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Front. Energy Res. | doi: 10.3389/fenrg.2018.00137

Potential of acid-activated bentonite and SO3H-functionalized MWCNTs for biodiesel production from residual olive oil under biorefinery scheme

Hadi Rahimzadeh1,  Meisam Tabatabaei2*, Moratza Aghbashlo3, Alimorad Rashidi4, Sayed Amir Hossein Goli5, Mostafa Mostafaei6, Mehdi Ardjmand1 and  Abdul-Sattar Nizami7
  • 1Islamic Azad University System, Iran
  • 2Agricultural Biotechnology Research Institute of Iran, Iran
  • 3University of Tehran, Iran
  • 4Research Institute of Petroleum Industry (RIPI), Iran
  • 5Isfahan University of Technology, Iran
  • 6Razi University, Iran
  • 7King Abdulaziz University, Saudi Arabia

Application of acid-activated bentonite and SO3H-functionlized multiwall carbon nanotubes (SO3H-MWCNTs) for lowering free fatty acids (FFAs) content of low-quality residual olive oil, prior to alkali-catalyzed transesterification was investigated. The used bentonite was first characterized by Scanning Electron Microscopy (SEM), Inductively Coupled Plasma mass spectrometry (ICP-MS), and X-ray fluorescence (XRF), and was subsequently activated by different concentrations of H2SO4 (3, 5, and 10 N). Specific surface area of the original bentonite was measured by Brunauer, Emmett and Teller (BET) method at 45 m2/g and was best improved after 5 N-acid activation (95-98°C, 2 h) reaching 68 m2/g. MWCNTs was synthesized through methane decomposition (Co-Mo/MgO catalyst, 900°C) during the chemical vapor deposition (CVD) process. After two acid-purification (HCl, HNO3) and two deionized-water-neutralization steps, SO3H was grafted on MWCNTs (concentrated H2SO4, 110°C for 3 h) and again neutralized with deionized water and then dried. The synthesized SO3H-MWCNTs were analyzed using Fourier-Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microscopy (TEM). The activated bentonite and SO3H-MWCNTs were utilized (5 wt.% and 3 wt.%, respectively) as solid catalysts in esterification reaction (62°C, 450 rpm; 15:1 and 12:1 methanol-to-oil molar ratio, 27 h and 8 h, respectively) to convert FFAs to their corresponding methyl esters. The results obtained revealed an FFA to methyl ester conversion of about 67% for the activated bentonite and 65% for the SO3H-MWCNTs. More specifically, the acid value of the residual olive oil was decreased significantly from 2.5 to 0.85 and 0.89 mg KOH/g using activated bentonite and SO3H-MWCNTs, respectively. The total FFAs in the residual olive oil after esterification was below 0.5%, which was appropriate for efficient alkaline-transesterification reaction. Both catalysts can effectively pretreat low quality oil feedstock for sustainable biodiesel production under a biorefinery scheme. Overall, the acid-activate bentonite was found more convenient, cost-effective, and environment-friendly than the SO3H-MWCNTs.

Keywords: Biodiesel production, Acid-activated bentonite, SO3H-functionlized multiwall carbon nanotube (SO3H-MWCNTs), Waste olive oil, High free fatty acid, Biorefinery

Received: 22 Sep 2018; Accepted: 28 Nov 2018.

Edited by:

Saurabh Dhiman, South Dakota School of Mines and Technology, United States

Reviewed by:

Jaime Puna, Instituto Superior de Engenharia de Lisboa, Portugal
Konstantinos Moustakas, National Technical University of Athens, Greece  

Copyright: © 2018 Rahimzadeh, Tabatabaei, Aghbashlo, Rashidi, Goli, Mostafaei, Ardjmand and Nizami. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Meisam Tabatabaei, Agricultural Biotechnology Research Institute of Iran, Karaj, Iran,