This research, biodiesel production from waste cooking oil (WCO), was conducted using a montmorillonite-sulfonated carbon catalyst from molasses. The biodiesel product would be blended with diesel fuel with various volume variations to see its fuel properties. The catalyst was assessed by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), N₂ adsorption-desorption isotherm, and acidity analysis using the titration method. The effect of the weight ratio of montmorillonite to sulfonated carbon was also evaluated. The process of esterification reaction was optimized using the response surface methodology with a central composite design (RSM-CCD). The study showed that the weight ratio of montmorillonite to sulfonated carbon of 1:3 generated the highest acidity of 9.79 mmol/g with a prominent enhanced surface area and was further employed to optimize the esterification reaction. The optimum condition was obtained at a reaction temperature of 78.12°C, catalyst weight of 2.98 g, and reaction time of 118.27 with an FFA conversion of 74.101%. The optimum condition for the mixture of FAME and diesel fuel was achieved at the composition of the B20 blend, which met the FAME standard. The reusability study revealed that the catalyst had adequate stability at three consecutive runs, with a reduced performance was 18.60%. The reduction of FFA conversion was due to the leaching of the catalyst’s active site. This study disclosed that the FAME generated from the esterification of FFA on WCO-catalyzed montmorillonite-sulfonated carbon had a promising option as biodiesel blends for increasing the quality of commercial diesel.

• Abdelhady, H. H., Elazab, H. A., Ewais, E. M., Saber, M., & El-Deab, M. S. (2020). Efficient catalytic production of biodiesel using nano-sized sugar beet agro-industrial waste. Fuel, 261, Article 116481. https://doi.org/10.1016/j.fuel.2019.116481

• Akram, S., Mumtaz, M. W., Danish, M., Mukhtar, H., Irfan, A., Raza, S. A., Wang, Z., & Arshad, M. (2019). Impact of cerium oxide and cerium composite oxide as nano additives on the gaseous exhaust emission profile of waste cooking oil based biodiesel at full engine load conditions. Renewable Energy, 143, 898-905. https://doi.org/10.1016/j.renene.2019.05.025

• Ali, C. H., Asif, A. H., Iqbal, T., Qureshi, A. S., Kazmi, M. A., Yasin, S., Danish, M., & Mu, B. Z. (2018). Improved transesterification of waste cooking oil into biodiesel using calcined goat bone as a catalyst. Energy Sources, Part A: Recovery, Utilization and Environmental Effects, 40(9), 1076-1083. https://doi.org/10.1080/15567036.2018.1469691

• Almadani, E. A., Harun, F. W., Radzi, S. M., & Muhamad, S. K. (2018). Cu2+ montmorillonite K10 clay catalyst as a green catalyst for production of stearic acid methyl ester: Optimization using response surface methodology (RSM). Bulletin of Chemical Reaction Engineering & Catalysis, 13(1), 187-195. https://doi.org/10.9767/bcrec.13.1.1397.187-195

• Al-Sakkari, E. G., Abdeldayem, O. M., El-Sheltawy, S. T., Abadir, M. F., Soliman, A., Rene, E. R., & Ismail, I. (2020). Esterification of high FFA content waste cooking oil through different techniques including the utilization of cement kiln dust as a heterogeneous catalyst: A comparative study. Fuel, 279, Article 118519. https://doi.org/10.1016/j.fuel.2020.118519

• Alshabanat, M., Al-Arrash, A., & Mekhamer, W. (2013). Polystyrene/montmorillonite nanocomposites: Study of the morphology and effects of sonication time on thermal stability. Journal of Nanomaterials, 2013, Article 650725. https://doi.org/10.1155/2013/650725

• Amaya, J., Suarez, N., Moreno, A., Moreno, S., & Molina, R. (2020). Mo or W catalysts promoted with Ni or Co supported on modified bentonite for decane hydroconversion. New Journal of Chemistry, 44(7), 2966-2979. https://doi.org/10.1039/c9nj04878b

• Anguebes-Franseschi, F., Abatal, M., Bassam, A., Soberanis, M. A. E., Tzuc, O. M., Bucio-Galindo, L., Quiroz, A. V. C., Ucan, C. A. A., & Ramirez-Elias, M. A. (2018). Esterification optimization of crude African palm olein using response surface methodology and heterogeneous acid catalysis. Energies, 11(1), Article 157. https://doi.org/10.3390/en11010157

• Azman, N. S., Marliza, T. S., Asikin-Mijan, N., Hin, T. Y. Y., & Khairuddin, N. (2021). Production of biodiesel from waste cooking oil via deoxygenation using Ni-Mo/Ac catalyst. Processes, 9(5), Article 750. https://doi.org/10.3390/pr9050750

• Bahú, J., Hernandez, N., Bonon, A., Bonon, A. D. J., Mart, M., & Gregorio, J. (2017). Epoxy monomers obtained from castor oil using a toxicity-free catalytic system Related papers. Journal of Molecular Catalysis A: Chemical, 426, 550-556.

• Balajii, M., & Niju, S. (2021). Esterification optimization of underutilized Ceiba pentandra oil using response surface methodology. Biofuels, 12(5), 495-502. https://doi.org/10.1080/17597269.2018.1496384

• Banerjee, S., Sahani, S., & Sharma, Y. C. (2019). Process dynamic investigations and emission analyses of biodiesel produced using Sr-Ce mixed metal oxide heterogeneous catalyst. Journal of Environmental Management, 248, Article 109218. https://doi.org/10.1016/j.jenvman.2019.06.119

• Bastos, R. R. C., da Luz Corrêa, A. P., da Luz, P. T. S., da Rocha Filho, G. N., Zamian, J. R., & da Conceição, L. R. V. (2020). Optimization of biodiesel production using sulfonated carbon-based catalyst from an amazon agro-industrial waste. Energy Conversion and Management, 205, Article 112457. https://doi.org/10.1016/j.enconman.2019.112457

• Bayat, A., Baghdadi, M., & Bidhendi, G. N. (2018). Tailored magnetic nano-alumina as an efficient catalyst for transesterification of waste cooking oil: Optimization of biodiesel production using response surface methodology. Energy Conversion and Management, 177, 395-405. https://doi.org/10.1016/j.enconman.2018.09.086

• Boey, P. L., Ganesan, S., Maniam, G. P., Khairuddean, M., & Efendi, J. (2013). A new heterogeneous acid catalyst for esterification: Optimization using response surface methodology. Energy Conversion and Management, 65, 392-396. https://doi.org/10.1016/j.enconman.2012.08.002

• Boffito, D. C., Pirola, C., Galli, F., Di Michele, A., & Bianchi, C. L. (2013). Free fatty acids esterification of waste cooking oil and its mixtures with rapeseed oil and diesel. Fuel, 108, 612-619. https://doi.org/10.1016/j.fuel.2012.10.069

• Chandane, V. S., Rathod, A. P., Wasewar, K. L., & Jadhav, P. G. (2020). Response surface methodology and artificial neural networks for optimization of catalytic esterification of lactic acid. Chemical Engineering and Technology, 43(11), 2315-2324. https://doi.org/10.1002/ceat.202000041

• Chen, C., Chitose, A., Kusadokoro, M., Nie, H., Xu, W., Yang, F., & Yang, S. (2021). Sustainability and challenges in biodiesel production from waste cooking oil: An advanced bibliometric analysis. Energy Reports, 7, 4022-4034. https://doi.org/10.1016/j.egyr.2021.06.084

• Chen, S. Y., Attanatho, L., Chang, A., Laosombut, T., Nishi, M., Mochizuki, T., Takagi, H., Yang, C. M., Abe, Y., Toba, M., Chollacoop, N., & Yoshimura, Y. (2019). Profiling and catalytic upgrading of commercial palm oil-derived biodiesel fuels for high-blend fuels. Catalysis Today, 332, 122-131. https://doi.org/10.1016/j.cattod.2018.05.039

• Dawodu, F. A., Ayodele, O., Xin, J., Zhang, S., & Yan, D. (2014). Effective conversion of non-edible oil with high free fatty acid into biodiesel by sulphonated carbon catalyst. Applied Energy, 114, 819-826.

• de Oliveira, A. de N., de Lima, M. A. B., Pires, L. H. de O., da Silva, M. R., da Luz, P. T. S., Angélica, R. S., Filho, G. N. d. R., da Costa, C. E. F., Luque, R., & do Nascimento, L. A. S. (2019). Bentonites modified with phosphomolybdic heteropolyacid (HPMo) for biowaste to biofuel production. Materials, 12(9), Article 1431. https://doi.org/10.3390/ma12091431

• Dhawane, S. H., Kumar, T., & Halder, G. (2015). Central composite design approach towards optimization of flamboyant pods derived steam activated carbon for its use as heterogeneous catalyst in transesterification of Hevea brasiliensis oil. Energy Conversion and Management, 100, 277-287. https://doi.org/10.1016/j.enconman.2015.04.083

• Dhawane, S. H., Kumar, T., & Halder, G. (2016). Biodiesel synthesis from Hevea brasiliensis oil employing carbon supported heterogeneous catalyst: Optimization by Taguchi method. Renewable Energy, 89, 506-514. https://doi.org/10.1016/j.renene.2015.12.027

• Ding, J., Xia, Z., & Lu, J. (2012). Esterification and deacidification of a waste cooking oil (TAN 68.81 mg KOH/g) for biodiesel production. Energies, 5(8), 2683-2691. https://doi.org/10.3390/en5082683

• Endut, A., Abdullah, S. H. Y. S., Hanapi, N. H. M., Hamid, S. H. A., Lananan, F., Kamarudin, M. K. A., Umar, R., Juahir, H., & Khatoon, H. (2017). Optimization of biodiesel production by solid acid catalyst derived from coconut shell via response surface methodology. International Biodeterioration and Biodegradation, 124, 250-257. https://doi.org/10.1016/j.ibiod.2017.06.008

• Fadhil, A. B., Aziz, A. M., & Al-Tamer, M. H. (2016). Biodiesel production from Silybum marianum L. seed oil with high FFA content using sulfonated carbon catalyst for esterification and base catalyst for transesterification. Energy Conversion and Management, 108, 255-265. https://doi.org/10.1016/j.enconman.2015.11.013

• Farabi, M. S. A., Ibrahim, M. L., Rashid, U., & Taufiq-Yap, Y. H. (2019). Esterification of palm fatty acid distillate using sulfonated carbon-based catalyst derived from palm kernel shell and bamboo. Energy Conversion and Management, 181, 562-570. https://doi.org/10.1016/j.enconman.2018.12.033

• Fauziyah, M., Widiyastuti, W., & Setyawan, H. (2020). Sulfonated carbon aerogel derived from coir fiber as high performance solid acid catalyst for esterification. Advanced Powder Technology, 31(4), 1412-1419. https://doi.org/10.1016/j.apt.2020.01.022

• Fawaz, E. G., Salam, D. A., & Daou, T. J. (2020). Esterification of linoleic acid using HZSM-5 zeolites with different Si/Al ratios. Microporous and Mesoporous Materials, 294, Article 109855. https://doi.org/10.1016/j.micromeso.2019.109855

• Flores, K. P., Omega, J. L. O., Cabatingan, L. K., Go, A. W., Agapay, R. C., & Ju, Y. H. (2019). Simultaneously carbonized and sulfonated sugarcane bagasse as solid acid catalyst for the esterification of oleic acid with methanol. Renewable Energy, 130, 510-523. https://doi.org/10.1016/j.renene.2018.06.093

• Fonseca, J. M., Spessato, L., Cazetta, A. L., Bedin, K. C., Melo, S. A. R., Souza, F. L., & Almeida, V. C. (2020). Optimization of sulfonation process for the development of carbon-based catalyst from crambe meal via response surface methodology. Energy Conversion and Management, 217, Article 112975. https://doi.org/10.1016/j.enconman.2020.112975

• Fregolente, P. B. L., Fregolente, L. V., & Wolf MacIel, M. R. (2012). Water content in biodiesel, diesel, and biodiesel-diesel blends. Journal of Chemical and Engineering Data, 57(6), 1817-1821. https://doi.org/10.1021/je300279c

• Gan, S., Ng, H. K., Chan, P. H., & Leong, F. L. (2012). Heterogeneous free fatty acids esterification in waste cooking oil using ion-exchange resins. Fuel Processing Technology, 102, 67-72. https://doi.org/10.1016/j.fuproc.2012.04.038

• Giakoumis, E. G., & Sarakatsanis, C. K. (2018). Estimation of biodiesel cetane number, density, kinematic viscosity and heating values from its fatty acid weight composition. Fuel, 222, 574-585. https://doi.org/10.1016/j.fuel.2018.02.187

• Gupta, A. R., & Rathod, V. K. (2018). Waste cooking oil and waste chicken eggshells derived solid base catalyst for the biodiesel production: Optimization and kinetics. Waste Management, 79, 169-178. https://doi.org/10.1016/j.wasman.2018.07.022

• Hajilar, S., & Shafei, B. (2019). Thermal transport properties at interface of fatty acid esters enhanced with carbon-based nanoadditives. International Journal of Heat and Mass Transfer, 145, Article 118762. https://doi.org/10.1016/j.ijheatmasstransfer.2019.118762

• Hasanudin, H., Asri, W. R., Tampubolon, K., Riyant, F., Purwaningrum, W., & Wijaya, K. (2022). Dehydration isopropyl alcohol to diisopropyl ether over molybdenum phosphide pillared bentonite. Pertanika Journal of Science & Technology, 30(2), 1739-1754. https://doi.org/10.47836/pjst.30.2.47

• Hasanudin, H., Asri, W. R., Said, M., Hidayati, P. T., Purwaningrum, W., Novia, N., & Wijaya, K. (2022). Hydrocracking optimization of palm oil to bio-gasoline and bio-aviation fuels using molybdenum nitride-bentonite catalyst. RSC Advances, 12(26), 16431-16443. https://doi.org/10.1039/D2RA02438A

• Hasanudin, H., Putri, Q. U., Agustina, T. E., & Hadiah, F. (2022). Esterification of free fatty acid in palm oil mill effluent using sulfated carbon-zeolite composite catalyst. Pertanika Journal of Science & Technology, 30(1), 377-395. https://doi.org/10.47836/pjst.30.1.21

• Helmi, M., Tahvildari, K., Hemmati, A., Aberoomand Azar, P., & Safekordi, A. (2020). Phosphomolybdic acid/graphene oxide as novel green catalyst using for biodiesel production from waste cooking oil via electrolysis method: Optimization using with response surface methodology (RSM). Fuel, 287, Article 119528. https://doi.org/10.1016/j.fuel.2020.119528

• Ibeto, C. N., Okoye, C. O. B., & Ofoefule, A. U. (2012). Comparative study of the physicochemical characterization of some oils as potential feedstock for biodiesel production. ISRN Renewable Energy, 2012, 1-5. https://doi.org/10.5402/2012/621518

• Jamil, U., Khoja, A. H., Liaquat, R., Naqvi, S. R., Omar, W. N. N. W., & Amin, N. A. S. (2020). Copper and calcium-based metal organic framework (MOF) catalyst for biodiesel production from waste cooking oil: A process optimization study. Energy Conversion and Management, 215, Article 112934. https://doi.org/10.1016/j.enconman.2020.112934

• Jenie, S. N. A., Kristiani, A., Sudiyarmanto, Khaerudini, D. S., & Takeishi, K. (2020). Sulfonated magnetic nanobiochar as heterogeneous acid catalyst for esterification reaction. Journal of Environmental Chemical Engineering, 8(4), Article 103912. https://doi.org/10.1016/j.jece.2020.103912

• Kamaronzaman, M. F. F., Kahar, H., Hassan, N., Hanafi, M. F., & Sapawe, N. (2020a). Analysis of biodiesel product derived from waste cooking oil using fourier transform infrared spectroscopy. Materials Today: Proceedings, 31, 329-332. https://doi.org/10.1016/j.matpr.2020.06.088

• Kamaronzaman, M. F. F., Kahar, H., Hassan, N., Hanafi, M. F., & Sapawe, N. (2020b). Optimization of biodiesel production from waste cooking oil using eggshell catalyst. Materials Today: Proceedings, 31, 324-328. https://doi.org/10.1016/j.matpr.2020.06.080

• Karmakar, B., & Halder, G. (2021). Accelerated conversion of waste cooking oil into biodiesel by injecting 2-propanol and methanol under superheated conditions: A novel approach. Energy Conversion and Management, 247, Article 114733. https://doi.org/10.1016/j.enconman.2021.114733

• Karmakar, R., Kundu, K., & Rajor, A. (2018). Fuel properties and emission characteristics of biodiesel produced from unused algae grown in India. Petroleum Science, 15(2), 385-395. https://doi.org/10.1007/s12182-017-0209-7

• Kumar, S., Shamsuddin, M. R., Farabi, M. S. A., Saiman, M. I., Zainal, Z., & Taufiq-Yap, Y. H. (2020). Production of methyl esters from waste cooking oil and chicken fat oil via simultaneous esterification and transesterification using acid catalyst. Energy Conversion and Management, 226, Article 113366. https://doi.org/10.1016/j.enconman.2020.113366

• Kusumaningtyas, R. D., Prasetiawan, H., Putri, R. D. A., Triwibowo, B., Kurnita, S. C. F., Anggraeni, N. D., Veny, H., Hamzah, F., & Rodhi, M. N. M. (2021). Optimisation of free fatty acid removal in nyamplung seed oil (Callophyllum inophyllum l.) using response surface methodology analysis. Pertanika Journal of Science and Technology, 29(4), 2605-2623. https://doi.org/10.47836/PJST.29.4.20

• Lathiya, D. R., Bhatt, D. V., & Maheria, K. C. (2018). Synthesis of sulfonated carbon catalyst from waste orange peel for cost effective biodiesel production. Bioresource Technology Reports, 2, 69-76. https://doi.org/10.1016/j.biteb.2018.04.007

• Lin, C. Y., & Ma, L. (2020). Influences of water content in feedstock oil on burning characteristics of fatty acid methyl esters. Processes, 8(9), Article 1130. https://doi.org/10.3390/PR8091130

• Lin, J., Jiang, B., & Zhan, Y. (2018). Effect of pre-treatment of bentonite with sodium and calcium ions on phosphate adsorption onto zirconium-modified bentonite. Journal of Environmental Management, 217, 183-195. https://doi.org/10.1016/j.jenvman.2018.03.079

• Ma, Y., Wang, Q., Zheng, L., Gao, Z., Wang, Q., & Ma, Y. (2016). Mixed methanol/ethanol on transesterification of waste cooking oil using Mg/Al hydrotalcite catalyst. Energy, 107, 523-531. https://doi.org/10.1016/j.energy.2016.04.066

• Mahesh, S. E., Ramanathan, A., Begum, K. M. M. S., & Narayanan, A. (2015). Biodiesel production from waste cooking oil using KBr impregnated CaO as catalyst. Energy Conversion and Management, 91, 442-450. https://doi.org/10.1016/j.enconman.2014.12.031

• Mansir, N., Teo, S. H., Rabiu, I., & Taufiq-Yap, Y. H. (2018). Effective biodiesel synthesis from waste cooking oil and biomass residue solid green catalyst. Chemical Engineering Journal, 347, 137-144. https://doi.org/10.1016/j.cej.2018.04.034

• Mazubert, A., Aubin, J., Elgue, S., & Poux, M. (2014). Intensification of waste cooking oil transformation by transesterification and esterification reactions in oscillatory baffled and microstructured reactors for biodiesel production. Green Processing and Synthesis, 3(6), 419-429. https://doi.org/10.1515/gps-2014-0057

• Mishra, S., Anand, K., & Mehta, P. S. (2016). Predicting the cetane number of biodiesel fuels from their fatty acid methyl ester composition. Energy and Fuels, 30(12), 10425-10434. https://doi.org/10.1021/acs.energyfuels.6b01343

• Mulay, A., & Rathod, V. K. (2021). Microwave-assisted heterogeneous esterification of dibutyl maleate: Optimization using response surface methodology. Chemical Data Collections, 34, Article 100740. https://doi.org/10.1016/j.cdc.2021.100740

• Munir, M., Ahmad, M., Mubashir, M., Asif, S., Waseem, A., Mukhtar, A., Saqib, S., Munawaroh, H. S. H., Lam, M. K., Shiong Khoo, K., Bokhari, A., & Loke Show, P. (2021). A practical approach for synthesis of biodiesel via non-edible seeds oils using trimetallic based montmorillonite nano-catalyst. Bioresource Technology, 328, Article 124859. https://doi.org/10.1016/j.biortech.2021.124859

• Narula, V., Khan, M. F., Negi, A., Kalra, S., Thakur, A., & Jain, S. (2017). Low temperature optimization of biodiesel production from algal oil using CaO and CaO/Al2O3 as catalyst by the application of response surface methodology. Energy, 140, 879-884. https://doi.org/10.1016/j.energy.2017.09.028

• Nata, I. F., Putra, M. D., Irawan, C., & Lee, C. K. (2017). Catalytic performance of sulfonated carbon-based solid acid catalyst on esterification of waste cooking oil for biodiesel production. Journal of Environmental Chemical Engineering, 5(3), 2171-2175. https://doi.org/10.1016/j.jece.2017.04.029

• Ngaosuwan, K., Goodwin, J. G., & Prasertdham, P. (2016). A green sulfonated carbon-based catalyst derived from coffee residue for esterification. Renewable Energy, 86, 262-269. https://doi.org/10.1016/j.renene.2015.08.010

• Niu, S., Ning, Y., Lu, C., Han, K., Yu, H., & Zhou, Y. (2018). Esterification of oleic acid to produce biodiesel catalyzed by sulfonated activated carbon from bamboo. Energy Conversion and Management, 163(17923), 59-65. https://doi.org/10.1016/j.enconman.2018.02.055

• Noshadi, I., Amin, N. A. S., & Parnas, R. S. (2012). Continuous production of biodiesel from waste cooking oil in a reactive distillation column catalyzed by solid heteropolyacid: Optimization using response surface methodology (RSM). Fuel, 94, 156-164. https://doi.org/10.1016/j.fuel.2011.10.018

• Omidvarborna, H., Kumar, A., & Kim, D. (2016). Science of the total environment variation of diesel soot characteristics by different types and blends of biodiesel in a laboratory combustion chamber. Science of the Total Environment, 544, 450-459. https://doi.org/10.1016/j.scitotenv.2015.11.076

• Özbay, N., Oktar, N., & Tapan, N. A. (2008). Esterification of free fatty acids in waste cooking oils (WCO): Role of ion-exchange resins. Fuel, 87(10-11), 1789-1798. https://doi.org/10.1016/j.fuel.2007.12.010

• Palmonari, A., Cavallini, D., Sniffen, C. J., Fernandes, L., Holder, P., Fagioli, L., Fusaro, I., Biagi, G., Formigoni, A., & Mammi, L. (2020). Short communication: Characterization of molasses chemical composition. Journal of Dairy Science, 103(7), 6244-6249. https://doi.org/10.3168/jds.2019-17644

• Rabie, A. M., Mohammed, E. A., & Negm, N. A. (2018). Feasibility of modified bentonite as acidic heterogeneous catalyst in low temperature catalytic cracking process of biofuel production from nonedible vegetable oils. Journal of Molecular Liquids, 254(2018), 260-266. https://doi.org/10.1016/j.molliq.2018.01.110

• Rafati, A., Tahvildari, K., & Nozari, M. (2019). Production of biodiesel by electrolysis method from waste cooking oil using heterogeneous MgO-NaOH nano catalyst. Energy Sources, Part A: Recovery, Utilization and Environmental Effects, 41(9), 1062-1074. https://doi.org/10.1080/15567036.2018.1539139

• Rahimzadeh, H., Tabatabaei, M., Aghbashlo, M., Panahi, H. K. S., Rashidi, A., Goli, S. A. H., Mostafaei, M., Ardjmand, M., & Nizami, A. S. (2018). Potential of acid-activated bentonite and SO3H-functionalized MWCNTs for biodiesel production from residual olive oil under biorefinery scheme. Frontiers in Energy Research, 6, 1-10. https://doi.org/10.3389/fenrg.2018.00137

• Rocha, P. D., Oliveira, L. S., & Franca, A. S. (2019). Sulfonated activated carbon from corn cobs as heterogeneous catalysts for biodiesel production using microwave-assisted transesterification. Renewable Energy, 143, 1710-1716. https://doi.org/10.1016/j.renene.2019.05.070

• Rodríguez-Fernández, J., Hernández, J. J., Calle-Asensio, A., Ramos, Á., & Barba, J. (2019). Selection of blends of diesel fuel and advanced biofuels based on their physical and thermochemical properties. Energies, 12(11), Article 2034. https://doi.org/10.3390/en12112034

• Sahani, S., Roy, T., & Sharma, Y. C. (2020). Smart waste management of waste cooking oil for large scale high quality biodiesel production using Sr-Ti mixed metal oxide as solid catalyst: Optimization and E-metrics studies. Waste Management, 108, 189-201. https://doi.org/10.1016/j.wasman.2020.04.036

• Sari, E. P., Wijaya, K., Trisunaryanti, W., Syoufian, A., Hasanudin, H., & Saputri, W. D. (2021). The effective combination of zirconia superacid and zirconia-impregnated CaO in biodiesel manufacturing: Utilization of used coconut cooking oil (UCCO). International Journal of Energy and Environmental Engineering, 13, 967-978. https://doi.org/10.1007/s40095-021-00439-4

• Sharma, A., Kodgire, P., & Kachhwaha, S. S. (2019). Biodiesel production from waste cotton-seed cooking oil using microwave-assisted transesterification: Optimization and kinetic modeling. Renewable and Sustainable Energy Reviews, 116, Article 109394. https://doi.org/10.1016/j.rser.2019.109394

• Singh, V., Belova, L., Singh, B., & Sharma, Y. C. (2018). Biodiesel production using a novel heterogeneous catalyst, magnesium zirconate (Mg2Zr5O12): Process optimization through response surface methodology (RSM). Energy Conversion and Management, 174, 198-207. https://doi.org/10.1016/j.enconman.2018.08.029

• Soegiantoro, G. H., Chang, J., Rahmawati, P., Christiani, M. F., & Mufrodi, Z. (2019). Home-made ECO green biodiesel from chicken fat (CIAT) and waste cooking oil (pail). Energy Procedia, 158, 1105-1109. https://doi.org/10.1016/j.egypro.2019.01.267

• Sree, J. V., Chowdary, B. A., Kumar, K. S., Anbazhagan, M. P., & Subramanian, S. (2021). Optimization of the biodiesel production from waste cooking oil using homogeneous catalyst and heterogeneous catalysts. Materials Today: Proceedings, 46(10), 4900-4908. https://doi.org/10.1016/j.matpr.2020.10.332

• Suganuma, S., Nakajima, K., Kitano, M., & Hayashi, S. (2012). sp3-linked amorphous carbon with sulfonic acid groups as a heterogeneous acid catalyst. ChemSusChem, 5(9), 1841-1846. https://doi.org/10.1002/cssc.201200010

• Suresh, R., Antony, J. V., Vengalil, R., Kochimoolayil, G. E., & Joseph, R. (2017). Esterification of free fatty acids in non-edible oils using partially sulfonated polystyrene for biodiesel feedstock. Industrial Crops and Products, 95, 66-74. https://doi.org/10.1016/j.indcrop.2016.09.060

• Suwannasom, P., Tansupo, P., & Ruangviriyachai, C. (2016). A bone-based catalyst for biodiesel production from waste cooking oil. Energy Sources, Part A: Recovery, Utilization and Environmental Effects, 38(21), 3167-3173. https://doi.org/10.1080/15567036.2015.1137998

• Tan, Y. H., Abdullah, M. O., Nolasco-Hipolito, C., & Zauzi, N. S. A. (2017). Application of RSM and Taguchi methods for optimizing the transesterification of waste cooking oil catalyzed by solid ostrich and chicken-eggshell derived CaO. Renewable Energy, 114, 437-447. https://doi.org/10.1016/j.renene.2017.07.024

• Tang, Z. E., Lim, S., Pang, Y. L., Shuit, S. H., & Ong, H. C. (2020). Utilisation of biomass wastes based activated carbon supported heterogeneous acid catalyst for biodiesel production. Renewable Energy, 158, 91-102. https://doi.org/10.1016/j.renene.2020.05.119

• Wu, Z., Li, H., & Tu, D. (2015). Application of fourier transform infrared (FT-IR) spectroscopy combined with chemometrics for analysis of rapeseed oil adulterated with refining and purificating waste cooking oil. Food Analytical Methods, 8(10), 2581-2587. https://doi.org/10.1007/s12161-015-0149-z

• Xincheng, T., Niu, S., Zhao, S., Zhang, X., Li, X., Yu, H., Lu, C., & Han, K. (2019). Synthesis of sulfonated catalyst from bituminous coal to catalyze esterification for biodiesel production with promoted mechanism analysis. Journal of Industrial and Engineering Chemistry, 77, 432-440. https://doi.org/10.1016/j.jiec.2019.05.008

• Yahya, S., Wahab, S. K. M., & Harun, F. W. (2020). Optimization of biodiesel production from waste cooking oil using Fe-Montmorillonite K10 by response surface methodology. Renewable Energy, 157, 164-172. https://doi.org/10.1016/j.renene.2020.04.149

• Yuliana, M., Santoso, S. P., Soetaredjo, F. E., Ismadji, S., Ayucitra, A., Angkawijaya, A. E., Ju, Y. H., & Tran-Nguyen, P. L. (2020). A one-pot synthesis of biodiesel from leather tanning waste using supercritical ethanol: Process optimization. Biomass and Bioenergy, 142, Article 105761. https://doi.org/10.1016/j.biombioe.2020.105761

• Zhang, B., Gao, M., Geng, J., Cheng, Y., Wang, X., Wu, C., Wang, Q., Liu, S., & Cheung, S. M. (2021). Catalytic performance and deactivation mechanism of a one-step sulfonated carbon-based solid-acid catalyst in an esterification reaction. Renewable Energy, 164, 824-832. https://doi.org/10.1016/j.renene.2020.09.076

• Zhang, H., Gao, J., Zhao, Z., Chen, G. Z., Wu, T., & He, F. (2016). Esterification of fatty acids from waste cooking oil to biodiesel over a sulfonated resin/PVA composite. Catalysis Science and Technology, 6(14), 5590-5598. https://doi.org/10.1039/c5cy02133b

• Zhang, M., Sun, A., Meng, Y., Wang, L., Jiang, H., & Li, G. (2015). High activity ordered mesoporous carbon-based solid acid catalyst for the esterification of free fatty acids. Microporous and Mesoporous Materials, 204, 210-217. https://doi.org/10.1016/j.micromeso.2014.11.027

• Zik, N. A. F. A., Sulaiman, S., & Jamal, P. (2020). Biodiesel production from waste cooking oil using calcium oxide/nanocrystal cellulose/polyvinyl alcohol catalyst in a packed bed reactor. Renewable Energy, 155, 267-277. https://doi.org/10.1016/j.renene.2020.03.144