The presence of small amounts of free glycerol in fatty acid methyl esters used as diesel fuel or as heating fuel may represent the reason for some failures in engines and heating systems as well. Several methods are actually available for the determination of free-glycerol traces in biodiesel, and most on them are based on gas-chromatographic techniques. After a review of the existing methods, a new procedure based on periodate oxidation of glycerol, leading to the preparation of formaldehyde, on reaction with acetylacetone and on spectrophotometric measurement at 410 nm is illustrated. This method is simple, quick and economic and seems to be sufficiently reliable. Data related to recovery tests and analyses of real samples are shown, also in correlation with the existing reference method.

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Biodiesel stability under commercial storage conditions over one yearResults obtained from a long-term storage study using eleven different biodiesel samples are presented. Samples prepared from several feedstocks using different manufacturing technologies (with or without biodiesel distillation), some containing an antioxidant additive, were stored in 200 l drums. These were periodically monitored during the complete storage period by analysis of fifteen different properties.Several properties do not show any significant change during storage, while others such as viscosity, peroxide value and more dramatically, Rancimat Induction Period demonstrated changes related to the nature of the starting product.A parallel test, carried out in simulated wrong storage conditions (occasional shaking promoting intimate contact between biodiesel and air oxygen) lead to some strong changes in biodiesel composition and can be used as a guide for devising biodiesel production set-up, storage and distribution chain.

Evaluation of biodiesel storage stability using reference methodsThe recorded changes in 8 different samples of biodiesel (from 4 different feedstocks, both undistilled and distilled) during accelerated ageing are shown in this paper. ASTM D 4625 method for quick ageing of common diesel fuels, carried out at 43 °C, allows to simulate the changes taking place in fuel during a long-term storage. All quality parameters of biodiesel are changing during time, according to the storage stability of different samples. The changes in other parameters not included in CEN tentative specification such as polymer content and peroxide value were recorded and plotted against storage time. Samples were also evaluated in terms of insoluble formation (filterable + adherent) but in any case significant insoluble formation was observed. The conclusion was that polymers formed during storage of biodiesel in controlled conditions are soluble in oxidised biodiesel, thanks to its high polarity and become insoluble only when oxidised biodiesel is mixed with diesel fuel.

The paper discusses the levels of degradation of some co-and by-products of the food chain intended for feed uses. As the first part of a research project, Feeding Fats Safety, financed by the 6 th Framework Programme-EC, a total of 123 samples were collected from 10 European countries, corresponding to fat co-and by-products such as animal fats, fish oils, acid oils from refining, recycled cooking oils, etc. Several composition and degradation parameters (moisture, acid value, diacylglycerols and monoacylglycerols, peroxides, secondary oxidation products, polymers of triacylglycerols, fatty acid composition, tocopherols and tocotrienols) were evaluated. These findings lead to the conclusion that some fat by-and co-products, such as fish oils, lecithins and acid oils, show poor, non-standardized quality and that production processes need to be greatly improved. Conclusions are also put forward about the applicability and utility of each analytical parameter for characterization and quality control.