NIR spectroscopy in the petrochemical and refinery industry: The ASTM compliant tool for QC and product screening – Part 2

Oct 4, 2021

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This article is Part 2 of a series.

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Differences between gasoline, diesel, and jet fuel

Gasoline is a fuel made from crude oil and other petroleum-based liquids, containing carbon numbers generally between 4 and 12, and exhibiting boiling points of up to 120 °C. Gasoline is primarily used as a fuel for vehicles. Petroleum refineries and blending facilities produce motor gasoline for sale at gas (or petrol) stations. Most of the gasoline that petroleum refineries produce is unfinished gasoline. This unfinished product requires blending with other liquids to control parameters such as octane rating and volatility to make gasoline meet the basic requirements for fuel that is suitable for use in spark ignition engines.

Diesel fuel is refined from crude oil at petroleum refineries. «Diesel» is the common term for the petroleum distillate fuel oil sold for use in motor vehicles that use the compression ignition engine, invented by the German engineer Rudolf Diesel (1858–1913). He patented his original design in 1892. One of the fuels that Rudolf Diesel originally considered for his engine was vegetable seed oil, an idea that eventually contributed to the biodiesel production process of today.

Prior to 2006, most diesel fuel contained high quantities of sulfur. Sulfur emissions from combusting diesel fuel leads to air pollution that is quite harmful to human health. Therefore, the U.S. Environmental Protection Agency issued requirements to reduce the sulfur content of diesel fuel to be as low as 15 mg/L. Diesel fuel contains components with a carbon number range from 8 to 21 (though mainly between 16–20) and is the fraction that boils between 200 °C and 350 °C.

Jet fuels (or aviation fuels) are one of the basic products used by aircraft. Jet fuel is comprised of refined petroleum products with carbon numbers between 10 to 16 (although they can range from 6 to 16), and it boils between 150 °C and 275 °C. This type of fuel is heavily regulated by national and international bodies. There are two main types of jet fuel: Jet A and Jet B. The main difference between the two is the freezing point. Jet B is usually used for military operations and locations with inclement weather. Jet A is mainly used to fuel commercial airplanes.

Near-infrared spectroscopy—an ASTM compliant tool to assess the quality of gasoline, diesel, and jet fuel

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, available turnkey solutions for gasoline, diesel, and jet fuel are outlined which have been developed according the NIRS implementation guidelines of ASTM E1655 (method development), ASTM D6122 (method validation), and ASTM D8340 (results validation). Afterward is a discussion about the return on investment (ROI) of using NIRS as an alternative to the CFR Engine.

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

Benefits of NIRS: Part 1

Benefits of NIRS: Part 2

Benefits of NIRS: Part 3

Benefits of NIRS: Part 4

NIRS expedites and simplifies fuel quality control

Without high quality fuels (e.g., gasoline, diesel, and jet fuel), our daily lives would look much different. At the end of the production process as well as at various steps in the distribution chain, the quality of the product needs to be determined. Typically, key quality parameters such as RON/MON (research and motor octane numbers), cetane index, and flash point are determined in the laboratory by chemical and physical methods. These methods not only incur high running costs but they are also quite time consuming.

NIRS on the other hand requires neither chemicals nor sample preparation. This technique can even be used by non-technical people (no chemistry degree necessary) and it provides results in less than a minute. 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.

Metrohm offers the NIRS DS2500 Petro Analyzer for quality control and routine analysis of fuels and is compliant with ASTM D6122. Resistant to dust, moisture, and vibrations, this instrument is not only suitable for laboratory use, but also use in direct production environments.

Learn more in the link below.

NIRS DS2500 Petro Analyzer

Turnkey solutions: available pre-calibrations for gasoline, diesel, and jet fuel

Table 1 lists all constituents covered by the pre-calibrations for these different fuels. Click on the fuel type in the table to learn more about its pre-calibrations offered by Metrohm.

**Table 1.** Pre-calibrations available for a variety of key quality parameters in gasoline, diesel, and jet fuel.
Fuel type	Parameters	Range	SECV	R²
Gasoline	RON	81–100	0.68	0.958
MON	81–88	0.53	0.889
Anti-Knock Index	85–94	0.45	0.948
Aromatics	20–45%	0.011	0.959
Benzene	0.15–0.70 %	0.0004	0.902
Density	0.74–0.76 g/cm³	0.0024 g/cm³	0.797
Olefins	0–25 %	0.013	0.909
Oxygen	0.2–2.0 %	0.00045	0.994
Diesel	Cetane index	46–77	0.62	0.987
Cetane number	45–60	0.942	0.942
Density	0.82–0.89 g/cm³	0.0021 g/cm³	0.968
CFPP	-22–(+19) °C	2.8 °C	0.963
T95	325–410 °C	7.04 °C	0.799
Flash Point	56–120 °C	2.7 °C	0.97
Viscosity	2–5.5 cSt	0.15	0.91
Kerosene / Jet Fuel	Cetane index	36–50	1.1	0.871
API gravity	38–48 °	0.56 °	0.931
Aromatics	10–25 %	0.01	0.851
T10	158–200 °C	4.1 °C	0.801
T20	165–205 °C	3.1 °C	0.88
T50	180–220 °C	4.1 °C	0.789
Density	0.78–0.83 g/cm³	0.003 g/cm³	0.936
Flash Point	38–65 °C	4.3 °C	0.62
Freeze Point	-65–(-40) °C	3. 5°C	0.576
Hydrogen	13.2–14.2 %	0.0005	0.934
Saturates	75–90 %	0.009	0.888
Viscosity at 20 °C	3–7 cSt	0.33 cSt	0.804

Learn more about the possibilities of petrochemical analysis with Metrohm NIRS DS2500 Analyzers in our free brochure.

DS2500 Analyzer – Boosting efficiency in the QC laboratory with Near-Infrared Spectroscopy (NIRS)

Application example: quality control of diesel with the NIRS DS2500 Petro Analyzer

The cetane index (ASTM D613), flash point (ASTM D56), cold filter plugging point (CFPP) (ASTM D6371), D95 (ISO 3405), and viscosity at 40 °C (ISO 3104) are among some of the key parameters to determine the quality of diesel. The primary test methods for these parameters are labor intensive and challenging due to the need for multiple analytical methods.

Figure 1. Quality control of diesel fuel as performed by the Metrohm NIRS DS2500 Petro Analyzer.

In this turnkey solution, diesel samples were measured in transmission mode with a NIRS DS2500 Petro Analyzer 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 (Figure 1), which made a cleaning procedure unnecessary.

The obtained Vis-NIR spectra (Figure 1) were used to create prediction models for the determination of key diesel parameters. The quality of the prediction models was evaluated using correlation diagrams which display the correlation between Vis-NIR prediction and primary method values. The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis (Figure 2).

This solution demonstrates that NIRS is excellently suited for the analysis of multiple parameters in diesel fuel, providing results in less than one minute without the need for sample preparation or any chemical reagents.

Want to learn more? Download our free Application Note.

Quality Control of Diesel – Fast and straightforward determination of cetane index, flash point, CFPP, D95, and viscosity with NIRS

Return on investment: CFR Engine vs. NIRS

Gasoline requires intensive checks on several quality parameters which must be within certain specifications before commercialization. These parameters which can also be controlled by NIRS analysis include the research octane number (ASTM D2699) and motor octane number (ASTM D2700), also known as RON/MON.

The importance of measuring these values precisely is not only to comply with regulations, but also because of the further potential to save costs for manufacturers. As an example, RON values exceeding the stated requirements will still be accepted by the market, but these products will then include a higher amount of lucrative long-chain organic molecules. This so-called «RON giveaway» is estimated at approximately 0.5 RON per barrel, resulting in $2.25 million USD/month in lost revenue for a production process of 100,000 barrels per day.

Figure 3. CFR® F1/F2 Octane Rating Unit Combination Research & Motor Method. (Source: CFR Engines Inc.)

The Combination Cooperative Fuel Research (CFR) octane rating engine (model F1/F2) is used to determine the octane quality of gasoline and fuel blending components. This unit is recognized and approved by ASTM D2699 and D2700. The engine is equipped with a heavy-duty crankcase, variable compression cylinder, carburetor with adjustable fuel to air ratio, and knock measurement equipment (Figure 3).

Ready-to-use NIRS systems are also available for monitoring several gasoline quality parameters which cover varied ranges and their respective precisions (Table 1). Additionally, the manufacturers of NIRS analyzers usually offer application support to extend these ranges or improve upon the precision.

An overview of estimated costs for the analysis of RON and MON with a CFR Engine compared to the Metrohm NIRS DS2500 Petro Analyzer is shown in Table 2. The full payback is achieved within two years if considering only 50% of the primary analysis method (CFR Engine) is replaced by NIRS. This calculation is based on 2000 analyses per year (1000 RON + 1000 MON), with total running costs of approximately $32.50 per analysis (chemicals, maintenance, and labor).

**Table 2.** Cost of ownership CFR engine vs. DS2500 Petro Analyzer.

¹*Assumption that the instrument had previously been purchased, and therefore this cost is not included in the ROI calculation.*
Total analyses RON + MON per year	2000	2000
Cost of operator per hour	$25.00	$25.00
Cost of Analyzer	CFR Engine	NIRS DS2500 Petro Analyzer
Analyzer	$500,000.00	$55,000.00
Total initial costs	$0.00¹	$55,000.00
Running costs consumables / chemicals / maintenance
Chemicals per year (ASTM D2699/D2700)	$20,000.00	$0.00
Maintenance cost per year	$20,000.00	$1,500.00
Chemicals plus maintenance cost per analysis	$20.00	$0.75
Total running costs per year	$40,000.00	$1,500.00
Time spent per analysis	30 minutes	< 1 minute
Labor cost of 1000 analyses of RON (ASTM D2699)	$12,500.00	$416.50
Labor cost of 1000 analyses of MON (ASTM D2700)	$12,500.00	$416.50
Labor cost per analysis	$12.50	$0.42
Total labor costs per year	$25,000.00	$833.00
Total running costs per year	$65,000.00	$2,333.00

More information about the analysis of RON/MON and other parameters in gasoline can be found in our free Application Notes below.

Quality Control of Gasoline – Rapid determination of RON, MON, AKI, aromatic content, and density with NIRS

Online process monitoring of octane number during catalytic reforming by NIRS following ASTM D2699 and ASTM D2700

In this example, RON/MON analysis was used to show cost savings and ROI when using NIRS to supplement a primary method. However, when expanding this to consider other key quality parameters such as the ones indicated in Table 1, the financial incentives for such an investment are even more compelling.

Summary

Near-infrared spectroscopy is very well suited for the analysis of key quality parameters in gasoline, diesel, and jet fuel. Available pre-calibrations are developed and validated in accordance with the ASTM guidelines. 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.

Other installments in this series

This blog article was dedicated to the topics of gasoline, diesel, and jet fuel and how NIR spectroscopy can be used as the ideal QC tool for the petrochemical / refinery industry. Other installments are dedicated to: