Síntese de biodiesel metílico via esterificação utilizando nanopartículas magnéticas funcionalizadas com lignina sulfonada como catalisadores heterogêneos

Abstract

Esterification represents an important alternative route for biodiesel production, since it allows the use of low-cost lipid feedstocks with a high content of free fatty acids (FFA). Esterification is usually developed in homogeneous phase in the presence of mineral acid catalysts such as H2SO4, which present serious drawbacks that affect biodiesel production and increase its costs such as corrosivity, difficult removal of the reaction medium and impossibility of catalyst reuse. Thus, developing new routes that overcome these problems becomes important to the process. In this sense, heterogeneous acid catalysis is inserted. In this research, methylic biodiesel was synthesized via esterification of oleic acid using as heterogeneous catalysts sulfonated lignin (SL) and cobalt (CoFe2O4) and manganese (MnFe2O4) ferrites magnetic nanoparticles (MNP) functionalized with SL. SL was obtained through sulfonation of sugarcane bagasse lignin employing H2SO4 (98%) and acetic anhydride. Two different proportions of reactants were adopted, obtaining the solids SL5 and SL7.5 – later incorporated into the MNPs. In the esterification reactions were valuated the catalysts CoFe2O4-SL5; CoFe2O4-SL7.5; MnFe2O4-SL5; and MnFe2O4-SL7.5, considering as process variables: methanol/oleic acid molar ratio 10:1; catalyst mass of 5% relative to the fatty acid (w/w); reaction times of 4 and 6 hours; and temperatures of 80 and 100 °C. Elemental Analysis revealed that SL5 and SL7.5 has 2.68% sulfur content by mass and the following minimal molecular formulas: C9H10,52O5,62(SO3H)0,18 and C9H10,52O5,62(SO3H)0,17. The results evidenced that this stage was successful, since the diffractograms clearly exhibited the presence of the lignin typical broad amorphous halo at 2θ (10-30°) for CoFe2O4-SL5 and CoFe2O4-SL7.5, however something lower evident for MnFe2O4-SL5 and MnFe2O4-SL7.5. In addition, the thermograms showed that all functionalized NPMs exhibit percentages of incorporated SL greater than 50%, with the best results observed for CoFe2O4-SL5 (79.5%) and CoFe2O4-SL7.5 (78.5%). Gas Chromatography Mass Spectrometry (GC-MS) and Fourier Transform Infrared Spectroscopy (FTIR) revealed 6 h and 100 °C as the best reaction conditions considering time and temperature factors. In addition, CoFe2O4-SL5 and MnFe2O4-SL7.5 exhibited the best performances in the esterification experiments, presenting maximum conversions of oleic acid into fatty acid methyl esters of approximately 80%. The results evidence that the solid catalysts synthesized in the present work shows potential for use in the biodiesel production via esterification reaction, especially by using low-cost lipid feedstocks with high FFA content.