Accepted Manuscript Bio-fuel oil characteristic from catalytic cracking of hydrogenated palm oil Zhi-Xiang Xu, Peng Liu, Gui-Sheng Xu, Qing Liu, Zhi-Xia He, Qian Wang PII:
S0360-5442(17)30944-1
DOI:
10.1016/j.energy.2017.05.155
Reference:
EGY 10963
To appear in:
Energy
Received Date: 6 February 2017 Revised Date:
21 April 2017
Accepted Date: 27 May 2017
Please cite this article as: Xu Z-X, Liu P, Xu G-S, Liu Q, He Z-X, Wang Q, Bio-fuel oil characteristic from catalytic cracking of hydrogenated palm oil, Energy (2017), doi: 10.1016/j.energy.2017.05.155. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Bio-fuel oil Characteristic from Catalytic Cracking of Hydrogenated Palm Oil Zhi-Xiang Xu1*, Peng Liu2, Gui-Sheng Xu1, Qing Liu1, Zhi-Xia He3 Qian Wang*1 1 School of Energy and Power Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, China 2 Wuxi Research Institute of Petroleum Geology, Sinopec Petroleum Exploration & Production Research Institute, Wuxi, Jiangsu 214126, China 3 Institute for energy research, Jiangsu University, Zhenjiang, Jiangsu 212013, China
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Abstract: Pyrolysis characteristic of hydrogenated palm oil (HPO) was analyzed using TG, TG-FTIR-MS and Py-GC-MS. Bio-fuel oil (BFO) was obtained using catalytic cracking method. The BFO was analyzed by FTIR, 1H-NMR,
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C-NMR,
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GC-MS and ESI FT-ICR MS to provide complementary and comprehensive adequate information. TG-DTG results showed that the HPO pyrolysis was different with other plant oil. It was clear that HPO pyrolysis was mainly in temperature range of 350 o
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C-500 oC. The mean activation energy of HPO pyrolysis calculated from KAS and
FWO models was 161.10 kJ/mol and 164.28 kJ/mol, respectively. According to TG-FTIR-MS results, little amount of gas components was detected. Py-GC-MS result found heavy compounds, which carbon number exceeds 18. FTIR, 1H-NMR, 13
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C-NMR and GC-MS results found the BFO mainly contained long-chain alkane and
alkene. According to ESI FT-ICR MS, the oxygen containing compounds in BFO were from O2–O6 classes, with the O2 being the major class. The RSFTIR was first used to analyze biomass pyrolysis. The results found that in the decarboxylation
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process, the carbon chain also was cracked to form short carbon chain carboxyl firstly. According to above experiments results, we can confirm HPO pyrolysis path was
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different with palm oil. The key conclusion was that HPO maybe was a good bio-resource to obtain BFO, and it was mainly contained diesel-like components. Compared to palm oil pyrolysis products, HPO pyrolysis products were mainly contained long-chain alkane and alkene. The recommended pyrolysis path was also proposed. Keyword: hydrogenated palm oil, pyrolysis, bio-fuel oil, ESI FT-ICR MS
Corresponding author:
[email protected](zhixiang xu),
[email protected](qian wang) 1
ACCEPTED MANUSCRIPT 1. Introduction In recent decades, with a consequence of the greenhouse gas emissions and other air pollution, like fog and haze, serious climatic alterations have drawn much attention to human living environment. The primal problem of pollution is over-use of fossil fuel.
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With the shortage of depleting available cheap fossil fuel and serious pollution, it needs to develop renewable energy resources to sustain human society developing [1-2]. Bio-fuel oil has aroused much attention around the world many years ago for its renewable energy resources, negligible toxicity, and biodegradability. There are many
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technology pathways to develop bio-fuels at present. Hydrodeoxygenation [3], thermal pyrolysis [4] and transesterification [5, 6] are main promising technology to
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develop bio-fuel oil, especial transesterification. At present, fatty acid methyl ester, which also called bio-diesel, has been widely used around the world. Bio-diesel is advantageous in higher flash point, ultra-low sulfur concentration, and superior cetane number [7]. The above-mentioned characteristics of fatty acid methyl ester make it use in diesel engine as an excellent alternative to petroleum diesel. For high cost of
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plant oil, many papers have been reported waste triglycerides were used to production bio-fuel oil (including thermal pyrolysis and transesterification paths) because these feedstocks have no competition from human consumption [8, 9]. And this path can
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also solve environmental issues of waste organic materials.
For low requirement of raw materials, catalyst and equipment, pyrolysis is considered
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as a very promising technology in the future biorefinery. Many researchers have been reported oil and fat pyrolysis at different experiment condition with or without catalyst [11-13]. For double bond presented, plant oil was pyrolyzed to form low molecular hydrocarbon compounds, which main component is gasoline [2, 13]. And large amount of gas was generated [14]. Pyrolysis products of plant oil were difficult to obtain diesel–like hydrocarbon. In order to develop diesel-like bio-fuel oil, it needed to reduce organic carbon atom loss as much as possible. Hydrogenated plant oil, in which double bond was hydrogenated to become single bond, was a good path to obtain long chain diesel -like bio-oil according to pyrolysis method. According to 2
ACCEPTED MANUSCRIPT plant oil pyrolysis mechanism, this method effective decreased amount of gas. And it is possible to obtain long chain diesel -like bio-oil. Hydrogenated plant oil has been used in industry widely [15,16]. Palm oil was hydrogenated to obtain hydrogenated palm oil (HPO). HPO is a commonly used industrial product. And it is also a low-
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cost product. Hence, it was selected as a renewable resource to crack. Palm oil pyrolysis has been reported with or without catalyst by many researchers [17-19]. The palm oil pyrolysis partial conclusion also can be introduced to HPO pyrolysis.
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In this paper, HPO as a renewable resource was selected to crack to obtain long chain diesel–like bio-fuel oil. First, it was carried out thermal decomposition experiments to
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obtain pyrolysis characteristic at different heating rates by TG. The results can guide HPO pyrolysis temperature selecting. TG-FTIR-MS was utilized to confirm the functional groups change in pyrolysis process. The Py-GC-MS experiment was utilized to preliminary analyze pyrolysis products components. The bio-fuel oil (BFO), which was obtained by HPO pyrolysis, was analyzed using FTIR, 13
1
H-NMR,
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C-NMR, GC-MS and FT-ICR MS. In order to analysis pyrolysis path of HPO,
RSFTIR also was used to analyze pyrolysis mechanism. The above results were utilized to reason possible fast pyrolysis characteristic of HPO. And it can provide
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information about BFO characteristic.
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ACCEPTED MANUSCRIPT 2. Experiments 2.1. Materials and FTIR experiment The HPO was supplied by Zhejiang Dongteng Wax Industry Co., Ltd. HPO was pulverized to below 50 mesh. And then KOH was added to HPO. The component of
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mixture was 90% HPO and 10% KOH. Then HPO with KOH sample was mixed uniformly. The FTIR study was conducted with use of a Bruker (55FT-IR) FTIR Spectrometer (500 cm-1-4000 cm-1).
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2.2. Thermal analysis experiments of sample
Non-isothermal experiments were carried out by TG-DTG (NETZSCH STA 409).
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About 10 mg sample was loaded in a closed Al2O3 crucible with a pinhole in the cap. It was heated up from room temperature to 800 oC. The heating rate was 5 K/min, 10 K/min, 20 K/min and 40 K/min, respectively. The experiments were performed under a constant N2 flow of 40 mL/min to sweep away HPO pyrolysis products.
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2.3. TG-FTIR-MS experiments
The TG-FTIR-MS experiments were performed using thermogravimetry (NETZSCH STA 409) coupled with FTIR (Nicolet IS10) and mass spectrometer (NETZSCH QMS
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403C). About 10 mg sample was carried in Al2O3 crucibles. The temperature was raised from 40 °C temperature to 800 °C under heating rates of 10 K/min. High-purity argon was used as carrier gas with a gas flow rate of 35 mL/min. The MS conditions:
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quartz capillary gas connector, pressure injection 1000 mbar, ionizing electron energy of 70 eV. In this experiment, detected range of molecular weight was 2-100.
2.4. Py-GC- MS experiments Py-GC-MS analysis was performed on a CDS 5000 series pyrolyser coupled with Agilent Technologies 7890A GC system and Agilent Technologies 5975C MS system. About 2 mg pure HPO was cracked at 800 oC. The gas chromatographic separation was performed using a TR-35MS capillary column (30m× 0.25 mm×0.25µm). The GC oven was maintained at 50 °C for 5 min, and increased to 280 °C at 10 °C/min. 4
ACCEPTED MANUSCRIPT Helium was used as the carrier gas with a constant flow rate of 3 mL/min.
2.5 1H-NMR analysis and 13C-NMR 1
H-NMR (Proton nuclear magnetic resonance) spectra were recorded by using a 400
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MHz, BRUKER DPX-400. The chloroform-d was used as a solvent. TMS (tetramethylsilane) was used as the internal standard. The results were scanned at a rate of 128 files every minute.
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C-NMR spectra were recorded from chloroform-d
solutions at 400 MHz using a BRUKER 400 MHz spectrometer. The results were
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scanned at a rate of 2048 files every minute. The experiments were carried out at 25 o
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C.
2.6. Kinetic analysis
There are many methods available in the literature to analyze non-isothermal kinetic from TG data, like KAS method and FWO method. In the paper, the KAS method and FWO method were selected to solve kinetic parameters. The KAS method was
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expressed as follows: β Aα R Ea ln 2i = ln − Ea(G(α )) RTα Tα
(R1)
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The FWO method was expressed as follows: (R2)
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AEa Ea lgβ = lg − 2.315 − 0.4567 RTα R(G(α ))
Where βi was the heating rate (K/min), Tα was temperature, A was pre-exponential factor, G (α ) was mechanism function, α was conversion rate. The FWO method was the same with KAS method in definition parameter. The slope and intercept from the line plot of against 1/Tα were used to obtain the activation energy and pre-exponential factor, respectively. It was important to note that activation energy values did not convey any mechanism information in the HPO pyrolysis process.
2.7. RSFTIR (remote sensing Fourier transform infrared) experiments 5
ACCEPTED MANUSCRIPT The advantage of RSFTIR was the sample or pyrolysis (intermediate) product was not removed. According to FTIR results change, the pyrolysis reaction can be observed. It was in situ experiments. The measurements were conducted using a Thermo Nicolet 6700 FTIR Instrument and in situ thermolysis cell (HT32, Xiamen University, China)
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in the temperature range of 20 oC - 350 oC. Heating rate was selected at 10 K/min. Sample pellet (ø13mm) was pressed with KBr. When cell temperature arrived set temperature, the temperature was sustained 2 min. After 1.5 min, the experiment was carried out to obtain the FTIR files. Infrared spectra in the range of 4000 cm-1 - 400
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cm-1 was obtained by model detector at a rate of 15 files/min and 10 scans/file with 4
2.8 Pyrolysis experiments
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cm-1 resolution. The different temperature conditions were scanned.
Pyrolysis experiments were carried out in a vertical stainless steel tube. It was a batch reaction. High pressure nitrogen was used as carrier gas to provide an inert environment. The constant flow rate of N2 was 80 mL/min. The inner diameter of tube
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was 38mm. The length of tube was 600 mm. The tube was connected with bio-oil collected device, which was cooled using ice bath. After N2 purged air and tube temperature arrived setting temperature for holding 120 min, HPO with KOH sample was then subjected to pyrolysis. Products were collected using mineral ether in bath of
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ice. The pyrolysis temperature was setting 500 oC. After pyrolysis, the mixture was
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separated to obtain pure crude pyrolysis BFO.
2.9 ESI FT-ICR MS experiments The detail information of ESI FT-ICR MS experiments condition was described in our previous work [20].
2.10 GC-MS experiments An Agilent 7890A-5975C GC-MS coupled with a DB-5MS column (30 m × 0.32 mm × 0.25 µm) was used to analyze the composition of BFO. The GC oven was maintained at 60 °C for 2 min, and increased to 140 °C at 15 °C/min, and further increased to 300 6
ACCEPTED MANUSCRIPT °C at 5 °C/min. It was then kept constant at 300 °C for 10 min. The sample was injected and the EI ionization source was operated with 70 eV ionization energy. The Mass range was set to 35-500 Da at a 1 s scanning interval. The ion source temperature was
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200 °C. The ion current was 250 µA.
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ACCEPTED MANUSCRIPT 3. Results and discussion 3.1 Thermal pyrolysis characteristics and kinetics of HPO In order to obtain BFO from HPO, it is necessary to know thermal decomposition characteristic of HPO. It can guide the catalytic pyrolysis experiments of HPO. Hence,
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thermal decomposition characteristic of HPO was carried out firstly by TG-DTG. The TG-DTG profiles as a function of temperature at the different heating rate was given in Fig.1 and Fig.S1. It was clear that HPO pyrolysis was mainly in temperature range of 350 oC-500 oC, especially at about 450 oC. The pyrolysis temperature was higher
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than other plant oil [21, 22]. Maybe it was related with saturated bond. Hence, HPO needed higher temperature to sustain pyrolysis than other plant oil. In TG curves, it
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was found that little amount of residue presented, which showed HPO could be cracked completely. According to Fig.S1, typical DTG curve has only one typical peak. In the range of 300 oC - 350 oC, the HPO started to pyrolysis according to TG-DTG curves. The main mass loss was carried out in the range of 350 oC - 500 oC. After major weight loss, there was almost no further weight loss from temperature of
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500 oC - 800 oC. And it was found that the pyrolysis of HPO was related with heating rate. With heating rate elevated, the decomposition temperature also was increased. According to experiment results, pyrolysis temperature of HPO was selected at 500 o
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C to obtain BFO.
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In order to deep-understanding pyrolysis characteristic of HPO, it needed to analysis pyrolysis kinetic. According to TG-DTG results, pyrolysis temperature was influenced by heating rate. And in different temperature range, pyrolysis rate of HPO was different, which means activation energy of pyrolysis was different. Though, activation energy alone was not enough to understand pyrolysis process and property, activation energy can provide reasonable information about the critical energy needed to start the pyrolysis of HPO. In turn the activation energy values would help to understand the pyrolysis difficult degree.
The activation energy values, computed using KAS and FWO method, were listed in 8
ACCEPTED MANUSCRIPT Fig.2. It was found that with the conversation (reaction depth) increased, the activation energy values of HPO pyrolysis also increased, especially at low conversation. When conversation exceeded 50 %, the difference of activation energy was slight. In other means, at relative low temperature, HPO pyrolysis was relative
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easy. The activation energy value of HPO was higher than other plant oil [22-23]. It is reasonable to think that unsaturated bond influenced on oil thermal pyrolysis compared with plant oil pyrolysis. The activation energy values of HPO pyrolysis showed the dependence of activation energy on the reaction proceeds and in turn HPO
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pyrolysis was a multi-step reaction kinetics process. And it was found that the difference of activation energy values was slight using KAS method and FWO
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method. The mean activation energy calculated from KAS and FWO models was 161.10 kJ/mol and 164.28 kJ/mol, respectively. Satisfactory agreement with a deviation of 1.94 % indicated that the activation energy calculated using KAS and FWO models were believable, which reference investigated the activation energy with a deviation below 4% using KAS and FWO [24]. Hence, the activation energy values
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were credible by using KAS and FWO method, respectively.
3.2. TG–FTIR–MS analysis
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The TG–FTIR–MS analysis was used to investigate the small molecule compound products and functional groups change of real-time pyrolysis process of HPO. The
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typical FTIR results were showed in Fig.3. The MS results were showed in Fig. S2. In the Fig.3, it was found that the functional group of pyrolysis products changed with time. For the TG-FTIR-MS analysis process was temperature-programming, we can obtain temperature information in the pyrolysis process. After 27 min, the peak at about 2900 cm−1 was changed, but still very weak. It means the pyrolysis of HPO started. At this point, the temperature was about 310 oC. It was accordance with Fig.1 at 10 k/min. After 33 min (about 370 oC), the FTIR characteristic signal of functional group became stronger gradually. It means pyrolysis reaction was accelerated. The strong peaks at 2920 cm−1 and 2851 cm−1 were attributed to the presence of methylene groups (CH2). And another characteristic peak was at 1750 cm-1. The peak at this 9
ACCEPTED MANUSCRIPT point corresponding to C=O was attributed to the presence of the ketones, ester groups or carboxylic acids [25]. After 55 min, the change of peak was not found. It means the pyrolysis reaction almost completely.
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According to MS results, it was found that in the pyrolysis products, main components were m/e=2, 14, 18, 28 and 44. Other small molecule compounds signals were very weak, like aromatic compounds. It means little fraction of these compounds presented in the mixture. Hence, they were not listed in this paper. In this paper, the
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detected range of molecular weight was main 2 - 100. Main materials maybe were H2, CH4, H2O, ethylene, CO, CO2 or propane in mixture according to MS results. In the
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previous published paper, many researchers thought in the plant oil pyrolysis process, 2-propenal can be detected [2, 13]. However, in this paper, we cannot found 2-propenal. It was a notable difference between HPO and plant oil pyrolysis products. Key difference was saturated bond of samples. And in the plant oil pyrolysis process, a large amount of gas generated [14]. However, amount of gas was relative low as HPO
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pyrolysis. Hence, we can confirm pyrolysis characteristic of HPO was different with other plant oil. The double bond played an important role in gas generation. And it was found that the concentrate of CO was higher than CO2. And m/e=28, 44 was
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contained other compounds, but most probable was CO, CO2. The results were listed in Fig.S3. Fig.S3 results showed ester group break was mainly formed CO not CO2. In
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the pyrolysis process, hydrogen also was found. It means the dehydrogenation reaction occurred. Maybe it was a reaction route of diene. Other saturated ester compounds also found the diene presented in pyrolysis products [26, 27]. The illustration of diene formation was little. We thought dehydrogenation reaction was a key step.
3.3. Py-GC–MS analysis According to TG-DTG and TG-FTIR-MS results, it was found that HPO pyrolysis needed relative high temperature to sustain pyrolysis and little amount of small molecule compounds presented. The components of pyrolysis products were needed 10
ACCEPTED MANUSCRIPT to analyze. Hence, Py-GC-MS experiment was carried out to analyze pure HPO pyrolysis products. The pyrolysis vapors of HPO cracking was directly analyzed by GC-MS. The chromatogram results were listed in Fig.S4 and products results were listed in Table 1. The corresponding peaks areas of the compounds can be compared
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to reveal the changing of their yields. It was found that the main hydrocarbon component was alkane and alkene. And oxygenated compounds were found in products, but the fraction was very low. Little fraction of fatty acid was found. The pyrolysis temperature maybe played an important role in HPO Py-GC-MS experiment
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for its temperature was 800 oC. The temperature of Py-GC-MS was higher than plant oil pyrolysis. Maybe heavy compounds were further cracked to form small molecule
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compounds. And diene was found in products. It was demonstrated that dehydrogenation reaction was carried out in pyrolysis process. The TG-FTIR-MS results found hydrogen presented in pyrolysis products, which also demonstrated dehydrogenation reaction presented. And it was found that the compounds, which carbon number exceed 18, were also found. It needed further analysis by other
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experiments.
3.4. FTIR analysis of the BFO
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According to above experiments analysis, we can confirm HPO was a potential renewable bio-resource material to obtain long chain bio-fuel oil by fast pyrolysis.
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Hence, HPO was cracked at 500 oC. The pyrolysis products were analyzed by FTIR firstly. The FTIR spectrum of BFO was given in Fig.4. In the HPO FTIR results, the strong peaks at 2920 cm−1 and 2850 cm−1 were attributed to the presence of methylene groups (CH2). The peak at 1740 cm−1 corresponding to C=O was attributed to ester group. The strong peak at 1470 cm−1 was attributed to the C-H vibration. The strong peak at 1175 cm−1 was attributed to the C-O vibration of ester group. The vibration peak at 720 cm-1 was attributed to long saturated carbon chain compounds [28]. In the BFO, no peak appeared at about 3500 cm-1. It means -OH stretching vibration was not found. In other means, no liquid acid, alcohol, water or phenol was found in BFO. The strong peaks at 2920 cm−1 and 2851 cm−1 were attributed to the presence of 11
ACCEPTED MANUSCRIPT methylene groups (CH2) [29, 30]. The peak at 1705 cm−1 corresponding to C=O was attributed to the presence of the aldehydes, ketones, ester groups or carboxylic acids [25]. The aldehyde has a sharp peak at about 2730 cm−1 corresponding to C-H, and Fig.4 showed a weak peak at this point. It means high fraction of aldehyde presented
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in BFO. The peak at 980 cm-1 was attributed to the C-H vibration of aldehyde. And at about 1710 cm-1, the peak was split. And another sharp peak was 1740 cm−1. It means in the BFO mixture, it contained fatty acid. And the peak located at 1260 cm-1 was C-O stretching vibration of acid. The peak located at 1410 cm-1 was H-O vibration of
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acid [28,31]. The C=C stretching vibration between 1645 cm-1 indicated the presence of alkene or aromatics. The peak at 1470 cm−1 was attributed to the asymmetric
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deformation vibrations of CH2 and CH3 groups. In addition, the peak at 1375 cm-1 was attributed to bending vibration of CH3 groups [30]. The peak at 1110 cm−1 corresponds to bending vibration of C-H functional groups associated with aromatic structures [28, 32]. And other possibility was the ester vibration. The peak located at 1160 cm−1 corresponds to acetate. The peak located at 1100 cm−1 and 1030 cm−1 was
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attributed to the different alcohol ester. According to 1740 cm-1 vibration, we can confirm the ester compounds presented in BFO. The references thought the peak at 721 cm−1 was attributed the aromatic stretching vibrations [33]. If the aromatic compounds presented, the C-H vibration at about 3050 cm-1 would be appeared. In
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this paper, at this location the peak was very weak. But the peak located at 910 cm−1 and 800 cm−1 maybe was attributed the aromatic vibrations. And they were
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substituted benzenes [28]. Another probability was that the peak at 721 cm−1 was attributed to saturated long carbon chain in products [28]. It needed other experiments to assist confirm the complexity of the BFO composition.
3.5. 1H-NMR and 13C-NMR analysis of BFO In order to confirm the functional group of BFO component, we carried out 1H NMR experiment and
13
C NMR experiment, which was an effective method to confirm
functional group of BFO mixture. The results were listed in Fig.S5 and Fig.S6. The Fig.S5 showed the
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H NMR spectrum of BFO, which provided the detailed 12
ACCEPTED MANUSCRIPT information about aromatic, olefinic, alkane and other materials. From the spectrum, the mainly peaks appeared in the range of 0.5 ppm to 2 ppm. The chemical makeup difference of BFO was notable. From 0.5 ppm to 2 ppm, the region of the spectrum protons was aliphatic, indicating their higher saturated aliphatic content [34]. From1.3 the spectrum proton was β-CH2 [35]. And carbonyl proton
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ppm to 1.6 ppm region
appeared in the chemical shift region of 2 ppm ~ 2.5 ppm [35]. From 4 ppm to 7 ppm regions, almost no peak was found. It means little amount of olefinic presented in the BFO. In the chemical shift region of 6.5 ppm ~ 8.5 ppm range was aromatic proton
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occurred [34]. However, the peak was weak. It means little amount of aromatic compound presented in BFO. The results were also accordance with TG-MS and
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FTIR results.
In order to further confirm the composition of BFO, we also carried out
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C NMR
experiment. According to results, it was found that the main regions were 0 ppm ~ 50 ppm and 75 ppm ~ 80 ppm. Before 40 ppm regions, it was main saturated aliphatic
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compound [36]. The peak at about 13.5 ppm was attributed to terminal methyl carbon. The peak in the range of 22 ppm ~ 29 ppm was attributed to carbon branched methyl carbon. The peak at about 30 ppm was attributed to tertiary carbon [35]. The results
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indicated in the BFO mixture, hydrocarbon was not all straight-chain compounds. It means free radical reaction presented in pyrolysis process. The peak at about 77 ppm
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was attributed to the CH3-O- groups [37]. However, according to FTIR and 1H NMR results, no ether trace information appeared. Hence, we thought it was methylene at about 77 ppm [28]. The peak, in the range of 100 ppm ~170 ppm, was attributed to the aromatic carbon [35]. According to NMR results, we can confirm that the fraction of aromatic compounds and olefinic was very low. The FTIR results and the NMR results were consistent with the early discussion in detail characterization results of BFO.
3.6. Composition of BFO The GC-MS analysis of BFO from the pyrolysis of HPO with KOH at the 13
ACCEPTED MANUSCRIPT temperatures of 500 oC was carried out to confirm the component of BFO. GC–MS analysis provided adequate information of components BFO. The chromatogram result was listed in Fig.S7. The vegetable oil (like soybean oil) pyrolysis compounds using base catalyst mainly contained alkanes, alkenes, aromatic compounds and
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oxygenated compounds, such as carboxylic acids and ketone. For double bond presented, high fraction of vegetable oil pyrolysis products was short-chain alkanes and alkenes. The BFO also mainly contained alkanes, alkenes, and oxygenated compounds. It was observed that large amount of BFO was long-chain alkanes and
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alkenes. The Py-GC-MS results also showed that the pyrolysis products of HPO were long-chain alkanes and alkenes. The difference of HPO and vegetable oil pyrolysis
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products was notable. And it was very interesting that the fraction of aromatic compounds in BFO was very low. In vegetable oil and animal fat pyrolysis products, the fraction of aromatic compounds was relative high [25, 38]. Maybe it was related with double bond, which reference result found that double bond influenced on fraction of aromatic compounds in BFO [39]. And the heavy fraction compounds
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were found. The carbon number was exceeded 18, especially oxygen containing compounds. In the oxygen containing compounds, we found it mainly contained acid, ketone, ester and aldehyde. It was surprised that octadecanoic acid ethyl ester was
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found. It was difficult to explain the product formation. The reference also found the octadecanoic acid ethyl ester presented in pyrolysis products [40]. And it was found
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that the peaks of 16-hentriacontanone, 17- tritriacontanone and 18- pentatriacontanone were very strong. It means the acid anhydride can further pyrolysis to form ketone. Little paper reported similar result. In our previous work, heavy compounds were also found [20]. The reference also found carbon number was even exceeded 30 [41]. Hence, the previous mechanism about triglyceride pyrolysis was difficult to elucidate heavy fraction formation. No paper has reported this pyrolysis path. It needed other experiments to confirm the BFO composition, especially oxygenated compounds.
3.7 ESI FT-ICR MS experiments In order to illustrate oxygenated compounds, especially heavy compounds, the BFO 14
ACCEPTED MANUSCRIPT was analyzed by negative-ion ESI FT-ICR MS experiments. ESI FT-ICR MS experiment was an effective method to analyze BFO. It can provide information regarding more polarity compounds, mainly oxygenated compounds e.g., which GC-MS technique cannot obtain. Hence, it has been used to analyze bio-fuel oil. The
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oxygenated heteroatom classes species derived from negative-ion ESI FT-ICR MS was corresponding to acidic compounds, containing -COOH or -OH groups. The ESI FT-ICR MS results were listed in Fig.5. It was found that the BFO contained many other oxygenated organic compounds even amount of these compounds was low,
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which were O3, O4, O5 and O6 class species. And the carbon number exceeded 18. In other means, according to ESI FT-ICR MS condition, carboxylic acid even
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dicarboxylic acid and alcohol in BFO, except ketone. It was a very interesting phenomenon. At present, no researcher reported heavy compounds formation path. Most researchers focused on small molecule compounds formation [42, 43]. The reference thought the main reaction was C-O cleavage of triglyceride to form fatty acid [44]. This conclusion can explain little amount of fatty acid presented in BFO.
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But why the carbon and oxygen number of compounds increased? It was a very complex issue. In Fig.5, sodium-containing compounds also were detected. These species were presumably sodium salts of the corresponding Ox class compounds.
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Similar species were also reported [45]. Hence, ESI FT-ICR MS experiment was an effective method to analyze pyrolysis heavy compounds. And it also provided a new
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way to probe the triglyceride pyrolysis reaction.
3.8 Recommended reaction mechanism There many papers reported triglyceride reaction path. The drawback was notable according to above analysis. For example, water and heavy compounds was not detailed in above reaction mechanism. But, they were all detected. It was wide accepted that carboxyl group was converted to acid. And how was fatty acid converted to heavy compounds like the O2-O6 class?
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ACCEPTED MANUSCRIPT The reference [44] thought carboxyl group was more stable than carbon chain of fatty acids. In other means, carbon chain cracking of fatty acid occurred firstly, not carboxyl group. And they thought heavy compounds can be formed at low temperature. But the authors did not provide direct evidence. In order to analysis
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pyrolysis mechanism, RSFTIR experiments were carried out. The RSFTIR experiments of HPO with and without catalyst were listed in Fig.6. It was found that ester group of HPO with or without catalyst showed little change even at 350 oC. Maybe it was related with HPO decomposition temperature. As TG-DTG results, at
found.
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this temperature HPO started to decomposition. Little change of spectrum can be And according to the peak located at 1580 cm-1 change, it was found that
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carboxylate anion was formed when KOH was added [28]. The reference [2] thought base catalyst promoted triglyceride deoxygenation according to salt deformation. The peak located at 1580 cm-1 showed that the salt formed in the HPO pyrolysis process when KOH was added. However, we cannot confirm HPO has cracked for HPO high pyrolysis temperature. The peak located at 1150 cm-1 was torsional vibration and out
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of plane of CH2 in solid long chain ester [28]. Other peak explanation referred to FTIR description. As we all known, in the triglycerides cracking process, fatty acid was first formed. In order to further analysis pyrolysis path, we selected stearic acid
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with or without KOH to carry out RSFTIR for HPO is a saturated ester. The results were listed in Fig.7. Pure stearic acid characteristic peaks have notable change with temperature elevated. The typical peak located at 1750 cm-1 was formed. And the peak
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located at 1406 cm-1,1280 cm-1,930 cm-1 was weakened, respectively. The peak located at 1406 cm-1 was ascribed to O-H bending vibration. The peak located at 1280 cm-1 was ascribed to C-O stretching vibration. The peak located at 930 cm-1 was ascribed to O-H out of plane bending vibration [28]. And the peak (721 cm-1) was weakened with temperature elevated. It means the carbon chain was cracked. According to the characteristic peaks change, we can confirm that carboxylic group was broken. And most possibility was ester formed according to above experiments results. When KOH was added, the notable peak change was 1580 cm-1, which means the salt formed in the stearic acid pyrolysis process when KOH was added [28]. And 16
ACCEPTED MANUSCRIPT with the 1710 cm-1 weakened, we can confirm that base catalyst promoted fatty acid deoxygenation. And no notable alkene peak appeared. Reference [4] also thought basic catalysts reacted with fatty acids to produce metal salts, which cracked into hydrocarbons. The peak located at 1460 cm-1 was attributed to O-H bending vibration.
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This peak was overlapped with C-H vibration. With the peak weakened, it means the fatty acid effective deoxygenation. The peak located at 1400 cm-1 was ascribed to CH2 vibration. For carboxyl presented, the vibration increased to 1400 cm-1. Hence, the vibration stepped to strengthen. And according to 721 cm-1 weakened, we can confirm
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the C-C bond was cracked in the pyrolysis process. In other means, the short chain fatty acid was first formed in stearic acid pyrolysis process when KOH was added.
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The results verified the reference [44] speculation. However, no ester compound was found. The carbonyl vibration almost disappeared completely at 230 oC. Hence, from Fig.6 and Fig.7 we can conclude that KOH promoted fatty acid decarboxylation. And pure stearic acid was converted to heavy compounds (ester) and water was formed. The reference thought stearic acid cracking to form stearic aldehyde and then further
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reaction to form other compounds [46]. The results maybe were used to explain the
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ESI FT-ICR MS experiment. Hence, recommended path was as followed:
This new pyrolysis path can explain the above experiments results. And this path was not final path. It also can further pyrolysis to form small molecular materials. Reaction 1 also can form CO by acid anhydride pyrolysis [46]. Reaction 3 explained short carbon chain carboxyl present in product. And it can further decarboxylation to form short carbon chain short carbon chain. Reaction 3 explained the ester formed in 17
ACCEPTED MANUSCRIPT the triglyceride process. And it was just one of probabilities. Ester formation in the steric pyrolysis maybe was free radical reaction. And the carbon chain of unsaturated fatty acid cracking was not listed. Because above reported mechanism has been listed. These reactions can use as a part of main reaction path to explain triglyceride
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pyrolysis, especially heavy compounds.
18
ACCEPTED MANUSCRIPT 4. Conclusions The characteristic pyrolysis of HPO and its bio-fuel oil were analyzed. TG-DTG results showed that the HPO pyrolysis was different with other plant oil. It was clear that HPO pyrolysis was mainly in temperature range of 350 oC-500 oC. The mean
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activation energy of HPO pyrolysis calculated from KAS and FWO models was 161.10 kJ/mol and 164.28 kJ/mol, respectively. Little amount of aromatic compound was found. The main component of pyrolysis product was alkane, alkane. The ESI FT-ICR MS results found large amount of carbon number exceeded 18 and oxygen
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atom number of compounds exceeded two. RSFTIR results found that in the decarboxylation process, the carbon chain also was cracked to form short carbon
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chain carboxyl. Without KOH, fatty acid was easy to form ester. Combining with very low fraction of aromatic compounds and 2-propenal and other gas component, the above experiments results elucidated the pyrolysis path of HPO was different with other plant oil. The key conclusion was that HPO maybe was a good bio-resource to obtain bio-fuel oil, and it was mainly contained diesel-like component, which was a
also proposed.
Acknowledgements was
supported by China
National Science
and
Technology
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This paper
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good alternative fuel to use in diesel engine. The recommended pyrolysis path was
(2015BAD21B06) and the Foundation of Jiangsu University of Advanced scholars
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(15JDG159).
19
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Polyvinylidene fluoride with and without Pine Sawdust, J. Anal. Appl. Pyrol., 123(2017)402-408.
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[32] Takwa K., Aïda B.H., SlimNaoui, et al., Characterization of the liquid products obtained from Tunisian waste fish fats using the pyrolysis process, Fuel process. Technol. 138(2015)404–412. [33] Lu Q., Yang X., Zhu X., Analysis on chemical and physical properties of bio-oil pyrolyzed from rice husk, J. Anal. Appl. Pyrol. 82(2008)191–198. [34] Pradhan D., Singh R.K., Bendu H., et al., Pyrolysis of Mahua seed (Madhuca indica) – Production of biofuel and its characterization, Energ. Convers. Manage. 108(2016) 529–538. [35] Biswas S, Mohanty P, Sharma D K., Studies on synergism in the cracking and co-cracking of Jatropha oil, vacuum residue and high density polyethylene: Kinetic 22
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ACCEPTED MANUSCRIPT Fig.1 TG curves of HPO at different heating rate Fig.2 activation energy of HPO Fig.3 FTIR results in different time Fig.4 FTIR results of HPO and BFO
showed the expanded mass scale spectrum at m/z 500-650. Fig.6 RSFTIR experiments HPO with or without KOH
Fig.S1 DTG curves of HPO at different heating rate Fig.S2 MS results in pyrolysis process
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Fig.S3 Results of m/e=28, 44
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Fig.7 RSFTIR experiments stearic acid with or without KOH
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Fig.5. Broadband negative-ion ESI FT-ICR mass spectrum of the BFO. The insert
Fig.S4 Py-GC-MS chromatogram results of HPO Fig.S5 1H NMR results of BFO Fig.S6 13C NMR results of BFO Fig.S7.GC-MS of BFO
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Table 1 compounds identified by Py-GC-MS in the pyrolysis vapor of HPO
25
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Fig.1 TG curves of HPO at different heating rate
Fig.2 activation energy of HPO
26
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Fig.3 FTIR results in different time
27
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Fig.4 FTIR results of HPO and BFO
Fig.5. Broadband negative-ion ESI FT-ICR mass spectrum of the BFO. The insert showed the expanded mass scale spectrum at m/z 500-650. 28
ACCEPTED MANUSCRIPT
1580
1150
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350 340 330 320 310 300 290 280 270 260 250 230
720
25 3450
1740
2850 2915 2700
1800
900
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3600
-1
wavenumber (cm )
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(a) HPO RSFTIR experiments
1580
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350 340 330 320 310 300 290 280 270 260 250 230
721
1745
2845
EP
2930
2800
2100
1400
700
-1
wavenumber(cm )
AC C
3500
(b) HPO with 10% KOH RSFTIR experiments
Fig.6 RSFTIR experiments HPO with or without KOH
29
ACCEPTED MANUSCRIPT
1580
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260 250 230 210 190 170 150 140 120 110 100 25
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721
1710
1400
1460
2850 2915 2800
2100
1400
700
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3500
-1
wavenumber (cm )
(a) stearic acid with 10% KOH RSFTIR experiments 1708
930
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1280
EP
250 230 210 190 170
721
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150 140 120
3600
1406
110 100
2700
1800
900
-1
wavenumber (cm )
(b) stearic acid RSFTIR experiments Fig.7 RSFTIR experiments stearic acid with or without KOH
30
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Fig.S1 DTG curves of HPO at different heating rate
Fig.S2 MS results in pyrolysis process
31
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Fig.S3 Results of m/e=28, 44
35000000
28000000
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14000000
7000000
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0
13
26
39
52
time (min)
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Fig.S4 Py-GC-MS chromatogram results of HPO
32
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Fig.S5 1H NMR results of BFO
Fig.S6 13C NMR results of BFO
33
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Fig.S7.GC-MS of BFO
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Table 1 compounds identified by Py-GC-MS in the pyrolysis vapor of HPO R. T
Peak area
1
1.215
11.87
Cyclopropane
2
1.258
6.27
1,3-Butadiene
3
1.337
5.94
2-Pentene
4
1.466
1.17
Cyclopentene
5
1.558
4.35
1-Hexene
6
1.919
7
2.067
8
2.943
9
3.292
10
6.000
Materials
1.12
Benzene
1.93
1-Heptene
0.6
Toluene
1.54
1-Octene
1.88
1-Nonene
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NO.
11
8.696
2.39
1-Decene
12
10.865
2.19
1-Undecene
13
12.697
2.82
1-Dodecene
14
14.315
2.16
1-Tridecene
15
14.431
0.5
Tridecane
16
15.798
3.95
1-Tetradecene
17
16.692
0.34
unknown
18
17.164
1.83
1-Pentadecene 34
ACCEPTED MANUSCRIPT 19.262
1.17
Pentadecane
20
18.457
2.73
1-Hexadecene
21
19.670
0.75
1-Heptadecene
22
19.750
0.93
Heptadecane
23
19.952
1.03
Hexadecanal
24
20.908
21.71
25
21.110
0.44
26
21.392
0.5
27
21.767
1.2
28
22.035
0.33
29
22.313
0.29
30
22.538
0.34
unknown
31
22.630
0.42
n-Hexadecanoic acid
32
23.880
7.33
unknown
33
24.627
0.39
unknown
34
26.478
1.99
unknown
35
26.680
36
26.723
37
27.568
38 39
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19
unknown
unknown
unknown
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unknown
2-Heptadecanone
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Hexadecanal
1,19-Eicosadiene
0.31
Cyclotetracosane
0.58
9-Tricosene,
27.599
0.31
Tetracosane
28.389
0.7
Cyclotetracosane
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0.2
40
28.886
1.16
unknown
41
33.549
0.77
unknown
42
36.992
0.96
unknown
35
ACCEPTED MANUSCRIPT
The main component of HPO pyrolysis product was alkane and alkane.
2
Little fraction of aromatic compounds presented in bio-fuel oil.
3
KOH promoted steric acid carboxylation.
4
HPO maybe was a good bio-resource to obtain bio-oil, which mainly contained
5
diesel-like component.
6
ESI FT-ICR MS and RSFTIR experiments were effective method to analyze pyrolysis
7
path, especially heavy compounds.
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1
8
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9
1
