The Synthesis of Biodiesel from Crude Palm Oil (CPO) using CaO Heterogeneous Catalyst Impregnated H2SO4,Variation of Stirring Speed and Mole Ratio of Oil to Methanol

Biodiesel is a diesel engine fuel produced from renewable material and contains fatty acid alkyl ester from triglyceride or oils through transesterification reactions with short chain alcohols and catalysts. In this study biodiesel was synthesized using crude palm oil (CPO) using CaO catalyst from blood cockle shells calcined at 900 °C for 5 hours and impregnated with H2SO4 (1,2 and 3M). The catalyst was characterized by XRD and XRF. The biodiesel was synthesized with variation of stirring speed (300, 400, 500, 600 rpm) and mole ratio of oil to methanol (1:6, 1:9, 1:12, 1:15 and 1:18. The maximum biodiesel results obtained on a H2SO4 (3M)/CaO catalyst with a stirring speed of 500 rpm and mole ratio of oil to methanol was 1:12 at the transesterification reaction stage and using a CaO catalyst calcined at 900 °C for 5 hours produced a yield of 96.69%. The characteristics of biodiesel produced was water content 0.05%, specific gravity 890 kg/m3, viscosity 4.46 mm2s−1, carbon residue 0.05% and acid number 0.5 mg KOH g−1. It can be concluded biodiesel, meets the quality requirements of SNI 7182-2015


Introduction
The world energy crisis and global warming are two big problems caused by increasing population growth, industry and increasing use of fossil fuels. This causes the need for renewable energy potential as an energy source [1]. Biodiesel is known as an environmentally friendly material that has the potential as an alternative to replace fuel derived from diesel. As a renewable energy source, biodiesel is non-toxic, biodegradable, produces less pollution and has lower sulfur and aromatic content compared to fossil fuels [2].
The biodiesel manufacturing process generally uses a transesterification process of plant oil with short chain alcohol, using a homogeneous catalyst of acid or base, namely H 2 SO 4 , NaOH, and KOH. The process of making biodiesel has several disadvantages, which are sensitive to the content of free fatty acids (FFA) contained in oil, the complexity of separating biodiesel products produced by catalysts, the formation of by-products in the form of soap, the presence of alkaline waste which requires quite complex follow-up processes and requires quite high energy and ultimately increases production costs. This weakness can be overcome by using heterogeneous catalysts. The advantages of using heterogeneous catalysts including easy separation of biodiesel products from catalysts, catalysts can be regenerated and reused, so that the cost of biodiesel production becomes more economical [3]. Heterogeneous catalysts that can be used in biodiesel production are blood cockle shells (Anadara granosa) because they contain CaCO 3 which when calcined at temperatures > 800°C produces CaO [4].
The raw material for producing biodiesel used in this study is crude palm oil (Crude Palm Oil) because Indonesia is the world's largest supplier of palm oil, reaching 42,869,429 tons/year. The main centers of palm oil production in Indonesia are Riau, North Sumatra, Central Kalimantan, Sumatra Selatan and Jambi provinces with annual production of 8,864,883; 5,623,054; 6,279,857; 3,767,108 and 37,939 tons / year respectively [5]. Based on these data it can be concluded that palm oil (CPO) has the potential as a raw material for making biodiesel. However, CPO has a relatively high free fatty acid (FFA) content of > 5% [4]. The high FFA content can influent to the catalyst performance in the reaction, reduce biodiesel yield and can trigger saponification reactions or soap formation.
The synthesis biodiesel from CPO has already been done through two reaction stages, namely the esterification stage which converts free fatty acids into methyl esters and the transesterification stage which is carried out separately [6,7]. CPO produced through a two-stage process (esterification and transesterification) has high purity, and the biodiesel yield was 71.90% [6]. However, a two-stages reaction was less efficient and consumed a lot of energy, so it is necessary to modify the catalyst to save energy in biodiesel synthesis [8]. Istadi, et all [9] used an impregnated sulfuric acid at ZnO catalyst for transesterification in the biodiesel synthesis process and obtained yield of methyl esters was 80.19%. The addition of SO 4 -2 -ZnO increased the active acid site on the surface of the catalyst. For this reason, the use of calcium oxide (CaO) heterogeneous catalyst impregnated with sulfuric acid (H 2 SO 4 ) is expected to be the best solution to improve catalyst performance and to be a solution to prevent the occurrence of saponification or soap formation.
In this study the synthesis of CaO catalyst impregnated by Sulfuric Acid from a shell of BCS was calcined at 900 ° C for 5 hours. Sulfuric acid impregnation in base catalysts (CaO) aims to make this catalyst capable of catalyzing FFA and triglycerides into methyl esters simultaneously (esterification and transesterification) in one stage of the transesterification reaction and to prevent the saponification reaction or the formation of soap caused by high free fatty acids on the methyl ester together transesterification process. According to Nurhayati [4] on calcination 900 °C for 5 hours, CaO has been formed which is sufficient to provide active catalysts in the reaction, so that it can reduce energy consumption and time and licensing the biodiesel synthesis process.
Stirring affects the reaction speed due to the mass transfer between the oil and the catalyst, besides the variation of the stirring speed of the CaO catalyst has never been done so that in this study biodiesel synthesis carried out variations in the stirring speed in the transesterification reaction stage using CaO catalyst impregnated with Sulfuric Acid 1, 2 and 3 M. This research also studies the effect of the mole ratio of oil to methanol (1: 6, 1: 9, 1: 12.1: 15, 1:18). The use of excess oil to methanol mole ratio is expected to be able to shift the reaction towards product formation, resulting in maximum biodiesel yield conversion.

Catalyst Preparation and Characterization
The catalyst preparation begin with calcination of blood clam shells (Anadara granosa) at 900℃ for 5 hours, crushed and sieved until they pass through a 100 mesh sieve and were held at 200 mesh. Preparation of CaO catalyst impregnated with H 2 SO 4 using the wet impregnation method. Calcined BCS samples (100 g) were added 500 ml of H 2 SO 4 solution with variations of H 2 SO 4 concentration (1, 2 and 3M), drop by drop using a burette while stirring using a stirring rod, and the mixture was stirred using magnetic stirrer for 6 hours. Then it was dried in the oven at 105 °C for ± 24 hours continued by calcination at a temperature of 300 °C for ±3 hours. The H 2 SO 4 -CaO catalyst was characterized by FTIR to identify functional group of catalyst (Anadara granosa), and X-ray flourescense (XRF) to analyse the chemical composition.

Biodiesel synthesis
100 g of CPO was heated to 105 ± 5 °C and stirred using a magnetic stirrer for 30 minutes. After being heated, the CPO is then cooled to a temperature of 50 °C. In a 500 mL three neck flask, mixed 3 g of H 2 SO 4 /CaO catalyst with concentrations of H 2 SO 4 1, 2 and 3M (before use, the catalyst is heated in an oven at 105 °C for at least 30 minutes) and 47.66426 g of methanol (mole ratio of oil: methanol 1 : 12) refluxed for 1 hour. CPO (temperature 50 °C) was added to the catalyst-methanol mixture and stirred for 3 hours at a stirring speed of 300, 400, 500 and 600 rpm at 60 °C. After reacting, the mixture is put into a separating funnel and left overnight to separate crude biodiesel from the catalyst and the glycerol formed. Repetition is carried out for catalysts that have been impregnated with H 2 SO 4 with variation of mole ratio of oil: methanol (1:6, 1:9, 1:12, 1:15 and 1:18). The synthesized methyl ester was characterized including acid number, water content, specific gravity, viscosity, carbon residue and the results were compared to biodiesel standard ASTM D6751.

Catalyst characterization
CaO and H 2 SO 4 /CaO catalysts 1, 2 and 3 M were analyzed using X-Ray Fluorescence (XRF) which is a test tool that qualitatively provides information on the types of elements contained in the material being analyzed. The results of the analysis with XRF can be seen in Table 1  The functional group of CaO catalystfrom the shells of blood clam (anadara granosa) and CaO impregnated H 2 SO 4 were analyzed using Fourier Transform Infra Red (FTIR) spectroscopy. The results of the analysis can be seen in Figure 1  According to Ruiz et all, 2016 [10] the wave number at 1456-1409 cm -1 was related to symmetrical stretching vibration of C-O from monodentate. However, on catalyst H 2 SO 4 (3M)/CaO it was shown that no symmetrical stretching vibration and bending vibration of C-O appeared. The higher the concentration of H 2 SO 4 impregnated on CaO, the intensity of C-O decreased. According to Ruiz et all [10] and .,Liu et all, [11]. From the FTIR spectrum, it also shown the presence of S=O functional group at 1170-1126 cm -1 .

The biodiesel results
Crude palm oil (CPO) has high Free Fatty Acid (FFA). Crude palm oil (CPO) which has FFA content below 2% can be directly processed by transesterification to be biodiesel without going through the esterification process. The transesterification process begins by reacting the CPO with methanol which CaO/H 2 SO 4 1, 2 and 3M added as a catalyst. The reaction takes place at 60 °C for 3 hours on a three-neck flask. The results of transesterification with a variation of stirring speed was obtained data as in Figure 2.  From the variation of the stirring speed seen in figure 2, that the higher the stirring rate the higher the biodiesel conversion is due to the reaction process, the speed of contact between reactants greatly influences the conversion of the result. The greater the contact rate between reactants will increase the reaction or increase the conversion. However, each reaction has an optimum condition, where in the process of transesterification of this cooking oil, 500 rpm stirring speed gives an optimum result with the volume conversion reaches 91,16 %. The increased of stirring speed after equilibrium does not increase biodiesel conversion, the reaction which continues and the stirring speed that is too high after achieving equilibrium will result in a backlash so that the acquisition of biodiesel yield decreases [13].
In addition to stirring speed, the effect of mole ratio of oil to methanol on the biodiesel yield was also studied. This synthesis was carried out under reaction condition with a catalyst weight of 3%, a reaction temperature of 60 o C for 3 hours ang stirring speed of 500 rpm (Figure 3). The increasing of the oil :methanol mole ratio from 1:6 to 1:12 will increase the yield of biodiesel, however after reaching an optimum condition (at 1:12) the resulting biodiesel yield decreased. This is because excessive use of methanolwill lead to increased glycerol formation. It is understood tha glycerol will dissolve in excess methanol and then inhibits the methanol reaction, thereby influent to the separation of glycerol which in turn will decrease the biodiesel conversion by shifting the equilibrium in the opposite derection [14].The optimum biodiesel yield is 96.69%, with a mole ratio of oil: methanol 1:12, using H 2 SO 4 (3M) / CaO catalyst.  Table 2. Characteristics of biodiesel from crude palm oil (CPO)

The result characteristics of biodiesel from crude palm oil
The results of biodiesel obtained from transesterification were analyzed for their characteristics in several laboratories. The biodiesel characteristic test results are shown in Table 2.