Name: on-line analysis of nitrogen containing compounds in complex hydrocarbon matrixes
Uploaded: 2016-08-05T13:00:00
Description: Watch this Scientific Journal Video about On-line Analysis of Nitrogen Containing Compounds in Complex Hydrocarbon Matrixes at JoVE.com

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.

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 ...

The overall goal of this experiment is to detect and quantify nitrogen containing compounds in a complex hydrocarbon matrix. This method addresses questions in the field of chemical engineering and petrochemical industry, such as a complete analysis of the effluent stream of a steam cracker or other petrochemical streams. The main advantage of this technique is that it is comprehensive and quantitative.The implications of this technique extend to the detection spectrum of steam tracking products because it provides reliable, quantitative analysis of nitrogen containing compounds in the reactor effluent stream. This method provides insight into the chemistry of nitrogen containing hydrocarbons, but it can also be applied to other processes, such as the fast paralysis of biomass. Generally, researchers new to this method will struggle with challenges related to high temperature sampling.To begin this procedure, weigh two glass vials using an analytical balance and note the measured values. Add approximately 25 milligrams of the internal standard, 2-Chloropyridine, to the first vial. Following this, tare the balance with the first vial and add approximately 1, 100 milligrams of a shale oil sample.Gently shake the vial to mix the mixture. Place the second vial on the balance and tare the balance. Transfer approximately 25 milligrams of the prepared mixture into the second vial, and then add approximately 450 milligrams of the original shale oil sample.Perform the two-dimensional GC-NCD analysis using a two-dimensional GC instrument equipped with a dual stage cryogenic liquid carbon dioxide modulator. First, connect the first dimension non-polar PONA column directly to the second dimension mid-polar BPX50 column. Apply the two dimensional operating conditions optimized for detection of nitrogen containing compounds in shale oil by setting the parameters in the software.For the NCD, set the flow rates at five and 11 milliliters per minute for hydrogen and oxygen respectively, while keeping the burner temperature at 925 degrees Celsius on the detector's dual plasma controller. Next, inject the sample using the auto sampler by starting the analysis via the software. During the online analysis experiment feed heptane and water using a computer controlled rotary pump by setting the flow rate using the programmable logical controller, or PLC and introduce pyridine to the reactor convection section by manually setting the speed of the piston pump.Prior to the reaction section of the furnace evaporate and mix the feed stock in two separately heated zones kept at the temperature of 500 degrees Celsius. Now, impose a temperature profile to the alloyed steel 12.4 meter long and 9 millimeter internal diameter reactor by setting the temperatures in the five heated zones using the PLC. Then add liquid nitrogen inside the GC oven to lower the temperature to minus 40 degrees Celsius.For the NDC, manually set the flow rates at 5 and 11 milliliters per minute for hydrogen and oxygen respectively, while keeping the burner temperature at 925 degrees Celsius. Next, sample the pilot plant effluent on line between 400 and 500 degrees Celsius by first turning the pneumatic six port two way valve to the purging position using the PLC and flushing the sample loop for at least two minutes. Following this, turn the pneumatic six port two way valve to the injection position using the PLC.For internal standard preparation, dissolve two chloropyradine in n hexane and manually stir the mixture. Add the internal standard continuously by pumping the prepared mixture through a capillary transfer line which is centrally positioned in the product stream before the sampling system. The chromatocgram obtained using the offline two-dimensional GC-NCD for characterization of nitrogen containing compounds in shale oil is shown here.Several compounds were identified and their concentrations were determined. The analyzed sample contained 4.21 weight percent of nitrogen containing compounds, mainly belonging to the pyridine class. On line two-dimensional GC tof MS analysis of the reactor affluent during pirolysis of a pyridine heptane mixture was used for identifying the reaction products and establishing the compound retention times for the selected chromatographic conditions.Two-dimensional GC FID analysis was used for determining the reactor affluent composition while using steam as a diluent. The obtained product concentrations are listed here. The on line two-dimensional GC-NCD method was tested at conditions selected to avoid decomposition of pyridine and the pyridine concentration of 819 parts per million weight was measured using the obtained detector response and known internal standard concentration.The relative error of the measurement was less than three percent. The two-dimensional FID and GC NCD chromatograms of a heptane steam cracking experiment with pyridine are show here. Several nitrogen containing compounds were detected and the nitrogen concentration and the reaction affluent was determined to be 124.5 parts per million weight which corresponds to a nitrogen recovery of 98.5 percent.Once mastered this technique can generate accurate results even for trace concentrations of nitrogen containing components. While attempting this procedure, it is important to remember to add an amount of the internal standards that will give a concentration similar to the concentration of detectable products. After its development, this technique paved the way for researchers in the field of chemical kinetics of the paralysis of nitrogen containing hydrocarbons.And this with a substantially higher precision. After watching this video, you should have a good understanding of how to prevent discrimination of high boiling point compounds during on line sampling. The high separation power of a two-dimensional GC combined with a very sensitive and selective detector allow us to go way beyond the state of the art, and it provides results which are quantifiable, accurate and reproducible.Don't forget that working with nitrogen containing compounds can be extremely hazardous. Solutions and samples should be prepared in a ventilated area.

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