Determinação de Cu e Fe em Biodiesel por Espectrometria de Absorção Atômica com Atomização Eletrotérmica e Estudo do Efeito Catalítico destes Metais sobre a Estabilidade Oxidativa do Biodiesel / Determination of Cu and Fe in Biodiesel by Absorption Spectrometry Electrothermal atomic and Study of the Effect of Catalytic Metals on the Oxidative Stability of Biodiesel

AUTOR(ES)

MIRELA GHISI

DATA DE PUBLICAÇÃO

2011

RESUMO

The metals content in biodiesel is directly related with the raw material used and also with the utilized biodiesel production method. In this work, an evaluation of the main metals present in biodiesel samples from different sources was done. The qualitative analysis of the metal content was assessed using the Inductively Coupled Plasma Mass Spectrometry technique after sample digestion in microwave oven. The main metals identified in the analyzed biodiesel samples were Al, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sr and Zn. Metals like Ag, As, Ba, Cd, Co, Tl and V have not significant presence in the samples. Among these, Cu and Fe were selected due to their relevance and importance in oxidative process of biodiesel, to the development of an analytical methodology to be used in the determination by Electrothermal Atomic Absorption Spectrometry, and also evaluate the effect of these metals over the oxidative stability of the soy biodiesel. The samples were prepared with tetramethylammonium hydroxide (TMAH), and the pyrolysis and atomization temperatures were optimized pyrolysis and atomization curves. The high pyrolysis temperature adopted, 1000 oC, certainly minimized potential interferences, but calibration had to be carried out with aqueous standard solutions in the presence of the TMAH. The detection limits in the sample (3s, n=10), were quite low 15 ng g-1 and 24 ng g-1 for Cu and Fe, respectively. Seven biodiesel samples, produced from different raw materials, including vegetable seed, waste frying oil and animal fat were analyzed. Accuracy was validated by applying the recovery test (recoveries from 105% to 120%) and through comparison with the obtained results by High Resolution Continuum Source Electrothermal Atomic Absorption Spectrometry. The precision, expressed by the relative standard deviation, was better than 3% for Cu and than 7% for Fe. Copper could be quantified in two and Fe in three of the seven samples. The biodiesel sample from fodder turnip was especially rich in the analytes in comparison to the other samples. The influence of metals Cu and Fe on soy biodiesel oxidative stability was evaluated by Rancimat method through induction period, according with the Standard EN 14112. The metals Cu2+ and Fe3+ were added to the biodiesel samples in the form of theirs salts, and different storage times of the samples were evaluated. Due to the catalytic behaviour of these metals, the oxidative stability of the samples was affected, even under low metal concentrations. Compared to Cu2+, the effect over the biodiesel stability was higher when Fe3+ was added.

ASSUNTO(S)

metais biodiesel digestão em micro-ondas cu fe et aas hidróxido de tetrametilamônio (tmah) estabilidade oxidativa período de indução rancimat quimica biodiesel metals microwave oven digestion cu fe et aas tetramethylammonium hydroxide (tmah) oxidative stability induction period rancimat

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