Characterization of Biodiesel and Biodiesel Particulate Matter by TG, TG−MS, and FTIR

Abstract

Biodiesel is a potential renewable and carbon-neutral alternative to fossil fuels, and it is environmentally and economically attractive. This paper studies the decomposition kinetics of biodiesel using thermal gravimetric analysis (TGA) in one-stage pyrolysis. Biodiesel can be decomposed at 119−237 °C. The kinetic parameters for biodiesel pyrolysis were obtained from the TGA experiments. The global rate equation for biodiesel pyrolysis can be expressed as dX/dt = 2.6 × 107 exp(−16.2/8.314 × 10−3T)(1 − X)0.52 (X denotes the reaction conversion). Characteristics of diesel and biodiesel and the associated diesel particulate matter (DPM) emitted from a nonroad diesel generator were also analyzed by Fourier transform infrared (FTIR) spectroscopic methods. The FTIR spectra of biodiesel showed a C═O stretching band of methyl ester at 1743 cm−1 and C−O bands at 1252, 1200, and 1175 cm−1. Furthermore, the FTIR spectra of DPM were similar to those of the fuels, an indication that the chemical structures of DPM are closely related to the fuel and engine oil properties, consistent with our previous study. The temperature series of 11 fragments have been analyzed in nitrogen, which include m/z 29, 31, 44, 74, 87, 105, 143, 263, 294, 296, and 298. The fragments at m/z 294, 296, and 298 represent the methyl ester components of biodiesel, and the fragment at m/z 44 is carbon dioxide, fragments at m/z 29 and 105 represent aldehyde compounds, and fragments at m/z 87 and 143 are shorter chain methyl esters, all of which can be byproducts from biodiesel combustion. The fragments at m/z 57, 67, 95, and 109 represent hydrocarbon components, which may be fragmented from the long carbon chains of methyl esters, and the fragment at m/z 31 is a methoxy group, which may be fragmented from methyl esters. The information of TG−MS as analyzed above can offer a better understanding of the byproduct formation mechanisms of biodiesel combustion.