Name: original experimental approach for assessing transport fuel stability
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The authors would like to thank the French National Association of Research and Technology (ANRT) for funding this research through the PhD grant awarded to Dr. Kenza Bacha.

NOTE: Please consult all relevant material safety data sheets (MSDS) before use. The operator needs to be equipped with personal protective equipment, including gloves, gown and goggles. Before use, fresh reagents need to be stored in a refrigerator. Oxidized fuels are rich in corrosive acidic species. They cannot be stored in metal flasks and must be stored in the refrigerator in suitable glass vessels, with limited headspace air, in a vertical position to avoid contact between the fuel and the flask cap. The refrigerator was kept at 6 &#176;C. The oxidation produces volatile oxidation products that may cause respiratory irritation. Thus, all oxidation experiments need to be carried under an extraction hood.
1. Advanced Oxidation Procedure in Reactor 1
NOTE: Reactor 1 was used to perform the controlled oxidation of methyl oleate (MO), a mono-unsaturated model molecule representative of commercial FAME3. The tests aimed at monitoring MO oxidation through the following steps.
<ol>
	<li>Determine the average induction period (IP)
	<ol>
		<li>Prepare the reaction vessels and the measurement cells according to the standard test method4.</li>
		<li>Remove possible dust or contaminants from the reaction vessels before fuel introduction using compressed air.</li>
		<li>Fill the reaction vessels of Block A: 1 to 4 with 7 ml of a fresh fuel sample of methyl oleate using a pipette.</li>
		<li>Configure the test.
		<ol>
			<li>Set the heating setpoint temperature of Block A to 110 &#176;C (&#177; 0.3 &#176;C).</li>
			<li>Set the air flow rate to be bubbled through the sample to 10 L/hr.</li>
			<li>Set the shutoff criteria to either a conductivity threshold of 400 &#181;S/cm or an IP determined by the software. The test stops when one of the two criteria is reached.</li>
		</ol>
		</li>
		<li>Enter the name and reference of each of the samples of Block A in the software.</li>
		<li>Launch the test by pressing the &#34;start&#34; button. 
		NOTE: This implies simultaneously bubbling air through the sample and raising the heating block temperature (the heating time is about 45 min for a setpoint temperature of 120 &#176;C). When the shutoff criterion is reached, the air bubbling and the block heating are automatically interrupted.</li>
		<li>Extract the reaction vessels from the heating block.</li>
		<li>Manually and thoroughly agitate the contents of the reaction vessel in order to homogenize the fuel composition. Transfer the contents of each reaction vessel into a 10 ml glass flask and place the glass flasks vertically in the refrigerator immediately after extraction.</li>
		<li>Determine the induction period (IP) from the conductivity signal using the method of tangents intersection illustrated in Figure 2. The induction period is given by the position of the intersection of the extrapolated baseline (T1) and the tangent line drawn from the curve inflection (T2) on the x-axis.</li>
		<li>Calculate the average IP (IPavg) using the IP measurements that are within 10% of IP dispersion according to: IPavg = &#931;IPvalid/n, where IPvalid represents the IP measurements within 10% of IP dispersion and n their number.</li>
	</ol>
	</li>
	<li>Generate samples with different oxidation levels
	<ol>
		<li>Using Block B, repeat steps 1.1.-1.5. However, modify the shutoff criterion by indicating an ending time equal to 4 times the&#160;IPavg determined in step 1.1.9.</li>
		<li>Extract &#34;manually&#34; the first reaction vessel from the heating block at 0.5 the IP, the second reaction vessel at the IP, the third reaction vessel at 2 times the IP and the fourth and last reaction vessel at 4 times the IP.</li>
		<li>For each reaction vessel, manually and thoroughly agitate the contents of the vessel to have a homogenous sample. Transfer the entire contents in to 10 ml glass flask, label each sample (0.5 IP, IP, 2 IP and 4 IP, respectively) and place the glass flasks vertically in the refrigerator immediately after extraction.</li>
	</ol>
	</li>
</ol>
<img alt="Figure 2" src="/files/ftp_upload/54361/54361fig2.jpg" /> 
Figure 2. Induction period determination method by tangents intersection; test on methyl oleate at 110 &#176;C. The induction period is given by the position of the intersection of the extrapolated baseline (T1) and the tangent line drawn from the curve inflection (T2) on the x-axis. <a href="https://www.jove.com/files/ftp_upload/54361/54361fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol start="3">
	<li>Analyze the generated samples
	<ol>
		<li>Determine the TAN of methyl oleate sampled at increasing oxidation stages using the &#181;TAN method (derived from ASTM D6649).
		<ol>
			<li>Rinse all parts in contact with the sample (sample vessel, electrode, and magnetic stirrer) with ultrapure water followed by isopropanol.</li>
			<li>Weigh out 2 g of the sample and place it in the measurement vessel.</li>
			<li>Dilute the sample in 10 g of isopropanol in the measurement vessel.</li>
			<li>Gradually add a solution of 0.1 mol/L KOH diluted in isopropanol until the equivalence point is reached. This is indicated by a significant potential variation (above 9 mV) measured by using a glass electrode.</li>
			<li>Report the TAN of the sample in milligram KOH per gram of fuel (mg KOH/g).</li>
		</ol>
		</li>
		<li>Analyze methyl oleate sampled at increasing oxidation stages by GC-MS.
		<ol>
			<li>Inject 1 &#181;l of the sample into a GC-MS equipped with an FFAP column (60 m, 0.250 mm, 0.25 &#181;m) using a split ratio of 1:75.</li>
			<li>Perform the following heating program of the column: 40 &#176;C for 10 min, then heated at 5 &#176;C/min to 100 &#176;C, finally at 1 &#176;C/min up to 250 &#176;C.</li>
			<li>Use the following parameters on the mass spectrometer: potential of the electron ionization source: 70 eV - mass range: m/z = 10 to 400 - full-scan mode.</li>
			<li>Report the gas chromatogram spectra and proceed to the identification of significant peaks.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
2. Advanced Oxidation Procedure in Reactor 2
Note: Reactor 2 was used to perform successive oxidation cycles on biodiesel-free diesel fuel (B0) and Rapeseed Methyl Ester (RME). The tests aimed at monitoring fuel oxidation through the following procedure.
<ol>
	<li>Perform the first oxidation cycle.
	<ol>
		<li>Configure the test.
		<ol>
			<li>Set the heating temperature to 150 &#176;C using the user interface. Set the pressure in the cell to 7 bar using the user interface. Set the shutoff criterion: pressure drop (&#916;P) of 10% of the maximum pressure reached.</li>
		</ol>
		</li>
		<li>Prepare the test cell. Remove possible dust or contaminants using laboratory wipers soaked with acetone and replace the sealing ring.
		<ol>
			<li>Fill the cell with 5 ml of the fuel sample using a pipette. Close the test cell with a screw cap followed by a protective locked cover.</li>
		</ol>
		</li>
		<li>Launch the test by pressing the &#34;RUN&#34; button in the user interface of Reactor 2. 
		NOTE: First, the cell is pressurized with oxygen, injected through a supply line, then the cell is depressurized to evacuate the gases through an extraction duct. Then, pressurized again with oxygen. When the head space pressure reaches 7 bar, the test starts. Temperature is raised to 150 &#176;C, and the pressure rises alongside with the temperature until a stable maximum value is reached.</li>
		<li>Record using the computer the pressure variation at intervals of 1 second until the shutoff criterion is reached. At this time, the measurement and the cell heating automatically stop.</li>
		<li>Wait for 15 min until the temperature is reduced around 20 &#176;C.</li>
		<li>Depressurize the test cell using the user interface. This purge allows to reach atmospheric pressure in the cell. Open the protective cover and the screw cap.</li>
	</ol>
	</li>
	<li>Perform &#34;x&#34; successive oxidation cycles.
	<ol>
		<li>Repeat steps 2.1.3 to 2.1.6 the desired &#34;x&#34; times.</li>
		<li>At the end of the &#34;x&#34; tests, transfer all of the oxidized fuel remaining in the cell using a pipette to a 10 ml glass flask and place the glass flask vertically in the refrigerator.</li>
		<li>Clean the cell using laboratory wipers soaked with acetone.</li>
	</ol>
	</li>
	<li>Analyze the generated samples
	<ol>
		<li>Analyze the samples using FTIR-ATR.
		<ol>
			<li>Clean the ATR diamond cell using laboratory paper soaked with ethanol.</li>
			<li>Configure the software parameters: Set 100 scans to build the FTIR spectrum, fix the resolution at 4 cm-1 and set the spectral range from 600 to 4,000 cm-1.</li>
			<li>Extract the fuel flask from the refrigerator and agitate its contents thoroughly in order to homogenize the fuel composition.</li>
			<li>Sample 10 &#181;l of fuel from the fuel flask using a pipette and place the droplet on a horizontal ATR diamond cell at ambient temperature, then start the analysis.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

An advanced oxidation protocol (AOP) was developed in this work using two oxidation reactors (Reactor 1 and Reactor 2). This protocol was applied to study the oxidation of commercial diesel and biodiesel fuels as well as pure reagents such as methyl oleate. In this section we discuss some aspects of the protocol and its application.
When using Reactor 1 and Reactor 2 as ageing devices, the homogeneity of the oxidized samples should be considered as the oxidation can lead to the formation of insoluble products that can stick to the internal surfaces of the apparatus. Those cannot be collected entirely with a pipette after the cooling of the apparatus. Even after the sample collection, two phases can sometimes be observed at high oxidation levels. In such cases, a part of the supernatant is collected to be analyzed but cannot be considered to be representative of the whole oxidized sample. Besides, the collected samples do not contain intermediate species that are important to assess the oxidation kinetics. Online analysis of the sample during the oxidation may help addressing this issue. Previous works have implemented online analysis during hydrocarbon oxidation using different reactors such as stirred reactors16,17 or autoclaves18. These reactors allow the monitoring of the oxidation products in both the liquid and the gas phases at a higher sampling frequency. They may cover wider range of oxidation conditions (e.g., air flow rate, temperature, mixing speed). However, they require specific and costly test equipment and are more time consuming. In addition, as their design and test conditions are different from standard oxidation stability tests, it is difficult to establish accurately the relationship between fuel reactivity in the standard and alternative tests.
Typical oxidation tests in Reactor 1 or Reactor 2 produce lower than 5 ml and 7 ml, respectively. These small quantities are not sufficient to carry out multiple analyses in optimal conditions. For example, conventional total acid number analysis requires a minimum of 20 grams of the analyzed sample (ASTM D664) which explains the use of &#181;TAN in this work.
The IP calculation (in Reactor 1) was based on the tangents intersection method. A second possible methodology is to calculate the induction period using the secondary derivative4 where the IP is indicated by a maximum in the second derivative. However, this method is limited when the conductivity signal is fluctuating which frequently occurs. The use of the tangents method allows the user to overcome this limitation. However, the tangent method is user-dependent, as it relies on the user for drawing the tangents. In the present study, the determination was performed by the same operator for all the samples. Replicate analyses were performed to validate the results accuracy. According to the experimental results, the induction period precision (IPp) depends on the IP following the equation IPp (hr) = 0.15 IP&#8722;0.37, with IP being the induction period, in agreement with the precision of around 0.6 hr previously reported in standard conditions5.
The TAN is a gross indicator for acidic species formation, however, the precision of the &#181;TAN measurement is still dependent on the amount of the sample, particularly, for samples with a low acid number. Besides, the TAN does not provide any molecular information. Nevertheless, it is an interesting technique since a strong relationship between the TAN increase and insoluble deposits formation during oxidation process has been reported in the literature16,19,20. Therefore, a more detailed characterization of oxidized MO samples was performed with GC-MS.
Concerning the GC-MS technique, the system should be checked for possible contamination by injecting a solvent (blank) before analyzing the samples. As this technique is very sensitive, the formation of trace compounds can be monitored. By this means, the absence of any parasite peak can be verified.
Whichever the analytical technique, the sample characterization should be carried out as soon as possible after the oxidation process. In fact, oxidized samples are highly unstable and a long storage time would lead to a change in the sample composition. If storage is unavoidable, attention should be paid to use glass flasks hermetically selected and to store them at a low temperature (e.g., 6 &#176;C).
In conclusion, the AOP allowed the user to monitor the oxidation process of several single and multi-component systems. First, by characterizing the global reactivity through the induction period, then, by generating oxidized samples under controlled conditions. Several characterization techniques such as GC-MS, FTIR, or &#181;TAN can be employed with the generated samples to monitor the variation of their properties and chemical composition. The results provide rich and original information on the oxidation kinetics, the main degradation pathways and the oxidation products. Besides, AOP represents a very useful tool to study the influence of the oxidation conditions such as temperature, oxidation time and oxygen concentration. This work provides an efficient and promising approach that may be of use for studying the oxidation kinetics for transport or biological applications.

Oxidation stability is a criterion for evaluating fuel quality. The oxidation stability of a fuel can be monitored by several methods such as induction period, peroxides, acids, and insolubles. The induction period (IP) is the period at the beginning of the oxidation process during which the reactions are slow, due to a low concentration of reaction intermediates or the presence of antioxidants.
Figure 1 represents a simplified mechanism of the oxidation of hydrocarbons. As reported1,2, the oxidation of hydrocarbons in the liquid phase mainly follows a radical mechanism. It proceeds according to three steps: initiation, propagation and termination. During the initiation step, free radicals are formed by hydrogen abstraction from the initial hydrocarbon (RH) or the decomposition of hydroperoxides already present in the fuel (R1a-c). The addition of di-oxygen to the formed radical results in peroxide formation according to reaction (R2). The propagation step proceeds mainly through the peroxide route. The peroxide formed reacts with the initial hydrocarbon by hydrogen abstraction or by addition producing hydroperoxides or polyperoxides, according to reactions (R3a) and (R3b), respectively. The decomposition of hydroperoxides generates different oxygenated products, mainly, alcohols, carbonyls, epoxides and alkanes (R4). The termination step occurs when stable products are formed through free radical recombination (R5-R7). In this work we developed a procedure to monitor the oxidation process using two existing oxidation reactors.
<img alt="Figure 1" src="/files/ftp_upload/54361/54361fig1.jpg" /> 
Figure 1. Simplified mechanism of hydrocarbon oxidation.&#160;The mechanism represents globalized key-steps of the oxidation of hydrocarbons including several known steps: initiation propagation and termination. This figure has been reprinted with permission from8, Copyright 2015 American Chemical Society. <a href="http://www.jove.com/files/ftp_upload/54361/54361fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Accelerated oxidation was performed using a Rancimat device (Reactor 1). This device is used for the standard test of FAME and FAME containing diesel fuels according to the standard EN 157513. Reactor 1 is equipped with two heating blocks: heating block A and heating block B. Each heating block contains 4 reaction vessels, numbered from 1 to 4, linked to 4 measuring cells. A part of the volatile species, generated during the oxidation is entrained by the circulating air and captured by a measuring cell filled with distilled water. The variation in the water conductivity signal is monitored continuously. The induction period (IP) is characterized by a sudden rise of conductivity associated especially with volatile acid species. Further details about the standard method can be found elsewhere4,5.
The PetroOxy device (Reactor 2) was also used to perform an accelerated fuel oxidation test. This equipment is used for the measurement of the oxidation stability of middle distillate and gasoline fuels according to the ASTM D 7545 and ASTM D 7525 standards6,7. The induction period measured by the apparatus is defined as the time necessary to reach a 10% pressure drop (&#916;P) measured in the test cell head space.
These techniques have been largely used for the standard characterization of oxidation stability of middle distillate fuels as well as for oxidation kinetics studies8, 9, 10,11.

<table><tbody><tr><td>Rancimat&amp;nbsp;</td><td>Metrohm</td><td>Rancimat 843</td><td>Standard test apparatus for diesel and biodiesel oxidation stability&amp;nbsp;&amp;nbsp;</td></tr><tr><td>PetroOxy</td><td>Petrotest&amp;nbsp;</td><td>&amp;nbsp;13-3000</td><td>Standard test apparatus for diesel and biodiesel oxidation stability&amp;nbsp;&amp;nbsp;</td></tr><tr><td>FTIR spectrometer</td><td>Brucker</td><td>Brucker IFS66</td><td>Apparatus for chemical composition analysis through chemical functions identification</td></tr><tr><td>Total acid number titrator</td><td>Metrohm</td><td>Titrino Plus 848&amp;nbsp;</td><td>Test apparatus for diesel and biodiesel oxidation stability&amp;nbsp;&amp;nbsp;</td></tr><tr><td>Gas Chromatograph</td><td>Agilent</td><td>6890 Agilent GC/MS</td><td>Analatical chemistry technique used to separate the compounds present in a sample</td></tr><tr><td>Gas Chromatography column</td><td>Agilent</td><td>DB-FFAP column&amp;nbsp;</td><td>Component of Gas Chromatogram that separates the molecules</td></tr><tr><td>Mass Spectrometer</td><td>Agilent</td><td>5973 inert mass spectrometer</td><td>Analytical chemistry technique used to identify the compounds present in a sample</td></tr><tr><td>Methyl Oleate 99%</td><td>SIGMA ALDRICH&amp;nbsp;</td><td>311111&amp;nbsp;ALDRICH</td><td>Pure reagent</td></tr><tr><td>EMAG-free ultra-low sulfur diesel</td><td>Total ACS</td><td>CEC RF-06-03</td><td>Commercial Diesel fuel</td></tr><tr><td>Rapeseed methyl Ester</td><td>ASG</td><td>Biodiesel 3826 00 10</td><td>Commercial Biodiesel</td></tr><tr><td>Isopropanol &gt;99.9%</td><td>VWR</td><td>84881.290</td><td>Solvent for Total Acid Number determination</td></tr><tr><td>KOH 0.1 M in isopropanol</td><td>VWR</td><td>1.05544.1000</td><td>Titration agent for Total Acid Number determination</td></tr></tbody></table>

original experimental approach for assessing transport fuel stability

The study of fuel oxidation stability is an important issue for the development of future fuels. Diesel and kerosene fuel systems have undergone several technological changes to fulfill environmental and economic requirements. These developments have resulted in increasingly severe operating conditions whose suitability for conventional and alternative fuels needs to be addressed. For example, fatty acid methyl esters (FAMEs) introduced as biodiesel are more prone to oxidation and may lead to deposit formation. Although several methods exist to evaluate fuel stability (induction period, peroxides, acids, and insolubles), no technique allows one to monitor the real-time oxidation mechanism and to measure the formation of oxidation intermediates that may lead to deposit formation. In this article, we developed an advanced oxidation procedure (AOP) based on two existing reactors. This procedure allows the simulation of different oxidation conditions and the monitoring of the oxidation progress by the means of macroscopic parameters, such as total acid number (TAN) and advanced analytical methods like gas chromatography coupled to mass spectrometry (GC-MS) and Fourier Transform Infrared - Attenuated Total Reflection (FTIR-ATR). We successfully applied AOP to gain an in-depth understanding of the oxidation kinetics of a model molecule (methyl oleate) and commercial diesel and biodiesel fuels. These developments represent a key strategy for fuel quality monitoring during logistics and on-board utilization.

Study of methyl oleate oxidation using AOP in Reactor 1
The IP of methyl oleate (MO) was measured at 110 &#176;C three times, with an error of less than 5% (absolute deviation 0.06 hr). IP measurements according to the tangent intersection method indicate an average IP time of 1.8 hr. The AOP was performed according to the abovementioned protocol to achieve oxidized samples at 0.5 IP, IP, 2 IP and 4 IP, respectively.
Figure 3 presents the variation of total acid number during the oxidation procedure. The TAN measurement allows the evaluation of the overall oxidation status of the fuel. The TAN of fresh MO is lower than the quantification limit of the TAN device and therefore can be considered as insignificant. From 0 to 0.5 IP, the TAN remains very low (around 0.1 mg KOH/g), and then increases from 0.5 to 1 IP by a factor larger than 8 times. At 4 IP, the TAN is around 52 times higher than at 0.5 IP indicating an exponential increase of TAN with the oxidation time. This behavior suggests that acid species formation is relatively slow during the initial oxidation regime. However, it becomes significant at intermediate and advanced oxidation regimes: i.e., from 0.5 to IP and after the IP.
<img alt="Figure 3" src="/files/ftp_upload/54361/54361fig3.jpg" /> 
Figure 3. Variation of total acid number (TAN) at different oxidation levels of methyl oleate from 0 IP to 4 IP.&#160;The Total Acid Number of methyl oleate increases with the oxidation progress. <a href="https://www.jove.com/files/ftp_upload/54361/54361fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Total-ion currents (TIC), acquired during GC-MS coupling, are presented in Figure 4 for the various oxidation stages of the MO sample. TIC, which is equivalent to a GC/FID trace, represents the overall signal coming out of the gas chromatograph.
<img alt="Figure 4" src="/files/ftp_upload/54361/54361fig4.jpg" /> 
Figure 4. Gas chromatograms of MO samples at different oxidation levels from 0 IP to 4 IP.&#160;Overall comparison of the gas chromatograms on a wide range of retention times (0-180 min) presenting the formation of several new peaks related to the oxidation products. <a href="https://www.jove.com/files/ftp_upload/54361/54361fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
In the fresh MO (0 IP), there are already several peaks but with very low intensities, most likely from impurities. As the purity of standard, MO is above 99%, the sum of the concentrations of all impurities is less than 1%. The peaks associated with the impurities can be identified, which underlines the sensitivity of this analytical technique. All chromatograms are normalized to the same scale to qualitatively compare the relative intensities of the peaks. It is interesting to notice the increase of intensities of several peaks from 0 IP (fresh sample) to 4 IP (highly oxidized sample). Besides, some species that were not present in the initial chromatogram are formed at mid to high oxidation levels with gradually increasing intensities. For ease of readability, Figure 7 presents only the range from 0 to 30 minutes. MO, having a retention time of 115 minutes, does not appear in this time range. The coupling with mass spectrometry (MS) enables the user to perform a molecular identification of the oxidation products. The identification was performed on the MO sample oxidized at 4 times the IP. In fact, this latter sample presents almost all the oxidation products generated at earlier stages with a higher concentration.
For each peak on the chromatogram (Figure 5), the identification of the associated compound was made through comparison between the experimental mass spectrum and the theoretical one (NIST database). For example, the peak with a retention time of 26.5 minutes was methyl-6-heptenoate according to MS identification. Results indicate that methyl-6-heptenoate, initially absent from the fresh product, is produced during the oxidation process. Qualitatively, from 0.5 to 4 times the IP, the intensity of the associated peak rises by a factor of around 10.
Results obtained on the entire chromatogram (from 0 to 190 minutes) highlight the formation, then the rise of concentration of molecules, originally absent, as the oxidation time increases.
The identification of all molecules indicates the formation of various chemical moieties during the oxidation process. First, through the molecular cleavage, several short chain molecules are formed such as C5 to C8 alkenes, C6 to C8 alkanes, C7-C8 methylesters with retention times around 90-120min. Through the direct reaction of molecular oxygen with the alkyl radicals or hydroperoxides, C8-C9 aldehydes, C8-C9 methyl esters containing other oxygenated functional groups (e.g., alcohol or epoxides) are formed at similar retention times. Methylesters and aldehydes with longer chain lengths are also found at retention times greater than 30 minutes such as 2-decenal and 2-undecenal.
Some of the products identified in the present work with GC-MS were consistent with what has been previously reported in literature. For example, Berdeaux et al.12 carried out the oxidation of MO under slightly different experimental conditions (180 &#176;C, 15 hr heating, no oxygen). A separation was carried out to remove the nonpolar compounds and the polar fraction was injected into a GC-MS device. The authors found various aldehydes and methylesters, thus in agreement with our results. Because the non-polar fraction was not characterized by these authors, no comparison is possible concerning alkanes and alkenes. The consistency of our findings with literature results highlights the potential of the AOP for studying the oxidation kinetics of fuels and biofuels.
<img alt="Figure 5" src="/files/ftp_upload/54361/54361fig5.jpg" /> 
Figure 5. Gas chromatograms of MO oxidized at 4 IP. Molecular identification of the products within a retention time range of 0 - 30 min (top graph) and a focus on methyl-6-heptenoate peak (bottom graph) the upper mass spectrum corresponds to the experimental data and the lower one to the theoretical mass spectrum (NIST database). <a href="https://www.jove.com/files/ftp_upload/54361/54361fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Study of biodiesel oxidation using the AOP in Reactor 2
Figure 6 presents samples of B0, and oxidized B0 following 1, 4 and 6 oxidation cycles (B0-1) (B0-4) and (B0-6), respectively. The fuel color changes during the oxidation from transparent to yellowish then brownish. This change is due to the formation of polar compounds. The molecular weight of these products increases along with the oxidation level. Oxidized B0 samples show the formation of a dark viscous phase composed of high molecular weight polar products.
<img alt="Figure 6" src="/files/ftp_upload/54361/54361fig6.jpg" /> 
Figure 6. B0 and oxidized B0 samples in reactor 2 following 1, 4 and 6 oxidation cycles in Reactor 2.&#160;Color variation of B0 during the oxidation. <a href="https://www.jove.com/files/ftp_upload/54361/54361fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Figure 7 presents the evolution of the RME composition identified with FTIR during oxidation at 1, 4 and 6 runs in Reactor 2. Three regions are studied (Figure 7). Peaks observed in the region R1 at [800-1,400 cm-1] suggest the presence of C-O and C-O-C bonds that could be attributed to alcohol, epoxy and oxirane functions. R2 shows the formation of polar products such as acids, aldehydes, ketones and esters. The peaks identified between 1,650 and 1,760 cm-1 broaden along with the oxidation level. In parallel, a pronounced decrease of the double bonds (C=C-H) represented here by the peak at 3,010 cm-1 is observed13: a conversion rate of nearly 30%, 90% and almost 100% were observed after 1, 4 and 6 runs in Reactor 2, respectively. This trend suggests the formation of the oxidation products described in R1 and R2 following the conversion of the double bonds in unsaturated FAME.
<img alt="Figure 7" src="/files/ftp_upload/54361/54361fig7.jpg" /> 
Figure 7. FTIR spectra for RME and oxidized RME samples in reactor 2 following 1, 4 and 6 oxidation cycles.&#160;Overall comparison of the FTIR spectra of fresh and oxidized RME on a wide wavelength range (600-3,800 cm-1) presenting the variation of the absorbance signal associated with the oxidation. This figure has been reprinted with permission from8, Copyright 2015 American Chemical Society. <a href="https://www.jove.com/files/ftp_upload/54361/54361fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Figure 8 represents FTIR analysis of B0 and oxidized B0 following 1, 4 and 6 oxidation cycles. Three regions are shown R1 (600 - 1,300 cm-1), R2 (1,600 - 1,800 cm-1) and R3 (3,000 - 3,600 cm-1). The carbonyl bond (C=O) was detected in the region R2 of B0-1, B0-4 and B0-6. The area of the carbonyl bond was used for a comparison of the oxidation level 14,15, as the carbonyl peak at 1,710 cm-1 increases with the oxidation level. This peak is attributed to the formation of polar products such as aldehydes, ketones, acids. The peak in the region R3 shows the formation of (OH) functional groups, indicating the presence of alcohols and acids.
<img alt="Figure 8" src="/files/ftp_upload/54361/54361fig8.jpg" /> 
Figure 8. FTIR spectra for B0 and oxidized B0 samples in reactor 2 following 1, 4 and 6 oxidation cycles.&#160;Overall comparison of the FTIR spectra of fresh and oxidized B0 on a wide wavelength range (600 - 3,800 cm-1) presenting the variation of the absorbance signal associated with the oxidation. This figure has been reprinted with permission from8, Copyright 2015 American Chemical Society. <a href="https://www.jove.com/files/ftp_upload/54361/54361fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
In summary, the AOP applied here to the oxidation of commercial diesel and biodiesel allowed to monitor the global oxidation rate of these fuels and the formation of several polar oxygenated compounds throughout the oxidation process on a wide molecular weight range. According to the FTIR results on B0 fuel, a small amount of carbonyl products, mainly ketones and aldehydes, are formed after the first oxidation cycle (B0-1). After 6 oxidation cycles (B0-6), the brownish and more viscous sample indicates a more severe oxidation level. The FTIR analysis provides further knowledge on the main functional groups present, including polar oxidation products such as alcohols, acids and lactones. A higher oxidation rate was observed on RME compared to B0. FTIR results on RME show the conversion of unsaturated molecules (peak at 3,010 cm-1) and the formation of polar oxidation products. Thus, suggesting that unsaturated molecules in RME are driving the oxidation process and leading to a higher oxidation rate compared with B0.

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Original Experimental Approach for Assessing Transport Fuel Stability

Oxidation stability of transport fuels has become a concern for future fuel development. This work presents an original methodology developed by IFP Energies Nouvelles for assessing fuel stability using two different reactors. This methodology was successfully applied to gain an in-depth understanding of the oxidation kinetics and pathways of model molecules and commercial fuels.

The study of fuel oxidation stability is an important issue for the development of future fuels. Diesel and kerosene fuel systems have undergone several ...

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9.3K Views.  Institut de Science des Matériaux de Mulhouse. Oxidation stability of transport fuels has become a concern for future fuel development. This work presents an original methodology developed by IFP Energies Nouvelles for assessing fuel stability using two different reactors. This methodology was successfully applied to gain an in-depth understanding of the oxidation kinetics and pathways of model molecules and commercial fuels.

Video: Original Experimental Approach for Assessing Transport Fuel Stability

Biomass Conversion to Produce Hydrocarbon Liquid Fuel Via Hot-vapor Filtered Fast Pyrolysis and Catalytic Hydrotreating

Lignocellulosic biomass conversion to produce biofuels has received significant attention because of the quest for a replacement for fossil fuels. Among the various thermochemical and biochemical routes, fast pyrolysis followed by catalytic hydrotreating is considered to be a promising near-term opportunity. This paper reports on experimental methods used 1) at the National Renewable Energy Laboratory (NREL) for fast pyrolysis of lignocellulosic biomass to produce bio-oils in a fluidized-bed reactor and 2) at Pacific Northwest National Laboratory (PNNL) for catalytic hydrotreating of bio-oils in a two-stage, fixed-bed, continuous-flow catalytic reactor. The configurations of the reactor systems, the operating procedures, and the processing and analysis of feedstocks, bio-oils, and biofuels are described in detail in this paper. We also demonstrate hot-vapor filtration during fast pyrolysis to remove fine char particles and inorganic contaminants from bio-oil. Representative results showed successful conversion of biomass feedstocks to fuel-range hydrocarbon biofuels and, specifically, the effect of hot-vapor filtration on bio-oil production and upgrading. The protocols provided in this report could help to generate rigorous and reliable data for biomass pyrolysis and bio-oil hydrotreating research.

Experimental methods for fast pyrolysis of lignocellulosic biomass to produce bio-oils and for the catalytic hydrotreating of bio-oils to produce fuel range hydrocarbons are presented. Hot-vapor filtration during fast pyrolysis to remove fine char particles and inorganic contaminants from bio-oil was also assessed.

Lignocellulosic biomass conversion to produce biofuels has received significant attention because of the quest for a replacement for fossil fuels. Among ...

Biochemistry

Laboratory Production of Biofuels and Biochemicals from a Rapeseed Oil through Catalytic Cracking Conversion

The work is based on a reported study which investigates the processability of canola oil (bio-feed) in the presence of bitumen-derived heavy gas oil (HGO) for production of transportation fuels through a fluid catalytic cracking (FCC) route. Cracking experiments are performed with a fully automated reaction unit at a fixed weight hourly space velocity (WHSV) of 8 hr-1, 490-530 &#176;C, and catalyst/oil ratios of 4-12 g/g. When a feed is in contact with catalyst in the fluid-bed reactor, cracking takes place generating gaseous, liquid, and solid products. The vapor produced is condensed and collected in a liquid receiver at -15 &#176;C. The non-condensable effluent is first directed to a vessel and is sent, after homogenization, to an on-line gas chromatograph (GC) for refinery gas analysis. The coke deposited on the catalyst is determined in situ by burning the spent catalyst in air at high temperatures. Levels of CO2 are measured quantitatively via an infrared (IR) cell, and are converted to coke yield. Liquid samples in the receivers are analyzed by GC for simulated distillation to determine the amounts in different boiling ranges, i.e., IBP-221 &#176;C (gasoline), 221-343 &#176;C (light cycle oil), and 343 &#176;C+ (heavy cycle oil). Cracking of a feed containing canola oil generates water, which appears at the bottom of a liquid receiver and on its inner wall. Recovery of water on the wall is achieved through washing with methanol followed by Karl Fischer titration for water content. Basic results reported include conversion (the portion of the feed converted to gas and liquid product with a boiling point below 221 &#176;C, coke, and water, if present) and yields of dry gas (H2-C2's, CO, and CO2), liquefied petroleum gas (C3-C4), gasoline, light cycle oil, heavy cycle oil, coke, and water, if present.

This paper presents an experimental method to produce biofuels and biochemicals from canola oil mixed with a fossil-based feed in the presence of a catalyst at mild temperatures. Gaseous, liquid, and solid products from a reaction unit are quantified and characterized. Conversion and individual product yields are calculated and reported.

The work is based on a reported study which investigates the processability of canola oil (bio-feed) in the presence of bitumen-derived heavy gas oil ...

Experimental Methodology for Estimation of Local Heat Fluxes and Burning Rates in Steady Laminar Boundary Layer Diffusion Flames

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex interactions occurring at the interface between gas-phase flames and condensed-phase fuels. The current research provides a technique to explore the dynamic relationship between a combustible condensed fuel surface and gas-phase flames in laminar boundary layers. Experiments have previously been conducted in both forced and free convective environments over both solid and liquid fuels. A unique methodology, based on the Reynolds Analogy, was used to estimate local mass burning rates and flame heat fluxes for these laminar boundary layer diffusion flames utilizing local temperature gradients at the fuel surface. Local mass burning rates and convective and radiative heat feedback from the flames were measured in both the pyrolysis and plume regions by using temperature gradients mapped near the wall by a two-axis traverse system. These experiments are time-consuming and can be challenging to design as the condensed fuel surface burns steadily for only a limited period of time following ignition. The temperature profiles near the fuel surface need to be mapped during steady burning of a condensed fuel surface at a very high spatial resolution in order to capture reasonable estimates of local temperature gradients. Careful corrections for radiative heat losses from the thermocouples are also essential for accurate measurements. For these reasons, the whole experimental setup needs to be automated with a computer-controlled traverse mechanism, eliminating most errors due to positioning of a micro-thermocouple. An outline of steps to reproducibly capture near-wall temperature gradients and use them to assess local burning rates and heat fluxes is provided.

We describe the use of micro-thermocouples to estimate local temperature gradients in steady laminar boundary layer diffusion flames. By extension of the Reynolds Analogy, local temperature gradients can be further used to estimate the local mass burning rates and heat fluxes in such flames with high accuracy.

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex ...

Engineering

Metal Corrosion and the Efficiency of Corrosion Inhibitors in Less Conductive Media

Material corrosion can be a limiting factor for different materials in many applications. Thus, it is necessary to better understand corrosion processes, prevent them and minimize the damages associated with them. One of the most important characteristics of corrosion processes is the corrosion rate. The measurement of corrosion rates is often very difficult or even impossible especially in less conductive, non-aqueous environments such as biofuels. Here, we present five different methods for the determination of corrosion rates and the efficiency of anti-corrosion protection in biofuels: (i) a static test, (ii) a dynamic test, (iii) a static test with a reflux cooler and electrochemical measurements (iv) in a two-electrode arrangement and (v) in a three-electrode arrangement. The static test is advantageous due to its low demands on material and instrumental equipment. The dynamic test allows for the testing of corrosion rates of metallic materials at more severe conditions. The static test with a reflux cooler allows for the testing in environments with higher viscosity (e.g., engine oils) at higher temperatures in the presence of oxidation or an inert atmosphere. The electrochemical measurements provide a more comprehensive view on corrosion processes. The presented cell geometries and arrangements (the two-electrode and three-electrode systems) make it possible to perform measurements in biofuel environments without base electrolytes that could have a negative impact on the results and load them with measurement errors. The presented methods make it possible to study the corrosion aggressiveness of an environment, the corrosion resistance of metallic materials, and the efficiency of corrosion inhibitors with representative and reproducible results. The results obtained using these methods can help to understand corrosion processes in more detail to minimize the damages caused by corrosion.

The testing of processes associated with material corrosion can often be difficult especially in non-aqueous environments. Here, we present different methods for short-term and long-term testing of corrosion behavior of non-aqueous environments such as biofuels, especially those containing bioethanol.

Material corrosion can be a limiting factor for different materials in many applications. Thus, it is necessary to better understand corrosion processes, ...

Environment

Fluorescent Paper Strips for the Detection of Diesel Adulteration with Smartphone Read-out

Three fluorescent molecular rotors of 4-dimethylamino-4-nitrostilbene (4-DNS) were investigated for their potential use as viscosity probes to indicate the content of kerosene in diesel/kerosene blends, a wide-spread activity to adulterate fuel. In solvents with low viscosity, the dyes rapidly deactivate via a so-called twisted intramolecular charge transfer state, efficiently quenching the fluorescence. Measurements of diesel/kerosene blends revealed a good linear correlation between the decrease in fluorescence and the increase of the fraction of the less viscous kerosene in diesel/kerosene blends. Immobilization of the hydroxy derivative 4-DNS-OH in cellulose paper yielded test strips that preserve the fluorescent indicator&#39;s behavior. Combination of the strips with a reader based on a smartphone and a controlling app allowed to create a simple field test. The method can reliably detect the presence of kerosene in diesel from 7 to 100%, outperforming present standard methods for diesel adulteration.

Here, we present a protocol to detect the adulteration of diesel with kerosene using test strips coated with a fluorescent viscosity probe together with a smartphone-based analysis system.

Three fluorescent molecular rotors of 4-dimethylamino-4-nitrostilbene (4-DNS) were investigated for their potential use as viscosity probes to indicate ...

Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power generation and micro combustion as well as development in fuel cell research has created new means of power generation that combine solid oxide fuel cells with open flames and combustion exhaust. Instead of relying upon the heat of combustion, these solid oxide fuel cell systems rely on reforming of the fuel via combustion to generate syngas for electrochemical power generation. Procedures were developed to assess the combustion by-products under a wide range of conditions. While theoretical and computational procedures have been developed for assessing fuel-rich combustion exhaust in these applications, experimental techniques have also emerged. The experimental procedures often rely upon a gas chromatograph or mass spectrometer analysis of the flame and exhaust to assess the combustion process as a fuel reformer and means of heat generation. The experimental techniques developed in these areas have been applied anew for the development of the micro-tubular flame-assisted fuel cell. The protocol discussed in this work builds on past techniques to specify a procedure for characterizing fuel-rich combustion exhaust and developing a model fuel-rich combustion exhaust for use in flame-assisted fuel cell testing. The development of the procedure and its applications and limitations are discussed.

A protocol for creating a model fuel-rich combustion exhaust is developed through combustion characterization and is applied for micro-tubular flame-assisted fuel cell testing and research.

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In Situ Visualization of the Phase Behavior of Oil Samples Under Refinery Process Conditions

To help address production issues in refineries caused by the fouling of process units and lines, we have developed a setup as well as a method to visualize the behavior of petroleum samples under process conditions. The experimental setup relies on a custom-built micro-reactor fitted with a sapphire window at the bottom, which is placed over the objective of an inverted microscope equipped with a cross-polarizer module. Using reflection microscopy enables the visualization of opaque samples, such as petroleum vacuum residues, or asphaltenes. The combination of the sapphire window from the micro-reactor with the cross-polarizer module of the microscope on the light path allows high-contrast imaging of isotropic and anisotropic media. While observations are carried out, the micro-reactor can be heated to the temperature range of cracking reactions (up to 450 &#176;C), can be subjected to H2 pressure relevant to hydroconversion reactions (up to 16 MPa), and can stir the sample by magnetic coupling. 
Observations are typically carried out by taking snapshots of the sample under cross-polarized light at regular time intervals. Image analyses may not only provide information on the temperature, pressure, and reactive conditions yielding phase separation, but may also give an estimate of the evolution of the chemical (absorption/reflection spectra) and physical (refractive index) properties of the sample before the onset of phase separation.

In Situ Visualization of the Phase Behavior of Oil Samples Under Refinery Process Conditions

This article describes a setup and method for the in situ visualization of oil samples under a variety of temperature and pressure conditions that aim to emulate refining and upgrading processes. It is primarily used for studying isotropic and anisotropic media involved in the fouling behavior of petroleum feeds.

To help address production issues in refineries caused by the fouling of process units and lines, we have developed a setup as well as a method to ...

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This flexible tool offers a detailed observation of chemical gas-phase kinetics in reacting flows under well-controlled conditions. The vast range of operating conditions available in a laminar flow reactor enables access to extraordinary combustion applications that are typically not achievable by flame experiments. These include rich conditions at high temperatures relevant for gasification processes, the peroxy chemistry governing the low temperature oxidation regime or investigations of complex technical fuels. The presented setup allows measurements of quantitative speciation data for reaction model validation of combustion, gasification and pyrolysis processes, while enabling a systematic general understanding of the reaction chemistry. Validation of kinetic reaction models is generally performed by investigating combustion processes of pure compounds. The flow reactor has been enhanced to be suitable for technical fuels (e.g. multi-component mixtures like Jet A-1) to allow for phenomenological analysis of occurring combustion intermediates like soot precursors or pollutants. The controlled and comparable boundary conditions provided by the experimental design allow for predictions of pollutant formation tendencies. Cold reactants are fed premixed into the reactor that are highly diluted (in around 99 vol% in Ar) in order to suppress self-sustaining combustion reactions. The laminar flowing reactant mixture passes through a known temperature field, while the gas composition is determined at the reactors exhaust as a function of the oven temperature. The flow reactor is operated at atmospheric pressures with temperatures up to 1,800 K. The measurements themselves are performed by decreasing the temperature monotonically at a rate of -200 K/h. With the sensitive MBMS technique, detailed speciation data is acquired and quantified for almost all chemical species in the reactive process, including radical species.

An investigation of the oxidative combustion chemistry of novel biofuels, fuel components, or jet fuels by comparison of quantitative speciation data is presented. The data can be used for kinetic model validation and enables fuel assessment strategies.This manuscript describes the atmospheric high-temperature flow reactor and demonstrates its capabilities.

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This ...

Experimental Procedure for Laboratory Studies of In Situ Burning : Flammability and Burning Efficiency of Crude Oil

A new method for the simultaneous study of the flammability and burning efficiency of fresh and weathered crude oil through two experimental laboratory setups is presented. The experiments are easily repeatable compared to operational scale experiments (pool diameter &#8805;2 m), while still featuring quite realistic in situ burning conditions of crude oil on water. Experimental conditions include a flowing water sub-layer that cools the oil slick and an external heat flux (up to 50 kW/m2) that simulates the higher heat feedback to the fuel surface in operational scale crude oil pool fires. These conditions enable a controlled laboratory study of the burning efficiency of crude oil pool fires that are equivalent to operational scale experiments. The method also provides quantitative data on the requirements for igniting crude oils in terms of the critical heat flux, ignition delay time as a function of the incident heat flux, the surface temperature upon ignition, and the thermal inertia. This type of data can be used to determine the required strength and duration of an ignition source to ignite a certain type of fresh or weathered crude oil. The main limitation of the method is that the cooling effect of the flowing water sub-layer on the burning crude oil as a function of the external heat flux has not been fully quantified. Experimental results clearly showed that the flowing water sub-layer does improve how representative this setup is of in situ burning conditions, but to what extent this representation is accurate is currently uncertain. The method nevertheless features the most realistic in situ burning laboratory conditions currently available for simultaneously studying the flammability and burning efficiency of crude oil on water.

Experimental Procedure for Laboratory Studies of In Situ Burning : Flammability and Burning Efficiency of Crude Oil

Here, we present a protocol to simultaneously study the flammability and burning efficiency of fresh and weathered crude oil under conditions that simulate in situ burning operations on the sea.

A new method for the simultaneous study of the flammability and burning efficiency of fresh and weathered crude oil through two experimental laboratory ...

Nitrogen Compound Characterization in Fuels by Multidimensional Gas Chromatography

Certain nitrogen-containing compounds can contribute to fuel instability during storage. Hence, detection and characterization of these compounds is crucial. There are significant challenges to overcome when measuring trace compounds in a complex matrix such as fuels. Background interferences and matrix effects can create limitations to routine analytical instrumentation, such as GC-MS. In order to facilitate specific and quantitative measurements of trace nitrogen compounds in fuels, a nitrogen-specific detector is ideal. In this method, a nitrogen chemiluminescence detector (NCD) is used to detect nitrogen compounds in fuels. NCD utilizes a nitrogen-specific reaction that does not involve the hydrocarbon background. Two-dimensional (GCxGC) gas chromatography is a powerful characterization technique as it provides superior separation capabilities to one-dimensional gas chromatography methods. When GCxGC is paired with a NCD, the problematic nitrogen compounds found in fuels can be extensively characterized without background interference. The method presented in this manuscript details the process for measuring different nitrogen-containing compound classes in fuels with little sample preparation. Overall, this GCxGC-NCD method has been shown to be a valuable tool to enhance the understanding of the chemical composition of nitrogen-containing compounds in fuels and their impact on fuel stability. The % RSD for this method is &#60;5% for intraday and &#60;10% for interday analyses; the LOD is 1.7 ppm and the LOQ is 5.5 ppm.

Here, we present a method utilizing two-dimensional gas chromatography and nitrogen chemiluminescence detection (GCxGC-NCD) to extensively characterize the different classes of nitrogen-containing compounds in diesel and jet fuels.

Certain nitrogen-containing compounds can contribute to fuel instability during storage. Hence, detection and characterization of these compounds is ...

Original Experimental Approach for Assessing Transport Fuel Stability

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Chapters in this video

Biomass Conversion to Produce Hydrocarbon Liquid Fuel Via Hot-vapor Filtered Fast Pyrolysis and Catalytic Hydrotreating

Laboratory Production of Biofuels and Biochemicals from a Rapeseed Oil through Catalytic Cracking Conversion

Experimental Methodology for Estimation of Local Heat Fluxes and Burning Rates in Steady Laminar Boundary Layer Diffusion Flames

Metal Corrosion and the Efficiency of Corrosion Inhibitors in Less Conductive Media

Fluorescent Paper Strips for the Detection of Diesel Adulteration with Smartphone Read-out

Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells

In Situ Visualization of the Phase Behavior of Oil Samples Under Refinery Process Conditions

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer

Experimental Procedure for Laboratory Studies of In Situ Burning : Flammability and Burning Efficiency of Crude Oil

Nitrogen Compound Characterization in Fuels by Multidimensional Gas Chromatography