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Fuel properties and chemical compositions of the tar produced from a 5 MW industrial biomass gasification power generation plant
Journal of the Energy Institute xxx (2014) 1e10
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Fuel properties and chemical compositions of the tar produced from a 5 MW industrial biomass gasification power generation plant Liang Li a, Sheng Huang a, b, Shiyong Wu a, b, *, Youqing Wu a, b, Jinsheng Gao a, b, Junwen Gu a, Xiaogang Qin c a
Department of Chemical Engineering for Energy Resources, East China University of Science and Technology, Shanghai 200237, China Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry of Education, East China University of Science and Technology, Shanghai 200237, China c Technology Center, Dongfang Boiler Group Co. Ltd, Dongfang Electric Group, Chengdu 611731, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 May 2014 Received in revised form 8 July 2014 Accepted 15 July 2014 Available online xxx
The industrial biomass gasification tar (IBGT) was analyzed for its basic fuel properties and chemical compositions. The results suggested that IBGT had some special properties (high water content, high ash content, high viscosity, etc.). IBGT was subjected to extraction to obtain n-hexane soluble, n-hexane insoluble/toluene soluble, toluene insoluble/tetrahydrofuran soluble, and tetrahydrofuran insoluble fractions, which were characterized by FTIR. The n-hexane soluble fraction was further fractionated by column chromatography into four fractions, which were characterized by gas chromatography-mass spectrometry (GC/MS). The n-hexane insoluble/toluene soluble and toluene insoluble/tetrahydrofuran soluble fractions were characterized by 1H NMR. The results showed that the first fraction (6.96 wt.%) contained alkanes and alkenes; the second fraction (15.68 wt.%) contained 1e3 ring aromatics; the third fraction (29.20 wt.%) contained oxygen compounds, such as phenols; the fourth fraction (6.40 wt.%) contained nitrogen compounds, such as quinoline, isoquinoline, amine and amide; the fifth fraction (21.07 wt.%) mainly contained polycyclic aromatic structure with short aliphatic side chain and long aliphatic bridge bond; the sixth fraction (12.32 wt.%) mainly contained polycyclic aromatic structure with heteroatom side chain; the seventh fraction (8.38 wt.%) contained ash, coke and unreacted biomass. These results may present an effective solution to utilization of IBGT. © 2014 Energy Institute. Published by Elsevier Ltd. All rights reserved.
Keywords: Tar Fuel property Chemical composition Biomass gasification
1. Introduction Biomass energy is chemical energy which is transformed from solar energy through the photosynthesis of green plants and can be directly or indirectly converted into conventional solid, liquid and gaseous fuels [1,2]. Biomass gasification technology, which experiences relatively rapid development in recent years, is a kind of biomass thermochemical treatment technology. It can convert the low grade solid biomass into the high grade gas which can be used in the synthesis, heating, power generation and other utilization. It also can improve the efficiency of energy, so the research and development of biomass gasification have drawn wide attention from the world [3]. Biomass gasification tar (BGT) is a by-product in biomass gasification process [4]. Its yield depends on gasification process. Meanwhile, BGT is a potential feedstock for chemical products and transportation fuels. The direct emission of the tar will cause not only the waste of resources, but also serious pollution of the environment. The chemical composition of BGT is distinctly different from that of coal tar, such as high heteroatom content, high viscosity, high ash content, high oxygen content and high corrosiveness [5,6]. In fact, the compositions of BGT have not been thoroughly defined, especially industrial biomass gasification tar (IBGT). From the literatures [7e10], BGT is composed of acids, alcohols, aldehydes, esters, ketones, sugars, phenols, guaiacols, syringols, furans, lignin derived phenols and extractible terpene with multi-functional groups. Several analytical tools, such as gas chromatography and gas
* Corresponding author. Department of Chemical Engineering for Energy Resources, East China University of Science and Technology, Shanghai 200237, China. Tel.: þ86 21 64253236. E-mail addresses: [email protected] (L. Li), [email protected] (S. Wu). http://dx.doi.org/10.1016/j.joei.2014.07.002 1743-9671/© 2014 Energy Institute. Published by Elsevier Ltd. All rights reserved.
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chromatography/mass spectroscopy could provide molecular composition information [11e15], but the chromatographic peaks of various compounds overlapped because of the complexity and structural similarity of the components in BGT. Therefore, column chromatography pretreatment step, which is prior to characterization of organic compounds in BGT, is an effective separation method [16e18]. For valuable, efficient, reliable and environmental friendly utilization of tar which was produced from biomass gasification, it is essential to study its organic composition and fuel properties. In this paper, a series of experiments were performed to systematically characterize basic fuel properties of industrial biomass gasification tar (IBGT) obtained from 5 MW industrial biomass gasification power generation plant, and to investigate the compounds composition of the tar by analytical techniques including GC/MS, FTIR and 1H NMR. The results are expected to demonstrate the potential application prospects of tar and provide useful information for the industrial scale biomass gasification. 2. Materials and methods 2.1. Tar materials IBGT sample was obtained from a 5 MW industrial biomass gasification power generation plant of Gaoyou Linyuan Technology Co., Ltd. of China. As can be observed in Fig. 1, rice straw was fed into the gasifier, which was an up-draft, fixed-bed type. The gas passed through water scrubber. The majority of tar (almost 95% of totals) in gas was washed and collected in tar tank. Most of the remained tar in the gas would be removed through the electrostatic tar-catcher and assembled in the same tar tank. The purified gas was sent to purification towers to achieve the requirements of power generation, subsequently it was transported to gas engine sets. Biomass material of gasification was characterized. The results of elemental analysis were Cdaf ¼ 54.99%, Hdaf ¼ 7.20%, Ndaf ¼ 1.64% and St,d ¼ 0.23%, while the results of approximate analysis were Mad ¼ 9.37%, Vdaf ¼ 78.23% and Ad ¼ 20.14%. IBGT sample derived from the tar tank, which collected almost 98% of total tar, was provided for the study without further treatment. During the period of sampling, the operation parameters for the plant were as follows: biomass consumption rate of 5e6 t/h, gasification temperature of around 1100 C, net power output of 5 MW. The typical values of the dry gas compositions used in the plant were as follows: CO 24.5%, H2 18.4%, CH4 3.8%, CO2 12.0%, CnHm 0.5%, N2 40.4%, O2 0.4% and LHV 6.59 MJ/m3. 2.2. Basic fuel properties of IBGT The basic fuel properties of IBGT include water content, total acid value, ash content, heating value, volatile content, viscosity, elemental analysis and the inorganic composition of IBGT ash. The water content, total acid value, ash content and high heating value were determined according to GB/T 2288e2008, GB/T 18609e2011, GB/T 28731e2012 and GB/T 384-1981, respectively. The volatile content was determined in an oven, and maintained at the temperature of 915 C for 7 min. The rotational viscosity was monitored by an NDJ-1B rotational viscometer and the temperature was controlled by a CH1015 super thermostatic bath. Variations of rotational viscosity under constant speeds of 60 rpm were recorded. The elemental analysis of IBGT was determined using an Elementar vario macro cube analyzer. All element contents in ash were measured by a sequential X-ray fluorescence spectrometer (XRF-1800). 2.3. Group separation for IBGT The group separation scheme in this study was shown in Fig. 2. IBGT sample was separated into n-hexane soluble and insoluble fractions by Soxhlet extraction for 10e12 h. The n-hexane insoluble fraction was vacuum dried and preserved for further analysis. The n-hexane in the n-hexane soluble fraction was removed by rotary evaporator. The column chromatography was firstly packed with 20 g of activated neutral alumina (heating at 500 C for 5 h), followed by 20 g of activated silica gel (heating at 120 C for 5 h). The n-hexane soluble fraction (approximately 1 g) dissolved in a small volume of n-hexane was loaded at the top of the column. The four fractions were obtained by sequential solvent elution using n-hexane (150 ml), toluene (200 ml),
Water scrubber Electrostatic Gas purification tower tar-catcher To generate electricity
Gasifier
Tar tank
Fig. 1. The 5 MW industrial biomass gasification power generation process.
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Tar Extracted by n-hexane
N-hexane soluble fraction
N-hexane insoluble fraction Extracted by toluene
Column chromatography
Soluble fraction
Removed solvent F-I
Toluene 200ml Removed solvent F-II
Ether 200ml Removed solvent F-III
Extracted by tetrahydrofuran
Removed solvent
Eluted successively
N-hexane 150ml
Insoluble fraction
Methanol 200ml
Soluble fraction
Removed solvent F-IV
Removed solvent F-V
F-VI
Insoluble fraction Removed solvent F-VII
Fig. 2. The group separation process of IBGT.
ether (200 ml) and methanol (200 ml), respectively. The solvent was removed by a rotary evaporator. Then the weight of each fraction (marked as F-I, F-II, F-III, F-IV in sequence) was measured. The dried n-hexane insoluble fraction was extracted with toluene, tetrahydrofuran in sequence by Soxhlet extraction for 10e12 h. Then the solvent in the toluene solution and the tetrahydrofuran solution was removed by rotary evaporator, respectively. The toluene soluble fraction (F-V), the toluene insoluble/tetrahydrofuran soluble fraction (F-VI) and the tetrahydrofuran insoluble fraction (F-VII) were obtained. Pictures at the bottom in Fig. 2 were fractions obtained from the group separation with removing solvent. 2.4. Characterization of separation fractions The elemental analysis of F-I ~ F-VII were determined using an Elementar vario macro cube analyzer. A mixture was prepared by grinding and thoroughly mixing approximately 0.001 g of each of F-I ~ F-VII with approximately 0.1 g of potassium bromide (KBr). Then the mixture was compressed to thin film in a bead machine. Infrared spectra were obtained within the region of 4000 and 400 cm1 with a spectral resolution of 4 cm1 by using a Thermofisher Nicolet 6700. To ensure an acceptable signal-tonoise ratio, 32 scans were collected for each sample. Air was used as the background spectra. GC/MS analysis of F-I ~ F-IV was carried out using a 6890 model gas chromatography and a mass selective detector (HewlettePackard, USA). HP-5MS capillary column (30 m 0.25 mm i.d.; 0.25 mm thickness) supplied by HewlettePackard, USA was used. Helium (99.999%) was used as the carrier gas with a constant flow rate of 0.6 ml/min. The oven temperature was held at 60 C for 2 min, then programmed from 60 C to 280 C at a heating rate of 6 C/min and maintained at 280 C for 20 min. MS was conducted with the following operation conditions: transfer line 280 C, ion source 250 C and electron energy 70 eV. The mass spectrometer was set to scan for molecular masses ranging from 20 to 550 total ion current (TIC). The organic compounds were identified by comparing the mass spectra to NIST05 library data. The distribution of compounds in each fraction was determined by a semi-quantitative method using the percentage area of the chromatographic peaks. The organic compounds, whose content was lower than 0.01%(g/g IBGT), were ignored in F-I ~ F-IV. 1 H NMR analysis of F-V and F-VI was performed using Bruker 400 MHz spectrometer. Deuterated acetone ((CD3)2CO) and dimethyl sulfoxide ((CD3)2SO) containing Tetra Methyl Silane (TMS) as an internal standard were used as solvent for F-V and F-VI, respectively. 3. Results and discussion 3.1. Basic fuel properties of IBGT The basic fuel properties of IBGT were shown in Table 1. The water and ash contents were 18.99 wt.% and 6.56 wt.%, respectively. Both water and ash were undesirable because they can bring many negative effects to the storage and combustion. Meanwhile, water was usually miscible with the lignin-derived components because of the solubilizing effect of other polar hydrophilic compounds (low-molecularPlease cite this article in press as: L. Li, et al., Fuel properties and chemical compositions of the tar produced from a 5 MW industrial biomass gasification power generation plant, Journal of the Energy Institute (2014), http://dx.doi.org/10.1016/j.joei.2014.07.002
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L. Li et al. / Journal of the Energy Institute xxx (2014) 1e10 Table 1 Basic fuel properties of IBGT. Properties
Value
Water content, wt.% Elemental composition, wt.%a Carbon Hydrogen Oxygenb Sulphur Nitrogen Volatile, wt.%a Ash, wt.%c H/C molar ratio Total acid value, mg KOH/g High heating value, mj/kg
18.99
a b c
77.38 6.66 12.74 0.22 3.00 61.82 6.56 1.03 16.88 30.24
Dry ash free basis. By difference. Dry basis.
weight acids, alcohols, hydroxyaldehydes and ketones) mostly originating from the decomposition of carbohydrates [19]. High nitrogen content would be a shortcoming for employing IBGT to produce tar [20]. Fig. 3 shows the viscosityetemperature curve of IBGT. It was observed that the viscosity value was quite high (2393 mPa s at 65 C) [20]. Ba et al. [21,22] investigated the steady and dynamic rheological properties of the vacuum pyrolysis tar and discovered a phase-transition temperature of the tar was 46 C. According to these results, it could be concluded that the waxy materials, pyrolytic lignins and solids in the tar formed three-dimensional structures (<46 C). This structure would melt and disappear at relative high temperatures. Boucher [23] confirmed that the rheological behavior of tar was a Bingham plastic fluid and a Newtonian liquid before and after 46 C, respectively. At temperature higher than 95 C, the whole properties of tar would be totally altered as a result of the polymer structure breaking and light volatiles evaporation [24]. It was a general point that the addition of methanol remarkably decreased the viscosity of the tar [25]. So the IBGT would be suited for transportation at a moderate temperature or by adding methanol [26]. Table 2 was inorganic elements found in IBGT ash. It showed that Si was the most abundant element. The high content of Fe in the IBGT ash was observed. Other important alkali and alkali earth metals including K, Ca and Mg were from the feedstock. They can cause hightemperature corrosion during combustion of IBGT. In addition, it was worth paying attention to the presence of harmful elements, such as Pb (0.0285%), Cu (0.0142%) and Cr (0.0081%). The metallic elements, such as Fe, K and Ca, can be used as catalysts in the up-grading process of IBGT.
3.2. Elemental analysis of F-I ~ F-VII Table 3 showed the yields and the ultimate analysis results of all fractions separated from IBGT. Yields of fractions displayed that IBGT consisted of 6.96 wt.% FeI, 15.68 wt.% F-II, 29.20 wt.% F-III, 6.4 wt.% F-IV, 21.07 wt.% FeV, 12.32 wt.% F-VI and 8.38 wt.% F-VII. The yield of F-III eluted by ether was the highest (29.2 wt.%). Yields of FeI and F-IV, which were eluted by n-hexane and methanol respectively, were very few in IBGT. The result suggested that IBGT mainly consists of the strong polar compounds and some macromolecules. Further observation of FI ~ F-IV element analysis results showed that C% and H% decreased, and N% increased with the increase of the eluant polarity. F-V showed higher C% and H% than F-VI, but lower N% and O%. It suggested that F-VI contained complex with more oxygen-containing group and nitrogen-containing group. Associated with ash content (6.56%) in Table 2, F-VII was mainly composed of ash, a small amount of carbon and unreacted biomass materials.
Fig. 3. The viscosityetemperature curve of IBGT.
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Table 2 Inorganic elemental composition of IBGT ash (area%). Element
Relative content
Element
Relative content
Si Fe K Ca Cla Mg Sa Pa Na Mn Al Zn
32.35 8.25 6.54 3.52 1.94 1.85 1.48 1.28 0.978 0.592 0.525 0.0839
Ti Ba Pb Rb Cu Sr Cr Bra Ni Zr Y Ge
0.045 0.0408 0.0285 0.0162 0.0142 0.0123 0.0081 0.0062 0.0054 0.004 0.0023 0.0009
a
Inorganic.
Table 3 The elemental analysis of F-I ~ F-IV Fraction
F-I F-II F-III F-IV F-V F-VI F-VII a
Yield (wt.%)
Elemental analysis (wt.%, daf)
6.96 15.68 29.20 6.40 21.07 12.32 8.38
H/C
C
H
N
S
Oa
86.58 87.43 75.74 73.19 73.15 69.15 75.68
12.69 8.61 8.72 7.33 7.07 6.34 3.64
0.05 0.68 1.62 8.21 4.16 5.94 3.55
0.21 0.20 0.17 0.49 0.40 0.50 0.40
0.47 3.08 13.74 10.79 15.22 18.07 16.72
1.76 1.18 1.38 1.20 1.15 1.10 0.58
By difference.
3.3. FTIR characteristics of F-I ~ F-VII Fig. 4 shows FTIR spectrums of F-I ~ F-VII. The F-I spectrum gave significant insights into the compounds and showed strong peaks of CalH stretching vibrations (2956 cm1, 2925 cm1, 2854 cm1) and a weak peak of OH (3420 cm1), while their intensities were in agreement with the high H/C and low O% listed in Table 3. Moreover, The FTIR spectrums of F-I also displayed an obvious rocking vibration peak of (CH2)n (n 4) at 722 cm1 [27], which was hardly observed in other fractions. These peaks meant that F-I contained long chain aliphatic compounds. Compared with F-I, the spectrum of F-II presented an obvious absorption peak of aromatic C]C ring stretching at 1610 cm1, ketone C]O stretching at 1700 cm1 and aliphatic ester C]O stretching at 1740 cm1 [28], which indicated that F-II contains aromatic compound. The stronger absorption peak intensity of OH stretching (3420 cm1) indicated that F-II has more hydroxyl structure than F-I. From the spectra of F-III, the peak of C]O stretching shifted to 1700 cm1, which was stronger than F-II and may be attributed to the stretching vibration of C]O in acid and ketone, and the peak of 1270 cm1 was attributed to the stretching vibration of CeO in phenolic compound. Further integrating the peak of 3420 cm1, it showed that F-III was composed of oxygen-containing and nitrogen-containing compound. The spectrum of F-IV showed the peak of C]O stretching at 1664 cm1, which may corresponded to amide and the shoulder
3420
2956 2854
I
1740
1455
1662
1120
722
1270 812 750
II
T/%
III IV V VI VII
1700 1610
2925
4000
3500
3000
2500
2000
1500 Wavenumber / cm-1
1100
806
1000
465
500
Fig. 4. The FTIR spectrums of F-I ~ F-VII.
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peak of aromatic C]C ring stretching at 1610 cm1. It indicated that F-IV may contain various amounts of nitrogen-containing compounds. The spectra of F-V and F-VI showed that the weak peak of C]O stretching at 1700 cm1 and the strong peak of aromatic C]C ring stretching at 1610 cm1. Combined with the peak of 3420 cm1 and element analysis in Table 3, it meant that F-V and F-VI may contain nitrogencontaining compound with macromolecular aromatic structure. The broad peak at 1100 cm1 and the peak at 795 cm1 and 465 cm1 in the spectra of F-VII, were caused by amorphous silica and iron aluminosilicates [29].
3.4. GC/MS characteristics of F-I ~ F-IV Fig. 5 showed the total ion chromatogram and mass chromatograms of F-I. Peaks marked with a dot were identified as n-alkenes. Nalkanes and n-alkenes were abundant in F-I, while the content of n-alkanes was higher. The aliphatic hydrocarbon in biomass pyrolysis tar was also found. The tar from the fixed-bed pyrolysis of rice straw under steam contained more aliphatic compound than other atmosphere [30], but rarely found in other feed, such as sawdust and wheat shell [13,31,32]. Funda [33] found that the carbon range of the aliphatic compounds in wheat straw tar is C14eC31. The distribution patterns of n-alkanes in biomass tars (maize and rye straw) changed with different temperatures and the long-chain n-alkanes were strongly reduced by increasing temperature [34]. Hence, the content of C25 ~ C31 n-alkanes was extraordinary high, due to epicuticular wax sources in rice straw [35]. The n-alkenes were formed through the thermal dehydration of n-alkanols [36]. The GC/MS analysis also showed that cyclic alkanes accounted for a small fraction of the saturate hydrocarbons. Fig. 6 shows total ion and mass chromatograms of F-II. It indicated the enrichment of 1e3 ring aromatics in F-II. The alkyl chains of aromatic hydrocarbons were relatively short. The major aromatic hydrocarbons were the monocyclic compounds such as benzene and its alkylated derivatives, the PAH (naphthalene, acenaphthene, anthracene, phenanthrene) and their derivatives. The concentration of PAH was minimal in IBGT due to low temperature of gasification operation parameters. The PAH increased with increasing operation temperature of gasification. Hence, aromatization and partial dealkylation as an intermediate step occurred at the high temperature [34,37e39]. Other compounds containing oxygen and nitrogen, such as multi-substituted phenol, furan, indole and ester, were in minor concentration in F-II. Fig. 7 shows total ion and mass chromatograms of F-III. The mass chromatograms of m/z 94, 107, 122 and 136 belonged to the phenol and substituent phenol. The mass chromatogram of m/z 60 belonged to the 6-ring rearrangement of g-H and aC-bC cleavage in acid without branched chain in a-C position. In Supplementary table, F-III was rich with phenol derivatives, especially 4-ethylphenol (7.99% in F-III). Phenol usually originated from pyrolytic degradation of lignin, which was a complex aromatic structure composed by substituted phenyl propane units and linked by hydroxyl and methoxy groups [40]. In general, the content of methoxyphenol and its derivatives were greatest at lower pyrolysis temperature. Increasing gasification temperatures would increase the possibility of secondary reactions which could be
Fig. 5. Total ion and mass chromatograms of F-I.
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Relative Abundance
Relative Abundance
Relative Abundance
Relative Abundance
L. Li et al. / Journal of the Energy Institute xxx (2014) 1e10
7
100 m/z 78, 91, 92
80 60 40 20 100 80
m/z 128, 142, 156, 170
60 40 20 100
m/z 178, 192, 206, 220
80 60 40 20 100
TIC
80 60 40 20 7
14
21
28 Time / min
35
42
49
Fig. 6. Total ion and mass chromatograms of F-II.
responsible for the thermal breakdown of the larger phenolic compounds [38], followed with aromatization and dealkylation. These were in agreement with F-II. Meanwhile, the n-hexadecanoic acid (9.11% in F-III) was abundant. It may be related to basic units in plant fats, oils and phospholipids and identified as the free acids or esters. Fig. 8 was total ion and mass chromatograms of F-IV. Mass chromatogram of m/z 59 and 72 showed the distribution of amides, which were normally seen in the 6-ring rearrangement of g-H in amide and substitution reaction, respectively. Nitrogen-containing compounds were dominant, such as pyridine, quinoline, isoquinoline, amine, amide and their derivatives in Supplementary table.
Relative Abundance
100 80 m/z 94, 107, 122, 136
60 40 20
Relative Abundance
100 80
m/z 60
60 40 20
Relative Abundance
100 TIC
80 60 40 20 7
14
21
28
35
42
Time / min Fig. 7. Total ion and mass chromatograms of F-III.
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Relative Abundance
100
m/z 59, 72 80 60 40 20
Relative Abundance
100 TIC
80 60 40 20 7
14
21
28
35
42
Time / min Fig. 8. Total ion and mass chromatograms of F-IV.
3.5.
1
H NMR characteristics of F-V and F-VI
Based on the chemical shifts of specific proton types [41,42], the chemical shifts and the distributions of different types of protons in F-V and F-VI were listed in Table 4. The groups, found in the region of 4.0e3.0 ppm, were ring-joining methylene, methine or methoxy and NH2 attached to aromatic, and were in agreement with the content of oxygen and nitrogen in Table 3. The region of 2.0e1.5 ppm contained about 9.57% and 19.52% in F-V and F-VI. It represented NH2 attached to paraffin, CH2 and CH attached to naphthenes. That meant F-V and F-VI had similar long side chain of aromatic, but F-V had more short side chain of aromatic, such as eCH3 and eCH2. The results showed large proportions of aromatic structure with aliphatic side chain units in F-V and F-VI. F-VI had more heteroatom side chain of aromatic and polycyclic aromatic structure than F-V.
Table 4 Hydrogen type distribution of F-V and F-VI from 1H NMR spectra. Type of protons
Chemical shift/ppm
F-V/%
F-VI/%
CH3 g or further from aromatic ring and paraffinic CH3 CH3, CH2 and CH b to aromatic ring NH2 attached to paraffin; CH2 and CH attached to naphthenes CH3, CH2 and CH a to aromatic ring-joining methylene, methine or methoxy; NH2 attached to aromatic Phenols; non-conjugated olefins Aromatics; conjugated olefins; aldehydes; heteroaromatics
1.0e0.5 1.5e1.0 2.0-1.5 3.0e2.0 4.0e3.0 6.0e4.0 9.0e6.0
6.67 14.49 9.57 24.35 6.96 8.99 28.99
6.64 9.86 19.52 15.49 17.51 10.87 20.12
100
OHs OOCHs
Relative content / %
80
ONCHs Acids
60 Quinolines Phenols
40
Aromatics Alkyne
20
Alkenes
0
Alkanes
F-I
F-II
F-III
F-IV
Fig. 9. Group components distribution of F-I ~ F-IV.
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9
3.6. Potential applications of the fractions In Supplementary table, 577 organic species in F-I ~ F-IV were identified. They can be grouped into alkanes, alkenes, alkynes, aromatics, phenols, quinoines, acids, other nitrogen-containing hydrocarbons (ONCHs), other oxygen-containing hydrocarbons (OOCHs) and other hydrocarbons (OHs) in Fig. 9. These results were consistent with the elemental analysis (Table 3) and FTIR analysis (Fig. 4). Among the identified species, aliphatic hydrocarbons (most of which were alkanes and alkenes), aromatics, phenols and nitrogen-containing hydrocarbons (most of which were quinolines, amines, amides) were mainly group components of F-I ~ F-IV, respectively. According to the analysis of F-I ~ F-VI, the IBGT can be transformed to fuel and chemical source through fractioning process. F-I ~ F-IV can be purified to produce chemicals (such as aliphatic hydrocarbons, aromatics, phenols, quinolines, etc.) through the appropriate process. F-V and F-VI can be used directly as conventional solid fuels. Further investigations of purification and hydrogenation of IBGT will be carried out in our future paper. 4. Conclusions The fuel properties of IBGT were studied using different analytical techniques. The IBGT exhibits the shortcoming of high water content, high ash content, high nitrogen content and high viscosity, which limited the utilization as fuel. IBGT was subjected to extraction to obtain n-hexane soluble, n-hexane insoluble/toluene soluble, toluene insoluble/tetrahydrofuran soluble and tetrahydrofuran insoluble fractions, which were characterized by FTIR. The n-hexane soluble fraction was further fractionated by column chromatography into four fractions, which were characterized by gas chromatography-mass spectrometry (GC/MS). The nhexane insoluble/toluene soluble and toluene insoluble/tetrahydrofuran soluble fractions were characterized by 1H NMR. The results showed that the first fraction (6.96 wt.%) contained alkanes, and alkenes; the second fraction (15.68 wt.%) contained 1e3 ring aromatics; the third fraction (29.20 wt.%) contained oxygen compounds, such as phenols; the fourth fraction (6.40 wt.%) contained nitrogen compounds, such as quinoline, isoquinoline, amine and amide; the fifth fraction (21.07 wt.%) mainly contained polycyclic aromatic structure with short aliphatic side chain and long aliphatic bridge bond; the sixth fraction (12.32 wt.%) mainly contained polycyclic aromatic structure with heteroatom side chain; the seventh fraction (8.38 wt.%) contained ash, coke and unreacted biomass. These results may present an effective solution to utilization of IBGT. Acknowledgments This work was supported by the National High Technology Research and Development Program of China (No. 2012AA101810) and the National Science Foundation of China (20906025). Appendix A. Supplementary data Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.joei.2014.07.002. References [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]
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Fuel properties and chemical compositions of the tar produced from a 5 MW industrial biomass gasification power generation plant Liang Li a, Sheng Huang a, b, Shiyong Wu a, b, *, Youqing Wu a, b, Jinsheng Gao a, b, Junwen Gu a, Xiaogang Qin c a
Department of Chemical Engineering for Energy Resources, East China University of Science and Technology, Shanghai 200237, China Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry of Education, East China University of Science and Technology, Shanghai 200237, China c Technology Center, Dongfang Boiler Group Co. Ltd, Dongfang Electric Group, Chengdu 611731, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 May 2014 Received in revised form 8 July 2014 Accepted 15 July 2014 Available online xxx
The industrial biomass gasification tar (IBGT) was analyzed for its basic fuel properties and chemical compositions. The results suggested that IBGT had some special properties (high water content, high ash content, high viscosity, etc.). IBGT was subjected to extraction to obtain n-hexane soluble, n-hexane insoluble/toluene soluble, toluene insoluble/tetrahydrofuran soluble, and tetrahydrofuran insoluble fractions, which were characterized by FTIR. The n-hexane soluble fraction was further fractionated by column chromatography into four fractions, which were characterized by gas chromatography-mass spectrometry (GC/MS). The n-hexane insoluble/toluene soluble and toluene insoluble/tetrahydrofuran soluble fractions were characterized by 1H NMR. The results showed that the first fraction (6.96 wt.%) contained alkanes and alkenes; the second fraction (15.68 wt.%) contained 1e3 ring aromatics; the third fraction (29.20 wt.%) contained oxygen compounds, such as phenols; the fourth fraction (6.40 wt.%) contained nitrogen compounds, such as quinoline, isoquinoline, amine and amide; the fifth fraction (21.07 wt.%) mainly contained polycyclic aromatic structure with short aliphatic side chain and long aliphatic bridge bond; the sixth fraction (12.32 wt.%) mainly contained polycyclic aromatic structure with heteroatom side chain; the seventh fraction (8.38 wt.%) contained ash, coke and unreacted biomass. These results may present an effective solution to utilization of IBGT. © 2014 Energy Institute. Published by Elsevier Ltd. All rights reserved.
Keywords: Tar Fuel property Chemical composition Biomass gasification
1. Introduction Biomass energy is chemical energy which is transformed from solar energy through the photosynthesis of green plants and can be directly or indirectly converted into conventional solid, liquid and gaseous fuels [1,2]. Biomass gasification technology, which experiences relatively rapid development in recent years, is a kind of biomass thermochemical treatment technology. It can convert the low grade solid biomass into the high grade gas which can be used in the synthesis, heating, power generation and other utilization. It also can improve the efficiency of energy, so the research and development of biomass gasification have drawn wide attention from the world [3]. Biomass gasification tar (BGT) is a by-product in biomass gasification process [4]. Its yield depends on gasification process. Meanwhile, BGT is a potential feedstock for chemical products and transportation fuels. The direct emission of the tar will cause not only the waste of resources, but also serious pollution of the environment. The chemical composition of BGT is distinctly different from that of coal tar, such as high heteroatom content, high viscosity, high ash content, high oxygen content and high corrosiveness [5,6]. In fact, the compositions of BGT have not been thoroughly defined, especially industrial biomass gasification tar (IBGT). From the literatures [7e10], BGT is composed of acids, alcohols, aldehydes, esters, ketones, sugars, phenols, guaiacols, syringols, furans, lignin derived phenols and extractible terpene with multi-functional groups. Several analytical tools, such as gas chromatography and gas
* Corresponding author. Department of Chemical Engineering for Energy Resources, East China University of Science and Technology, Shanghai 200237, China. Tel.: þ86 21 64253236. E-mail addresses: [email protected] (L. Li), [email protected] (S. Wu). http://dx.doi.org/10.1016/j.joei.2014.07.002 1743-9671/© 2014 Energy Institute. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: L. Li, et al., Fuel properties and chemical compositions of the tar produced from a 5 MW industrial biomass gasification power generation plant, Journal of the Energy Institute (2014), http://dx.doi.org/10.1016/j.joei.2014.07.002
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chromatography/mass spectroscopy could provide molecular composition information [11e15], but the chromatographic peaks of various compounds overlapped because of the complexity and structural similarity of the components in BGT. Therefore, column chromatography pretreatment step, which is prior to characterization of organic compounds in BGT, is an effective separation method [16e18]. For valuable, efficient, reliable and environmental friendly utilization of tar which was produced from biomass gasification, it is essential to study its organic composition and fuel properties. In this paper, a series of experiments were performed to systematically characterize basic fuel properties of industrial biomass gasification tar (IBGT) obtained from 5 MW industrial biomass gasification power generation plant, and to investigate the compounds composition of the tar by analytical techniques including GC/MS, FTIR and 1H NMR. The results are expected to demonstrate the potential application prospects of tar and provide useful information for the industrial scale biomass gasification. 2. Materials and methods 2.1. Tar materials IBGT sample was obtained from a 5 MW industrial biomass gasification power generation plant of Gaoyou Linyuan Technology Co., Ltd. of China. As can be observed in Fig. 1, rice straw was fed into the gasifier, which was an up-draft, fixed-bed type. The gas passed through water scrubber. The majority of tar (almost 95% of totals) in gas was washed and collected in tar tank. Most of the remained tar in the gas would be removed through the electrostatic tar-catcher and assembled in the same tar tank. The purified gas was sent to purification towers to achieve the requirements of power generation, subsequently it was transported to gas engine sets. Biomass material of gasification was characterized. The results of elemental analysis were Cdaf ¼ 54.99%, Hdaf ¼ 7.20%, Ndaf ¼ 1.64% and St,d ¼ 0.23%, while the results of approximate analysis were Mad ¼ 9.37%, Vdaf ¼ 78.23% and Ad ¼ 20.14%. IBGT sample derived from the tar tank, which collected almost 98% of total tar, was provided for the study without further treatment. During the period of sampling, the operation parameters for the plant were as follows: biomass consumption rate of 5e6 t/h, gasification temperature of around 1100 C, net power output of 5 MW. The typical values of the dry gas compositions used in the plant were as follows: CO 24.5%, H2 18.4%, CH4 3.8%, CO2 12.0%, CnHm 0.5%, N2 40.4%, O2 0.4% and LHV 6.59 MJ/m3. 2.2. Basic fuel properties of IBGT The basic fuel properties of IBGT include water content, total acid value, ash content, heating value, volatile content, viscosity, elemental analysis and the inorganic composition of IBGT ash. The water content, total acid value, ash content and high heating value were determined according to GB/T 2288e2008, GB/T 18609e2011, GB/T 28731e2012 and GB/T 384-1981, respectively. The volatile content was determined in an oven, and maintained at the temperature of 915 C for 7 min. The rotational viscosity was monitored by an NDJ-1B rotational viscometer and the temperature was controlled by a CH1015 super thermostatic bath. Variations of rotational viscosity under constant speeds of 60 rpm were recorded. The elemental analysis of IBGT was determined using an Elementar vario macro cube analyzer. All element contents in ash were measured by a sequential X-ray fluorescence spectrometer (XRF-1800). 2.3. Group separation for IBGT The group separation scheme in this study was shown in Fig. 2. IBGT sample was separated into n-hexane soluble and insoluble fractions by Soxhlet extraction for 10e12 h. The n-hexane insoluble fraction was vacuum dried and preserved for further analysis. The n-hexane in the n-hexane soluble fraction was removed by rotary evaporator. The column chromatography was firstly packed with 20 g of activated neutral alumina (heating at 500 C for 5 h), followed by 20 g of activated silica gel (heating at 120 C for 5 h). The n-hexane soluble fraction (approximately 1 g) dissolved in a small volume of n-hexane was loaded at the top of the column. The four fractions were obtained by sequential solvent elution using n-hexane (150 ml), toluene (200 ml),
Water scrubber Electrostatic Gas purification tower tar-catcher To generate electricity
Gasifier
Tar tank
Fig. 1. The 5 MW industrial biomass gasification power generation process.
Please cite this article in press as: L. Li, et al., Fuel properties and chemical compositions of the tar produced from a 5 MW industrial biomass gasification power generation plant, Journal of the Energy Institute (2014), http://dx.doi.org/10.1016/j.joei.2014.07.002
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Tar Extracted by n-hexane
N-hexane soluble fraction
N-hexane insoluble fraction Extracted by toluene
Column chromatography
Soluble fraction
Removed solvent F-I
Toluene 200ml Removed solvent F-II
Ether 200ml Removed solvent F-III
Extracted by tetrahydrofuran
Removed solvent
Eluted successively
N-hexane 150ml
Insoluble fraction
Methanol 200ml
Soluble fraction
Removed solvent F-IV
Removed solvent F-V
F-VI
Insoluble fraction Removed solvent F-VII
Fig. 2. The group separation process of IBGT.
ether (200 ml) and methanol (200 ml), respectively. The solvent was removed by a rotary evaporator. Then the weight of each fraction (marked as F-I, F-II, F-III, F-IV in sequence) was measured. The dried n-hexane insoluble fraction was extracted with toluene, tetrahydrofuran in sequence by Soxhlet extraction for 10e12 h. Then the solvent in the toluene solution and the tetrahydrofuran solution was removed by rotary evaporator, respectively. The toluene soluble fraction (F-V), the toluene insoluble/tetrahydrofuran soluble fraction (F-VI) and the tetrahydrofuran insoluble fraction (F-VII) were obtained. Pictures at the bottom in Fig. 2 were fractions obtained from the group separation with removing solvent. 2.4. Characterization of separation fractions The elemental analysis of F-I ~ F-VII were determined using an Elementar vario macro cube analyzer. A mixture was prepared by grinding and thoroughly mixing approximately 0.001 g of each of F-I ~ F-VII with approximately 0.1 g of potassium bromide (KBr). Then the mixture was compressed to thin film in a bead machine. Infrared spectra were obtained within the region of 4000 and 400 cm1 with a spectral resolution of 4 cm1 by using a Thermofisher Nicolet 6700. To ensure an acceptable signal-tonoise ratio, 32 scans were collected for each sample. Air was used as the background spectra. GC/MS analysis of F-I ~ F-IV was carried out using a 6890 model gas chromatography and a mass selective detector (HewlettePackard, USA). HP-5MS capillary column (30 m 0.25 mm i.d.; 0.25 mm thickness) supplied by HewlettePackard, USA was used. Helium (99.999%) was used as the carrier gas with a constant flow rate of 0.6 ml/min. The oven temperature was held at 60 C for 2 min, then programmed from 60 C to 280 C at a heating rate of 6 C/min and maintained at 280 C for 20 min. MS was conducted with the following operation conditions: transfer line 280 C, ion source 250 C and electron energy 70 eV. The mass spectrometer was set to scan for molecular masses ranging from 20 to 550 total ion current (TIC). The organic compounds were identified by comparing the mass spectra to NIST05 library data. The distribution of compounds in each fraction was determined by a semi-quantitative method using the percentage area of the chromatographic peaks. The organic compounds, whose content was lower than 0.01%(g/g IBGT), were ignored in F-I ~ F-IV. 1 H NMR analysis of F-V and F-VI was performed using Bruker 400 MHz spectrometer. Deuterated acetone ((CD3)2CO) and dimethyl sulfoxide ((CD3)2SO) containing Tetra Methyl Silane (TMS) as an internal standard were used as solvent for F-V and F-VI, respectively. 3. Results and discussion 3.1. Basic fuel properties of IBGT The basic fuel properties of IBGT were shown in Table 1. The water and ash contents were 18.99 wt.% and 6.56 wt.%, respectively. Both water and ash were undesirable because they can bring many negative effects to the storage and combustion. Meanwhile, water was usually miscible with the lignin-derived components because of the solubilizing effect of other polar hydrophilic compounds (low-molecularPlease cite this article in press as: L. Li, et al., Fuel properties and chemical compositions of the tar produced from a 5 MW industrial biomass gasification power generation plant, Journal of the Energy Institute (2014), http://dx.doi.org/10.1016/j.joei.2014.07.002
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L. Li et al. / Journal of the Energy Institute xxx (2014) 1e10 Table 1 Basic fuel properties of IBGT. Properties
Value
Water content, wt.% Elemental composition, wt.%a Carbon Hydrogen Oxygenb Sulphur Nitrogen Volatile, wt.%a Ash, wt.%c H/C molar ratio Total acid value, mg KOH/g High heating value, mj/kg
18.99
a b c
77.38 6.66 12.74 0.22 3.00 61.82 6.56 1.03 16.88 30.24
Dry ash free basis. By difference. Dry basis.
weight acids, alcohols, hydroxyaldehydes and ketones) mostly originating from the decomposition of carbohydrates [19]. High nitrogen content would be a shortcoming for employing IBGT to produce tar [20]. Fig. 3 shows the viscosityetemperature curve of IBGT. It was observed that the viscosity value was quite high (2393 mPa s at 65 C) [20]. Ba et al. [21,22] investigated the steady and dynamic rheological properties of the vacuum pyrolysis tar and discovered a phase-transition temperature of the tar was 46 C. According to these results, it could be concluded that the waxy materials, pyrolytic lignins and solids in the tar formed three-dimensional structures (<46 C). This structure would melt and disappear at relative high temperatures. Boucher [23] confirmed that the rheological behavior of tar was a Bingham plastic fluid and a Newtonian liquid before and after 46 C, respectively. At temperature higher than 95 C, the whole properties of tar would be totally altered as a result of the polymer structure breaking and light volatiles evaporation [24]. It was a general point that the addition of methanol remarkably decreased the viscosity of the tar [25]. So the IBGT would be suited for transportation at a moderate temperature or by adding methanol [26]. Table 2 was inorganic elements found in IBGT ash. It showed that Si was the most abundant element. The high content of Fe in the IBGT ash was observed. Other important alkali and alkali earth metals including K, Ca and Mg were from the feedstock. They can cause hightemperature corrosion during combustion of IBGT. In addition, it was worth paying attention to the presence of harmful elements, such as Pb (0.0285%), Cu (0.0142%) and Cr (0.0081%). The metallic elements, such as Fe, K and Ca, can be used as catalysts in the up-grading process of IBGT.
3.2. Elemental analysis of F-I ~ F-VII Table 3 showed the yields and the ultimate analysis results of all fractions separated from IBGT. Yields of fractions displayed that IBGT consisted of 6.96 wt.% FeI, 15.68 wt.% F-II, 29.20 wt.% F-III, 6.4 wt.% F-IV, 21.07 wt.% FeV, 12.32 wt.% F-VI and 8.38 wt.% F-VII. The yield of F-III eluted by ether was the highest (29.2 wt.%). Yields of FeI and F-IV, which were eluted by n-hexane and methanol respectively, were very few in IBGT. The result suggested that IBGT mainly consists of the strong polar compounds and some macromolecules. Further observation of FI ~ F-IV element analysis results showed that C% and H% decreased, and N% increased with the increase of the eluant polarity. F-V showed higher C% and H% than F-VI, but lower N% and O%. It suggested that F-VI contained complex with more oxygen-containing group and nitrogen-containing group. Associated with ash content (6.56%) in Table 2, F-VII was mainly composed of ash, a small amount of carbon and unreacted biomass materials.
Fig. 3. The viscosityetemperature curve of IBGT.
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Table 2 Inorganic elemental composition of IBGT ash (area%). Element
Relative content
Element
Relative content
Si Fe K Ca Cla Mg Sa Pa Na Mn Al Zn
32.35 8.25 6.54 3.52 1.94 1.85 1.48 1.28 0.978 0.592 0.525 0.0839
Ti Ba Pb Rb Cu Sr Cr Bra Ni Zr Y Ge
0.045 0.0408 0.0285 0.0162 0.0142 0.0123 0.0081 0.0062 0.0054 0.004 0.0023 0.0009
a
Inorganic.
Table 3 The elemental analysis of F-I ~ F-IV Fraction
F-I F-II F-III F-IV F-V F-VI F-VII a
Yield (wt.%)
Elemental analysis (wt.%, daf)
6.96 15.68 29.20 6.40 21.07 12.32 8.38
H/C
C
H
N
S
Oa
86.58 87.43 75.74 73.19 73.15 69.15 75.68
12.69 8.61 8.72 7.33 7.07 6.34 3.64
0.05 0.68 1.62 8.21 4.16 5.94 3.55
0.21 0.20 0.17 0.49 0.40 0.50 0.40
0.47 3.08 13.74 10.79 15.22 18.07 16.72
1.76 1.18 1.38 1.20 1.15 1.10 0.58
By difference.
3.3. FTIR characteristics of F-I ~ F-VII Fig. 4 shows FTIR spectrums of F-I ~ F-VII. The F-I spectrum gave significant insights into the compounds and showed strong peaks of CalH stretching vibrations (2956 cm1, 2925 cm1, 2854 cm1) and a weak peak of OH (3420 cm1), while their intensities were in agreement with the high H/C and low O% listed in Table 3. Moreover, The FTIR spectrums of F-I also displayed an obvious rocking vibration peak of (CH2)n (n 4) at 722 cm1 [27], which was hardly observed in other fractions. These peaks meant that F-I contained long chain aliphatic compounds. Compared with F-I, the spectrum of F-II presented an obvious absorption peak of aromatic C]C ring stretching at 1610 cm1, ketone C]O stretching at 1700 cm1 and aliphatic ester C]O stretching at 1740 cm1 [28], which indicated that F-II contains aromatic compound. The stronger absorption peak intensity of OH stretching (3420 cm1) indicated that F-II has more hydroxyl structure than F-I. From the spectra of F-III, the peak of C]O stretching shifted to 1700 cm1, which was stronger than F-II and may be attributed to the stretching vibration of C]O in acid and ketone, and the peak of 1270 cm1 was attributed to the stretching vibration of CeO in phenolic compound. Further integrating the peak of 3420 cm1, it showed that F-III was composed of oxygen-containing and nitrogen-containing compound. The spectrum of F-IV showed the peak of C]O stretching at 1664 cm1, which may corresponded to amide and the shoulder
3420
2956 2854
I
1740
1455
1662
1120
722
1270 812 750
II
T/%
III IV V VI VII
1700 1610
2925
4000
3500
3000
2500
2000
1500 Wavenumber / cm-1
1100
806
1000
465
500
Fig. 4. The FTIR spectrums of F-I ~ F-VII.
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peak of aromatic C]C ring stretching at 1610 cm1. It indicated that F-IV may contain various amounts of nitrogen-containing compounds. The spectra of F-V and F-VI showed that the weak peak of C]O stretching at 1700 cm1 and the strong peak of aromatic C]C ring stretching at 1610 cm1. Combined with the peak of 3420 cm1 and element analysis in Table 3, it meant that F-V and F-VI may contain nitrogencontaining compound with macromolecular aromatic structure. The broad peak at 1100 cm1 and the peak at 795 cm1 and 465 cm1 in the spectra of F-VII, were caused by amorphous silica and iron aluminosilicates [29].
3.4. GC/MS characteristics of F-I ~ F-IV Fig. 5 showed the total ion chromatogram and mass chromatograms of F-I. Peaks marked with a dot were identified as n-alkenes. Nalkanes and n-alkenes were abundant in F-I, while the content of n-alkanes was higher. The aliphatic hydrocarbon in biomass pyrolysis tar was also found. The tar from the fixed-bed pyrolysis of rice straw under steam contained more aliphatic compound than other atmosphere [30], but rarely found in other feed, such as sawdust and wheat shell [13,31,32]. Funda [33] found that the carbon range of the aliphatic compounds in wheat straw tar is C14eC31. The distribution patterns of n-alkanes in biomass tars (maize and rye straw) changed with different temperatures and the long-chain n-alkanes were strongly reduced by increasing temperature [34]. Hence, the content of C25 ~ C31 n-alkanes was extraordinary high, due to epicuticular wax sources in rice straw [35]. The n-alkenes were formed through the thermal dehydration of n-alkanols [36]. The GC/MS analysis also showed that cyclic alkanes accounted for a small fraction of the saturate hydrocarbons. Fig. 6 shows total ion and mass chromatograms of F-II. It indicated the enrichment of 1e3 ring aromatics in F-II. The alkyl chains of aromatic hydrocarbons were relatively short. The major aromatic hydrocarbons were the monocyclic compounds such as benzene and its alkylated derivatives, the PAH (naphthalene, acenaphthene, anthracene, phenanthrene) and their derivatives. The concentration of PAH was minimal in IBGT due to low temperature of gasification operation parameters. The PAH increased with increasing operation temperature of gasification. Hence, aromatization and partial dealkylation as an intermediate step occurred at the high temperature [34,37e39]. Other compounds containing oxygen and nitrogen, such as multi-substituted phenol, furan, indole and ester, were in minor concentration in F-II. Fig. 7 shows total ion and mass chromatograms of F-III. The mass chromatograms of m/z 94, 107, 122 and 136 belonged to the phenol and substituent phenol. The mass chromatogram of m/z 60 belonged to the 6-ring rearrangement of g-H and aC-bC cleavage in acid without branched chain in a-C position. In Supplementary table, F-III was rich with phenol derivatives, especially 4-ethylphenol (7.99% in F-III). Phenol usually originated from pyrolytic degradation of lignin, which was a complex aromatic structure composed by substituted phenyl propane units and linked by hydroxyl and methoxy groups [40]. In general, the content of methoxyphenol and its derivatives were greatest at lower pyrolysis temperature. Increasing gasification temperatures would increase the possibility of secondary reactions which could be
Fig. 5. Total ion and mass chromatograms of F-I.
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Relative Abundance
Relative Abundance
Relative Abundance
Relative Abundance
L. Li et al. / Journal of the Energy Institute xxx (2014) 1e10
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100 m/z 78, 91, 92
80 60 40 20 100 80
m/z 128, 142, 156, 170
60 40 20 100
m/z 178, 192, 206, 220
80 60 40 20 100
TIC
80 60 40 20 7
14
21
28 Time / min
35
42
49
Fig. 6. Total ion and mass chromatograms of F-II.
responsible for the thermal breakdown of the larger phenolic compounds [38], followed with aromatization and dealkylation. These were in agreement with F-II. Meanwhile, the n-hexadecanoic acid (9.11% in F-III) was abundant. It may be related to basic units in plant fats, oils and phospholipids and identified as the free acids or esters. Fig. 8 was total ion and mass chromatograms of F-IV. Mass chromatogram of m/z 59 and 72 showed the distribution of amides, which were normally seen in the 6-ring rearrangement of g-H in amide and substitution reaction, respectively. Nitrogen-containing compounds were dominant, such as pyridine, quinoline, isoquinoline, amine, amide and their derivatives in Supplementary table.
Relative Abundance
100 80 m/z 94, 107, 122, 136
60 40 20
Relative Abundance
100 80
m/z 60
60 40 20
Relative Abundance
100 TIC
80 60 40 20 7
14
21
28
35
42
Time / min Fig. 7. Total ion and mass chromatograms of F-III.
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L. Li et al. / Journal of the Energy Institute xxx (2014) 1e10
Relative Abundance
100
m/z 59, 72 80 60 40 20
Relative Abundance
100 TIC
80 60 40 20 7
14
21
28
35
42
Time / min Fig. 8. Total ion and mass chromatograms of F-IV.
3.5.
1
H NMR characteristics of F-V and F-VI
Based on the chemical shifts of specific proton types [41,42], the chemical shifts and the distributions of different types of protons in F-V and F-VI were listed in Table 4. The groups, found in the region of 4.0e3.0 ppm, were ring-joining methylene, methine or methoxy and NH2 attached to aromatic, and were in agreement with the content of oxygen and nitrogen in Table 3. The region of 2.0e1.5 ppm contained about 9.57% and 19.52% in F-V and F-VI. It represented NH2 attached to paraffin, CH2 and CH attached to naphthenes. That meant F-V and F-VI had similar long side chain of aromatic, but F-V had more short side chain of aromatic, such as eCH3 and eCH2. The results showed large proportions of aromatic structure with aliphatic side chain units in F-V and F-VI. F-VI had more heteroatom side chain of aromatic and polycyclic aromatic structure than F-V.
Table 4 Hydrogen type distribution of F-V and F-VI from 1H NMR spectra. Type of protons
Chemical shift/ppm
F-V/%
F-VI/%
CH3 g or further from aromatic ring and paraffinic CH3 CH3, CH2 and CH b to aromatic ring NH2 attached to paraffin; CH2 and CH attached to naphthenes CH3, CH2 and CH a to aromatic ring-joining methylene, methine or methoxy; NH2 attached to aromatic Phenols; non-conjugated olefins Aromatics; conjugated olefins; aldehydes; heteroaromatics
1.0e0.5 1.5e1.0 2.0-1.5 3.0e2.0 4.0e3.0 6.0e4.0 9.0e6.0
6.67 14.49 9.57 24.35 6.96 8.99 28.99
6.64 9.86 19.52 15.49 17.51 10.87 20.12
100
OHs OOCHs
Relative content / %
80
ONCHs Acids
60 Quinolines Phenols
40
Aromatics Alkyne
20
Alkenes
0
Alkanes
F-I
F-II
F-III
F-IV
Fig. 9. Group components distribution of F-I ~ F-IV.
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3.6. Potential applications of the fractions In Supplementary table, 577 organic species in F-I ~ F-IV were identified. They can be grouped into alkanes, alkenes, alkynes, aromatics, phenols, quinoines, acids, other nitrogen-containing hydrocarbons (ONCHs), other oxygen-containing hydrocarbons (OOCHs) and other hydrocarbons (OHs) in Fig. 9. These results were consistent with the elemental analysis (Table 3) and FTIR analysis (Fig. 4). Among the identified species, aliphatic hydrocarbons (most of which were alkanes and alkenes), aromatics, phenols and nitrogen-containing hydrocarbons (most of which were quinolines, amines, amides) were mainly group components of F-I ~ F-IV, respectively. According to the analysis of F-I ~ F-VI, the IBGT can be transformed to fuel and chemical source through fractioning process. F-I ~ F-IV can be purified to produce chemicals (such as aliphatic hydrocarbons, aromatics, phenols, quinolines, etc.) through the appropriate process. F-V and F-VI can be used directly as conventional solid fuels. Further investigations of purification and hydrogenation of IBGT will be carried out in our future paper. 4. Conclusions The fuel properties of IBGT were studied using different analytical techniques. The IBGT exhibits the shortcoming of high water content, high ash content, high nitrogen content and high viscosity, which limited the utilization as fuel. IBGT was subjected to extraction to obtain n-hexane soluble, n-hexane insoluble/toluene soluble, toluene insoluble/tetrahydrofuran soluble and tetrahydrofuran insoluble fractions, which were characterized by FTIR. The n-hexane soluble fraction was further fractionated by column chromatography into four fractions, which were characterized by gas chromatography-mass spectrometry (GC/MS). The nhexane insoluble/toluene soluble and toluene insoluble/tetrahydrofuran soluble fractions were characterized by 1H NMR. The results showed that the first fraction (6.96 wt.%) contained alkanes, and alkenes; the second fraction (15.68 wt.%) contained 1e3 ring aromatics; the third fraction (29.20 wt.%) contained oxygen compounds, such as phenols; the fourth fraction (6.40 wt.%) contained nitrogen compounds, such as quinoline, isoquinoline, amine and amide; the fifth fraction (21.07 wt.%) mainly contained polycyclic aromatic structure with short aliphatic side chain and long aliphatic bridge bond; the sixth fraction (12.32 wt.%) mainly contained polycyclic aromatic structure with heteroatom side chain; the seventh fraction (8.38 wt.%) contained ash, coke and unreacted biomass. These results may present an effective solution to utilization of IBGT. Acknowledgments This work was supported by the National High Technology Research and Development Program of China (No. 2012AA101810) and the National Science Foundation of China (20906025). Appendix A. Supplementary data Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.joei.2014.07.002. References [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]
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