Introduction to the petrochemical and refining industry

Oil and gas for fuel are produced in nearly every corner of the globe, from small private wells generating around 100 barrels a day, to the large bore wells producing upwards of 40 times that volume. Despite this great variation in size, many parts of the refining process are quite similar.

The basic products from fractional distillation are shown in Figure 1.

Figure 1. Illustration of a fractionating distillation column used for the purposes of refining crude oil into several desirable end products.

Near-infrared (NIR) spectroscopy is a technique that is particularly suited for making quality control of these end products more efficient and cost-effective for manufacturers. Furthermore, NIRS is recognized and accepted by ASTM as an alternative method to other techniques. Dedicated ASTM methods for method development, method validation, and results validation are presented later in this article.

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

NIR technology: a brief overview

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

A NIR spectrometer such as the Metrohm NIRS DS2500 Petro Analyzer measures this light-matter interaction to generate spectra such as those displayed in Figure 2. NIRS is especially sensitive to the presence of certain functional groups like -CH, -NH, -OH, and -SH. Therefore, NIR spectroscopy is an ideal method to quantify different QC parameters like water content (moisture), cetane index, RON/MON (research and motor octane numbers), flash point, and cold filter plugging point (CFPP), just to name a few. Furthermore, the interaction is also dependent upon the matrix of the sample itself, which also allows the detection of physical and rheological parameters like density and viscosity.

Figure 2. Diesel spectra resulting from the interaction of NIR light with the respective samples.

All of this information is contained in a single spectrum, making this method suitable for quick multiparameter analysis. Liquid samples such as oils are secured within an appropriate container or vial (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.

The measuring mode is referred to as «transmission», generally an appropriate procedure for analyzing liquids. For transmission measurement (Figure 4), the NIR light will travel through the sample while being absorbed. Unabsorbed NIR light passes to the detector. In less than 60 seconds the measurement is completed and the results are displayed.

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).

The procedure to obtain NIR spectra already highlights two major advantages of NIR spectroscopy compared to other analytical techniques: simplicity regarding sample measurement, and speed:

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

Read our previous blog posts to learn more about NIRS as a secondary technique.

Where can NIRS be used in the refining process?

The refining process can be divided into three different segments:

• Upstream
• Midstream
• Downstream

Upstream describes the process of converting crude oil into intermediate products. Refineries are usually very large complexes with several hazardous explosive areas. Therefore, operators are reluctant to transport samples from the different processes to the laboratory. Even the process of obtaining samples for analysis at external QC laboratories is laborious and can require significant paperwork and certified transport services. For obvious reasons, in most cases inline measurements are preferred. These types of measurements are typically done by process NIRS analyzers.

Midstream, shown here in Figure 5, offers many more opportunities for the Metrohm DS2500 Petro Analyzer to assist in quality control.

Figure 5. Flowchart of how crude oil becomes gasoline at the local gas station, and where NIRS can perform quality checks during the process.

Fuel is constantly checked for quality when it is received as well as supplied, and in addition to this many terminals also test fuel quality prior to offloading the trucks. The total time for receiving and offloading fuel into a storage tank is approximately 30 minutes, so a fast analysis technique like NIRS is very advantageous.

Downstream at fuel depots and gas stations, the regulatory agencies require measurement of many of the same quality parameters as in the production of gasoline and diesel, and this can also be accomplished with NIRS. There is a significant advantage if the analysis can be done on-site using fresh samples and without the hassle of needing to transport them to testing laboratories.

Figure 6. Examples of mobile fuel testing with the Metrohm DS2500 Petro Analyzer.

NIRS as an ASTM compliant tool for QC

Method development

ASTM E1655: Standard Practices for Infrared Multivariate Quantitative Analysis

«These practices cover a guide for the multivariate calibration of infrared spectrometers used in determining the physical or chemical characteristics of materials. These practices are applicable to analyses conducted in the near infrared (NIR) spectral region (roughly 780 to 2500 nm) through 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 covers a guide for the multivariate calibration of infrared (IR) spectrophotometers and Raman spectrometers used in determining the physical, chemical, and performance properties of petroleum products, liquid fuels including biofuels, and lubricants. This practice is applicable to analyses conducted in the near infrared (NIR) spectral region (roughly 780 nm to 2500 nm) through the mid infrared (MIR) spectral region (roughly 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 laboratory, field, or process (online or at-line) infrared (near- or mid-infrared analyzers, or both), and Raman analyzers, used in the calculation of physical, chemical, 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 establishing performance-based qualification of vibrational spectroscopic analyzer systems intended to be used 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.»

Typical NIRS applications and parameters for the petrochemical and refinery industry

Petrochemicals are subject to standardized test methods to determine their chemical, physical, and tribological properties. Laboratory testing is an indispensable part of both research and development and quality control in the production of petrochemicals. The following test parameters are typically important to measure in the petrochemical and refinery industry (Table 1).

Table 1. Examples for use of NIRS for selected petrochemical QC parameters.

This article is a general overview of the use of NIR spectroscopy as the ideal QC tool for the petrochemical / refinery industry. Future installments will be dedicated to the most important applications and will include much more detailed information. Don’t miss our next blogs on the topics of:

• Gasoline / Diesel / Jet fuel
• Pyrolysis gasoline (Pygas)
• Lubricants
• ASTM Norms

Post written by Wim Guns, International Sales Support Spectroscopy at Metrohm International Headquarters, Herisau, Switzerland.