5
Figure 2: Scheme of the seven parallel reactor setup coupled to an analytical scale GC instrument. The front inlet of the GC contained GC-GC which heart cut by means of a Deans Switch the permanent gasses to a molesieve column and the TCD detector, while the remaining light fraction was separated and sent to one of the FID detectors. The back inlet contained the GCxGC column setup which included a fl ow modulator and was connected to the second FID.
Experimental
Offl ine GCxGC Offl ine GCxGC was performed using a reversed column set; the 1D column was a DB-17 (10 m x 0.100 mm x 0.20 µm), and the 2D column was a DB-1 (5 m x 0.250 mm x 0.12 µm). Both columns were purchased from Agilent. An Agilent fl ow modulated GCxGC instrument was utilized for these experiments. Injection was performed using the split/splitless inlet of the GC at 0.1 µL SPLIT 1:500 at 280˚C. The injection volume and split ratio were optimised such that the samples were injected without the need for sample preparation/ dilution. Hydrogen was used as the carrier gas for both the fi rst and second dimension separations. The fi rst dimension was operated at 0.2 mL/min (ramped pressure), while the second dimension was operated at 25 mL/ min (constant fl ow). Both the fi rst and second dimension columns were exposed to the same oven program: 30˚C (3 min) –2˚C/min –200˚C (5 min). A forward fl ow modulator was installed between the fi rst and second dimension columns with a modulation time of 7 sec. The signal from the fl ame ionisation detector (FID) was collected at 100 Hz and recorded the signal obtained from the eluent exiting the second dimension column. GC Image Software (v 2.4 and 2.7) purchased from JSB Nederland was used to process the offl ine GCxGC data.
Parallel Reactor
The seven parallel reactor setup was applied for catalyst performance evaluations in a range of chemistries that can feed both liquids and gasses and can operate at pressures up to 100 bar and temperatures up to 700°C (Figure 2). The reactors with their heating blocks were all separately insulated and located in a heated box (typical at 150°C). Gasses were fed to the reactors through the process stream via individual mass fl ow controllers (for each gas and each reactor). Helium was used as an internal standard. The exits of the individual reactors were connected to knock-out pots to condense heavy products, while the gaseous outlet fl ows of the reactors were connected to a sample selection valve to allow for on- line analysis by using GC.
Online GCxGC
Online GCxGC was performed using similar conditions to the offl ine confi guration stated above. Differences between the two systems was limited to the sample introduction. The injector was modifi ed in-house to allow selective injection onto the front and back inlets of the GC from the selected parallel reactor using fi xed loops. A heat traced transfer line was used to connect the selected reactor to the GC. The GCxGC separation focusing on hydrocarbons C7 through C30 was performed using the back inlet, while a different column combination for Heart- cut GC-GC was installed on the front inlet for permanent gasses and hydrocarbons from C2 through C10. To accomplish this, an Agilent CP-Porabond-Q column (30 m x 0.32 mm x 5 µm) was connected to a Deans Switch (also from Agilent), which either directed fl ow to a second FID (hydrocarbons from C2-C10) or performed a heart-cut to an Agilent CP-Molsieve 5A column (15 m x 0.32 mm x 10 µm) connected to a thermal conductivity detector (TCD) for evaluation of the permanent gasses. Agilent OpenLab CDS, EZChrom Edition (version A.04.04),
and GC Project (v 2.4) were used for data interpretation. A schematic of the setup is given in Figure 2.
Results and Discussion
Offl ine GCxGC For quantifi cation of the hydrocarbon content from hydrocarbon streams, method development began on an offl ine GCxGC instrument. While both normal and reversed column sets were evaluated, it was determined that a reversed column set afforded better separation of the different hydrocarbon groupings (i.e. PIONA). The modulation time and temperature program were optimised in order to obtain the best group type separation in the second dimension. The GCxGC plot obtained from FID detection of a hydrocarbon stream analysed using the optimised offl ine conditions is shown in Figure 3.
To confi rm that the GCxGC method provided the same accuracy and precision as the DHA, a comparison study was performed where the same hydrocarbon stream was analysed by both techniques. Five injections per day over three days were made. In order to compare data from two different instruments, total abundance normalisation was performed on the data, which eliminated detector bias. Only compounds that were fully resolved in both the GCxGC and DHA data were chosen for comparison; additionally, elution time (e.g. early, middle, and late eluting), signal intensity (e.g. low, middle, and high signal intensity), and compound class (e.g. paraffi n/
Figure 3: Offl ine GCxGC plot of a hydrocarbon stream using a reversed column set; full separation conditions are given in the experimental. The bands are identifi ed from top to bottom: Paraffi n + Iso-paraffi n, Olefi n, Naphthene, Mono-aromatic, Di-aromatic, Tri-aromatic. The two grey bands correspond to column bleed and are excluded from integration.
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