Fuel and Combustion

Fuel and Combustion

Acid-Modified Clinoptilolite Zeolite as an Efficient Catalyst for Green Fuel Production through Oleic Acid Esterification

Document Type : Original Article

Authors
Reza Khoshbin 1
Kobra Pourabdollah 2
1 Department of Chemical Technologies, Iranian Research Organization for Science and Technology (IROST),
2 Department of Chemical and Petroleum Engineering, Chemistry and Chemical Engineering Research Center of Iran
10.22034/jfnc.2026.543874.1437
Abstract
A series of catalysts based on natural clinoptilolite zeolite were synthesized and characterized for biodiesel production through the esterification reaction of oleic acid. For this purpose, sulfur-containing functional groups were incorporated into the clinoptilolite framework through ion-exchange treatment with sulfuric acid solutions at concentrations of 0.5, 1, and 2 M. The structural properties of the synthesized catalysts were investigated using XRD, FESEM, EDX dot mapping, FTIR, as well as N2 adsorption–desorption isotherms. XRD patterns and FTIR spectra revealed that the crystallinity of clinoptilolite gradually decreased during sulfuric acid treatment, with a pronounced reduction observed for the sample modified with 2 M acid. N2 adsorption–desorption isotherms analysis demonstrated that the specific surface area of the sample treated with 1 M sulfuric acid increased by 45% compared to the raw zeolite. Furthermore, EDX dot mapping confirmed the homogeneous distribution of sulfur species across all modified samples. Catalytic performance evaluation in the esterification of oleic acid indicated that the incorporation of sulfur functionalities significantly enhanced catalytic activity, with the highest conversion of 70.6% achieved by the sample treated with 1 M sulfuric acid.

Highlights

Among the various methods employed for biodiesel production, transesterification is the most widely used due to its simplicity and cost-effectiveness [1]. In this process, triglycerides react with an alcohol in the presence of a catalyst to produce fatty acid alkyl esters and glycerol. Various catalysts, including zinc aluminate- and magnesium aluminate-based spinel catalysts, have been developed to facilitate the transesterification reaction [2,3]. However, the presence of free fatty acids (FFAs) in the feedstock adversely affects the performance of alkaline catalysts, leading to soap formation and reduced efficiency. Consequently, acid catalysts have attracted considerable attention for esterification reactions aimed at reducing FFAs prior to transesterification [4]. Among natural zeolites, clinoptilolite is one of the most abundant and stable materials, characterized by a robust microporous structure. To enhance the performance of natural zeolites, their structural and surface properties can be tailored through various modification techniques, such as acid leaching, surfactant treatment, ion exchange with alkaline solutions, hydrothermal processing, and thermal treatment [5,6]. These modification approaches can significantly alter porosity, increase active surface area, and influence surface acidity and electrostatic properties [7].

In this study, biodiesel production was investigated through the esterification of oleic acid using sulfuric acid–modified natural clinoptilolite zeolite. The structural properties of the modified catalysts were characterized by XRD, nitrogen adsorption–desorption isotherms, SEM, and EDX dot mapping.

Keywords
Clinoptilolite zeolite
Biodiesel
Esterification
Oleic acid
Subjects

در این پژوهش زئولیت طبیعی کلینوپتیلولیت فراوری شده و گروه‌های عاملی سولفاته بر روی آن بارگذاری شد. برای این منظور، فرآورش با سولفوریک اسید در غلظت­های 5/0، 1 و 2 مولار صورت گرفت. مشخصات ساختاری کاتالیست­های سنتز شده، توسط آنالیزهای XRD، SEM، FTIR، هم‌دماهای جذب و دفع سطحی نیتروژن و نیز EDX dot mapping مورد بررسی قرار گرفت. نتایج نشان داد که پیک­های شاخص الگوی استاندارد XRD زئولیت طبیعی کلینوپتیلولیت در تمامی نمونه­های سنتز شده، قابل مشاهده است. با افزایش غلظت سولفوریک اسید تا 1 مولار، ساختار بلوری زئولیت کلینوپتیلولیت حفظ شده است و در نمونه فراوری با غلظت 2 مولار، ساختار بلوری زئولیت دچار تخریب نسبی شد. لکن با افزایش غلظت سولفوریک اسید، ساختار بلوری زئولیت تا حدودی تحت تاثیر قرار می­گیرد و در غلظت 2 مولار، کاهش در میزان بلورینگی زئولیت طبیعی قابل مشاهده است. مورفولوژی نمونه­های سنتز شده تحت تأثیر افزودن سولفوریک اسید، تغییر محسوسی نداشتند. توزیع عناصر سیلیسیم، آلومینیوم و نیز گوگرد توسط آنالیز EDX dot mapping نشان می‌دهد که با افزودن غلظت سولفوریک اسید، عملکرد کاتالیست‌های سنتز شده، در واکنش استریفیکاسیون اولئیک اسید مورد ارزیابی قرار گرفت. نتایج نشان داد که نمونه فراوری شده با سولفوریک اسید 1 مولار، بالاترین میزان تبدیل اولئیک اسید را ارائه می­کند. علت این امر را می‌توان به اثر هم افزایی گروه­های عاملی سولفاتی و نیز حفظ ساختار بلوری زئولیت کلینوپتیلولیت نسبت داد.

[1]           Y. Xue, F. Chen, B. Sun, H. Lin, B. Dai, and S. Han, "Effect of nanocomposite as pour point depressant on the cold flow properties and crystallization behavior of diesel fuel," Chinese Chemical Letters, vol. 33, no. 5, pp. 2677-2680, 2022.
[2]           K. Ghavami, F. Akhlaghian, and F. Rahmani, "Potassium compounds-Al2O3 catalyst synthesized by using the sol-gel urea combustion method for transesterification of sunflower and waste cooking oils," Biomass Conversion and Biorefinery, vol. 12, no. 4, pp. 1139-1152, 2022.
[3]           A. Godarzi, P. Vaziri, F. Akhlaghian, F. Rahmani, and M. Khaledian, "Innovative magnetic catalyst facilitates biodiesel production via transesterification of sunflower and waste cooking oils," Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, vol. 45, no. 4, pp. 12277-12294, 2023.
[4]           I. Ambat, V. Srivastava, and M. Sillanpää, "Recent advancement in biodiesel production methodologies using various feedstock: A review," Renewable and sustainable energy reviews, vol. 90, pp. 356-369, 2018.
[5]           R. Khoshbin, M. Naeimi, F. M. Alikhani, M. S. Hosseini Hashemi, and H. Moradi, "Novel approach for synthesis of highly active nanostructured MgO/ZnAl2O4 catalyst via gel-combustion method used in biofuel production from sunflower oil: Effect of mixed fuel," Advanced Powder Technology, vol. 34, no. 11, p. 104226, 2023/11/01/ 2023, doi: https://doi.org/10.1016/j.apt.2023.104226.
[6]           B. R. Vahid and M. Haghighi, "Biodiesel production from sunflower oil over MgO/MgAl2O4 nanocatalyst: effect of fuel type on catalyst nanostructure and performance," Energy Conversion and Management, vol. 134, pp. 290-300, 2017.
[7]           B. Ebadinezhad and M. Haghighi, "Sono-solvothermal decoration of pore size controlled SAPO-34 by nano-ceria for green fuel production via esterification reaction," Chemical Engineering Journal, vol. 402, p. 125146, 2020.
[8]           M. C. Nongbe, T. Ekou, L. Ekou, K. B. Yao, E. Le Grognec, and F.-X. Felpin, "Biodiesel production from palm oil using sulfonated graphene catalyst," Renewable Energy, vol. 106, pp. 135-141, 2017.
[9]           G. N. Shao, R. Sheikh, A. Hilonga, J. E. Lee, Y.-H. Park, and H. T. Kim, "Biodiesel production by sulfated mesoporous titania–silica catalysts synthesized by the sol–gel process from less expensive precursors," Chemical engineering journal, vol. 215, pp. 600-607, 2013.
[10]         Gardy, J., Nourafkan, E., Osatiashtiani, A., Lee, A. F., Wilson, K., Hassanpour, A., & Lai, X., "A core-shell SO4/Mg-Al-Fe3O4 catalyst for biodiesel production," Applied Catalysis B: Environmental, vol. 259, p. 118093, 2019.
[11]         S. Karimi and M. Saidi, "Application of nano hydrophobic sulfated mordenite as a novel catalyst for biodiesel production from neem seed-derived oil by electrochemical method," Energy Conversion and Management, vol. 299, p. 117886, 2024.
[12]         L. Yosefi, M. Haghighi, S. Allahyari, and S. Ashkriz, "The beneficial use of HCl‐activated natural zeolite in ultrasound assisted synthesis of Cu/clinoptilolite–CeO2 nanocatalyst used for catalytic oxidation of diluted toluene in air at low temperature," Journal of Chemical Technology & Biotechnology, vol. 90, no. 4, pp. 765-774, 2015.
[13]         L. Yosefi, M. Haghighi, S. Allahyari, and S. Ashkriz, "Effect of ultrasound irradiation and Ni-loading on properties and performance of CeO2-doped Ni/clinoptilolite nanocatalyst used in polluted air treatment," Process Safety and Environmental Protection, vol. 95, pp. 26-37, 2015.
[14]         F. Rahmani, M. Haghighi, and M. Amini, "The beneficial utilization of natural zeolite in preparation of Cr/clinoptilolite nanocatalyst used in CO2-oxidative dehydrogenation of ethane to ethylene," Journal of Industrial and Engineering Chemistry, vol. 31, pp. 142-155, 2015.
[15]         R. Khoshbin, M. Haghighi, and N. Asgari, "Direct synthesis of dimethyl ether on the admixed nanocatalystsof CuO–ZnO–Al2O3 and HNO3-modified clinoptilolite at high pressures: Surface properties and catalytic performance," Materials Research Bulletin, vol. 48, no. 2, pp. 767-777, 2013.
[16]         S. M. Sajjadi, M. Haghighi, and F. Rahmani, "Sol-gel synthesis and catalytic performance of Ni-Co/Al 2 O 3-MgO-ZrO 2 nanocatalyst with different ZrO 2-loadings used in CH 4/CO 2 reforming for hydrogen production," International Journal of Oil, Gas and Coal Technology, vol. 8, no. 3, pp. 304-324, 2014.
[17]         Oliveira, Claudinei F., Luiz M. Dezaneti, Fillipe AC Garcia, Julio L. de Macedo, José A. Dias, Sílvia CL Dias, and Kayne SP Alvim., "Esterification of oleic acid with ethanol by 12-tungstophosphoric acid supported on zirconia," Applied Catalysis A: General, vol. 372, no. 2, pp. 153-161, 2010.
[18]         L. A. S. do Nascimento, L. M. Tito, R. S. Angélica, C. E. Da Costa, J. R. Zamian, and G. N. da Rocha Filho, "Esterification of oleic acid over solid acid catalysts prepared from Amazon flint kaolin," Applied Catalysis B: Environmental, vol. 101, no. 3-4, pp. 495-503, 2011.
[19]         Y.-T. Wang, Z. Fang, and F. Zhang, "Esterification of oleic acid to biodiesel catalyzed by a highly acidic carbonaceous catalyst," Catalysis Today, vol. 319, pp. 172-181, 2019.
[20]         S. Niu, Y. Ning, C. Lu, K. Han, H. Yu, and Y. Zhou, "Esterification of oleic acid to produce biodiesel catalyzed by sulfonated activated carbon from bamboo," Energy Conversion and Management, vol. 163, pp. 59-65, 2018.
[21]         Z. Gao, S. Tang, X. Cui, S. Tian, and M. Zhang, "Efficient mesoporous carbon-based solid catalyst for the esterification of oleic acid," Fuel, vol. 140, pp. 669-676, 2015.
[22]         K.-H. Chung and B.-G. Park, "Esterification of oleic acid in soybean oil on zeolite catalysts with different acidity," Journal of Industrial and Engineering Chemistry, vol. 15, no. 3, pp. 388-392, 2009.
[23]         A. L. Cardoso, S. C. G. Neves, and M. J. Da Silva, "Esterification of oleic acid for biodiesel production catalyzed by SnCl2: a kinetic investigation," Energies, vol. 1, no. 2, pp. 79-92, 2008.
[24]         L. Elizabeth, A. R. Maulana, A. D. Febriani, and E. Andrijanto, "Effectiveness of Silica Sulphate Catalyst Based on Rice Husk Ash in The Oleic Acid Esterification Process," Fluida, vol. 17, no. 2, pp. 57-64, 2024.