The SBO project &#8220;Bioleum&#8221; (IWT-SBO 130039) supported by the Institute for Promotion of Innovation through Science and Technology in Flanders (IWT) and the &#8216;Long Term Structural Methusalem Funding by the Flemish Government&#8217; are acknowledged.

Caution: Please consult relevant material safety data sheets (MSDS) of all compounds before use. Appropriate safety practices are recommended. Solutions and samples should be prepared in the fume hood, while using personal protective equipment. Best practice implies use of safety glasses, protection laboratory gloves, lab coat, full length pants, and closed-toe shoes. The reactor should be properly sealed as several reactants and reaction products can be acutely toxic and carcinogenic.
1. Offline GC &#215; GC&#8211;...

The described experimental procedures enabled a successful comprehensive off-line and on-line identification and quantification of nitrogen containing compounds in the studied samples.
The separation of nitrogen containing compounds in shale oil was accomplished using GC &#215; GC&#8211;NCD, as shown in Figure 3. Since the NCD cannot be used for identification, the retention times of the observed species need to be established in advance by carrying out analyses on the GC &#21...

The reserves of light sweet crude oils are gradually diminishing, and hence, alternative fossil resources are being considered to be used in the energy and petrochemical industry. In addition, renewables such as bio-oils produced by fast pyrolysis of biomass are becoming a more attractive resources of bio-based fuels and chemicals. Nevertheless, heavy crude oil is a logical first choice because of the large proven reserves in Canada and Venezuela1-3. The latter are being recognized as the largest crude oil reserves in the world and their composition is similar to the composition of natural bitumen. Similar to bio-oils, heavy crude oils differ from light crude oils by their high viscosity at reservoir temperatures, high density (low API gravity), and significant contents of nitrogen, oxygen, and sulfur containing compounds4,5. Another promising alternative is shale oil, derived from oil shale. Oil shale is a fine-grained sedimentary rock containing kerogen, a mixture of organic chemical compounds with a molar mass as high as 1,000 Da6. Kerogen can contain organic oxygen, nitrogen, and sulfur in the hydrocarbon matrix; depending on the origin, age, and the extraction conditions. Global characterization methods have shown that the concentration of heteroatoms (S, O and N) in shale oil and heavy crude oils is typically substantially higher than the specifications set for the products used in for example the petrochemical industry6. It is well documented that nitrogen containing compounds present in heavy conventional crude oil and shale oil have a negative effect on the catalyst activity in hydrocracking, catalytic cracking and reforming processes7. Similarly, it has been reported that the presence of nitrogen containing compounds are a safety concern because they promote gum formation in the cold-box of a steam cracker8.
These processing and safety challenges are a strong driver to improve the current methods for off-line and on-line characterization of nitrogen containing compounds in complex hydrocarbon matrices. Two-dimensional gas chromatography (GC &#215; GC) coupled with a nitrogen chemiluminescence detector (NCD) is a superior characterization technique compared to one-dimensional gas chromatography (GC) for analyzing conventional diesels or liquefied coal samples7. Recently a method has been developed and applied to the offline characterization of nitrogen content in shale oil6, the identification of extracted nitrogen compounds present in middle distillates9, and the determination of the detailed composition of plastic waste pyrolysis oil10.
It is thus clear that GC &#215; GC analysis is a powerful offline processing technique for analyzing complex mixtures11-17. However, on-line application is more challenging due to the need for a reliable and non-discriminating sampling methodology. One of the first developed methodologies for comprehensive on-line characterization was demonstrated by analyzing steam cracking reactor effluents using a TOF-MS and a FID18. The optimization of the GC settings and an appropriate column combination enabled analysis of samples consisting of hydrocarbons ranging from methane up to polyaromatic hydrocarbons (PAHs)18. The present work takes this method to a new level by extending it to the identification and quantification of nitrogen compounds present in the complex hydrocarbon mixtures. Such a method is among others needed to improve fundamental understanding of the role these compounds play in several processes and applications. To the authors&#39; best knowledge, information concerning kinetics of conversion processes of nitrogen containing compounds is scarce19, partly due to the lack of an adequate method to identify and quantify nitrogen containing compounds in the reactor effluent. Establishing the methodology for offline and on-line analyses is thus a prerequisite before one can even attempt feedstock reconstruction20-27 and kinetic modeling. One of the fields which would benefit from the accurate identification and quantification of nitrogen containing compounds is steam cracking or pyrolysis. Bio and heavy fossil feeds for steam cracking or pyrolysis reactors contain thousands of hydrocarbons and compounds that contain heteroatoms. Moreover, because of the complexity of the feed and the radical nature of the occurring chemistry, ten thousands of reactions can occur among the thousands free radical species28, which makes the reactor effluent even more complex than the starting material.
In hydrocarbon mixtures nitrogen is mainly present in aromatic structures, e.g., as pyridine or pyrrole; hence most experimental efforts have been dedicated to the decomposition of these structures. Hydrogen cyanide and ethyne were reported as major products for the thermal decomposition of pyridine studied in a temperature range of 1,148-1,323 K. Other products such as aromatics and nonvolatile tars were also detected in minor quantities29. The thermal decomposition of pyrrole was investigated in a broader temperature range of 1,050-1,450 K using shock wave experiments. The main products were 3-butenenitrile, cis and trans 2-butenenitrile, hydrogen cyanide, acetonitrile, 2-propenenitrile, propanenitrile, and propiolonitrile30. Additionally thermal decomposition shock tube experiments were performed for pyridine at elevated temperatures resulting in comparable product spectra31,32. Product yields in these studies have been determined by applying GC&#39;s equipped with a FID, a nitrogen-phosphorus detector (NPD)31, a mass spectrometer (MS)32 and a Fourier transform infrared (FTIR) spectrometer32. A similar methodology implementing the FID and the NPD was applied to analyze the shale oil pyrolysis products in a continuous flow reactor8. Using a cold trap at 273.15 K and GC-MS, Winkler et al. 33 showed that during pyridine pyrolysis heteroatom-containing aromatic compounds are formed. Zhang et al.34 and Debono et al.35 applied the method of Winkler et al. for studying the pyrolysis of organic waste. The nitrogen rich reaction products were analyzed on-line, using a GC coupled to a thermal conductivity detector (TCD)34. The collected tars were analyzed offline using GC-MS34,35. Simultaneous pyrolysis of toluene and pyridine showed a difference in soot formation tendency compared to pyridine pyrolysis, indicating the complex nature of the free-radical reactions31,36.
One of the most comprehensive analytical methodologies was developed by Nathan and co-workers37. They used FTIR, nuclear magnetic resonance (NMR) and GC-MS for analyzing decomposition products of pyridine and diazine and electron paramagnetic resonance (EPR) spectroscopy for tracing free radical species. FTIR analysis can be a very effective approach for the identification of a large range of products, even PAHs38-40, nevertheless quantification is extremely challenging. Calibration requires a full set of infrared spectra at different concentrations for each target species at a specific temperature and pressure41. Recent work of Hong et al. demonstrated the possibilities of using molecular-beam mass spectrometry (MBMS) and tunable synchrotron vacuum ultraviolet photoionization for determination of products and intermediates during pyrrole and pyridine decomposition42,43. This experimental method enables selective identification of isomeric intermediates and near-threshold detection of radicals without inflicting fragmentation of the analyzed species44. However, the uncertainty on the measured concentrations using MBMS analysis is also substantial.
In this work, first the offline comprehensive characterization results of the complex shale oil are reported. Next, the limitations of using an on-line GC &#215; GC-TOF-MS/FID for the analysis of nitrogen compounds in a complex hydrocarbon matrix are discussed. Finally, the newly developed methodology for the on-line quantification of nitrogen containing compounds by GC &#215; GC&#8211;NCD is demonstrated. The qualitative analysis of products was carried out using TOF-MS, while FID and NCD were used for quantification. The application of the NCD is a substantial improvement compared to using the FID because of its higher selectivity, lower detection limit and equimolar response.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>2-Chloropyridine, 99%</td>
			<td>Sigma Aldrich</td>
			<td>C69802</td>
			<td>Highly toxic</td>
		</tr>
		<tr>
			<td>Shale oil</td>
			<td>Origin Colorado, US</td>
			<td>Piceance Basin in 
			Colorado, USA</td>
			<td>Toxic</td>
		</tr>
		<tr>
			<td>Pyridine, 99.8%</td>
			<td>Sigma Aldrich</td>
			<td>270970</td>
			<td>Highly toxic</td>
		</tr>
		<tr>
			<td>Carbon Dioxide, industrial grade refrigerated liquid</td>
			<td>PRAXAIR</td>
			<td>CDINDLB0D</td>
			<td>Wear safety gloves and glasses</td>
		</tr>
		<tr>
			<td>Helium, 99.99%</td>
			<td>PRAXAIR</td>
			<td>6.0</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrogen, 99.95%</td>
			<td>Air Liquide</td>
			<td>695A-49</td>
			<td>Flammable</td>
		</tr>
		<tr>
			<td>Oxygen</td>
			<td>Air Liquide</td>
			<td>905A-49+</td>
			<td>Flammable</td>
		</tr>
		<tr>
			<td>Air</td>
			<td>Air Liquide</td>
			<td>365A-49X</td>
			<td></td>
		</tr>
		<tr>
			<td>Nitrogen</td>
			<td>Air Liquide</td>
			<td>765A-49</td>
			<td></td>
		</tr>
		<tr>
			<td>Hexane, 95+%</td>
			<td>Chemlab</td>
			<td>CL00.0803.9025</td>
			<td>Toxic</td>
		</tr>
		<tr>
			<td>Heptane, 99+%</td>
			<td>Chemlab</td>
			<td>CL00.0805.9025</td>
			<td>Toxic</td>
		</tr>
		<tr>
			<td>Nitrogen, industrial grade refrigerated liquid</td>
			<td>PRAXAIR</td>
			<td>P0271L50S2A001</td>
			<td>Wear safety gloves and glasses</td>
		</tr>
		<tr>
			<td>Autosampler</td>
			<td>Thermo Scientific, Interscience</td>
			<td>AI/AS 3000</td>
			<td></td>
		</tr>
		<tr>
			<td>High temperature 6 port/2 position valve</td>
			<td>Valco Instruments Company Incorporated</td>
			<td>SSACGUWT</td>
			<td></td>
		</tr>
		<tr>
			<td>Gas chromatograph</td>
			<td>Thermo Scientific, Interscience</td>
			<td>Trace GC ultra</td>
			<td></td>
		</tr>
		<tr>
			<td>Rafinery Gas Analyzer</td>
			<td>Thermo Scientific, Interscience</td>
			<td>KAV00309</td>
			<td></td>
		</tr>
		<tr>
			<td>rtx-1-PONA column</td>
			<td>Restek Pure Chromatography</td>
			<td>10195-146</td>
			<td></td>
		</tr>
		<tr>
			<td>BPX-50 column</td>
			<td>SGE Analytical science</td>
			<td>54741</td>
			<td></td>
		</tr>
		<tr>
			<td>TOF-MS</td>
			<td>Thermo Scientific, Interscience</td>
			<td>Tempus Plus 1.4 SR1 Finnigan</td>
			<td></td>
		</tr>
		<tr>
			<td>NCD</td>
			<td>Agilent Technologgies</td>
			<td>NCD 255</td>
			<td></td>
		</tr>
		<tr>
			<td>Chrom-card</td>
			<td>Thermo Scientific, Interscience</td>
			<td>HyperChrom 2.4.1</td>
			<td></td>
		</tr>
		<tr>
			<td>Xcalibur software</td>
			<td>Thermo Scientific, Interscience</td>
			<td>1.4 SR1</td>
			<td></td>
		</tr>
		<tr>
			<td>Chrom-card software</td>
			<td>Thermo Scientific, Interscience</td>
			<td>HyperChrom 2.7</td>
			<td></td>
		</tr>
		<tr>
			<td>GC image software</td>
			<td>Zoex Corporation</td>
			<td>GC image 2.3</td>
			<td></td>
		</tr>
	</tbody>
</table>

on-line analysis of nitrogen containing compounds in complex hydrocarbon matrixes

The shift to heavy crude oils and the use of alternative fossil resources such as shale oil are a challenge for the petrochemical industry. The composition of heavy crude oils and shale oils varies substantially depending on the origin of the mixture. In particular they contain an increased amount of nitrogen containing compounds compared to the conventionally used sweet crude oils. As nitrogen compounds have an influence on the operation of thermal processes occurring in coker units and steam crackers, and as some species are considered as environmentally hazardous, a detailed analysis of the reactions involving nitrogen containing compounds under pyrolysis conditions provides valuable information. Therefore a novel method has been developed and validated with a feedstock containing a high nitrogen content, i.e., a shale oil. First, the feed was characterized offline by comprehensive two-dimensional gas chromatography (GC &#215; GC) coupled with a nitrogen chemiluminescence detector (NCD). In a second step the on-line analysis method was developed and tested on a steam cracking pilot plant by feeding pyridine dissolved in heptane. The former being a representative compound for one of the most abundant classes of compounds present in shale oil. The composition of the reactor effluent was determined via an in-house developed automated sampling system followed by immediate injection of the sample on a GC &#215; GC coupled with a time-of-flight mass spectrometer (TOF-MS), flame ionization detector (FID) and NCD. A novel method for quantitative analysis of nitrogen containing compounds using NCD and 2-chloropyridine as an internal standard has been developed and demonstrated.

The chromatogram obtained using the offline GC &#215; GC&#8211;NCD for characterization of nitrogen containing compounds in a shale oil sample is given in Figure 3. The following classes were identified: pyridines, anilines, quinolines, indoles, acridines, and carbazoles. Moreover, detailed quantification of the individual compounds was possible. The gathered data was used to determine the individual compound concentrations, and the obtained values are presented in <stron...

Watch this Scientific Journal Video about On-line Analysis of Nitrogen Containing Compounds in Complex Hydrocarbon Matrixes at JoVE.com

On-line Analysis of Nitrogen Containing Compounds in Complex Hydrocarbon Matrixes

A method combining comprehensive two-dimensional gas chromatography with nitrogen chemiluminescence detection has been developed and applied to on-line analysis of nitrogen containing compounds in a complex hydrocarbon matrix.