FZC.

For more information on this source, please visit Metrohm Middle East FZC.