title: Theoretical Study on Free Fatty Acid Elimination Mechanism for Waste Cooking Oils to Biodiesel over Acid Catalyst.
abstract: A theoretical investigation on the esterification mechanism of free fatty acid (FFA) in waste cooking oils (WCOs) has been carried out using DMol(3) module based on the density functional theory (DFT). Three potential pathways of FFA esterification reaction are designed to achieve the formation of fatty acid methyl ester (FAME), and calculated results show that the energy barrier can be efficiently reduced from 88.597kcal/mol to 15.318kcal/mol by acid catalyst. The molar enthalpy changes (ΔrHm°) of designed pathways are negative, indicating that FFA esterification reaction is an exothermic process. The obtained favorable energy pathway is: H(+) firstly activates FFA, then the intermediate combines with methanol to form a tetrahedral structure, and finally, producing FAME after removing a water molecule. The rate-determining step is the combination of the activated FFA with methanol, and the activation energy is about 11.513kcal/mol at 298.15K. Our results should provide basic and reliable theoretical data for further understanding the elimination mechanism of FFA over acid catalyst in the conversion of WCOs to biodiesel products.
authors.affiliation: College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, PR China.
authors.forename: Kai
authors.initials: K
authors.lastname: Wang
authors.affiliation: College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, PR China. Electronic address: zhangxiaochao@tyut.edu.cn.
authors.forename: Xiaochao
authors.initials: X
authors.lastname: Zhang
authors.affiliation: College of Mining Engineering, Taiyuan University of Technology, Taiyuan 030024, PR China.
authors.forename: Jilong
authors.initials: J
authors.lastname: Zhang
authors.affiliation: College of Mining Engineering, Taiyuan University of Technology, Taiyuan 030024, PR China.
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, PR China. Electronic address: fancm@163.com.
authors.forename: Caimei
authors.initials: C
authors.lastname: Fan
authors.affiliation: College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, PR China.
authors.forename: Peide
authors.initials: P
authors.lastname: Han
mesh_terms: D000143:Acids / Q000737:chemistry*; D056804:Biofuels; D002384:Catalysis; D003296:Cooking; D004951:Esterification; D005230:Fatty Acids, Nonesterified / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry; D008962:Models, Theoretical; D010938:Plant Oils / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D000143:Acids; D056804:Biofuels; D005230:Fatty Acids, Nonesterified; D010938:Plant Oils; D014867:Water; D000432:Methanol
keywords: DMol(3) module; Esterification mechanism; Free fatty acid; Waste cooking oils