Sequential Extraction and Thermal Dissolution of Baiyinhua Lignite in

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Sequential Extraction and Thermal Dissolution of Baiyinhua Lignite in Isometric CS2/Acetone and Toluene/Methanol Binary Solvents Yun-Peng Zhao, Jian Xiao, Man Ding, Eric G. Eddings, Xian-Yong Wei, Xing Fan, and Zhi-Min Zong Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b01775 • Publication Date (Web): 18 Nov 2015 Downloaded from http://pubs.acs.org on November 24, 2015

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Sequential Extraction and Thermal Dissolution of Baiyinhua Lignite in Isometric CS2/Acetone and Toluene/Methanol Binary Solvents Yun-Peng Zhao,*,†‡ Jian Xiao,† Man Ding,† Eric G. Eddings,‡ Xian-Yong Wei,*,† Xing Fan,† and Zhi-Min Zong† †

Key Laboratory of Coal Processing and Efficient Utilization (Ministry of Education), China

University of Mining & Technology, Xuzhou 221116, Jiangsu, China ‡

Department of Chemical Engineering, University of Utah, Salt Lake City, 84112, Utah, United

States ABSTRACT Baiyinhua lignite (BL) was sequentially extracted and thermally dissolved in isometric CS2/acetone and toluene/methanol binary solvents, respectively, to produce an extract in isometric CS2/acetone (EICA) and a soluble portion (SP) in isometric toluene/methanol (SPITM). The yields of EICA and SPITM are notably higher than the total extract yield from sequential extraction with CS2 and acetone (or acetone and CS2), and the total SP yield from sequential thermal dissolution in toluene and methanol (or methanol and toluene), respectively, indicating that there exists an obvious synergic effect between CS2 and acetone during the extraction and between toluene and methanol during the thermal dissolution. EICA and SPITM mainly consist of hydrocarbons and oxygen-containing organic species, respectively. Little difference in the FTIR spectra of BL and its extraction residue was observed, while the intensities of absorbance assigned to the phenolic–OH, C=O and C–O/C–O–C groups of the thermal dissolution residue are obviously lower than those of BL and its extraction residue. XPS analysis shows that C–O/C–O–C groups in BL remarkably decreased after thermal dissolution, corresponding to the abundant phenols dissolved in SPITM. The difference in weight loss between BL and its extraction residue is close to the yield of EICA, while 1

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the difference in weight loss between extraction and thermal dissolution residues is significantly lower than the yield of SPITM. Keywords: lignite; extraction; thermal dissolution; binary solvents; organic species 1. INTRODUCTION With the depletion of petroleum and high-quality coal resources, the utilization of lignite has attracted the attention of researchers recently.

1

Unfortunately, high inherent moisture and oxygen

contents, and low calorific values greatly restrict the large-scale application of lignite in traditional industry.2 Therefore, it is necessary to develop alternative processing technologies for their effective utilization. Extraction and thermal dissolution (TD) have attracted more and more attention as efficient approaches to identify the structural characteristics of coals, and to utilize them in a clean and environmentally friendly manner.3-5 Takanohashi et al solvents and

binary solvents, such as pyridine,

6,7

pointed out that some strongly polar

tetrahydrofuran

(THF),

and carbon

disulfide/N-methyl-2-pyrrolidinone (CS2/NMP) are excellent solvents to dissolve the organic species of bituminous coals. Additionally, a small amount of additives, such as tetracyanoethylene and halogenide salt are beneficial for increasing the extract yield of bituminous coals in CS2/NMP.8,9 Ashida et al10,11fractionated two bituminous coals and a lignite into six fractions by tetralin and 1-methylnaphthalene (1-MN) using a sequential TD method, and examined the difference in chemical structure and thermal properties of the fractions. Shui et al12 investigated the TD behavior of Shenfu sub-bituminous coal in different solvents. They found that 1-MN/NMP and 1-MN/methanol binary solvents greatly increased the soluble portion (SP) yield. Nevertheless, it is difficult to separate the soluble organic species from above involved high boiling solvents, resulting in the difficulty to identify the composition and structural characteristics of the extracts or soluble 2


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portions (SPs), and to further upgrade them as fuels or fine chemicals. Yan et al13 found that high boiling solvents can tightly coupled with extraction or TD residues and cannot be removed completely, which may cause some problems when using these residues as a feedstock for combustion or gasification. Moreover, the poor recoverability of high boiling point solvents also influences the economics of extraction process. Therefore, it is necessary to develop an extraction technology using solvents with low boiling points that can be easily separated with both extract and residue. Coal is a sedimentary rock with a large three-dimensional crosslinked macromolecular network of polynuclear aromatic clusters connected by relatively strong chemical bonds, along with the soluble part embedded in the macromolecular network.14,15 Because the soluble part can be extracted out with suitable organic solvents at room temperature, it can be defined as free organic species in coals, whereas a high extraction temperature is necessary in order to dissolve more organic species from coals through the destruction of the weak bridge bonds in macromolecular network, such as ether bond, thioether bond, methylene bond, and methylene ether bond. Therefore, a sequence of extraction at room temperature followed by TD with recyclable solvents is a potential method to isolate the free organic species embedded in the macromolecular network and the organic species originated from the destruction of the weak bridge bonds in macromolecular network, and to provide the possibility for identifying the composition and structural characteristics of the organic species in coals in detail.2 Although several investigations have been carried out previously on the extraction or TD of coals in binary solvents with high boiling points, to the best of our knowledge, sequential extraction and thermal dissolution of lignite in binary solvents with low boiling points, along with delineate the differences in the composition and structural characteristics between the free organic species and the organic species originated from the destruction of the weak 3


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bridge bonds in the macromolecule network of lignite, have not been reported. China possesses nearly 130 billion tons of lignite proven reserves, accounting for about 13% of the total coal reserves of the country.16 In this work, Baiyinhua lignite (BL) was sequentially extracted and thermally dissolved in an isometric CS2/acetone binary solvent and an isometric toluene/methanol binary solvent. To investigate the synergic effect of the binary solvents during extraction and thermal dissolution, BL was also sequentially extracted with CS2 and then acetone (or acetone and then CS2), and the extraction residue in isometric CS2/acetone binary solvent was also sequentially thermally dissolved in toluene and then methanol (or methanol and then toluene). The extract and SP from the binary solvents were characterized with Fourier transform infrared spectroscopy (FTIR) and gas chromatography/mass spectrometer (GC/MS), and the BL, and its extraction and thermal dissolution residues from the binary solvents were analyzed with FTIR, X-ray photoelectron spectroscopy (XPS) and Thermogravimetric analysis (TGA). 2. EXPERIMENTAL SECTION 2.1. Materials. The BL sample was collected from the Baiyinhua 1# basin in Inner Mongolia Autonomous Region of China. It was pulverized to pass through a 200-mesh sieve (99.8%) that were also distilled with a Büchi R-134 rotary evaporator prior to use. 2.2. Extraction and thermal dissolution procedure. As depicted in Figure 1, About 30 g of BL was first extracted with CS2 in an ultrasonic bath at room temperature to produce the extract (E1) and extraction residue (ER1). Each run of the extraction was conducted for 2 h, followed by filtration and distillation. Such operations were repeated with fresh CS2 until few GC/MS-detectable 4


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compounds were detected in the solvent, indicating that the exhaustive extraction was achieved. Then the ER1 was extracted exhaustively with acetone to produce the extract (E2) and extraction residue (ER2). All of the concentrated filtrates from the extraction with the same solvent were incorporated. Similarly, BL was sequentially extracted with acetone and CS2 to produce the extracts, E1' and E2', respectively. BL was extracted in isometric CS2/acetone binary solvent to produce EICA and ERICA. The extract yield Y was calculated according to the formula: Y = mE/mBL,daf, where mE and mBL,daf denote the masses of the extract and BL used (dry ash-free basis), respectively. ERICA was dried in a vacuum oven at 105 oC for 24 h. As exhibited in Figure 2, 2 g of ERICA and 40 mL of toluene were placed into a 100 mL stainless-steel, magnetically-stirred autoclave. Then the autoclave was sealed and the air inside the reactor was replaced with high-purity nitrogen (99.99%) at an initial pressure of 1 MPa. Afterwards, the autoclave was heated to 300 oC by an external electric furnace and held for 1 h, after which the autoclave was cooled down to room temperature in a water bath. The reaction mixture was taken out as cleanly as possible with the appropriate TD solvents from the autoclave, and filtered through a Teflon membrane filter with 0.45 µm pore size, and repeatedly washed with the appropriate solvents to produce filtrates and filter cakes. The filtrate was concentrated with a rotary evaporator to remove solvent under reduced pressure to produce SP1. The filter cake was dried at 105 oC for 24 h in a vacuum oven to produce a TD residue in toluene, TDR1. Then the TDR1 was thermally dissolved in 40 mL methanol at 300 oC to produce SP2 and TDR2. Similarly, ERICA was sequentially thermally dissolved in methanol and toluene to produce SP1' and SP2', respectively. ERICA was thermally dissolved in isometric toluene/methanol binary solvent to produce SPITM and TDRITM. The SP yield was calculated according to the formula: mSP/mBL,daf, where mSP and mBL,daf denote the weight of SP and BL used (dry ash-free basis), respectively. 5


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2.3. Characterization. FTIR spectra of BL, EICA, SPITM, ERICA and TDRITM were recorded from 4000 to 400 cm-1 at a resolution of 2 cm-1 by an EQUINOX55 spectrometer using the KBr pellet technique. EICA and SPITM were analyzed with a Hewlett-Packard 7890/5975 GC/MS equipped with a capillary column coated with HP-5 (cross-link 5% PH ME siloxane, 60 m length, 0.25 mm inner diameter, 0.25 µm film thickness) and a quadrupole analyzer and operated in electron impact (70 eV) mode. GC column temperature was raised from 60 to 300 °C at a rate of 5 °C/min and held at 300 °C for 10 min. The mass range scanned was from 30 to 500 amu and compounds were identified by comparing mass spectra to NIST11 library data. BL, ERICA and TDRITM were analyzed by use of an X-ray photoelectron spectrometer ESCALAB 250Xi (Thermo Fisher, USA) equipped with an Al Kα source and 180 o hemisphere energy analyzer. The spectra were recorded in the FAT mode (∆E=constant) with a pass energy of 20 eV. The calibration was carried out with the main C 1s peak at 284.8 eV. TGA of BL, ERICA and TDRITM were performed on a Mettler Toledo TGA/SDTA851e analyzer. During the experiment, about 15 mg of sample was placed in a ceramic crucible and heated from 25 to 900 °C at 10 oC/min using N2 as the carrier gas at a constant flow rate of 60 mL/min. 3. RESULTS AND DISCUSSION 3.1 Yields of extracts and SPs. As listed in table 2, the yields of E1, E2, E'1 and E'2 from BL are 0.33, 2.69, 2.69 and 0.10%, respectively, whereas the yield of EICA is 6.10%, which is clearly higher than the total extract yield in sequential individual solvents, regardless of the solvent sequence. The yields of SP1, SP2, SP'1 and SP'2 are 4.08, 13.83, 17.60 and 1.55%, respectively, whereas the yield of SPITM is 30.32%, which is also substantially higher than the total SP yield in sequential individual solvents, regardless of the solvent sequence. Previous researches demonstrated that low liquid yields were obtained during coal TD in toluene even the temperature higher than 400 oC.17,18 During 6


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extraction and TD, a synergic effect arising between two or more solvent possibly produces higher yield of extract or SP than the total yield of the extracts or SPs from individual solvents. Therefore, the results from this work suggest that there exists obvious synergic effects both between CS2 and acetone during the extraction of BL, and between toluene and methanol during the TD of ERICA. Additionally, it is observed that the total yields of EICA and SPITM are higher than the volatile matter content of BL (Table 1), indicating the organic species in EICA and SPITM not only originate from the release of the volatile matter, but also from the breakage of weak bridge bonds in the macromolecular network of BL. The extraction of coal is mainly controlled by two factors, one is the solubility of solvent to coal, and another is the penetration ability of solvent into the coal cross-link structure.19 A number of studies have carried out to examine the existence of synergic effects between two solvents.7-9,12,15,19 The viscosities of high boiling solvents, such as NMP, are too high to enter the cross-link structure of coals. Shui et al19 reviewed the speculations about the reasons for extraction enhancement in CS2/NMP mixed solvent, and they pointed out that CS2 may disrupt the dipole based association of NMP thus decrease the viscosity of CS2/NMP mixed solvent, resulting in NMP penetrate more quickly into the macromolecular network structure of coal and break the stronger coal-coal interaction. Nevertheless, the solvents used in this work are low boiling solvents with low viscosity, therefore, the reasons for the extraction and TD enhancement in isometric CS2/acetone and toluene/methanol binary solvents are different from those in CS2/NMP mixed solvent. CS2 and acetone tent to extract different type of organic species in BL for their different polarity and solubility. The dissolution of extractable organic species in CS2 and the swelling effect of CS2 on the macromolecular network possibly accelerate the dissolution of extractable organic species in acetone, and vice versa. As a nucleophilic and H-donor solvent, methanol can attack and break the 7


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oxygen bridge bonds in coals and stabilize radicals, resulting in more organic species release from the macromolecular network.20,21These organic species released from the breakage of oxygen bridge bonds possible easily dissolve in toluene rather polymerize each other into residue. 3.2 Analyses of EICA and SPITM. As presented in Figure 3, the FTIR spectra of both EICA and SPITM have absorption peaks attributed to phenolic–OH (3700-3000 cm-1), aliphatic moieties (2929, 2865, 1450 and 1376 m-1), C=O (1702 cm-1), aromatic C=C (1600 cm-1), and C–O (1330-1000 cm-1) groups.22,23 Nevertheless, the intensity of the absorption peak assigned to phenolic–OH in the FTIR spectra of SPITM is stronger and the peak center shifts to a higher wavenumber region compared with those of EICA, indicating that more phenols exist in the SPITM than in EICA. Additionally, the absorption peak ascribed to ether bond vibration (1090 cm-1) is only detected in the FTIR spectrum of SPITM, implying that there are abundant compounds containing ether bonds in SPITM.24 Moreover, there are more absorption peaks assigned to the C–H bending vibrations of aromatics at the band of 650-920 cm-1 in the FTIR spectrum of SPITM than with those of EICA, indicating more types of alkyl substituents in the arenes of SPITM than those of EICA. To further investigate the component difference between the EICA and SPITM, they were characterized with GC/MS analysis. As presented in Figure S1 and Table 2, there are significant differences in the components between EICA and SPITM. It should be noted that the compounds presented in Table 2 only represent the detected compounds with relative content over 1% by GC/MS analysis. The main compounds identified in EICA are hydrocarbons, including condensed arenes (54.11%) and alkanes (9.41%), which suggests that the majority free organic species embedded in the macromolecular network of BL are hydrocarbons. Among the detected condensed arenes, the relative contents of naphthalene and 7-isopropyl-1-methylphenanthrene are greater than 10%. 8


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Condensed arenes have the properties of teratogenicity, carcinogenicity and mutagenicity, therefore, the generation of condensed arenes during coal utilization processes including combustion, gasification and carbonization has received considerable attention.25 It was proposed that the condensed arenes in the “mobile” phase of coals are of particular environmental concern, since they can be more easily released into the environment than those interlinked with the macromolecular network.26,27

Additionally,

two

organonitrogen

compounds,

i.e.

7-ethyl-2,4-dimethylbenzo[b][1,8]naphthyridin-5(10H)-one (9.06%) and 4'-cyanobiphenyl-4-yl 4-(4-pentylcyclohexyl)benzoate (1.29%) were extracted from BL. Nitrogen atoms are considered as precursors for pollutant formation when coals are used as fuels, therefore, the isolation and identification of organonitrogen compounds in coals before use are benefit for the clean utilization of coals.28 Differing from those of EICA, the dominant compounds identified in SPITM are oxygen-containing organic

compounds

including

phenols

(37.04%),

alcohols

(9.05%)

and

3,4,5-trimethylcyclopent-2-enone (3.64%) and methyl heptacosanoate (1.39%). In accord with the strong phenolic–OH absorption peak in the FTIR spectrum of SPITM, the phenols are the most abundant compounds in SPITM. Most of the phenols in SPITM are alkylphenols, suggesting that there possibly exist abundant (CH3)nAr–OAr structural units in the macromolecular network of BL.29 Among these oxygen-containing organic compounds in SPITM, both 2-methoxypropan-1-ol and 3-methoxy-2,4,6-trimethylphenol contain a methoxyl group. Actually, many compounds with relative content less than 1% in SPITM also contain a methoxyl group, such as 2-methoxy-4-methylphenol (0.57%), 2-methoxy-3-methylphenol (0.21%), dimethoxybenzene (0.20%) and 2-methoxy-1,3,5-trimethylbenzene (0.38%), etc. These results are in agreement with the obvious peak at 1090 cm-1 assigned to ether bond vibration in the FTIR spectrum of SPITM. 9


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3.3 Analyses of BL, ERICA and TDRITM. As shown in Figure 4, the FTIR spectra of BL and ERICA exhibit similar functionalities reflecting that the extraction process has little influence on the macromolecular network of BL, which also indicate that the extract mainly comes from the free organic species in BL. Nevertheless, the FTIR spectrum of TDRITM is clearly different from the FTIR spectra of BL and ERICA. In particular, the intensities of the absorption peaks assigned to the oxygen-containing groups including phenolic–OH (3600-3000 cm-1), C=O (1700 cm-1), and C–O (1100 cm-1) in the FTIR spectrum of TDRITM are weaker than those in the FTIR spectra of BL and ERICA. These results indicate that abundant organic species with oxygen-containing groups are dissolved out and that the macromolecular network was partly destroyed during TD of ERICA in isometric toluene/methanol binary solvent. X-ray photoelectron spectroscopy (XPS) is an effective non-destructive method to determine the occurrence forms of elements in coals.30,31 As seen in Figure 5, the O 1s spectra were curve-resolved into three peaks at 531.4, 532.8, and 534.0 eV, which were assigned to C=O, C– O/C–O–C, and O–C=O groups, respectively. The N 1s spectra were curve-resolved into three peaks at 398.8, 400.2, and 401.4 eV, which were ascribed to pyridinic–N (Np), pyrrolic–N (Np'), and quaternary–N (Nq), respectively. As shown in Table 4. The relative content of the O–C=O group decreases in the order of BL > ERICA > TDRITM due to the gradual dissolution of esters or decomposition of carboxyl groups in BL. It is proposed that carboxylic groups in coals can be decomposed to aldehydes, then to alcohols during TD, which may be the reason why some alcohols exist in SPITM.32 The amount of the C=O group in ERICA is clearly less than that in BL, corresponding to the high content of compounds with C=O group in EICA, e.g. 7-ethyl-2,4-dimethylbenzo[b][1,8]naphthyridin-5(10H)-one (Table 3). The TD treatment results in the dramatic decrease of C–O/C–O–C groups in TDRITM compared with 10


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ERICA, which coincides with the high content of phenols in SPITM, and the low intensity of the phenolic–OH absorption peak in the FTIR spectrum of TDRITM. The relative content of Np, Np' and Nq in BL are 38.19, 38.59, and 23.22%, respectively. Corresponding

to

the

high

relative

content

of

7-ethyl-2,4-dimethylbenzo[b][1,8]naphthyridin-5(10H)-one with Np' in EICA, the relative content of Np' in ERICA is less than that in BL. The relative content of Nq decreases in the order of BL > ERICA > TDRITM. It was reported that The decomposition of acidic oxygenic functional groups, such as the carboxyl group, possibly leads to the deprotonation of Nq to produce Np' during TD; therefore, the relative content of Np' in TDRITM is slightly higher than that of ERICA.32 The relative amount of Np in ERICA is more than that in BL due to the decrease of Np' and Nq, while there is almost no difference in the relative content of Np between ERICA and TDRITM. Geng et al

32

found that the

relative content of Np in the residues of lignite from hydrothermal treatment did not change with temperature, and they proposed that Np has not been involved in acid-base interactions. TGA is a useful technique to obtain the weight loss and rate of weight loss of solid fuels with increasing temperature, which can be used to determine the pyrolysis reactively and the information of composition and physicochemical structure of solid fuels to some extent.33 The TG/DTG curves of BL, ERICA and TDRITM are shown in Figure 6. For these three samples, the weight loss is in the order of BL > ERICA > TDRITM as expected. The difference in weight loss between BL and ERICA at 900 oC is 7.11%, which is slightly higher than the yield of EICA, demonstrating that the extraction process mainly extracts the free organic species embedded in the macromolecular network of BL, which are easily released during pyrolysis. However, the difference in weight loss at 900 oC between ERICA and TDRITM is only 6.15%, which is clearly less than the SPITM yield (30.32%). This result indicates that most organic species in the SPITM originate from the breakage of the 11


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macromolecular network rather than the release of volatile matter in BL. Due to the remove of free organic species in BL during extraction, the temperature corresponding to the maximum weight loss rate (Tp) of ERICA is slightly higher than that of BL, whereas the maximum weight loss rate of ERICA is slightly higher than that of BL, which may possibly be ascribed to the swelling effect of isometric CS2/acetone binary solvent on the macromolecular network of BL. Swelling of coal could break weaker non-covalent bonds and increase macropores in coals, resulting in the relaxation of coal macromolecular network and the decrease of diffusive limitation.34,35 Shui et al

19

defined the height ratio of the peak originated from OH self-associated

hydrogen bond vibration to the peak assigned to aromatic vibration in FTIR spectra are 1.0 for raw coal. Compared with the ratio for raw coal, the ratios for the tetrahydronaphthalene swollen coal and the NMP swollen coal are 0.97 and 0.74. According to Figure 4, the height ratio of the peak originated from OH self-associated hydrogen bond vibration (3170 cm-1) to the peak assigned to aromatic vibration (1600 cm-1) for ERICA is 0.78 compared with the ratio for BL (1.0), indicating the extraction process of BL in isometric CS2/acetone binary solvent obviously decreased OH self-associated hydrogen bonds in BL, resulting in structural relaxation of ERICA compared with BL. Moreover, a small weight loss peak appears at around 700 oC in the DTG curve of ERICA, which also may be due to the swelling effect of isometric CS2/acetone binary solvent on the macromolecular network of BL. The Tp of TDRITM is notably higher and the maximum weight loss rate is considerably lower than those of ERICA, indicating TD process enhances the cross-linking strength of the macromolecular network structure of BL.36,37 4. CONCLUSIONS The yields of extract and SP in isometric CS2/acetone and isometric toluene/methanol binary solvents were found to be substantially higher than the total yields of extracts and SPs obtained 12


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from extraction and TD using the same solvents individually but in sequence, indicating that synergic effects exist between CS2 and acetone during the extraction, and between toluene and methanol during the TD. The compounds in EICA and SPITM mainly consist of by hydrocarbons and oxygen-containing organic species, respectively. FTIR and XPS analysis results show that the extraction in isometric CS2/acetone binary solvent has little influence on the macromolecular network structure of BL, while the TD in isometric toluene/methanol binary solvent results in dramatic breakage of oxygen bridge bonds or decomposition of the oxygen-containing functional groups. TG/DTG analysis results demonstrate that almost all the components in EICA come from the free organic species embedded in the macromolecular network of BL, while most of the components in SPITM originate from the breakage of the macromolecular network rather than the release of volatile matter. These findings indicate that sequential extraction and TD in the two binary solvents are beneficial for isolating and identifying the organic species from lignites and facilitating the development of alternative utilization technologies for lignites. AUTHOR INFORMATION Corresponding Author *Telephone: +86-516-83995916. E-mail address: [email protected], [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was subsidized by the Fundamental Research Funds for the Central Universities (China University of Mining & Technology; Grant 2015QNA25), and the Priority Academic Program Development of Jiangsu Higher Education Institutions. 13


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ABBREVIATIONS BL = Baiyinhua lignite EICA = extract in isometric CS2/acetone binary solvent ERICA = extraction residue in isometric CS2/acetone binary solvent FTIR = Fourier transform infrared spectroscopy GC/MS = gas chromatography/mass spectrometer NMP = N-methyl-2-pyrrolidinone SP = soluble portion SPITM = SP in isometric toluene/methanol binary solvent TD = thermal dissolution TDRITM = TD residue in isometric toluene/methanol binary solvent TGA = Thermogravimetric analysis THF = tetrahydrofuran XPS = X-ray photoelectron spectroscopy 1-MN = 1-methylnaphthalene REFERENCES (1) Thielemann, T.; Schmidt, S.; Gerling, J. P. Lignite and hard coal: Energy suppliers for world needs until the year 2100-An outlook. Int. J. Coal Geol 2007, 72, 1–14. (2) Katalambula, H.; Gupta, R. Low-grade coals: a review of some prospective upgrading technologies. Energy Fuels 2009; 23, 3392–405. (3) van Bodegom, B.; van Veen, J. A. R.; van Kessel, G. M. M.; Sinnige-Nijssen, M. W. A.; Stuiver, H.C.M. Action of solvents on coal at low temperatures. 1. Low rank coals. Fuel 1984, 63, 346– 54. 14


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(4) Okuyama, N.; Komatsu, N.; Shigehisa, T.; Kaneko, T.; Tsutuya, S. Hyper-coal process to produce the ash-free coal. Fuel Process. Technol. 2004, 85, 947–96. (5) Makgato, M. H.; Moitsheki, L. J.; Shoko, L.; Kgobane, B. L.; Morgan, D. L.; Focke, W. W. Alkali-assisted coal extraction with polar aprotic solvents. Fuel Process. Technol. 2009, 90, 591–8. (6) Takanohashi, T.; Iino, M. Insolubilization of coal soluble constituents in some bituminous coals by refluxing with pyridine. Energy Fuels 1991, 5, 708–11. (7) Takanohashi, T.; Xiao, F.; Yoshida, T.; Saito, I. Difference in extraction yields between CS2/NMP and NMP for Upper Freeport coal. Energy Fuels 2003, 17, 255–56. (8) Takahashi, K.; Norinaga, K.; Masui, Y.; Iino, M. Effect of addition of various salts on coal extraction with carbon disulfide/N-methyl-2-pyrrolidinone mixed solvent. Energy Fuels 2001, 15, 141–46. (9) Dyrkacz, G.R.; Bloomquist, C. A. A. Changes in coal extractability with timed addition of tetracyanoethylene in carbon disulfide/N-methylpyrrolidone extractions. Energy Fuels 2000, 14, 513–14. (10) Ashida, R.; Nakgawa, K.; Oga, M.; Nakagawa, H.; Miura, K. Fractionation of coal by use of high temperature solvent extraction technique and characterization of the fractions. Fuel 2008, 87, 576–82. (11) Ashida, R.; Morimoto, M.; Makino, Y.; Umemoto, S.; Nakagawa, H.; Miura, K.; Saito, K.; Kato, K. Fractionation of brown coal by sequential high temperature solvent extraction. Fuel, 2009, 88, 1485–90. (12) Shui, H. F.; Zhou, Y.; Li, H. P.; Wang, Z. C.; Lei, Z. P.; Ren, S. B.; Pan C, X.; Wang, W. W. Thermal dissolution of Shenfu coal in different solvents. Fuel 2013, 108, 385–90. 15


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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

(13) Yan, J. C.; Bai, Z. Q.; Bai, J.; Li, W. Chemical structure and reactivity alteration of brown coals during thermal treatment with aromatic solvents. Fuel Process. Technol. 2015, 137, 117– 23. (14) Given, P. H.; Marzec, A.; Barton, W. A.; Lynch, L.J.; Gerstein, B.C. The concept of a mobile or molecular phase within the macromolecular network of coal: a debate. Fuel 1986, 65, 155– 63. (15) Shui, H. F.; Wang, Z. C.; Cao, M. X. Effect of pre-swelling of coal on its solvent extraction and liquefaction properties. Fuel 2008, 87, 2908–13. (16) Li, X. H.; Xue, Y. L.; Feng, J.; Yi, Q.; Li, W. Y.; Guo, X. F.; Liu, K. Co-pyrolysis of lignite and Shendong coal direct liquefaction residue. Fuel 2015, 144, 342–48. (17) Amestica, L. A.; Wolf, E. E. Supercritical toluene and ethanol extraction of an Illinois No. 6 coal. Fuel 1984, 63, 227–30. (18) Cahill, P.; Harrison, G.; Lawson, G. J. Extraction of intermediate and low-rank coal with supercritical toluene. Fuel 1989, 68, 1152–7. (19) Shui, H. F.; Wang, Z. C.; Gao, J. S. Examination of the role of CS2 in the CS2/NMP mixed solvents to coal extraction. Fuel Process. Technol. 2006, 87, 185–90. (20) Chen. B.; Wei, X. Y.; Zong, Z. M.; Yang, Z. S.; Qing ,Y. Difference in chemical composition of supercritical methanolysis products between two lignites. Appl. Energy 2011, 88, 4570–6. (21) Yuan, Q. C.; Zhang, Q. M.; Hu, H. Q.; Guo, S. C. Investigation of extracts of coal by supercritical extraction. Fuel 1998, 77, 1237–41. (22) Lei, Z. P.; Cheng, L. L.; Zhang, S. F.; Shui, H. F.; Ren, S. B.; Kang, S. G.; Pan, C. X.; Wang, Z. C. Dissolution of lignite in ionic liquid 1-ethyl-3-methylimidazolium acetate. Fuel Process. Technol. 2015, 135, 47–51. 16


Page 16 of 29

Page 17 of 29

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

(23) Ding, M.; Zhao, Y. P.; Dou, Y. Q.; Wei, X. Y.; Fan, X.; Cao, J. P.; Wang, Y. L.; Zong, Z. M. Sequential extraction and thermal dissolution of Shengli lignite. Fuel Process. Technol. 2015, 135, 20–4. (24) Sun, Y.; Wang, X. J.; Feng, T. T.; Yu, G. S.; Wang, F. C. Evaluation of coal extraction with supercritical carbon dioxide/1-methyl-2-pyrrolidone mixed solvent. Energy Fuels 2014, 28, 816–24. (25) Mastral, A. M.; Callén, M. S. A review on polycyclic aromatic hydrocarbon (PAH) emission from energy generation. Environ. Sci. Technol. 2000, 34, 3051–57. (26) Haenel, M. W. Recent progress in coal structure research. Fuel 1992, 71, 1211–23. (27) Achten, C.; Hofmann, T. Native polycyclic aromatic hydrocarbons (PAH) in coals-A hardly recognized source of environmental contamination. Sci. Total Environ. 2009, 24, 2461–73. (28) Kawashima, H.; Koyano, K.; Takanohashi, T. Changes in nitrogen functionality due to solvent extraction of coal during Hypercoal production. Fuel Process. Technol. 2013, 106, 275–80. (29) Siskin, M.; Aczel, T. Pyrolysis studies on the structure of ethers and phenols in coal. Fuel 1983, 62, 1321–26. (30) Kelemen, S. R.; Afeworki, M.; Gorbaty, M. L. Characterization of organically bound oxygen forms in lignites, peats, and pyrolyzed peats by X-ray photoelectron spectroscopy (XPS) and solid-state 13 C NMR methods. Energy Fuels 2002, 16, 1450–62. (31) Nowicki, P.; Pietrzak, R.; Wachowska, H. X-ray photoelectron spectroscopy study of nitrogen-enriched active carbons obtained by ammoxidation and chemical activation of brown and bituminous coals. Energy Fuels 2010, 24, 1197–206. (32) Geng, W. H.; Kumabe. Y.; Nakajima, T.; Takanashi, H.; Ohki, A. Analysis of hydrothermally-treated and weathered coals by X-ray photoelectron spectroscopy. Fuel 2009, 17


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

88, 644–9. (33) Takagi, H.; Isoda, T.; Kusakabe, K.; Morooka, S. Relationship between pyrolysis reactivity and aromatic structure of coal. Energy Fuels 2000, 14, 646–53. (34) Takanohashi, T.; Yanagida, T.; Iino, M. Extraction and swelling of low-rank coals with various solvents at room temperature. Energy Fuel 1996; 10, 1128–32. (35) Joseph, J. T. Beneficial effects of preswelling on conversion and catalytic activity during coal liquefaction. Fuel 1991, 70, 459–64. (36) Wang, Z.Q.; Bai, Z.Q.; Li, W.; Chen, H. K.; Li, B.Q. Quantitative study on cross-linking reactions of oxygen groups during liquefaction of lignite by a new model system. Fuel Process. Technol. 2010 91, 410–3. (37) Miknis, F. P.; Netzel, D. A.; Turner, T. F.; Wallace, J. C.; Butcher, C.H. Effect of different drying methods on coal structure and reactivity toward liquefaction. Energy Fuels 1996, 10, 631–40.

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Table 1. Proximate and ultimate analyses (wt. %) of BL Proximate analysis Mad Ad Vdaf 35.07 17.01 40.60

Ultimate analysis (daf) H N Oa 5.06 1.44 > 22.19

C 69.91

St,d 1.40

Mad: moisture (air dried base); Ad: ash (dry base, i.e., moisture-free base); Vdaf: volatile matter (dry and ash-free base); a By difference.

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Table 2.Yields (wt. %, daf) of the extracts and SPs extracts E1 E2 E1' E2' EICA SP1 0.33

2.69

2.69

0.1

6.10

4.08

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SP2

SPs SP1'

SP2'

SPITM

13.83

17.60

1.55

30.32

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Energy & Fuels

Table 3. Compounds detected in EICA and SPITM compound 2-methoxypropan-1-ol (2E,4E)-hexa-2,4-diene 3,4,5-trimethylcyclopent-2-enone naphthalene dimethylphenol azulene ethylmethylphenol trimethylphenol 2-ethyl-4,5-dimethylphenol 4-isopropyl-3-methylphenol methylnaphthalene 2,6,10,14-tetramethylhexadecane 3-methoxy-2,4,6-trimethylphenol tetramethylphenol tetradecane (4-tert-butylphenyl)methanol pentadecane 1,2-dihydroacenaphthylene fluorene 4-isopropyl-1,6-dimethylnaphthalene N1,N1,N4,N4-tetramethylbenzene-1,4-diamine trimethylnaphthalene phenanthrene 1,2-diethyl-3,4,5,6-tetramethylbenzene 7-isopropyl-1,1,4a-trimethyl-1,2,3,4,4a,9,10,10a-octahydrophenanthrene 7-butyl-1-hexylnaphthalene 7-ethyl-2,4-dimethylbenzo[b][1,8]naphthyridin-5(10H)-one 7-isopropyl-1-methylphenanthrene tricosane tetracosane methyl heptacosanoate heptacosane (5α)-ergost-14-ene 4'-cyanobiphenyl-4-yl 4-(4-pentylcyclohexyl)benzoate total n, Not including the small peaks with an area less than 1% of the total area.

21


relative content (%) EICA SPITM n 7.62 n 3.27 n 3.64 13.67 n n 6.11 1.17 n n 1.21 n 14.49 n 1.26 n 4.99 1.71 n 1.40 n n 1.80 n 7.15 1.95 n n 1.43 2.32 n 3.84 n 1.46 n 1.34 n n 6.11 n 1.25 1.35 n n 1.41 5.83 n 1.18 n 9.06 n 22.56 1.01 1.24 n 1.35 n n 1.39 1.15 n 1.07 n 1.29 n 74.94 64.14

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Table 4. Distribution of oxygen and nitrogen forms (molar content, %) in BL, ERICA and TDRITM from XPS analysis Sample

C=O

Oxygen forms C–O/C–O–C O–C=O

Np

Nitrogen forms Np'

Nq

BL

54.35

20.75

25.02

38.19

38.59

23.22

ERICDA TDRITM

22.28 67.74

66.68 22.75

11.04 9.51

48.35 48.07

30.48 32.20

21.17 19.73

Np, Pyrrolic-N; Np', Pyridinic-N; Nq, Quaternary-N

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Energy & Fuels

Figure captions Figure 1. Sequential extraction of BL in CS2 and acetone. Figure 2. Sequential TD of ERICA in toluene and methanol. Figure 3. FTIR spectra of EICA and SPITM. Figure 4. FTIR spectra of BL, ERICA and TRDITM. Figure 5. O 1s and N 1s XPS spectra of BL, ERICA and TDRITM. Figure 6. TG and DTG curves of BL, ERICA and TDRITM.

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Energy & Fuels

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BL extraction with CS2

E1

ER1 extraction with acetone

E2

ER2

Figure 1. Sequential extraction of BL in CS2 and acetone.

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Energy & Fuels

ER ICA TD in toluene

SP 1

TDR 1 TD in methanol

SP 2

TDR 2

Figure 2. Sequential TD of ERICA in toluene and methanol.

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Energy & Fuels

EICA

2865

1702 1600 1450 1376 1220 1090

815 871 754

SPITM

2929

Transmittance (%)

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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4000

3000

2000

1000 -1

Wavenumber (cm )

Figure 3. FTIR spectra of EICA and SPITM.

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BL ERICA

Transmittance

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

4000

TDRITM

3000

2000

1000 -1

Wavenumber (cm )

Figure 4. FTIR spectra of BL, ERICA and TDRITM.

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Energy & Fuels

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C-O

C=O

O-C=O

O 1s

Np

BL

BL

ERICA

ERICA

TDRITM

TDRITM

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Np'

Nq

N 1s

538 537 536 535 534 533 532 531 530 529 406 405 404 403 402 401 400 399 398 397 396

Binding energy (eV)

Binding energy (eV)

Figure 5. O 1s and N 1s XPS spectra of BL, ERICA and TDRITM.

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BL

Weight (wt.%, daf)

100

ERICA TDRITM

90 80 70 60

Weight-loss rate (%/oC, daf)

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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0.00 -0.04 -0.08 -0.12 -0.16 200

400 600 Temperature (oC)

800

Figure 6. TG and DTG curves of BL, ERICA and TDRITM.

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Sequential Extraction and Thermal Dissolution of Baiyinhua Lignite in

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