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NIR spectroscopy in the petrochemical and refinery industry: The ASTM compliant tool for QC and product screening – Part 5

NIR spectroscopy in the petrochemical and refinery industry: The ASTM compliant tool for QC and product screening – Part 5

History of ASTM International

The American Society for Testing and Materials (ASTM) is an organization that currently provides over 12,500 international standards. Its roots date back to 1898, when ASTM was formed by a group of scientists and engineers to address the frequent rail breaks affecting the fast-growing railroad industry. The group developed a standard for the steel used to fabricate rails.

Originally, this organization was called the «American Society for Testing Materials» (1902) and was changed to the «American Society for Testing and Materials» in 1961. In 2001, ASTM officially changed its name to «ASTM International» and added the tagline «Standards Worldwide». This tagline was modified in 2014 to «Helping our world work better». Now, aside from the US, ASTM International also has offices in Belgium, Canada, China, and Peru.

ASTM International aims to ensure that quality and standard requirements are met when using materials for engineering projects. Therefore, they had to agree upon a single language for engineers and technicians to enhance compatibility, and ultimately developed a system grouped according to industries in the form of letters A–G. Currently, there are over 12,500 ASTM standards used by about 150 countries. This has increased trade in different markets by instilling and strengthening consumer confidence.

ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants

Formed in 1904, ASTM Committee D02 currently meets twice per year for five days of technical meetings, attended by approximately 1000 members (out of around 2500). D02 has jurisdiction over 814 standards with a prominent role in all aspects relating to the standardization of petroleum products and lubricants, which are published in the Annual Book of ASTM Standards (Volumes 05.01 through 05.06).

Near-infrared spectroscopy—an ASTM compliant tool to assess the quality of petrochemical products

Near-infrared spectroscopy (NIRS) has been an established method for fast and reliable quality control within the petrochemical industry for more than 30 years. However, many companies still do not consistently consider the implementation of NIRS in their QA/QC labs. The reasons could be either limited experience regarding application possibilities or a general hesitation about implementing NIRS as an alternative technology.

Many companies are not aware that now there are many ASTM standards about how to implement NIR spectroscopy as an alternative to conventional methods. Several NIRS-related ASTM guidelines are shown in Figure 1.

ASTM E1655 (method development quantitative NIR analysis) and ASTM E1790 (method development qualitative NIR analysis) are applicable for all industries (e.g., polymer, chemical, petrochemical, etc.).

ASTM D6122 (method validation), ASTM D8321 (development and validation of multivariate analysis), and ASTM D8340 (performance qualification) are dedicated for the petrochemical industry. These three standards were released recently in 2020, and ASTM D8340 was updated at the end of 2021.

Figure 1. Overview of NIRS-related ASTM guidelines.

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).»

ASTM E1790: Standard Practice for Near Infrared Qualitative Analysis

«This practice covers the use of near-infrared (NIR) spectroscopy for the qualitative analysis of liquids and solids. The practice is written under the assumption that most NIR qualitative analyses will be performed with instruments designed specifically for this purpose and equipped with computerized data handling algorithms.»

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.»

These requirements include the following topics:

  • Analyzer calibration
  • Correlation of NIRS vs. lab method (treated and untreated samples)
  • Probationary validation
  • General & Continual validation

Results validation

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).»

The main purpose for this standard is to establish the validity of test results during calibration.

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.»

Furthermore, it includes the prescriptive requirements regarding multivariate models, including Multi Linear Regression (MLR), Partial Least Square (PLS), Principal Component Regression (PCR), Cross validation, and Outlier statistics, as well as instrument considerations.

Regarding the required accuracy of the NIRS method the expected agreement and user requirements is that the Standard Error of Prediction for the NIRS value should be equal to or smaller than the laboratory method reproducibility.

ASTM D8340 compliance with the NIRS DS2500 Petro Analyzer and Vision Air

Temperature stability, section 5.4:

There are prescriptive requirements included in this norm regarding temperature stability of the NIRS Analyzer. Section 5.4 requires sample temperature to be carefully controlled in the analyzer system hardware or that effects of temperature change be compensated in the modeling or software. Metrohm’s solution to this issue for the NIRS DS2500 Petro Analyzer is shown in Figure 2.

Figure 2. Temperature stability for the NIRS DS2500 Petro Analyzer.
Learn more about the possibilities of petrochemical analysis with Metrohm NIRS DS2500 Petro Analyzers in our free brochure.
Analyzer wavelength accuracy and precision, section 6.3:

Section 6.3 requires that the analyzer shall include a means of demonstrating that it is operating within the vendor’s specification. Therefore, the analyzer shall incorporate instrument performance tests to demonstrate that it is operating within historically expected limits. Furthermore, the analyzer shall have a means of validating wavelength/frequency precision and accuracy. Also, the wavelength precision must be sufficient to allow spectra to be collected and used in creating a multivariate model that meets or exceeds user’s specifications. The wavelength precision of the analyzer used for calibration and the analyzer-to-analyzer wavelength accuracy and reproducibility must be sufficient to allow analyzers to be validated by Practice D6122. Metrohm’s solution to this is the Vision Air software shown in Figure 3.

Figure 3. Analyzer wavelength accuracy and precision for ASTM D8340 section 6.3 (click to enlarge image).
Vendor created global multivariate model, section 8.2.2:

The multivariate model can be that of a standardized test method, a user/vendor-created global multivariate model, or a user-created site-specific multivariate model. A global multivariate model is one developed by use of samples and data that may represent materials produced at multiple facilities or locations. Some locations may start with a global model and add site-specific sample to it. Metrohm offers several pre-calibrations for the NIRS DS2500 Petro Analyzer, listed in Figure 4.

Figure 4. Available NIRS pre-calibrations for the petrochemical industry.
Discover our selection of NIRS pre-calibrations available for the petrochemical industry in our free brochure.
Outlier statistics, sections 9.3, 9.4, and 9.5:

The requirements of outlier handling are described in these sections. Identification and handling of outliers is important to the success of meeting this performance-based practice. It is permissible for the identification and handling of outliers to be performed by the same or separate software used for generating predictions from spectra. For analysis of a sample for the purposes of determining property values, the software shall indicate whether the spectrum is identified as an outlier, based on the criteria set by the user. The sample analysis may indicate that expected performance is not reached for a sample identified as an outlier.

Vision Air is Metrohm’s universal software for Vis-NIR spectroscopy. Vision Air accounts for the unique needs of each type of instrument user. It offers specific interfaces optimized for the most common tasks – simplifying routine measurement, method development, outlier handling, and both data and instrument management. Vision Air is also compatible with third-party software like Unscrambler (Figure 5).

Figure 5Vision Air—Metrohm’s universal software for lab Vis-NIR spectroscopy.

Summary

In the petrochemical industry, typical requirements from management are usually that quality control should be quick, operating costs should be low, feedback should be fast, and operation should be safe.

Typical requirements from the user are that the analysis should be accurate and precise, and the instrumentation should be easy to use, fast, and safe.

NIR spectroscopy is compliant with all of these requirements, and as shown in this blog series, the technology is supported by several ASTM guidelines for method development, method validation, and results validation.

By utilizing NIRS in the petrochemical industry, manufacturers not only improve the efficiency of screening and quality control of petrochemical products, but also fully adhere to internationally accepted standards.

For more information

About spectroscopy solutions provided by Metrohm, visit our website!

We offer NIRS for lab, NIRS for process, as well as Raman solutions

Post written by Wim Guns, International Sales Support Spectroscopy at Metrohm International Headquarters, Herisau, Switzerland.
NIR spectroscopy in the petrochemical and refinery industry: The ASTM compliant tool for QC and product screening – Part 4

NIR spectroscopy in the petrochemical and refinery industry: The ASTM compliant tool for QC and product screening – Part 4

What is a lubricant?

A lubricant is defined as a petroleum-derived product used to control and reduce the friction and wear of moving machinery parts (e.g., in engines and turbines). The main purpose of lubricants  is to help protect and prolong the lifetime of the equipment.

Machinery and lubricants go hand in hand, as shown here.
These goals are accomplished in the following ways:

Lubrication by reducing friction and wear. The lubricant forms a film between the mechanical moving parts of the equipment. In this way the metal-to-metal contact and, thus, the wear is reduced.

Cooling by acting as a heat sink. This causes the heat to dissipate away from critical parts of the equipment so that deformation due to increased temperature is prevented.

Protection by building a film. This film is unaffected by oxygen or corrosive substances and therefore prevents metal damage and oxidation (rust) and therefore also prevents wear.

Types of lubricants

For the most part, lubricants consist of oils to which additives and other chemical substances are added. There are two common types of lubricants which are based on the origin of the oil:

1. Lubricants based on mineral oils (Figure 1a) are the most commonly used type. They are comprised of petroleum products (base stock) to which synthetic additives are added. These types of lubricants are used in applications where there are no high temperature requirements. Typical areas where mineral oil-based lubricants are used include: engines, hydraulics, gears, and bearings.
2. Lubricants based on synthetic oils (Figure 1b) are artificially developed substitutes for mineral oils. They are less common and more expensive. Synthetic oils are specifically developed to create lubricants with superior properties to mineral oils. For example, heat-resistant synthetic oils are used in high performance machinery operating at high temperatures.
a)
b)
Figure 1. Difference in the molecular structure found in lubricants: a) mineral oil and b) synthetic oil.
In the following table, different lubricant types with sub-classes are listed.
Table 1. Different lubricating oil types.

Lubricant type

Sub-classes

Automotive oil Engine oil

Gear oil

Transmission fluids

Industrial oil Hydraulic oil

Turbine oil

Greases
Metal working fluids Forming fluids

Cutting fluids

The physical properties of a lubricant (such as viscosity and density) mostly depend on the oil base stock, whereas the additives fine-tune the chemical properties, e.g., the acid number or base number. For each application, the oil is typically formulated to meet the physical and chemical properties required by the customer. Therefore, various types of oil exist (Table 1).

Near-infrared spectroscopy—an ASTM compliant tool to assess the quality of lubricants

Near-infrared spectroscopy (NIRS) has been an established method for fast and reliable quality control within the petrochemical industry for more than 30 years. However, many companies still do not consistently consider the implementation of NIRS in their QA/QC labs. The reasons could be either limited experience regarding application possibilities or a general hesitation about implementing new methods.

There are several advantages of using NIRS over other conventional analytical technologies. For one, NIRS is able to measure multiple parameters in just 30 seconds without any sample preparation! The non-invasive light matter interaction used by NIRS, influenced by physical as well as chemical sample properties, makes it an excellent method for the determination of both property types.

In the remainder of this post, available solutions for lubricants are discussed which have been developed according the NIRS implementation guidelines of ASTM E1655 (method development), ASTM D6122 (method validation), and ASTM D8340 (results validation).

Did you miss the first parts in this series about NIRS as a QC tool for the petrochemical industry? Find them all below!

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

Applications and parameters for lubricant analysis with NIRS

The main NIRS application for lubricants is to easily monitor the oil condition, i.e., checking if the oil is still of suitable quality for proper lubrication of the equipment. Reducing unnecessary oil changes means significant cost savings. On the other hand, changing the oil too infrequently can result in possible damage of the equipment, leading to costly repairs. Therefore optimizing the usage of the lubricating oil is very important.

The following parameters can be correlated between NIRS and the values from a primary method: kinematic viscosity, viscosity index, color, density, water content, TAN (total acid number), and TBN (total base number). A large set of samples provided by several different companies was used to develop working NIRS models of these parameters, including hydraulic oil, gear oil, and others. In some cases, it was not clear for what application the lubricant was used, so the exact identity of the oil was unknown.

The most relevant application notes for NIRS analysis of lubricants are listed below in Table 2.

Table 2. Metrohm’s NIRS solutions for lubricants including application details and benefits.
Parameter Reference method Norm NIRS Application Notes NIRS benefits
Acid number Titration ASTM D664 AN-NIR-071

AN-NIR-041

All parameters are measured simultaneously within a minute, without requiring any sample preparation or chemical reagents.
Kinematic viscosity at 40 °C Viscosimeter ASTM D445
Kinematic viscosity at 100 °C Viscosimeter ASTM D445
Viscosity index Calculation ASTM D2270
Color number Colorimeter ASTM D1500
Moisture content Karl Fischer titration ASTM D6304
Base number Titration ASTM D2896
Density Density meter ASTM D4052

 

Solutions by means of starter models—expedite and simplify quality control of lubricants

Lubricants keep our modern lives running smoothly. During use, the oil needs to be monitored to check if it still of good enough quality or whether it needs to be exchanged.

The data obtained here indicate that lubricants vary per application and per supplier. This means that there is still not sufficient information for each oil type and subtype to prepare a model robust enough to transform into a pre-calibration. However, if a partner provides the samples, a feasibility study can quickly indicate if the NIR spectra are able to be correlated to the primary method values.

Typically, several key parameters such as the acid and base numbers (AN and BN), viscosity, moisture content, color, and density are determined in the laboratory by various chemical and physical methods. These methods not only incur high running costs, they are also quite time consuming to perform.

NIRS on the other hand requires neither chemicals nor sample preparation, and provides results in less than a minute. This spectroscopic technique is also easy enough to be used by non-chemists. Furthermore, multiple chemical and physical parameters can be determined simultaneously. The combined benefits of this technology make NIRS the ideal solution for many daily QA/QC measurements or ad-hoc atline analysis.

Application example: starter model for lubricants with the NIRS DS2500 Liquid Analyzer

For lubricant analysis, determination of the acid number (ASTM D664), viscosity (ASTM D445), moisture content (ASTM D6304), and color number (ASTM D1500) require the use of multiple analytical technologies and, in part, large volumes of chemicals. The time to result can therefore be quite a long and costly process.

In this example, different lubricant samples were measured with a Metrohm NIRS DS2500 Liquid Analyzer in transmission mode over the full wavelength range (400–2500 nm). The built-in temperature controlled sample chamber was set to 40 °C to provide a stable sample environment. For convenience reasons, disposable vials with a pathlength of 8 mm were used, which made a cleaning procedure obsolete.

Learn more about the possibilities of petrochemical analysis with Metrohm NIRS DS2500 Analyzers in our free brochure.
Figure 2. Quality control of lubricants as performed by the Metrohm NIRS DS2500 Liquid Analyzer.
The obtained Vis-NIR spectra (Figure 2) were used to create prediction models for the determination of key lubricant parameters (such as those in Table 2). The quality of the prediction models was evaluated using correlation diagrams, which display the correlation between the Vis-NIR prediction and primary method values. The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis (Figure 3).
Figure 3. Correlation plots and figures of merit (FOM) for different parameters measured in lubricants.
This solution demonstrates that NIR spectroscopy is excellently suited for the analysis of multiple parameters in lubricants in less than one minute without sample preparation or using any chemical reagents.

In case a large series of samples must be analyzed, there is also the possibility to measure lubricant samples in a fully automated way, as detailed in our free Application Note below.

Here, the samples were measured in transmission mode over the full wavelength range (400–2500 nm) using a NIRS XDS RapidLiquid Analyzer in combination with an 815 Robotic USB Sample Processor, which can carry a total of 141 samples (Figure 4).
Figure 4. Metrohm NIRS XDS RapidLiquid Analyzer equipped with a with 5.0 mm flow cell (left) and the 815 Sample Processor (right).

Summary

Near-infrared spectroscopy is very well suited for lubricant analysis. Available starter models are developed and validated in accordance with the ASTM guidelines. Positive aspects of using NIRS as an alternative technology to primary methods are the short time to result (less than one minute), no chemicals or other expensive equipment needed, and ease of handling so that even shift workers and non-chemists can perform these analyses in a safe manner.

Future installments in this series

This blog article was dedicated to the topic of lubricants and how NIR spectroscopy can be used as the ideal QC tool for the petrochemical / refinery industry. The final installment will be dedicated to:

 

  • ASTM Norms

For more information

About spectroscopy solutions provided by Metrohm, visit our website!

We offer NIRS for lab, NIRS for process, as well as Raman solutions

Post written by Wim Guns, International Sales Support Spectroscopy at Metrohm International Headquarters, Herisau, Switzerland.
Ph. Eur. 2.2.48 Raman Spectroscopy: How Raman instruments from Metrohm comply with the 2022 update

Ph. Eur. 2.2.48 Raman Spectroscopy: How Raman instruments from Metrohm comply with the 2022 update

The European Pharmacopoeia (Ph. Eur.) is a single reference work for the quality control of medicines. Ph. Eur. contains norms, suggests analytical methods, and lists many properties that define quality control (QC) during the production of medicines, the raw materials used, and the instruments required to perform such tests. These official standards are legally binding in several countries – not only in Europe, but worldwide.

Raman spectrometers—especially handheld and portable instruments—are increasingly used for QC of medicines and raw materials (RMID). Instrument interfaces are user-friendly, requiring little technical expertise, and they provide flexible sampling options for most sample types with rapid, non-destructive measurements.

Metrohm’s Raman systems exhibit great flexibility—from see-through to standoff to immersion sampling.
An excerpt from the Ph. Eur. 2.2.48 Raman Spectroscopy chapter says:
«Raman spectroscopy is commonly used for qualitative and quantitative applications and can be applied to solid, liquid, and gaseous samples. Raman spectroscopy is a rapid and non-invasive analytical method and can be performed off-line, at-line, on-line, or in-line[…] Raman spectrometers can be situated far from the point of measurement using long-distance optical fibres to collect the Raman signal.»

Technological developments and their increasing adoption in the pharmaceutical industry prompted a revision of Ph. Eur. 2.2.48 which ensures the reliability of Raman results. The updated chapter 2.2.48 was published in the Ph. Eur. Supplement 10.7 (October 2021) and will ultimately take effect in April 2022.

While much of the Ph. Eur. 2.2.48 chapter has remained the same, the latest revision features:

  • new requirements for spectral resolution for qualitative Raman analysis using a suitable reference material
  • updated requirements for the Raman response-intensity scale
  • detailed procedures for the comparison of spectra

We will address these new requirements across our Raman spectroscopy product lines in the rest of this article.

Spectral Resolution

«Spectral resolution is the ability of a spectroscopic system to separate adjacent bands, which makes it possible to characterise complex samples (e.g., brand analysis, crystallinity, polymorphism).

[…] For identity tests, unless otherwise prescribed in a monograph, the spectral resolution must be less than or equal to 15cm-1 (measured in the wavenumber range between 1000cm-1 and 1100cm-1).

The spectral resolution is verified using a suitable reference material. The instrument parameters used for the test, such as laser, slit-width and grating for dispersive instruments and circular aperture […] for FT-instruments, must be the same as those applied for sample measurements. For example record the Raman spectrum of calcium carbonate for equipment qualification CRS, and determine the full width at half height (W1085) of the band located at 1085 cm-1. The spectral resolution (R) using calcium carbonate is then given by the following relation:»

Handheld Raman instruments: MIRA P and NanoRam

All MIRA P and NanoRam devices (including both NanoRam and NanoRam-1064) for the pharmaceutical industry are designed and tested to meet stringent resolution requirements. During QC, the resolution of each instrument is tested to be less than 15 cm-1 against a secondary USP (US Pharmacopeia) reference standard of calcium carbonate according to ASTM E2529, which is the same procedure recommended in this newly released Ph. Eur. chapter.

The measured spectral resolution value for each instrument, along with its identifying serial number, is included in the instrument final test report. A certificate or final test report is packaged with the device and sent to the customer (starting in April 2022 for MIRA P). This resolution is fixed by the optical design of the instrument and is stable over time.

Portable Raman instruments: i-Raman series, QTRam, STRam, and PTRam

The instrument resolution for all of Metrohm’s portable Raman instruments from B&W Tek are factory-tested with calcium carbonate and displayed on final instrument test reports. The spectral resolution is dependent on the instrument design and defined for each specific instrument configuration. Depending on the instrument model, the spectral resolution is between 3.5–11 cm-1. Additionally, the instrument control softwares Vision and BWAnalyst have the performance test function that verifies spectral resolution using the 1001.4 cm-1 peak of polystyrene.

Handheld and portable Raman instruments from B&W Tek.

Response-Intensity Scale

«The verification of the response-intensity scale is principally performed for quantitative methods.

Appropriate acceptance criteria will vary with the application. A maximum variation of ± 10 per cent in band intensities compared to the previous instrument qualification is achievable in most cases. Response calibration may involve the use of white-light standards or luminescent glass (e.g., NIST SRM 2241).»

Handheld Raman instruments: MIRA P, MIRA M-3, and NanoRam series

MIRA P, MIRA M-3, and NanoRam systems are designed for qualitative analysis, not for quantitative purposes. Therefore, this criterion is not a strict requirement for handheld Raman products.

However, the relative intensity response of MIRA P and NanoRam series instruments is calibrated with a NIST standard SRM calibration material (SRM 2241, SRM 2242) or NIST SRM 2241-traceable calibration standard to achieve better uniformity from instrument-to-instrument.

The NanoRam series instruments have an acceptance criterion for relative intensity response in the instrument performance validation in alignment with Ph. Eur. 2.2.48 and USP<858>. To pass the performance validation, <10% relative intensity error is required using the factory-supplied polystyrene cap.

Portable Raman instruments: i-Raman series, QTRam, STRam, and PTRam

The relative intensity response of these portable Raman instruments is calibrated using a proper NIST standard SRM calibration material to achieve better uniformity from instrument-to-instrument. Additionally, the Vision instrument control software includes the performance test function that verifies the intensities of several Raman peaks of polystyrene relative to its 1001.4 cm-1 peak, to a maximum variation of ±10% compared to the previous instrument qualification.

Comparison Procedures

For qualitative methods, additional information for identification has been defined.

«Several comparison procedures may be used, and the analyst must document and justify the method used and the specific acceptance criteria that allow a conclusion for identification. The spectra can be compared by either overlaying the spectra (in the whole spectral range or in the region of interest specified in the monograph) or by using mathematical calculations of the software. It is possible for example to perform:

  • visual comparison based on band positions and relative intensities unless otherwise specified[…]
  • a statistical determination of the similarity between the spectra of the material to be examined and the reference standard[…]
  • evaluation by chemometric methods[…]»

While an experienced Raman spectroscopist can certainly compare spectra visually and assess sample validity based on peak location, fluorescence, saturation, and signal-to-noise ratio, the widespread implementation of Raman in the real world means that complex analysis must be done by the device and not the user. Statistical comparison methods are used primarily for identification of unknowns through correlation of a sample spectrum with library spectra. The software performs library searches and returns a Hit Quality Index (HQI) value indicating the level of correlation as defined by a user-defined threshold.

Chemometric methods rely on dimensionality-reduction methods that are performed by the software, such as Principal Component Analysis (PCA), where new sample data is compared within a multivariate model created from representative samples. This permits highly accurate verification of known materials according to how well a spectrum fits into the model limits, which are determined by a confidence interval. In the analysis of medicines and raw materials, chemometric methods are used to distinguish the quality and consistency of a material. MIRA P (and its dedicated software, MIRA Cal P) and NanoRam instruments use both statistical and chemometric methods for sample identification and verification based on the needs of the end-user.

For more information, download our free technical and application notes as well as a White Paper below.

Wavenumber accuracy requirements of Ph. Eur. 2.2.48

«Verify the wavenumber scale for Raman shifts using a suitable standard that has characteristic maxima at the wavenumbers under investigation, for example an organic substance such as polystyrene, paracetamol or cyclohexane[..]

A minimum of 3 wavenumbers covering the working range of the instrument intended for measurements should be selected.[…]»

This chapter maintains the same requirements for Raman wavenumber accuracy and is consistent with the USP <858> and JP 2.26. All of Metrohm’s handheld Raman instruments meet these requirements. Users are recommended to run performance validation tests at regular intervals using polystyrene or another ASTM Raman shift calibration material.

Download our free White Paper below to learn more about instrument calibration, system verification, and performance validation.

The Calibrate/Verify Attachment (CVA) shown here is a dual-ended accessory containing a toluene/acetonitrile ASTM standard for calibration/verification of the wavenumber axis and polystyrene for a second wavenumber verification according to Ph. Eur. 2.2.48.
Performance tests for Raman wavenumber accuracy are included the Vision and BWAnalyst softwares for the i-Raman series and other portable Raman products (STRam, QTRam, PTRam), with acceptance criteria in accordance with the pharmacopeial requirements.

Metrohm’s unique way of compliance with Ph. Eur. 2.2.48

Better representation of the material

«When using Raman spectroscopy[…] care must be taken to ensure that the measurement is representative. This can be achieved by, for example rotation of the sample, performing multiple measurements on different preparations of the sample, using orbital raster scanning (ORS), increasing the area of illumination by reducing the magnification, by demagnification of the laser beam or by changing the focal length between measurements to scan at different depths.»

ORS™ is Metrohm Raman’s proprietary method for moving the excitation laser in a pattern over a sample in order to collect more representative data from a larger area of the sample, especially on heterogeneous samples. All MIRA and MISA instruments are equipped with ORS.
Learn more about ORS by downloading the related Application Note.
For more details about how we comply, please check the U.S. Pharmacopeia Raman Chapters Updates page on the B&W Tek website. For more general information, download this General Compliance Statement for MIRA handheld Raman systems
For a more comprehensive look at raw material identification and verification in the pharmaceutical industry, there is a significant amount of information on this topic in our related blog post.
Post written by Dr. Melissa Gelwicks (Technical Writer at Metrohm Raman, Laramie, Wyoming), and Dr. Xiangyu (Max) Ma (Handheld Raman Product Manager) and Dr. Jun Zhao (R&D Director) at B&W Tek, Newark, Delaware.
NIR spectroscopy in the petrochemical and refinery industry: The ASTM compliant tool for QC and product screening – Part 3

NIR spectroscopy in the petrochemical and refinery industry: The ASTM compliant tool for QC and product screening – Part 3

What is Pyrolysis gasoline or «Pygas»?

Pyrolysis gasoline, also known as Pygas, is a byproduct of naphtha cracking during the production of ethylene and propylene. Pyrolysis gasoline is an easily flammable, colorless liquid with high aromatic contents and represents a mixture of light hydrocarbons (Figure 1). It is a high octane number mixture which contains aromatics, olefins, and paraffins ranging from C5 to C12.

Figure 1. Pyrolysis gasoline (or Pygas) shown here is nearly colorless, but extremely flammable.
Because of its high octane number, Pygas has a high potential for blending in various end-user products.  In addition, pyrolysis gasoline can be used as a component separator for benzene, toluene, and xylene. For this purpose, it is used as a component separation additive.

Pygas contains some undesired conjugated diolefins that when present in high quantities makes them unsuitable as a motor fuel. These conjugated diolefins are highly reactive to polymerization and can plug the downstream refining processes causing unwanted shutdowns and high costs for remediation. These compounds also affect the stability of commercial gasoline. Therefore, the conjugated diolefins content must be controlled.

The content of conjugated diolefins is indirectly measured as the «maleic anhydride value» (MAV), or as the «diene value» (DV). This parameter is usually determined by the Diels-Alder wet chemical method (UOP 326). Furthermore, the determination of Bromine Number (ASTM D1159) in pygas is useful as it indicates the degree of aliphatic unsaturation. These determination methods require several hours and must be analyzed by highly trained analysts. In contrast to using primary methods, near-infrared spectroscopy (NIRS) is a cost-efficient and fast alternative solution for the determination of MAV or DV and Bromine Number in pyrolysis gasoline.

Near-infrared spectroscopy—an ASTM compliant tool to assess the quality of pygas

Near-infrared spectroscopy (NIRS) has been an established method for both fast and reliable quality control within the petrochemical industry for more than 30 years. However, many companies still do not consistently consider the implementation of NIRS in their QA/QC labs. The reasons could be either limited experience regarding application possibilities or a general hesitation about implementing new methods.

There are several advantages of using NIRS over other conventional analytical technologies. For one, NIRS is able to measure multiple parameters in just 30 seconds without any sample preparation! The non-invasive light-matter interaction used by NIRS, influenced by physical as well as chemical sample properties, makes it an excellent method for the determination of both property types.

In the remainder of this post, an available solution for the determination of maleic anhydride value (MAV) or diene value (DV) and Bromine number are outlined which have been developed according to the NIRS implementation guidelines of ASTM E1655 (method development), ASTM D6122 (method validation), and ASTM D8340 (results validation).

Did you miss the first parts in this series about NIRS as a QC tool for the petrochemical industry? Find them all below!

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

Analysis of Diene Value (DV) and Bromine Number (BN) in pygas with the DS2500 Liquid Analyzer

Historically, NIRS analysis of the diene value and Bromine Number in pygas has been considered to be complicated due to the presence of other non-conjugated dienes as well as alkenes that have similar molecular functional groups. In addition, the majority of the samples are a complex mixture of aromatics and alkanes that varies with process conditions in the ethylene production process, as well with as the different feedstocks used to produce ethylene (e.g., alkanes, naphtha, or gas oil). Also, DV is not reliant on one specific conjugated diolefin, but over a dozen different compounds including cyclopentadiene (a ring structure) and straight-chain diolefins with different chain lengths and side chains. As explained earlier, the diene value is usually determined by the Diels-Alder wet chemical method (UOP 326). Bromine Number (BN) is determined by electrochemical titration at 5 °C (ASTM D1159).

Now, spectroscopic analysis of these parameters in such a complicated system is made successful through a combination of stable NIRS measurements with the DS2500 Liquid Analyzer, and the Partial Least-Squares (PLS) modelling capabilities in the Vision Air complete software package.

Learn more about the Metrohm NIRS DS2500 Liquid Analyzer and Vision Air software here!
Results from NIRS analysis are obtained very rapidly, with no sample preparation required aside from the temperature equilibration of the sample prior to scanning. This makes it possible to monitor and control the process, which is simply not possible using other methods. NIRS measurements do not require highly trained analysts—disposable glass vials are the only things needed for the analysis!

Metrohm offers a related application note for the proper use of NIRS for pyrolysis gas analysis (Table 1).

Table 1. Metrohm’s NIRS solutions for pygas including application details and benefits.
Parameter Reference method   Norm NIRS Application Notes  NIRS benefits
Maleic Anhydride Value (MAV) or Diene Value (DV) Reflux / Hydrolysis / Titration UOP 326 AN-NIR-024 MAV or DV measured within one minute, without requiring sample preparation or use of any chemicals.  A major difference compared to 6–7 hours when using the primary reference methods.
Bromine Number (BN) Cooling / Titration ASTM D1159 AN-NIR-094 Bromine Number measured within one minute without needing chemical reagents or sample preparation.
Learn more about the possibilities of petrochemical analysis with Metrohm NIRS DS2500 Analyzers in our free brochure.

Application example: determination of DV and BN in pygas using the NIRS DS2500 Liquid Analyzer

The diene value and Bromine Number are key parameters for the quality control of pygas.  According to UOP 326, the maleic anhydride is refluxed with the sample in boiling toluene for three hours. Any unreacted maleic anhydride is hydrolyzed to maleic acid, extracted from the reaction mixture, and then titrated with sodium hydroxide. This wet chemical method requires several hours to perform by highly trained analysts. 

For the determination of the Bromine Number according to ASTM D1159, the sample must be cooled down below 5 °C to minimize side reactions like oxidation or substitution.

In contrast to primary methods, near-infrared spectroscopy (NIRS) is a cost-efficient and fast analytical solution for the determination of DV and BN in pyrolysis gasoline.

Figure 2. Quality control of pygas as performed by the Metrohm NIRS DS2500 Liquid Analyzer.
The obtained Vis-NIR spectra (Figure 2) were used to create a prediction model for the determination of DV and BN. The quality of the prediction model was evaluated using a correlation diagram, which displays the correlation between the Vis-NIR prediction and primary method value. The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis (Figure 3).
Figure 3. Correlation plots and figures of merit (FOM) for DV and Bromine Number in pygas.
This solution demonstrates that NIR spectroscopy is excellently suited for the analysis of diene value or maleic anhydride value in pygas in less than one minute without sample preparation or using any chemical reagents. In comparison to the wet chemical method in UOP 326, the time to result is a major advantage of using NIRS since a single measurement is performed within one minute instead of taking 6–7 hours with the primary method. Additionally, Bromine Number is easy to measure with NIRS without requiring any chemicals or sample preparation (such as cooling) as mentioned in ASTM D1159.

Want to learn more? Download our free Application Notes.

Summary

Near-infrared spectroscopy is an excellent choice for measuring MV / DV and BN in pygas. A simple feasibility study using your own pyrolysis gasoline samples will quickly indicate if the NIR spectra will be able to be correlated to the primary method values.  Positive aspects of using NIRS as an alternative technology are the short time to result (less than one minute), no chemicals or other expensive equipment needed, and ease of handling so that even shift workers and non-chemists can perform these analyses in a safe manner.

Future installments in this series

This blog article was dedicated to the topic of pyrolysis gasoline (pygas) and how NIR spectroscopy can be used as the ideal QC tool for the petrochemical / refinery industry. Future installments will be dedicated to other important applications in this industry. These topics will include:

 

For more information

About spectroscopy solutions provided by Metrohm, visit our website!

We offer NIRS for lab, NIRS for process, as well as Raman solutions

Post written by Wim Guns, International Sales Support Spectroscopy at Metrohm International Headquarters, Herisau, Switzerland.
Guide to online and inline surface finishing analysis

Guide to online and inline surface finishing analysis

What is surface finishing?

Surface finishing is a series of industrial processes with the main goal to alter the surface of a certain workpiece in order to obtain specific properties. This can be performed chemically, mechanically, or even electronically with the aim of removing, altering, adding or reshaping the material that is being treated.

Industries that use surface finishing techniques

Surface finishing techniques are used by most industries that manufacture industrial parts (e.g., metals, wafers, tools, and more). The use of surface finishing processes has been on the rise globally and is expected to grow further. An article published by Grand View Research (2019) predicted that the market size for metal finishing chemicals is expected to grow to $13.52 billion USD by 2025.

People mostly think about polishing and sanding when surface finishing is brought up, but it is much more than that. Several industries use different processes to treat surfaces with the main objective of obtaining the highest product quality. According to Grand View Research, the top three industries with the biggest market share for metal surface chemicals are automotive and aerospace, semiconductors, and the metal industry (e.g., industrial machinery, construction).

Figure 1 shows that surface finishing is mainly used in the automotive industry. Here, electroplating and electroless plating are the main processes used to protect against corrosion. The electroplating process consists of using electricity to coat a material (e.g. copper) with a thin layer of another material (e.g. nickel). Electroless plating is accomplished with chemical processes that reduce metal cations in a bath and deposit them as an even layer, even on non-conductive surfaces.

Next is the semiconductor industry, which includes the manufacturing and cleaning surface process of electrical and electronic parts as well as silicon wafers. This industry involves plating processes (e.g., electroless plating) as well as chemical cleaning baths. Chemical cleaning baths are used here to remove any contaminants from the wafer surfaces.

Figure 1. Diagram with top five industrial applications that incorporate surface finishing techniques (graphic repurposed from Metal Finishing Chemicals Market Global Forecast to 2021). (Click image to enlarge.)
Finally comes the metal industry, responsible for creating the infrastructure that our modern world depends on. Here, the process of galvanization is used to make metal corrosion- and heat-resistant. Galvanization is an anti-corrosive measure taken with iron and steel (as well as other metals) by applying a protective zinc coating which does not allow oxidation to occur. The zinc also acts as a sacrificial anode which still protects the underlying metal in the event of a scratch in the galvanized surface. Pickling baths are another common surface finishing process for this industry. These acidic baths are used to remove the oxide layer which formed on the surface during the hot strip mill. If the base steel is over-pickled, it can result in pitting of the metal surface, leading to an undesirable rough, blistered coating in the subsequent galvanizing steps and also excessively consumes the pickling acid (e.g. HCl).

Much more than just decorative coatings

Do appearances matter? When talking about products, absolutely! One of the reasons product surfaces are treated is so they have a more pleasant appearance for consumers, but also for more technical reasons that go beyond looks. Since surface finishing processes are used in a broad range of industries, they serve different purposes depending on the uses of the final products.

In the semiconductor industry, any defect on the components (e.g., silicon wafers, microelectronics, printed circuit boards (PCB), etc.) can impact the performance of the final product. Therefore, maintaining the proper concentrations of all components in the chemical cleaning bath ensures a repeatable etching process, which for this purpose means the elimination of surface defects.

Another example includes phosphating baths, which are used to improve corrosion resistance of the product parts used in the automotive and aerospace industry. This process is performed prior to any painting to protect the body structure from environmental factors. Phosphating baths also need to be kept consistent to guarantee the correct (and identical) thickness of the protective layer in each of the products subjected to this process.

Check out our free webinar about how Process Analytical Technology (PAT) brings analytical measurements directly to the process for real-time decision-making, ensuring a high level of control for coating and finishing baths and eliminating unnecessary risk to plant personnel. Learn about real-world case studies and field-tested applications that demonstrate the advantages of optimized bath chemistry and PAT in the surface treatment industry. 

Challenges in surface finishing processes: daily bath maintenance

Like any process, surface finishing has day to day challenges which can be improved upon. Improvement can only come from knowing the bath composition and how it affects the final product. Generally, monitoring the concentration of chemical baths is done via manual sampling and titration in a laboratory on site (in some cases, by a contract lab offsite). While this method works, it can lead to long waiting times from the moment the sample is taken until the final result—therefore the results are no longer representative of the current process conditions. Because of this delay,  bath replenishment can be impaired by over- or under- dosing components, leading to suboptimal bath composition and resulting product quality (Figure 2).

Figure 2. A jagged graph such as this denotes bath quality that suffers from suboptimal conditions. A relatively flat line would suggest a stable bath composition over time, resulting in reproducible high quality surface finishing.
Manual bath analysis and chemical dosage based on old data directly influences the company’s bottom line since the manufacturer loses money either by overusing bath chemicals or producing subpar products. The larger the plating bath volume, the greater the cost of chemicals utilized. Surface finishing baths can be as large as 3500 L (1,000 gallons) or more. Thus, it is extremely important to optimize chemical dosing to reduce unnecessary costs and waste while still providing maximum quality.

If the baths are overdosed, more chemicals are used than necessary which increases overall operational costs. However, if the baths are underdosed based on old data, then the final products may be defective, which results in increased operational costs as well.

Additionally, surface finishing processes involve many hazardous substances. When carrying out any risk assessment, the first resort is the use of personal protective equipment (PPE), and any potential exposure risks should ideally be engineered out of any process.

Automated analysis of the bath components with an online or inline process analyzer completely eliminates the risk of exposure by plant personnel to the hazards associated with the chemicals used, as well as taking care of the sample preconditioning and sampling itself. With a closed loop control, quick measurements are obtained which lead to fast results and response times for optimized process adjustments.

The solution: operate more safely and efficiently with automated process analysis

Process analysis by manual titration typically takes several steps: sample collection, sample preconditioning, volumetric manipulations, calculation, logging and checking results, and finally sending feedback to the process. All of these can be totally eliminated by using online and inline analysis.

The benefits of this are very clear. By limiting the manual handling steps, any risk of exposure to hazardous chemicals is removed. Sampling error, volumetric errors, and end point ambiguity from analyst to analyst are no longer an issue. Furthermore, sampling can be carried out on a timed basis and can be programmed to occur more frequently than possible with manual methods, giving much greater process control.

The analyzer can be used to fully control a process with direct feedback of results for the correct dosage of chemicals to aging baths. Data is automatically recorded and calculated. On-screen plots and signals can warn about deviating process conditions along with alarm outputs to notify operators of bath issues. The user interface is programmed by simple intuitive operation, and can be performed even by non-chemists.

Benefits of online and inline analysis in surface finishing processes:
  • Decrease manual labor – save time and money
  • Safer working environment – avoid contact with hazardous chemicals
  • Faster response time to process changes – better product quality
  • Optimized chemical consumption – less waste, reduced costs
Learn about the differences between inline, online, atline, and offline measurements in our previous blog post.
Metrohm Process Analytics has more than 50 years of experience in process analysis and optimization. The following examples show our expertise with configuring inline and online process analyzers for different surface finishing processes.

Automated monitoring of clean and etch baths

Metal surfaces can have scratches, impurities, and other imperfections which may interfere with further manufacturing processes (e.g., plating or painting). Therefore, clean and etch baths are a key step to obtain clean, polished, and undamaged surfaces.
Figure 3. Trend chart of NH3 and H2O2 concentrations in an SC1 bath. Note the spiking of the baths to maintain their concentrations.
Traditionally, these bath chemicals are measured offline in the lab after taking a sample from the process. However, as mentioned earlier, manual laboratory methods result in long response times in case of process changes (e.g., reaction mixture, moisture levels, …), and the sample preparation can also introduce errors, altering the precision of the analysis. Additionally, it can be quite cumbersome since different operating procedures need to be implemented to analyze multiple parameters including alkalinity, ammonium hydroxide, hydrogen peroxide, and more.
Figure 4. The Metrohm Process Analytics NIRS XDS Process Analyzer is shown here with a diagram of the inline near-infrared spectroscopy (NIRS) system configuration for cleaning bath analysis.
Another example of cleaning baths are mixed acid baths, generally comprised of sulfuric acid, hydrofluoric acid, and nitric acid. Titration only provides the acid value of the sample analyzed; therefore, it is not possible to know how much of a specific acid is present in the baths. However, near infrared spectroscopy (NIRS) is the perfect analytical technique to monitor each acid individually.
Reagent-free NIRS XDS Process Analyzers enable comparison of real-time spectral data from the process to a primary method (e.g. titration) to create a simple, yet indispensable model for process optimization. NIRS is economical and fast, enabling qualitative and quantitative analyses that are noninvasive and nondestructive. Integration of inline spectroscopic techniques allows operators to gain more control over the production process and increase overall safety.

In addition to NIRS process analyzers, Metrohm Process Analytics can design and customize flow-through cells (Figure 5). These clamp on to tubing already present onsite for easy installation with no need to modify the existing setup.

Figure 5. PTFE single fiber clamp-on flow cell from Metrohm Process Analytics.

Automated monitoring of phosphatizing baths

The phosphatizing process produces a hard, electrically non-conducting surface coating that adheres tightly to the underlying metal. This layer protects against corrosion and improves the adhesion of paints and organic finishes to be subsequently applied.

Phosphatization consists of two parts: an etching reaction with phosphoric acid which increases the surface roughness, and a second reaction at the surface between the alkali phosphates and the previously generated metal ions. This coating is quite thin and offers only basic corrosion protection. The addition of metal cations (such as zinc, manganese, and calcium) to the phosphatizing bath results in the formation of very resistant zinc phosphates with a coating thickness between 7–15 times thicker, perfectly suited for outdoor use.

Figure 6. Schematic diagram of the various process stages and baths used in the phosphatizing process. (Click image to enlarge.)

In the cleaning, degreasing, and rinsing baths, and also in the phosphatizing bath itself (Figure 6), the various parameters involved in the process must be kept stable. Conductivity, pH value, free alkalinity, and total alkalinity are among the main parameters that must be determined in the degreasing and rinsing baths. Free and total acids, accelerator, zinc, and fluoride are monitored in phosphatizing baths. The 2060 Process Analyzer from Metrohm Process Analytics (Figure 7) monitors, records, and documents all of these critical parameters at the same time. The combination of different analytical methods within one system as well as the intuitive handling via the well-arranged user interface ensure easy and reliable monitoring of the entire process.

Check out our free related Process Application Note to learn more.

Figure 7. The 2060 Process Analyzer from Metrohm Process Analytics is an ideal solution for online phosphating bath applications.
To sum up, online and inline process analyzers from Metrohm Process Analytics are the ideal solution to automate the analysis of surface finishing processes because of the comprehensive benefits they provide:
  • No manual sampling needed, thus less exposure of personnel to dangerous chemicals
  • Extended bath life by tightening process windows (less chemicals required)
  • Minimize risk of downtime with faster and more precise data
  • Easier compliance with final product requirements by process automation

If you want to learn more about all the applications that we have to offer, download our free application e-book based on 45 years of global installations.

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Post written by Andrea Ferreira, Technical Writer at Metrohm Applikon, Schiedam, The Netherlands.