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Hydrodeoxygenation of oleic acid into n- and iso-paraffin biofuel using zeolite supported fluoro-oxalate modified molybdenum catalyst: Kinetics study O.B. Ayodele a,d,∗, Hamisu U. Farouk b, Jibril Mohammed c, Y. Uemura d, W.M.A.W. Daud a,∗ a
Department of Chemical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur, Malaysia Department of Pure and Industrial Chemistry, Faculty of Science, Bayero University Kano, P.M.B. 3011, Kano State, Nigeria Department of Chemical Engineering, Abubakar Tafawa Balewa University, P.M.B 0248, Bauchi, Bauchi State, Nigeria d Centre for Biofuel and Biochemical Research, Department of Chemical Engineering, Universiti Teknologi PETRONAS, Tronoh, Perak, Malaysia b c
a r t i c l e
i n f o
Article history: Received 18 August 2014 Revised 11 December 2014 Accepted 14 December 2014 Available online xxx Keywords: Molybdenum oxalate Hydrodeoxygenation Oleic acid Isomerization Biofuel
a b s t r a c t The activity of zeolite supported fluoride-ion functionalized molybdenum-oxalate catalyst (FMoOx/Zeol) and its kinetic study on the hydrodeoxygenation (HDO) of oleic acid (OA) is presented in this report. The FMoOx/Zeol was synthesized via simple dissolution method and characterized. The results revealed formation of highly reactive octahedral Mo species with enhanced textural and morphological properties. The FMoOx/Zeol activity on the HDO of OA at the best observed experimental conditions of 360°C, 30 mg FMoOx/Zeol and 20 bar produces 64% n-C18 H38 and 30% iso-C18 H38 in 60 min. The acidity of FMoOx/Zeol was responsible for the production of the iso-C18 H38 . The kinetic data showed that sequential hydrogenation of OA into stearic acid (SA) was faster than the HDO of SA into biofuel with activation energies of 98.7 and 130.3 kJ/mol, respectively. The reusability studies showed consistency after three consecutive runs amounting to 180 min reaction time. The results are encouraging towards industrial application. © 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction Globally, attention is fast shifting to the application of biomass as a source of fuel for the nearest future especially for transportation due to the projected decline in fossil fuel reserves. Other reasons include rise in petroleum prices and the attendant environmental impact of its exploration, processing and especially the exhaust gases from petrol/diesel engines [1,2]. As an alternative to this fossil fuel shortcoming, production of both bio-ethanol fuel (BEF) from carbohydrate especially corn via enzymatic transformation, and fatty acid methyl ester (FAME) biodiesel from transesterification of triglycerides with methanol have received tremendous attention in recent years. However, the conflict of BEF from carbohydrate feedstock has limited the expected popularity of its production since most developing countries still largely rely on carbohydrate as the commonest staple food source. On the other hand, the shortcoming of FAME biodiesel such as higher viscosity, higher cloud point temperature, poor oxidation stability, poor storage ability, glycerol by-product menace and lower energy density is challenging its future economic and technical reliability [3,4]. Consequently, it is blended with conventional
∗
Corresponding author. Tel:. +60 164955453. E-mail address:
[email protected] (O.B. Ayodele).
petroleum diesel to produce a blended fuel of 20% biodiesel and coded B20 in the US. In an attempt to achieve a 100% renewable fuel, catalytic deoxygenation of triglycerides and free fatty acids (FFAs) has been proposed and is currently being widely studied both in the presence of hydrogen gas – hydrodeoxygenation (HDO) [1,3–6] and in the absence of hydrogen gas – decarboxylation and decarbonylation (Decarbs) [7,8]. Details of the two processes that have been carefully reviewed [6] and compared [8] showed that HDO is more prospective because its products are mostly paraffin with similar properties to the conventional diesel fuel compared to mixtures of paraffin and other condensation products such as esters and ketones observed in Decarbs which adversely reduces the energy density [1,4,8]. In addition, HDO process can be adapted into hydrotreating units (HDTU) of existing conventional refineries without serious modification [9]. Finally, the fast rate of catalyst deactivation in Decarbs processes has eventually made it less attractive as compared to the HDO [7]. In attempt to deepen research into the HDO process, effects of process variables such as temperature, H2 gas flow rate, pressure and type of the catalyst have been well studied [1–4,9]. However, since it has been considered that the existing HDTU of conventional refineries can be adapted, studies on developing suitable catalysts such as types of the support and metals [10], catalyst preparation procedure [2,9] and additives such as sulfur [2] and phosphorus [11] are currently at the
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Please cite this article as: O.B. Ayodele et al., Hydrodeoxygenation of oleic acid into n- and iso-paraffin biofuel using zeolite supported fluoro-oxalate modified molybdenum catalyst: Kinetics study, Journal of the Taiwan Institute of Chemical Engineers (2015), http://dx.doi.org/10.1016/j.jtice.2014.12.014
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fore. Various sulfide catalysts such as NiMo/Al2 O3 and CoMo/Al2 O3 have been synthesized and tested on various feed stocks and their results according to the authors [12,13] showed enhanced HDO efficiency compared to the non-sulfide ones, and in addition isomerized products were also observed. As an alternative to sulfide modification, NiMo/Al2 O3 catalyst was modified with fluorine to increase the acidity and it was reported to be highly favorable for paraffin skeletal isomerization, although it gradually loses its isomerization activity due to leaching of the fluoride contents [4]. Generally, the presence of isomerized product is considered an advantage due to the ability of iso-paraffin to lower the biofuel freezing point which in turn will enhance its cold flow properties such as cold filter plugging point [4]. Recently, Li et al. [2] in a study on series of NiMo/γ -Al2 O3 catalysts with organic functionalization using different quantities of urea reported that urea improves the solubility of Mo and Ni salt in the support and also facilitates the formation of molybdate and polymolybdate, which in turn enhances its morphology, textural and catalytic activity due to better porosity, well dispersed active particles, increased octahedral molybdenum/nickel oxides and proper acidity. Similarly, Sousa et al. [9] reported that expedient synthesis (such as temperature programmed carburization methodology) of supported molybdenum carbide (Mo2 C/Al2 O3 ) as single metal catalyst gives excellent hydrotreating activity as an alternative to the sulfide and bimetal catalysts. In view of the aforementioned studies, this study investigates the applicability of an expediently synthesized organometallic catalyst via the functionalization of molybdenum with oxalic acid to form poly-molybdenum-oxalate complex (MoOx). The MoOx was modified with fluoride ion (to increase the acidity for paraffin skeletal isomerization) and supported on zeolite A in view of its high thermal and structural stability. In addition, it is currently being cheaply produced with improved structural stability from coal fly ash (CFA) which hitherto is the waste product of combustion of coal in coal-fired power stations with about 800 million tons per annum CFA production [14]. The synthesized fluoro-molybdenum-oxalate zeolite supported catalyst (FMoOx/Zeol) was characterized for the physical and chemical properties and its HDO and isomerization activities were tested on the upgrading of oleic acid into biofuel. 2. Experimental 2.1. Materials Analytical grade zeolite A and hydrofluoric acid (68%) were purchased from F.S. Chemicals, while bis(acetylacetonato)dioxomolybdenum(VI) and anhydrous oxalic acid are from Sigma–Aldrich. High purity oleic acid (99%) used as the model bio oil was purchased from Sigma–Aldrich, Germany. All materials were used without any pretreatment. 2.2. Catalyst development The catalyst was developed by first synthesizing the molybdenum oxalate catalyst precursor from stoichiometric ratio of 6.81 g of bis(acetylacetonato)dioxomolybdenum(VI) and oxalic acid (OxA) at 60 ºC in an aluminum foil wrapped conical flask because of metal oxalate high photo sensitivity index [15]. As the reaction proceeds drops of 4 M hydrofluoric acid were intermittently added until the pH was observed to decrease from the in situ 5.2 to 3.7 ± 0.3 [16] (as monitored by EcoScan SC11-4115, Exatech Enterprise pH meter) to ensure the formation of the fluoro-molybdenum-oxalate (FMoOx) complex. The FMoOx was then added to 20 g zeolite (Zeol) dispersion under brisk stirring at 70 ºC for 4 h and allowed to age for 1 h, followed by filtration, washing and drying in the oven at 120 ºC for 12 h. The synthesized fluoro-molybdenum-oxalate zeolite supported catalyst (FMoOx/Zeol) was then grinded and calcined at 400 ºC since higher
temperatures can completely decompose the MoOx. For the purpose of study of effect of fluoride ion and oxalic acid functionalization in FMoOx/Zeol, molybdenum-oxalate and inorganic Mo salt were incorporated into Zeol to synthesize MoOx/Zeol and Mo/Zeol, respectively using the same synthesis condition of FMoOx/Zeol. 2.3. Catalyst characterization Thermal gravimetric analysis (TGA) was carried out with a SHIMADZU DTG-60/60H instrument to determine the heat treatment required during calcination. 2 g of each sample was heated in a silica crucible at a constant heating rate of 10 °C/min operating in a stream of N2 atmosphere with a flow rate of 40 mL/min from 30 to 800 °C and the weight loss per time, weight loss per temperature increment and temperature increment versus time were recorded. X-ray fluorescence (XRF) analysis of the samples were done using a μXay μEDX 100 Schmadzu, NY and X-ray tube of rhodium anode and scintillation detector operating on a 40 mA current and 40 mV voltage to determine the chemical composition of the sample. High-energy X-rays were used to bombard the samples pressed into circular discs to cause ionization of their component atoms. The X-ray reflections from the excited samples were detected by the scintillation detector which essentially consists of a 3–5 mm thick silicon junction type p-i-n diode with a bias of −1 kV across it. The detected spectra were amplified and recorded using the computer program installed on the XRF analyzer. Energy dispersive X-ray (EDX) was performed to determine the elemental composition variation in the FMoOX/Zeol compared with the Zeol using EDX microanalysis system (Oxford INCA 400, Germany) connected to the FESEM machine. The EDX analysis used Mn-Kα as the energy source operated at 15 kV of accelerating voltage, 155 eV resolutions and 22.4° take off angle. Scanning electron microscopy (SEM) was used to study the surface morphology of all the samples. The analysis was carried out using a scanning electron microscope (Model EMJEOL- JSM6301-F) with an Oxford INCA/ENERGY-350 microanalysis system. The samples were evenly distributed on a black double sided carbon tape attached to the aluminum stub and vacuumed for about 10 min prior to analysis. X-ray diffraction (XRD) patterns of the samples were measured with Philip PW 1820 diffractometer to determine the crystal phase and structure of the metal oxides earlier detected by XRF analysis. Diffraction patterns of the samples were recorded with Cu Kα radiation and recorded in the range of 5–90° (2 theta) with a scanning rate of 2°/min and a step size of 0.01°. The X-ray tube was operated at 40 kV and 120 mA. Fourier transformed infrared (FTIR) spectroscopy analyses were performed on the samples to determine the functional groups present in order to understand the chemistry of the synthesized catalyst with respect to the support. The instrument used is Perkin-Elmer Spectrum GX Infrared Spectrometer with resolution of 4 cm−1 operating in the range of 4000–400 cm−1 . The Raman spectra of all the samples were obtained with a Spex Triplemate spectrograph coupled to a Tracor Northern 1024 large area intensified diode array detector. The excitation source was a 488-nm line (Lexel Model No. 95 Ar+ ) laser with a grating monochromator used to reject any spurious lines and background from the laser before the radiation entered the spectrometer. The spectra were taken with 1 cm−1 resolution. Nitrogen adsorption–desorption measurements (BET method) were performed at liquid nitrogen temperature (−196 °C) with an autosorb BET apparatus, Micromeritics ASAP 2020, surface area and porosity analyzer to determine the surface area, pore size and structure, and the pore volume. Before each measurement, the samples were first degassed at 350 °C for 2 h and thereafter kept at liquid nitrogen temperature to adsorb nitrogen. 2.4. Oleic acid hydrodeoxygenation experiments Hydrodeoxygenation of oleic acid (OA) was conducted using a 100 mL high pressure semi-batch reactor. The reaction temperature
Please cite this article as: O.B. Ayodele et al., Hydrodeoxygenation of oleic acid into n- and iso-paraffin biofuel using zeolite supported fluoro-oxalate modified molybdenum catalyst: Kinetics study, Journal of the Taiwan Institute of Chemical Engineers (2015), http://dx.doi.org/10.1016/j.jtice.2014.12.014
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3
100 Zeol
Weight loss (%)
95
FMoOx/Zeol FMoOx/Zeol (uncalcined)
90
85
80
0
100
200
300 400 Temperature (ºC)
500
600
Fig. 1. TGA profiles of Zeol, FMoOX/Zeol (uncalcined) and FMoOX/Zeol.
and the catalyst loading were varied within 320–380 °C and 10– 30 mg FMoOX/Zeol, respectively. The reaction pressure was 20 bar which was the best observed during preliminary studies and was also in accordance with the works of Arend et al. [7]. The flow of carrier gas and reaction pressure inlet and outlet were controlled by a flow (Brooks 58505 S) and a pressure controller (Brooks 5866), respectively. In a typically experiment, 20 mg of FMoOX/Zeol (except during the study of effect of catalyst loading) was reduced in situ under flowing H2 at 200 °C for 1 h prior to use after which the reactor was purged with He and 40 g (45 mL) of OA was added. The operating temperature was established and monitored by a type-K Omega thermocouple placed inside the reactor. Before the reaction started, 50 mL/min of 90 vol% N2 and 10 vol% H2 was passed through the reactor until the desired reaction pressure was reached and the reaction commences by turning on the stirrer at a speed of 2000 rpm. Based on preliminary studies, all experiments were performed under 60 min and the reactor set up was cooled by forced air before dismantled for product analysis. Liquid samples withdrawn from the reactor were dissolved in pyridine and thereafter silylated with (100 wt% excess of) N,O-bis(trimethyl)-trifluoroacetamide, BSTFA in an oven at 60 °C for 1 h prior to GC analysis. The internal standard eicosane, C20 H42 was added for quantitative calculations. The withdrawn samples were analyzed with a gas chromatograph (GC, HP 6890) equipped with DB-5 column (60 m × 0.32 mm × 0.5 mm) and a flame ionization detector. 1 mL sample was injected into the GC with split ratio of 50:1 and helium was used as the carrier gas. The chromatographic pressure program was well-adjusted to achieve satisfactory separation of the desired product and the product identification was validated with a gas chromatograph–mass spectrometer (GC–MS). Since there was technical difficulty in online analysis of the evolved gases (Ŋgas) during the study they were calculated according to Eq. (1), and the product distribution was evaluated using Eq. (2).
Ŋgas = [Mb + MH2 − Ma ] ni
ωi (%) = j
i=1
ni
× 100
(1)
(2)
where Mb is the mass of reactor with the OA and FMoOx/Zeol before reaction, MH2 is the mass of total H2 gas required during the experiment evaluated from the H2 flow rate and its density and Ma is the mass of the reactor with the liquid product and FMoOx/Zeol after reaction. Similarly, ωi (%) is the mass fraction of the components in the liquid product.
3. Results and discussion 3.1. Catalyst characterization 3.1.1. Thermal gravimetric analysis (TGA) Three characteristics weight loss regions (WLR) typical of the alumino-silicates are shown in Fig. 1 for the Zeol, FMoOx/Zeol (uncalcined) and FMoOx/Zeol TGA profiles. Previous reports on aluminosilicates have shown that the first WLR corresponds to loosely bonded and physisorbed water molecules that can be readily removed at a temperature below 200 °C [15] as seen in the TGA profile of the three samples. Similarly, the second WLR has been ascribed to the presence of strongly bonded water molecules that are usually domiciled in the first coordination sphere and can be removed at a temperature between 200–500 °C. The third WLR is due to the structural hydroxyl group that condenses and dehydrates at temperatures above 500 °C. In the first WLR both the Zeol and uncalcined FMoOx/Zeol samples showed almost same weght loss which implied that the drying stage was able to remove the hydration effect of the FMoOx precursor during the catalyst synthesis stage with some physisorbed and loosely bonded water molecules. However, in the second and even third WLR the uncalcined FMoOx/Zeol profile showed that there is slight increment in the amount of the strongly bonded water molecules which indicates that the catalyst synthesis protocol was able to guarantee the incorporation of the FMoOx precursor into the Zeol support. After calcination at 400 °C, both the physisorbed and strongly bonded water were seen to have drastically reduced in the FMoOx/Zeol sample leaving behind FMoOx in the Zeol structure. Proper calcination has been reported to ensure large surface area and improved porosity hence guarantee a high active metal dispersion which in turn increases the number of active sites on the catalyst [5,17]. 3.1.2. Elemental composition and spectra The elemental composition of Zeol and FMoOx/Zeol samples in Table 1 showed that the Zeol composition comprises of silica and alumina with some oxides of sodium and calcium. The Si/Al ratio of Zeol sample is 1.02 which suggests zeolite A type [18], the ratio increased to 2.16 in FMoOx/Zeol sample after the catalyst synthesis. This increment was ascribed to dealumination in FMoOx/Zeol due to the effect of oxalic acid (OxA) and fluoride ion functionalization during FMoOx/Zeol synthesis as well as thermal treatment during the calcination stage, respectively. Acid and thermal treatments have been reported to cause dealumination of extra-framework alumina and framework alumina, respectively which eventually resulted into increase in the Si/Al ratio [14,19] as shown in Table 1. The successful
Please cite this article as: O.B. Ayodele et al., Hydrodeoxygenation of oleic acid into n- and iso-paraffin biofuel using zeolite supported fluoro-oxalate modified molybdenum catalyst: Kinetics study, Journal of the Taiwan Institute of Chemical Engineers (2015), http://dx.doi.org/10.1016/j.jtice.2014.12.014
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O.B. Ayodele et al. / Journal of the Taiwan Institute of Chemical Engineers 000 (2014) 1–11 Table 1 Elemental composition and textural properties of Zeol and FMoOx/Zeol samples. Sample
Zeol FMoOx/Zeol a b
Elemental compositiona (%)
BETb
Si
Al
O2
Na + Ca
F
Mo
Si/Al
Surface area (m2 /g)
Average particle size (nm)
16.88 15.72
16.48 7.27
49.58 57.74
16.61 5.32
0.0 4.74
0.45 9.21
1.02 2.16
202 316
10404 2534
Determined by elemental dispersive X-ray. Determined by the nitrogen adsorption–desorption measurements (BET method).
Fig. 2. X-ray flourescence spectra of Zeol and FMoOx/Zeol samples.
incorporation of FMoOx into the structure of Zeol is shown in the XRF spectra (Fig. 2) which showed the growth of Mo peak at Kα value of 17.44 keV and at Kβ value of 19.5 keV. The intensity of the peak at the former is stronger than the latter which suggests there could be two different species of Mo present in the FMoOx/Zeol. All the peaks are in good agreements with the standard card of peak identification (EDXRF-EPSILON 3 XL, PANalytical). All the observations in Table 1 and Fig. 2 are corroborated by the EDX spectra in Fig. 3 which also confirmed the successful fluoride ion functionalization. However, the observed 9.21% quantity of the Mo species was slightly below the expected value of 10% Mo probably due to the high hydration degree at the FMoOx/Zeol synthesis stages [15]. 3.1.3. Morphological and textural changes Fig. 3 (insets) shows the morphology of Zeol (a) and FMoOx/Zeol (b), the morphology of Zeol revealed agglomerates of micro-sized cubical symmetry sharp crystal structure, however, there is a huge degree of morphological variation in the FMoOx/Zeol sample owing
to loss of crystallinity. The variation in the morphology is due to dealumination of FMoOx/Zeol at the catalyst synthesis stage which in turn increased the Si/Al ratio from 1.02 to 2.16 as a result of the OxA attack, functionalization with fluoride ion, thermal treatment during calcination and incorporation of Mo as earlier observed in the EDX and XRF results. Recent studies [19–21] have also reported similar observation of alumino-silicate gradually transformation from crystalline into amorphous form under various degrees of acid attacks and such transformation enhances the catalytic activity of the supported catalyst. The loss of crystallinity is also seen to be accompanied by reduction in particle size according to the BET result (Table 1) which in turn increased the specific surface area and the amount of N2 adsorbed as seen in the isotherms of Zeol and FMoOx/Zeol samples (Figure S1). The changes in the textural properties are also in accordance with earlier reports [19,21] and it was also ascribed to dealumination and removal of impurities and organic matters that might have blocked the samples pores. The enhanced surface area is considered an advantage for the HDO of OA into biofuel.
Fig. 3. Energy dispersive X-ray of Zeol and FMoOx/Zeol samples.
Please cite this article as: O.B. Ayodele et al., Hydrodeoxygenation of oleic acid into n- and iso-paraffin biofuel using zeolite supported fluoro-oxalate modified molybdenum catalyst: Kinetics study, Journal of the Taiwan Institute of Chemical Engineers (2015), http://dx.doi.org/10.1016/j.jtice.2014.12.014
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5
16000 14000 Zeol
Intensity (a.u.)
12000
FMoOx/Zeol
10000 8000 6000 4000
2000 0 0
10
20
30
40 50 2 Theta (deg)
60
70
80
Fig. 4. X-ray diffraction patterns of Zeol and FMoOx/Zeol samples.
The isotherms of both Zeol and FMoOx/Zeol (Figure S1) exhibited characteristic formation of monolayer followed by multilayer typical of Type II isotherm. However, after catalyst synthesis FMoOx/Zeol isotherm systematically exhibited steep increase in the N2 uptake emphasizing increase in the catalyst porosity. The variation of hysteresis loop of FMoOx/Zeol at P/Po = 0.3–0.9 is very obvious compared to Zeol which suggest the possible presence of inter-particle voids formed as a result of the presence of some developed mesopores due to combined protonation effect of oxalic acid and HF drops [19–23]. This observation also supports the morphology variation earlier observed in the SEM of the FMoOx/Zeol as compared to the parent Zeol sample which was ascribed to the catalyst synthesis protocol.
3.1.4. X-ray diffraction (XRD) Fig. 4 shows the X-ray diffraction pattern of Zeol and FMoOx/Zeol samples, the characteristics peaks at 2θ value of 7.2, 10.0, 12.4, 16.0, 21.6, 24.0, 27, 30.0 and 34.0° confirmed that the Zeol support is zeolite A according to the JCPDS card 43-0142 [14]. The XRD peaks showed that Zeol sample is highly crystalline which also supports the observation in the morphology of the Zeol in Fig. 3a (inset). However, there is intense loss of crystallinity in the FMoOx/Zeol due to the presence of OxA, fluoride ion functionalization and thermal treatment during calcination. This phenomenon is in accordance with the earlier observation in the EDX, BET and SEM result which showed increase in the Si/Al ratio, enhanced textural properties and morphological transformation from crystalline into amorphous, respectively. Other studies [15,19,20] also showed varying degree of loss of crystallinity with increase in the Si/Al ratio under various degrees of acid attacks and thermal treatments which in turn ensured proper anchoring of the active metal. The peaks at 11.7°, and 29.8° in the FMoOx/Zeol catalyst reflect the presence of octahedral polymeric molybdooxalates species of the form [Mo2 O5 (OH)(C2 O4 )2 ]3− due to the effect of protonation from the fluoride ion and the adequate MoOx loading of 10% on the Zeol [15,24,25]. Similarly, the peak at 21.4° is ascribed to the presence of bulk MoO3 in the catalyst probably due to partial decomposition of MoOx during calcination process. Generally, octahedral polymeric molybdates structures are observed for MoOx catalyst synthesized in the pH range 3.75 > pH > 1.25 and they have higher catalytic and isomerization activity compared to both monomeric molybdodioxalate specie of the form [MoO2 (OH)2 (C2 O4 )2 ]4− and the simple molybdates which are synthesized at relative higher pH values and are tetrahedral in structure [24,26].
3.1.5. Fourier’s transform infrared spectroscopy (FTIR) The FTIR spectroscopy of the Zeol and FMoOx/Zeol samples is shown in Fig. 5 with Zeol sample showing vibration in the region 3700–2900 cm−1 with a minimal around 3317 cm−1 which can be assigned to the vibration of the Si─OH and adsorbed water molecules. Another band is seen at 1650 cm−1 which can be ascribed to the bending vibration of the adsorbed water molecules [2]. The water vibration with a minimal around 3317 cm−1 disappeared in the FMoOx/Zeol sample after calcinations which implied that the thermal treatment during the calcination stage was sufficient to guarantee the Mo ligand dispersion in the FMoOx/Zeol sample since the presence of water molecules usually cause agglomeration of active metals in zeolite structure resulting in loss of catalytic activity [17]. Incorporation of transition and noble metals into zeolite and other aluminosilicates structure is typically observed in the lower wavenumber below 1000 cm−1 as seen in the spectrum of FMoOx/Zeol which showed significant deviation from the Zeol spectrum indicating structural change caused by the presence of Mo specie [2]. The decrease in the intensity of the band at 880 cm−1 for the FMoOx/Zeol sample can be ascribed to the Mo=O stretching and Mo─O─Mo asymmetric vibrations, while the asymmetric ν Mo=O stretching modes of the MoO4 2− at 985 and 680 cm−1 are assigned to polymolybdates species due to the ionic equilibrium between molybdate and polymolybdate species (Eq. (3)) which are present in the FMoOx/Zeol solution as Si─O─Mo due to protonation (fluoride ion functionalization) during the FMoOx/Zeol synthesis stage [2,24]. Since FTIR spectroscopy is more sensitive to carbon–oxygen and water vibrations and Raman spectroscopy is more sensitive to metal–oxygen [24], there is need to validate the Mo presence and structure using Raman spectroscopy.
7MoO4 2– + 8H+ Mo7 O24 6– + 4H2 O
(3)
3.1.6. Raman spectroscopy The spectra in Fig. 6 compared the characteristic bands of Zeol and FMoOx/Zeol based on the incorporation of fluoride ion functionalized MoOx into Zeol matrix. Based on previous studies [14] the bands at 280, 330, 405, 490, 700, 977, 1030, 1150 and 1457 cm−1 are typical of zeolite A having 4-, 6- and 8-membered rings. Inspecting from the low wavenumber towards the high wavenumber, the band at 280 cm−1 in the Zeol sample can be assigned to the bending mode of rings higher than 4- and 6-membered rings, possibly of the 8 membered rings of zeolite A since previous studies had shown that higher rings give bands at lower wavenumber and vice versa [18]. Similarly, the bands
Please cite this article as: O.B. Ayodele et al., Hydrodeoxygenation of oleic acid into n- and iso-paraffin biofuel using zeolite supported fluoro-oxalate modified molybdenum catalyst: Kinetics study, Journal of the Taiwan Institute of Chemical Engineers (2015), http://dx.doi.org/10.1016/j.jtice.2014.12.014
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110 1650
880
Transmittance (%T)
100 90 3317
80
1306 3700
70
680
2900 Zeol
60 FMoOx/Zeol 50 4000
3600
3200
2800
2400
2000
Wavenumber
985 1600
1200
463 800
400
(cm-1)
Fig. 5. FTIR spectra of Zeol and FMoOx/Zeol samples.
1415
1120
1457
928
1030
0 -2
1150
700
2
405
4
800
490
6
1020 1060
660
8
1290
FMoOx/Zeol
280 330
Raman Intensity cps.
10
1510
Zeol
470
12
1440
14
-4 200
400
600
800
1000
Wavenumber
1200
1400
1600
(cm-1)
Fig. 6. Raman spectra of Zeol and FMoOx/Zeol samples.
at 330 and 405 cm−1 are due to the bending mode of 6-membered Si─O─Al rings while the strongest band at 490 cm−1 is assigned to the bending mode of 4-membered Si─O─Al rings [18], while those at 977, 1030 and 1150 cm−1 are ascribed to asymmetric T─O stretching motions [18]. The effect of FMoOx incorporation into the Zeol can be observed to have developed series of multiple stretches of vibrations in FMoOx/Zeol which are reflections of the presence of carbonate anion (CO3 2− ) from organics, i.e. oxalate. The free ion of CO3 2− with D3h symmetry usually exhibits four normal vibrational modes namely, a symmetric stretching vibration (ν 1 ) around 1063 cm−1 , an out-ofplane bend (ν 2 ) around 879 cm−1 , a doubly degenerate antisymmetric stretch (ν 3 ) around 1415 cm−1 and lastly doubly degenerate bending mode (ν 4 ) around 680 cm−1 [27]. After the FMoOx/Zeol synthesis, the distinctive bands at 490 cm−1 lost its uniqueness and moved to 470 cm−1 , while those at 330 and 800 disappeared completely probably due to the effect of fluoride ion functionalization and calcinations. This observation supports the loss of crystallinity earlier observed in the SEM and XRD results. The miniature peak at 660 cm−1 can be assigned to symmetric Mo─O─Mo stretches present in the dimeric structure which further confirmed the possible presence of MoO3 due to partial decomposition of MoOx at the calcination stage as earlier observed in the XRD peak at 21.4°.
The peak at 928 cm−1 can be assigned to Mo=O since octahedral polymeric molybdooxalates species of the form [Mo2 O5 (OH)(C2 O4 )2 ]3− are usually found in the stretch region 900–950 cm−1 [16,24]. The new peak at 1060 cm−1 as well as the shift of 1030 and 1150 cm−1 peaks in Zeol to 1020 and 1120 cm−1 , respectively in FMoOx/Zeol confirmed the presence of FMoOx bonding to the lower rings in the Zeol lattice structure. Raman bands observed at 1290 and 1440 cm−1 regions correspond to υ (C─O) and υ (C─C) vibration, and υ (C─O) and δ (OC0) vibration of the Mo=oxalate ligand, respectively [24]. 3.2. Catalytic hydrodeoxygenation of oleic acid using FMoOx/Zeol catalyst Prior to the catalytic evaluation of FMoOx/Zeol and the study of effects of process variables on the HDO of oleic acid, few preliminary studies were conducted to gain insight into the contributory catalytic role of Zeol support, effect of oxalic acid and fluoride ion functionalization. In the first place, a repeated experiment without catalyst dosage was carried out in the semi continuous reactor with only OA and hydrogen gas at 360 °C and 20 bar for 60 min. This study became imperative in view of the reactor and/or its accessories having any possible contributory auto-catalytic effects such as hydrogenation or
Please cite this article as: O.B. Ayodele et al., Hydrodeoxygenation of oleic acid into n- and iso-paraffin biofuel using zeolite supported fluoro-oxalate modified molybdenum catalyst: Kinetics study, Journal of the Taiwan Institute of Chemical Engineers (2015), http://dx.doi.org/10.1016/j.jtice.2014.12.014
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Components distribution (%)
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60 50 40
7
Mo/Zeol MoOx/Zeol FMoOx/Zeol
30 20 10 0
Fig. 7. Preliminary study on the HDO of oleic acid at 360 °C, 20 bar, 100 mL H2 /min and 20 mg each of Mo/Zeol, MoOx/Zeol and FMoOx/Zeol catalysts.
thermal cracking on the OA feed stock which may influence with the accuracy of the HDO process kinetics. Though the result actually showed a minuscule conversion of OA, but there was no formation of any C18 hydrocarbon except about 3% stearic acid (SA) formation. There was no appreciable difference in the result even when Zeol support was added to the reactor instead of FMoOx/Zeol. This suggests that a fraction of OA was marginally hydrogenated to form saturated SA (Eq. 4) and that cracking of the OA was not imminent at those prevailing operating conditions. Arend et al. [7] also reported similar observation in a catalytic deoxygenation of OA into diesel-like hydrocarbons using a continuous gas flow reactor. It can therefore be concluded that during subsequent experimental studies on the activities of the synthesized catalysts at those prevailing operating conditions, there would be only marginal hydrogenation contribution towards the formation of SA from the reactor and its associated internals made of stainless steel.
C17 H33 COOH + H2 → C17 H35 COOH
(4)
Furthermore, from Fig. 7, it is obvious that the HDO activity of FMoOx/Zeol and MoOx/Zeol are superior to Mo/Zeol which was undoubtedly due to the oxalic acid functionalization at the synthesis stage which increased their acidity and enhances higher Mo species dispersion as well as ensures the formation of the highly reactive octahedral Mo species compared to the tetrahedral Mo species commonly found in Mo-oxide catalysts [2]. Previous studies [24,28] have also shown that meta-oxalate catalysts usually possesses higher reactivity than metal-oxide catalysts due to their versatile metal-oxalate ligands that can act as a mono-, bi-, tri-, and tetradentate ligands. In addition, the effect of oxalic acid functionalization that increased the catalyst acidity was thought to be responsible for the production of isomerized fraction (i.e. iso-C18 H38 ) when using MoOx/Zeol and FMoOx/Zeol. Furthermore, since there is increment in the amount of iso-C18 H38 produced when using FMoOx/Zeol which has higher acidity, it can therefore be concluded that increase in the catalysts acidity was principally responsible for the production of iso-C18 H38 (Figure S2 shows one of the reacting species chromatograms). Recently, Kovacs et al. [4] also reported that supported metal catalysts with enhanced acidity in the presence of H2 are highly effective and favorable for n-paraffin skeletal isomerization. Typically, isomerized compounds are value added components to biofuel due to their comparably lower freezing point which enhances the biofuel cold flow properties such as cold filter plugging points [4]. It is worth noting that there are also instances of decarboxylation/decarbonylation reaction as evident by the presence of C17 H36 in the products of Mo/Zeol which were not observed in both the MoOx/Zeol and FMoOx/Zeol due
to the presence of the metal-oxalate ligands. This corroborates earlier US Patent claim that metal-oxalate catalysts are reaction specific thus minimizing the tendency of multiple side reactions [28]. Finally, it is obvious that Mo/Zeol has the highest amount of gases and combined unreacted species (OA and SA), while the former confirmed the claim that there are indeed instances of decarboxylation/decarbonylation (producing C17 H36 with CO2 , CO and water vapor as by-products), the latter confirmed that metal-oxalate catalysts have higher activities than their metal-oxide counterparts [24,28]. 3.2.1. Effect time of reaction on the hydrodeoxygenation of oleic acid The product distribution profile of effect of HDO time on OA using the FMoOx/Zeol catalyst is shown in Fig. 8. It can be observed that as the reaction progresses stearic acid (StA) was formed and reaches its peak of formation at about 30 min but disappeared after 60 min of reaction time. This was in agreement with earlier reports [1,4,21] that hydrodeoxygenation of unsaturated compound proceed via sequential hydrogenation to saturate the double bond followed by deoxygenation. The amount of both normal and isomerized octadecane (n-C18 H38 and iso-C18 H38 ) which are considered as yield of target fractions (YTF) were observed to increase progressively until a maximum at 60 min producing about 59 and 26%, respectively. The presence of the isomerized product was due to the combined effect of OxA and fluoride ion functionalization at the FMoOx/Zeol synthesis stage which increased it acidity thus making it favorable and active for n-paraffin skeletal isomerization as previously discussed elsewhere. At 90 min of HDO time, the YTF were observed to reduce probably due to the prevalence of certain secondary reactions such as cracking and oligomerization which were evidenced by the increase in the amount of gases/vapor fraction. At 120 min, it became clear that oligomerization reactions is becoming prevalent over any possible cracking process as the fraction of >C18 which was first observed at 60 min increases from about 3 to 14 % while the fraction of gases decreases. 3.2.2. Effect of temperature on the hydrodeoxygenation of oleic acid The profile of effects of temperature and FMoOx/Zeol loading over a range of 320–380 °C and 10–30 mg, respectively on the yield of target fractions (YTF) of the HDO of OA at 20 bar and 100 mL H2 /min is shown in Fig. 9a. It can be observed that irrespective of the FMoOx/Zeol loading, temperature increments greatly enhanced the yield of both n-C18 H38 and iso-C18 H38 . For example, considering the effect of temperature at the best observed FMoOx/Zeol loading of 30 mg, about 53% n-C18 H38 and 64% n-C18 H38 were obtained at 320 and 360 °C, respectively, similar observation was also true for the iso-C18 H38 which showed about 19% and 30% at those temperatures. This shows that both the HDO and isomerization process of OA into high grade biofuel
Please cite this article as: O.B. Ayodele et al., Hydrodeoxygenation of oleic acid into n- and iso-paraffin biofuel using zeolite supported fluoro-oxalate modified molybdenum catalyst: Kinetics study, Journal of the Taiwan Institute of Chemical Engineers (2015), http://dx.doi.org/10.1016/j.jtice.2014.12.014
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100 Oleic acid Stearic acid n-C18H38 iso-C18H38 Gases >C18
Components distribution (%)
80
60
40
20
0 0
20
40
60 Time (min)
80
100
120
Fig. 8. Effect of time on the HDO of oleic acid into biofuel at 360 °C, 20 bar, 100 mL H2 /min and 20 mg FMoOx/Zeol catalyst.
Yield of target fractions (%)
(a) 80
n-C18: continous line i-C18: broken line
10 mg FMoOx/Zeol 20 mg FMoOx/Zeol 30 mg FMoOx/Zeol 60
40
20
0 300
320
340
360
380
400
Temperature (°C) 0.5
10 mg FMoOx/Zeol 20 mg FMoOx/Zeol 30 mg FMoOx/Zeol viscosity
0.5
0.45
iso-C18/n-C18
0.4
0.4
0.35 0.3
0.3
y = 1E-05x2 - 0.0103x + 2.5463 R² = 1
Viscosity (cP)
0.6
(b)
0.25
0.2
0.2 310
320
330
340
350
360
370
380
390
Temperature (°C) Fig. 9. (a) Effect of temperature and FMoOx/Zeol loading on the HDO of oleic acid into biofuel at 20 bar and 100 mL H2 /min. (b) Effect of temperature and FMoOx/Zeol loading on the ratio of iso-C18 /n-C18 biofuel compositions at 20 bar and 100 mL H2 /min (also showing the effect of temperature on viscosity of oleic acid according to Aspen Hysys simulation).
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were in accordance with the established Arrhenius theory of temperature dependence of reaction rates, which implied that as the temperature was increased the molecules of the OA react more vigorously with the H2 gas at the FMoOx/Zeol active sites. Furthermore, since the viscosity of triglycerides has an inverse relation with temperature, as the temperature was increased from 320 to 360 °C, the viscosity of OA decreased from 0.4021 to 0.2963 cp (according to Aspen Hysys simulation) as seen in Fig. 9b which in turn enhances both the H2 mass transfer into the bulk of OA and its propensity for solubility in the reaction mixture. However, at 380 °C there was reduction in the YTF due to possible cracking of the already deoxygenated paraffin into smaller molecules [4,7,29]. Another possible cause for this reduction could be what Krár et al. [29] referred to as secondary reactions such as polymerization/oligomerization, water–gas-shift (WGS) reaction, methanization and cyclization which could not be monitored at the time of this study due to technical limitations in online measurement of evolved gases. 3.2.3. Effect of FMoOx/Zeol loading on the hydrodeoxygenation of oleic acid The effect of FMoOx/Zeol loading at different temperature showed that its increase also increased the YTF as shown in Fig. 9a because more FMoOx/Zeol active sites are made available for the reaction. The result showed more obvious increment in the YTF at all temperature as the FMoOx/Zeol loading was increased from 10 to 20 mg compared to the slight increment when increased from 20 to 30 mg. This was because at 10 mg loading the amount of FMoOx/Zeol was far too low for the process while the slight increment between 20 and 30 mg loading is a reflection that the FMoOx/Zeol loading is approaching stoichiometric saturation which implied that further loading may not increase the YTF rather a reduction could be observed due to initiation of some parallel (secondary) reactions [30,31]. It is important to point out that at 320 °C the YTF at 20 and 30 mg FMoOx/Zeol loading does not reflect any significant increment which implied that FMoOx/Zeol increment cannot enhance the HDO process beyond the thermodynamically feasible extent at that temperature. A careful study of the effect of FMoOx/Zeol loading on the YTF (Fig. 9b) showed that the ratio of iso-C18 /n-C18 was not constant but varied from 0.279 to 0.523 representing 10 mg FMoOx/Zeol loading at 320 °C and 30 mg FMoOx/Zeol loading at 380 °C, respectively. This varied observation implied that increased temperature and catalyst loading is important in order to increase the biofuel isomerized fraction which is an important component due to its low freezing point. This phenomenon can be explained from the stand point that isomerization process just like any other secondary reactions such as oligomerization process will definitely increase the demand of certain process requirements as earlier observed with the formation and increase in >C18 fraction ascribed to oligomerization process due to longer reaction time [6,30].
Scheme 1. Simplified lumped mechanism for the HDO kinetics of oleic acid.
where SA represents all the intermediate compounds since its concentration is in excess of any other possible intermediate products [32,33]. Similarly, since the concentration of OA is far in excess of H2 gas, a pseudo-first-order kinetics was assumed with respect to OA to determine the rate constants, ki (i = 1, 2, 3) [32,33] and also to verify if the SA formation step or its consumption step is the YTF rate controlling step. Prior to this study, three different agitation speed of 2000, 2500 and 3000 rpm were tested to study if there was any mass transfer limitation and the results showed negligible differences. As earlier commented that HDO of OA usually proceed via sequential hydrogenation to saturate its double bond thus forming SA which implied that direct formation of the C18 biofuel may not be readily feasible. Therefore k1 in Scheme 1 can be set to zero, consequently, the following sets of differential equations (Eqs. (6)–(12)) were obtained.
−dCOA = k2 COA dt
(6)
dCSA = k2 COA − k3 CSA dt
(7)
From Eq. (6),
COA = COAo · e−(k2 )t
(8)
Substituting Eq. (8) into Eq. (7) gives Eq. (9), which upon integration with boundary limits: when t = 0, COA = COAo and CSA = CSAo = 0 gives rise to Eq. (10).
dCSA = k2 COAo · e−(k2 )t − k3 CSA dt CSA =
k2 COAo
(k3 − k2 )
(9)
[e−(k2 )t − e−(k3 )t ]
(10)
Consequently, the formation of C18 biofuel can be obtained by substituting Eqs. (8) and (10) into Eq. (11a). It is important to note that for ease of kinetic study both n-C18 H38 and iso-C18 H38 formed are summed together as C18 since their molecular formula and weight are same.
i.e. C18 = COAo − COA − CSA
3.3. Kinetics studies of hydrodeoxygenation of oleic acid In view of the new catalyst synthesis protocol via the functionalization of Mo with OxA to develop an organometallic catalyst with considerable high acidity via fluoride ion modification, it is imperative to compare the kinetics and the Arrhenius parameter of FMoOx/Zeol with at least one of the recent literature reports. In the previous section and studies [21,29,31], HDO of OA has been observed to proceed via sequential hydrogenation to form saturated SA due to the presence of double bond in the OA structure (Eq. (4)), followed by oxygen molecule extraction to produce the final biofuel (Eq. (5)).
C17 H35 COOH + 3H2 → C18 H38 + 2H2 O
9
(5)
In order to obtain the kinetic data for the stage-wise formation of the biofuel, a lumped kinetic model shown in Scheme 1 was adopted
C18 = COAo − COAo · e−(k2 )t −
(11a)
k2 COAo
(k3 − k2 )
[e−(k2 )t − e−(k3 )t ]
(11b)
Rearranging Eq. (11b) gives Eq. (12) which relates the C18 biofuel production to the initial OA concentration as a function of reaction time.
1 C18 = [k (1 − e−(k2 )t ) − k2 (1 − e−(k3 )t )] COAo (k3 − k2 ) 3
(12)
The experimental data of C18 formation using FMoOx/Zeol at temperature range of 320–360 ºC were fitted into Eq. (12) using MathCAD v13 and plotted as shown in Fig. 10. The plots showed reasonable degree of correlation between the experimental and the developed model with observed R2 of 0.975, 0.963 and 0.955 for 320, 340 and 360 ºC, respectively. As previously observed, there was increase in
Please cite this article as: O.B. Ayodele et al., Hydrodeoxygenation of oleic acid into n- and iso-paraffin biofuel using zeolite supported fluoro-oxalate modified molybdenum catalyst: Kinetics study, Journal of the Taiwan Institute of Chemical Engineers (2015), http://dx.doi.org/10.1016/j.jtice.2014.12.014
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Fig. 10. Experimental data fitting of the HDO of oleic acid at 20 mg catalyst loading, 10% H2 gas flow and 20 bar. Inset: Arrhenius parameter fitting plot. Table 2 Evaluated rate constants for the hydrodeoxygenation of oleic acid. Temperature (ºC) −1
k2 (s ) k3 (s−1 )
320
340
360
0.150 0.038
0.200 0.045
0.280 0.052
recently reported by Kumar et al. [34]. The lower Ea obtained in this study can be ascribed to the effect of OxA functionalization which enhanced the catalytic activity of the FMoOx/Zeol via enhancement of textural properties, development of highly reactive octahedral Mo structure and the presence of the Mo-oxalate ligands [2,9,24,31,35] as seen in the characterization results. 3.4. Catalyst reusability
the production of C18 biofuel as both reaction time and temperature increased. The rate constants obtained from Fig. 10 are shown in Table 2 (after conversion to sec) and the results showed that the effect of temperature on the kinetics of HDO of OA perfectly conformed to the Arrhenius theory of temperature dependence of reaction rates as earlier observed. In addition, it can be observed that the sequential hydrogenation of the OA double bond to form SA is comparably favored and faster than the eventual C18 formation which implied that the latter step is the reaction controlling step. Generally, the hydrogenation of OA (which is an addition reaction) is expected to be more feasible/spontaneous than deoxygenation at the same temperature especially considering their heat of reactions (HR ) which is a measure of the amount of energy per mole either released or produced in a reaction. According to Aspen Hysys process simulator v7.2, the HR for Eq. (4) and (5) are −1.091 × 105 and −1.176 × 105 kJ/mol, respectively using PRSV thermodynamic fluid package (Figure S3 supporting information). The kinetic data in Table 2 were fitted into the Arrhenius equation (Eq. (13)) and plotted as shown in Fig. 10 (inset) to evaluate the pre-exponential factor, Ao (s−1 ) and the activation energy, Ea (J/mol K).
ln k = ln Ao −
Ea RT
(13)
The Ao values (which is the total number of collisions per second either leading to a reaction or not) evaluated from Fig. 10 (inset) showed that SA formation step (k2 ) has 2.85 × 1013 s−1 which is higher than 3.97 × 1012 s−1 obtained for the C18 formation step (k3 ). According to the collision theory, the higher the amount of gas (H2 ) present, the higher the Ao values would be, however, since the H2 gas would have been partly used in the OA sequential hydrogenation for the SA formation, some degree of reduction in the Ao values for C18 formation is expected as observed. The Ea for the SA and C18 formation steps were 98.7 and 130.3 kJ/mol, respectively, the latter for the C18 formation step is comparably lower than 190.9 kJ/mol
The catalyst reusability was tested at 360 °C, 100 mL/min H2 gas flow rate and 20 bar in 60 min reaction time. The result showed that after three consecutive experiments the HDO and the isomerization efficiency were consistent. This is definitely due to the FMoOx/Zeol synthesis protocol that employs Mo-oxalate and functionalization with fluoride ion to form the fluoro-molybdenum-oxalate (FMoOx) complex. Generally supported metal-oxalate catalysts have been reported to me more reactive and highly resistance to leaching of the active metal due to the presence of the strong M+ -oxalate ligand which also minimizes the tendencies of multiple side reactions [35,36]. Similarly, fluoro-oxalate which belongs to the family of organofluoride compounds with a carbon–fluorine chemical bond has the strongest bond in organic chemistry with very high thermal and chemical stability [37]. These explain why both the HDO and the isomerization ability were consistent even after third experiment making a cumulative of 180 reaction minutes. 4. Conclusion A new catalyst has been developed in this study via the incorporation of freshly prepared fluoride ion functionalized molybdenum oxalate (FMoOx) into the supercage structure of zeolite A (Zeol) as the support. The FMoOx/Zeol catalyst was characterized and the successful incorporation of the FMoOx precursor into the support and other associated textural and morphological variations were observed by the EDX, XRF, XRD, FTIR and Raman spectroscopy. The FMoOx/Zeol activity was tested on the hydrodeoxygenation of oleic acid into biofuel and the result showed that effect of reaction time, temperature and the FMoOx/Zeol loading have tremendous impacts on the overall process. The best observed conditions were 360 °C, 30 mg FMoOx/Zeol loading using 100 mL/min H2 gas flow rate and 20 bar to produce 64% n-C18 H38 and 30% iso-C18 H38 in 60 min. The presence of isomerized product was due to the fluoride ion functionalization of the FMoOx/Zeol which increased its acidity. A lumped pseudo-first-order
Please cite this article as: O.B. Ayodele et al., Hydrodeoxygenation of oleic acid into n- and iso-paraffin biofuel using zeolite supported fluoro-oxalate modified molybdenum catalyst: Kinetics study, Journal of the Taiwan Institute of Chemical Engineers (2015), http://dx.doi.org/10.1016/j.jtice.2014.12.014
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kinetics was developed to study the HDO process and the kinetic data showed that sequential hydrogenation of OA into stearic acid (SA) step was faster than the conversion of SA into biofuel step, and their activation energies were 98.7 and 130.3 kJ/mol, respectively. The synthesized FMoOx/Zeol activity was consistent in three consecutive experimental runs making a cumulative reaction time of 180 min. This ability was ascribed to the presence of both the metal-oxalate ligand and the fluoro-oxalate bonding which is considered the strongest bond in organic chemistry in terms of thermal and chemical stability. Acknowledgment The authors sincerely acknowledge the financial support from Higher Impact Research – Ministry of Higher Education project no. D000011-16001 of the Faculty of Engineering, University of Malaya. Supplementary materials Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.jtice.2014.12.014. References [1] Immer JG, Kelly MJ, Lamb HH. Catalytic reaction pathways in liquid-phase deoxygenation of C18 free fatty acids. Appl Catal A 2010;375:134–9. [2] Li J, Xia Z, Lai W, Zheng J, Chen B, Yi X, et al. Hydrodemetallation (HDM) of nickel-5,10,15,20-tetraphenylporphyrin Ni-TPP over NiMo/γ -Al2 O3 catalyst prepared by one-pot method with controlled precipitation of the components. Fuel 2012;97:504–11. [3] Danuthaia T, Sooknoi T, Jongpatiwut S, Rirksomboon T, Osuwan S, Resasco DE. Effect of extra-framework cesium on the deoxygenation of methylester over CsNaX zeolites. Appl Catal A 2011;409-410:74–81. [4] Kovacs S, Kasza T, Thernesz A, Horvath IW, Hancsok J. Fuel production by hydrotreating of triglycerides on NiMo/Al2 O3 /F catalyst. Chem Eng J 2011;176177:237–43. [5] Liu Y, Sotelo-Boyas R, Murata K, Minowa T, Sakanishi K. Hydrotreatment of jatropha oil to produce green diesel over trifunctional Ni–Mo/SiO2 –Al2 O3 catalyst. Chem Lett 2009;38:552–7. [6] Mortensen PM, Grunwaldt JD, Jensen PA, Knudsen KG, Jensen AD. A review of catalytic upgrading of bio-oil to engine fuels. Appl Catal A 2011;407:1–19. [7] Arend M, Nonnen T, Hoelderich WF, Fischer J, Groos J. Catalytic deoxygenation of oleic acid in continuous gas flow for the production of diesel-like hydrocarbons. Appl Catal A 2011;399:198–204. [8] Do PT, Chiappero M, Lobban LL, Resasco DE. Catalytic deoxygenation of methyloctanoate and methyl-stearate on Pt/Al2 O3 . Catal Lett 2009;130:9–18. [9] Sousa LA, Zotin JL, Teixeira da Silva V. Hydrotreatment of sunflower oil using supported molybdenum carbide. Appl Catal A 2012;449:105–11. [10] Park J, Lee J-K, Miyawaki J, Kim Y, Yoon S, Mochida I. Hydro-conversion of 1-methyl naphthalene into alkyl benzenes over alumina-coated USY zeolite-supported NiMoS catalysts. Fuel 2011;90:182–9. [11] Yang Y, Ochoa-Hernández C, de la Peña O’Shea VA, Coronado JM, Serrano DP. Ni2 P/SBA-15 as a hydrodeoxygenation catalyst with enhanced selectivity for the conversion of methyl oleate into n-octadecane. ACS Catal 2012;2:592–8. [12] Guzman A, Torres JE, Prada LP, Nunez ML. Hydropressing of crude palm oil at pilot plant scale. Catal Today 2010;156:38–43. [13] Simácek P, Kubicka D. Hydrocracking of petroleum vacuum distillate containing rapeseed oil: evaluation of diesel fuel. Fuel 2010;89:1508–13. [14] Ayodele OB. Effect of phosphoric acid treatment on kaolinite supported ferrioxalate catalyst for the degradation of amoxicillin in batch photo-Fenton process. Appl Clay Sci 2013;72:74–83.
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Please cite this article as: O.B. Ayodele et al., Hydrodeoxygenation of oleic acid into n- and iso-paraffin biofuel using zeolite supported fluoro-oxalate modified molybdenum catalyst: Kinetics study, Journal of the Taiwan Institute of Chemical Engineers (2015), http://dx.doi.org/10.1016/j.jtice.2014.12.014
