Utilization of Coconut Shell as Cr 203 Catalyst Support for Catalytic Cracking of Jatropha Oil into Biofuel

Received: 3 December 2019 Revised: 20th January 2020 Accepted:17 February 2020 Online: 29 February 2020 Coconut shell waste is a waste that has a high carbon content. Carbon in coconut shell waste can be converted into activated carbon having a large surface area. This potential property is suitable to apply the coconut shell as catalyst support. To increase the catalytic activity, metal oxides such as Cr203 are impregnated. The purpose of this study is to synthesize Cr203/carbon catalyst and test its catalytic activity on catalytic cracking of Jatropha oil. The first stage was the synthesis of activated carbon and the determination of its proximate and ultimate. The second step was impregnation to produce Cr203/carbon catalyst. Furthermore, X-Ray Diffraction to determine crystallinity, Surface Area Analyzer to identify its surface area and Fourier Transform Infrared to analyze functional groups. Then the catalytic activity was tested on the catalytic cracking of Jatropha oil. In addition, the chemical compound composition and biofuel selectivity of the catalytic cracking product was determined using Gas Chromatography-Mass Spectrometer. Proximate analysis results showed that activated carbon contains 9%, 1%, 23%, and 67% of water, ash, evaporated substances, and bound carbon, respectively. The results of the ultimate analysis resulted in carbon (C), hydrogen (H), and nitrogen (N) contents of 65.422%, 3.384%, and 0.465%, correspondingly. The catalyst crystallinity test showed the presence of Cr203 peaks at 2 : 24.430; 33.470 and 36.25° according to JCPDS No. 841616. In the absorption area of 400-1000 cm 1 and the range of 2000 cm-1 showed the presence of Cr-0 stretching due to Cr203 adsorbed into the activated carbon structure. The surface area of activated carbon and Cr203/carbon catalysts with a concentration of 1.3, and 5% was 8.930 m/g; 47.205 m/g; 50.562 m2/g; and 38.931 m2/g, respectively. The catalytic activity test presented that the best performance was showed by Cr203/carbon catalyst with a concentration of 5% indicated by conversion of Jatropha oil into biofuel of 67.777% with gasoline selectivity, kerosene, and diesel of 36.97%, 14.87%, and 15.94%, correspondingly.


Introduction
Biofuel is alternative energy to substitute petroleum sourced from vegetable or animal material. Jatropha curcas oil is one of the most potential vegetable materials used as raw material for biofuel production because it is easily produced and non-edible. The oil content in the castor bean core is around 50 % [1]. Jatropha oil contains 16-18 carbon atoms in each molecule, while petroleum contains 8-10 carbon atoms (gasoline) and [12][13][14][15][16][17][18] carbon atoms (diesel). The higher carbon atom content of Jatropha oil results in higher viscosity (thicker) when compared to petroleum viscosity [2]. For this reason, a process which enables to reduce the number of carbon atoms from Jatropha oil is necessary.
Conversion of Jatropha oil into biofuel can be carried out by catalytic cracking. Catalytic cracking is the  ℃ process of terminating a heavy fraction compound into a mild fraction with the help of a catalyst. The catalyst customarily applied is heterogeneous because it is easy to separate from the product and can be regenerated. Aziz etal. [ 3 ] used natural zeolite as a catalyst in catalytic cracking of Jatropha curcas oil ( Jatropha curcas L) into biofuel. The optimum process conditions were obtained at 375 C, 2 hours, a catalyst with a size of 180 pm and 5 % concentration with selectivity to gasoline 34.52 %, kerosene 11.87 %, and diesel 13.64 %. Meanwhile, Novia et al. [2] used a Co / Mo Montmorillonite pillared Ti02 catalyst in castor oil hydrocracking. The yield of the product is 77.7127 % at a temperature of 500°C , a gas flow rate of 2.5 mL / s, and 2 grams of the amount of catalyst.
The function of zeolites and Ti02 is a catalyst supports. Zeolites are minerals in nature that are of limited availability. Likewise, Ti02 is a synthetic compound, and the price is high. Another type of catalyst support that can be applied is activated carbon since it has a large surface area of around 300 -3500 m 2 / g [ 4 ]. A large surface area will affect the rate of reaction. The greater the surface area of the catalyst, the higher the reaction rate.
In this study, the raw material used for the manufacture of activated carbon came from coconut shell waste. So far, coconut shells have only been used as briquettes [ 5 , 6, 7 ] or adsorbents [8,9 ]. Conversion of coconut shell to activated carbon (catalyst support) increases the economic value of the coconut shell. It also reduces the cost of biofuel production when using a coconut shell as catalyst support. Kurniawan et al. [ 4 ] synthesized activated carbon from coconut shells with activation using 3 M phosphoric acid, producing a surface area of 386.447 m 2 / g. Ain et al. [10] used activated carbon (synthetic) as a buffer for the Ru-Sn / C catalyst for the hydrogenation of hexadecanoic acid to l-hexadecanol. The advantages of activated carbon as a supported catalyst are a large surface area, resistant to acids, stable at high temperatures, and inert [11]. The active catalyst components used are usually derived from transition metals such as Cr, Ni, Mo [12], Pd [ 13 ], and Fe [ 14 ] because they have vacant d orbitals. The presence of vacant d orbitals allows the availability of Lewis acid groups so that they can provide an active site of the catalyst [ 15 ]. In this study, chromium was used because it had higher acidity, smaller pore size, and high surface area [16].
This research varied the concentration of Cr 203 impregnated into activated carbon by 1, 3 , and 5 %. The characteristics of the resulting catalysts were analyzed using X-Ray Diffraction (XRD), Fourier Transform Infrared (FTIR), and Surface Area Analyzer (SAA). The catalytic activity test was conducted in a reactor batch at 375°C for 5 hours. The resulting product was then analyzed its chemical composition using Gas Chromatography-Mass Spectroscopy (GC-MS) to determine the conversion and selectivity of the resulting biofuel.

Synthesis of Activated Carbon
The coconut shell was cleaned from dirt and cut into smaller sizes. After that, it was put into the furnace for carbonization to be carried out at a temperature of 450°C for 2 hours. The resulting carbon was crushed until smooth and soaked in 300 mL of 3 M phosphoric acid (H 3 P 04 ) solution for 7 hours. Activated carbon was then washed with hot water till neutral pH was achieved and then dried [ 4 ]. The activated carbon produced was tested for proximate analysis, including water, ash, volatile substances, bound carbon, and ultimate analysis, including C, H , and N contents.

. Production of Cr 203/ carbon catalysts
Chromium nitrate (Cr(N 03 ) 3.9 H20) divided into three parts with a different mass that was 1.576 ; 4.738 and 7.890 grams were dissolved in 20 mL distilled water and stirred until homogeneous. Every sample was then added activated carbon ( 28.423 ; 25.261 and 22.109 grams), stirred at 6o°C for 3 hours and evaporated. The sample was then dried at 120°C in the oven and then calcined at 450°C for 1 hour to produce a Cr 203/ carbon catalyst.

Catalyst Characterization
Surface area analysis was carried out using the Surface Area Analyzer (SAA). 0.1 gram of sample was put in an empty tube then degassing for 2 hours at 200 while flowing 275 KPa of N2 gas and cooled. After degassing, the sample was analyzed immediately. N2 gas flowed at 275 KPa and 20 Psi H2 gas. The analysis conditions were then adjusted. The analysis time was around ± 5 hours per sample. The catalyst crystallinity test uses X-Ray Diffraction (XRD). The crystallinity test was carried out at a voltage of 40 kV and a current of 25 mA with an angular range of 5 -900. The identification of functional groups was conducted using Fourier Transform Infrared (FTIR). Samples were mashed together with KBr in a ratio of 1:10 and measured at wavelengths of 500 -4000 cm 1 . The product was removed from the reactor and separated from the catalyst.

Analysis of Jatropha Cracking Catalytic Cracking Products
Catalytic cracking products of Jatropha curcas oil were tested for their chemical composition using Gas Chromatography-Mass Spectrometer (GC-MS). A sample of 1 pL was injected into the column (DB 5 -MS UI stationary phase, 30 m; 0.25 mm; 0.25 pm and Helium gas mobile phase). The resulting chromatogram data were then compared with the standards database so that the chemical compounds produced can be determined. From the product area data produced, product selectivity can be calculated for each Cr 203/ carbon catalyst. Biofuel selectivity is calculated using the formula [ Figure 1 shows the XRD patterns of activated carbon and Cr 203/ carbon catalysts at concentrations of 1%, 3 %, and 5 %. The activated carbon produced has an irregular shape, and there are no sharp peaks. This shows that activated carbon has an amorphous phase [ 19 ]. A wideangle range and a soft peak in the range of 240 indicate the phase for activated carbon [20]. The Cr 203/ carbon XRD patterns show Cr 203 peaks at 2 24.520 ; 33.61°; 36.25°w ith hkl index (012, 104 and 110) according to JCPDS No. 84 -1616. The peaks at 2 24°; 33°; and 36°a re the typical peaks for Cr 203 [21,22]. The peaks are not very clearly seen because the amorphous phase of carbon is more dominant, but as shown in Table 3 , it appears that the increase in Cr 203 concentration increases the intensity of the peaks.

. Characterization of Cr 203/ Carbon Catalyst
(1) Table 1 shows the results of the proximate analysis of activated carbon. The water content contained in activated carbon is 9.756 % smaller than the maximum limit stipulated by SNI 06-3730 -1905 . In addition, ash and volatile substance contents are 0.961 %, 22.660%, respectively. The bound carbon content is 66.662% greater than the minimum limit stipulated by SNI. These results show that the activated carbon produced meets SNI 06-3730 -1905 standards. The value of bound carbon content is inverse with the content of ash, water, and volatile substances. This indicated that the surface of activated carbon became more open because the impurities that cover the surface of the activated carbon are released so that the surface area becomes larger [18]. The ultimate analysis results, as listed in Table 2, show carbon (C) content of 65.422 %, hydrogen 3.384 %, and nitrogen 0.465 %. This result also shows that the quality of activated carbon produced meets SNI standards that require a minimum carbon content of 65 %. The ultimate analysis results for carbon content are in line with the bound carbon levels produced in the proximate analysis.  Fanani et al. [26] also found an increase in the surface area of the catalyst when Cr was applied to activated carbon. The area of activated carbon with the addition of chromium metal increased from 1527.80 m 2 / g to 1652.58 m 2 / g. According to Lillo-Rodenas et al. [ 27 ], the increase of the catalyst surface area is due to the pores becoming more open after chemical activation and impregnation of the metal led to the surface area of the catalyst became larger. The increase in the surface area occurs at a concentration of 1% to 3 %. The surface area of the catalyst represents the active surface, which can interact with the reactants. The reactant molecule will move freely before experiencing adsorption on the surface of the catalyst, then reacts to generate a product.

. Results Analysis of Proximate and Ultimate of Activated Carbon
The surface area of 5 % Cr 203/ carbon catalyst is 38.931 m 2 / g smaller than 1% and 3 % Cr 203/ carbon catalysts. This is due to the addition of more metal concentration resulted in competition among the transitions metals to diffuse into the supporting pores [28]. It also can be caused by the high concentration of Cr 203 , leading to an agglomeration of metal oxide particles; as a result, the formation of unevenly distributed aggregate on the pore surfaces thereby reducing the surface area [ 29 ].  [ 19 ] also stated that the hydroxyl group (O-H) appeared in the region of the 3300 -3399 cm-i wave range assigned as the Bronsted acid site. In addition, there is also a carbonyl group (C = 0) observed at 1716.65 cm 1 . Mentari et al. [ 23 ] stated that the absorption peak at 1820-1600 cm 1  Rahmani et al. [ 24 ] stated that the addition of the transition metal into the material support only causes a slight change in the position of the absorption band. The new peak is also observed at of 2054. 19

. Cr 203/ carbon catalyst activity test
The results of GC -MS analysis show that the Jatropha oil fatty acid constituents used as raw material for making biofuels can be seen in Table 5 and Figure 3 . The surface area of activated carbon and catalysts produced can be seen in   Figure 3 . Chromatograms of fence castor oil Catalytic cracking of fence Jatropha oil can occur through 2 stages, namely the formation of oxygenated components such as fatty acids, ketones, aldehydes, esters, and others caused by the decomposition of triglyceride molecules [28]. These are evidenced by the presence of fatty acids in fence Jatropha oil cracking results. The reaction is as follows: In Table 5 , it can be seen that fatty acids containing in Jatropha oil consist of palmitic acid, linoleic acid, oleic acid, stearic acid, and eicosuric acid with the value of 9.88 %, 33.83 %, 37 -44 %, 15.59 %, and 330 %, respectively. Most of them are unsaturated fatty acids, i.e., oleic and linoleic acids. Weinert et al. [ 30 ] stated that the most fatty acids containing in Jatropha oil were unsaturated fatty acids 76.8 % while saturated fatty acids were 23.2 %. After catalytic cracking using a Cr 203/ carbon catalyst 1%, 3 %, and 5 %, the results obtained are as shown in Table 6. The second stage is indicated by cracking oxygenated components to form hydrocarbons [ 31 ]. Oxygenated compounds will break the C-0 and C-C bonds by breaking the carbon chain at the beta position.
Breaking of the C-0 and C-C bonds through 2 reaction routes i.e., the decarboxylation and the decarbonation reactions. Decarboxylation reaction is a reaction to break the carboxylic bonds to produce C02 gas and hydrocarbons [ 32 ]. Decarboxylation reaction example in Jatropha curcas oil is the conversion of stearic acid becomes heptadecane by cracking process as follows: CI7H 33 COOH -> CI7H 36 + C02 Decarbonylation reaction is a reaction indicating the release of the ester group to produce hydrocarbons, CO, and H20. Decarbonylation reaction example is the decomposition of undecanoic acid to decane ( In Table 6, it can be seen that the two largest classes of compounds produced from catalytic cracking of fence castor oil consist of hydrocarbons (biofuels) and fatty acids. The hydrocarbons produced vary from C 5 to C20. These hydrocarbons are biofuel compounds ( the desired products of this reaction). The types of fatty acids produced from the three types of catalysts are different from the constituents of castor oil, including heptanoic acid, octanoic acid, and others. These show that all fatty acids from castor oil can be converted into biofuels and fatty acids with shorter carbon chains.
Of all the products available, all of them are new compounds; these show that all reactants (Jatropha oil) can be converted 100% into products (hydrocarbons and fatty acids). The greater the concentration of Cr 203 impregnated into the supporting material, the greater the conversion (Table 5 ). Cr 203/ carbon 1%, Cr 203/ carbon 3 % and Cr 203/ carbon 5 % catalysts resulted in conversion of Jatropha oil to biofuel at 58.55 %, 60.10% and 67.77 %, respectively. This is also in agreement with the selectivity of the resulting biofuel fraction. The increase in Cr 203 concentration caused the selectivity of light fractions (gasoline) to increase ( Table 7 ). The more light fraction content in biofuels, indicating the catalytic cracking process was running optimally. This also proves that the Cr 203/ carbon catalyst has a good cracking ability in breaking the heavy fraction (castor oil) into the light CnH2202 CIOH20 + H20 + CO

. Conclusion
Activated carbon from coconut shell waste can be used as a Cr 203/ carbon catalyst supporting material. The XRD pattern of the catalyst showed typical peaks of Cr 203 observed at 2