Influence of Water and Ultraviolet Irradiation on the Induction Period of the Oxidation of Biodiesel

Abstract

Biodiesel degrades due to oxidative processes, causing a decrease in its quality. In the present work, it has been clearly shown that the incidence of ultraviolet radiation on biodiesels obtained from soy, canola, linseed and microalgae oils initiate oxidative processes which lead to the decrease in the induction period (IP) of the fuel. The influence of the residual water content of the same biodiesels on the oxidation process was also investigated with and without the incidence of ultraviolet radiation. Between 190 and 850 ppm of water in the biodiesel and without UV irradiation, no significant change in the IP values was observed under the experimental conditions. Keywords: biodiesel, oxidative stability, photo-oxidation, residual water IntroductionBiodiesel is a biofuel derived from renewable sources such as vegetable oils and animal fats. It presents physicochemical characteristics similar to that of petrodiesel and can therefore be directly used in diesel engines. Because biodiesel is produced from renewable and biodegradable raw materials, it presents some advantages over petrodiesel, for example, the absence of sulfur in emissions, a high flash point, and good lubricity. 1,2 Biodiesel is composed of a mixture of alkyl esters, usually methyl or ethyl derivatives, obtained through transesterification reactions of vegetable oils and animal fats with methanol or ethanol in the presence of a catalyst.Oxidation reactions of biodiesel can occur on account of various factors, such as high unsaturation and total number and position of allylic and bis-allylic carbons that are adjacent to the double bonds of the molecules of alkyl esters, exposure to light, temperature, presence of transition metals, and exposure to oxygen. [3][4][5] It was also reported that hydrolysis reactions can occur depending on the environmental humidity or even on the humidity present in the storage tanks. Residual water is particularly problematic because it can hydrolyze the biodiesel, producing free fatty acids and alcohol and increasing the acid number of biodiesel. 6Similar to lipids, the oxidation of biodiesel occurs mainly through two processes called auto-oxidation and photo-oxidation. Auto-oxidation is the main cause of the oxidation of biodiesel. It involves the formation of free radicals and can be summarized in three steps called initiation, propagation, and termination, as schematized in Figure 1. 7 In the first phase, known as the induction or initiation period, the initial formation of free radicals occurs. In the second phase, known as propagation, the formation of a great quantity of peroxides and hydroperoxides occurs. Finally, the termination step occurs, forming high concentrations of degradation products, such as alcohols, aldehydes, ketones, organic acids, and polymers, whose presence changes the properties of the biodiesel. Vol. 28, No. 4, 2017 Another type of oxidation reaction that biodiesel can undergo is the photo-oxidation. Free radicals, which are known as initiators of oxidation processes, are formed as a...

Mechanisms of Methylparaben Adsorption onto Activated Carbons: Removal Tests Supported by a Calorimetric Study of the Adsorbent–Adsorbate Interactions

“…The thermal treatments at 1073 and 1173 K generated a decrease of phenol groups concentration because their temperature of thermal stability (623–923 K) was overpassed [26,27]. However, the amount of carboxylic acids increased despite the fact that the temperature of their thermal stability is in the range 523–623 K. This behaviour can be attributed to the reaction of free radicals formed in the reduction of oxygenated groups and carbon dioxide during the treatment [28]. For the same reasons, it is assumed that the lactones have a similar trend to carboxylic acids.…”

Physicochemical Properties of Activated Carbon: Their Effect on the Adsorption of Pharmaceutical Compounds and Adsorbate–Adsorbent Interactions

“…The CAR1073, CAR1173, and CAR1273 activated carbons have a total acidity equivalent to that of the starting activated carbon. However, at the temperature of thermal treatment their reduction was expected, therefore the formation of acid groups after the thermal treatment was attributed to the reaction between free radicals generated by the breakdown of the carbonaceous chains in the heat treatment and environmental oxygen-forming groups such as carboxylic acids [24]. The formation of acid groups results in greater surface polarity.…”

The examination, evaluation and comparison of corrosion effect on different metal surface by various crops based biodiesel

“…6,7 Yet, the corrosive nature and self-oxidation characteristics of biodiesel seem to be a significant problem. 8–11 These severe problems may degrade the quality of fuel and surface of engine components material whenever directly exposed to biodiesel. The critical factors for the oxidation of biodiesel have been well identified.…”