Development of innovative processes and catalysts for the valorisation of bio-oil
Matayeva, Aisha; Palkovits, Regina (Thesis advisor); Basile, Francesco (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2019. - Dissertation, Università di Bologna, 2019
Hydrothermal liquefaction (HTL) is a process for converting waste biomass to bio-oil by contacting the biomass with water at high temperatures and sufficient pressures in order to keep the water in the liquid state. HTL process has the advantage of being energy efficient and capable of dealing with wet biomass, such as sorted domestic organic waste, sewage sludge, algae, etc. Despite being a very promising technology economically and environmentally, waste to fuels via HTL has not progressed from pilot scale to industry, primarily due to the issues associated with the recycling of the aqueous phase. Moreover, waste-derived bio-oil obtained by HTL contains high contents of oxygen and nitrogen because of the initial biomass composition. Therefore, the bio-oil has to be upgraded in order to produce advanced transport fuels. Information regarding the types of nitrogen compounds present in bio-oil is of major concern of any hydrotreatment, since the low hydrodenitrogenation rate and catalyst poisoning by nitrogen compounds make this process expensive. Therefore, the main goal of the present study is the investigation of the HTL reaction mechanism, focusing the attention on the nitrogen containing species pathways, with the goal to increase the energy yields and reduce the nitrogen content in the produced bio-oil. Due to the complexity of the biomass composition, model compounds that encompass all the biochemical components of biomass, namely proteins, lipid and carbohydrates, are emerged to predict important outcomes from HTL of any wet biomass feedstock. Furthermore, several microbial biomass types, such as oleaginous yeast and liamocins, were treated via HTL to produce bio-oil and commercially attractive chemicals. This work consists of main five parts. In the first part the decomposition behavior of amino acids alone and in binary mixtures with glucose and tripalmitin as representative model compounds of proteins, lipids, carbohydrates, respectively, is investigated. Most attention is paid to the carbon and nitrogen transferring into HTL product streams. Moreover, the effect of homogenous and heterogeneous catalysts, besides the solvents on the HTL product streams is investigated. The second part includes a comprehensive model study on albumin/starch/tripalmitin mixture in order to mimic a more reliable biomass model and evaluate all the the possible interactions within biomass macromolecular components. Importantly, the effect of biomass composition on the type of nitrogen compounds in the resulting bio-oil is determined. In the third part deamination of amino acids to produce α-hydroxycarboxylic acids under hydrothermal conditions is investigated in the presence of heterogeneous catalysts. The fourth part reports a potential application of the HTL process for the production of bio-oils from oleaginous yeasts. Finally, in the fifth part hydrothermal decomposition of liamocins, another microbial biomass, to produce commodity chemicals, e.g. ð-lactones containing alkyl chains, is reported. The whole study presented in this thesis helps to better understand the HTL of organic waste biomass and microbial biomass/oils, providing useful insights into the reaction products, pathways, and mechanisms for the production of bio-oils and chemicals.