A Study on the Application of Bio-oil Derived from Brown Macroalgae for Emulsified Biofuel Production

Abstract

In this thesis, the fixed bed pyrolysis and bio-oil fractions from different pretreated Saccharina japonica (S. japonica) were investigated via solvent extraction and the properties of the emulsified biofuel product were determined. First, the characterizations of the pyrolysis products, such as bio-oil, bio-char and bio-gas obtained from brown algae were investigated. The fast pyrolysis experiments were conducted in a fixed bed with a temperature of 350-490 °C, a gas flow rate of 0.6 L/min and a residence time of 10 min. The maximum yields of bio-oil produced from untreated, water pretreated and alcohol pretreated S. japonica at 450 °C, were 38.2 wt.%, 36.4 wt.% and 37.3 wt.%, respectively. As the pyrolysis temperature increases, the bio-char yield decreases, whereas the bio-gas relatively was increased. Then, the physicochemical properties of the bio-oil and bio-char were investigated. The ash content in the bio-char obtained from three different pretreated S. japonica samples was found to gradually increase, whereas the volatile matter, fixed carbon, and higher heating value (HHV) were decreased with increasing the pyrolysis temperature. The carbon and moisture content in bio-char produced from the untreated S. japonica were higher than those from the alcohol pretreated and water pretreated samples. However, the oxygen content in bio-char was lower than that in the alcohol pretreated and water pretreated S. japonica samples Second, the characteristics of the bio-oil fractions obtained via solvent extraction were determined. The reduced pressure distillation was performed at 40 mmHg and 40 °C. Then, distilled bio-oil was mixed with hexane solvent using the volume ratio (v/v) of =1:5. After the mixing process, three fractions were obtained: a non-aqueous oil (NAO) phase, an aqueous oil (AO) phase and a residue oil (polymer oil) phase. Consequently, experiment on the evaporation and vacuum distillation were performed on the NAO phase in order to reduce the amount of hexane while the AO phase also was distilled via reduce pressure distillation in order to reduce water content. Among these three pretreated materials (untreated, alcohol pretreated and water pretreated S. japonica), the yields of hexane extracted oil were 15.9 wt.%, 14.3 wt.% and 16.0 wt.%, respectively. The properties of the hexane extracted fractions were determined by Fourier transform infrared (FT-IR) spectroscopy, gas chromatography mass spectrometry (GC/MS) and nuclear magnetic resonance (NMR, 1H and 13C) spectroscopy. As FT-IR spectra illustrated, the stretching vibrations of 3000-2850 cm-1 exhibited the presence of alkanes with -CH2- and -CH3, and the bands at 1600 and 1470 cm-1 appeared to be characteristic of the C=C vibration of aromatic compounds that primarily originated from the hexane extracted oil. The bands of the O-H stretching vibrations between 3600 and 3200 cm-1 indicated the presence of carboxylic acids, alcohols and phenols in the hexane extracted aqueous oil. The stronger bands between 1700 and 1600 cm-1 were attributed to the C=O functional groups that possibly from carboxylic acids, ketones and aldehydes in all fractions. The bands between 1150 and 1000 cm-1 can be assigned to the C-O groups from ether present in the carbohydrate derivatives from the hexane extracted aqueous oil from the water pretreated S. japonica. From the GC/MS and NMR data, it is known that the aliphatic compounds, benzenes, phenol and polycyclic aromatic hydrocarbons (PAHs) were primarily determined to be biofuel sources in the NAO from the water pretreated and alcohol pretreated S. japonica. The esters, furan derivatives and cyclic components were found in the NAO pretreated S. japonica and alcohol pretreated S. japonica. The sugars were distributed in the AO of the untreated and water pretreated S. japonica. Finally, a mixture of hexane extracted NAO, AO and bio-heavy oil were mixed for homogenizing the biofuel and determined its properties.