Abstract
Bio-oils employed for various industrial purposes, such as biodiesel production, undergo extensive oxidation and degradation during transformation processes. Therefore, it is extremely important to predict their stability at high temperature. We report herein a new procedure based on the optically detected profile of headspace O2 concentration during isotherms at 130 °C for evaluating the oxidation kinetic parameters of several bio-oil feedstocks. The slope of O2 consumption and the induction period duration were related to the oil characteristics (molecular structure, acidity, and presence of intrinsic antioxidants or metals). The increase of the induction time caused by a standardized propyl gallate addition yielded a semiquantitative value of radical generation rate. Investigated oils included used cooking oils; mono-, di-, and triglycerides from natural sources; free fatty acids; transesterified oils; and their blends. With respect to other methods, this characterization presents the advantage of disentangling and evaluating the role of both fatty acids composition and naturally occurring antioxidants, and allows the development of rational strategies for antioxidant protection of oils and of their blends.
Highlights
Replacing fossil-derived energy sources with renewable feedstock is important to cope with the gradual depletion of nonrenewable fossil fuels, pollution, and excessive CO2 emissions [1].The conversion of waste and used cooking vegetable oils to renewable diesel is sought as a profitable source of biofuels, because it is less energy demanding than processes involving different feedstock, for instance lignocellulosic biomass [2]
The oils considered in the present study triglycerides; mixtures of mono, and triglycerides in different proportions; free fatty included acids; transesterified oils; waste oils; and oilsdi, deriving triglycerides in different proportions; fatty acids; transesterified oils; waste oils; and biodiesel oils deriving from wood processing, to reflect thefree diversity of bio-based matrixes used to produce
The analysis of the curves obtained by this experimental setup allowed measuring various parameters describing oil oxidation, and to disentangle the role of fatty acids composition from that of antioxidants or other minor compounds
Summary
The conversion of waste and used cooking vegetable oils to renewable diesel is sought as a profitable source of biofuels, because it is less energy demanding than processes involving different feedstock, for instance lignocellulosic biomass [2]. First-generation biofuels, mainly consisting of fatty acids methyl esters, has specific disadvantages caused by their high oxygen content, such as a poor calorific value, low storage stability, high viscosity, and density. This prompted the development of a second generation of biofuels, based on the simultaneous deoxygenation and hydrogenation of first-generation biodiesel [3]. Up-conversion, requires the storage and manipulation of feedstocks at relatively high temperatures, which is a well-known condition that increases degradation processes [4].
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