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 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.
