Estudo do processo de purificação e eterificação do glicerol residual proveniente da indústria do biodiesel

Abstract

The production of biodiesel, through transesterification routes, generate a high amount of glycerol, approximately 10 m3 for every 90 m3 of the produced biodiesel. As a result of this oversupply, which exceeds the capacity of absorption of the markets, the commercial value of glycerol has been decreasing. From this scenario, the valorization of glycerol using chemical routes is being highlighted. An interesting option is glycerol ether productions, which can be used as fuel additives in diesel engines to improve the combustion efficiency, reducing soot emission and increasing cetane index. In this study, a purification route applied to residual glycerol and its valorization by etherification was evaluated. The purification process is based on five stages that compose the methodology: acidification, separation, neutralization, adsorption and ion exchange. The glycerol content was analyzed by the sodium periodate method. In order to obtain comparison parameters, the etherification reaction tests were performed using pure glycerin initially. Following the reaction parameters previously determinate, the purified glycerin was also used to produce glycerol ethers. Subsequently tests were carried out for different alcohols: ethanol, isopropanol, 3-methyl butanol (isoamylic) and 2-ethylhexanol. According to experimental design, the reaction temperature was set up to 180 °C varying the molar ratio of the alcohol/glycerol (3/1–6/1). The catalyst (Amberlyst 15®) content was adjusted to 0.5 or 1.0 g and the reaction time to 6–8 h. The reaction product was purified by liquid-liquid extraction and distillation, which occurred at varied temperatures according to the boiling points (bp) of the corresponding alcohols. The conversion and selectivity of the reactions were evaluated by Gas Chromatography (GC), and the modification of the glycerol molecular structure was investigated by Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR). The purification process conduces to glycerol content above 98% pure. The results of the reaction planning for both the commercial and purified glycerin were similar, corroborating to the efficiency of the purification process. In terms of conversion, all the processed reactions showed values higher than 50%, but with respect to selectivity, it was noticed that the formation of the ethers showed only relevant values when using shorter chain alcohols (ethanol and isopropanol).