Chemicals derived from petroleum or natural gas, so-called «petrochemicals», are an essential part of the contemporary chemical industry. The field of petrochemistry became increasingly popular around the early 1940’s during the second world war. At that time there was a growing demand for synthetic products which was a great driving force for the development of petrochemical products.
Oil refining aims to provide a defined range of products according to agreed specifications. Simple refineries use a distillation column (Figure 1) to separate crude oil into different fractions based on their chemical properties, and the relative quantities are directly dependent on the crude oil used. Therefore, it is necessary to obtain a range of crudes that can be blended into a suitable feedstock to produce the required quantity and quality of end products.
The basic products from fractional distillation are shown in Figure 1.
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.
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.
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.
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.
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:
Read our previous blog posts to learn more about NIRS as a secondary technique.
can be divided into three different segments:
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.
Read more about the difference between atline, online, and inline analyses in our blog post.
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Curious about NIRS analyzers for inline process measurements, even in explosive areas? Click below to learn more.
Midstream, shown here in Figure 5, offers many more opportunities for the Metrohm DS2500 Petro Analyzer to assist in quality control.
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.
Mobile NIRS fuel testing using the Metrohm NIRS XDS RapidLiquid Analyzer (XDS-RLA) has been successfully implemented in a number of countries where they enjoy the benefits of having instantaneous on-site results for gasoline and diesel testing. The calibrations developed on the XDS-RLA are easily transferrable to the DS2500 Petro Analyzer. The DS2500 Petro Analyzer does not require trained analysts, and the calibrations do not require constant maintenance, making this an ideal way to monitor different fuels at service stations and more.
Learn more about the possibilities of petrochemical analysis with Metrohm DS2500 Analyzers in our free brochure.
DS2500 Analyzer – Boosting efficiency in the QC laboratory with Near-Infrared Spectroscopy (NIRS)
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).»
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.»
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.»
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).
| Parameter | Conventional method | ASTM method | Relevant NIRS Application Notes |
| Specific Gravity (API) | Gravity meter | ASTM D298 |
|
| Boiling Point | Distillation | ASTM D2887 | |
| Cold Filter Plugging Point (CFPP) | Standardized filter device | ASTM D6371 | |
| Pour Point | Pour Point analyzer | ASTM D97 | |
| Cloud Point | Cloud Point analyzer | ASTM D2500 | |
| Flash Point | Flash Point tester | ASTM D93 | |
| Viscosity | Viscometer | ASTM D445 | |
| Color | Colorimeter | ASTM D1500 | |
| Density | Densimeter | ASTM D792 | |
| Fatty Acid Methyl Ester (FAME) | FTIR | ASTM D7806 | |
| Reid Vapor Pressure | RVP analyzer | ASTM D323 | |
| PIANO (Paraffins, Isoparaffins, Aromatics, Naphthenes, Olefins) | Gas chromatograph | ASTM D6729 | |
Octane Number (RON/MON) |
CFR Engine |
ASTM D2699 ASTM D2700 |
|
| Cetane Number | CFR Engine | ASTM D613 | |
| Diene value / MAV index | Titration | UOP 327-17 |
This article is a general overview of the use of NIR spectroscopy as the ideal QC tool for the petrochemical / refinery industry. Other installments are dedicated to the most important applications and include much more detailed information. Don’t miss our related blogs on the topics of:
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