Oxidative stability of soybean oil fatty acid methyl esters by oil stability index (OSI)

Abstract

Biodiesel, an alternative diesel fuel derived from transesterification of vegetable oils or animal fats, is composed of saturated and unsaturated long-chain FA alkyl esters. During long-term storage, oxidation caused by contact with air (autoxidation) presents a legitimate concern with respect to monitoring and maintaining fuel quality. Extensive oxidative degradation may compromise quality by adversely affecting kinematic viscosity, acid value, or PV. This work examines the oil stability index (OSI) as a parameter for monitoring the oxidative stability of soybean oil FAME (SME). SME samples from five separate sources and with varying storage and handling histories were analyzed for OSI at 60°C using an oxidative stability instrument. Results showed that OSI may be used to measure relative oxidative stability of SME samples as well as to differentiate between samples from different producers. Although addition of α-tocopherol or TBHQ increased OSI, responses to these antioxidants varied with respect to SME sample. Variations in response to added antioxidant were attributed to aging and other effects that may have caused oxidative degradation in samples prior to acquisition for this study. Results showed that OSI was more sensitive than iodine value in detecting the effects of oxidative degradation in its early stages when monitoring SME during storage. FIG. 1.Oxidative stability instrument data (conductivity vs. time) for one replicate oil stability index (OSI) measurement each for neat SME-A and SME-A treated with 1000 ppm α-tocopherol and 500 ppm TBHQ. Results for each curve were: OSI = 9.45 h for SME-A, 23.55 h for α-tocopherol, and 53.75 h for TBHQ. SME = soybean oil FAME. OXIDATIVE STABILITY OF BIODIESEL 385 JAOCS, Vol. 82, no. 5 (2005) FIG. 2. Effect of antioxidant loading on OSI of SME-D. See Figure 1 for abbreviations.

The oxidative stability of biodiesel and its impact on the deterioration of metallic and polymeric materials: a review

“…26 It is one of the most important methods in the measurement and evaluation of the oxidation of biodiesel, and many works report its use. 6,18,23,[27][28][29][30][31][32][33][34][35][36][37] The European standard for biodiesel quality (EN 14214) uses the Rancimat method, developed by Hardon and Zürcher, for measuring oxidative stability. 34 At present, Metrohm is the company that manufactures the Rancimat ® equipment used for this method.…”

“…14,40 The acidity is also increased when the water that remains in the biodiesel causes the hydrolysis of esters, producing free fatty acids. 14,28 Acidity is a parameter regulated by international standards for biodiesel. European (EN 14214) and American standards (ASTM 6751) limit maximum values to 0.5 and 0.8 mg KOH g -1 , respectively.…”

Antioxidants for improving storage stability of biodiesel

“…31 In general, a maximum test temperature of 60ºC was recommended for testing any biodiesel derived from high-iodine value (IV > 110) feedstocks unless it has been treated with antioxidants. 29,51 Another earlier study recommended a maximum temperature in the range 75-90ºC for blends of biodiesel with jet fuel. However, corresponding peak maxima detected at 117, 18, and 5 min demonstrated that increasing degree of unsaturation decreases oxidation induction time (OIT).…”

Avaliação da estabilidade oxidativa de biodiesel de óleo de girassol com antioxidantes

“…Estes estudos geralmente mostram que a P-DSC tem a vantagem de aumentar o número total de moles de oxigênio presente na célula, permitindo a aceleração da reação a baixas temperaturas. 32 Talvez o primeiro estudo a examinar a oxidação de ésteres metílicos de ácidos graxos (biodiesel) tenha sido realizado por apontaram que a análise por P-DSC é uma técnica apropriada para verificação da atividade antioxidante em relação aos efeitos dos tipos e concentração dos antioxidantes na resistência relativa à oxidação do biodiesel. O objetivo do trabalho foi produzir biodiesel a partir de óleo de girassol e etanol anidro, caracterizá-lo quanto a alguns parâmetros físico-químicos estabelecidos pela Agência Nacional do Petróleo (ANP) e avaliar sua estabilidade oxidativa com adição de antioxi-ANP) e avaliar sua estabilidade oxidativa com adição de antioxidantes sintéticos.…”