Production of hydrocarbon-rich biofuels from extractives-derived materials

Abstract

This research concentrated on the preliminary possibility of utilizing saponified extractive-based raw materials for the production of bioliquids through fast pyrolysis. The primary purpose of this study was to clarify the pyrolysis chemistry involved by a laboratory-scale apparatus, rather than to make mass balances over the full-scale application. For this purpose, the versatile liquefiable volatile compounds were analyzed in detail by gas chromatography (GC). The pyrolysis was mainly done with soap (i.e., as sodium salts of acids), since the thermal cracking of vegetable oils compared to that of metal acid salts, is much more difficult to control. The knowledge gained from this can be utilized for the planning of larger-scale experiments with a more technical approach to a wider range of raw materials. In the first phase of the research, pyrolysis experiments with model compounds consisting of sodium salts from some commonly known fatty acids that have 18 carbon atoms and a varying degree of unsaturation were performed. The model compounds included sodium stearate (C18:0), sodium oleate (C18:1), and sodium linolate (C18:2). The main purpose was to get an idea of the product profile under varying pyrolysis conditions and to verify the dominant reaction pathways. The formation of pyrolysis products clearly depended on its temperature and the time it took to form the unsaturation of the fatty acid carbon chain. The highest relative proportions of various alkenes and alkanes were obtained with saturated sodium C18:0, whereas the lowest relative proportions of these compounds (and the highest proportions of aromatics and oxygen-containing compounds) were detected in sodium C18:2 pyrolysate. The primary aim of the second phase of the research was to further understand the pyrolysis chemistry of fatty acid soaps within natural matrices. Typical fragmentation patterns of the main product group were detected and the results were collected in accordance with the results of the model compounds, thus indicating only a slight matrix effect. The pyrolysis of the fatty acid sodium salts obtained from the alkaline hydrolysis of vegetable oils (palm, olive, and rapeseed oils) mainly resulted in the formation of volatile products. This similar to what is found within the boiling range of petroleum products like gasoline and diesel fuel. However, in this process, there were also some undesirable oxygen-containing products that were formed as well. Castor oil appeared to be an unsuitable raw material for the pyrolytic production of biofuels due its high content of ricinoleic acid. The primary purpose of the third phase of this study was to further understand the pyrolysis chemistry of crude tall oil soap, which contained some black liquor impurities. The results of washed crude tall oil and distilled tall oil after neutralization, suggests that typical small amounts of black liquor that are normally found, had no significant effect on product quality. In these cases, the most important factor affecting the quality of bioliquid was the amount of resin acids in the feedstock. Crude tall oil soap seemed to be suitable for feedstock when considering economically feasible processes for producing diesel fuel additives. To gain further knowledge about the effect of different tall oil fractions on pyrolysis product formation, the pyrolysis of a neutralized tall oil fatty acid mixture as well as a neutralized tall oil resin acid mixture was performed. In the former case, the pronounced formation of different aliphatic hydrocarbons was obtained, whereas the pyrolysis of neutralized tall oil rosin led to the considerable formation of various aromatics. These aromatics were mainly resin acid-derived polyaromatics. However, monoaromatics (formed mainly from unsaturated fatty acids) were also present as well. It could be concluded that the composition of this raw material had a particularly significant effect on the composition of liquefiable products. With respect to biodiesel production, the quality of a pyrolysate seemed to be better in the case of vegetable oils soaps than in various tall oil products. The best quality product was achieved with a raw material containing mostly saturated fatty acid (C18:0) salts.