Journal of Multidisciplinary Applied Natural Science ACCEPTED MANUSCRIPT • OPEN ACCESS Transesterification of Palm Oil Catalyzed by CaO/SiO2 Prepared from Limestone and Rice Husk Silica To cite this article before publication: S. Elfina, K. D. Pandiangan, N. Jamarun, F. Subriadi, H. Hafnimardiyanti, and R. Roswita. (2023). J. Multidiscip. Appl. Nat. Sci. in press. https://doi.org/10.47352/jmans.2774-3047.185. Manuscript version: Accepted Manuscript Accepted Manuscript is “the version of the article accepted for publication including all changes made as a result of the peer review process, and which may also include the addition to the article by Pandawa Institute of a header, an article ID, a cover sheet and/or an ‘Accepted Manuscript’ watermark, but excluding any other editing, typesetting or other changes made by Pandawa Institute and/or its licensors” This Accepted Manuscript is © 2023 The Author(s). 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View the article online for updates and enhancements. https://doi.org/10.47352/jmans.2774-3047.185 https://creativecommons.org/licenses/by/4.0/ https://doi.org/10.47352/jmans.2774-3047.185 Transesterification of Palm Oil Catalyzed by CaO/SiO2 1 Prepared from Limestone and Rice Husk Silica 2 3 Sri Elfina1,a*); Kamisah Delilawati Pandiangan2,b); Novesar Jamarun3,c); Fejri 4 Subriadi1,d); Hafnimardiyanti Hafnimardiyanti1,e); Roswita Roswita1,f) 5 6 1 Chemical Analysis Study Program, Politeknik ATI Padang, Padang-25771 (Indonesia) 7 2 Department Chemistry, Lampung University, Bandar Lampung-35145 (Indonesia) 8 3 Department Chemistry, Andalas University, Padang-26163 (Indonesia) 9 a)Correspondence: srielfina73@gmail.com 10 b)kamisah.delilawati@fmipa.unila.ac.id 11 c) novesar62@yahoo.com 12 d)fejri.subriadiatip@gmail.com 13 e)hafnimardiyanti11@gmail.com 14 f)roswitacaem@gmail.com 15 16 17 ORCIDs: 18 First AUTHOR : https://orcid.org/0009-0003-0788-3010 19 Second AUTHOR : https://orcid.org/0000-0001-6347-2361 20 Third AUTHOR : https://orcid.org/0000-0001-8284-145X 21 Fourth AUTHOR : https://orcid.org/0009-0005-1485-3252 22 Fifth AUTHOR : https://orcid.org/0009-0000-2706-3296 23 Sixth AUTHOR : https://orcid.org/0009-0005-5905-7946 24 25 ACKNOWLEDGEMENT 26 27 This research supported by Badan Pengembangan Sumber Daya Manusia Industri 28 (BPSDMI) the Ministry of Industry Republic Indonesia with contract number 29 8/BPSDMI.3/SPKP/I/2022. 30 31 AUTHOR CONTIBUTIONS 32 33 For research articles with several authors, a short paragraph specifying their individual 34 contributions must be provided. The following statements should be used "Conceptualization, 35 S. E.; K. D. P. and N. J.; Methodology, S. E. and K. D. P.; Formal Analysis, S. E.; K. D. P.; 36 Investigation, F. S.; Resources, N. J.; F. S. and H.; Data Curation, N. J.; Writing – Original 37 Draft Preparation, K. D. P. and S. E.; Writing – Review & Editing, K. D. P..; Visualization, F. 38 S.; Project Administration, R.”. 39 40 41 A CC EP TE D M A N U SC RI PT mailto:kamisah.delilawati@fmipa.unila.ac.id mailto:novesar62@yahoo.com https://orcid.org/0009-0003-0788-3010 https://orcid.org/0000-0001-8284-145X https://orcid.org/0009-0005-1485-3252 https://orcid.org/0009-0000-2706-3296 https://orcid.org/0009-0005-5905-7946 CONFLICT OF INTEREST 1 2 The authors declare no conflict of interest. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 A CC EP TE D M A N U SC RI PT Transesterification of Palm Oil Catalyzed by CaO/SiO2 1 Prepared from Limestone and Rice Husk Silica 2 3 Abstract. In this study, CaO/SiO2 composites were prepared from rice husk silica (RH-SiO2) 4 and limestone from a local company. The composites with different mass ratios of CaO to SiO2 5 (1:1, 1:2, 1:3, 1:5, and 1:10) were synthesized using the sol-gel technique and characterized 6 using XRF, XRD, and SEM. The composites were then used as catalysts for the 7 transesterification of palm oil, with the main purpose to investigate the effect of catalyst 8 compositions on the percentage of conversion of the oil. The results of XRD and SEM confirm 9 the existence of RH-SiO2 as an amorphous material, and CaO as crystalline material, while the 10 composites are a mixture of amorphous and crystalline phases. The catalysts were then used in 11 transesterification experiments and the percentage of oil conversion was calculated. To 12 confirm the successful conversion of palm oil into fatty acid methyl esters, the products of the 13 reactions were analyzed using GC-MS. The experimental results demonstrated that the 14 composites prepared exhibit catalytic activity, with the highest conversion (60%) achieved 15 using the catalyst with the CaO to SiO2 ratio of 1:3. 16 17 Keywords: Composite; catalyst; limestone; rice husk silica; palm oil; biodiesel 18 19 1. INTRODUCTION 20 21 In the realm of renewable energy, biodiesel is a non-fossil fuel that has reached a 22 commercial level. Biodiesel has been utilized in several countries in the form of a mixture with 23 petrochemical diesel in a certain ratio, depending on the policy implemented by the government 24 of the countries. As an example, the blend of 20% biodiesel and 80% petrochemical diesel and 25 known as B20, has been used in India [1]. The use of B20 has also been implemented in 26 Indonesia since the year of 2018 and it is projected to use B30 in the year 2030 [2]. Chemically, 27 biodiesel is a mixture of fatty acid methyl esters (FAME) produced from the reaction between 28 vegetable oil and methanol in the presence of a catalyst. 29 Apart from its increasing role as a fuel, higher price than that of fossil diesel remains a 30 fundamental challenge faced by the biodiesel industry. In this regard, previous workers have 31 suggested that catalyst has a significant role in the reduction of production cost [3][4]. To 32 overcome this problem, the search for low-cost catalyst that works effectively and is 33 A CC EP TE D M A N U SC RI PT environmentally friendly has become a priority of many workers involved in biodiesel studies. 1 In this respect, there has been a shift from homogeneous catalysts to heterogeneous catalysts, 2 leading to the development of various types of solid composites which are mainly composed 3 of metal oxide as active sites supported on porous solids. 4 One of the metal oxides that has been widely used as site active is CaO. In previous 5 studies, this metal oxide has been used as a pure compound to catalyze transesterification of 6 soybean oil [5][6], and waste cooking oil [7]. This oxide has been supported on various solids 7 and applied for transesterification of various vegetable oils, such as CaO/SiO2 prepared from 8 eggshell and Na2SiO3 for transesterification of palm oil [8] and CaO/SiO2 prepared from 9 eggshell and SiO2 for transesterification of palm oil [9]. In another study, Pandiangan et al. 10 [10] also reported the use of CaO/SiO2 for transesterification of rubber seed oil. The use of 11 CaO/Al2O3 as a catalyst has also been reported for transesterification of Nannochloropsis 12 oculata microalga’s lipid [11] and biodiesel production from corn oil [12]. The CaO 13 composites with the use of other supports have also been reported, such as NaY zeolites for 14 transesterification of soybean oil [13] and natural zeolite for transesterification of rapeseed oil 15 [14]. The wide utilization of CaO as an active site of heterogeneous catalyst is based on its 16 strong alkaline strength. This particular oxide is known to have higher alkalinity than MgO and 17 also availability since can be obtained from various sources, limestone, mollusc shells, and 18 eggshells [15][16]. 19 In this study, CaO/SiO2 composites with different compositions were synthesized using 20 a sol-gel technique from rice husk silica and limestone as raw materials, with the main goal to 21 investigate the effect of composition on the catalytic activity of the composites for 22 transesterification of palm oil. For this purpose, the catalysts with the mass ratios of CaO to 23 SiO2 of 1:1, 1:2, 1:3, 1:5, and 1:10 were prepared and then characterized using XRF, XRD, and 24 SEM. The catalysts were then used in transesterification experiments and the percentage of oil 25 conversion was calculated. To confirm the successful conversion of palm oil into FAME, the 26 products of the reactions were analyzed using GC-MS. 27 28 2. MATERIALS AND METHODS 29 30 2.1. Materials and equipments.Limestone was obtained from CV. Aikes Tanjung 31 Mandari, a local company in the city of Halaban, West Sumatra. The chemicals of analytical 32 grade sodium hydroxide (NaOH), nitric acid (HNO3), and methanol (CH3OH) were purchased 33 from Merck. Rice husk silica was collected from a local source in Bandar Lampung. Palm oil 34 A CC EP TE D M A N U SC RI PT was collected from a local company in Pesisir Selatan, West Sumatra. Equipments used were 1 analytical balance (AES 104 120-4), pH meter (Metrohm model), oven (Memmert UN 2 universal 321 model), electrical heater (Stuart AM 500C), furnace (Thermolyne Muffle 3 thermolyne 1100), hotplate stirrer, thermometer, and reflux apparatus. Instruments used were 4 XRF (PANalytical Epsilon 3), XRD (Bruker D8 Advance), SEM/EDS (S50 type EDAX 5 AMETEK), and GC-MS (GCMS-QP2010 SE SHIMADZU). 6 7 2.2. Methods 8 9 2.2.1. Extraction of RH-SiO2. Extraction of RH-SiO2 was carried out following the 10 previously reported procedure [10]. Rice husks were cleaned of impurities by soaking in hot 11 water and then allowed at room temperature overnight to separate the floating and sinking 12 husks. The sinking husks, presumably containing high silica content, were collected while the 13 floating husks were discharged. To extract the silica, a sample of 500 g of rice husk was soaked 14 in 500 mL of 1.5% NaOH solution. The mixture was boiled and allowed to stand for 30 min. 15 The sample was then filtered and the filtrate containing dissolved silica was collected. To 16 precipitate silica, a 10% HNO3 solution was added gradually to the filtrate. The gel was then 17 separated and washed with hot distilled water to remove excess acid. The silica obtained from 18 this treatment was then dried in an oven at 100 °C for 24 h to remove the water content. 19 20 2.2.2. Preparation of CaO. To obtain CaO, limestone (CaCO3) was subjected to 21 calcination treatment at 600 °C for 5 h. The obtained CaO solid was ground into powder and 22 then sieved with a 200 mesh sieve. 23 24 2.2.3. Preparation of CaO/SiO2 composites. In this study, the CaO/SiO2 composites with 25 different mass ratios of 1:1, 1:2, 1:3, 1:5, and 1:10 were prepared using the sol-gel procedure. 26 A specified mass of RH-SiO2 was dissolved in NaOH 1.5% solution and a specified mass of 27 CaO was dissolved in concentrated HNO3. After both raw materials were completely 28 dissolved, the solutions were mixed by slow addition of CaO solution into RH-SiO2 solution 29 and allowed to stand for the gel formation. The gel was oven dried at 100 °C for 8 h, and then 30 ground into powder and sieved using a 200 mesh sieve. The composites were then characterized 31 using XRF, XRD, and SEM. 32 33 A CC EP TE D M A N U SC RI PT 2.2.4. Catalytic activity test. The activity of the catalyst samples as heterogeneous 1 catalysts was then evaluated through the transesterification of palm oil using methanol, to 2 convert the oil into methyl esters. Each CaO/SiO2 catalyst was tested for the transesterification 3 reaction. All experiments were run at fixed oil-to-methanol ratio of 1:8 and a catalyst load of 4 10% relative to the mass of the oil. The experiments were run for 6 h at 70 °C in a 500 mL 5 round-bottom flask connected to a water condenser. After the completion of reaction time, the 6 reaction mixture was allowed to cool and then filtered into a separatory funnel and allowed at 7 room temperature for 24 h to allow the separation between the biodiesel and excess methanol 8 (upper layer) and the remaining oil (bottom layer). The excess methanol was removed from the 9 upper layer by evaporation, and the volume of biodiesel was measured to calculate the 10 percentage of conversion of the oil, according to the equation (1) reported by Pandiangan et al. 11 [17]. 12 13 % 𝑐𝑜𝑛𝑣𝑒𝑟𝑠𝑖𝑜𝑛 = 𝑉𝑖− 𝑉𝑓 𝑉𝑖 𝑥 100 % (1) 14 15 where Vi is the initial volume of oil (mL) and Vf is the volume of unreacted oil (mL). 16 17 3. RESULTS AND DISCUSSIONS 18 19 3.1. XRF analysis. The chemical composition of SiO2, CaO, and CaO/SiO2 composites 20 was determined using the XRF technique. The main components, in the form of oxide, are 21 shown in Table 1. 22 23 Table 1. Chemical composition of the samples investigated 24 Sample Oxide content (%) SiO2 CaO Al2O3 P2O5 Others CaO (from limestone) 1.018 95.943 1.205 0.969 2.865 SiO2 (from rice husk) 97.863 0.246 0.540 0.904 0.447 CaO/SiO2 1:1 61.152 31.28 1.357 3.047 3.164 CaO/SiO2 1:2 73.377 22.929 1.714 0.920 1.060 CaO/SiO2 1:3 81.796 12.041 0.939 2.850 2.374 CaO/SiO2 1:5 82.507 11.468 0.980 3.456 1.589 CaO/SiO2 1:10 83.981 9.161 1.149 3.727 1.982 25 A CC EP TE D M A N U SC RI PT The data presented in Table 1 display that the CaO and SiO2 from rice husk (RH-SiO2) 1 used in this study have a purity of 95.943 and 97.863 %, respectively, suggesting that the 2 characteristics and the catalytic activity of the CaO/SiO2 composites synthesized are practically 3 determined by these two main chemical components, although some minor components were 4 also detected. 5 6 3.2. XRD characterization. To investigate the phase composing the samples, the CaO, 7 RH-SiO2, and the composites prepared were characterized using XRD technique. The XRD 8 diffractograms of the samples are presented in Figure 1. 9 10 11 Figure 1. X-ray diffraction pattern of CaO (a) and rice husk silica (RH-SiO2) (b). 12 13 The XRD diffractogram of the CaO sample is characterized by the existence of sharp 14 peaks and agrees with the pattern for CaO standard recorded in PCPDF-WIN database (ICDD 15 04-0777 and 82-1690). The XRD diffractogram of RH-SiO2, which is characterized by a broad 16 peak at 2θ = 22.6°, is also in agreement with the pattern for SiO2 standard provided in PCPDF-17 WIN database (ICDD 01-0424) with diffraction peaks around 2θ = 22–24°. 18 To investigate the effect of composition on the structure of the composites, the samples 19 were characterized using XRD, and the diffractograms of the composites are shown in Figure 20 2. As can be seen in Figure 2, the diffractograms of the samples are very similar and resemble 21 the pattern observed for CaO. The only quite significant difference between the diffractograms 22 A CC EP TE D M A N U SC RI PT is the relative intensity of the peaks which tends to decrease with increasing amount of silica 1 in the composite material. 2 3 4 Figure 2. The X-ray diffraction patterns of composites at different compositions. 5 6 3.3. SEM characterization. To investigate the surface morphology, which is another 7 important characteristic of solid materials, the samples of RH-SiO2, CaO, and the composites 8 were characterized using SEM. The micrographs of the RH-SiO2 and CaO obtained are shown 9 in Figure 3. As displayed in Figure 3, the RH-SiO2 is characterized by heterogeneous surface 10 features, in terms of particle sizes and distribution of the particles on the surface. In addition, 11 the sample is marked by the irregular shapes of the particles, justifying the existence of the 12 sample as amorphous material, as has been demonstrated by the XRD diffractogram in Figure 13 A CC EP TE D M A N U SC RI PT 1(b). The heterogeneous surface morphology is also displayed by the micrograph of CaO, 1 however, the existence of rectangular particles can be observed, although the particles are not 2 well separated but tend to agglomerate to form large particles. 3 4 5 Figure 3. SEM micrographs of RH-SiO2 with 1000x magnification (a), 15000x 6 magnification (b), and micrographs of CaO with 1000x magnification (c), and 15000x 7 magnification (d). 8 9 The composites were also characterized using SEM and the micrographs obtained are 10 compiled in Figure 4. As can be seen in Figure 4, the surface morphologies observed suggest 11 the existence of all samples as a mixture of amorphous and crystalline materials, forming 12 agglomerates as has also been observed by others [18]. In addition, the heterogeneity of the 13 samples in terms of particle sizes and distribution of the particles on the surface of the samples 14 is very evident, as displayed by the micrographs. Related to the application of the composites 15 as catalyst, the amorphous phase, presumably the RH-SiO2 is the component to play the role 16 as the host for the reaction while the CaO as the crystalline component acted as an active site 17 of the catalyst, as depicted in reaction mechanism in Figure 5 [19]. 18 19 A CC EP TE D M A N U SC RI PT 1 Figure 4. SEM micrographs of the composites with different compositions: (a) CaO/SiO2 1:1, 2 (b) CaO/SiO2 1:2. (c) CaO/SiO2 1:3, (d) CaO/SiO2 1:5, and (e) CaO/SiO2 1:10. 3 4 5 6 7 8 A CC EP TE D M A N U SC RI PT 1 Figure 5. Transesterification mechanism of vegetable oil using CaO as an active site of 2 catalyst. 3 4 3.4. Catalytic Activity Test. A typical example of a transesterification reaction is shown 5 in Figure 6. The upper layer is the biodiesel layer mixed with excess methanol and the bottom 6 layer is unreacted oil. The volume of unreacted oil was measured to determine the percentage 7 of conversion using the equation presented in the experimental section. The results obtained 8 are presented in Table 2. 9 10 11 Figure 6. Typical example of transesterification product obtained in this study. 12 13 14 A CC EP TE D M A N U SC RI PT Table 2. Conversion of oil using catalyst with different compositions 1 No. Catalyst composition (CaO/SiO2 ratio) Oil conversion (%) 1 1:1 48 2 1:2 52 3 1:3 60 4 1:5 43 5 1:10 36 2 As can be seen in Table 2 there is no evident trend that shows the effect of composite 3 compositions on the oil conversion achieved. However, it can be noted that the highest oil 4 conversion (60%) was achieved with the use of the CaO/SiO2 composite with aratio of CaO to 5 SiO2 of 1:1. Based on these results, it should be noted that the oil conversion achieved in this 6 study relatively lower compared to those reported by others for the same oil [20][21]. In this 7 respect, it should be acknowledged that more study is required to optimize the performance of 8 the CaO/SiO2 composites, in recognition of the higher performance of this catalyst reported by 9 other works [3][19], together with the existence of the limestone and rice husk as low-cost raw 10 materials. 11 12 4. CONCLUSIONS 13 14 The experimental results obtained in this study demonstrated that the CaO/SiO2 15 composites with different CaO to SiO2 ratios prepared from limestone and rice husk silica exist 16 as a mixture of amorphous and crystalline phases according to XRD characterization. 17 According to SEM results, the surface morphology of the samples is characterized by 18 heterogeneous features in terms of particle size and shape, as well as particle distribution on 19 the surface of the samples. The transesterification experiments revealed that the highest oil 20 conversion achieved is 60% with the use of composite with the CaO to SiO2 ratio of 1: 3. This 21 conversion is relatively higher than the results for the same oil with the use of different 22 catalysts, but relatively lower compared to the results reported by others. In this respect, it 23 should be acknowledged that more study is required to optimize the performance of the 24 CaO/SiO2 composites. 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