Determination of sulfur-containing compounds in diesel oils by comprehensive two-dimensional gas chromatography with a sulfur chemiluminescence detector

Opportunities and challenges for the application of post-consumer plastic waste pyrolysis oils as steam cracker feedstocks: To decontaminate or not to decontaminate?

Thermochemical recycling of plastic waste to base chemicals via pyrolysis followed by a minimal amount of upgrading and steam cracking is expected to be the dominant chemical recycling technology in the coming decade. However, there are substantial safety and operational risks when using plastic waste pyrolysis oils instead of conventional fossil-based feedstocks. This is due to the fact that plastic waste pyrolysis oils contain a vast amount of contaminants which are the main drivers for corrosion, fouling and downstream catalyst poisoning in industrial steam cracking plants. Contaminants are therefore crucial to evaluate the steam cracking feasibility of these alternative feedstocks. Indeed, current plastic waste pyrolysis oils exceed typical feedstock specifications for numerous known contaminants, e.g. nitrogen (∼1650 vs. 100 ppm max.), oxygen (∼1250 vs. 100 ppm max.), chlorine (∼1460vs. 3 ppm max.), iron (∼33 vs. 0.001 ppm max.), sodium (∼0.8 vs. 0.125 ppm max.)and calcium (∼17vs. 0.5 ppm max.). Pyrolysis oils produced from post-consumer plastic waste can only meet the current specifications set for industrial steam cracker feedstocks if they are upgraded, with hydrogen based technologies being the most effective, in combination with an effective pre-treatment of the plastic waste such as dehalogenation. Moreover, steam crackers are reliant on a stable and predictable feedstock quality and quantity representing a challenge with plastic waste being largely influenced by consumer behavior, seasonal changes and local sorting efficiencies. Nevertheless, with standardization of sorting plants this is expected to become less problematic in the coming decade.

Detailed kinetic model for hexyl sulfide pyrolysis and its desulfurization by supercritical water

The automated reaction mechanism generator is used to model the decomposition of hexyl sulfide with and without supercritical water.

Elemental sulfur in sediments: analytical problems

In the paper, a modified method for elemental sulfur (S₈) determining using gas chromatography coupled with mass spectrometry (GC-MS) is proposed with estimation of selected validation parameters. The aim of this work was a review of problems associated with the determination of S₈ and selection of the most optimal conditions for S₈ analysis with GC-MS. The presented studies have shown that the temperature of the injector and the chromatographic column during S₈ determination should not exceed 180 °C. At temperatures over 180 °C, the sulfur S₈ is decomposed to the other sulfur species such as S₂, S₃, S₄, S₅, and S₆. During decreasing injector and column temperature below 180 °C the chromatographic peak eluted as S₈ is badly extended and asymmetric. To minimize the problems of S₈ decomposition to other sulfur species during chromatographic process also other parameters of the GC-MS have been selected. In order to apply the proposed method for real sediments samples, determination of sulfur S₈ in bottom sediments, collected in the Gulf of Gdansk (southern Baltic Sea), has been performed. The concentration of S₈ fell in the range from below the limit of detection to 0.1432 ± 0.0095 mg/g d.w. The research has also shown that addition of approx. 200 mg of activated copper is effective for removing sulfur from bottom sediment extracts.

Simultaneous chemiluminescence determination of citric acid and oxalic acid using multi-way partial least squares regression

A novel kinetic chemiluminescent method proposed for the simultaneous determination of oxalic acid and citric acid in their mixtures.

Multidimensional gas chromatography in combination with accurate mass, tandem mass spectrometry, and element-specific detection for identification of sulfur compounds in tobacco smoke

A method is developed for identification of sulfur compounds in tobacco smoke extract. The method is based on large volume injection (LVI) of 10μL of tobacco smoke extract followed by selectable one-dimensional ((1)D) or two-dimensional ((2)D) gas chromatography (GC) coupled to a hybrid quadrupole time-of-flight mass spectrometer (Q-TOF-MS) using electron ionization (EI) and positive chemical ionization (PCI), with parallel sulfur chemiluminescence detection (SCD). In order to identify each individual sulfur compound, sequential heart-cuts of 28 sulfur fractions from (1)D GC to (2)D GC were performed with the three MS detection modes (SCD/EI-TOF-MS, SCD/PCI-TOF-MS, and SCD/PCI-Q-TOF-MS). Thirty sulfur compounds were positively identified by MS library search, linear retention indices (LRI), molecular mass determination using PCI accurate mass spectra, formula calculation using EI and PCI accurate mass spectra, and structure elucidation using collision activated dissociation (CAD) of the protonated molecule. Additionally, 11 molecular formulas were obtained for unknown sulfur compounds. The determined values of the identified and unknown sulfur compounds were in the range of 10-740ngmg total particulate matter (TPM) (RSD: 1.2-12%, n=3).

Sulfur 1s near edge x-ray absorption fine structure spectroscopy of thiophenic and aromatic thioether compounds

Thiophenic compounds are major constituents of fossil fuels and pose problems for fuel refinement. The quantification and speciation of these compounds is of great interest in different areas such as biology, fossil fuels studies, geology, and archaeology. Sulfur 1s Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy has emerged as a qualitative and quantitative method for sulfur speciation. A firm understanding of the sulfur 1s NEXAFS spectra of organosulfur species is required for these analytical studies. To support this development, the sulfur 1s NEXAFS spectra of simple thiols and thioethers were previously examined, and are now extended to studies of thiophenic and aromatic thioether compounds, in the gas and condensed phases. High-resolution spectra have been further analyzed with the aid of Improved Virtual Orbital (IVO) and Δ(self-consistent field) ab initio calculations. Experimental sulfur 1s NEXAFS spectra show fine features predicted by calculation, and the combination of experiment and calculation has been used to improve the assignment of spectroscopic features important for the speciation and quantification of sulfur compounds. Systematic differences between gas and condensed phases are also explored; these differences suggest a significant role for conformational effects in the NEXAFS spectra of condensed species.

Studies on thermionic ionisation detection in comprehensive two-dimensional gas chromatography

This study explores the application of specific thermionic ionisation detection in comprehensive 2-D GC (GC x GC) and represents the first report of GC x GC with nitrogen phosphorus detection (GC x GC-NPD). Of particular interest is the performance of the NPD with respect to peak parameters of asymmetry and sensitivity. Since GC x GC produces much narrower peaks than obtained with fast GC (e.g. 100 ms vs. <1 s) the effect of detector response time and any lack of symmetry arising from the detection step is important if peak separation (resolution) is to be maintained. It was observed that detector gas flows had a significant impact on peak asymmetry and peak magnitude, and that optimisation of the detector was critical, particularly for complex sample analysis by GC x GC-NPD. Peak asymmetries ranging from As = 1.8 to 8.0 were observed under different conditions of detector gas flows. Comparison of GC x GC-NPD with GC x GC-flame ionisation detection (FID) showed the former to be approximately 20 times more sensitive for the detection of nitrogen-containing methoxypyrazines analytes, and GC x GC-NPD had a larger linear detection range compared to GC x GC-FID. Furthermore, comparison of GC x GC-NPD and GC x GC-TOFMS chromatograms for the analysis of coffee head-space demonstrated the benefits of selective detection, ultimately realised in a comparatively simplified contour plot.

Application of comprehensive two-dimensional gas chromatography with nitrogen-selective detection for the analysis of fungicide residues in vegetable samples

Comprehensive two-dimensional gas chromatography (GCxGC) with nitrogen-phosphorus detection (NPD) has been investigated for the separation and quantitation of fungicides in vegetable samples. The detector gas flows (H(2), N(2) and air) were adjusted to achieve maximum response of signal whilst minimizing peak width. The comparison of different column sets and selection of the temperature program were carried out with a mixture of nine N-containing standard fungicides, eight of which were chlorinated. The results from GCxGC-NPD and GCxGC with micro electron-capture detection (muECD) were compared. External calibrations of fungicides were performed over a concentration range from 1 to 1,000 microgL(-1). The peak area calibration curves generally had regression coefficients of R(2)>0.9980, however for iprodione which was observed to undergo on-column degradation, an R(2) of 0.990 was found. The limit of detection (LOD) and limit of quantitation (LOQ) were less than about 74 and 246 ng L(-1), respectively. The intra-day and inter-day RSD values were measured for solutions of concentration 0.100, 0.500 and 1.50 mg L(-1). For the 0.500 mg L(-1) solution, intra- and inter-day precision of peak area and peak height for most of the pesticides were about 2% and 8%, respectively. Excellent linearity was observed for these standards, from 0.001 to 25.00 mg L(-1). The standard mixture peak positions were identified by using GCxGC with quadrupole mass spectrometry (qMS). To illustrate the potential and the versatility of both GCxGC-NPD and GCxGC-muECD, the method was applied to determination of fungicides in a vegetable extract. Decomposition of one fungicide standard (iprodione) during chromatography elution was readily observed in the two-dimensional (2D) GCxGC plot as a diagonal ridge response in the 2D chromatogram between the degrading compound and the decomposition product.