Zirconocene-catalysed biodiesel synthesis from vegetable oil with high free fatty acid contents

Accepted Manuscript Zirconocene-catalysed biodiesel synthesis from vegetable oil with high free fatty acid contents Yiqiang Deng, Xiaojian Hu, Lihua Cheng, Hanlu Wang, Linhai Duan, Renhua Qiu PII:

S0022-328X(18)30517-5

DOI:

10.1016/j.jorganchem.2018.06.021

Reference:

JOM 20480

To appear in:

Journal of Organometallic Chemistry

Received Date: 27 April 2018 Revised Date:

12 June 2018

Accepted Date: 24 June 2018

Please cite this article as: Y. Deng, X. Hu, L. Cheng, H. Wang, L. Duan, R. Qiu, Zirconocene-catalysed biodiesel synthesis from vegetable oil with high free fatty acid contents, Journal of Organometallic Chemistry (2018), doi: 10.1016/j.jorganchem.2018.06.021. 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

Zirconocene-catalysed biodiesel synthesis from vegetable oil with high free fatty acid contents

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Yiqiang Denga,*, Xiaojian Hub,c,*, Lihua Chenga, Hanlu Wanga, Linhai Duana, Renhua Qiuc,*

College of Chemical Engineering, Guangdong University of Petrochemical

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a

b

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Technology, Maoming 525000, Guangdong, China

Department of Chemistry, School of Basic Medicine, Changsha Medical University, Changsha, 410219, Hunan, China. c

College of Chemistry and Chemical Engineering, Hunan University, Changsha,

*

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410082, Hunan, China.

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Corresponding author:

Y.Q. Deng, Tel/Fax: +86-668-2981080; E-mail: [email protected], X.J. Hu, Tel/Fax: +86-731-88602817; E-mail: [email protected], R.H. Qiu, Tel/Fax: +86-731-88821171; E-mail: [email protected]

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ACCEPTED MANUSCRIPT 1. Introduction The quest for alternative sources of energy has become a main research area in chemical industries owing to the increasing demand for energy, necessity to lower

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the emission of greenhouse gases and environmental pollution, and fast diminishing supply of fossil fuels [1]. Biodiesel is a diesel-fuel substitute composed of fatty acid esters obtained from renewable sources (i.e. vegetable oils,

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VOs) by catalytic transesterification with primary aliphatic alcohols, regarded as a

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promising alternative sources of energy [2]. The alcoholysis of VOs for biodiesel production has attracted much attention, since VOs are relatively cheap raw materials widely abundant in nature [3]. However, because of the undesirable saponification of their high free fatty acid contents, biodiesel synthesis usually

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involves direct esterification of free fatty acids (FFAs) and transesterification of triglycerides (TGs) with alcohols [4]. A recent example of industrial biodiesel production from VOs using alkaline catalysts still required the pre-esterification of

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FFAs before the transesterification of TGs, resulting in energy waste [5]. Instead,

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the enzymatic production of biodiesel from VOs successfully combines these two reactions [6]. However, the requirements for a high-quality final product and reduction in wastewater production during the separation and purification steps, together with the high cost of the enzyme, makes the production of biodiesel by clean and sustainable biocatalysis still doubtful [7]. Our interest in Lewis acid chemistry has greatly contributed to organic synthesis, especially in the above two key reactions used in biodiesel production, namely

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ACCEPTED MANUSCRIPT esterification and transesterification [8-11]. Various Lewis acid catalytic systems have been used in (trans)esterifications, including organotin complexes as well as alkylphenylsulfates [12-13]. Zirconocene shows high catalytic activity in a variety

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of Lewis-acid-catalysed reactions [14], such as the Mannich reaction, allylation of aldehydes, Friedel–Crafts acylation, as well as esterifications, such as Iglesias et al. prepared Zirconium-containing SBA-15 materials and used as catalyst in the

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production of fatty acid methyl esters from low grade oleaginous feedstock.

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Catalytic assays in continuous mode in a fixed bed reactor showed a higher resistance of Zr-SBA-15/bentonite pellets against catalyst deactivation[15-17]. Herein, we report that the incorporation of a large electron-withdrawing and hydrophobic counter anion results in an efficient air-stable and water-tolerant

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zirconocene catalyst (1) for biodiesel synthesis from vegetable oil with high free fatty acid contents. The efficiency of the reaction results from a combination of the direct esterification of free fatty acids (FFAs) and transesterification of

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triglycerides (TGs) in one-pot. Furthermore, we found that this catalyst behaves as

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a reaction-induced self-separation catalyst in the synthesis of biodiesel from commercial oleifera. During the course of the reaction, the reaction switches from homogeneous to heterogeneous. Upon completion of the reaction, the catalyst precipitates as a white solid, which after a simple separation can be easily recycled five times. 2. Experimental 2.1. General method

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ACCEPTED MANUSCRIPT All chemicals were purchased from Aldrich. Co. Ltd and used as received unless otherwise indicated. The preparation of catalyst was carried out under nitrogen atmosphere with freshly distilled solvents unless otherwise noted. THF and hexane

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were distilled from sodium/benzophenone. Acetonitrile was distilled from CaH2. The NMR spectra were recorded at 25 °C on INOVA-400M (USA) calibrated with tetramethylsilane (TMS) as an internal reference. Elemental analyses were

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performed by VARIO EL III. TG-DSC analysis was performed on a HCT-1

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(HENVEN, Beijing, China) instrument. The acidity was measured by Hammett indicator method as described previously. Acid strength was expressed in terms of Hammett acidity function (Ho) as scaled by pKa value of the indicators. 2.2 Preparation of Cp2Zr(H2O)3(OSO2C8F17)2·THF (1)

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To a solution of Cp2ZrCl2 (292 mg, 0.99 mmol) in THF (20 mL) was added a solution of AgOSO2C8F17 (1.21 g, 2.0 mmol) in THF (10 mL). The mixture was stirred in the dark at 25 °C for 1 h, and subject to filtration. The filtrate was

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combined with dry hexane (40 mL). Then, the solution was stored in the

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refrigerator for 24 h to furnish colorless crystals of 1· THF(794 mg, 65%): M.p.133-136 °C. 1H NMR (400 MHz, Acetone-d6): δ = 6.76 (s, 10 H, CpH), 3.63 (t, J = 5.6 Hz, 4 H, THF), 1.82 – 1.76 (m, 4 H, THF);

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F NMR (376 MHz;

Acetone): δ = -81.65 (t, J = 9.8 Hz, 3 F, CF3–), -115.02 (s, 2 F, –CF2–), -121.05 (s, 2 F, –CF2– ), -122.17 – -122.48 (m, 6 F, –(CF2)3–), -123.28 (s, 2 F, –CF2–), -126.75 – -126.82 (m, 2 F, –CF2–).

Elemental analysis for Cp2Zr(OSO2C8F17)2

after pumping for a week: calcd. (%) for C26H10F34O6S2Zr: C, 25.60; H, 0.83;

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ACCEPTED MANUSCRIPT found: C, 25.67; H, 0.82. Elemental analysis for Cp2Zr(OSO2C8F17)2·4H2O after standing in open air for 2 days: calcd (%) for C26H18F34O10S2Zr: C, 24.18; H, 1.40; found: C, 24.34; H, 1.33. C30H24F34O10S2Zr, Prismatic, colorless, Mr = 1345.83,

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Dx = 1.905 Mg m−3, Triclinic, P¯ 1, a = 9.9295 (13) Å, b = 11.9551 (16) Å, c = 20.269 (3) Å, α = 82.833 (3)°, β = 79.491 (3)°, γ = 87.397 (3)°, V = 2346.7 (5) Å3, Z = 2, θ = 1.7–25.5°, 0.50 × 0.24 × 0.21 mm,T = 293 (2) K, measured

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reflections/independent reflections 12436/8583, Rint = 0.104, h = −12-11,k =

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−14-11, l = −24-22, R1 = 0.095,wR2 = 0.277, S = 0.95.CCDC No. 631296. 2.3 Typical procedure for direct esterification of alcohol with oleic acid using catalyst 1.

To a round-bottom flask was added ethanol (46 mg, 1.0 mmol) and 1 equivalent of oleic acid (282 mg, 1.0 mmol) and catalyst 1 (12.6 mg, 0.01 mmol, 1.0 mol% relative

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to ethanol). The mixture was stirred at 100°C for 24 h and monitored by TLC. Then the mixture was diluted with petroleum ether (10 mL × 3). By means of filtration, the catalyst was separated and used for the next cycle, and the filtrate was washed twice with 10 mL of saturated brine, and extracted by petroleum ether (10 mL × 2).

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Subsequently the portions of petroleum ether were combined together, dried by sodium sulfate, and evaporated to obtain the crude ester. Finally, the ester was subject

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to short flash column chromatography on silica gel (petroleum ether: ethyl acetate = 20:1, Rf = 0.4) to afford the colorless liquid, yield, 89%. 2.4 Typical procedure for transesterification of alcohol with triolein using catalyst 1.

To a round-bottom flask was added ethanol (138 mg, 3.0 mmol) and 1 equivalent of triolein (885 mg, 1.0 mmol) and catalyst 1 (37.8 mg, 0.03 mmol, 1.0 mol% relative to ethanol). The mixture was stirred at 100 °C for 24 h and monitored by TLC. Then the mixture was diluted with petroleum ether (10 mL × 3). By means of filtration, the catalyst was separated and used for the next cycle, and the filtrate was washed twice 5

ACCEPTED MANUSCRIPT with 10 mL of saturated brine, and extracted by petroleum ether (10 mL × 2). Subsequently the portions of petroleum ether were combined together, dried by sodium sulfate, and evaporated to obtain the crude ester. Finally, the ester was subject to short flash column chromatography on silica gel (petroleum ether: ethyl acetate =

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20:1, Rf = 0.4) to afford the colorless liquid, yield, 85%. Methyl oleate (5) 1

H NMR (400 MHz, CDCl3) δ 5.35 – 5.29 (m, 2H), 3.63 (s, 3H), 2.29-2.25 (m, 2H),

2.05 – 1.98 (m, 4H), 1.61-1.58 (m, 2H), 1.26-1.23 (m, 20H), 0.87-0.85 (m, 3H);

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C

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NMR (101 MHz, CDCl3) δ 174.19, 129.97, 128.02, 51.35, 34.05, 31.91, 31.52, 29.76, 29.67, 29.58, 29.53, 29.46, 29.35, 29.32, 29.26, 29.16, 29.11, 29.08, 27.19, 27.17,

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25.61, 24.93, 22.68, 22.57, 14.08, 14.04. Ms (EI): m/z = 296.2 [M+H]+ . Ethyl oleate (7) 1

H NMR (400 MHz, CDCl3) δ 5.35-5.33 (m, 2H), 4.14-4.09 (m, 2H), 2.34 – 2.21 (m,

2H), 2.05-2.00 (m, 4H), 1.63-1.61 (m, 2H), 1.30-1.23 (m, 23H), 0.88 (t, J = 5.6 Hz, 3H);13C NMR (101 MHz, CDCl3) δ 173.89, 130.05, 128.04, 60.15, 34.38, 31.92,

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31.54, 29.78, 29.70, 29.60, 29.54, 29.33, 29.18, 29.12, 27.21, 25.63, 24.98, 22.70, 22.59, 14.26, 14.12, 14.08.Ms(EI) : m/z = 310.2 [M+H]+.

The

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3. Results and discussion synthesis

of

zirconocene

bis(perfluorooctanesulfonate)

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[Cp2Zr(H2O)3(OSO2C8F17)2] (1) is straightforward and involves the treatment of Cp2ZrCl2 with AgOSO2C8F17 in THF in the absence of light for one hour according to our reported procedure (Fig. 1) [10]. Complex 1 shows strong Lewis acidity (0.8
ACCEPTED MANUSCRIPT direct esterification and transesterification reactions (Scheme 1). Thus, the (trans)esterification of pure oleic acid or triolein with ethanol in a strict 1:1 ratio (ratio of R groups of 2 or 3 to ethanol) in the presence of 1 mol% of 1 at 100 °C for

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24 h affords product 5 in 89% and 85% yield, respectively. Increasing the ratio from 1:1 to 1:2 relatively increases the yield of 5 to 93% and 92%, respectively. Therefore, the two basic reactions for the transformation of VOs into biodiesel are

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successfully achieved.

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We hence applied catalyst 1 for the transformation of VOs to biodiesel.Various types of crude VOs containing FFAs and TGs in different molar ratios were selected as the raw material to test the catalytic efficiency; the results are summarized in Table 1.

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Since oleifera is mainly composed of FFAs and TGs, we first applied our catalyst to the transformation of a mixture containing the reported ratio of pure FFAs and TGs for oleifera, thus simulating the composite of the commercial

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oleifera. This mixture was efficiently and simultaneously transesterified and

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directly esterified using 1 mol% of catalyst 1 and two equivalents of ethanol at 100 °C (the loadings of catalyst 1 and ethanol were based on the oleic functional group in oleifera) to produce biodiesel in 94% yield (Table 1, entry 1); the conversion of FFAs and TGs was 93% and 97%, respectively (entry 1). The products were analysed by comparing their 1H NMR spectra with that of biodiesel obtained via the commercial synthetic method using the same tea seed oil as starting material. Subsequently, we applied our catalyst to transform mixtures of

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ACCEPTED MANUSCRIPT pure FFAs and TGs simulating other VOs, such as canola, palm, soybean, cottonseed and sunflower (entries 2–6); the yield of the desired ester 5 was 78%, 77%, 82%, 66% and 84%, respectively. These results suggest that the higher the

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concentration of FFAs in the VO mixture, the higher is the yield of biodiesel produced via our method, and that the TGs are transesterified before FFAs are

between the products and TGs and FFAs.

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transformed to the desired ester, which may be due to the dynamic balance

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The reaction can be scaled up to 31 mmol (8.83 g of oleifera), affording 5 with a 92% yield (Scheme 2). Moreover, the catalyst loading can be reduced to 0.5 mol%, affording 5 in 82% yield. Similarly, the reaction with methanol gives the corresponding product (7) in 92% and 80% yields using 1 mol% and 0.5 mol% of

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1, respectively. The reduction of catalyst loading represents a significant reduction in the amounts of fluorine-containing compounds that might leak into the

applications.

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environment, which makes the use of this catalyst advantageous in industrial

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Since the mixture simulating oleifera was successfully converted to desired biodiesel, we then used commercial oleifera (containing 2‒4 wt% H2O) as starting material; the result is show in Fig. 2. The reaction using 1 mol% of catalyst 1 afforded 5 in only 60% isolated yield possibly due to the water contained in the starting material. Interestingly, when the volume of ethanol was increased tenfold (40 mL) and catalyst 1 loading was 2.7 mol%, a self-separation of the catalyst from the reaction mixture occurred after 48 hat 80 °C and product 5 was obtained

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ACCEPTED MANUSCRIPT with 92% yield (Fig. 2). At the beginning of the reaction, the reactants are well dissolved, except for complex 1 (Fig. 2a), which only dissolves partially at a loading of 2.7 mol% (the

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loading of catalyst 1 and ethanol are based on the oleic functional group in oleifera). At the end of the reaction, complex 1 precipitates from the reaction mixture plausibly due to a polarity change of the reaction system (Fig. 2c). In

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homogeneous catalysis (Fig. 2b), all catalytic sites are accessible and fully utilized,

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and the chemoselectivity of the reaction can be easily modified. On the other hand, in heterogeneous catalysis, the catalyst can be easily recovered and recycled. Hence, our method offers the advantages of both homogeneous and heterogeneous catalysis.

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Since the catalyst can be easily recovered from the transformation of commercial oleifera into biodiesel, we then evaluated its recyclability. As shown in Table 2, the catalyst can be easily recycled five times without a significant loss

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in catalytic efficiency. The recovered catalyst was analysed by

1

H NMR

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spectroscopy,which showed that the recovered catalyst was the same as the fresh catalyst, implying that the catalyst is suitable for recycling, chemically stable, as its structure is not destroyed by the reaction media and substrates, and thermally stable as it withstands a temperature of 80 °C for five cycles. A possible explanation for the reaction-induced self-separation ability of catalyst 1 in the transformation of commercial oleifera to biodiesel is the special structure of the catalyst. As shown in Fig. 3, the C8F17 chains of the anion are

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ACCEPTED MANUSCRIPT clustered together to produce hydrophobic domains, which generate three separate areas in the crystal structure of the catalyst. One area is the hydrophobic and lipophobic C8F17 group, which acts as a shield and enables the Lewis acid centre to

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be water-tolerant and air-stable. A second area is the lipophilic cyclopentadienyl region, which dissociates from the organic substrate and acts as an organic directing group; the third area is the zirconium cationic ion Lewis acid centre,

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which acts as a hydrophilic area and allows the coordination of water molecules,

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and is where the reaction takes place. Upon completion of the reaction, the lipophilic ester dissociates from the cyclopentadienyl group and the hydrophilic side products (alcohol or water) dissociate from the coordinated water molecules, pushing the equilibrium towards the formation of the product. The produced ester

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and water molecules leave the catalyst due to the hydrophobic nature of its interior. Furthermore, the self-separation ability of the desired ester and side

step.

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products (alcohol or water) facilitates the precipitation of the catalyst in the final

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Based on the current findings and literature reports, we proposed the catalytic process as follows (Fig. 4): first, the organic substrates approach the C8F17 hydrophobic

and

lipophobic

area,

then

dissociate

from

the

organic

cyclopentadienyl ligand, and consequently coordinate with the zirconium Lewis acid centre through exchange of the three coordinated water molecules. This leads to the activation of the carbonyl group of the starting material, which can then easily react with the alcohol to form a new C–O bond. After rearrangement of the

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ACCEPTED MANUSCRIPT carbonyl group, the desired product is formed and the catalyst liberated. However, the real catalytic mechanism is still under investigation in our lab. 4. Conclusion

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In summary, we have developed a highly efficient simultaneous transformation of the two components (FFAs and TGs) of vegetable oils (VOs) to biodiesel by combining the direct esterification of free fatty acids (FFAs) and transesterification of (TGs)

using

the

air-stable

and

water-tolerant

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triglycerides

zirconocene

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perfluorooctanesulfonate Lewis acid. The catalyst, when used for the transformation of commercial oleifera to biodiesel, behaves as a reaction-induced self-separation catalyst that facilitates the separation, recovery, and recyclability of the catalyst. Acknowledgment

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This work was financially supported by Science and Technology Planning Project of Guangdong Province (2014A010105051, 2016B020211002), National Natural Science Foundation of China (21403038, 21676076), the Scientific Research

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Starting Foundation for Doctors of Guangdong University of Petrochemical

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Technology (2015rc04) and the Funding for the scientific research project of the Hunan Provincical Education Department (17C0150). The authors thank Profs. Akihiro Orita and Junzo Otera (Okayama University of Science) and Profs. Xinhua Xu and Shuang-Feng Yin (Hunan University) and Prof. Lifen Peng (Hunan University of Science and Technology) for their helpful discussion.

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ACCEPTED MANUSCRIPT References [1] D.S. Mannel, M.S. Ahmed, T.W. Root, S.S. Stahl, J. Am. Chem. Soc. 139 (2017) 1690-1698.

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[2] H. Zhong, M. Watanabe, H. Enomoto,F. Jin, A. Kishita, TM. Aida, R.L. Smith Jr, Energy Fuels 30 (2016) 4841-4847.

[3] J.D. Roo, I.V. Driessche, J.C. Martins, Z. Hens. Nature Mat. 15 (2016) 517.

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[4] N. Budisa, J.S. Völler, B. Koksch, C.G. Acevedo-Rocha, V. Kubyshkin F.

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Agostini, Angew. Chem. Int. Ed. 56 (2017) 9680-9703.

[5] M. Al-Sabawi, J. Chen S. Ng, Energy Fuels 26 (2012) 5355-5372. [6] E. Su, P. You, D. Wei, Bioresour. Technol. 100 (2009) 5813-5817. [7] A.F. Lee, J.A. Bennett, J.C. Manayil, K. Wilson, Chem. Soc. Rev. 43 (2014)

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7887-7916.

[8] P. Wang, C.T. Au, R. Qiu, X. Xu, S.F. Yin, Adv. Synth. Catal. 358 (2016), 1302-1308.

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[9] J. Wang, N. Li, R. Qiu, X. Zhang, X. Xu, S.F. Yin, J. Organomet Chem. 2015,

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785(36): 61-67.

[10] X. Zhang, X. Xu, N. Li, z. Liang, Z. Tang. Tetrahedron, 2018, 74: 1926-1932. [9] N. Li, R. Qiu, X. Zhang, Y. Chen, S.F. Yin, X. Xu, Tetrahedron 71 (2015) 4275-4281. [10] R. Qiu, X. Xu, L. Peng, Y. Zhao, N. Li, S.F. Yin, Chem. Eur. J. 18 (2012), 6172-6182.

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ACCEPTED MANUSCRIPT [11] Z. Tang, Q. Jiang, L. Peng, X. Xu, J. Li, R. Qiu, C.T. Au. Green Chem. 19 (2017), 5396-5402. [12] A. Orita, S. Tanabe, T. Ono, J. Otera, Adv. Synth. Catal. 352 (2010)

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1419-1423. [13] K. Manabe, S. Iimura, X. Sun, S. Kobayashi, J. Am. Chem. Soc. 124 (2002) 11971-11978.

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[14] A. Saito, Y. Uematsu, K. Sodo, Y. Hanzawa, Adv. Synth. Catal. 357 (2015)

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1049-1052.

[15] J. Iglesias, J.A. Melero, L.F. Bautista, G. Morales, R. Sánchez-Vázquez. Catalysis Today, 2014, 234(7): 174-181.

[16] R. Sánchez-Vázquez, C. Pirez, J. Iglesias, K. Wilson, A. Lee, J.A. Melero.

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ChemCatChem, 2013, 5(4): 994-1001.

[17] J. Iglesias, J.A. Melero, L.F. Bautista, G. Morales, R. Sánchez-Vázquez, M.

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Andreola, A. Lizarraga-Fernández. Catalysis Today, 2011, 167(1): 46-55.

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ACCEPTED MANUSCRIPT Figure captions Fig. 1 Synthesis of zirconocene bis(perfluorooctanesulfonate) Fig. 2 Photographs of the transformation of commercial oleifera to biodiesel

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catalysed by zirconocene bis(perfluorooctanesulfonate).(a, left) At the beginning of the reaction; (b, middle) homogeneous mixture during the reaction at 80 °C; (c, right) upon completion, the reaction becomes heterogeneous: the upper layer

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contains the product and unconsumed reactants, while the precipitate at the bottom

Fig. 3 X-ray structure of catalyst 1.

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is catalyst 1 in its hydrated form.

Fig. 4 A possible catalytic mechanism for the current catalytic reaction. Scheme 1. Zirconocene(1)-catalysed (trans)esterification(the loadings of catalyst 1

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and ratio of 2:4 or 3:4 are based on the oleic functional group R and R’ of 4). Scheme 2. Application of zirconocene bis(perfluorooctanesulfonate) in biodiesel synthesis from oleifera (the loadings of catalyst 1 are based on the oleic functional

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group in oleifera)

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ACCEPTED MANUSCRIPT Table 1 Transformation of various types of VOs to biodiesel catalysed by 1a

Conv. of

2:3

3 (%)

Ent. VOs

1:12.5

97

93

94

2

canola

1:5

98

66

78

3

palm

1:2.08

99

44

77

4

soybean

1:1.04

99

31

82

5

cottonseed

1:0.78

92

-

66

6

sunflower

1:0.55

98

9

84

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oleifera

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1

Catalyst 1 (0.01 mmol); loadings of

5 (%)

1 and 4 as well as isolated yield of 5 were

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a

2 (%)

Yield of

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Molar ratio Conv. of

calculated based on R groups in 2 and 3.

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biodiesela

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Table 2 Recyclability of catalyst 1 in the transformation of commercial oleifera to

a

Cycle

1

2

3

4

5

Yield(%)

92

92

92

90

90

Recov. Cat.(%)

95

94

92

93

94

Conditions: EtOH (40 mL), Catalyst 1(1 mol%), commercial olefiera (9.03 g), reflux,

48 h.

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commercial oleifera

80 oC, 48 hrs

4 40 mL

9.03 g 31 mmol ,oleic functional group

OH

RCOOEt + HO 5, 92%

OH 6

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R = CH3(CH2)7CH=CH(CH 2)6CH2-

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Fig. 3

+ EtOH

1 (2.7 mol%)

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Fig. 2

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Fig. 1

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Fig. 4

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Scheme 2.

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Scheme 1.

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ACCEPTED MANUSCRIPT Fig. 2 Photographs of the transformation of commercial oleifera to biodiesel catalysed by zirconocene bis(perfluorooctanesulfonate).(a, left) At the beginning of the reaction; (b, middle) homogeneous mixture during the reaction at 80 °C; (c,

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right) upon completion, the reaction becomes heterogeneous: the upper layer

is catalyst 1 in its hydrated form.

Fig. 2

4

9.03 g 31 mmol ,oleic functional group

40 mL

1 (2.7 mol%) 80 o C, 48 hrs

OH

RCOOEt + HO

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commercial oleifera

+ EtOH

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contains the product and unconsumed reactants, while the precipitate at the bottom

5, 92%

OH 6

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R = CH 3(CH 2) 7 CH=CH(CH2) 6CH2-

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Highlights: Air-stable and water-tolerant Zirconocene Lewis acid catalysts were synthesized. The catalyst is highly efficient for transformation of vegetable oils into biodiesel. Zirconocene behaves as a reaction-induced self-separation catalyst in the

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reaction.