CHARACTERIZATION OF PHENOLIC COMPOUNDS IN PARTIALLY UPGRADED BIO-OILS BY SFCGC×GC

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Characterization by One-dimensional Gas Chromatography

Gas Chromatography has been widely used for the characterization of coal-derived products. O-FID is probably the first detector one thinks about for oxygen speciation. This detector was created to enable the selective identification of oxygen-containing species in hydrocarbon matrices. It appeared in 1980 and only a few articles mention its use. Most of these papers concern the ASTM D5599 which enables to quantify O-species at concentrations up to 0.1%w/w. The detector is composed of two microreactors and a Flame Ionization Detector installed in series. With this configuration, the oxygenated compounds eluted from the column enter the first reactor (cracking reactor with Pt/Rh catalyst) where they are selectively converted into CO. The methanizer installed downstream then converts this into methane. CH4 is finally detected by the Flame Ionization Detector.
This detection device involves two main limitations as it is not compatible with products containing water and the presence of sulphur (>10ppm) poisons the catalyst. Hence, even if this detection is appealing for oxygen speciation it is understandable that it was never applied to coal-derived matrices. Therefore Atomic Emission Detection and Mass spectrometry are much more widespread and a review of different applications of gas chromatography coupled to these detectors is summarized in Table 1-3.

Selective characterization of oxygenates in coal-derived liquids by GC-AED

A few papers mention the coupling between Gas Chromatography and Atomic Emission Detector (AED) for the analysis of coal-derived products. This device is a multielement detector that can be used to measure up to 23 different elements. GC-AED played an important role in the detection of nitrogen and sulphur species in hydrocarbon matrices [30-32]. Thus, it enabled the identification of benzothiophenes, dibenzothiophenes, indols, and carbazoles in coal–derived liquids. Applications to oxygenated compounds have not been as widespread and concern mainly the petroleum field. However, Murti et al. in 2002, and in 2005 used this selective tool to analyze kerosene-gas oil cuts respectively derived from the liquefaction of a sub-bituminous coal and South Banko coal [10, 25]. They highlighted the presence of many oxygenated compounds: alkylated phenols, benzofurans, naphthols and dibenzofurans [10, 25] (Figure 1-2).
Quantification could also be established for O-species which represent 3.7% of the fraction compared to 677ppm for S-species, 8400ppm for N-species, and 84.97%w/w for hydrocarbons. Among detected oxygenated compounds, phenols content is 51.16%w/w, compared to 33.07 %w/w for benzofurans, and 8.23 %w/w for dibenzofurans. Only 5.12% of oxygenated compounds are unknown which involves that phenols and benzofurans are the most predominant oxygen containing compounds. Bartle et al. also demonstrated in 2009 the potential of GC-AED for the analysis of oxygen-containing polycyclic aromatic compounds in coal-derived liquids [25]. Figure 1-3 shows the identified oxygenated species in an oil obtained from Samca coal treatment at 400 °C with a process-derived hydrogen donor solvent. It emphasizes the presence of dibenzofuran and its alkylated derivatives. Quantification was performed using a parent of benzonaphthofuran as an external standard. Oxygenated Poly Aromatic Cyclic (O-PACs) represent 0.03–0.3% in the tars, and 0.2– 0.1% in the neutral Poly Aromatic Cyclic (PAC) fraction of the pentane soluble product. Besides, in a recent study, this technique allowed the identification of phenyl-dibenzofuran, benzobisbenzofurans, triphenyleno[1,12-bcd]furan and 6-Oxa-12thia-indenol[1,2-b] fluorene [17] in coal tars, pitches and related materials. Other types of detectors are however preferred because AED device has a weak robustness and its sensibility to oxygen is not as appropriate as the one for carbon, hydrogen and sulphur. In fact, Gurka et al. studied detection limits for heteroatomic species i.e. hydrogen, nitrogen, oxygen, chlorine, and sulphur detection limit ranges are 0.17−3.0, 1.0−5.0, 0.65−11, 0.07−3.0, and 0.023−0.028 ng, respectively. This indicates that the order of increasing sensitivity to molecular structure is O < N < H < Cl < S.

Applications of GC-MS to characterize oxygenates in coal liquids

Furthermore, mass spectrometry detection was used to identify and quantify phenolic compounds in 175-425°C fractions of coal-derived distillates. In order to concentrate this fraction, a solvent extraction was used by Pauls et al. [18]. It consists on isolating an acidic concentrate by extraction with sodium hydroxide and in neutralizing the solution by acid addition. This strategy was also used in 1984 by Uchino et al. in order to separate the basic fraction and the acidic fraction from the hydrocarbon matrix [33]. In a phenol-containing fraction that Pauls et al. managed to separate, four types of ring structures with different short alkylated chains were characterized by GC-MS: phenols, indanols, naphthols, and biphenylols (Table 1-4). The recovery of phenol in the fraction of interest is only 42% whereas recovery of the other compounds up to C3 is 70%. The quantification of these species is given in Table 1-4 for the atmospheric flash distillates of Illinois N ° 6 coal-derived oil obtained by a two stage liquefaction process. Another study using GC-MS also demonstrates that the phenols are essentially monocyclic and that methyl groups are the main substituents in an Irati shale Oil AGO cut [26]. It was found that phenols represent 4 w/%w/w using GC/MS. This product is however quite different from the matrix of interest.

Applications of Two-dimensional Gas Chromatography to unravel oxygenated structures in DCL

One-dimensional gas chromatography rests on only one separation criterion and is not sufficient if the vapour pressures of many analytes of a mixture are too close [43]. Separation of coeluted species requires the integration of another separation criterion. Hyphenated to a mass spectrometer or flame ionization detector or a specific detector of oxygen, two-dimensional gas chromatography can offer outstanding separations and appears as a very useful tool for the analysis of complex mixtures such as coal-derived products. Even if a few studies used this technique to characterize coal-derived products [44-46], as far as we know, by 2010, only one paper gives information about oxygenated compounds by GC×GC [1].
In fact, Bertoncini et al. focused on Direct Coal Liquefaction distillates and carried out two different analyses of oxygenated species by GC×GC-ToF/MS: one applied to the kerosene cut and the other to the atmospheric gas oil cut [1]. For quantification purposes, FID detection was also used. Modulation was carried out using by a thermal nitrogen modulator with a frequency of 50 Hz. Results as well as chromatographic conditions are displayed in Figure 1-4 concerning the kerosene cut. In a nutshell, the analysis of the kerosene cut gives structured chromatograms. As illustrated, elution zones of saturates, mono-aromatics, naphtheno-aromatics and oxygenates are delimited. These works are very successful in the separation of oxygenated compounds from the hydrocarbon matrix. As far as the analysis of the AGO cut is concerned, it enables the identification of 250 oxygenated molecular structures belonging mainly to the two families mentioned before i.e. phenols and benzofurans. These species are however not completely separated from the paraffins, naphthenes and aromatics. The column set on stake was PONA (10mx0.2mmx0.5µm) x BPX-50 (0.8×0.1mmx0.1µm). Moreover, a quantification of hydrocarbons with a classification by group type was carried out for naphtha, kerosene, and AGO cuts. However, quantitative information about oxygenated compounds is given only for the naphtha cut using a one-dimensional PIONA analysis. Additionally, another study used GC×GC ToF/MS to characterize hydrocracking products. It was lead by Hamilton et al. in 2007 [44] and showed a comparative study between GC-MS and GC×GC-ToF/MS. Although one-dimensional results enabled the identification of more than a hundred compounds, the combination of two polarities clearly performs a separation between alkanes and aromatics, but no specific oxygenates zone was highlighted. The combination of HP-5 and DB-17 columns enabled the identification of many hydrocarbons with a good resolution. The use of the selective m/z ratio option allowed the identification of single ion m/z specific families. Apart from aromatic and paraffinic structures, this work highlights the presence of benzonaphtofuran (Figure 1-5). Many hydrogen donors structural isomers were also detected in the recycle solvent. Nevertheless, the maximal reachable mass of 210 units does not give access to heavier molecules highlighted by SEC analyses.
To conclude the use of new coupled techniques such as GC×GC would be of great interest to unravel oxygenated structures contained in these types of matrices. In fact GC×GC overcomes the limits of classical GC in terms of resolution and peak capacity. Recent advances also show the possibility to use an atomic emission detector (AED) coupled to a GC×GC device to improve the understanding of petroleum matrices.

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Characterization by Liquid Chromatography

Liquid chromatography may be preparative or analytical. In the first case, its purpose is to separate the analytes from a matrix for further use. Coupled with various detectors, analytical liquid chromatography leads to structural information of the analytes.

Preparative Liquid Chromatography

Preparative Liquid Chromatography is broadly used in the petroleum field where it is referred as SESC (Sequential Elution Solvent Chromatography) [47]. In the petroleum industry a particular case of SESC called SARA (Saturates, Aromatics, Resin, Asphaltenes) is often used to unravel hydrocarbons composition and is mainly applied to vacuum distillates and residual cuts [48-50]. The intent of this analysis is double: on the one hand it gives quantitative information about each of these four classes, on the other hand it results in fractions that can be further subjected to other analytical tools [51].
According to Farcasiu et al. [47], SARA can definitely not be applied successfully on coal oils firstly, because some species can irreversibly be adsorbed on the substrates. Thus, other solvents are used for the fractionation of DCLs and enable the separation of oxygenated analytes from the hydrocarbon matrix. Many researchers used SESC to obtain simpler fractions [52] or to isolate target compounds such as phenols and indanols [20, 52]. A detail of the different solvents used in the literature for the fractionation of coal liquefaction products is shown in Table 1-6.

Table of contents :

CHAPTER 1. CHARACTERIZATION OF OXYGENATED SPECIES IN COAL LIQUEFACTION PRODUCTS: AN OVERVIEW 
1.1 Introduction
1.2 Properties of coal-derived liquids
1.3 Characterization by One-dimensional Gas Chromatography
1.3.1 Selective characterization of oxygenates in coal-derived liquids by GC-AED
1.3.2 Applications of GC-MS to characterize oxygenates in coal liquids
1.4 Applications of Two-dimensional Gas Chromatography to unravel oxygenated structures in DCL
1.5 Characterization by Liquid Chromatography
1.5.1 Preparative Liquid Chromatography
1.5.2 High Performance Liquid Chromatography
1.6 Selective analysis of phenols and alcohols by NMR spectroscopy
1.7 Characterization of oxygenated compounds by FT-ICR/MS
1.8 Conclusion
CHAPTER 2. INVESTIGATING GC×GC TO OPTIMIZE THE SEPARATION OF OXYGENATED COMPOUNDS IN A DIRECT COAL LIQUEFACTION MIDDLE DISTILLATE
2.1 Introduction
2.2 Experimental
2.2.1 Samples
2.2.2 GC×GC-FID setup
2.2.3 GC×GC-ToF/MS
2.2.4 Data handling
2.2.5 Two-dimensional decisive factors
2.3 Results and discussion
2.3.1 Investigated configurations
2.3.2 Selection of the most adapted configuration
2.3.3 GC×GC-ToF/MS analysis of the selected configuration
2.4 Conclusion
CHAPTER 3. USING GAS CHROMATOGRAPHY TO CHARACTERIZE A DIRECT COAL LIQUEFACTION NAPHTHA
3.1 Introduction
3.2 Experimental
3.2.1 Materials
3.2.2 GC-ToF/MS setup
3.2.3 GC-GC-FID setup
3.2.4 GC×GC-FID
3.2.5 GC×GC-ToF/MS
3.3 Results and discussion
3.3.1 Speciation of oxygenated compounds by GC-ToF/MS
3.3.2 Towards a detailed characterization of oxygenates by GC-GC-FID
3.3.3 Speciation of oxygenated compounds using GC×GC
3.3.4 Comparison of the three techniques
3.4 Conclusion
CHAPTER 4. A NOVEL ANALYTICAL APPROACH FOR OXYGEN SPECIATION IN COAL-DERIVED LIQUIDS 
4.1 Introduction
4.2 Materials and methods
4.2.1 Samples
4.2.2 Gas chromatography analysis
4.2.3 Mass spectrometry analysis
4.2.4 31P Nuclear Magnetic Resonance analysis
4.2.5 UV-visible spectroscopy analysis
4.3 Results and discussion
4.3.1 Methodology
4.3.2 Detailed quantification of alcohols and phenols by GC×GC
4.3.3 Identification of phenols and carboxylic acids by FT-ICR/MS in the coal derived AGO
4.3.4 Global quantification of alcohols, phenols and carboxylic acids by 31P NMR
4.3.5 Global quantification of ketones by UV-visible spectroscopy
4.3.6 Final quantitative assessment
4.4 Conclusion
SPECIATION IN BIO-OIL UPGRADING PRODUCTS
CHAPTER 5. CHARACTERIZATION OF OXYGENATED COMPOUNDS IN UPGRADED BIO-OILS: A CRITICAL REVIEW 
5.1 Introduction
5.2 Generalities on upgraded bio-oils
5.2.1 Properties
5.2.2 Chemical functional groups
5.3 Characterization by one-dimensional gas chromatography
5.4 Characterization by two-dimensional gas chromatography
5.5 Discussion
5.6 Conclusion
CHAPTER 6. OXYGEN SPECIATION IN PARTIALLY UPGRADED BIO-OILS BY COMPREHENSIVE TWODIMENSIONAL GAS CHROMATOGRAPHY
6.1 Introduction
6.2 Experimental
6.2.1 Samples
6.2.2 GC×GC-FID setup
6.2.3 GC×GC-ToF/MS
6.2.4 Capillary columns
6.2.5 Data handling
6.3 Results and discussion
6.3.1 Investigating different column sets for oxygen speciation by GC×GC-FID
6.3.2 Identification by GC×GC-ToF/MS
6.3.3 Quantification by GC×GC-FID
6.4 Conclusion
CHAPTER 7. CHARACTERIZATION OF PHENOLIC COMPOUNDS IN PARTIALLY UPGRADED BIO-OILS BY SFCGC×GC
7.1 Introduction
7.2 Materials and methods
7.2.1 Samples
7.2.2 SFC-FID
7.2.3 Online GC×GC-FID
7.2.4 Offline GC×GC-FID and GC×GC-ToF/MS
7.2.5 SFC fractions transfer into the GC×GC system
7.2.6 Stationary phases
7.3 Results and discussion
7.3.1 SFC separation
7.3.2 Offline GC×GC analysis of SFC fractions
7.3.3 Online SFC-GC×GC analysis
7.4 Conclusion
ON ORTHOGONALITY IN GC×GC
CHAPTER 8. CONSIDERATIONS ON ORTHOGONALITY DUALITY IN COMPREHENSIVE TWO-DIMENSIONAL GAS CHROMATOGRAPHY 
8.1 Introduction
8.2 Theory
8.3 Experimental section
8.3.1 Samples
8.3.2 GC×GC systems
8.4 Results and discussion
8.5 Conclusion
CHAPTER 9. REVERSAL OF ELUTION ORDER IN A SINGLE SECOND DIMENSION BY CHANGING THE FIRST COLUMNS NATURE IN COMPREHENSIVE TWO-DIMENSIONAL GAS CHROMATOGRAPHY
9.1 Introduction
9.2 Experimental section
9.2.1 Samples
9.2.2 GC×GC systems
9.2.3 GC-FID conditions
9.3 Results and discussion
9.3.1 One column, two elution orders.
9.3.2 Influence of the first dimension on the second separation
9.3.3 van’t Hoff plots
9.3.4 Equations of the problem
9.3.5 Guidance on columns sets selection
9.4 Conclusion

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