Chemical composition of carbon disulfide-extractable fraction from oil shales of three Chinese deposits.
Rapid increase in consumption of energy and chemicals leads to dramatic increase in the prices of conventional fossil resources and thereby makes fuel chemists to pay more attention to alternative resources. Oil shales could be promising alternative ones because their reserves are large [1, 2] and hydrogen to carbon molar ratio in organic matter is high. Understanding of the composition of organic matter in oil shales is of significance not only to organic geochemistry but also to efficient utilization, especially value-added utilization of them.
Most of the related work, however, have been focused on supercritical fluid extraction, extraction yield and composition of biomarkers [3-8]. Only few researchers [9-13] have paid attention to detailed characterization of molecular structure of oil shales.
Our previous work showed that separable and non-destructive techniques are effective for determination of molecular structures of organic species present in oil shales , coals [15-18] and their reaction mixtures [19-21]. Because of its low boiling point and good penetrability in pores of solid fossils such as coals and oil shales, carbon disulfide ([CS.sub.2]) was used as an effective solvent for extracting aliphatic and aromatic hydrocarbons of lower molecular mass [14-18]. Using the techniques, we investigated the composition of organic species in carbon disulfide-extractable fraction (CDEF) from three Chinese oil shales.
Solvent and oil shale samples
[CS.sub.2] used as the solvent in the experiment is an analytical-pure reagent and distilled before use. GC/MS analysis shows no species in the distilled solvent except for [CS.sub.2] itself.
Oil shales (OSSs) used in the experiment were taken from the following deposits: Fushun (FS), Longkou (LK) and Huadian (HD), China, pulverized to pass through a 200-mesh screen and dried in vacuum at 80[degrees]C for 24 h before use. Table 1 shows the proximate and ultimate analyses of the OSSs.
Organic groups of OSSs were characterized using a Nicolet Magna IR-560 FTIR. The FTIR spectra were generated by collecting 50 scans at a resolution of 8 [cm.sup.-1] in reflectance mode. Measuring regions were 4000-500 [cm.sup.-1]. Figure 1 displays FTIR spectra of OSSs.
[FIGURE 1 OMITTED]
Extraction with [CS.sub.2] and analysis of the extracts using GC/MS
Each OSS was extracted with 300 mL of [CS.sub.2] under the nitrogen atmosphere in a Soxhlet extractor during at least 10 days. The extraction solution was concentrated to ca 1 mL using a rotary evaporator, and ca 0.5 [micro]L of the concentrated solution was analyzed using a Hewlett-Packard 6890/5973 GC/MS equipped with a capillary column coated with HP-5MS (30 m x 0.25 mm inner diameter (ID), film thickness of 0.25 [micro]m) and with a Hewlett-Packard 6890 GC equipped with a capillary column coated with HP-101 (30 m x 0.32 mm ID, film thickness of 0.3 [micro]m). The columns were heated at a rate of 10[degrees]C/min from 100[degrees]C (and held at the temperature for 2 min) to 300[degrees]C (and held at temperature for 5 min). Both injector and detector temperatures were set at 300[degrees]C. Mass spectra were obtained at an electron impact potential of 70 eV within a range of 30-500 amu. A series of authentic compounds purchased from Aldrich Chemical Co., Inc. was used for confirmation and quantification of the compounds identified with GC/MS. The yields (wt.%, daf) of extracts in the OSSs from FS, LK and HD were 7.1, 4.2 and 8.9, respectively.
Results and discussion
FTIR analysis of OSSs
As shown in Fig. 1 and Table 2, OSS from HD contains much more aliphatic moieties (AM) along with more carboxylic moieties than those from LK and FS. The content of free hydroxyl groups and epoxide along with aromatic moiety in the OSSs decreases in the order: FS > HD > LK. OSSs from HD and LK contain more alkenyl moiety than that from FS. There is more alkanol moiety in OSSs from FS and LK than in that from HD. Silicate content in OSSs decreases in the order: FS > HD >> LK, just being consistent with the order of their ash content.
Interestingly, a remarkable and appreciable amount of -C[H.sub.2]Br moiety can be observed in FTIR spectra of OSSs from FS and HD, but no organobromines were detected in CDEFs from FS and HD using GC/MS, implying that the -C[H.sub.2]Br moiety in both OSS may exist as organic macromolecular species.
Figure 2 shows total ion chromatograms (TICs) of all CDEFs. The compounds identified fall into the following categories: normal alkanes (NAs), isoprenoids (IPs), cyclanes, alkenes, alkylated arenes (AAs) and organo-oxygen compounds (OOCs), as listed in Tables 3 to 8, respectively.
Organic compounds (OCs) identified in CDEFs account for 15.12% from FS, 13.75% from HD and 7.34% from LK, suggesting that OCs identified in CDEFs are only a minority, and majority of CDEFs may consist of macromolecular and/or strongly polar species, which cannot be detected with GC/MS.
[FIGURE 2 OMITTED]
As shown in Figs. 3-5, alkanes are predominant in all CDEFs, and NAs are main components detected in CDEFs from HD and LK. The amounts of alkenes detected in CDEF from LK were much larger than those in CDEFs from HD and LK. The total yield of AAs in CDEF from FS is higher than that in CDEF from LK, while no AAs were observed in CDEF from HD. The total yield of OOCs detected in CDEF from HD is higher than that in those from FS and LK.
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
As Fig. 6 illustrates, cyclanes and NAs are the largest group components in CDEFs from FS and LK respectively, whereas NAs are predominant in CDEF from HD.
[FIGURE 6 OMITTED]
NAs. In total, seventeen NAs, from [C.sub.16] to [C.sub.33], were detected in CDEFs (Table 3), and all NAs were observed in CDEF from HD (Fig. 2c). Most of compounds detected are NAs, and heptacosane is predominantly abundant as a single compound in CDEF from HD. NAs are also primary components in CDEF from LK (Fig. 2b), but secondary ones in CDEF from FS (Fig. 2a). Much lower concentration of NAs with carbon number below 20 in CDEFs indicates that catalytic hydrocracking is necessary for converting the extracts to a clean liquid fuel.
IPs. In total, five IPs, from [C.sub.15] to [C.sub.20], were detected in CDEFs (Table 4) and all IPs were observed from CDEF from FS (Fig. 2a). Pristane and phytane predominate in IPs, being the only two IPs in CDEF from LK, while pristane is the only IP detected in CDEF from HD.
Cyclanes. Totally twenty five cyclanes were identified in CDEFs (Table 5), including two bicyclic sesquiterpanes, six cholestanes, sixteen hopanes in addition to 17[beta]H,21[alpha]H-normoretane. Twenty one of them were observed in CDEF from FS (Fig. 2a) and 17[alpha]H-22,29,30-trisnorhopane and 17[alpha]H,21[beta]H-hopane are predominantly abundant, while only five cyclanes were found in CDEF from LK (Fig. 2b), 17[beta]H,21[beta]H-30-norhopane being the most abundant one. As a possible product at thermolysis of pentacyclic triterpanes , 8,14-seco-hopane was detected only in CDEF from LK. The number of cyclanes detected in CDEF from HD is also five, but all the cyclanes differ from those detected in CDEF from LK and their concentration is much lower.
Alkenes. In all, five alkenes were identified in CDEFs (Table 6), including three hopenes and two disasterenes. All five were detected in CDEF from LK (Fig. 2b) and 30-norneohop-13(18)-ene was detected in CDEF from HD. Noteworthily, 30-norneohop-17(21)-ene is the most abundant compound in CDEF from LK. Only one alkene occurs in CDEF from HD (Fig. 2c) except for 30-norneohop-13(18)-ene.
AAs. Totally five AAs were detected (Table 7), including alkyl-substituted tetralins (peaks 4 and 8), naphthalene (peak 12) and diphenylmethane (peak 22) along with a sterane (peak 31). All of them appear in CDEF from FS (Fig. 2a) and one in CDEF from LK (Fig. 2b), but there is no AA in CDEF from HD. The concentration of all the AAs detected is low.
OOCs. In all, five OOCs were detected in CDEFs (Table 8), including a phenol (peak 7), two esters (peaks 9 and 18), an alkanone (peak 15) and an alkanoic acid (peak 21). Both esters appear in all CDEFs, and the alkanone was detected in CDEFs from both LK and HD.
The yield (wt.%, daf) of extract and the share of GC/MS-detectable species in the OSS from LK are lower than corresponding characteristics of samples from FS and HD. [CS.sub.2]-extractable fractions of three Chinese oil shales mainly consist of alkanes along with small amounts of alkenes, aromatic ring- and oxygen-containing compounds. Large amounts of NAs and cyclanes along with small amounts of IPs, alkenes, AAs and OOCs are detected in CDEF from FS. OCs detected in CDEF from LK mainly consist of NAs and alkenes, in which 30-norneohop-17(21)-ene is the most abundant compound. NAs (from [C.sub.16] to [C.sub.33]) are predominant in CDEF from HD, whereas no AAs are observed in this extract. The amount of OOCs detected in CDEF from HD is much greater than those in extracts from FS and LK.
This work was subsidized by the Special Fund for Major State Basic Research Project (Project 2004CB217801).
Presented by Qian Jialin
Received January 11, 2007
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JING-PEI CAO (a), ZHI-MIN ZONG (a), XIAO-YAN ZHAO (a), GUANG-FENG LIU (a), JIE MOU (a), FENG WANG (a), YAO-GUO HUANG (a), GUO-JIANG ZHOU (b), HAO-QUAN HU (c), XIAN-YONG WEI (a,b) *
(a) School of Chemical Engineering China University of Mining and Technology Xuzhou 221008, Jiangsu, China
(b) Institute of Coal Chemical Engineering Dalian University of Technology Dalian 116012, Liaoning, China
(c) School of Resources and Environmental Engineering Heilongjiang Institute of Science and Technology Harbin 150027, Heilongjiang, China
* Corresponding author: e-mail email@example.com, firstname.lastname@example.org
Table 1. Proximate and ultimate analyses (wt.%) of OSSs * Proximate analysis Oil shale deposit [M.sub.ad] [A.sub.ad] [V.sub.daf] Fushun 2.1 76.1 88.5 Longkou 11.6 35.0 59.7 Huadian 7.8 60.8 86.0 Ultimate analysis (daf) Oil shale [S.sub.t,d], deposit C H N wt.% Fushun 42.1 8.8 2.1 2.6 Longkou 76.1 7.5 0.4 2.4 Huadian 66.2 10.4 1.3 3.3 * Data for proximate and ultimate analyses were obtained with Leco Mac-400 Thermogravimetric Analyzer, Leco CHN-2000 Elemental Determinator and Leco SC-132 Sulfur Determinator, respectively. Table 2. Structural features of OSSs characterized by FTIR Wavenumber, Oil shale [cm.sup.-1] Assignment Fushun 3692, 3651, 3621 -OH (free) S 3432 -OH (bonded) S 2919, 2852, 1435 [MATHEMATICAL EXPRESSION S NOT REPRODUCIBLE IN ASCII] 1705 -COOH VW 1629 >C=C< O 1096 >C-OH (alcohols) VS 1029, 461 Silicates VS 906 Epoxide S 789, 686 C-H (m-disubstituted benzene) (Obv) S 538 -C[H.sub.2]Br VS Wavenumber, Oil shale [cm.sup.-1] Huadian Longkou 3692, 3651, 3621 O VW 3432 S S 2919, 2852, 1435 VS S 1705 W VW 1629 S S 1096 VS VS 1029, 461 VS VS 906 S N 789, 686 O O 538 VS VW VS: very strong; S: strong; O: ordinary; W: weak; VW: very weak; N: none; Obv: Out-of-plane bending vibration Table 3. Yields of NAs detected in CDEFs Yield, [micro]g/g OSS, daf No. Compound Fushun Longkou Huadian 6 Hexadecane 119.8 13 Octadecane 169.3 16 Nonadecane 83.2 129.7 17 Eicosane 80.5 110.8 19 Heneicosane 157.1 47.1 265.1 20 Docosane 221.2 65.5 327.4 23 Tricosane 472.3 170.9 781.7 24 Tetracosane 362.8 89.6 428.4 25 Pentacosane 513.8 116.7 997.3 26 Hexacosane 485.0 198.1 663.6 27 Heptacosane 575.5 279.6 2628.1 30 Octacosane 303.5 152.8 537.8 33 Nonacosane 358.6 212.6 993.5 37 Triacontane 87.9 48.4 297.9 42 Hentriacontane 127.8 480.3 46 Dotriacontane 191.1 54 Tritriacontane 221.8 Table 4. Yields of IPs detected in CDEFs Yield, [micro]g/g OSS, daf No. Compound Fushun Longkou Huadian 3 2,6,10-Trimethyldodecane 102.5 5 2,6,10-Trimethyltridecane 162.5 10 2,6,10-Trimethylpentadecane 155.5 11 Pristane 723.1 119.7 330.1 14 Phytane 502.8 60.5 Table 5. Yields of cyclanes detected in CDEFs Yield, [micro]g/g OSS, daf No. Compound Fushun 146.1 1 [C.sub.13]-bicyclic sesquiterpane 2 [C.sub.14]-bicyclic sesquiterpane 217.6 34 Cholestane 133.6 35 18[alpha]H-22,29,30-Trisnorneohopane 205.7 36 14[alpha]-Methylcholestane 21.4 38 17[alpha]H-22,29,30-Trisnorhopane 305.9 39 24-Methyl-5[alpha]H-cholestane 89.4 40 17[beta]H-22,29,30-Trisnorhopane 81.1 41 24-Ethyl-5[beta]H-Cholestane 81.9 43 8,14-seco-Hopane 44 24-Ethyl-5[alpha]H-Cholestane 85.9 48 17[alpha]H,21[beta]H-30-Norhopane 523.0 49 17[beta]H,21[beta]H-30-Norhopane 181.3 50 17[beta]H,21[alpha]H-Normoretane 51 Trimethylcholestane 194.0 52 17[alpha]H,21[beta]H-Hopane 873.1 53 17[alpha]H,21[beta]H-Hopane 150.3 55 17[alpha]H,21[beta]H-22S-Homohopane 181.8 56 17[alpha]H,21[beta]H-22R-Homohopane 182.4 57 17[beta]H,21[alpha]H-Hopane 58 17[beta]H,21[alpha]H-Homohopane 108.1 59 17[alpha]H,21[beta]H-22S-Bishomohopane 99.1 60 17[alpha]H,21[beta]H-22R-Bishomohopane 101.6 61 17[alpha]H,21[beta]H-22S-Trishomohopane 73.5 62 17[alpha]H,21[beta]H-22R-Trishomohopane 61.3 Yield, [micro]g/g OSS, daf No. Longkou Huadian 1 2 34 35 59.2 36 38 39 40 251.3 41 43 63.4 44 48 61.4 49 70.3 50 216.3 51 52 77.9 53 55 99.9 56 57 95.4 58 182.2 59 60 61 62 Table 6. Yields of alkenes detected in all CDEFs Yield, [micro]g/g OSS, daf No. Compound Longkou Huadian 28 Hopene 91.1 29 24S-Ethyl disaster-13(17)-ene 80.7 32 24R-Ethyl disaster-13(17)-ene 96.6 45 30-Norneohop-17(21)-ene 414 277.1 47 30-Norneohop-13(18)-ene 180.4 122.4 Table 7. Yields of ASAs detected in CDEFs Yield, [micro]g/g OSS, daf No. Compound Fushun Longkou 4 1,1,6-Trimethyltetralin 125.8 8 5,6,7,8-Tetramethyltetralin 169.3 12 Cadalene 84.4 22 1,1'-Di(2,3-xylyl)ethane 212.1 31 [C.sub.27]-Monoaromatic sterane 166.8 95.6 Table 8. Yields of OOCs detected in the CDEFs Yield, [micro]g/g OSS, daf No. Compound Fushun Longkou Huadian 7 3-Methyl-1,5-di(tert-butyl)phenol 81.1 9 BTMPMM 244.0 65.1 211.4 15 6,10,14-Trimethyl-2-pentadecanone 57.7 173.9 18 Isopropyl palmitate 80.7 108.6 301.7 21 Stearic acid 631.8
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|Author:||Cao, Jing-Pei; Zong, Zhi-Min; Zhao, Xiao-Yan; Liu, Guang-Feng; Mou, Jie; Wang, Feng; Huang, Yao-Guo;|
|Date:||Sep 1, 2007|
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