Article pubs.acs.org/EF
Effect of the Temperature on the Characteristics of Retorting Products Obtained by Yaojie Oil Shale Pyrolysis Xinzhe Lan,†,‡ Wanjiang Luo,† Yonghui Song,*,† Jun Zhou,† and Qiuli Zhang† †
Research Center of Metallurgical Engineering and Technology of Shaanxi Province, Xi’an University of Architecture and Technology, Xi’an, Shaanxi 710055, People’s Republic of China ‡ Shaanxi Radio and Television University, Xian, Shaanxi 710068, People’s Republic of China ABSTRACT: Oil shale samples were retorted in a quartz tube reactor to determine the effect of the retorting temperature on the product yield and release characteristics of gases and shale oil produced and then analyzed using a gas chromatograph (GC), micro sulfur analyzer, gas chromatograph−mass spectrometer (GC−MS), Fourier transform infrared spectrometer (FTIR), and X-ray diffractometer (XRD). The results demonstrate that, as the gas production rate increases, char gradually reduces with an increasing temperature and remains unchanged above 850 °C. The primary components of the non-condensable gas are H2, CO2, C2H4, and C2H6, and more hydrogen sulfide is released at 475 °C. The ratios of ethene/ethane, propene/propane, and butene/butane in the non-condensable gases increases, and the ratio of the total alkene/alkane in the gas also slightly increases when the temperature increases from 475 to 1000 °C. The shale oil yield increases with an increasing temperature, and the maximum value of the shale oil yield is 10.5 wt % at 550 °C. The composition of shale oil is relatively complex; the content of alkanes and phenols decreases; and the other contents in shale oil increase with an increasing temperature. Alkanes are the primary component in shale oil and lighter components. The results from this study are socially and economically important to the exploration of oil shale pyrolysis and benefit the subsequent processing and utilization of shale oil and gaseous products.
1. INTRODUCTION With an increasing demand for crude oil, the utilization of nonconventional energy will receive increasing global attention.1,2 Oil shale, an organic-rich and fine-grained sedimentary rock, consists of a mineral porous matrix that contains insoluble kerogen. Oil shale is one of the most promising sources of energy for potential liquid fuel; with great resource potential and development benefits, it is considered to be a potential replacement for petroleum in the future.3 It is a great potential energy source and an internationally recognized alternative for traditional oil resources. Liquid hydrocarbons (shale oil) and combustible shale gas can be obtained from kerogen in oil shale through heat treatments. During the oil shale pyrolysis process, the oil shale is fractured and heated to approximately 520 °C or higher. The kerogen decomposes, and a large proportion is converted into an oily vapor, which condenses to form a viscous liquid shale oil or is distilled to form naphtha, kerosene, and heavy oil.4 In addition, some gases (H2, CO, CO2, light hydrocarbons, and sulfur compounds, such as H2S, COS, CS2, and C4H4S) are released.5,6 Various process parameters,7−14 such as the type of sweeping gas, catalyst, particle size, heating rate, and retorting temperature, have been investigated to maximize the output and conversion efficiency of oil shale retorting. At present, there are several studies on the effect of the retorting temperature on the pyrolysis behavior of oil shale. Some studies focused on the effect of the retorting temperature on the total weight loss or product yield generated by the retorting oil shale. Al-Harahsheh et al.9 found that the content of the aliphatic fraction increased and the content of the aromatic fraction decreased in the shale oil with an increase in the heating rate. Normal paraffins of C10−C32 are identified in © XXXX American Chemical Society
the aliphatic fraction. The maximum concentration of these paraffins is found to be 9.9 wt % at a heating rate of 2.5 °C min−1. Therefore, both the yield and properties of the produced shale oil should be considered for its use as a substitutive crude oil. Xie et al.10 and Rose et al.11 used a Fourier transform infrared spectrometer (FTIR) to study raw shales and their products. The results showed that shale oil had similar functional groups as the organic matter of oil shale, primarily aliphatic hydrocarbons, and that the shale oil contained more of these functional groups than the raw material. The shale with more aliphatic oil yielded more oil. The shale with less aliphatic oil and more aromatic fraction yielded less oil, and its coke was rich in condensed aromatics. The pyrolysis reaction was nearly complete at 500 °C. The oil yield did not increase further with the temperature; however, the secondary pyrolysis strengthened, and the release of non-condensable gas increased. Carbonates began to decompose at 700 °C. Jaber12 indicated that the oil yield and the extent of any oil cracking were greatly influenced by the final retorting temperature. It was shown that higher weight losses occur at higher retorting temperatures. Wang et al.13 indicated that the product yield and properties of shale oil and non-condensable gases were greatly influenced by the final retorting temperature. Increasing the temperature from 430 to 520 °C increased both the oil and gas yields but reduced the oil/gas yield ratio. The nitrogen content in the derived shale oil increased, and the atomic H/C ratio and oxygen content decreased; however, there was no significant effect on the sulfur content. However, this study only investigated the Received: July 22, 2015 Revised: November 9, 2015
A
DOI: 10.1021/acs.energyfuels.5b01645 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels retorting temperature from 430 to 520 °C; little is known of the possible results at a higher retorting temperature. Olukcu et al.14 investigated Beypazari oil shale using conventional and free-falling pyrolysis at different temperatures to obtain their optimum liquefaction temperatures. Free-falling pyrolysis and conventional pyrolysis resulted in the maximum degree of conversion of 61.9% at 650 °C and 50.5% at 500 °C, respectively. Conventional pyrolysis resulted in less n-alkenes-1 than free-falling pyrolysis at a similar temperature. Polymerization reactions are predominant during conventional pyrolysis as a result of the longer reaction time, and more cracking reactions occurred during the free-falling pyrolysis. In this paper, oil shale samples from the Yaojie (YJ) mine located in the Gansu province of China were retorted in a fixedbed reactor at different retorting temperatures to determine the dependence of the product yield and properties of the shale oil, gases, and sulfur compound gas with the final retorting temperature ranging from 475 to 1000 °C. Gas chromatograph−mass spectrometer (GC−MS) analysis, high-temperature simulated distillation, and saturate, aromatic, nonhydrocarbon, and asphaltene (SANA) fractionation were performed on the produced shale oils. Additionally, the hydrocarbon gases up to C3 in the non-condensable gases were analyzed. Such information is needed to understand the process reaction mechanism, optimize the process, and enhance the shale oil yield and quality. The results have important social and economic meaning for oil shale pyrolysis and would benefit the subsequent processing and utilization of gaseous products.
Figure 1. Schematic chart of oil shale pyrolysis: (1) electric heater, (2) quartz tube reactor, (3) thermocouple, (4) liquid product collector, (5) cold trap, (6) airbag, (7) low-temperature cooling circulating pump, and (8) temperature controller. conductivity detector, the detector temperature was 100 °C and the injector temperature was 100 °C. The sulfur-containing gas was identified using a microsulfur analyzer (China). H2S and COS were determined using a GDX-104 column at room temperature with high-purity hydrogen (99.999%, 0.40 MPa) as the carrier gas and a flame ionization detector. The TCP column with high-purity hydrogen (99.999%, 0.40 MPa) as the carrier gas and a flame ionization detector were used for the analysis of CS2 and C4H4S at 70 °C. The shale oil components were separated and identified using a GC−MS (Shimadzu GCMS-QP2010 Plus instrument, Japan) and elucidated on the standard mass spectral data. The extraction used chromatographic-grade/pure dichloromethane. The GC was fitted with a RXI-5 ms column (0.25 μm film) with internal dimensions of 30 m × 0.25 μm × 0.25 μm. High-purity helium (99.999%) was used as the carrier gas at a flow rate of 1.14 mL min−1. With the carrier gas flow, a 0.40 μL liquid sample was injected through the injector in splitless injection mode at 300 °C. The oven temperature was initially held at 60 °C for 1 min, heated to 90 °C at 3 °C min−1, held for 1 min, then heated to 170 °C at 3 °C min−1, and held for 1 min. Finally, the oven was heated to 300 °C at 3 °C min−1 and held for 8 min. The mass spectrometer (MS) was operated in electron impact ionization mode with an energy level of 70 eV. The interface temperature was 300 °C, whereas the ion source temperature and quadrupole temperature were 230 and 130 °C, respectively. The mass scan ranged from 33 to 550 amu with a solvent delay time of 4 min. The qualitative and quantitative analyses were performed using a search program of the National Institute of Standards and Technology (NIST) mass spectral library and the area normalization method, respectively.
2. MATERIALS AND METHODS 2.1. Materials. The oil shale samples used in this work were collected from the YJ mine located in the Gansu province in the northwest area of China. The original oil shale samples were sampled, crushed, ground, and sieved to a particle size of ≤1 mm according to the National Standards of China (GB 474-1996). All samples were dried in an oven at 105 °C for a period of 10−12 h and then stored in airtight wide-mouth jars for subsequent experiments. 2.2. Experiment Equipment and Methods. All experiments were conducted in a quartz tube reactor (50 mm inner diameter and 100 mm height). Dried oil shale samples (50 g) were placed inside the retort before each test and electrically heated from room temperature to final retorting temperatures of 475, 550, 650, 850, and 1000 °C at a fixed heating rate of 10 °C min−1 and held at the final retorting temperature for 60 min. The liquid products (oil plus water) were collected using a cold trap after the reactor, and the volume of the gas product was collected using airbags and then analyzed. The device used for the experiment is shown in Figure 1. 2.3. Analysis and Testing. The X-ray diffractometer (XRD) was performed using a XRD-7000 diffractmeter (Japan, Shimadzu) with Cu Ka radiation at 40.0 kV and 30.0 mA. The scan range of 2θ was from 2° to 75°. The FTIR spectra were obtained using a VERTEX70 series FTIR (Bruker, Germany). The samples were dried at 110 °C for 12 h and prepared by finely grinding 1.0 mg of the sample and homogenizing it with 100.0 mg of ground KBr [dried under an infrared (IR) lamp]. The spectra were collected in the mid-IR region from 4000 to 400 cm−1. The gaseous products were analyzed off-line by a packed column gas chromatograph (GC). The GC analysis used a SP-3420A GC (China). The external standard method used detects the content of gaseous products. Hydrogen was determined from the difference. A 5A molecular sieve column with high-purity hydrogen (99.999%, 0.40 MPa) as the carrier gas and a thermal conductivity detector were used for the analysis of CO, N2, CH4, and O2. CO2, C2H4, C2H6, C3H6, and C3H8 were determined using a GDX-104 column with high-purity hydrogen (99.999%, 0.40 MPa) as the carrier gas. Using a thermal
3. RESULTS AND DISCUSSION 3.1. Sample Characterization. YJ oil shale is a typical oil shale found in Chinese oil shale mines. The degree of metamorphism of its kerogen is higher, type II with a less aliphatic structure, more methylene carbon and branched chains, and more carbon−oxygen bonds and aromatic carbons.15 The samples were characterized with respect to their proximate, ultimate, and oil content analyses. Table 1 shows the general characteristics of the samples. The oil content of the studied sample was determined according to the petroleum and chemical industry standard of China [oil content determination method of oil shale (low-temperature carbonization method) SH/T 0508-92] and found to be 9.42 wt %. The FTIR analyses of raw oil shale samples are shown in Figure 2a. Various functional groups can be observed in the FTIR spectrum of the YJ oil shale. The presence of calcite and B
DOI: 10.1021/acs.energyfuels.5b01645 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels Table 1. Proximate, Ultimate, and Oil Content Analyses of YJ Oil Shales proximate analysis (wt %)a moisture ash volatile matter fixed carbon
a
ultimate analysis (wt %)a 0.84 64.73 22.50 11.93
oil analysis (wt %)a,b
C 23.88 H 2.26 N 0.54 St 0.89 ash analysis (wt %)
shale oil water char gases
9.42 2.08 82.57 5.93
SiO2
Fe2O3
Al2O3
CaO
MgO
TiO2
SO3
P2O5
K2O
Na2O
55.69
11.22
25.50
0.91
2.41
0.92
0.18
0.19
3.98
1.18
b
On a dry basis. Under the national standard of China (SH/T 0508-92).
Through a comprehensive analysis of inorganic minerals in oil shale, this analysis indicates that the major minerals present in oil shale are silica, quartz, aluminosilicates, and pyrite, with traces of illite, kaolinite, and other minor minerals. Additionally, the variable pattern between 5° and 30° reveals that the organics are largely amorphous in nature, as shown in Figure 2b, which provides the XRD spectra of kerogen. 3.2. Effect of the Temperature on the Shale Oil Yield. Figure 3 shows the shale oil, non-condensable gases, and shale
Figure 3. Product distribution of oil shale pyrolysis under different temperatures.
Figure 2. (a) FTIR and (b) XRD spectra of YJ oil shale: Q, quartz; I, illite; K, kaolinite; C, calcite; Ca, calcium carbonate; I/S, illite/smectite mixed layer; and P, pyrite.
char yields of oil shale pyrolysis at 475, 550, 650, 850, and 1000 °C. There was an increase in the shale oil yield with an increasing temperature from 475 to 650 °C, and the gas yield also increased as the temperature increased. However, with an increase in the retorting temperature, the char yield decreased with the gradual decomposition of kerogen and minerals. At 475 °C, the yield of the shale oil is 7.62 wt % and the gas yield is 2.60 wt %. The char yield decreased from 88.20 wt % at 475 °C to 76.40 wt % at 1000 °C as a result of the increased secondary cracking reactions of heavy compounds. However, the shale oil yield began to raise, reaching a peak of 8.42 wt % at 550 °C, and the gas yield also increased, attaining a maximum value of 13.70 wt % at 1000 °C, which indicates that the increase in the gas yield is larger than that of the shale oil with the increase in the retorting temperature. This larger increase is likely because pyrolysis becomes more active as the retorting temperature increases and large amounts of kerogen are directly converted into gases. The decrease in the shale oil yield may have been due to the coking reactions of the shale oil at a high retorting temperature or the incomplete pyrolysis at a low retorting temperature.
quartz in the oil shale was also confirmed by the FTIR spectra. In Figure 2a, the sharp bands at 1430 and 877 cm−1 are characteristic of calcite minerals; the sharp bands in the ranges of 1170−1060 and 804−780 cm−1 are attributed to quartz. Aliphatic hydrocarbon stretching bands are observed at 2920 cm −1 [ν as (CH 2 )], 2850 cm −1 [ν s (CH 2 )], 1450 cm −1 [δas(CH2)], and 1380 cm−1 [δs(CH2)]. The frequency range of aromatic bands is at 3100−3000, 1620, and 736 cm−1. The bands at 3000−2850 cm−1 present in oil shale are due to the asymmetric and symmetric C−H stretching of methylene groups.16 The band at 1600 cm−1 is associated with aromatic ring stretching vibrations, and the band at approximately 1700 cm−1 is related to the CO stretching of carbonyl and/or carboxyl groups. The band located at 3350 cm−1 contributes to the OH stretching vibration. The XRD patterns of the raw oil shale support some of the FTIR results, especially those of inorganic minerals (Figure 2b). C
DOI: 10.1021/acs.energyfuels.5b01645 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels Table 2. Gas Compounds from Oil Shale Pyrolysis at Different Temperatures pyrolysis temperature (°C)
a
product
475
gases (wt %)a,b
2.6
hydrogen carbon monoxide carbon dioxide total
38.71 2.68 31.73 73.12
methane ethane ethene propane propene total sum of alkanes (C1−C3) sum of alkenes (C2−C3) ethene/ethane propene/propane alkenes/alkanes
15 5.77 1.13 3.09 1.89 26.88 23.86 3.02 0.20 0.61 0.10
550 4.7 Non-hydrocarbon Gases (vol %) 35.01 3.26 34.44 72.71 Hydrocarbon Gases (vol %) 16.06 5.53 1.19 2.83 1.67 27.28 24.42 2.86 0.22 0.59 0.10
650
850
1000
5.8
12.3
13.7
33.77 2.94 35.31 72.02
42.25 14.05 21.6 77.9
44.85 18.82 16.14 79.81
19.26 4.54 1.32 1.44 1.42 27.98 25.24 2.74 0.29 0.99 0.10
16.75 2.29 1.62 0.62 0.82 22.1 19.66 2.44 0.71 1.32 0.11
14.93 1.84 2.23 0.46 0.72 20.18 17.23 2.95 1.21 1.57 0.15
850 2707.92
1000 2848.66
On a dry basis. bBy difference.
Table 3. Total Sulfur in Oil Shale Non-condensable Gases at Different Temperatures temperature (°C) total sulfur (mg of S/Nm3)
475 5060.41
550 2908.18
3.3. Effect of Gas Release at Different Temperatures. As shown in Table 2, the main gas product by volume was hydrogen, followed by CO2, CO, and C1−C3 hydrocarbons. CO2 was produced primarily from the decarboxylation of the molecular structure in kerogen and the decomposition of minerals,8 such as calcite, calcium carbonate, and other carbonate minerals, whereas decarbonylation released CO. The aliphatic structure of kerogen in the YJ oil shale was as much as 59.58%, with methylene carbon comprising 77.3%, and most of the aliphatic structures were straight-chained and more alicyclic or branched.17 With an increasing retorting temperature, the pyrolysis reaction intensified and the secondary decomposition of pyrolysis products occurred at higher temperatures and released low-molecular-weight gases. This trend can be confirmed further by the change in the compositions of non-condensable gases, including methane, ethane, ethene, and propane, as illustrated in Table 2. The change in hydrogen and the hydrocarbon gases also indicated that the cracking reactions of shale oil vapor might also occur at different temperatures. Table 2 shows that increasing the temperature results in increases in the ethene/ethane, propene/propane and butene/ butane ratios. The total alkene/alkane gas ratio also increases slightly from 0.10 to 0.15 with an increasing temperature from 475 to 1000 °C. The ratio of alkene/alkane gases in the derived non-condensable gases had been used to determine the reaction mechanisms and indicate pyrolysis conditions.18,19 The increased ratios of ethene/ethane and propene/propane were related to an increase in vapor-phase cracking and a decreased oil yield. Consequently, the increasing trend of ethene/ethane and propene/propane in this work may have resulted from the output energy, and the subsequent secondary cracking reactions were different. The increased alkene/alkane ratio is related to a higher retorting temperature, which is, in
650 4389.28
turn, related to increased secondary gas-phase cracking reactions. The composition of hydrocarbon gases was 26.88 vol % at 475 °C, and the maximum yield of hydrocarbon gases in the gas composition was 27.98 vol % at 650 °C. The calorific value of non-condensable gases was increased from 16.32 MJ/ Nm3 at 475 °C to 18.50 MJ/Nm3 at 1000 °C. The optimal temperature of the maximum oil yield was 550 °C, and the energy consumption of the pyrolysis process was lower at 550 °C than any other temperature. 3.4. Effect of the Sulfurous Gas Release at Different Temperatures. The release of sulfur compounds in noncondensable gases at different temperatures is shown in Table 3. The content of the sulfur elements in non-condensable gases of the oil shale pyrolysis is 5060.41, 2908.18, 4389.28, 2707.92, and 2848.66 mg of S/Nm3, with the temperature increasing from 475 to 1000 °C. The sulfur compounds are derived from H2S, COS, CS2, and C4H4S in the non-condensable gases. The results indicated that the release of sulfur compounds from oil shale into non-condensable gases was greatly influenced by the final retorting temperature; there was a greater release of sulfur compounds into non-condensable gases at low temperatures and less of a release at higher temperatures. Because the release rate of the non-condensable gases was higher than that of the sulfur compounds when the temperature increased, the contents of the sulfur compounds in the non-condensable gases decreased. This indicated that the temperature has a significant effect on the release of sulfur compounds in noncondensable gases. Figure 4 shows the amounts of H2S, COS, CS2, and C4H4S released in the non-condensable gases at different temperatures. As the retorting temperature increases from 475 to 1000 °C, the releases of H2S in the non-condensable gases change considerably. The releases of H2S are 5272.66, 2961.19, 4417.34, 2620.66, and 2768.34 mg/Nm3 at retorting temperD
DOI: 10.1021/acs.energyfuels.5b01645 Energy Fuels XXXX, XXX, XXX−XXX
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shale oil. The typical organic constituents of kerogen in oil shale are algae and woody plant material. As a result of kerogen disintegration, the shale oil might be transformed into products having different molecular structures contained in shale oil. The GC−MS total ion current chromatograms of shale oil from retorting at different temperatures are shown in Figure 5.
Figure 4. Sulfur compound release in oil shale non-condensable gases at different temperatures.
atures of 475, 550, 652, 850, and 1000 °C, respectively; the largest H2S release in the non-condensable gases is at 475 °C. As reported, H2S is produced by the pyrolysis of pyrite and organic sulfur compounds. Pyrite starts to break down at 360 °C, releasing active sulfur. H2S reacts with hydrogen radicals, and the organic sulfur compounds of pyrolysis formed by H2S when the temperature increases from 475 to 520 °C include aliphatic sulfur, aromatic sulfide, and thiophene sulfur.20,21 H2S that is released between 450 and 500 °C has a peak release with the decomposition of pyrite. With an increase in the retorting temperature, there is a second peak release of H2S at 650 °C as the C−S bonds in kerogen decompose and H2S is generated by hydrogenation. In addition, H2S is generated from the decomposition of aromatic sulfur heterocycles at 900 °C and thiophene at 950 °C.22 The releases of COS in the non-condensable gases increased with an increase in the retorting temperature from 475 to 1000 °C. The releases of COS are 168.19 mg/Nm3 at 475 °C and as high as 416.25 mg/Nm3 at 650 °C, reaching a peak release of 444.66 mg/Nm3 at 1000 °C. There is a close relationship between COS and pyrite in oil shale pyrolysis.23 A portion of sulfur in the pyrite will be converted into COS at a high retorting temperature, because active sulfur and the CO group reaction produce COS with pyrite pyrolysis, whereas pyrite and the CO reaction generate COS. The release of CS2 in the noncondensable gases increased with an increase in the retorting temperature. The releases of CS2 are 0.2159 mg/Nm3 at 475 °C and as high as 0.5535 mg/Nm3 at 850 °C for the peak releases. Research has shown that the generation of CS2 is closely associated with the pyrolysis of pyrite in oil shale. With pyrite pyrolysis, FeS2 and FeS will simultaneously react with carbongenerated CS2 but the amount generated is small. The releases of C4H4S in the non-condensable gases are 21.08 mg/Nm3 at 475 °C, as much as 24.52 mg/Nm3 at 650 °C, and 1455 and 1458 mg/Nm3 at 850 and 1000 °C, respectively. Calkins24 suggested that C4H4S is released from the decomposition of organic sulfur compounds in kerogen and that more is released into non-condensable gases at low temperatures. Additionally, releases of thiophene-type compounds create structural stability generated by condensation reactions and are converted into a carbonaceous residue in the char with an increase in the retorting temperature. 3.5. Effect of the Temperature on the Components of Shale Oil. GC−MS has become a quick, convenient, and powerful tool for characterizing complex and heterogeneous
Figure 5. GC−MS total ion current chromatogram of shale oil from oil shale pyrolysis at different temperatures.
The composition and distribution of shale oil change with an increase in the temperature from 475 to 650 °C. There are more components of shale oil at a relatively low retention time at 475 °C. The composition distribution of shale oil tends to be concentrated with an increasing temperature. Using quantitative analysis, the number of compounds whose mass fraction is greater than 0.1% in shale oil was identified to be more than 137, 140, and 142 with a final retorting temperature of 475, 550, and 650 °C, respectively. The results indicate that the types of compositions of shale oil whose mass fraction is greater than 0.1% increased with an increase in the temperature. The identified compounds of shale oil pyrolysis at 475−650 °C are shown in Figure 6. Shale oil has complex mixtures of organic compounds. The compounds can be classified as alkanes, alkenes, cyclanes, phenols, and aromatics with a single ring (benzene and toluene), oxygenates (carboxylic acids, alcohols, and aldehydes), polycyclic aromatic hydrocarbons (PAHs) with more than a single ring, and others whose mass fraction is less than 0.1%. The principal identified compounds
Figure 6. Compound classification of shale oil pyrolysis at different retorting temperatures. E
DOI: 10.1021/acs.energyfuels.5b01645 Energy Fuels XXXX, XXX, XXX−XXX
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and the characteristics of shale oil, non-condensable gases, and sulfur-containing gases in non-condensable gases. The following conclusions are inferred: (1) As the retorting temperature increases from 475 to 1000 °C, the non-condensable gas yield increases considerably, whereas the shale char yield decreases and the shale oil yield reaches a peak at 550 °C. The shale oil yield decreases at a higher retorting temperature as a result of second cracking reactions. In addition, the optimum temperature in terms of the maximum yield of shale oil and the consumption of retorting energy is 550 °C. (2) Increasing the retorting temperature from 475 to 650 °C causes an increase in the content of hydrocarbon gases and a decrease in the content of non-hydrocarbon gases. However, the opposite changes occur at temperatures above 650 °C, where the situation is reversed: the content of hydrocarbon gases decreases, and the content of non-hydrocarbon gases increases. However, the calorific value of non-condensable gas increased with an increase in the retorting temperature from 475 to 1000 °C. (3) The retorting temperature has a great effect on the content of sulfur-containing gases in non-condensable gases. The content of sulfur elements in non-condensable gases of oil shale pyrolysis changes with an increase in the retorting temperature. Among sulfur-containing gases, including H2S, COS, CS2, and C4H4, H2S is the primary component in noncondensable gases and more of this gas than any of the others is released at low temperatures. (4) The main types of shale oil from the pyrolysis of oil shale were alkanes, alkenes, and PAHs. There was an increase in the contents of cyclanes, alkenes, aromatic hydrocarbons, oxygenates, and PAHs and a decrease in the content of alkanes as the temperature increased from 475 to 650 °C. Alkanes are the main components, along with lighter components, in shale oil. The carbon number distribution of the alkane components was C13−C22. The present study shows that the temperature is one of the most influential factors in the composition of shale oil.
of shale oils were alkanes and their derivatives, which comprised approximately 39.78, 31.87, and 15.06 wt % in the proportion of the total mass with an increase in the temperature from 475 to 650 °C. Phenols are valuable products because of their commercial values, reaching a peak of 9.44 wt % at 550 °C. The increased content of oxygenate compounds consisted of carboxylic acids, alcohols, and aldehydes. The PAHs increased from 11.66 wt % at 475 °C to 13.91 wt % at 650 °C. The content of alkenes reached a peak of 12.70 wt % at 550 °C. The results indicate that the decomposition reactions and types of pyrolysis products increased with an increase in the temperature. Li et al.25 prepared and analyzed critical organic intermediates from Huadian oil shale by heating them to a critical temperature point (350 °C). As the results show, there are approximately 84.3 aliphatic carbons per 100 carbons in the critical organic intermediates, less than that in the kerogen matrix studied previously, showing that the aliphatic carbons will decrease during thermal decomposition from kerogen to the critical organic intermediates. That is primarily attributed to the separation of aliphatic carbon chains and the resulting hydrocarbon gas emissions. Methylene carbon and the branched chain break down fast at low temperatures. With an increase in the temperature, carbon−oxygen bonds and aromatic carbons begin to decompose, the shale oil yield increases, and the alkane compositions decrease. Several complex phenomena occur in the oil shale retorting process. According to Tiikma et al.,26 in the heating process, the kerogen in oil shale changes into bitumen and then the bitumen converts to non-condensable gas, shale oil, and coke through pyrolysis reactions, such as cracking and coking. Additionally, the product amount of volatile matter changes depending upon the temperature, resulting in different qualities of oil recovered. When the retorting temperature increases, more low-molecularweight hydrocarbons, i.e., light oil fractions, heterocyclic compounds, and non-condensable gas, are generated. The GC−MS analysis of alkane compounds of shale oil (Table 4) reveals that the distribution of alkanes ranges from
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AUTHOR INFORMATION
Corresponding Author
Table 4. Distribution of Alkane Carbon Numbers for Shale Oil at Different Retorting Temperatures
*Telephone/Fax: 8629-82201248. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
carbon number (wt %) temperature (°C)
C8−C12
C13−C22
C23−C43
475 550 650
17.43 22.07 29.71
57.41 58.45 44.33
25.16 19.48 25.96
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ACKNOWLEDGMENTS This work was supported by the National High Technology Research and Development Program of China (863 Program, Grant 2011AA05A202).
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C8 to C43. The alkenes produced from different temperatures were classified by carbon number,13,24,27 with the results given in Table 4. In this classification, the lightweight hydrocarbons (C8−C12) were combined into one group, as shown in Table 4. The C13−C22 and C23−C43 fractions were also similarly grouped. C13−C22 of hydrocarbons is the main component of alkenes in shale oil containing 57.41, 58.45, and 44.33 wt %, with temperatures from 475 to 650 °C. C13−C22 of alkanes increased from 17.43 wt % at 475 °C to 29.71 wt % at 650 °C. The results show that the retorting temperature has an important influence on the components of alkanes and shale oil.
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4. CONCLUSION The overall experimental results show that the retorting temperature has an important influence on the product yield F
DOI: 10.1021/acs.energyfuels.5b01645 Energy Fuels XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.energyfuels.5b01645 Energy Fuels XXXX, XXX, XXX−XXX
