title: Optimization and kinetic modeling of esterification of the oil obtained from waste plum stones as a pretreatment step in biodiesel production.
abstract: This study reports on the use of oil obtained from waste plum stones as a low-cost feedstock for biodiesel production. Because of high free fatty acid (FFA) level (15.8%), the oil was processed through the two-step process including esterification of FFA and methanolysis of the esterified oil catalyzed by H2SO4 and CaO, respectively. Esterification was optimized by response surface methodology combined with a central composite design. The second-order polynomial equation predicted the lowest acid value of 0.53mgKOH/g under the following optimal reaction conditions: the methanol:oil molar ratio of 8.5:1, the catalyst amount of 2% and the reaction temperature of 45°C. The predicted acid value agreed with the experimental acid value (0.47mgKOH/g). The kinetics of FFA esterification was described by the irreversible pseudo first-order reaction rate law. The apparent kinetic constant was correlated with the initial methanol and catalyst concentrations and reaction temperature. The activation energy of the esterification reaction slightly decreased from 13.23 to 11.55kJ/mol with increasing the catalyst concentration from 0.049 to 0.172mol/dm(3). In the second step, the esterified oil reacted with methanol (methanol:oil molar ratio of 9:1) in the presence of CaO (5% to the oil mass) at 60°C. The properties of the obtained biodiesel were within the EN 14214 standard limits. Hence, waste plum stones might be valuable raw material for obtaining fatty oil for the use as alternative feedstock in biodiesel production.
authors.affiliation: Faculty of Technology, University of Niš, 16000 Leskovac, Bulevar Oslobodjenja 124, Serbia.
authors.forename: Milan D
authors.initials: MD
authors.lastname: Kostić
authors.affiliation: Faculty of Technology, University of Niš, 16000 Leskovac, Bulevar Oslobodjenja 124, Serbia.
authors.forename: Ana V
authors.initials: AV
authors.lastname: Veličković
authors.affiliation: Faculty of Science and Mathematics, Department of Biology and Ecology, University of Niš, Višegradska 33, 18000 Niš, Serbia.
authors.forename: Nataša M
authors.initials: NM
authors.lastname: Joković
authors.affiliation: Faculty of Technology, University of Niš, 16000 Leskovac, Bulevar Oslobodjenja 124, Serbia.
authors.forename: Olivera S
authors.initials: OS
authors.lastname: Stamenković
authors.affiliation: Faculty of Technology, University of Niš, 16000 Leskovac, Bulevar Oslobodjenja 124, Serbia. Electronic address: veljkovicvb@yahoo.com.
authors.forename: Vlada B
authors.initials: VB
authors.lastname: Veljković
mesh_terms: D056804:Biofuels; D002384:Catalysis; D004736:Energy-Generating Resources; D004951:Esterification; D005230:Fatty Acids, Nonesterified / Q000737:chemistry; D019649:Food Industry; D005735:Garbage; D007700:Kinetics; D008697:Methane / Q000737:chemistry; D000432:Methanol / Q000737:chemistry; D015233:Models, Statistical; D010938:Plant Oils / Q000737:chemistry*; D000068242:Prunus domestica / Q000737:chemistry*; D012639:Seeds / Q000737:chemistry*; D013672:Technology / Q000379:methods*; D013696:Temperature
chemical_list: D056804:Biofuels; D005230:Fatty Acids, Nonesterified; D010938:Plant Oils; D008697:Methane; D000432:Methanol
keywords: Biodiesel; Esterification; Kinetics; Methanolysis; Optimization; Plum kernel oil