Effect of Shale Ash-Based Catalyst on the Pyrolysis of Fushun Oil Shale

catalysts

Article Eﬀect of Shale Ash-Based Catalyst on the Pyrolysis of Fushun Oil Shale

Hao Lu 1, Fengrui Jia 1,*, Chuang Guo 1, Haodan Pan 1, Xu Long 2 and Guangxin Liu 3

1 College of Petroleum Engineering, Liaoning Shihua University, Fushun 113001, China; [email protected] (H.L.); [email protected] (C.G.); [email protected] (H.P.) 2 School of mechanics and civil architecture, Northwestern Polytechnical University, Xi’an 710129, China; [email protected] 3 School of Environment, Tsinghua University, Beijing 100084, China; [email protected] * Correspondence: [email protected]; Tel.: +86-1384-131-4860

Received: 6 October 2019; Accepted: 24 October 2019; Published: 28 October 2019

Abstract: The effect of shale ash (SA)-based catalysts (SA as carriers to support several transition metal salts, such as ZnCl , NiCl 6H O, and CuCl 2H O) on oil shale (OS) pyrolysis was studied. 2 2· 2 2· 2 Results showed that SA promoted OS pyrolysis, and the optimum weight ratio of OS:SA was found to be 2:1. The SA-supported transition metal salt catalyst promoted the OS pyrolysis, and the catalytic effect increased with increasing load of the transition metal salt within 0.1–3.0 wt%. The transition metal salts loaded on the SA not only promoted OS pyrolysis and reduced the activation energy required but also changed the yield of pyrolysis products (reduced shale oil and semi-coke yields and increased gas and loss yield). SA-supported 3 wt% CuCl 2H O catalyst not only exhibited the 2· 2 highest ability to reduce the activation energy in OS pyrolysis (32.84 kJ/mol) but also improved the gas and loss yield, which was 4.4% higher than the uncatalyzed reaction. The supporting transition metal salts on the SA also increased the content of short-chain hydrocarbons in aliphatic hydrocarbons in shale oil and catalyzed the aromatization of aliphatic hydrocarbons to form aromatic hydrocarbons. The catalytic activity of the transition metal salt on the SA-based catalyst for OS pyrolysis decreased in the order of CuCl 2H O > NiCl 6H O > ZnCl . 2· 2 2· 2 2 Keywords: shale ash; transition metal salt; oil shale; catalytic effect; kinetics; pyrolysis

1. Introduction Since the 20th century, the massive use of traditional fossil fuel has led to rapid depletion of its reserve. The lack of fossil fuel encourages some countries to develop alternative energy sources, such as synthetic oil from coal and other fossil fuels. For many countries, oil shale (OS) represents a valuable potential source of liquid hydrocarbons and energy. In China, OS resources are estimated at 978 billion tons; of which, OS resources in extensional basins are approximately 632 billion tons, which account for 65% of the China’s total OS resources or approximately 32 billion tons of in situ shale oil [1–4]. Shale oil has high H/C atomic ratio and is similar to crude oil. OS has become an ideal substitute for fossil fuel [5]. Dry distillation is an attractive conversion method, where OS is converted into different phases, including shale oil, semi-coke, and gas. Many influencing factors, including shale particle size, pyrolysis atmosphere, pyrolysis temperature, heating rate, and residence time, have been studied to improve the production of shale oil and its quality [6,7]. Various types of catalysts have been investigated for the catalytic pyrolysis of OS. Williams et al. [8,9] studied the effect of zeolite catalysts in a two-stage reactor and reported that the catalysts decrease the overall contents of N and S and the yield of the derived Pakistan shale oil. Gai et al. [10]

Catalysts 2019, 9, 900; doi:10.3390/catal9110900 www.mdpi.com/journal/catalysts Catalysts 2019, 9, 900 2 of 15 studied the effect of pyrite on OS pyrolysis; inherent pyrite improves the oil yield, but additional pyrite increases the amount of volatiles. Hu et al. [11] found that montmorillonite and gypsum enhance oil formation and minimize residue formation during kerogen pyrolysis, whereas calcite inhibits oil formation. Jiang et al. [12] investigated the catalytic effects of CoCl2 and MnSO4 on OS pyrolysis. The results showed that CoCl2 can function as an activation center to accelerate the decomposition of chemical bonds in organic matter, thereby increasing the shale oil yield. Chang et al. [13] studied the effects of FeCl 4H O, CoCl 6H O, NiCl 6H O, and ZnCl on OS pyrolysis by fixed bed and 2· 2 2· 2 2· 2 2 thermogravimetric analyses. These pyrolysis experiments indicated that all transition metal salts can enhance the secondary cracking of shale oil, thereby reducing the oil production and increasing pyrolysis the gas production. Transition metal salts can also catalyze the aromatization of aliphatic hydrocarbons to obtain aromatic hydrocarbons. Coal chars have a good catalytic effect on coal pyrolysis and can be used as a carrier to support metal chloride and maximize the utilization of its surface. Metal minerals and metal chlorides inside the coal char synergistically lead to heavy tar cracking effect [14,15]. Coal and OS are fossil fuel sources with similar properties. Thus, the solid product shale ash (SA), after pyrolysis or combustion of OS has good catalytic effect similar to coal char. Shi et al. [16] studied the effect of SA on the pyrolysis of Huadian OS. SA exerts a negligible effect on product yield but significant effect on gas and oil components. Lai et al. [17] demonstrated that OS ash has a catalytic effect on the secondary cracking and upgrading of shale oil to facilitate the conversion of the heavy oil fraction to light oil and gas. Up to now, few studies pay attention to the effect of catalysts loaded with the carrier of Cu and SA on pyrolysis of the OS. Therefore, the mixed pyrolysis behavior of the Fushun OS and SA based catalyst was investigated, as well as the effect of SA loaded with a different transition metal salt (ZnCl2, NiCl 6H O, and CuCl 2H O) on the pyrolysis behavior and product. 2· 2 2· 2 2. Experimental

2.1. Materials OS and SA were obtained from Fushun City, Liaoning Province, China, and their main properties are shown in Table1. The OS samples were pulverized by a jaw crusher (Zhengzhou, China) and screened with molecular sieves. The OS sample had a particle size of 40–60 mesh. Before the experiment, the OS samples were washed seven to eight times with deionized water and dried overnight at 80 C[12,18–20]. Transition metal salts such as ZnCl , NiCl 6H O, and CuCl 2H O ◦ 2 2· 2 2· 2 were all analytically pure. The transition metal salt loading referred to herein is the transition metal loading, with values of 0.1, 0.5, 1, and 3 wt%, which are the ratio of transition metal quality to the sum of transition metal and SA. The OS:SA mass ratios were 1:0, 2:1, and 1:1, and the loss of SA in the thermogravimetric and pyrolysis experiments was considered negligible. SA-based catalysts were prepared by equal-volume impregnation.

Table 1. Industrial analysis and elemental analysis of oil shale (OS) and shale ash (SA).

Industrial Analysis, % Elemental Analysis, %

Sample Mad Aad Vad FCad *Cad Had Nad Oad *Sad OS 2.88 77.19 17.76 2.17 10.86 1.89 0.74 6.16 0.28 SA 0.55 90.69 5.97 2.79 4.98 0.56 1.16 1.31 0.75 * subtraction method.

The sample with SA-based catalyst mixed with OS was denoted as OS–SA–Q, where Q represents the type of the transition metal element used. For example, OS–SA refers to an OS sample mixed with OS and SA, and OS–SA–Ni refers to an OS sample mixed with OS and SA-loaded NiCl 6H O. 2· 2 Furthermore, the pyrolyzed semi-coke sample is denoted as M–SC, where M represents the pyrolyzed Catalysts 2019, 9, 900 3 of 15 sample used. For example, OS–SA–SC refers to a semi-coke sample, and SC refers to a semi-coke after pyrolysis with OS alone. The components of Fushun OS and SA were analyzed by X-ray diﬀraction (XRD). The XRD spectrum indicated that the minerals in the OS were mainly composed of quartz and aluminosilicates, of which the aluminosilicates included kaolinite and illite. In addition, a small amount of carbonates, such as siderite, existed. The composition of SA was mainly composed of SiO2, and the signals of Fe2O3 and MnO2 could also be clearly detected. However, some metal oxides or salts may not be crystallized after high-temperature treatment; as such, even high levels cannot be detected by XRD analysis. In addition, some peaks overlap and cannot be fully recognized [16]. In this regard, SA composition was also analyzed by X–ray ﬂuorescence (Table2).

Table 2. Ash XRF (X–ray ﬂuorescence) analysis of Fushun oil shale.

Constituent SiO2 Al2O3 Fe2O3 SO3 K2O MgO TiO2 P2O5 CaO Other Content, % 58.14 23.19 10.27 1.51 1.44 1.42 1.36 1.27 1.07 0.33

Table2 shows that Fushun SA was mainly composed of SiO 2, Al2O3, and Fe2O3, which account for 91.6% of the total composition. Small amounts of K2O, MgO, TiO2, and CaO were also present.

2.2. OS Pyrolysis Thermal behavior analysis: As one of the most important thermochemical methods, thermogravimetric analysis was applied to observe changes in the pyrolysis behavior of OS samples with/without SA-based catalysts. The thermal analyzer used (US TA company, Shenyang, China) has microbalance sensitivity of less than 0.1 C and temperature accuracy of 0.5 C. In each experiment, ± ◦ ± ◦ the initial weight of the sample loaded into the crucible was 10 0.5 mg to avoid heating transfer ± limitation, and then was set to increase the temperature from room temperature to 900 ◦C at a heating rate of 10 ◦C/min. The Ar, as carrier gas and shielding gas, was maintained at 50 and 20 mL/min during the whole experiment process to ensure the inert atmosphere. The inﬂuence of buoyancy and weight loss of the crucible was calibrated by the baseline carried out with a blank experiment before the sample experiment. To ensure the reasonable reproducibility, all the potentiodynamic polarization tests were normally repeated at least three times under the same condition. The conversion rate formula used in the thermogravimetric analysis is as follows.

m mt α = 0 − , (1) m0 m − ∞ where m0 is the initial mass of the oil shale, mt is the remaining mass of the oil shale at time t, and m ∞ is the mass of the final non-decomposable residue. Pyrolysis experiment: A homemade fixed bed pyrolysis device was used. The device was mainly composed of five parts, namely, a feeding device, a pyrolysis device, a condensing device, a drying device, and a gas analysis device. The pyrolysis unit was decomposed into a three-part pyrolysis furnace. Cool water was added to the furnace mouth and tail to ensure appropriate operation of the unit. In each experiment, the samples (10 0.5 g) were placed in a pyrolysis furnace and purged with ± N2 to ensure the inertness of the pyrolysis atmosphere. The temperature was then raised at a rate of 5 ◦C/min from room temperature to 520 ◦C, which was maintained for 20 min. The volatile products formed by pyrolysis were purged by N2 into the system for condensation. The non-condensable gas was passed through an infrared in-line analyzer after drying for real-time detection. The yield of the pyrolysis product was then obtained according to the work of Jiang et al. [12].

2.3. Analytical Methods The characteristics of shale semi-coke and shale oil were analyzed by Fourier transform attenuated total reﬂection infrared spectroscopy (ATR–FTIR, Nicolet iS50 model, Shanghai, China). Spectral Catalysts 2019, 9, 900 4 of 15

1 1 recording was conducted between 400 and 4000 cm− with a spectral resolution of 4 cm− . An Agilent 7890A gas chromatograph equipped with an Agilent 5975C mass spectrometer (Shenyang, China) was used to detect the chemical composition of the product.

3. Results and Discussion

3.1. Inﬂuence of SA Content on OS Pyrolysis

CatalystsFigure 2019, 9,1 x showsFOR PEER the REVIEW TG (Thermal Gravity) and DTG (Di fferential Thermal Gravity) curves4 of 15 of the mixed pyrolysis of OS and SA. The TG curve shows that the thermal decomposition of the OS withoutsample catalysts without catalystscould be could outlined be outlined in three in threestages. stages. The first The firststage, stage, which which occurred occurred from from room room temperaturetemperature to to 300 300 °C,◦C, mainly mainly involved thethe dehydrationdehydration of of water. water. A A drum drum wind wind drying drying oven oven was was used usedprior prior to the to trial,the trial, and and the weightlessnessthe weightlessness was relativelywas relatively gentle. gentle. The secondThe second stage stage occurred occurred from 300from◦C 300to 600°C to◦C, 600 at °C, which at which the weight the weight loss rate loss was rate as was high as as high 16.8 as wt%, 16.8 accounting wt%, accounting for 80.6 for wt% 80.6 of wt% the total of theweight total loss.weight Therefore, loss. Therefore, the second the stagesecond was stag thee mainwas the stage main of thermalstage of decomposition. thermal decomposition. The third The stage thirdoccurred stagefrom occurred 600 ◦ Cfrom to 900 600◦ C,°C at to which 900 °C, organic at which matter organic was completely matter was degraded. completely The degraded. decomposition The decompositionreaction of some reaction clay mineralsof some clay and minerals siderite wasand observedsiderite was [21 observed] but was [21] relatively but was weak. relatively This weak. finding Thisindicates finding that indicates the Fushun that the OS Fushun contained OS contain less carbonateed less carbonate minerals minerals [22], which [22], conforms which conforms to the XRD to theanalysis XRD analysis results. results.

(a) (b)

Figure 1. (a) TG (Thermal Gravity) and (b) DTG (Differential Thermal Gravity) curves for different Figuremass ratios 1. (a) ofTG OS:SA. (Thermal Gravity) and (b) DTG (Differential Thermal Gravity) curves for different mass ratios of OS:SA. Figure1 shows the same trends of the three TG and DTG curves. In the TG curve, the total weight lossFigure rate of 1 pyrolysis shows the gradually same trends decreased of the three with graduallyTG and DTG increasing curves. SAIn the content TG curve, because the oftotal the weight dilution lossof OSrate organic of pyrolysis matter asgradually the SA ratio decreased increased. with Moreover, gradually the increasing volatile matter SA content remained because in the pyrolysis of the dilutionsystem of for OS a longorganic time, matter resulting as the in SA a secondaryratio increased. reaction Moreover, and changing the volatile the oil matter yield remained and composition. in the pyrolysisThe secondary system reactionfor a long of volatiletime, resulting materials in a during secondary diffusion reaction in the and reactor changing is primarily the oil yield due toand the composition.coking of the The hydrogen-depleted secondary reaction species of volatile and materials the cracking during of the diffusion aliphatic in portionthe reactor [23 ].is Theprimarily coking duecauses to the the coking shale of oil the to formhydrogen-depleted solid product orspecies coke, and which the iscracking dominant of the at relativelyaliphatic portion low temperatures [23]. The cokingsuch ascauses below the 450 shale◦C[24 oil,25 to]. Theform catalytic solid product action ofor SAcoke, caused which the is cracking dominant and at coking relatively of organic low temperaturesmatter at relatively such as lowbelow temperatures. 450 °C [24,25]. The catalytic action of SA caused the cracking and coking of organicThe matter DTG curve at relatively shows thatlow thetemperatures. maximum weight loss rate gradually decreased as the SA ratio increased.The DTG The curve corresponding shows that temperature the maximum was weight approximately loss rate gradually 5 ◦C lower decreased than that atas thethe maximumSA ratio increased.weight loss The rate corresponding of OS when thetemperature OS:SA ratio was was approximately 2:1. However, 5 °C when lower the than ratio that of OS: at the SA maximum was 1:1, the weightdecreasing loss rate temperature of OS when at thethe maximumOS:SA ratio weight was 2: loss1. However, rate was lesswhen than the 5 ratio◦C. Thus,of OS: the SA ratio was of1:1, OS:SA the decreasingquality was temperature 2:1. at the maximum weight loss rate was less than 5 °C. Thus, the ratio of OS:SA quality was 2:1. Figure 2 shows the conversion curves for different mass ratios of OS:SA. The graph shows that at less than 434 °C, the conversion rate of OS gradually increased as the SA ratio increased; the conversion rate of OS:SA (2:1) was higher than the other two at 434–500 °C. At greater than 500 °C, the conversion rate of the individual OS pyrolysis was the largest possibly because of the good thermal conductivity of SA [26], resulting in rapid decomposition of the organic matter of OS containing a high ratio of SA; most of which was decomposed at lower than 500 °C. Above this temperature, the decomposition of minerals in the OS mainly occurs.

Catalysts 2019, 9, 900 5 of 15

Figure2 shows the conversion curves for di ﬀerent mass ratios of OS:SA. The graph shows that at less than 434 ◦C, the conversion rate of OS gradually increased as the SA ratio increased; the conversion rate of OS:SA (2:1) was higher than the other two at 434–500 ◦C. At greater than 500 ◦C, the conversion rate of the individual OS pyrolysis was the largest possibly because of the good thermal conductivity of SA [26], resulting in rapid decomposition of the organic matter of OS containing a high ratio of SA; most of which was decomposed at lower than 500 ◦C. Above this temperature, the decomposition of Catalystsminerals 2019 in, 9 the, x FOR OS PEER mainly REVIEW occurs. 5 of 15

FigureFigure 2. 2. ConversionConversion curves curves of of different different mass ratios of OS and SA. In summary, SA as a catalyst promoted OS decomposition. However, the SA ratio should not be In summary, SA as a catalyst promoted OS decomposition. However, the SA ratio should not be large. When SA was used as the supported metal catalyst, the optimum ratio of OS:SA was 2:1. large. When SA was used as the supported metal catalyst, the optimum ratio of OS:SA was 2:1. 3.2. Effects of Different Loading of Transition Metal Salts on SA on OS Pyrolysis 3.2. Effects of Different Loading of Transition Metal Salts on SA on OS Pyrolysis Figure3 shows the TG, DTG, and conversion curves of the mixed pyrolysis of OS and SA-based Figure 3 shows the TG, DTG, and conversion curves of the mixed pyrolysis of OS and SA-based catalysts. The pyrolysis of the supported transition metal salts and OS on SA considerably differed from catalysts. The pyrolysis of the supported transition metal salts and OS on SA considerably differed that of OS. Figure3a,d,g show that when OS and SA–Q were mixed and pyrolyzed, the total weight from that of OS. Figure 3a, 3d and 3g show that when OS and SA–Q were mixed and pyrolyzed, the loss rate of the OS was less than the weight loss rate of the mixed pyrolysis of OS and SA. In addition, total weight loss rate of the OS was less than the weight loss rate of the mixed pyrolysis of OS and the initial pyrolysis temperature of the OS gradually decreased with increasing transition metal salt SA. In addition, the initial pyrolysis temperature of the OS gradually decreased with increasing loading. This result may have been due to the fact that the supported transition metal salt reduced transition metal salt loading. This result may have been due to the fact that the supported transition the activation energy required for OS pyrolysis, thereby allowing OS organics to pyrolyze in the low metal salt reduced the activation energy required for OS pyrolysis, thereby allowing OS organics to temperature range [27,28]. When the temperature increased, the volatile substances remaining in the pyrolyze in the low temperature range [27,28]. When the temperature increased, the volatile pyrolysis system for a long time undergo a secondary reaction, which leads to an increase in carbon substances remaining in the pyrolysis system for a long time undergo a secondary reaction, which deposits and a consequent decrease in the weight loss rate. Figure3b,e,h show that the maximum leads to an increase in carbon deposits and a consequent decrease in the weight loss rate. Figure 3b, weight loss rate of OS–SA–Ni and OS–SA–Cu at different loadings was lower than that of OS–SA. 3e and 3h show that the maximum weight loss rate of OS–SA–Ni and OS–SA–Cu at different loadings However, the maximum weight loss rate was lower than OS–SA when ZnCl2 has the largest amount in was lower than that of OS–SA. However, the maximum weight loss rate was lower than OS–SA when OS–SA–Zn. In addition, when the transition metal salt loading was low, the temperature corresponding ZnCl2 has the largest amount in OS–SA–Zn. In addition, when the transition metal salt loading was to the maximum weight loss rate did not change. When the transition metal salt loading was 3 wt%, the low, the temperature corresponding to the maximum weight loss rate did not change. When the temperature of the maximum weight loss rate changed remarkably and was approximately 5 ◦C lower transition metal salt loading was 3 wt%, the temperature of the maximum weight loss rate changed than the OS–SA pyrolysis temperature. The conversion curve Figure3c,f,i show that at large transition remarkably and was approximately 5 °C lower than the OS–SA pyrolysis temperature. The metal salt loading, the conversion rate in the organic decomposition stage (300–520 ◦C) was high. conversion curve Figure 3c, 3f and 3i show that at large transition metal salt loading, the conversion rate in the organic decomposition stage (300–520 °C) was high.

(a) OS–SA–Zn (b) OS–SA–Zn (c) OS–SA–Zn

Catalysts 2019, 9, x FOR PEER REVIEW 5 of 15

Figure 2. Conversion curves of different mass ratios of OS and SA.

In summary, SA as a catalyst promoted OS decomposition. However, the SA ratio should not be large. When SA was used as the supported metal catalyst, the optimum ratio of OS:SA was 2:1.

3.2. Effects of Different Loading of Transition Metal Salts on SA on OS Pyrolysis Figure 3 shows the TG, DTG, and conversion curves of the mixed pyrolysis of OS and SA-based catalysts. The pyrolysis of the supported transition metal salts and OS on SA considerably differed from that of OS. Figure 3a, 3d and 3g show that when OS and SA–Q were mixed and pyrolyzed, the total weight loss rate of the OS was less than the weight loss rate of the mixed pyrolysis of OS and SA. In addition, the initial pyrolysis temperature of the OS gradually decreased with increasing transition metal salt loading. This result may have been due to the fact that the supported transition metal salt reduced the activation energy required for OS pyrolysis, thereby allowing OS organics to pyrolyze in the low temperature range [27,28]. When the temperature increased, the volatile substances remaining in the pyrolysis system for a long time undergo a secondary reaction, which leads to an increase in carbon deposits and a consequent decrease in the weight loss rate. Figure 3b, 3e and 3h show that the maximum weight loss rate of OS–SA–Ni and OS–SA–Cu at different loadings was lower than that of OS–SA. However, the maximum weight loss rate was lower than OS–SA when ZnCl2 has the largest amount in OS–SA–Zn. In addition, when the transition metal salt loading was low, the temperature corresponding to the maximum weight loss rate did not change. When the transition metal salt loading was 3 wt%, the temperature of the maximum weight loss rate changed remarkably and was approximately 5 °C lower than the OS–SA pyrolysis temperature. The Catalystsconversion2019, 9, 900 curve Figure 3c, 3f and 3i show that at large transition metal salt loading, the conversion6 of 15 rate in the organic decomposition stage (300–520 °C) was high.

Catalysts 2019, 9, x FOR PEER REVIEW 6 of 15 (a) OS–SA–Zn (b) OS–SA–Zn (c) OS–SA–Zn

(d) OS–SA–Ni (e) OS–SA–Ni (f) OS–SA–Ni

(g) OS–SA–Cu (h) OS–SA–Cu (i) OS–SA–Cu

FigureFigure 3. Thermogravimetric3. Thermogravimetric curvescurves of OS under shale shale ash-based ash-based catalyst: catalyst: (a,d (a,g,d) ,TG;g) TG; (b,e (,bh),e DTG;,h) DTG; (c,f,(ic),f conversion,i) conversion rate. rate.

Therefore,Therefore, various various transition transition metal metal salts salts on on the th SAe SA promoted promoted OS OS pyrolysis, pyrolysis, and and the the catalytic catalytic eﬀ ect improvedeffect improved as the amount as the amount of the transition of the transi metaltion metal salt increased salt increased within within 0.1–3 0.1–3 wt%. wt%.

3.3.3.3. Eﬀ ectsEffects of Diof Differentﬀerent Transition Transition Metal Metal Salts Salts ofof SASA LoadingLoading on on OS OS Pyrolysis Pyrolysis

3.3.1.3.3.1. Analysis Analysis of of Catalytic Catalytic Pyrolysis Pyrolysis BehaviorBehavior FigureFigure4 presents 4 presents a grapha graph of of TG, TG, DTG, DTG, andand conversionconversion of of mixed mixed pyrolysis pyrolysis of ofSA SA loaded loaded with with 3 3 wt% ZnCl2, NiCl2·6H2O, and CuCl2·2H2O with OS. The graphs of the samples with 3 wt% ZnCl2, wt% ZnCl2, NiCl2 6H2O, and CuCl2 2H2O with OS. The graphs of the samples with 3 wt% ZnCl2, NiCl2·6H2O, and· CuCl2·2H2O were compared· to study the effects of different transition metal salts NiCl2 6H2O, and CuCl2 2H2O were compared to study the effects of different transition metal salts loaded· on SA on OS pyrolysis.· The TG curve (Figure 4a) shows that the temperature of OS–SA–Zn at loaded on SA on OS pyrolysis. The TG curve (Figure4a) shows that the temperature of OS–SA–Zn at the same weight loss rate was lower than the other two other samples throughout the experiment. the same weight loss rate was lower than the other two other samples throughout the experiment. The The mass loss demarcation temperature of OS–SA–Ni and OS–SA–Cu was 444.1 °C, prior to which massthe loss temperature demarcation required temperature for OS–SA–Cu of OS–SA–Ni was low at th ande same OS–SA–Cu weight loss was rate. 444.1 At temperatures◦C, prior to whichhigher the temperaturethan 444.1 required°C, OS–SA–Ni for OS–SA–Cu was smaller was than low OS–SA–Cu at the same at the weight same weight loss rate. loss Atrate. temperatures In addition, OS– higher thanSA–Zn 444.1 had◦C, the OS–SA–Ni lowest total was mass smaller loss of than pyrolysis, OS–SA–Cu which was at the less same than the weight total lossmass rate. loss of In OS–SA addition, OS–SA–Znpyrolysis. had Thus, the ZnCl lowest2, NiCl total2·6H mass2O, lossand ofCuCl pyrolysis,2·2H2O synergistically which was less function than theed total with mass SA to loss promote of OS–SA pyrolysis.OS pyrolysis, Thus, ZnClreduced, NiCl the temperature6H O, and CuClrequired2H forO synergisticallypyrolysis, induced functioned a secondary with SAreaction to promote of 2 2· 2 2· 2 OSvolatile pyrolysis, products, reduced and the ultimately temperature led to required a decrease for in pyrolysis, total weight induced loss rate. a secondary This finding reaction is consistent of volatile products,with previous and ultimately analysis. The led tototal a decreaseweight loss in totalrate of weight OS–SA–Zn loss rate.was the This smallest finding possibly is consistent because with ZnCl2 started to volatilize rapidly at 450 °C and the OS interacted with ZnCl2, thereby decreasing the previous analysis. The total weight loss rate of OS–SA–Zn was the smallest possibly because ZnCl2 total weight loss rate of OS [13,29]. started to volatilize rapidly at 450 ◦C and the OS interacted with ZnCl2, thereby decreasing the total weight loss rate of OS [13,29].

Catalysts 2019, 9, 900 7 of 15 Catalysts 2019, 9, x FOR PEER REVIEW 7 of 15

(a) (b) (c)

FigureFigure 4. 4. ThermogravimetricThermogravimetric curves curves of of OS OS with with SA SA loading loading 3 3 wt% of ZnClZnCl2, NiCl2·6H6H2OO and and 2 2· 2 CuClCuCl2·2H2H2O:O: (a ()a )TG; TG; (b (b) )DTG; DTG; (c ()c )conversion conversion rate. rate. 2· 2 TheThe DTG DTG curve curve (Figure (Figure 4b)4b) shows that the temper temperaturesatures corresponding to the maximum weight lossloss rate rate of of OS–SA–Zn, OS–SA–Zn, OS–SA–Ni, OS–SA–Ni, and and OS–SA–Cu OS–SA–Cu were were the the same. same. However, However, the the maximum maximum weight weight lossloss rate rate of of OS–SA–Cu OS–SA–Cu was was the the smallest, smallest, followed followed by by OS–SA–Zn OS–SA–Zn and, and, finally, finally, OS–SA–Ni. OS–SA–Ni. In In addition, addition, thethe main main pyrolysis pyrolysis intervals intervals of of OS–SA–Zn, OS–SA–Zn, OS–SA– OS–SA–Ni,Ni, and and OS–SA–Cu OS–SA–Cu moved moved to to the the low low temperature temperature zone.zone. Figure Figure 44cc showsshows that that the the SA-based SA-based catalyst catalyst primarily primarily a ff ectedaffected OS pyrolysisOS pyrolysis during during the main the main stage. stage.At this At stage, this stage, the conversion the conversi rateon ofrate OS–SA–Q of OS–SA–Q was greaterwas greater than than that that the conversionthe conversion rate rate of OS of andOS andOS–SA. OS–SA. The The conversion conversion rate ofrate OS–SA–Cu of OS–SA–Cu was higherwas higher than thatthan of that the of two the other two other samples samples at 200–520 at 200–◦C. 520Furthermore, °C. Furthermore, the conversion the conversion of OS–SA–Zn of OS–SA–Zn was greater was thangreater the than conversion the conversion of OS and of OS–SAOS and atOS–SA above at370 above◦C. Thus,370 °C. when Thus, SA when was usedSA was as support,used as support the catalytic, the sequencecatalytic sequence of the transition of the transition metal salts metal was saltsCuCl was2H CuClO >2·2HNiCl2O 6H> NiClO >2·6HZnCl2O >. ZnCl2. 2· 2 2· 2 2 3.3.2.3.3.2. Kinetics Kinetics Analysis Analysis TheThe related related kinetics kinetics parameters parameters in in the the thermochem thermochemicalical system system were were calculated calculated to to investigate investigate the the underlyingunderlying mechanism. mechanism. In In the the numerous numerous analytical analytical models, models, Coats–Redfern Coats–Redfern (C–R) (C–R) method method [30,31] [30,31] has has consistentlyconsistently been been used used to to calculate calculate the the related related kineti kineticscs parameters parameters of of solid solid fu fuelel pyrolysis. pyrolysis. Therefore, Therefore, thisthis study study used used the the C–R C–R model model to to analyze analyze the the mech mechanismanism of of mixed mixed pyrolysis pyrolysis of of SA-supported SA-supported 3 3 wt% wt% ZnCl , NiCl 6H O, and CuCl 2H O with OS. The formula can be expressed as follows: ZnCl22, NiCl2·6H2· 2O,2 and CuCl2·2H2· 2O2 with OS. The formula can be expressed as follows: −𝑙𝑛ln(1 (1α) − 𝛼) AR𝐴𝑅 22𝑅𝑇RT E𝐸 lnln[ [− − ]] = =lnln [[ ((11 − )])] − ,, (2) (2) T𝑇2 β𝛽𝐸E − E𝐸 − RT𝑅𝑇 where α was the conversion rate; T was the absolute temperature, K; β was the heating rate under where α was the conversion rate; T was the absolute temperature, K; β was the heating rate under non-isothermal conditions, K/min; E is the apparent activation energy, kJ/mol; A is the pre- non-isothermal conditions, K/min; E is the apparent activation energy, kJ/mol; A is the pre-exponential exponential factor; R is the gas constant. For the general reaction temperature range and2RT most E, factor; R is the gas constant. For the general reaction temperature range and most E, was far less E() ( ) was far less thanAR 1, so 2 lnRT [ (1 − )] could be regarded as a constant. Therefore,ln 1 α ln [ 1 ] and than 1, so ln [ βE (1 E )]could be regarded as a constant. Therefore, ln [ − 2− and T could be − T could be used for drawing. The values of the activation energy E and the frequency factor A could used for drawing. The values of the activation energy E and the frequency factor A could be obtained beby obtained the slope by theE and slope intercept − and ofthe intercept line ln of[ AR the(1 line2RT ln)] [. (1 − )]. − R βE − E TableTable 3 showsshows thethe thermodynamicthermodynamic parameters of thethe main pyrolysis stage of oil shale with and withoutwithout catalyst. The The main pyrolysis stagestage indicatedindicated thatthat the the weight weight loss loss rate rate accounted accounted for for 60 60 wt% wt% or ormore more of theof the weight weight loss loss rate rate of the of secondthe second pyrolysis pyrolysis section. section. The curve The curve and fitting and fitting results results of C–R methodof C–R methodindicated indicated that the mainthat the stage main of OSstage pyrolysis of OS pyroly was thesis first-order was the first-order reaction, andreaction, the correlation and the correlation coefficient 2 coefficientR was greater R2 was than greater 0.995. than This high0.995. correlation This high coecorrelationfficient proved coefficient the reliability proved the of the reliability computational of the computationalmodel. The remaining model. The fitting remaining results arefitting shown results in Table are shown3. The activationin Table 3. energy The activation required energy for OS requiredpyrolysis for in theOS mainpyrolysis pyrolysis in the stage main was pyrolysis 116.04 kJstage/mol. was When 116.04 SA kJ/mol. and SA–Q When were SA added and SA–Q as catalysts, were addedthe activation as catalysts, energy the required activation for energy the main required pyrolysis for stage the main of OS pyrolysis was reduced. stage The of OS activation was reduced. energy Therequired activation for the energy pyrolysis required of OS addedfor the withpyrolysis SA was of reducedOS added by with 11.08 SA kJ/ mol,was reduced accounting by for11.08 9.5% kJ/mol, of the accountingactivation energy for 9.5% required of the for activation OS pyrolysis. energy The activationrequired for energy OS decreasedpyrolysis. when The theactivation transition energy metal decreased when the transition metal salt was loaded on the SA; the energy was reduced the most at 32.84 kJ/mol in the sample containing CuCl2·2H2O with a load of 3 wt%, followed by the samples

Catalysts 2019, 9, 900 8 of 15 Catalysts 2019, 9, x FOR PEER REVIEW 8 of 15 withsalt was 3 wt% loaded by weight on the SA;of NiCl the energy2·6H2O was(24.43 reduced kJ/mol) the and most ZnCl at2 32.84 (22.7 kJ kJ/mol)./mol in theThis sample finding containing suggests thatCuCl SA-based2H O with catalysts a load can of accelerate 3 wt%, followed the decomposition by the samples of chemical with 3 wt% bonds by weightin organic of NiClmatter.6H TheO 2· 2 2· 2 (24.43decrease kJ/ mol)in apparent and ZnCl activation2 (22.7 kJ energy/mol). Thisalso findingindicated suggests the highly that SA-basedcomplicated catalysts pyrolysis can acceleratereactions, includingthe decomposition the decomposition of chemical of bonds long-chain in organic alkane matter.s, aromatization The decrease of in apparentalicyclic compounds, activation energy and rupturealso indicated of heterocyclic the highly compounds. complicated Therefore, pyrolysis reactions,from the perspective including the of decompositionactivation energy, of long-chain SA could promotealkanes, aromatizationOS pyrolysis. After of alicyclic the transition compounds, metal andsalt rupturewas added of heterocyclic to SA, the catalytic compounds. effect Therefore,improved infrom the the order perspective of CuCl of activation2·2H2O > energy,NiCl2·6H SA2O could > ZnCl promote2. This OS pyrolysis.finding was After consistent the transition with metal the thermogravimetricsalt was added to SA, an thealysis catalytic results. eff ect improved in the order of CuCl 2H O > NiCl 6H O > ZnCl . 2· 2 2· 2 2 This finding was consistent with the thermogravimetric analysis results. Table 3. Thermal kinetic parameters of oil shale with and without catalyst. Table 3. Thermal kinetic parameters of oil shale with and without catalyst. Sample T (K) E (kJ/mol) A (min−1) R2 1 7 2 OS Sample 697–778 T (K) E (kJ 116.04/mol) A (min 1.9− )× 10 R 0.9962 6 OS–SA OS 696–768 697–778 116.04 104.96 1.9 3.1107 × 10 0.9962 0.9957 × OS–SA–ZnOS–SA 681–761 696–768 104.96 93.34 3.1 4.8106 × 105 0.9957 0.9986 × OS–SA–NiOS–SA–Zn 682–758 681–761 93.34 91.61 4.8 4.2105 × 105 0.9986 0.9985 × 5 OS–SA–Ni 682–758 91.61 4.2 10 4 0.9985 OS–SA–Cu 688–753 83.20 × 9.9 × 10 0.9987 OS–SA–Cu 688–753 83.20 9.9 104 0.9987 × 3.4. Product Yield in Fixed Bed Pyrolysis Experiments 3.4. Product Yield in Fixed Bed Pyrolysis Experiments Figure 5 shows the yield of mixed pyrolysis products of Fushun OS and SA and supported with 3 wt%Figure ZnCl5 shows2, NiCl the2·6H yield2O, and of mixed CuCl pyrolysis2·2H2O. The products mixed of Fushunpyrolysis OS of and OS SA and and SA supported promoted with the 3 wt%formation ZnCl2 of, NiCl shale2 6H oil2 andO, and reduced CuCl2 the2H 2productionO. The mixed of shale pyrolysis semi-coke of OS andandSA gas promoted and loss. theThis formation result is · · similarof shale to oil that and reported reduced by the Niu production et al. [32], of who shale cl semi-cokeaimed that and SA gascan andincrease loss. the This yield result and is quality similar of to shalethat reported oil. When by ZnCl Niu2, et NiCl al. [2·6H32],2 whoO, and claimed CuCl2·2H that2O SA were can added increase to the the SA, yield and and the quality OS was of pyrolyzed shale oil. Whenand the ZnCl amount2, NiCl of2 shale6H2O, oil and produced CuCl2 2H decreased2O were addedcompared to the with SA, the and shale the OSoil wasformed pyrolyzed by OS–SA and · · pyrolysis.the amount In of addition, shale oil the produced pyrolysis decreased of OS–SA–Zn compared resulted with in the larger shale semi-coke oil formed yield by OS–SA compared pyrolysis. with thatIn addition, of the two the other pyrolysis metals; of OS–SA–Znhowever, the resulted semi-cok in largere yield semi-coke remained yieldlower compared than that in with OS that pyrolysis of the (Figuretwo other 5). metals;The catalyst however, increased the semi-coke the mass yieldloss of remained OS pyrolysis, lower and than the that trend in OS of forming pyrolysis shale (Figure semi-5). cokeThe catalystwas consistent increased with the mass the lossthermogravimetric of OS pyrolysis, analysis and the trendresults. of formingMoreover, shale these semi-coke results wasare consistent withwith the the thermogravimetric report of Chang analysis et al. results.[13], who Moreover, observed these that results FeCl are2·4H consistent2O, CoCl with2·6H2 theO, NiClreport2·6H of2 ChangO, and etZnCl al. [213 can], who enhance observed the secondary that FeCl2 cracking4H2O, CoCl of shale2 6H2 O,oil, NiCl reduce2 6H the2O, oil and production, ZnCl2 can · · · andenhance increase the secondarythe gas produced cracking during of shale pyrolysis. oil, reduce Th thee reduction oil production, of shale and oil increasemay have the been gas due produced to the factduring that pyrolysis. SA loaded The with reduction the transition of shale metal oil maysalt promotes have been OS due pyrolysis, to the fact which that caused SA loaded the shale with gas the totransition remain metalin the saltpyrolysis promotes system OS pyrolysis,for a long whichtime. Moreover, caused the the shale transition gas to remainmetal of in the the activation pyrolysis centersystem could for a longhave time. exerted Moreover, a catalytic the transitioncracking effe metalct on of theshale activation gas, which center resulted could in have a secondary exerted a reaction.catalytic cracking effect on shale gas, which resulted in a secondary reaction.

Figure 5. Eﬀects of SA and its supported transition metal salts on the yield of OS pyrolysis products. Figure 5. Effects of SA and its supported transition metal salts on the yield of OS pyrolysis products.

Catalysts 2019, 9, 900 9 of 15 Catalysts 2019, 9, x FOR PEER REVIEW 9 of 15

InIn addition, addition, the the yields yields of of gas gas and and loss loss generate generatedd by by OS–SA–Q OS–SA–Q pyrolysis pyrolysis we werere higher higher than than those those derivedderived from from pyrolysis ofof OSOS and and OS–SA. OS–SA. The The yields yields from from the the pyrolysis pyrolysis of OS–SA–Cu of OS–SA–Cu were were the largest the largestand 4.4% and higher 4.4% higher than those than of those OS. Hence, of OS. theHence, SA-based the SA-based catalystpromoted catalyst promoted the secondary the secondary reaction of reactionthe OS toof producethe OS to several produce non-condensable several non-condensable gases. gases.

3.5.3.5. Characteristics Characteristics of of Semi-Coke Semi-Coke after after Pyrolysis Pyrolysis FigureFigure 66 showsshows an ATR–FTIR diagramdiagram ofof OSOS andand semi-coke,semi-coke, where where Figure Figure6a 6a presents presents the the total total in insitu situ Fourier Fourier infrared infrared spectrum, spectrum, andand FigureFigure6 6bbillustrates illustrates thethe spectrum with a wavenumber wavenumber between between −1 1 30003000 and and 2800 2800 cm cm−. The. The overall overall trends trends were were the the same same for for OS OS and and SC. SC. The The wavenumber wavenumber showed showed a a −1 1 strongstrong absorption absorption band band at at 1100–900 1100–900 cm cm−, which, which is is the the absorption absorption peak peak of of silicate silicate [33,34]. [33,34]. The The medium medium −1 1 −1 1 intensityintensity band band near near 690 690 cm cm− andand the the double double band band at at 796 796 and and 776 776 cm cm− werewere attributed attributed to to quartz quartz and and areare characteristic characteristic absorption absorption peaks peaks of of quartz, quartz, respectively respectively [35]. [35]. The The stretching stretching vibration vibration of of hydroxyl hydroxyl −1 1 −1 1 (OH)(OH) in in silicate silicate kaolinite kaolinite is isbetween between 3700 3700 and and 3500 3500 cm cm, −particularly, particularly at 3695 at 3695 and and 3620 3620 cm cm[36,37].− [36 ,In37 ]. addition,In addition, the thespectrum spectrum of the of thesemi-coke semi-coke of OS–SA–Cu of OS–SA–Cu exhibited exhibited an an absorption absorption band band at atapproximately approximately −1 1 34003400 cm cm−, which, which was was an an absorption absorption peak peak not not found found in thethe otherother spectraspectra and and may may have have been been caused caused by bywater water absorption absorption of of the the sample sample in in air air [35 [35,38].,38].

(a) (b)

Figure 6. FTIR spectra of OS and SC (a) without catalyst and (b) with catalyst. Figure 6. FTIR spectra of OS and SC (a) without catalyst and (b) with catalyst. Numerous mineral peaks will have covered some of the organic matter peaks due to the high mineralNumerous content mineral in the OS.peaks Figure will 6havea,b show covered that some the most of the evident organic absorption matter peaks peaks due of to the the organic high 1 mineralmatter content of Fushun in the OS wereOS. Figure at 2923 6a,b and show 2857 that cm− the, which most areevident the characteristicabsorption peaks absorption of the organic peaks of matteraliphatic of Fushun hydrocarbons OS were and at the2923 stretching and 2857 vibration cm−1, which of aliphatic are the hydrocarboncharacteristic C–Habsorption (methylene) peaks[ 39of ], aliphaticrespectively. hydrocarbons Thus, the and main the component stretching ofvibratio the organicn of aliphatic matter of hydrocarbon OS was aliphatic C–H (methylene) hydrocarbon. [39], The 1 respectively.absorption peaks Thus, at the 2923 main and component 2857 cm− ofdisappeared the organic after matter OS pyrolysis,of OS was indicating aliphatic hydrocarbon. that the OS organic The absorptionmatter was peaks completely at 2923 pyrolyzedand 2857 cm at− this1 disappeared stage. The after absorption OS pyrolysis, peaks ofindicating the remaining that the wavenumbers OS organic matterslightly was changed. completely pyrolyzed at this stage. The absorption peaks of the remaining wavenumbers slightly changed. 3.6. Characteristics of Shale Oil 3.6. Characteristics of Shale Oil 3.6.1. Characterization of Shale Oil Produced from Catalytic OS Pyrolysis

3.6.1. CharacterizationFigure7 shows the of ATR–FTIR Shale Oil spectraProduced of shale from oil Catalytic produced OS with Pyrolysis and without a catalyst. The overall trend of the five shale oils was the same, and the main functional groups fluctuated within wavenumber Figure 7 shows the ATR–FTIR spectra of shale oil produced with and without a catalyst. The ranges of 3000–2800, 1800–1000, and 900–700 cm 1. Wavenumber 3000–2800 cm 1 is mainly assigned overall trend of the five shale oils was the same, −and the main functional groups− fluctuated within to an aliphatic substance. Shale oil was the most evident in this range and mainly fluctuated near two −1 −1 wavenumber ranges of 3000–2800, 1800–1000,1 and 900–700 cm . Wavenumber 3000–2800 cm is wavenumbers, namely, 2920 and 2850 cm− , which were methylene (CH2) C–H stretching vibration mainly assigned to an aliphatic substance. Shale oil was the most evident in this range and mainly 1 absorption peaks (Figure7)[ 40,41]. An aliphatic C–H bending vibration was at 1462 and 1377 cm− fluctuated near two wavenumbers, namely, 2920 and 2850 cm−1, which were methylene (CH2) C–H within the wavenumber range of 1800–1000 cm 1 [42]. The catalyst-added shale oil did not change stretching vibration absorption peaks (Figure 7) [40,41].− An aliphatic C–H bending vibration was at 1462 and 1377 cm−1 within the wavenumber range of 1800–1000 cm−1 [42]. The catalyst-added shale oil did not change considerably, although the change was remarkable at the wavenumber of 1263

Catalysts 2019, 9, 900 10 of 15

Catalysts 2019, 9, x FOR PEER REVIEW 10 of 15 1 considerably, although the change was remarkable at the wavenumber of 1263 cm− ; in particular, cmOS–SA–Zn−1; in particular, was prominent. OS–SA–Zn Adding was prominent. catalysts promoted Adding thecatalysts formation promoted of aromatic the formation structure of oxygenates, aromatic 1 structureas evident oxygenates, by the peak as at evident 1263 cm by− , the which peak was at the1263 stretching cm−1, which vibration was the of aromatic stretching ether vibration C–O [43 of]. 1 aromaticShale oil afterether OS C–O pyrolysis [43]. Shale exhibited oil after a peak OS assigned pyrolysis to long-chainexhibited hydrocarbona peak assigned at 720 to cmlong-chain− within 1 hydrocarbonthe wavenumber at 720 range cm−1 within of 900–700 the wavenumber cm− . After therange addition of 900–700 of the cm SA-based−1. After the catalyst, addition the of shale the SA- oil 1 baseddisappeared catalyst, and the became shale oil a short-chaindisappeared hydrocarbon and became ata short-chain 740 cm− [44 hydrocarbon]. The shale oilsat 740 of OScm− and1 [44]. SA–Q The 1 shalepyrolysis oils of were OS and stronger SA–Q at pyrolysis 740 cm− werewavenumber stronger at than740 cm OS−1 andwavenumber SA pyrolysis than shaleOS and oil. SA Hence, pyrolysis the shalesupported oil. Hence, transition the supported metal salt ontransition SA promoted metal sa thelt crackingon SA promoted of long-chain the cracking hydrocarbons of long-chain to form hydrocarbonsshort-chain hydrocarbons. to form short-chain OS–SA–Zn hydrocarbons. had strong ﬂuctuations,OS–SA–Zn had indicating strong thatfluctuations, ZnCl2 could indicating promote that the ZnClformation2 could of promote short-chain the hydrocarbons formation of inshort-chain shale oil. Inhydroc addition,arbons ﬁve in types shale of oil. shale In oiladdition, had characteristic five types 1 ofpeaks shale of oil bending had characteristic vibration at peaks approximately of bending 810 vibration cm− . Davisat approximately et al. [45] suggested 810 cm−1. thatDavis the et peakal. [45] at 1 suggested810 cm− isthat attributed the peak to aromaticat 810 cm C–H−1 is out-of-plane attributed to bending aromatic mode. C–H Therefore, out-of-plane the shalebending oil hadmode. an Therefore,aromatic component. the shale oil had an aromatic component.

FigureFigure 7. 7. FTIRFTIR analysis analysis of of shale shale oil oil produc produceded with with and and without without catalysts. catalysts.

ThisThis analysis analysis revealed revealed that that the the main main component component in in the the shale oil was an aliphatic hydrocarbon substance.substance. Adding Adding SA–Q SA–Q addition addition promoted promoted not not only only the the decomposition decomposition of of long-chain aliphatic hydrocarbonshydrocarbons intointo short-chainshort-chain aliphatic aliphatic hydrocarbons hydrocarbons but alsobut thealso formation the formation of aliphatic of aliphatic and aromatic and aromaticcompounds compounds in shale oils.in shale Therefore, oils. Therefore, the loading the ofloading transition of transition metal salts metal on SAsalts and on OS SA pyrolysis and OS pyrolysischanged thechanged composition the composition of shale oil, of therebyshale oil, providing thereby providing a basis for a improving basis for improving the quality the of shale quality oil ofin shale engineering oil in engineering practice. practice.

3.6.2. Shale Oil Composition Analysis 3.6.2. Shale Oil Composition Analysis The composition of shale oil is complex and diverse. Under the set instrument conditions (GC–MS, The composition of shale oil is complex and diverse. Under the set instrument conditions (GC– Gas Chromatography–Mass Spectrometry), the composition of shale oil with a mass fraction of greater MS, Gas Chromatography–Mass Spectrometry), the composition of shale oil with a mass fraction of than 0.1% was analyzed and found to include alkanes, olefins, oxygenates, and aromatic hydrocarbons. greater than 0.1% was analyzed and found to include alkanes, olefins, oxygenates, and aromatic Oxygen-containing compounds mainly included acids, alcohols, esters, and ketones, whereas aromatic hydrocarbons. Oxygen-containing compounds mainly included acids, alcohols, esters, and ketones, hydrocarbons included naphthalene, anthracene, benzene, and benzene series. These results are whereas aromatic hydrocarbons included naphthalene, anthracene, benzene, and benzene series. consistent with previous reports [13,46]. These results are consistent with previous reports [13,46]. TheThe area area of of the the ion ion peak peak was was used used to to provide provide re relativelative content content of ofthe the major major class class components components to estimateto estimate the the effect effect of ofSA SA and and its its supported supported transi transitiontion metal metal salt salt catalyst catalyst on on shale shale oil oil composition (Figure(Figure 88))[ [47].47]. The The main main components components in in shale shale oil oil were were alkanes alkanes and and alkenes alkenes in in aliphatic aliphatic hydrocarbons, hydrocarbons, accountingaccounting for for more more than than 75% 75% of of the total mass, consistent with with the the analysis of of major aliphatic hydrocarbonshydrocarbons in in shale shale oil oil and and the the results results of ofLai Lai et al. et al.[23]. [23 Adding]. Adding SA increased SA increased the olefin the olefin content content and decreasedand decreased the alkane the alkane contents contents compared compared with uncatalyzed with uncatalyzed pyrolysis pyrolysis of shale of oil, shale leading oil, leading to a small to a reductionsmall reduction in the in total the totalamount amount of aliphatic of aliphatic comp compounds.ounds. The The gas gas phase phase cracking cracking of of the the aliphatic aliphatic compoundcompound during during pyrolysis pyrolysis caused caused the the aromatization aromatization of of the the hydrocarbon hydrocarbon species and and leds leds to to a a small small increase in the contents of aromatics [16]. However, when the transition metal salt was supported on SA, the amounts of aromatic and aliphatic components in the shale oil increased. Hence, adding transition metal salt on SA decreased the pyrolysis temperature of the OS. During fixed bed pyrolysis

Catalysts 2019, 9, 900 11 of 15 increase in the contents of aromatics [16]. However, when the transition metal salt was supported on SA, Catalyststhe amounts 2019, 9, of x FOR aromatic PEER REVIEW and aliphatic components in the shale oil increased. Hence, adding transition11 of 15 metal salt on SA decreased the pyrolysis temperature of the OS. During ﬁxed bed pyrolysis experiments, experiments,the catalyst promoted the catalyst the secondarypromoted reaction the secondary of volatile reaction products of with volatile increasing products temperature, with increasing thereby temperature,promoting the thereby formation promoting of hydrocarbons the formation in the resulting of hydrocarbons oil, including in aliphaticthe resulting cracking, oil, crackingincluding of aliphaticaromatic hydrocarbonscracking, cracking and asphaltene of aromatic side chains,hydrocarbons and hydrogenolysis and asphaltene of hetero-carbon side chains, bonds and of hydrogenolysispolar compounds of hetero-carbon [48,49]. For example, bonds of during polar comp crackingounds of an[48,49]. aliphatic For example, group, the during long cracking chain alkyl of angroup aliphatic is cleaved group, to the an oleﬁn,long chain and thealkyl short group alkyl is cleaved group can to an be olefin, further and cracked the short or converted alkyl group into can an bealkane further by attractingcracked or a converted hydrogen into atom. an alkane by attracting a hydrogen atom.

FigureFigure 8. RelativeRelative content content of of main main components components in in shale shale oil. oil. The catalyst promoted not only the formation of an aromatic compound but also the formation of The catalyst promoted not only the formation of an aromatic compound but also the formation an oxygen-containing compound. The content of the oxygen-containing compound was proportional of an oxygen-containing compound. The content of the oxygen-containing compound was to the catalytic action of the catalyst. The pyrolysis oil of OS–SA–Zn had a high oxygenated compound proportional to the catalytic action of the catalyst. The pyrolysis oil of OS–SA–Zn had a high of 4.692%, leading to the stronger total ionogram of OS–SA–Zn shale oil at approximately 20 min oxygenated compound of 4.692%, leading to the stronger total ionogram of OS–SA–Zn shale oil at than the other shale oil. The pyrolysis oil of OS–SA–Ni had the highest aromatic content of 4.774%. approximately 20 min than the other shale oil. The pyrolysis oil of OS–SA–Ni had the highest However, the increase in aromatics negatively affects the stability of shale oil [32]. For the pyrolysis aromatic content of 4.774%. However, the increase in aromatics negatively affects the stability of shale oil of OS–SA–Cu, the content of aromatics was considerably lower than that of OS–SA–Ni because oil [32]. For the pyrolysis oil of OS–SA–Cu, the content of aromatics was considerably lower than that SA–Cu had a strong catalytic effect on OS pyrolysis, resulting in a prolonged residence time of volatile of OS–SA–Ni because SA–Cu had a strong catalytic effect on OS pyrolysis, resulting in a prolonged substances in the pyrolysis system. Aromatic hydrocarbons tend to coke before volatilization due to residence time of volatile substances in the pyrolysis system. Aromatic hydrocarbons tend to coke the prolonged residence time, thereby decreasing the amount of aromatics [32]. Therefore, the effect of before volatilization due to the prolonged residence time, thereby decreasing the amount of aromatics promoting the formation of aliphaticity and the stability of shale oil suggest that the sequence of the [32]. Therefore, the effect of promoting the formation of aliphaticity and the stability of shale oil catalytic effect of transition metal salts loaded on SA was CuCl2 2H2O > NiCl2 6H2O > ZnCl2. suggest that the sequence of the catalytic effect of transition metal· salts loaded on· SA was CuCl2·2H2O The n-paraffins and n-olefins in the shale oil sample can be divided based on the number of > NiCl2·6H2O > ZnCl2. + carbon atoms into C8–C16,C17–C24, and C25 (Figure9). The presence of the catalyst decreasesd The n-paraffins+ and n-olefins in the shale oil sample can be divided based on the number of the contents of C25 long-chain alkane and olefin and increased the contents of C8–C16 and C17–C24 carbon atoms into C8–C16, C17–C24, and C25+ (Figure 9). The presence of the catalyst decreasesd the chain hydrocarbons as well as the alkane and olefin contents of C17–C24. The number of short-chain contents of C25+ long-chain alkane and olefin and increased the contents of C8–C16 and C17–C24 chain hydrocarbon products of C8–C16 in the shale oil generated by OS–SA–Zn pyrolysis was the highest, hydrocarbons as well as the alkane and olefin contents of C17–C24. The number of short-chain which was consistent with the FTIR analysis of shale oil. Hence, OS–SA–Zn shale oil has many hydrocarbon products of C8–C16 in the shale oil generated by OS–SA–Zn pyrolysis was the highest, short-chain hydrocarbons. This result provided direct evidence for the catalysis of the catalyst for which was consistent with the FTIR analysis of shale oil. Hence, OS–SA–Zn shale oil has many short- aliphatic pyrolysis. In addition, the content of aliphatic hydrocarbons changed after loading the chain hydrocarbons. This result provided direct evidence for the catalysis of the catalyst for aliphatic transition metal salt on SA, indicating that SA had strong catalytic activity after loading the transition pyrolysis. In addition, the content of aliphatic hydrocarbons changed after loading the transition metal salt. Thus, transition metal salts considerably affected the composition of shale oil and promoted metal salt on SA, indicating that SA had strong catalytic activity after loading the transition metal aliphatic formation. salt. Thus, transition metal salts considerably affected the composition of shale oil and promoted aliphatic formation.

Catalysts 2019, 9, x FOR PEER REVIEW 12 of 15 Catalysts 2019, 9, 900 12 of 15

(a) (b)

Figure 9. Distribution of (a) n-paraffins and (b) n-olefins within shale oil. Figure 9. Distribution of (a) n-paraffins and (b) n-olefins within shale oil. 4. Conclusions 4. ConclusionThis studys investigated the effects of SA and SA loaded with ZnCl , NiCl 6H O, and CuCl 2H O 2 2· 2 2· 2 on the pyrolysis of Fushun OS. The following conclusions can be drawn from the experimental results. This study investigated the effects of SA and SA loaded with ZnCl2, NiCl2·6H2O, and CuCl2·2H2O (1) SA-based catalysts can promote OS pyrolysis. The optimum ratio of OS to SA weight is 2:1. on the pyrolysis of Fushun OS. The following conclusions can be drawn from the experimental The SA-supported transition metal salt catalyst can reduce the initial pyrolysis temperature of the OS, results. and the catalytic effect increases with the loading of transition metal salt within the range of 0.1–3 wt%. (1) SA-based catalysts can promote OS pyrolysis. The optimum ratio of OS to SA weight is 2:1. (2) The catalytic effects of different transition metal salts vary. The analysis of the catalytic cracking The SA-supported transition metal salt catalyst can reduce the initial pyrolysis temperature of the behavior indicates that CuCl 2H O exhibits the best catalytic effect. Based on the kinetic analysis, the OS, and the catalytic effect increases2· 2 with the loading of transition metal salt within the range of 0.1– activation energy required for OS pyrolysis is 116.04 kJ/mol, which is reduced by 11.08 kJ/mol (2:1) 3 wt%. after adding SA. The loading of 3 wt% transition metal salts on the SA reduces the activation energy (2) The catalytic effects of different transition metal salts vary. The analysis of the catalytic required for OS pyrolysis. CuCl2 2H2O has the best catalytic effect, reducing the activation energy of cracking behavior indicates that· CuCl2·2H2O exhibits the best catalytic effect. Based on the kinetic OS pyrolysis by 32.84 kJ/mol. analysis, the activation energy required for OS pyrolysis is 116.04 kJ/mol, which is reduced by 11.08 (3) SA catalyst can increase the amount of shale oil produced. However, loading the transition kJ/mol (2:1) after adding SA. The loading of 3 wt% transition metal salts on the SA reduces the metal salt on the SA catalyzes the secondary cracking reaction of the shale oil and leads to decreased activation energy required for OS pyrolysis. CuCl2·2H2O has the best catalytic effect, reducing the oil yield and increased gas yield. The samples with 3 wt% CuCl 2H O have the largest gas and loss activation energy of OS pyrolysis by 32.84 kJ/mol. 2· 2 during pyrolysis, which are 4.4% higher than those of OS alone. (3) SA catalyst can increase the amount of shale oil produced. However, loading the transition (4) The loading of the transition metal salt on the SA not only increases the oxygenate content metal salt on the SA catalyzes the secondary cracking reaction of the shale oil and leads to decreased but also promotes the cracking and aromatization of the aliphatic hydrocarbons to form short-chain oil yield and increased gas yield. The samples with 3 wt% CuCl2·2H2O have the largest gas and loss aliphatic and aromatic hydrocarbons. Furthermore, the contents of aliphatic compounds, represented during pyrolysis, which are 4.4% higher than those of OS alone. by an alkane and an olefin, increase. When SA is used as support, the order of the catalytic effect of the (4) The loading of the transition metal salt on the SA not only increases the oxygenate content transition metal salt is CuCl 2H O > NiCl 6H O > ZnCl . but also promotes the cracking2· and2 aromatization2· 2 of the 2aliphatic hydrocarbons to form short-chain The catalyst of shale ash cannot only accelerate the pyrolysis of the shale ash, but also change aliphatic and aromatic hydrocarbons. Furthermore, the contents of aliphatic compounds, represented the compositions of the shale ash. It guides reducing pyrolysis temperature and obtaining the stable by an alkane and an olefin, increase. When SA is used as support, the order of the catalytic effect of shale oil. On the base of the present research, further work is suggested on the effect of the catalysis on the transition metal salt is CuCl2·2H2O > NiCl2·6H2O > ZnCl2. the composition and structure of shale oil. Moreover, the mechanic strength of the block SA-based The catalyst of shale ash cannot only accelerate the pyrolysis of the shale ash, but also change catalysts should also be investigated. the compositions of the shale ash. It guides reducing pyrolysis temperature and obtaining the stable Authorshale oil. Contributions: On the base ofConceptualization, the present research, F.J.; Investigation,further work H.L.is suggested and C.G.; on Resources,the effect of X.L. theand catalysis G.L.; Writing—originalon the composition draft, and H.L.; structure Writing—review of shale &oil. editing, Moreover, H.P. the mechanic strength of the block SA-based Funding:catalystsThis should research also wasbe investigated. funded by the Talent Scientific research fund of LSHU (No. 2018XJJ-011), the Open Foundation of Key Laboratory of Industrial Ecology and Environmental Engineering, MOE (No. KLIEEE-18-04), theAuthor Natural Contributions: Science Foundation Conceptualization, Guidance and F.J.; Planning Investigation, Program H.L. of and Liaoning C.G.; Province,Resources, China X.L. and (2019-ZD0065), G.L.; Writing— the Generaloriginal Projectdraft, H.L.; for Higher Writin Educationg—review Research & editing, of H.P. Education Department of Liaoning Province, China (L2016016), the National Natural Science Foundation of China (NO.51706091), the PhD research startup foundation of Liaoning ShihuaFunding: University This research (NO.2016XJJ-025), was funded theby Nationalthe Talent Natural Scientif Scienceic research Foundation fund of ofLSHU China (No. (Nos. 2018XJJ-011), 51508464, 11572249), the Open theFoundation Natural Scienceof Key Laboratory Foundation of of Industrial Shanxi Province Ecology (No. and 2017JM1013),Environmental the Engineerin Astronauticsg, MOE Supporting (No. KLIEEE-18-04), Technology the Natural Science Foundation Guidance and Planning Program of Liaoning Province, China (2019-ZD0065),

Catalysts 2019, 9, 900 13 of 15

Foundation of China (No. 2017-HT-XG), and the Fundamental Research Funds for the Central Universities (No. 3102018ZY015). Conﬂicts of Interest: The authors declare that there is no conﬂict of interests regarding the publication of this article.

References

1. Liu, Z.J.; Meng, Q.; Dong, Q.; Zhu, J.; Guo, W.; Ye, S.; Liu, R.; Jia, J.L. Characteristics and resource potential of oil shale in China. Oil Shale 2017, 34, 15–41. [CrossRef] 2. Liu, Z.J.; Yang, D.; Hu, Y.Q.; Zhang, J.W.; Shao, J.X.; Song, S.; Kang, Z.Q. Influence of In Situ Pyrolysis on the Evolution of Pore Structure of Oil Shale. Energies 2018, 11, 755. [CrossRef] 3. Fuke, D.; Zijun, F.; Yang, D.; Zhao, Y.S.; Derek, E. Permeability Evolution of Pyrolytically-Fractured Oil Shale under In Situ Conditions. Energies 2018, 11, 3033–3041. 4. Hu, S.Y.; Xiao, C.L.; Jiang, X.; Liang, X.J. Potential Impact of In-Situ Oil Shale Exploitation on Aquifer System. Water 2018, 10, 649. [CrossRef] 5. Wang, S.; Liu, J.X.; Jiang, X.M.; Han, X.X.; Tong, J.H. Effect of heating rate on products yield and characteristics of non-condensable gases and shale oil obtained by retorting Dachengzi oil shale. Oil Shale 2013, 30, 27–47. [CrossRef] 6. Araújo, A.M.M.; Queiroz, G.S.M.; Maia, D.O.; Gondim, A.; Souza, L.D.; Fernandes, V.J.; Araujo, A.S. Fast Pyrolysis of Sunflower Oil in the Presence of Microporous and Mesoporous Materials for Production of Bio-Oil. Catalysts 2018, 8, 261. [CrossRef] 7. Du, W.Z.; Wang, Y.; Liu, X.L.; Sun, L.L. Study on Low Temperature Oxidation Characteristics of Oil Shale Based on Temperature Programmed System. Energies 2018, 11, 2594–2605. [CrossRef] 8. Williams, P.T.; Chishti, H.M. Two stage pyrolysis of oil shale using a zeolite catalyst. J. Anal. Appl. Pyrolysis 2000, 55, 217–234. [CrossRef] 9. Williams, P.T.; Chishti, H.M. Influence of residence time and catalyst regeneration on the pyrolysis–zeolite catalysis of oil shale. J. Anal. Appl. Pyrolysis 2001, 60, 187–203. [CrossRef] 10. Gai, R.H.; Jin, L.J.; Zhang, J.B.; Wang, J.Y.; Hu, H.Q. Effect of inherent and additional pyrite on the pyrolysis behavior of oil shale. J. Anal. Appl. Pyrolysis 2014, 105, 342–347. [CrossRef] 11. Hu, M.J.; Cheng, Z.Q.; Zhang, M.Y.; Liu, M.Z.; Song, L.H.; Zhang, Y.Q.; Li, J.F. Effect of Calcite, Kaolinite, Gypsum, and Montmorillonite on Huadian Oil Shale Kerogen Pyrolysis. Energy Fuels 2014, 28, 1860–1867. [CrossRef] 12. Jiang, H.F.; Song, L.H.; Cheng, Z.Q.; Chen, J.; Zhang, L.; Zhang, M.Y.; Hu, M.J.; Li, J.N.; Li, J.F. Influence of pyrolysis condition and transition metal salt on the product yield and characterization via Huadian oil shale pyrolysis. J. Anal. Appl. Pyrolysis 2015, 112, 230–236. [CrossRef] 13. Chang, Z.B.; Chu, M.; Zhang, C.; Bai, S.X.; Lin, H.; Ma, L.B. Investigation of the effect of selected transition metal salts on the pyrolysis of huadian oil shale, china. Oil Shale 2017, 34, 354–367. [CrossRef] 14. Özta¸s,N.A.; Yürüm, Y. Effect of Catalysts on the Pyrolysis of Turkish Zonguldak Bituminous Coal. Fuel Energy Abstr. 2000, 14, 820–827. [CrossRef] 15. Zou, X.W.; Yao, J.Z.; Yang, X.M.; Song, W.L.; Lin, W.G. Catalytic Effects of Metal Chlorides on the Pyrolysis of Lignite. Energy Fuels 2007, 21, 619–624. [CrossRef] 16. Shi, W.J.; Wang, Z.; Song, W.L.; Li, S.G.; Li, X.Y. Pyrolysis of Huadian oil shale under catalysis of shale ash. J. Anal. Appl. Pyrolysis 2016, 123, 160–164. [CrossRef] 17. Lai, D.G.; Chen, Z.H.; Chen, Z.H.; Lin, L.X.; Zhang, Y.M.; Gao, S.Q.; Xu, G.W. Secondary Cracking and Upgrading of Shale Oil from Pyrolyzing Oil Shale over Shale Ash. Energy Fuels 2015, 29, 2219–2226. [CrossRef] 18. Jaber, J.; Abu-Rahmeh, T.; Al-Alawin, A.; Kloub, N.M. Surface Retorting of Jordanian Oil Shale and Associated

CO2 Emissions. Jordan J. Mech. Ind. Eng. 2010, 4, 591–596. 19. Yang, Y.C.; Jia, F.R.; Jian, W.W.; Zhang, S.P.; Ma, D.Z.; Liu, G.X. Inﬂuence of Cr3+ Concentration on SO2 Removal over TiO2 Based Multi-Walled Carbon Nanotubes. China Pet. Process. Petrochem. Technol. 2019, 1, 23–35. Catalysts 2019, 9, 900 14 of 15

20. Jia, F.R.; Li, Z.; Wang, E.G.; He, J.C.; Dong, H.; Liu, G.X.; Jian, W.W. Preparation and SO2 adsorption behavior of coconut shell-based activated carbon via microwave-assisted oxidant activation. China Pet. Process. Petrochem. Technol. 2018, 20, 67–74. 21. Wang, Z.J.; Deng, S.H.; Gu, Q.; Zhang, Y.M.; Cui, X.J.; Wang, H.Y. Pyrolysis kinetic study of Huadian oil shale, spent oil shale and their mixtures by thermogravimetric analysis. Fuel Process. Technol. 2013, 110, 103–108. [CrossRef] 22. Pan, L.W.; Dai, F.Q.; Huang, J.J.; Liu, S.; Li, G.Q. Study of the effect of mineral matters on the thermal decomposition of Jimsar oil shale using TG-MS. Thermochim. Acta 2016, 627, 31–38. [CrossRef] 23. Lai, D.G.; Shi, Y.; Geng, S.L.; Chen, Z.H.; Gao, S.Q.; Zhan, J.H.; Xu, G.W. Secondary reactions in oil shale pyrolysis by solid heat carrier in a moving bed with internals. Fuel 2016, 173, 138–145. [CrossRef] 24. Burnham, A.K. Chemistry and Kinetics of Oil Shale Retorting. In Oil Shale: A Solution to the Liquid Fuel Dilemma; ASC: Washington, DC, USA, 2010; Volume 1032, pp. 115–134. 25. Dung, N.V.; Yip, V. Basis of reactor design for retorting Australian oil shales. Fuel 1991, 70, 1336–1341. [CrossRef] 26. Xiong, L.P.; Hu, S.B.; Wang, J. Analysis on the thermal conductivity of rocks from se china. Acta Petrol. Sin. 1994, 10, 323–329. 27. Wu, Y.Y.; Qin, Y.; Liu, J.Z.; Wang, A.K. Catalysis Action of Mineral/Metal Elements during Coalderived Hydrocarbons Process, An Example of the Late Permian Coal from Dahebian Coal Mine in Eastern Yunnan and Western Guizhou. J. Nat. Gas Geosci. 2012, 23, 141–152. 28. Li, S.Y.; Lin, S.J.; Guo, S.H.; Liu, L.F. Effects of inorganic salts on the hydrocarbon generation from kerogens. Geochimica 2002, 31, 15–20. 29. Han, J.Z.; Wang, X.D.; Yue, J.R.; Gao, S.Q.; Xu, G.W. Catalytic upgrading of coal pyrolysis tar over char-based catalysts. Fuel Process. Technol. 2014, 122, 98–106. [CrossRef] 30. Bai, F.T.; Guo, W.; Lü, X.S.; Liu, Y.M.; Guo, M.Y.; Li, Q.; Sun, Y.H. Kinetic study on the pyrolysis behavior of Huadian oil shale via non-isothermal thermogravimetric data. Fuel 2015, 146, 111–118. [CrossRef] 31. Bai, F.T.; Sun, Y.H.; Liu, Y.M.; Liu, B.C.; Guo, M.Y.; Lü, X.S.; Guo, W.; Li, Q.; Hou, C.B.; Wang, Q.W. Kinetic Investigation on Partially Oxidized Huadian Oil Shale by Thermogravimetric Analysis. Oil Shale 2014, 31, 377–393. [CrossRef] 32. Niu, M.T.; Wang, S.; Han, X.X.; Jiang, X.M. Yield and characteristics of shale oil from the retorting of oil shale and fine oil-shale ash mixtures. Appl. Energy 2013, 111, 234–239. [CrossRef] 33. Yürüm, Y.; Dror, Y.; Levy, M. Effect of acid dissolution on the mineral matrix and organic matter of Zefa EFE oil shale. Fuel Process. Technol. 1985, 11, 71–86. [CrossRef] 34. Yariv, S. Infrared Evidence for the Occurrence of SiO Groups with Double-Bond Character in Antigorite, Sepiolite and Palygorskite. Clay Miner. 1986, 21, 925–935. [CrossRef] 35. Wu, L.M.; Tong, D.S.; Zhao, L.Z.; Yu, W.H.; Zhou, C.H.; Wang, H. Fourier transform infrared spectroscopy analysis for hydrothermal transformation of microcrystalline cellulose on montmorillonite. Appl. Clay Sci. 2014, 95, 74–82. [CrossRef] 36. Madejová, J. FTIR techniques in clay mineral studies. Vib. Spectrosc. 2003, 31, 1–10. [CrossRef] 37. Farmer, V.C. Transverse and longitudinal crystal modes associated with OH stretching vibrations in single crystals of kaolinite and dickite. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2000, 56, 927–930. [CrossRef] 38. Wang, Q.; Yan, Y.H.; Jia, C.X.; Zhu, Y.C. FTIR analysis and pyrolysis characteristics of oil shale from Gansu province. Chem. Ind. Eng. Prog. 2014, 33, 1730–1734. 39. Wang, Z.J.; Deng, S.H.; Gu, Q.; Cui, X.J.; Zhang, Y.M.; Wang, H.Y. Subcritical Water Extraction of Huadian Oil Shale under Isothermal Condition and Pyrolysate Analysis. Energy Fuels 2014, 28, 2305–2313. [CrossRef] 40. Wang, Q.; Hou, Y.C.; Yu, W.Z.; Ren, Z.; Liu, S.H.; Liu, Q.Y.; Liu, Z.Y. A study on the structure of Yilan oil shale kerogen based on its alkali-oxygen oxidation yields of benzene carboxylic acids, 13 C NMR and XPS. Fuel Process. Technol. 2017, 166, 30–40. [CrossRef] 41. Palayangoda, S.S.; Nguyen, Q.P. An ATR-FTIR procedure for quantitative analysis of mineral constituents and kerogen in oil shale. Oil Shale 2012, 29, 344–356. [CrossRef] 42. Xing, Q.Y.; Yang, M.; Yang, H.X.; Zu, E.D. Study on the Gemological Characteristics of Amber from Myanmar and Chinese Fushun. Key Eng. Mater. 2013, 544, 172–177. [CrossRef] 43. Wang, Q.; Ye, J.B.; Yang, H.Y.; Liu, Q. Chemical composition and structural characteristics of oil shales and their kerogens using FTIR and solid-state 13C NMR. Energy Fuels 2016, 30, 6271–6280. [CrossRef] Catalysts 2019, 9, 900 15 of 15

44. Wang, Q.; Xu, X.C.; Chi, M.S.; Zhang, H.X.; Cui, D.; Bai, J.R. FT-IR study on composition of oil shale kerogen and its pyrolysis oil generation characteristics. J. Fuel Chem. Technol. 2015, 43, 1158–1166. 45. Painter, P.C.; Snyder, R.W.; Starsinic, M.; Coleman, M.M.; Kuehn, D.W.; Davis, A. Concerning the Application of FTIR to the Study of Coal: A Critical Assessment of Band Assignments and the Application of Spectral Analysis Programs. Appl. Spectrosc. 1981, 35, 475–485. [CrossRef] 46. Lin, L.X.; Zhang, C.; Li, H.J.; Lai, D.G.; Xu, G.W. Pyrolysis in indirectly heated fixed bed with internals: The first application to oil shale. Fuel Process. Technol. 2015, 138, 147–155. [CrossRef] 47. Tiwari, P.K.; Deo, M. Compositional and kinetic analysis of oil shale pyrolysis using TGA–MS. Fuel 2012, 94, 333–341. [CrossRef] 48. Harfi, K.E.; Mokhlisse, A.; Chanâa, M.B. Yields and composition of oil obtained by isothermal pyrolysis of the Moroccan (Tarfaya) oil shales with steam or nitrogen as carrier gas. J. Anal. Appl. Pyrolysis 2000, 56, 207–218. [CrossRef] 49. Al-Harahsheh, A.; Al-Ayed, O.; Al-Harahsheh, M.; Abu-El-Halawah, R. Heating rate effect on fractional yield and composition of oil retorted from El-lajjun oil shale. J. Anal. Appl. Pyrolysis 2010, 89, 239–243. [CrossRef]

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).