Acid Value, Polar Compounds and Polymers as Determinants of the Efficient Conversion of Waste Frying Oils to Biodiesel

Abstract

The cost of starting materials for the production of biodiesel is typically 75 % of the final retail price. Oils previously used for frying, waste frying oils (WFO), are a very suitable resource. Repetitive use of oil for frying foods involves high temperature, moisture and aeration for extended periods. The most important deterioration processes triggered by these conditions are hydrolysis and oxidation. In this study, 24 WFO samples of different origins were analyzed and classified as potential starting materials for biodiesel production using three quality parameters representing the main factors that affect the conversion of WFO. These parameters were: acid value, content of polar compounds and content of polymers, which varied in the ranges from 0.2 to 7.6, 14.9 to 43.2 and 0.9 to 15.2 %, respectively. Ester content obtained using conventional transesterification (TE) for WFO conversion decreased with increased levels of WFO deterioration determined by any of the three parameters noted above. TE products obtained had ester content between 81.4 and 95.7 %. Total ester content of a WFO sample with relatively low %AV could be increased to 96.5 % using a twostage base catalysis TE. Finally, conversion of WFO samples resulted in ester contents of 89.0 and 91.3 %, respectively, when transesterified by conventional TE. After blending up to 10 % with refined oil, the ester content achieved was near 96.5 %. Thus, the blending represents an alternative for obtaining a product with suitable ester content.

Controlling the oxidative stability of biodiesel using oils or biodiesel blending or antioxidants addition

“…in biodiesel, increased with heating time and is correlated with the amount of dimeric fatty acid methyl esters [36]. Vieitez et al [37] also state that the ester content of WFO biodiesel decreased with increased levels of WFO deterioration compounds measured by the acid value and the contents of polar compounds and polymers.…”

“…As discussed above, Tables 2 and 3 show that in fact the FAME content of WFO biodiesel is lower than that of the other vegetable oils. This is due to the increase in the contents of several impurities like the free fatty acids, soaps, polar compounds and polymers that occurs during the heating and frying of food in vegetable oils that has a negative impact on the esters content of biodiesel [36,37]. Table 3 indicates that the FAME content and the oxidative stability of WFO biodiesel were lower than the values imposed by EN 14214 (96.5% and 8 h, respectively).…”

“…This is a typical behavior of these oils because during heating the oils undergo degradation by hydrolytic and oxidative reactions that change the chemical and physical properties of the oil [4]. Vieitez et al [37] also state that the ester content of WFO biodiesel decreased with increased levels of WFO deterioration compounds measured by the acid value and the contents of polar compounds and polymers. These authors found that the Conradson carbon residue value, which is a measure of the content of impurities like glycerides, free fatty acids, soaps, catalyst etc.…”

“…In fact, the vegetable oils used in industrial or household frying undergo degradation by hydrolytic and oxidative reactions, both processes being responsible for changes in the chemical and physical properties that, among other problems, lead to the decrease in the oxidative stability, as compared to the fresh parent oil [4]. This is due to the increase in the contents of several impurities like the free fatty acids, soaps, polar compounds and polymers that occurs during the heating and frying of food in vegetable oils that has a negative impact on the esters content of biodiesel [36,37]. This is due to the increase in the contents of several impurities like the free fatty acids, soaps, polar compounds and polymers that occurs during the heating and frying of food in vegetable oils that has a negative impact on the esters content of biodiesel [36,37].…”

Effect of Biodiesel Mixture Derived from Waste Frying-Corn, Frying-Canola-Corn and Canola-Corn Cooking Oils with Various ‎Ages on Physicochemical Properties

“…Utilizing WCVOs as a fuel could effectively reduce the cost of removing and treating residual oil [24][25][26][27]. In addition, due to chemical reactions during the food cooking process or raw food, the WCVOs contains other compounds such as water, free fatty acids (FFA), polar compounds and non-volatile compounds in addition to triacylglycerols, which mainly affect homogeneous catalytic transesterification reactions [28,29].…”