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Efficient Hydrogenation of Various Renewable Oils over Ru-HAP Catalyst in Water Guangyue Xu, Ying Zhang, Yao Fu, and Qingxiang Guo ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b03186 • Publication Date (Web): 23 Dec 2016 Downloaded from http://pubs.acs.org on December 26, 2016
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Efficient Hydrogenation of Various Renewable Oils over Ru-HAP Catalyst in Water Guangyue Xu, Ying Zhang*, Yao Fu* and Qingxiang Guo iChEM, CAS Key Laboratory of Urban Pollutant Conversion, Anhui Province Key Laboratory for Biomass Clean Energy and Department of Chemistry, University of Science and Technology of China. No.96 Jinzhai Road, Hefei 230026, P. R. China. E-mail:
[email protected],
[email protected] ABSTRACT: A catalytic system over Ru-HAP catalyst is established to hydrodeoxygenate various oils to long-chain alkanes in water, for potential large-scale renewable diesel production, which has the following advantages: i) This system is versatile to different oil sources including Jatropha oil, palm oil, waste cooking oil and cooking waste, ii) Ru-HAP is highly efficient to achieve full conversion from stearic acid to alkanes achieved at as low as 100 °C and the isolated yield from Jatropha oil, palm oil and waste cooking oil to long-chain alkanes reached up to 95 mol%, 96 mol% and 87 mol% at 180 °C, 2 MPa H2 within 4 to 4.5 h, respectively. iii) The catalyst showed high stability during 5 runs’ recycling, ICP-OES analysis and a hydrothermal treatment. The activity decreased less than 5% after the catalyst treated in water at 200 °C for 24 h with a stirring speed of 1000 rpm due to the strong metal and hydrothermal-stable support interaction. iv) Ru-HAP is compatible to most of impurities such as various salts, sugars and macromolecules. v) It required low cost for operation since no dehydration before reaction are necessary and the alkane product can be separated from water easily. The reaction route was investigated and indicated the co-existed hydrodehydration and hydrodecarbonylation are affected ACS Paragon Plus Environment
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by water, temperature and H2 pressure. The catalyst was also characterized in detail and its high reactivity and stability may result from the fact that a highly distributed Ru nanoclusters anchored on HAP support which absorbed fatty acid by forming a meta-stable calcium carboxyl phosphate.
KEYWORDS: heterogeneous catalysts, green chemistry, water, long-chain alkane fuel, hydroxyapatite.
1 Introduction Renewable biodiesel with the chemical structure of long-chain alkanes is mainly applied as the alternative or additive of regular petroleum-derived fuels.[1] Plant or algae oils, with the main components of fatty acids and glycerides, are applicable feedstock for renewable biodiesel production. Normal alkanes produced from plant or algae oils are generally in the range of n-C15 to n-C18, with a high cetane number above 98.[1b] Compared with original triglyceride (TG) oil [2] or the first generation biofuel fatty acid methyl ester (FAME)
[3]
, long-chain alkane biodiesel has no oxygen, better flow
properties at low temperature, better adaptation as diesel additive and better compatibility with current infrastructures and engines. After isomerization, long-chain alkanes can be further updated for jet fuel. Currently, two approaches are used for producing long-chain alkanes via hydrogenation: one is the traditional process over sulfide CoMo and NiMo catalysts at 250-400 °C and 2-8 MPa which suffers sulfide leaching, deactivation and harsh conditions;[4] the other is over supported transition metal catalysts such as Ni
[5a-h]
, Co [5f], Pd
[5g-i]
, Ru [5j, 6a], Pt
[5k-m]
, Mo
[5n-o]
and W
[5o-p]
. The feedstock which
has been converted successfully includes Jatropha oil (JO), a non-edible oil wide available in south China [6a-d]; palm oil (PO), soybean oil (SO) and rapeseed oil (RO), the top three largest production plant oils all over the world; [6e] and fatty acids, mainly as model compounds.
However, waste cooking oil
(WCO), another largely available biodiesel feedstock, is difficult to deal with due to the high water content, high acid value, unknown impurities and harsh treatment conditions
[7]
. Organic solvents have
been employed in most studies with a restrict requirement for dehydration pretreatment, especially for WCO and algae oil with high inherent water content. Furthermore, the employment of organic solvents ACS Paragon Plus Environment
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not only requires separation processes after reaction, but also potentially causes environment issues. Therefore, a green and efficient catalytic system using hydrothermal-stable catalyst in the aqueous phase is highly desirable for the hydrogenation of various oils. Hydroxyapatite (HAP), a calcium orthophosphate with apatite structure, is normally applied as a biocompatibility material in orthopedics and dentistry. heterogeneous catalytic oxidation
[9a-c]
, cross-coupling
[8]
[9d-e]
It also performs well as a support for
, addition
[9f]
and hydrogenation
[9g-h]
. We
have employed Pd-HAP catalyst for the selective hydrogenation of phenol to cyclohexanone in the aqueous phase and found out that Pd nanoparticles are anchored on the HAP surface by an electronicdonating interaction with phosphate groups.
[9h]
This interaction leads to a highly efficient and stable
heterogeneous catalyst. The Pd nanoparticles can be activated at room temperature and reveals no aggregation or leaching after reaction in water. [9h] It indicates that HAP supported catalyst may be suitable in the hydrogenation of oils in water under mild conditions. In addition, our research group has developed a series of supported Ru catalysts which showed great performance in the hydrotreatment process of JO into C15-C18 alkanes in hexane at 200 °C, revealing that Ru was benefit for hydrogen activation [6a], as is widely studied by previous works on Ru catalysts. In this work, to obtain a catalyst with high efficiency and high hydrothermal stability, Ru-HAP was designed and prepared by a green and simple ion-exchange method. The catalyst was employed in the hydrogenation of various kinds of oils and stearic acid in water to investigate the reaction conditions. The impact of impurities in WCO was studied in detail. Ru-HAP was characterized in detail by differential scanning calorimetry thermal gravity analysis (DSC-TGA), nitrogen adsorption-desorption measurements and powder X-ray diffraction (pXRD) for catalyst structure; transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) for catalyst morphology; X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-optical emission spectroscopy (ICP-OES) for catalyst composition; and Fourier transform infrared spectroscopy (FT-IR) for the interaction between catalyst and feedstock. The
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mechanism was then discussed in detail for the reaction pathway. The stability and recyclability were also studied by recycle reactions, characterizations and hydrothermal stability test. 2 Experimental 2.1 Reagents Hydroxylapatite(HAP, ≥97%), stearic acid (>99%), 1-octadecanol (99%) and C10-C20 alkane standard samples (≥99.5%) were purchased from Aladdin Chemistry Co., Ltd. Ruthenium trichloridehydrate (RuCl3-xH2O, 37%Ru) was purchased from Shaanxi Kaida Chemical Engineering Co., Ltd. Hexane (AP), ethanol (AP) and acetone (AP) were purchased from Sinopharm Chemical Reagent Co., Ltd. High purity H2 and high purity N2 were purchased from Nanjing Special Gas Factory Co., Ltd. All the reagents and solvents were used without any pretreatment. Crude Jatropha oil was provided by Yunnan Shenyu New Energy Co., Ltd. Crude Palm Oil was provided by Tianjin Longwei Foodstuffs Co., Ltd. Waste cooking oil was pretreated by Anhui Jindeyi Energy Oil Co., Ltd. Original cooking waste was collected from local cafeteria. They were used without further pretreatment. 2.2 Catalyst Preparation The Ru-HAP catalyst was prepared by ion-exchange method. 1.00 g of HAP powder was added into 100 mL of acetone in a round-bottom flask and was heated to 55 °C with magnetic stirring at 1000 rpm. 53.7 mg of RuCl3-xH2O was dissolved in 10 mL of acetone and was then added to the above HAP/acetone suspension drop-wise in 15 min. The mixture was then kept at 55 °C with magnetic stirring at 1000 rpm for 20 h, filtered, and dried at 40 °C overnight. The catalyst precursor was reduced in a quartz tube furnace at 280 °C under a forming gas mixture of 10%/90% H2/N2 flowing at approximately 100 mL/min for a period of 3 h using a 1 °C/min ramp rate. 2.3 Catalyst Characterization Nitrogen adsorption-desorption measurements were performed using a Coulter SA 3100 adsorption analyzer which reports adsorption/desorption isotherm, specific surface area and pore volume automatically. The Brunauer-Emmett-Teller (BET) equation was used to calculate the surface area in ACS Paragon Plus Environment
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the range of relative pressures between 0.05 and 0.20. The pore sizes were calculated from the adsorption branch of the isotherms using the thermodynamic based Barrett-Joyner-Halenda (BJH) method. XRD analysis was conducted on an X-ray diffractometer (TTR-III, Rigaku Corp., Japan) using Cu Kα radiation (λ= 1.54056 Å) at 40 kV and 40 mA. The data were recorded over 2θ ranges of 10-70 °. The sample after reaction was dried at 40 °C after filtration and acetone sequential washing. HAADF-STEM images were taken with a JEOL-2100F field emission transmission electron microscopy. XPS was obtained with an X-ray photoelectron spectrometer (ESCALAB250, Thermo-VG Scientific, USA) at room temperature under a vacuum of 10-8-10-9 torr using monochromatized Al Kα radiation (1486.92 eV). The binding energies (B. E.) were calibrated to the carbon with a C1s band at 284.6 eV. The sample after reaction was dried at 40 °C after filtration and acetone sequential washing. FT-IR spectra were recorded by a Nicolet 8700 FT-IR spectrometer at room temperature in the 4000400 cm-1 region. The stearic acid treated HAP sample was prepared as follows: 0.1 g of HAP support was mixed with 20 mL of a 0.05 M n-hexane solution of stearic acid and this mixture was stirred at room temperature for 12 h. Then the solid was separated by centrifugation with n-hexane washing for 50 times. The residue was dried at 80 °C (b.p. of n-hexane is 69 °C, b.p. of stearic acid is 232 °C) in a N2 atmosphere overnight. The chemical composition of catalysts was analyzed by an Optima 7300 DV ICP-OES. 2.4 Experimental procedure In a typical experiment, feedstock (1 mmol stearic acid or 0.2 g oil), catalyst (0.1 g Ru-HAP, 1.7 wt% Ru in Ru-HAP), and solvent (15 mL) were added into a 50 mL Parr reactor with a quartz lining. After purging the reactor with H2 for several times, the reactor was charged with H2 at the preset pressure. The reactor was put on a magnetic stirrer with a stirring speed of 1000 rpm. The reactor was heated from room temperature to the reaction temperature. Generally, it took about 10 min and 15 min to reach 120 °C and 180 °C, respectively. After reaction, the reactor was put into cold water at once to cool below ACS Paragon Plus Environment
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100 °C within 3 min and then to room temperature. The liquid, gas and solid were collected for further analysis. Since the alkane products floated on water, they were taken out simply by a spoon. When nhexane was employed as solvent, the liquid was directly analyzed by a gas chromatograph (GC, Kexiao 1690) with an HP-5 capillary column. Both injection and detection temperatures were 320 °C. The column temperature was increased from 100 to 250 °C at a ramp rate of 10 °C/min. n-Eicosane was used as the internal standards to quantify the products. Highly pure N2 (99.999%) was severed as carrier gas and the column head pressure was 0.1 MPa. The products were identified by a GC (Agilent 7890A)–mass spectrometer detector (Agilent 5975C with Triple-Axis Detector) with an HP-5 column. The column temperature was increased from 40 to 280 °C at a ramp rate of 10 °C/min. Both injection and detection temperatures were 320 °C. Highly pure helium was severed as carrier gas and the flow rate was 1 mL/min. When water was employed as solvent, the gray suspension (containing water and catalyst) was sucked out by a plastic dropper. Then the catalyst was separated by filtration. The white solid residue was taken out with a spoon, washed with diluted hydrochloric acid and pure water, and weighed by an electronic balance with minimum division value of 0.01 mg. Then it was dissolved in nhexane for GC and GC-MS analysis as described above. The gas products were analyzed by a GC (GCSP6890, Shandong Lunan Ruihong Chemical Instrument Co., Ltd., Tengzhou, China) with two detectors: a thermal conductivity detector (TCD) with TDX-01 column for H2, CH4, CO and CO2, and a flame ionization detector (FID) with Porapak Q column for hydrocarbons such as CH4, C2H6 and C3H8. Every experiment was carried out for at least three times repeatedly with errors less than 2%. Each result reported was the average value of repeated experiments. The conversion and yield were calculated by mol% when stearic acid or alcohol was used as feedstock. Conversion(mol%)=(1-
Yieldሺmol%ሻ=
n(feedstock after reaction) )×100% n(feedstock before reaction)
Σn(each product) ×100% n(feedstock before reaction)
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The yield was calculated by wt% and mol% when Jatropha oil, palm oil or waste cooking oil was used as feedstock. Yieldሺwt%ሻ=
Yieldሺmol%ሻ=
Σm(each product) ×100% m(feedstock before reaction)
Σn(each product) ×100% Σn(each fatty acid and its ester in feedstock before reaction)
The isolated yield was calculated by wt% and mol%. Isolated yieldሺmol%ሻ=
Isolated yieldሺmol%ሻ=
mሺalkane productሻ ×100% mሺfeedstock before reactionሻ
m(alkane product)/(average molar mass of alkane product) ×100% Σn(each fatty acid and its ester in feedstock before reaction)
The carbon balance was calculated based on the following equation: Carbon balanceሺ%ሻ=
n(carbon in products) ×100% n(total carbon in feedstock)
The separated catalyst was dried at 40 °C after filtration and acetone sequential washing. During the catalyst stability test, the catalyst was then directly characterized or reused without any further treatment. The catalyst hydrothermal stability was tested by the following method: 0.1 g of Ru-HAP and 15 mL of water were added into a 50 mL Parr reactor with a quartz lining. After purging the reactor with H2 for several times, the reactor was charged with H2 at ambient pressure. The reactor was put on a magnetic stirrer with a stirring speed of 1000 rpm and then heated to 200 °C and kept for 24 h. After these treatments, the reactor was cooled down to room temperature. The catalyst was collected and then directly characterized or reused without any further treatment. 3 Results and Discussions 3.1 Hydrogenation of Various Oils As different species of oil contains unique composition of fatty acids and impurities, three typical commercialized oils, JO, PO and WCO were selected for hydrogenation treatment. The composition of JO, PO and WCO are shown in Table 1. JO contains mainly C18 unsaturated fatty acid. PO contains ACS Paragon Plus Environment
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more C16 fatty acid than PO and JO. WCO has higher acid value and water content than JO and PO. These data were similar with previous reported values [5]. Table 1. Composition of JO, PO and WCO. Jatropha Oil
Palm Oil
Waste Cooking Oil
Acid value (mg KOH/g)
8.42
0.14
30.95
Water content (%)
0.18
0.40
5.21
C
76.99
76.94
76.72
H
11.77
11.57
11.88
O
10.58
10.71
10.67
N
0.66
0.77
0.13
S
n.d.
n.d.
0.60
Elementary composition (%)
Fatty composition (%) Lauric
12 : 0(a)
n.d.
0.3
0.1
Lauroleic
12 : 1
n.d.
trace
trace
Myristic
14 : 0
1.1
1.0
4.2
Tetradecenoic
14 : 1
n.d.
trace
trace
Palmitic
16 : 0
15.3
25.8
16.9
Palmitoleic
16 : 1
0.5
0.1
0.5
Hexadecadienoic
16 : 2
n.d.
0.4
trace
Stearic
18 : 0
7.0
3.5
8.9
Oleic
18 : 1
36.7
67.9
33.5
Linoleic
18 : 2
39.1
trace
35.5
Arachidic
20 : 0
0.2
0.3
0.2
Eicosenoic
20 : 1
trace
0.6
0.1
(a)The numbers mean the carbon number in fatty acid and the degree of instauration in alkyl chain.
The above oils were tested over Ru-HAP catalyst at 180 °C, 2 MPa H2 in water. The time-course of product distribution is shown in Figure 1. Although with different compositions, all these oils underwent similar reaction process. Saturated fatty acids, corresponding alcohols and esters were ACS Paragon Plus Environment
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detected at the beginning of the reaction, and the yield of which increased first and then decreased to zero. It took 4, 4 and 4.5 h to reach 100% conversion of JO, PO and WCO to reach isolated yields up to 95, 96 and 87% based on mole and 79, 80 and 72 % based on weight, respectively, which were very closed to the GC yield. The total alkane yields and carbon balance are shown in Table 1 and Table S1.The hydrogenation of oils in water leads to a complete self-separated product which can be seen in the pictures shown in Figure 2. Before reaction, waste cooking oil is a kind of reddish yellow viscous oil. After reaction, the alkane product floated on the water while the catalyst sank in the bottom of water, which thus significantly increases the separation efficiency and decrease the separation cost.
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Figure 1. Product distributions for the hydrogenation of (a) Jatropha oil, (b) Palm oil, and (c) Waste cooking oil. Reaction conditions: 200 mg oil, 100 mg Ru-HAP, 180 °C, 2 MPa H2, 15 mL water. Table 2. Yields and carbon balance in the hydrogenation of JO, PO and WCO. Jatropha Oil Palm Oil
Waste Cooking Oil
Reaction time (h) [a]
4
4
4.5
GC yield of total long-chain alkane (wt%)[b]
80.5
81.5
73.6
GC yield of total long-chain alkane (mol%)[b]
97
98
89
Isolated yield of total long-chain alkane (wt%)[b]
79
80
72
Isolated yield of total long-chain alkane (mol%)[b]
95
96
87
88.9
89.9
81.3
[b]
Carbon content in long-chain alkane (mol%)
[a] Reaction conditions: 200 mg oil, 100 mg Ru-HAP (1.68 mol% Ru feed), 180 °C, 2 MPa H2, 15 mL water. [b] The calculate methods were shown in Experimental section.
Figure 2. Photos before and after hydrotreatment of waste cooking oil. Left: waste cooking oil in water; middle: waste cooking oil with Ru-HAP catalyst in water; right: after reaction for 4.5 h at 180 °C, 2 MPa H2. ACS Paragon Plus Environment
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It is worth to mention that the untreated original cooking waste collected from local cafeteria was also catalyzed by Ru-HAP and achieved good results. As a random heterogeneous mixture, the composition of the original cooking waste could not be detected exactly so that the yield could not be calculated. As it contained about 87 wt% of water, 15 g original cooking waste mixture was hydrodeoxygenated without any additional solvent. After reacted for 6 h at 180 °C and 2 MPa H2, the isolated yields of total alkanes were 1.07 g, 0.95 g and 1.01 g in three parallel tests, respectively. In considering the water content and impurities, the yield was relative high. These results showed that the Ru-HAP was quite efficient for the hydrogenation of WCO, even without any pretreatment. Because most of the oils have similar composition and structure to the JO, PO and WCO, and have fewer impurities than untreated cooking waste, it can be deduced that the Ru-HAP is efficient for the hydrogenation of various kinds of oils in water into long-chain alkanes. 3.2 Hydrogenation of Stearic Acid As is known, oils mainly contain fatty acids and glycerides. In hydrogenation process, glyceride firstly converts into saturated fatty acid.
[1b]
The key step is the following fatty acid hydrotreating. As
fatty acids with 18 carbons are the principal components, stearic acid (n-octadecanoic acid, C18 acid) is chosen as the model compound to study the hydrogenation reaction. A series of Ru catalysts on different supports including active carbon, HBEA(Si/Al=25), SiO2, ZrO2, TiO2, La(OH)3 and HAP were screened, as shown in Table 3. The main products from stearic acid hydrogenation were n-heptadecane (C17 alkane), n-octadecane (C18 alkane), 1-octadecanol (C18 alcohol), cracking products (≤C16 alkanes) and stearyl stearate. From entries 1-7, Ru-HAP exhibited outstanding catalytic performance among the Ru catalysts. The Ni-HAP catalyst was also tested but showed poor activity at the same reaction conditionsand could only get alcohol product. The reaction over pure HAP would lead to trace hydrodecarboxylation product. The comparison with some reported works was listed in Table S2. Table 3. Comparison of stearic acid conversions over different catalysts in aqueous phase(a) Entry
Catalyst
Conv./%
Yield./mol% C17
C18
Cracking
Alcohol
Ester
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1
Ru/AC
26.9
3.1
0.6
0
22.8
0.4
2
Ru/HBEA(25)
27.9
0.4
0.1
0
26.2
1.2
3
Ru/SiO2
42.7
1.0
0.1
0
41.6
0
4
Ru/ZrO2
41.7
4.5
0.3
0
35.2
1.7
5
Ru/TiO2
57.3
38.4
9.8
0.6
8.5
0
6
Ru/La(OH)3
31.9
6.5
0.3
0.2
22.3
2.6
7
Ru-HAP
95.8
60.0
20.7
0.4
14.4
0.3
8
Ni-HAP
3.5
0
0
0
3.3
0.2
9
HAP
0.1
0.1
0
0
0
0
(a)Reaction conditions: 1 mmol stearic acid, 1.68 mol% Ru related to stearic acid in Ru catalysts, 180 °C, 2 MPa H2, 60 min in 15 mL water.
A series of experiments were carried out to further understand the reaction, such as the impacts of reaction temperature (Figure 3) and H2 pressure (Figure 4). It took 2 h to reach 100% conversion in 180 °C, 2 MPa H2. Higher temperature and H2 pressure will promote the reaction. The conversion can be compensated by extending reaction time at milder reaction conditions. For examples, to achieve full conversion, it took 5 h at 160 °C, 15 h at 140 °C and 72 h at 120 °C, respectively. Even when the reaction was performed at as low as 100 °C, after 2 weeks, full conversion to alkane with 84 wt% isolated yield could be achieved (Table 4).
Figure 3. Effect of temperature on stearic acid conversions and product yield. Reaction conditions: 1 mmol stearic acid, 100 mg Ru-HAP (1.68 mol% Ru feed), 2 MPa H2, 1 h in 15 mL water.
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Figure 4. Effect of hydrogen pressure on stearic acid conversions and product yield. Reaction conditions: 1 mmol stearic acid, 100 mg Ru-HAP (1.68 mol% Ru feed), 180 °C, 1 h in 15 mL water. Table 4. Effect of reaction conditions in the hydrogenation of stearic acid over Ru-HAP in aqueous phase (a) Entry
Temp. P(H2)/ Time/
Conv. Yield/mol% (wt%)(b)
Specific Rate to Alkane /min-1(c)
/°C
MPa
min
/%
C17
1
180
2
100
100
73.7 25.4
0.8 0.1
n.d. 99.9
2
180
2
60
95.8
60.0 20.7
0.4 14.4
0.3
3
200
2
60
100
77.8 21.0
1.2 n.d.
n.d. 100(84)
4
160
2
60
36.3
8.6
3.6
0.1 23.1
0.9
12.2
5
140
2
60
16.5
4.7
2.3
0
9.2
0.3
7.0
6
120
2
60
6.9
0.7
0.6
0
5.5
0.1
1.3
7
180
2
120
100
73.6 25.4
1.0 n.d.
n.d. 100(85)
0.496
8
160
2
300
100
69.9 29.3
0.8 n.d.
n.d. 100(85)
0.198
9
140
2
900
100
66.8 32.6
0.6 n.d.
n.d. 100(85)
0.066
10
120
2
4320
100
63.6 35.9
0.5 n.d.
n.d. 100(85)
0.014
11
100
2
20160
100
60.8 38.7
0.5 n.d.
n.d. 100(84)
0.003
12
180
4
60
100
70.7 21.4
0.8 6.9
0.2
92.9
13
180
1
60
63.1
31.9 12.7
0.2 17.9
0.4
44.8
C18
C.
A.
E.
T.A.
81.1
(a)Catalysts feed: 1.68 mol% Ru related to stearic acid in Ru-HAP. (b) The yields were based on mole by GC. C., the abbreviation for cracking products; A., the abbreviation for C18 alcohol; E., the abbreviation for stearyl stearate; and T. A., the abbreviation for total alkanes, respectively. The yield
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of total alkanes in brackets was isolate yield based on weight. (c) Specific rate to alkane equals to (Yield of all alkanes) * (Catalyst feed)-1* (Time)-1
As shown above, stearic acid, JO and PO led to better yields to long-chain alkane than WCO did, which could be due to various seasonings addition as well as pyrolysis and oxidized components produced during cooking. To further investigate the impacts of the impurities, a series of experiments were conducted. To magnify the effect for more clear comparison, 20% molar equivalents of each impurity was added into stearic acid hydrogenation reaction system, as shown in Table 5. NaCl, Na2S, Na3PO4 and CaCO3 were chosen as the model for mineral salts and they all promoted the reaction by different extents (Entries 2a-d). It reveals that table salt, Cl-, S2-, PO43- and Ca2+ would not hinder the hydrogenation reaction. The promotion was because that the inorganic ions would promote the ionization of fatty acid and thus facilitated the interaction between HAP and fatty acid. The nonelectrolyte sugar, such as sucrose and glucose, were also common seasonings in the kitchen. They barely affected the reaction (Entries 3a-b). The proteins in food would become mono amino acid during cooking, so glutamic acid (Glu), histidine (His) and lysine (Lys) were chosen as model impurities (Entries 4a-c). The acidic amino acid, Glu (pI=3.22), slightly decreased the reaction activity while basic amino acid, His (pI=7.59) and Lys (pI=9.74), hindered the reaction significantly. The extra alkalescent N (imidazole in His and amido in Lys) could competitively combine the fatty acid and thus impaired the reaction activity. As the main composition of aginomoto, monosodium glutamate (MSG) was introduced to the reaction system and showed similar influence to Glu (Entry 4d). Certain impact could be induced by acetic acid addition, and it is because of a competitive combination with HAP (Entry 5). Some macromolecules including cellulose, egg white (containing ovalbuin) and carbon black were chosen as model impurities of fiber, protein and charring (Entries 6a-c). Cellulose and carbon black barely affected the reaction, while egg white slightly decreased the fatty acid conversion. An equivalent weight of special spice mixes, which contained anise, pepper, ginger, paprika, chilli powder, et. al., would retard the reaction seriously (Entry 7). It could be due to the alkaloid in these spices. To ACS Paragon Plus Environment
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investigate the impact of basic groups, butyl amine was tested as the model compound and impaired the reaction seriously (Entry 8). The formation of amide would block the interaction between fatty acid and HAP surface remarkably. Accordingly, in the impure waste oil, most of impurities would not impact the reaction system except for basic material such as basic amino acid and alkaloids. Nevertheless, in actual oils, even untreated cooking waste, the concentration of impurities was far below 20 mol% equivalent as tested. Therefore, the impurities had little impact on the reaction system. Table 5. The impacts of impurities in the hydrogenation reaction. [a] Yield/mol%[b]
Impurity Addition Entry
Category
Species
1
Original
None
2a
Salts
Conv./%
Alkanes
A.& E.
95.8
81.1
14.7
NaCl
99.3
94.8
4.5
2b
Na2S
96.2
83.1
13.1
2c
Na3PO4
98.2
87.5
10.7
2d
CaCO3
96.0
81.8
14.2
Sucrose
96.1
82.9
13.2
Glucose
96.0
82.5
13.5
3a
Sugar
3b 4a
Amino Acid
Glu
88.3
71.4
16.9
4b
or Salts
His
28.7
11.2
17.5
4c
Lys
25.6
10.2
15.4
4d
MSG
87.9
71.2
16.7
5
Acid
Acetic acid
82.9
65.5
17.4
6a
Macromolecule
Cellulose
95.7
81.1
14.6
6b
Egg white
90.8
74.0
16.8
6c
Carbon black
95.9
80.8
15.1
7
Mixture
Spice mixes
25.4
15.3
10.1
8
Base
Butyl amine
33.2
10.6
22.6
[a] Reaction conditions: 1 mmol stearic acid, 100 mg Ru-HAP (1.68 mol% Ru feed), 180 °C, 2 MPa H2, 1 h in 15 mL water. For entries 1-5 and 8, 0.2 mmol of each compound was added; for entries 6-7, 284 mg of each material was added. [b] For the yield, alkane is the sum of C17, C18 alkanes and C13-
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C16 crackings, while A. & E. is the sum of alcohol and ester. 3.3 Catalyst Characterization The Ru-HAP was characterized to explore the activity in catalytic reactions. In our previous work, the thermal stability of HAP support was studied by differential scanning calorimetry - thermal gravity analysis (DSC-TGA) to show a less than 1% weight loss in N2 at 800 °C. [9h]
The nitrogen adsorption-desorption isotherm plots were type IV [10] and the surface area calculated by Brunauer-Emmett-Teller (BET) method (determined from the desorption branch) was 53.8 m2/g. From the isotherm curves shown in Figure S2, it could be seen that the surface morphology and structure nature of HAP varied a little bit before and after Ru loading. The narrow H3-type hysteresis loop indicated the random spontaneous stacking of HAP nano-clusters. [9h, 10] The powder XRD patterns of HAP and Ru-HAP are shown in Figure S3. It revealed pure crystalline HAP (hexagonal, space group P63/m, No. 176, JCPDS No. 73-0293) without Ru diffractograms.[8] Ru did not change the crystal structure of HAP and Ru nano-clusters were highly dispersed to show no long-range patterns. The broad peaks indicated small HAP crystallites, which, as well as the approximately non-porous structure of HAP, would jointly decrease the influence of internal diffusion on the reaction remarkably. The Ru nano-clusters could be observed directly in HAADF-STEM image, as shown in Figure 5. Because HAP would be ablated by high energy electron beam, the HAADF-STEM images were shot as fast as possible without focusing carefully, the slight defocusing and drifting were unavoidable. The average Ru particle size was about 1.2 nm estimated by HAADF-STEM analysis of randomly selected clusters. In our previous work, HAP was found to have an electron-donor effect to the supported metal.
[9h]
Besides the electron effect, Ru nano-clusters were highly dispersed on HAP surface by ion-exchange, leading to a high surface area of Ru.
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Figure 5. HAADF-STEM image of Ru-HAP. The inset is the particle size distribution of Ru in RuHAP XPS was used to investigate the chemical nature of Ru-HAP, as shown in Figure 6. Ru-HAP revealed a predominant distinct Ru 3p doublet indicative of Ru 3p3/2 at 462.6 eV and Ru 3p1/2 at 485.3 eV. The signal was relative weak to distinguish different valance state of Ru. From the scanning of the spectra, Ru barely changed before and after reaction. It indicated that Ru was stable during the reaction. After exposed to air for six months, the long-laid sample still kept similar state, demonstrating that the catalyst was stable in the air. Hydrogenation of stearic acid experiments also showed no catalytic activity decreasing. The peaks at about 475 eV and 497 eV did not belong to Ru species. They might be the Auger-electron lines for O KL1L1 and KL1L23 so they were not labeled in the figure.
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Figure 6. XPS spectra of Ru 3p in Ru-HAP. Experimental spectrum (black line) and deconvolution by peak fitting (colored lines) of fresh, used and long-laid catalyst were recorded. The interaction between support and fatty acid is significant for the catalytic efficiency. FT-IR was carried out and the spectra are shown in Figure 7. For stearic acid, two sets of characteristic peaks, the alkyl chain and the carboxyl group, were readily identified. The former showed characteristic peaks at 2954 cm-1, 2917 cm-1, 2849 cm-1, 1471 cm-1 and 719 cm-1 for the asymmetric stretching vibration of CH in -CH3, asymmetric stretching vibration of C-H in -CH2-, symmetric stretching vibration of C-H in CH2-, deformation vibration of C-H and skeleton vibration of C-C chain, respectively. The latter showed characteristic peaks at 1703 cm-1 and 941 cm-1 for the stretching vibration of C=O in carboxyl group and out-of-plane deformation vibration of –OH···O= in the dimer of acid, respectively. In original HAP, there were peaks at 3568 cm-1 for stretching vibration of –OH, 1093 cm-1 and 1037 cm-1 for vibration of v3(PO43-), 961 cm-1 for vibration of v1(PO43-), 630 cm-1 for deformation vibration of – OH along the c axis, 603 cm-1 and 565 cm-1 for vibration of v4(PO43-), and 472 cm-1 for vibration of v2(PO43-), respectively. [8, 11] After treated with stearic acid solution, it appeared some new peaks in the FT-IR spectra of HAP support. All the peaks for alkyl chain appeared in the spectra while the peaks for carboxyl group did not, indicating that there were no physical-adsorbed acids on the support. A brand new peak at 1554 cm-1 was observed to show the formation of bidentate carboxylate on HAP surface. This evidence for the existing of carboxylate proved the chemical adsorption of acid on HAP. This carboxylate species was ACS Paragon Plus Environment
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not dissociative calcium stearate, which showed the asymmetric stretching vibration at 1575 cm-1 and 1538 cm-1. Considering the structure of HAP, it may be a metastable calcium stearate phosphate which could be formed before reaction while be broken after hydrogenation. In this reaction, water showed outstanding performance. As discussed above, the fatty acid was chemo-adsorbed on the HAP surface by the formation of carboxylate. Meanwhile, as is well known, fatty acid was easier to be ionized in water than in hexane. Therefore, water could promote the formation of fatty acid radicals and thus lead to a better approach for negative acid radicals and positive surface Ca cations with electrostatic interaction.
Figure 7. IR spectra of HAP support with and without fatty acid adsorption. The dashed lines represent the original support while the solid lines represent the stearic acid treated one. 3.4 Reaction Route A series of experiments were carried out to study the reaction in our catalytic system. Firstly, the product distribution data were recorded at different reaction time, as shown in Figure 8. When heating up to 120 °C and cooling down in cold water immediately, as shown in data at -5 min, the reaction reached about 0.2% conversion. When heating up to 180 °C and cooling down in cold water immediately, as shown in data at 0 min, the conversion was 6.0%, and 3.8% alkane was detected. The yield of alcohol and ester increased fast at the first 30 min while decreased slowly afterwards. The yield ACS Paragon Plus Environment
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of alkanes increased continuously as the reaction progressing. After keeping at 180 °C for 60 min, 95.8% fatty acid was converted while still 14.7% alcohol and ester could be detected. Although it met 100% conversion with 2.2% alcohol yield at 90 min, it took 10 more minutes to reach >99.9% alkane yield. In all these records, 1-octadecanoland stearyl stearate were the only two intermediates detected.
Figure 8. Effect of reaction time on stearic acid conversion and product yield. Reaction conditions: 1 mmol stearic acid, 100 mg Ru-HAP (1.68 mol% Ru feed), 180 °C, 2 MPa H2, 15 mL water. It took 15 min to heat up to 180 °C. Time -15 min means before reaction; time -5 min means heating up to 120 °C and cooling down in cold water immediately; time 0 min means heating up to 180 °C and cooling down in cold water immediately. In previous studies, [5] the hydrogenation of fatty acid was investigated to proceed via three routes, as shown in Scheme 1. Fatty acid was firstly hydrogenated to corresponding aldehyde. As aldehyde was not stable, it would soon go on transforming. The first route was hydrogenation into alcohols followed by hydrodehydration into corresponding alkane. The second route was decarbonylation into alkane with one carbon less. Fatty acid could also go through decarboxylation into alkane with one carbon less. As shown in Figure 8, C17 and C18 alkanes were the final products. To investigate the reaction route, the reaction was conducted in argon atmosphere. Only about 0.1% C17 alkane was detected. Because the first step hydrogenation from acid to aldehyde required hydrogen, only decarboxylation could happen in argon. This result revealed that the route (3) decarboxylation barely happened in this reaction system. Thus the C18 alkane came from the route (1) hydrodehydration while the C17 alkane came ACS Paragon Plus Environment
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from the route (2) decarbonylation. After reaction in hydrogen, the gas product analysis detected CH4 and trace C2H6 but no CO, as shown in Table S1. It was because CO would be transformed into CH4 by methanation reaction, as shown in Equation (4) in Scheme 1. Trace C2H6 would come from the cracking reactions over Ru catalyst. [6a]
Scheme 1. Reaction routes of fatty acid hydrogenation As an intermediate, C18 alcohol (stearyl alcohol) was employed as separated feedstock. However, alcohol showed extreme low reactivity in this catalytic system. Even after 4 h at 200 °C under 4 MPa H2 with up to 1500 rpm stirring, only 6.1% conversion was reached. However, the reaction was very fast in hexane even under milder conditions (Table 6, Entry 3). It could be explained by the mass transfer resistance in water. When the reaction began with stearic acid, the adsorbed acid would produce adsorbed aldehyde intermediate for the favor of next step hydrogenation or decarbonylation, while the alcohol feedstock would hardly be adsorbed on HAP surface in water. [5d] Table 6. Studies on the C17/C18 ratio over Ru-HAP(a) Temp.
P(H2)
Time
/°C
/MPa
/min
1
180
2
2
180
3 4(c)
Entry
Feedstock
Solvent
60
acid
2
1080
180
2
180
2
Conv.
Yield./mol %(b)
C17/C18
/%
C17
C18
others
mol ratio
water
95.8
60
20.7
15.1
2.90
acid
hexane
95.5
82.5
10.4
2.6
7.93
90
alcohol
hexane
91.3
89.1
1.9
0.3
46.9
1080
acid
hexane
92.0
88.9
0.8
2.3
111
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5
180
2
1080
acid
mixture (d)
85.5
68.9
14.4
2.2
4.78
6
180
2
90
alcohol
mixture (d)
72.1
60.9
11.0
0.2
5.54
7
200
2
60
acid
water
100
77.8
21
1.2
3.70
8
160
2
60
acid
water
36.3
8.6
3.6
24.1
2.39
9
140
2
60
acid
water
16.5
4.7
2.3
9.5
2.04
10
120
2
60
acid
water
6.9
0.7
0.6
5.6
1.17
11
180
4
60
acid
water
100
70.7
21.4
7.9
3.30
12
180
1
60
acid
water
63.1
31.9
12.7
18.5
2.51
13
180
0
60
alcohol
hexane
15.8
0.0
0.0
15.8(e)
(a)Catalysts feed: 1.68 mol% Ru related to stearic acid in Ru-HAP.(b) The yields were based on mole by GC. Others contained cracking products, C18 alcohol and stearyl stearate. (c) 100 mg molecular sieve was added.(d) The solvent was 9:1 hexane: water mixture. (e) The products were: 12.3% C18 aldehyde and 3.5% C18 olefin.
What really interested us was the C17/C18 ratio in products. The hydrodehydration reaction to produce C18 alkane always need acid or acid cites for the favor of dehydration step.[6a]In previous literatures, it always produce C17 alkane over metal-basic catalyst while C18 alkane over metal-acid catalyst.[6]Stoichiometric HAP was a typical basic support,[8, 9h] while, the C17/C18 ratio in this work was about 2.9 in water. To explain the C17/C18 distribution in our catalytic system, a series of experiments were carried out, as shown in Table 6. The C17/C18 ratio was 7.93 in hexane solvent, which was much higher than that in water (Entry 2). It indicated water could promote the C18 production. Because the first step hydrogenation of acid will produce water in-situ unavoidably, two controlled experiments were carried out. Firstly, to avoid the water producing step, C18 alcohol was employed as feedstock. The reaction was very fast in hexane and lead to very low C18 yield (Entry 3). Secondly, to remove the in-situ generated water, 100 mg molecular sieve was added into the reaction in hexane. Only a small amount of C18 alkane was detected (Entry 4). Mixed solvent was also used to explore the reaction. Mixed solvent could lead to remarkable mass transfer resistance since the feedstock in organic phase and the catalyst in water phase. However, regardless of the decreasing ACS Paragon Plus Environment
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reaction rate, when water was added into hexane, the C17/C18 ratio decreased to show a relative favorable hydrodehydration process (Entries 5 and 6). In the 9 hexane: 1 water mixed solvent, the C17/C18 ratios were 4.78 and 5.54 when stearic acid and alcohol were employed as feedstock, respectively. The ratios were still higher than that in pure water, but were much lower than that in pure hexane. Therefore, no matter in-situ production or supplied from solvent, water would promote the hydrodehydration process to produce C18 alkane. Two species might contribute to this promotion: one is the hydrogen ion ionized in hot water, both from stearic acid and water itself, and the other is the calcium vacancy site occupied by hydrogen ion from water on HAP surface. Further investigation will be carried out to explain these results in the future. The variation of C17/C18 ratio in different reaction conditions was also studied. Since the ratio barely changed over different reaction extent, as shown in Figure 9. Thus in the following studies, the reaction time was kept as a constant of 60 min.
Figure 9. Effect of reaction time on stearic acid conversions and C17/C18 ratio. Reaction conditions: 1 mmol stearic acid, 1.68 mol% Ru feed, 180 °C, 2 MPa H2, 15 mL water.
Temperature would affect the C17/C18 ratio remarkably. As shown in Figure 3 and Table 6, entries 710, the C17/C18 ratio decreased from 3.70 to 1.17 as temperature decreasing from 200 to 120 °C. This variation tendency was explained by two synergistic mechanisms. As the reaction routes shown in Scheme 1, the hydrogenation of aldehyde into alcohol was an endothermic reaction, while the
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decarbonylation into C17 alkane was an exothermic one. Accordingly, higher temperature should be in favor of the hydrogenation into alcohol followed by C18 producing, while lower temperature would give rise to dehydrogenation into aldehyde followed by decarbonylation into C17. Moreover, higher temperature would promote the ionization of water and fatty acid to supply hydrogen ion for the acceleration of C18 producing. Therefore, higher temperature could promote the C18 producing process to decrease the C17/C18 ratio. The hydrogen pressure also influenced the C17/C18 ratio remarkably. In this catalytic system, as shown in Figure 4 and Table 6, entries 1, 11 and 12, under 4, 2 and 1 MPa of hydrogen pressure at 180 °C, the C17/C18 ratios were 3.30, 2.90, and 2.51, respectively. It reveals that hydrogen was favor of route (2) decarbonylation to C17 product. To explain this trend, a control experiment for alcohol under argon atmosphere was conducted. No alkanes but 12.3% C18 aldehyde and 3.5% C18 olefin were detected. The aldehyde and olefin came from the dehydrogenation and dehydration of alcohol, respectively. No decarbonylation happened without hydrogen. It indicated that the dehydrogenation and dehydration did not need hydrogen while decarbonylation did. Heyden et. al. have studied the reaction mechanism over Pd catalysts. They find out that the decarbonylation would go through direct C-C hydrogenolysis
or
dehydrogenation-decarbonylation-hydrogenation
tandem
route
via
ketene
intermediate and the former route over Pd catalysts requires hydrogen.[5h] No mechanism over Ru catalysts was reported, but based on the above, the decarbonylation over Ru-HAP would go through direct C-C hydrogenolysis which requires hydrogen. That is, although hydrogen did not exist in decarbonylation reaction equation, it was the activator of the reaction in this catalytic system over RuHAP. Hydrogen should be important to activate the aldehyde or the catalyst for the decarbonylation, but the detailed mechanism was not clear. The experimental results demonstrated that the hydrogen promoted not only the route (1) hydrodehydration, but also the route (2) decarbonylation. Low hydrogen pressure would hinder both routes to C17 and C18, while the former more significant, and thus led to the C17/C18 ratio decrease. 3.5 Catalyst Stability and Recyclability ACS Paragon Plus Environment
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To study the stability and recyclability of the catalyst, a series of experiments and characterizations were conducted. The Ru-HAP and Ru/TiO2 (which performs the second best among Ru catalyst shown in Table 3) were recycled for 5 runs to convert stearic acid, as shown in Figure 10. To demonstrate the possible activity variation, the reaction time was chosen on a non-full conversion node. The Ru-HAP showed almost no deactivation during 5 runs, while Ru/TiO2 showed about 13% deactivation on conversion. Then Ru-HAP catalyst was reused for 5 runs in water with JO, PO or WCO as feedstock, as shown in Figure 11. When JO and PO were employed as feedstock, after 5 runs in 180 °C for 3 h/run, the catalyst also kept stable. In all these recycling tests, the C17/C18 ratio kept same. Even with WCO as feedstock, the activity of the catalyst did not decrease significantly. The very small decrease could be due to the complex impurities in WCO.
Figure 10. Recycling experiments on the hydrogenation of stearic acid over Ru-HAP and Ru/TiO2. Reaction conditions: 1 mmol stearic acid, 1.68 mol% Ru feed, 180 °C, 2 MPa H2, 1 h, 15 mL water.
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Figure 11. Recycling experiments on the hydrogenation of stearic acid, JO, PO and WCO. Reaction conditions for stearic acid: 1 mmol stearic acid, 100 mg Ru-HAP (1.68 mol% Ru feed), 180 °C, 2 MPa H2, 1 h, 15 mL water. Reaction conditions for JO, PO and WCO: 200 mg JO, PO or WCO, 100 mg RuHAP, 180 °C, 2 MPa H2, 3 h, 15 mL water. The excellent stability of Ru-HAP was also studied by ICP-OES of both used catalyst and solution after reaction, as shown in Table 7. Considering of experimental error, Ru kept stable and barely leached in this reaction system because of the anchoring effect of the surface phosphate.[9h] The Ca atom leached about 0.03% each run. Compared with pure HAP, the Ru-HAP revealed much less Ca leach. In Ru-HAP catalyst, HAP not only protected Ru nanoclusters from leach, but also be protected by Ru covering. The supported Ru nanoclusters ion-exchanged the Ca atoms in unstable positions and then protected the adjacent Ca atoms by the interactions among Ca-PO4-Ru. Therefore, Ru-HAP catalyst was very stable during the reaction. Table 7. ICP analysis for the leach of Ru and Ca(a) Ru Runs
Ca
Percentage in
Content in
Percentage in
Content in
catalyst (wt%)
liquid (µg)
catalyst (wt%)
liquid (µg)
Fresh
1.70
-
-
38.26
-
-
1st
1.72
0.35
0.020
38.42
12.6
0.033
2nd
1.69
0.21
0.012
38.13
13.2
0.034
3rd
1.68
0.02
0.001
38.29
11.3
0.030
4th
1.71
0.28
0.017
38.33
12.1
0.032
1.69
0.13
0.008
38.21
11.6
0.030
Water
-
0.06
HAP(d)
-
-
5
th (c)
Leach (%)(b)
Leach (%)(b)
0.12 -
39.88
85.2
0.214
(a) Reaction conditions: 1 mmol stearic acid, 100 mg Ru-HAP (1.68 mol% Ru feed), 180 °C, 2 MPa H2, 1 h, 15 mL water. (b) Leach (%) = 100 * Content in liquid (µg) / [Percentage in catalyst in last run (wt%) * 105(µg) ]. (c) Pure water was also analyzed as blank control group. (d) Pure HAP was also tested in the same reaction conditions.
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To study the hydrothermal stability, hydrothermal test was carried out, as described in the Experimental Section. After treating in 200 °C hot water for 24 h, the catalyst was employed on stearic acid hydrogenation. Same experiment was done with Ru/TiO2 and Ru/La(OH)3 for comparison. The results are shown in Figure 12. After treatment, the activity of Ru/La(OH)3 decreased remarkably. The conversion of stearic acid decreased from 31.9% to 13.2%, and the yield of alkanes decreased from 6.8% to 1.1%. For Ru-HAP and Ru-TiO2, less than 5% and 10% conversion decrease were observed, respectively. For all catalysts, the C17/C18 ratio decreased in different extent. It was proposed that the hydrogen ion ionized from hot water would replace the cation (La3+, Ti4+, or Ca2+) or stay in cationic vacancy while decreased the number of catalytic sites for decarbonylation, and thus would be in favor of C18 production. The deactivation of Ru/TiO2 was not that serious compared with in the recycle experiments, which was because the deactivation was mainly caused by Ru leaching but not the water erosion of the catalyst structure. As discussed above, the anchoring of Ru nanoclusters not only promoted the stability of Ru nanoclusters, but also protected the HAP surface from water erosion.
Figure 12. Hydrothermal stability test of Ru-HAP, Ru/TiO2 and Ru/La(OH)3. Reaction conditions: 1 mmol stearic acid, 1.68 mol% Ru feed, 180 °C, 2 MPa H2, 1 h, 15 mL water. ACS Paragon Plus Environment
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4 Conclusion In summary, a hydroxyapatite-bound ruthenium catalyst (Ru-HAP) was designed, synthesized and employed in the hydrogenation of Jatropha oil, palm oil and waste cooking oil to reach 100% conversion to C15-C18 long-chain alkanes with isolated yields up to 95, 96 and 87 mol% at 180 °C, 2 MPa H2 within 4 h, 4 h and 4.5 h in water, respectively. Stearic acid, as a model compound, reached full conversion and 100 mol% yield to long-chain alkanes at 160 °C, 2 MPa H2 in 5 h or as low as 100 °C, 2 MPa H2 within a longer reaction time of 14 days. The reaction pathways were verified as co-existed hydrodehydration and hydrodecarbonylation routes in water. High temperature and hydrogen pressure promoted the hydrodecarbonylation more significantly than hydrodehydration, and thus lead to a higher C17/C18 alkane product molar ratio. The catalyst was characterized as a highly distributed Ru nanoclusters anchored on HAP support which absorbed fatty acid by forming a meta-stable calcium carboxyl phosphate. The catalyst was proven to be stable by 5 runs recycling, ICP-OES analysis and a hydrothermal treatment experiment. The hydrogenation of oils over Ru-HAP catalyst was high-efficient under mild conditions, and was compatible to most of the impurities except for high concentration of organic basic groups. The feeding oil requires no dehydration before reaction, and the long-chain alkane product can be separated from aqueous solution easily. This green, inexpensive, high-efficient and stable catalytic system revealed high potential for processing different kinds of oils and producing longchain alkanes for diesel fuels. Moreover, combining a commercial isomerization process, oils can also be converted to jet fuel in large scale. Supporting Information
Yield of gas products and carbon balance, summary of reported works, effect of catalyst loading, N2 adsorption/desorption isotherms, and powder XRD patterns.
ACKNOWLEDGMENT
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The authors are also grateful to NSFC (21572213, 21325208), the National Basic Research Program of China (2012CB215306), Anhui Provincial Natural Science Foundation (1408085MKL04), Program for Changjiang Scholars and Innovative Research Team in University of the Ministry of Education of China and the Fundamental Research Funds for the Central Universities (wk 2060190040) for the financial support. REFERENCES [1]
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TABLE OF CONTENT
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