ThermogravimetricâFourier Transform Infrared SpectroscopyâGas

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Thermogravimetric-Fourier-Transform Infrared SpectroscopyGas Chromatography/Mass Spectrometry Study of Volatile Organic Compounds from Coal Pyrolysis Jie Cheng, Yongsheng Zhang, Tao Wang, Pauline Norris, Wei-Yin Chen, and Wei-Ping Pan Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 12 Jun 2017 Downloaded from http://pubs.acs.org on June 12, 2017

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Thermogravimetric-Fourier-Transform Infrared Spectroscopy-Gas Chromatography/Mass Spectrometry Study of Volatile Organic Compounds from Coal Pyrolysis Jie Cheng 1, Yongsheng Zhang 1∗, Tao Wang 1, Pauline Norris 2, Wei-Yin Chen 3, Wei-Ping Pan1, 2 1

Key Laboratory of condition Monitoring and Control for Power Plant Equipment, Ministry of Education,

North China Electric Power University, Beijing 102206, China 2

Institute of Combustion Science and Environmental Technology, Western Kentucky University, Bowling

Green, KY 42101, USA 3

Department of Chemical Engineering, University of Mississippi, University, MS 38677, USA

Highlights 1. About 124 VOCs were identified using TG-FTIR-GC/MS during coal pyrolysis. 2. VOC release below 400°C was only 23.1% of total VOC release during coal pyrolysis. 3. Temperature has a positive effect on VOC emission during bituminous coal pyrolysis. 4. TG-FTIR-GC/MS was used to compare VOC releases in lignite and bituminous coals during pyrolysis.

Abstract:

The

simultaneous

use

of

thermogravimetric

(TG)

analysis,

Fourier-transform infrared (FTIR) spectroscopy, and gas chromatography/mass spectrometry (GC/MS) with the same sample provides a unique method for studying coal pyrolysis. About 124 volatile organic compounds (VOCs) were identified by TG-FTIR-GC/MS during coal pyrolysis based on the characteristic fragments or Kovats index. These compounds included alkanes, α-olefins, benzene, toluene, ethylbenzene, xylenes, and phenols. n-Alkanes from C5 to C24 with regular one-carbon retention intervals in the GC/MS system were used to calculate the Kovats indexes of all compounds. From this study, temperature was the key factor affecting ∗

Corresponding author E-mail: [email protected]

ACS Paragon Plus Environment

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VOC release. The VOCs released below 400 °C represented only 23.1% of the total VOCs released during the pyrolysis of bituminous (coal BA). Thus, the use of thermal desorption (TD) with GC/MS to analyze coal pyrolysis, only provides VOC release information before 400 OC. It would underestimate the VOC release because of the temperature limitation on the TD technique. The yields of phenolic hydrocarbons from lignite were higher than those from bituminous coal. This could be the result of a higher level of oxygen cross-linking in lignite than in bituminous coal, which was proven by the results of curve fitting and GC/MS. Thus, the release of VOC is a function of coal rank.

Keywords: Coal pyrolysis; Volatile organic compounds; Thermogravimetric; Fourier-transform infrared spectroscopy; Gas chromatography/mass spectrometry. 1. Introduction In the document ISO 16000-6, the World Health Organization defines a VOC as any organic compound with a boiling point in the range from 50–100 °C to 240–260 °C; this corresponds to a saturation vapor pressure greater than 100 kPa at 25 °C1. Many VOCs are toxic and can participate in photochemical reactions that lead to smog formation2. Coal has a considerable amount of VOCs in its structure and these can be transformed during combustion in a power plant. Even a very small amount of VOCs in a flue gas can be an important anthropogenic source of these compounds because of the large volume of flue gas emitted3-6. Coal combustion involves coal pyrolysis and evolved gas burning. Pyrolysis affects the ignition characteristics and evolution of pollutant gases. Information on the release of VOCs during coal pyrolysis can help in the qualitative and quantitative determination


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of VOCs from power plant emissions. This information, in turn, can be used to develop pollution control measures. Coal chemistry industries also need information on the release of VOCs during coal pyrolysis to guide production. Combinations of thermogravimetric (TG) analysis or thermal desorption (TD) with Fourier-transform infrared spectroscopy (FTIR) or gas chromatography/mass spectrometry (GC/MS) have been used by many researchers to study pyrolysis of coal or other solid samples7-11. Anthony and Howard studied the pyrolysis of coal and the variables affecting the yields of total volatiles12. Suuberg and Howard reported the yields of light hydrocarbons from coal pyrolysis13. Solomon’s team used FTIR to analyze the gaseous, liquid, and solid products from coal pyrolysis14-16. Shi, Zhiwei reported the initial volatile products of Shenhua coal with pyrolysis vacuum ultraviolet photoionization mass spectrometry17. Rathsack analyzed pyrolysis liquids obtained from the slow pyrolysis of a German brown coal18. Moreover, Kandasamy studied the TG-MS analysis and kinetics of coal-biomass blends19. These studies are fundamentally important to coal devolatilization and hydrogasification. Despite extensive studies of coal pyrolysis, qualitative information on the VOCs formed during coal pyrolysis is still lacking. In qualitative analysis, an automatic search of the NIST library generally identifies five to ten compounds corresponding to the GC/MS peaks. Usually the researcher chooses the one with the maximum matching degree. However, many compounds have similar molecular structures and similar MS spectra, and sometimes the qualitative information is inadequate and more information is needed for exact identification. A new simultaneous TG-FTIR-GC/MS technique


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combines more than one qualitative method and enables more information to be obtained. Our investigations showed that there were no reports on the analysis of coal pyrolysis using TG-FTIR-GC/MS. In this study, the simultaneous use of TG, FTIR and GC/MS, and the classification of the compounds by extracting characteristic fragments and calculating the Kovats indexes of the peaks was used to identify and understand the compositions of the evolved gases. In a quantitative analysis, Fernandez et al. used TD-GC/MS to quantify the VOCs produced during coal pyrolysis20, 21. Their research results indicate that the amount of VOCs did not significantly increase on heating to 400 °C after holding the temperature at 350 °C for 15 min. The TD-GC/MS systems currently on the market have a maximum operating temperature of 400 °C. This is suitable for analysis of sorbent tubes with VOCs desorption temperatures below 400 °C22, 23. However, for coal pyrolysis, most VOCs are released at temperatures higher than 400 °C. Therefore TD-GC/MS may be unsuitable for the analysis of VOCs released during coal pyrolysis. TG-GC/MS is different and can operate at temperatures of 1000 °C or higher. It is more suitable for analysis of VOCs released during coal pyrolysis. In this paper, the difference between VOCs released at temperatures below 400 °C and above 400 °C was determined using a systematic test on TG-GC/MS. In a study of covalent bonds breakage during coal pyrolysis, Lei Shi et al. used a differential thermal gravimetry (DTG) curve-fitting method which gives a rough estimate24. In this study, the DTG curve-fitting method and the simultaneous TG-FTIR-GC/MS technique were compared. This provided more detailed information


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on VOC release during coal pyrolysis. 2. Experimental 2.1 Coal samples Coal samples were obtained according to ASTM D-2234 (1989)25. Quartering was used for the sampling process and 500mg of coal remained for analysis. Twelve raw coals of different types (lignite and bituminous coals) were used in this study. These coals are denoted by L1-L5, BA, and B1-B6. The coal BA was analyzed as the typical bituminous. The ultimate and proximate analyses data for these samples are shown in Table 1, which is sorted by carbon content. The test results were an average of three trials. The fixed carbon percentages of the coals were between 18% and 67%. 2.2 TG-FTIR-GC/MS experiments Samples were placed in a ceramic crucible in a thermogravimetric analyzer (Perkin Elmer, STA8000). VOCs were evolved when the sample was heated. High-purity nitrogen (99.999%) at a flow rate of 30 mL min−1 was used to ensure an inert atmosphere. The sample (about 20 mg, approximately 200 mesh) was heated from 30 to 1000 °C at 40 °C min−1. High-purity nitrogen was also used as a carrier gas during the pyrolysis tests. The evolved gas was carried by the carrier gas to the sample cell of an FTIR spectrometer (Perkin Elmer, Frontier) and then transferred to the injection port of a GC/MS system (Perkin Elmer, Clarus SQ 8T). The FTIR sample cell temperature was kept at 280 °C and the resolution was set at 1 or 4 cm−1. The scanning range was 450– 4000 cm−1. Time Base

TM

software was used to record the spectrum based on TG


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sample temperature. The gases evolved at selected temperatures were analyzed. The gas sample loop volume was 1 mL and the injection time was 10 s. Gas analysis was performed using FTIR and GC/MS26-30. All transfer lines in the evolved gas analysis system (EGA Perkin Elmer, TL9000) were maintained at 280 °C to avoid condensation of volatile gases with boiling temperatures less than 280 °C. The GC system consisted of a gas chromatograph with a fused silica capillary column with 100% dimethyl polysiloxane (Extile, 60 m × 0.25 mm × 0.25 µm film thickness). The chromatographic conditions were as follows: the column temperature was held at 50 °C for 5 min, then increased at 10 °C min−1 to 280 °C and kept at this temperature for 5 min. The helium flow rate was 1.0 mL min−1. The transfer and source temperatures were 230 °C. Mass spectra were recorded in the mass range m/z = 35 to 500. Analytes were identified based on the mass spectra. The value of the total ion current was used to calculate the relative amount of a VOC. The retention time error of GC/MS is within ±0.1min and the relative standard deviation of peak area is lower than 5%. Experimental results were checked several times. The overall TG-FTIR-GC/MS experimental set-up is shown in Figure 1. In this study, the effects of coal rank, carbon content, particle size, and heating rate on VOCs release were studied. Both bituminous and lignite coals were tested. Coals with carbon contents ranging from 18% to 67% were tested. The particle size was kept between 55 and 200 mesh. Heating rates were maintained between 5 and 100 °C min−1. 3. Results and discussion 3.1 Mass loss characteristics of coal sample BA during pyrolysis


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TG curve describes the mass change as function of temperature. The differential TG (DTG) curve is the first derivative curve of the TG curve. The DTG curve indicates the rate of the mass loss. The DTG curve clearly shows the degree of mass loss at any temperature point caused by pyrolysis. Figure 2 shows the TG and DTG curves of the BA coal sample at a heating rate of 40 °C min−1. The first peak, which is usually attributed to moisture loss, was observed between 50 and 150 °C. Volatile matter was released between 350 and 650 °C and the DTGmax was 475 °C. 3.2 FTIR analysis of sample BA during coal pyrolysis The DTGmax of the BA coal in Figure 2 corresponded to region A in Figure 3. The region marked A shows VOC peaks at about 2800 to 3200 cm−1 and 400 to 600 °C. Figure 4 shows the evolved gas spectrum for region A. A combination of the standard signals for methane, alkanes (non-methane), α-olefins, BTEX (benzene, toluene, ethylbenzene, and xylenes), phenols, CO, CO2, and H2O multiplied by an estimated value provided a simulated graph (Figure 4 B) similar to the sample graph (Figure 4 A). The gases evolved at FTIRmax (the maximum absorb in online FTIR signal) were mainly VOCs, CO2, CO, and H2O. The VOCs included alkanes, α-olefins, BTEX, and phenols. In the fingerprint region, there was only one sharp peak, at 950 cm−1, corresponding to ethylene. The others were overlapped by the peaks from H2O. The online FTIR signal was extracted from the FTIR-3D graph. Figure 5 shows the online FTIR results based on temperature. The profiles at 950 cm−1 (ethylene), 2934 cm−1 (aromatic hydrocarbons, including BTEX), and 2970 cm−1 (aliphatic hydrocarbons, including alkanes and olefins) were very similar. The signals were


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maximum near FTIRmax. The pyrolysis properties of methane (3016 cm−1) were different from those of other alkanes. Methane released later than other alkanes. These results are in agreement with those from another study26. Water (1654 cm−1) was released at two different temperature ranges. The first peak is from moisture loss from the sample and the second peak is from breakage of molecular bonds in coal. CO2 (2358 cm−1) also gave two peaks. The first peak is from the breakage of molecular bonds in the coal, and the second peak arises from thermal decomposition of carbonate compounds in the coal. The CO signal is increased upon heating due to the fast reaction of carbon with oxygen in the coal as function of temperature. Another possibility is due to the char gasification at the higher temperature. 3.3 GC/MS analysis of sample BA during coal pyrolysis The simultaneous TG-FTIR-GC/MS technique demonstrates the strengths of these three individual techniques and provides a new instrumental method for evolved gas analysis during coal pyrolysis. 31. Evolved gas from region A between 400 and 6000C in the TG system was on-line transferred and analyzed using GC/MS, Figure 3. The GC/MS total ions chromatograph in Figure 6A did not give exact matches with the results of the automatic qualitative search of NIST library. The use of characteristic fragments can be helpful to identify the compounds. Among these compounds, alkanes produce fragments through breakage of σ bonds. The strongest peak was from C3, because it can rearrange to form stable propyl cations at m/z 43. Olefins easily generate stable allyl ions at m/z 41. Benzene compounds can generate benzene ions at m/z 77 and benzyl ions at m/z 91. The molecular ion peak of benzene at m/z 78 was


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stable. For phenolic compounds, the intensity of phenol molecular ion peak at m/z 94 was very strong. The cresol M – 1 ion can generate stable compounds containing the hydroxyl tropylium ion, at m/z 107. In Figure 6, therefore, m/z 43 and 41 represent the alkane and olefin series, m/z 77, 78, and 91 represent the benzene compounds, and m/z 94 and 107 represent phenolic compounds. The aliphatic compounds (43 and 41 m/z) were separated from the single aromatic hydrocarbon compounds (m/z 78, 77, 91) using ion extraction. The results indicate that the major single-species aromatic compounds were BTEX, and the aliphatic compounds included C5–C24 alkanes and their corresponding α-olefins. Alkanes and olefins from C5 to C24 were detected in the chromatograms. The retention time interval of these alkanes has the same pattern with one methylene (−CH2−) difference between every two adjacent alkanes. The aromatic hydrocarbon compounds consisted of benzene, toluene, ethylbenzene, and o/m/p-xylene. These compounds are in the macromolecular skeletal structure of the coal when it is cracked and they react with methyl radicals. Phenolic compounds were formed from oxygen-containing structures in the coal. Many isomeric compounds of cresol, ethylphenol, and propylphenol were detected. Regular n-alkanes with one-carbon retention intervals are shown in Figure 6C. The retention times of the n-alkanes were used to calculate the Kovats index of every peak using the equation for temperature-programmed chromatography; these can be used to assist identification of the peak in Table 2. Wei-Yin Chen et al. reported similar results for regular n-alkanes in solvent-refined coals24. These compounds are produced from


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the pyrolysis of aliphatic side chains. The distributions of regular n-alkanes can be used to help determine the sources of various VOCs in environmental air. About 124 compounds were identified using GC/MS based on characteristic fragments or the Kovats index. The compounds included alkanes and their corresponding olefins (from C5 to C24), aromatic hydrocarbons (mainly BTEX), and phenols (phenol and cresols)32-35. 3.4 Verification test for VOCs in coal BA In section 3.2, the temperature range for VOC release was between 400 and 600 °C. As stated in section 1, the TD-GC/MS systems currently on the market have a maximum operating temperature of 400 °C. This method is therefore unsuitable for the analysis of VOCs released during coal pyrolysis. In this study, a test system was designed to analyze the occurrence of VOC at temperatures above 400 °C. In the test, the sample was first heated to 400 °C and held at that temperature for several minutes until FTIR monitoring showed that VOC release had completed. Then the sample was removed from the sample pan. The system with the empty sample pan was heated to 1000 °C to remove any condensed VOC in the heated transfer line for the second step. The step one sample was placed back to the sample pan and heated to 1000 °C to identify VOCs release over 400 °C. The effects of particle size and heating rate on the release of VOCs were investigated first. Figure 7 shows the total amount of released VOCs as a function of temperature. The particle size had very little effect on the VOC release temperature. Higher heating rates shift the release of VOCs to a higher temperature because of a relative heating delay. Kandasamy reported the same trends


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in high ash coal pyrolysis—higher pyrolysis rate of coal would greatly increase the yield of light gases when compared to lower pyrolysis process36. The amount of VOC is increased during the fast heating rate. This is due to the fact that breakage of carbon bonding is much faster than that of the formation of char (rearrangement of the carbon structure to become a more ordered carbon structure) during the fast heating reaction. Figure 8A shows that a small amount of VOCs were released at 400 °C (indicated by A). The sample was removed and the empty sample pan was heated to 1000 °C (indicated by B). A small amount of VOCs were detected. These are probably VOCs previously released at 400 °C that were deposited in the transfer line. The sample was returned to the sample pan and heated to 1000 °C. A large amount of VOCs were released (indicated by C). Figure 8B shows the trends in VOC release (2934cm−1 and 2970cm−1 corresponds to VOCs including the aliphatic and aromatic hydrocarbons) with TG temperature during the release test; the amount released was calculated as the sum of the aromatic hydrocarbon and aliphatic hydrocarbon areas. The amount of VOCs in part A was 23.1% of that in part C, which indicates that most VOCs released occurred above 400°C. The quantification of VOCs in coal pyrolysis requires the use of a higher temperature to release the VOCs, adsorption of the VOCs with a sorbent tube, and analysis of the desorbed gas by heating the sorbent tube. 3.5 Comparison of VOCs released from different coal types during pyrolysis The DTG curve for coal pyrolysis mainly arises from breakage of large numbers of covalent bonds in the coal and can be fitted to a number of sub-curves, each


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representing a group of covalent bonds in the coal16, 24, 29, 37, 38. In Figure 9A, the DTG curve for coal BA between 200 and 800 °C is fitted to four sub-curves. The r2 value was 0.9924. Peak 1 occurred between 300 and 450 °C and resulted from the breakage of bonds between Cal (the carbon atom in an alkane) and O, S, and N. The peak area percentage was 2.0%. Peak 2 occurred between 400 and 500 °C and resulted from the breakage of bonds between Cal and Cal, H, and O. The peak area percentage was 69.5%. Peak 3 occurred between 450 and 600 °C and resulted from the breakage of bonds between Car (the carbon atom in aromatic hydrocarbons) and Cal, O, and S. The peak area percentage was 20.3%. Peak 4 occurred at about 700 °C and resulted from CO2 generation from decomposition of carbonate compounds in the coal. The peak area percentage was 8.2%. Most of the volatile matter generated from BA was emitted at Peak 2 temperature, and consisted of alkanes and olefins. Table 3 lists the DTGmax values for all coal samples discussed. The release of volatile matter occurred from 300 to 600 °C and the DTGmax was from 400 to 550 °C. The DTGmax average temperature of lignite coal was 459 °C and that of bituminous coal was 485 °C. The VOCs release range of lignite coal was from 350 to 600 °C and that of bituminous coal was from 400 to 600 °C. The DTGmax of lignite coal was observed at a lower temperature than that of bituminous coal, and the mass loss range was broader. The DTGmax temperature was shifted to the higher temperature as the carbon content increased, Figure 9B. This is due to the more aliphatic compounds in the lignite than that of bituminous. The bituminous coal also contains more aromatic compounds to shift the thermal decomposition of VOC to the higher temperature. It is


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also indicated that the VOC released from the higher rank coal will occur at a higher temperature relative to the lower rank coal. As in the case of DTG analysis of coal BA, the DTG curve can be fitted by four sub-curves. All the DTG curves of the coals used in this study (Figure 9B) were fitted by sub-curves; detailed information is listed in Table 3. There is no significant turning point on a TG curve, therefore the peak area percentage was used to represent the proportions of the sub-curves. The average areas of peaks 1 and 2 for lignite were 17% and 55.1%, and those average areas for bituminous coals were 4.1% and 67.1%, which indicates that there were more bonds between Cal and O, S, and N (peak 1), and fewer Cal–Cal bonds (peak 2) in lignite coal than in bituminous coal. The lignite coal contained more compounds with cross-linked oxygen or other heteroatoms than did the high-rank coal. However, this method gives only a rough estimate and is not exact. For more quantitative information on VOC release, GC/MS was used to analyze the VOCs released at DTGmax; the point at which the area of peak 2 was maximum and peaks 1 and 3 were also partly included for the calculation. The VOCs release from different coal types at DTGmax are shown in Figure 10. The bituminous coal contained large amounts of toluene, n-pentane, m/p-xylene, m/p-cresol, and phenol. The lignite coal contained large amounts of toluene, phenol, m/p-cresol, and p-xylene. The figure indicates that the amounts of aromatic hydrocarbon compounds in lignite coals were lower than those in bituminous coals. The concentrations of phenol and m/p-cresol in lignite were higher than those in bituminous coal. Bituminous coal had higher concentrations of aliphatic compounds, toluene, and n-pentane than did lignite coal.


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The data in Table 1 show that there was more oxygen in the lignite coal than in the bituminous coal. Two of the bituminous coals (#2 and #7) had oxygen contents exceeding 20%. These coals also had lower ash contents, higher aerobic acid salt contents, and lower C/O ratios. The concentration of oxygen compounds in the lignite coal was higher than that in the bituminous coal. This provides further information on the coal macromolecular structures: lignite contains more small crossed-linked oxygen compounds than does high-rank coal39. The DTG curve-fitting method gives rough information on bonds breakage and GC/MS identifies specific compounds released during coal pyrolysis. 4. Conclusions In this study, about 124 VOCs were identified in the gas evolved during coal pyrolysis using TG-FTIR-GC/MS assisted by the characteristic fragments or Kovats index; they included alkanes, α-olefins, BTEX, and phenols. During pyrolysis, lignite produced higher yields of phenolic hydrocarbons than did bituminous coal, probably because lignite contains more cross-linked-oxygen compounds. The temperature was the key factor affecting VOCs release. Verification results showed that the VOCs were released at temperatures between 300 and 600 °C; the VOCs released below 400 °C represented only 23.1% of the total VOCs released during coal pyrolysis. In general, DTG analysis only gives information on bond breakage not the exact compounds, FTIR only identifies the functional groups present not the exact compounds, and GC/MS can identify the exact compounds but only using offline data. TG-FTIR-GC/MS combines the strengths of these three techniques and provides a


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TG/MS/FTIR study of Late Permian coals from Southern China. Journal of Analytical and Applied Pyrolysis 2013, 100, 75-80. 10. Lievens, C.; Ci, D.; Bai, Y.; Ma, L.; Zhang, R.; Chen, J. Y.; Gai, Q.; Long, Y.; Guo, X., A study of slow pyrolysis of one low rank coal via pyrolysis–GC/MS. Fuel Processing Technology 2013, 116, 85-93. 11. Ischia, M.; Perazzolli, C.; DalMaschio, R.; Campostrini, R., Pyrolysis study of sewage sludge by TG-MS and TG-GC-MS coupled analyses. Journal of Thermal Analysis and Calorimetry 2007, 87, (2), 567-574. 12. Anthony, D. B.; Howard, J. B., Coal devolatilization and hydrogastification. AIChE Journal 1976, 22, (4), 625-656. 13. Solomon, P. R.; Serio, M. A.; Suuberg, E. M., Coal pyrolysis: experiments, kinetic rates and mechanisms. Progress in Energy and Combustion Science 1992, 18, (2), 133-220. 14. Solomon, P. R.; Carangelo, R. M., FTIR analaysis of coal. 1. Techniques and determination of hydroxyl concentrations. Fuel 1982, 61, (7), 663-669. 15. Solomon, P. R.; Carangelo, R. M., FT-ir analysis of coal: 2. Aliphatic and aromatic hydrogen


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concentration. Fuel 1988, 67, (7), 949-959. 16. Solomon, P.; Fletcher, T.; Pugmire, R., Progress in coal pyrolysis. Fuel 1993, 72, (5), 587-597. 17. Shi, Z.; Jin, L.; Zhou, Y.; Li, Y.; Hu, H., Online analysis of initial volatile products of Shenhua coal and its macerals with pyrolysis vacuum ultraviolet photoionization mass spectrometry. Fuel Processing Technology 2017, 163, 67-74. 18. Rathsack, P., Analysis of pyrolysis liquids obtained from the slow pyrolysis of a German brown coal by comprehensive gas chromatography mass spectrometry. Fuel 2017, 191, 312-321. 19. Jayaraman, K.; Kok, M. V.; Gokalp, I., Thermogravimetric and mass spectrometric (TG-MS) analysis and kinetics of coal-biomass blends. Renewable Energy 2017, 101, 293-300. 20. Fernández-Villarrenaga Martín, V.; López Mahía, P.; Muniategui Lorenzo, S.; Prada Rodríguez, D., Development of a thermal desorption-gas chromatography-mass spectrometry method for determination of styrene in air. Application to workplace air. Analusis 2000, 28, (8), 737-742. 21. Fernández-Martínez, G.; López-Mahía, P.; Muniategui-Lorenzo, S.; Prada-Rodríguez, D., Determination of volatile organic compounds in coal, fly ash and slag samples by direct thermal desorption/GC/ms. Analusis 2000, 28, (10), 953-959. 22. Ito, R.; Kawaguchi, M.; Sakui, N.; Okanouchi, N.; Saito, K.; Seto, Y.; Nakazawa, H., Stir bar sorptive extraction with in situ derivatization and thermal desorption–gas chromatography–mass spectrometry for trace analysis of methylmercury and mercury(II) in water sample. Talanta 2009, 77, (4), 1295-1298. 23. Elorduy, I.; Elcoroaristizabal, S.; Durana, N.; García, J. A.; Alonso, L., Diurnal variation of particle-bound PAHs in an urban area of Spain using TD-GC/MS: Influence of meteorological parameters and emission sources. Atmospheric Environment 2016, 138, 87-98. 24. Shi, L.; Liu, Q.; Guo, X.; Wu, W.; Liu, Z., Pyrolysis behavior and bonding information of coal — A TGA study. Fuel Processing Technology 2013, 108, 125-132. 25. Materials, A. S. f. T. a., ASTM D2234-98 Standard Practice for Collection of a Gross Sample of Coal In Annual book of ASTM standards, 1998; pp 262-272. 26. Wang, M.; Li, Z.; Huang, W.; Yang, J.; Xue, H., Coal pyrolysis characteristics by TG–MS and its late gas generation potential. Fuel 2015, 156, 243-253. 27. Tsytsik, P.; Czech, J.; Carleer, R., Thermal extraction coupled with gas chromatography–mass spectrometry as a tool for analysing dioxin surrogates and precursors in fly ash. Journal of Chromatography A 2008, 1210, (2), 212-221. 28. Nsaful, F.; Collard, F.-X.; Carrier, M.; Görgens, J. F.; Knoetze, J. H., Lignocellulose pyrolysis with condensable volatiles quantification by thermogravimetric analysis—Thermal desorption/gas chromatography–mass spectrometry method. Journal of Analytical and Applied Pyrolysis. 29. He, Q.; Wan, K.; Hoadley, A.; Yeasmin, H.; Miao, Z., TG–GC–MS study of volatile products from Shengli lignite pyrolysis. Fuel 2015, 156, 121-128. 30. Ding, L.; Zhou, Z.; Guo, Q.; Lin, S.; Yu, G., Gas evolution characteristics during pyrolysis and catalytic pyrolysis of coals by TG–MS and in a high-frequency furnace. Fuel 2015, 154, 222-232. 31. Kaljuvee, T.; Keelman, M.; Trikkel, A.; Petkova, V., TG-FTIR/MS analysis of thermal and kinetic characteristics of some coal samples. Journal of Thermal Analysis and Calorimetry 2013, 113, (3), 1063-1071. 32. O. David Sparkman; Zelda E. Penton; Kitson, F. G., Gas Chromatography and Mass Spectrometry: A Practical Guide (Second Edition). Elsevier Inc.: 2011. 33. Garcia, J. P.; Beyne-Masclet, S.; Mouvier, G.; Masclet, P., Emissions of volatile organic compounds


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by coal-fired power stations. Atmospheric Environment. Part A. General Topics 1992, 26, (9), 1589-1597. 34. Shi, J.; Deng, H.; Bai, Z.; Kong, S.; Wang, X.; Hao, J.; Han, X.; Ning, P., Emission and profile characteristic of volatile organic compounds emitted from coke production, iron smelt, heating station and power plant in Liaoning Province, China. Science of The Total Environment 2015, 515–516, 101-108. 35. Liu, Y.; Shao, M.; Fu, L.; Lu, S.; Zeng, L.; Tang, D., Source profiles of volatile organic compounds (VOCs) measured in China: Part I. Atmospheric Environment 2008, 42, (25), 6247-6260. 36. Jayaraman, K.; Gokalp, I.; Bostyn, S., High ash coal pyrolysis at different heating rates to analyze its char structure, kinetics and evolved species. Journal of Analytical and Applied Pyrolysis 2015, 113, 426-433. 37. van Heek, K. H.; Hodek, W., Structure and pyrolysis behaviour of different coals and relevant model substances. Fuel 1994, 73, (6), 886-896. 38. Hodek, W.; Kirschstein, J.; van Heek, K.-H., Reactions of oxygen containing structures in coal pyrolysis. Fuel 1991, 70, (3), 424-428. 39. Shuangquan, Z., Coal and Coal Chemistry. Chemical Industry Press: Beijing, 2013; p 37.


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Figure captions Fig. 1 TG-FTIR-GC/MS system Fig. 2 TG and DTG profile of sample BA pyrolysis Fig. 3 FTIR-3D graph of sample BA pyrolysis (A indicates VOC peaks) Fig. 4 FTIR spectra for region A (A) and simulated FTIR spectrum (B) Fig. 5 Online FTIR signals based on temperature Fig. 6 GC/MS chromatogram at region A and selected ion chromatograms Fig. 7 Effects of particle size (A), and heating rate (B) on VOC release at different temperatures Fig. 8 Verification test for VOCs Fig. 9 DTG curves of coal samples during pyrolysis and sub-curves Fig. 10 VOC release from different coals: (A) lignite coal and (B) bituminous coal


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Fig. 1 TG-FTIR-GC/MS system


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Fig. 2 TG and DTG profile of sample BA pyrolysis


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Fig. 3 FTIR-3D graph of sample BA pyrolysis (A indicates VOC peaks)


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 4 FTIR spectra for region A (A) and simulated FTIR spectrum (B)


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Fig. 5 Online FTIR signals based on temperature


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 6 GC/MS chromatogram at region A and selected ion chromatograms A: total ion chromatogram; B: m/z 77, 78, and 91; C: m/z 41 and 43; D: m/z 94 and 107


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A. Effects of particle sizes

B. Effects of heating rates Fig. 7 Effects of particle size (A), and heating rate (B) on VOC release at different temperatures


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A. FTIR-3D of the verification test

B. Profile of VOCs (2934cm−1 represent Aromatic Hydrocarbon, 2970cm−1 represent Aliphatic Hydrocarbon) Fig. 8 Verification test for VOCs


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A. profile of Coal BA and fitted by 4 sub-curves

Peak1

Peak2

Peak3

Peak4 L1 L2 L3 L4 L5 B1 B2 BA B3 B4 B5 B6

DerivativeMass,% min-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

200

300

400

500

600

700

800

900

Temperature,

B. Mass loss characteristics of coal samples during pyrolysis, and four sub-curves Fig. 9 DTG curves of coal samples during pyrolysis and sub-curves


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A. Lignite coal

B. Bituminous coal Fig. 10 VOC release from different coals: (A) lignite coal and (B) bituminous coal Note: 1 n-pentane; 2 1-hexene; 3 n-hexane; 4 benzene; 5 1-heptene; 6 heptane; 7 toluene; 8 1-octene; 9 n-octane; 10 ethylbenzene; 11 m/p-xylene; 12 o-xylene; 13 1-nonene; 14 n-nonane; 15 benzene, propyl-; 16 benzene,1-ethyl-3-methyl-; 17 phenol; 18 benzene, 1-ethyl-2-methyl-; 19 benzene,1,2,4-trimethyl-; 20 1-decene; 21 n-decane; 22 benzene,1,2,3-trimethyl-; 23 o- cresol; 24 m/p-cresol; 25 1-undecene; 26 n-undecane; 27 phenol, 2,5-dimethyl-; 28 1-dodecene; 29 n-dodecane; 30 n-tridecane


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Table captions Table 1 Proximate and ultimate analyses of coal samples Table 2 Compounds identified by GC/MS at region A Table 3 DTGmax values of coal samples during pyrolysis and fitting results for DTG curves


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Table 1 Proximate and ultimate analyses of coal samples Sample L1 L2 L3 L5 L4 B1 B2 BA B3 B4 B5 B6

C 32.33 44.74 47.29 51.60 60.43 64.00 64.29 64.34 66.44 66.47 75.68 80.04

Ultimate analysis/ d wt. % H N S 3.53 0.59 0.73 5.33 1.23 1.58 3.27 0.81 0.34 4.77 0.92 0.11 4.99 0.94 0.65 4.70 0.91 0.21 4.81 0.93 0.19 4.06 0.84 0.42 4.48 1.32 0.31 4.15 0.82 0.44 4.72 1.02 0.54 4.96 1.58 0.62

O* 36.10 32.94 9.71 34.57 22.29 19.71 27.04 15.00 16.35 20.00 12.73 4.69

Proximate analysis/ad, wt.% M V Ash C fix 31.63 22.73 26.73 18.91 19.60 39.59 14.18 26.64 1.59 22.50 38.58 37.34 27.66 29.72 8.03 34.59 5.97 38.46 10.71 44.88 12.05 26.51 10.48 50.96 21.87 26.51 2.74 48.88 6.52 26.44 15.34 51.70 6.12 26.99 11.10 55.79 11.80 29.05 8.12 51.03 3.81 28.60 5.31 62.28 0.97 24.12 8.12 66.79

Note: M-moisture; V-volatile matter; Cfix -fixed carbon; ad-air dry basis; d-dry basis; O* was calculated by difference.


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Energy & Fuels

Table 2 Compounds identified by GC/MS at region A RT

Name

Note

RT

Name

Note

5.07

n-Pentane

1

17.79

Benzene,1,2,3-trimethyl-

22*

5.44

Cyclopentene

18.18

Indane

5.54

Pentane,2-methyl-

*

18.38

Indene

5.75

1-Hexene

2

18.58

o- Cresol

5.90

n-Hexane

3

18.70

m/p-Diethyl benzene

6.31

Cyclopentane, methyl-

*

18.79

Benzene, 1-methyl-3-propyl-

*

6.43

1,3-Cyclopentadiene, 1-methyl-

*

18.91


*

6.69

Benzene

7.14

Cyclohexene

*

19.00

Benzene, 1-ethyl-3,5-dimethyl-

7.37

1-Heptene

5

19.09


*

7.65

n-Heptane

6

19.27

m/p-Cresol

24

7.96

2-Heptene,(E)-

*

19.63


*

8.21

Cyclohexane, methyl-

*

19.68


*

9.16

Toluene

7

19.87


*

9.31

Pentane, 3-ethyl-2-methyl-

*

20.08


*

10.13

1-Octene

8

20.23

Phenol, 2,6-dimethyl-

*

10.48

n-Octane

9

20.31

1-Undecene

25

10.60

2-Octene, (E)-

*

20.45

Benzofuran, 7-methyl-

10.89

2-Octene, (Z)-

*

20.51


*

11.74

Cyclohexane, 1,1,3-trimethyl-

*

20.67

n-Undecane

26

12.20

Ethylbenzene

10 21.22

Phenol, 2-ethyl-

*

12.50

m/p-Xylene

11 21.54

Phenol, 2,5-dimethyl

27*

12.96

Octane, 3-methyl-

21.61


*

13.13

Styrene

22.07

Phenol, 4-ethyl-

*

13.29

o-Xylene

12 22.15


*

13.54

1-Nonene

13 22.16

Phenol, 3-ethyl-

*

13.93

n-Nonane

14 22.43


*

15.47

Benzene, propyl-

15 22.78

Naphthalene

*

15.72

Benzene,1-ethyl-3-methyl-

16 * 22.87


*

15.79

Benzene, 1-ethyl-4-methyl-

*

23.00

1,2-Benzenediol

15.99

Mesitylene

*

23.04

1H-Indene, 2,3-dihydro-1,6-dimethyl-

16.16

Phenol

17 23.24

Phenol, 2,4,6-trimethyl-

*

16.34

Benzene,1-ethyl-2-methyl-

18 23.37

1-Dodecene

28

16.85

Benzene, 1,2,4-trimethyl-

19* 23.69

n-Dodecane

29

17.03

1-Decene

20 23.75

Benzofuran, 4,7-dimethyl-

17.40

n-Decane

21 23.91

Phenol, 2-ethyl-5-methyl-

17.50

2-Decene, (Z)-

24.04


4+ 18.94

23

Benzene, n-butyl-


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

RT

Name

24.19


24.34


24.78


25.06


25.12

Naphthalene, 1,2-dihydro-6-methyl-

25.16

Benzene, hexyl-

25.19


25.33

Page 32 of 33

RT

Name

32.95

Naphthalene, 1,2,4-trimethyl-

33.28

Fluorene

33.46


33.71

1-Hexadecene

*

33.93

n-Hexadecane

+

*

35.93

1-Heptadecene

*

*

36.14

n-Heptadecane

+


36.74

Naphthalene, 1,2,3,4-tetramethyl-

25.35

Benzene, (1-methylpentyl)-

37.13

Phenol, 4-(2-phenylethenyl)-

25.58

1,2-Benzenediol, 4-methyl-

38.04

1-Octadecene

*

26.21

Tridecene

38.23

n-Octadecane

+

26.50

n-Tridecane

30 40.04

1-Nonadecene

*

28.18

Biphenyl

40.23

n-Nonadecane

+

28.86

1-Tetradecene

41.96

1-Icosene

*

28.97

Naphthalene, 2,7-dimethyl-

42.12

n-Icosane

+

29.13

n-Tetradecane

43.78

1-Heneicosene

*

29.36


*

43.94

n-Heneicosane

+

29.45


*

45.54

1-Docosene

*

29.85


*

45.68

n-Docosane

+

31.26

1-Naphthalenol

*

47.22

1-Tricosene

*

31.36

1-Pentadecene

*

47.36

n-Tricosane

+

31.44

2-Naphthalenol

*

48.87

1-Tetracosene

*

31.60

n-Pentadecane

48.99

n-Tetracosane

+

32.01


32.15


32.51


32.87


Note

* *

*

Note

Note: RT is retention time The number in Note column were the mark for the TOP 30 of peak area in total ion chromatograph (TIC); + Identification assisted by extracting the characteristic fragments; * Identification assisted by Kovats Index


*

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 3 DTGmax values of coal samples during pyrolysis and fitting results for DTG curves Coal samples L1 L2 L3 L4 L5 Average of Lignite coal B1 B2 BA B3 B4 B5 B6 Average of Bituminous coal

DTG max ℃ 450 438 482 468 457

Max mass loss rate %·℃−1 2.48 4.85 3.56 4.06 4.10

C fix daf 27.6 33.1 37.9 47.8 47.7

Peak 1 % 23.5 27.6 7.1 15.9 11.0

Peak 2 % 44.9 55.8 44.3 65.9 64.4

Peak 3 % 25.2 11.4 37.8 13.4 19.1

Peak 4 % 6.4 5.1 10.8 4.8 5.4

459

3.81

38.8

17.0

55.1

21.4

6.5

482 477 478 477 477 490 515

3.21 4.00 4.90 5.68 5.69 5.28 9.43

57.9 62.5 55.3 59.4 57.8 64.7 67.4

2.1 5.6 2.0 4.0 2.6 2.7 9.9

66.6 64.5 69.5 61.0 72.5 65.3 70.1

23.2 21.2 20.3 23.5 17.9 19.7 13.4

8.2 8.6 8.2 11.4 6.9 12.2 6.5

485

5.46

60.7

4.1

67.1

19.9

8.9


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