Production of Biofuel via Catalytic Hydrocracking of Kapuk (Ceiba pentandra) Seed Oil with NiMo/HZSM-5 Catalyst

Biofuel is one of alternative energy that is being developed today to solve the problem of limited fossil fuel as an energy source. The goal of this study is to produce biofuel from kapuk (Ceiba pentandra) seed oil (KSO) through catalytic hydrocracking process using NiMo/HZSM-5 catalyst. NiMo/HZSM-5 catalyst was obtained by impregnation of nickel and molybdenum as metallic precursors on HZSM-5 catalyst as support using incipient wetness impregnation method. It was found that the surface area of the catalyst was 222.1350 m/g, the pore diameter was 3.0148 nm and the pore volume was 0.1674 cm/g. The diffraction peaks of nickel oxide phase and the metallic phase of nickel were observed at 2θ of 62.5102° and 51.7283°. Molybdenum oxide phases were observed at 2θ of 53.5674° and 60.4682°. The catalytic hydrocracking process was performed using slurry pressure batch reactor at the temperature of 350°C for 2 h. The obtained liquid product was analyzed using GC-MS in order to determine the organic content. It has been found that the highest compounds were the palmitic acid with 23.14 area%. Besides, the hydrocarbon composition consisted of 33.93 area% (i.e. 4.34 area% cycloparaffins, 16.02 area% n-paraffins, 12.26 area% olefins, and 1.30 area% of aromatics) and 58.73 area% of carboxylic acid. Thus, it can be concluded that NiMo/HZSM-5 catalyst can convert KSO into biofuel through catalytic hydrocracking process at the temperature of 350°C for 2 h.


Introduction
Biofuel production as renewable energy is promising alternatives to substitute fossil fuel from the depletion of world oil reserve [1]. Biofuel is referred to enrichedenergy chemicals derived from such plants, microalgae, and bacteria that used to fulfill the global energy demand. However, approximately 95% of the biofuels produced today are derived from edible vegetable oils. It caused an ongoing debate regarding the use of agricultural lands for fuel purposes. This resulting the exploration of biofuel production from inedible vegetable oil such as kapuk (Ceiba pentandra) seed oil (KSO).
Kapuk (Ceiba pentandra) is a tropical tree belongs to Malvales order and Malvaceae family. It was originally coming from Southeast Asia and grown naturally through tropical region [2]. KSO has the capability as a sustainable biodiesel feedstock because of simple cultivation and short harvest time (4-5 months) [3]. KSO contains a unique fatty acid (malvalic acid) which are more reactive than the double bond carbon (polyunsaturated) in reaction by atmospheric oxygen. The hydrocarbon chain has the ability to reduce oxidation stability of bio-oil [4].
Biofuel consists of hydrocarbon developed by many technologies such as hydrodeoxygenation, thermal pyrolysis, and transesterification [5]. Two main routes to converting vegetable oil into hydrocarbon were catalytic cracking using zeolites and hydrodeoxygenation using metals or metal-sulfidesbased catalyst [6]. Many study had applied cracking vegetable oil using HZSM-5 zeolite to produce hydrocarbons because of its large surface area, crystallinity, and high acidity [7]. HZSM-5 zeolite has acidic site favoring hydrogen transfer that able to produce high aromatic content and some polyaromatic [8] In another study, the renewable diesel produced through hydroprocessing using NiMo/titania catalyst has a high cetane number when it was compared to conventional diesel and hence has better combustion characteristics [9]. But it still contains high oxygen content.
Nowadays, the production of biofuel with inedible vegetable oil raw material has been developed through catalytic hydrocracking process to reduce the oxygen content in the long chain of trigliserides. Hydrocracking may be preferred conversion route of vegetable oil into biofuel using hydrogen to selectivity remove the oxygen atoms [10]. The selective catalyst in catalytic hydrocracking process was very important to obtain the appropriate conversion. Ni and Mo transitions metals used as active compounds and promoters to enhance the active site on the H-ZSM-5 catalyst used. Ni catalyst can promote the dehydrogenation, hydrogenation and hydrocracking reaction. Ni also can be used in more aggressive role of aromatic hydrocracking process because of its good hydrogenating properties [11]. Chen et al reported that when Ni/HZSM-5 used in catalytic hydroprocessing of FAMEs, the n-paraffin (C 17 -C 18 ) and isoparaffin (C 5 -C 16 ) compounds were increased as long as the increase of temperature.
[12] In another case Mo catalyst can promote the hydrodeoxygenation reaction [13]. The impregnation of Mo into HZSM-5 can promote the cyclization reaction and aromatization reaction in cracking of vegetable oil process [8]. In another study, the NiMo catalyst selectivity for renewable diesel source (C 15 -C 18 range hydrocarbon) using temperature at 320°C for 1 h reached 91%. The yield of paraffin C 15 -C 18 range hydrocarbon increased due to the cracking of heavier molecules of triglycerides into diesel range hydrocarbon as the increasing of temperature from 320 to 400°C but it slightly decreased at 420°C due to the cracking of C 18 and other triglyceride molecules into smaller molecules [9]. Thus, it is interesting to produce biofuel (C 15 -C 18 range hydrocarbons) from kapuk (Ceiba pentandra) seed oil through catalytic hydrocracking process at average temperature reaction of 350°C.

Catalyst Preparation
As the previous study, the HZSM-5 catalyst was prepared by calcined ammonium-ZSM-5 at 550°C for 5 h under at air atmosphere [14]. NiMo/HZSM-5 was prepared by incipient wetness impregnation method using 1.1247 M of nickel nitrate and 1.3761 M of ammonium heptamolybdatetetrahydrate. It was dissolved in the volume of the solution according to the total pore volume of the HZSM-5 support (0.2712 cm 3 /gram) [13]. The solution was pouring into HZSM-5 and stirred for 3 h to obtained homogenous metal impregnated catalyst. Then, the catalyst dried under the temperature at 120°C for 12 h and calcined at 400°C with air flow for 5 h. At last, the catalyst reduced with hydrogen flow at 450°C for 2 h to obtain activated site catalyst.

Catalyst Characterization
The pore volume, specific surface area, and average pore diameter were obtained by an automatic specific surface area measurement (Quantachrome Instruments version 10.01) with the N 2 adsorption-desorption isotherm at 77K. The total pore volume, specific surface area, and average pore diameter were calculated using the Brunauer-Emmet-Teller (BET) method. The phase analysis of the catalyst was obtained using an X-ray diffractometer (Philips X'PERT MPD) at 30 mA and 40 kV with Kα radiation. Morphology catalyst, actual metal content, and dispersion were performed by scanning electron microscopy-energy dispersive X-ray (SEM-EDX) at 20 kV.

Catalytic hydrocracking
Catalytic hydrocracking of KSO was performed in a slurry pressurized batch reactor system equipped with a mechanical stirrer (Parr USA 4563) as reported by the previous study [14]. About 200 mL of KSO and the catalyst approximately 0.56 wt% to KSO were loaded into the reactor. Furthermore, the reactor was purged with nitrogen to remove dissolved air in the oil. The operating condition of the experiment carried out at a temperature 350°C for 2 h with reactor pressure range of 10-15 bar after hydrogen flow for 1 h. The obtained liquid product was characterized using gas chromatography-mass spectrophotometry (GC-MS). Fig. 1. showed the XRD patterns of NiMo/HZSM-5 catalyst. As reported by the previous study [14], the main peaks of HZSM-5 zeolite observed at 2 of 7. Besides, after the impregnation process of nickel and molybdenum into the HZSM-5, the structure of NiMo/HZSM-5 catalyst still similar to HZSM-5. It indicates that metals impregnation did not change the main structure of HZSM-5 [15]. The diffraction peaks intensity of NiMo/HZSM-5 catalyst showed that the nickel metallic phase was formed at 2θ of 51.7283°, nickel oxide phase was formed at 2 of 62.5102°, whereas for molybdenum oxide phase for peaks intensity were formed at 2θ of 53.5674° and 60.4682°.

Catalyst characterization
The actual metal content of NiMo/HZSM-5 was observed by EDAX analysis as showed in Fig.2. It showed that the Ni and Mo loading were approximately 0.26%wt and 0.93%wt.

Fig. 1. XRD pattern of NiMo/HZSM-5 catalyst
The SEM image of NiMo/HZSM-5 in Fig. 2. showed that Ni and Mo metals are homogeneously dispersed over the microporous HZSM-5 support. Table 1 shows the textural properties of HZSM-5 and NiMo/HZSM-5 catalyst from BET analysis. The total surface area of NiMo/HZSM-5 is 255.653 m 2 /g, which is lower than the total surface area of HZSM-5 (375.121 m 2 /g). It seems that the metal content blocking some micropores, clogging the external mesopores and decreasing the total area of the parent zeolitic support [16]

Product analysis
The obtained liquid product compounds were shown in Fig. 3. The most abundant compound in the liquid product produced by KSO catalytic hydrocracking process using NiMo/HZSM-5 catalyst at 350°C was the palmitic acid with 23.14 area%. The formation of carboxylic acid in the liquid product shows that triglyceride contained in KSO is cracked into the form of free fatty acids. Free fatty acids that form trough hydrogenation reaction in hydrocracking process that cracked the triglycerides bond [14]. The hydrocarbon compounds observed of 33.93 area% (i.e. 4.34 area% cycloparaffins, 16.02 area% n-paraffins, 12.26 area% olefins, and 1.30 area% of aromatics). The aromatic content that found in the liquid product such as pentylbenzene of 1.22 area% was affected by the presence of polyunsaturated fatty acid in the raw KSO. Furthermore, the presence of olefin of 12.26 area% indicates that the hydrogenation reaction occurring in the hydrocracking process was followed by cyclization process.  4 showed carboxylic acid is quite abundant that was equal to 58.73 area% consisting mostly of palmitic acid proves that triglyceride in raw KSO has begun cracked through the catalytic hydrocracking process into saturated fatty acids. This indicates that the unsaturated fatty acids present in the raw material have begun to crack into saturated fatty acids. The contribution of Ni metal in the cracking process transforms the unsaturated carboxylic acid compounds into saturated carboxylic acid through hydrogenation reaction. The presence of Ni can reduce the barrier of C = O bonds [17]. After the saturated fatty acid is formed, the subsequent reaction is the decarbonylation reaction, but at this stage the decarbonylation reaction has not occurred maximally because the cracking activity has required higher reaction temperature because temperture increase will increasing the conversion [18,19]. Furthermore, hydrocarbon compounds such as olefin (12.26area%), n-paraffin ( [20]. Table 2. showed that the most abundant biofuel fraction was gasoil-range alkanes (C 15 -C 18 ) with 9.96 area%. Furthermore, another fraction was kerosene-range alkanes (C 10 -C 14 ) with 5.09 area%. Temperature above 350°C needed to crack more free fatty acid into biofuel fraction.

Conclusion
Catalytic hydrocracking of kapuk (Ceiba pentandra) seed oil (KSO) with NiMo/HZSM-5 catalyst can be applied to biofuel production. The NiMo/HZSM-5 catalyst surface area was 222.1350 m 2 /g, the pore diameter was 3.0148 nm and the pore volume was 0.1674 cm 3 /g. the biofuel contained hydrocarbon composition consisted of 16.64 area% (i.e. 4.34 area% of cycloparaffins, 16.02 area% of n-paraffins, 12.26 area% of olefins, and 1.30 area% of aromatics) and 58.73 area% of carboxylic acids. The higher temperature needed to convert more carboxylic acids into hydrocarbons fraction.