Biomass pyrolysis for liquid biofuels: production and use

Biomass pyrolysis is an advanced process in which an organic material is rapidly heated in a controlled environment and in the absence of oxygen to produce a liquid intermediate, the bio-oil, composed of hundreds of oxygenated compounds, which can be used directly to generate heat or further upgraded to a fossil-fuel substitute with improved properties, more suitable to be fed into a conventional oil refinery. This work deals with an experimental investigation in the production and use of biofuels and bioproducts from pyrolysis of several biomass species and alternative feedstock, for distributed energy generation or the production of chemical intermediates (biochemicals). Within the doctoral studies, a dedicated laboratory reactor was built for this scope and samples of pyrolysis oils have been produced from several biomasses, both lignocellulosic and microalgae, in sufficient amount to assess their properties as a fuel. Being a relatively novel bioliquid, material compatibility of microalgae bio-oil was addressed. Tests were carried out on selected metallic and elastomeric specimens to gain insight on handling and storage requirements and to compare the aggressiveness of pyrolysis oil from microalgae with the relatively more known pyrolysis oil from lignocellulosic biomasses. The results from the experimental test campaign, aimed at investigating the possibility of feeding pyrolysis oils to a modified micro gas turbine for power generation, are then presented in the final part of the work. The chapter “Pyrolysis for fuel, energy and chemicals” illustrates some generalities on the pyrolysis oil as a liquid intermediate, along with a brief state of the art of pyrolysis technologies and frontiers. The industrial perspective of generating energy from pyrolysis oils is also addressed, and examples of current demonstration activities in Europe are presented. A synthetic review of literature on two specialized subjects, microalgae and scrap tires pyrolysis, closes the chapter. The chapter “Bio-oil production in a pilot test bench” describes the experimental set-up that was used in this thesis for the production and collection of bio-oil samples. The chapter “Experimental results” discusses the results from production and analysis of pyrolysis oil from several biomass samples in a dedicated laboratory reactor. The yield and properties of the produced pyrolysis oils are presented, discussed and compared one against the other; a large quantity of microalgae from three distinct strains have been converted to pyrolysis oil for the first time in such amount. The chapter also reports the results from laboratory trials aimed at a preliminary assessment of the compatibility of pyrolysis oil from microalgae with 7 commercial specimens of metals and elastomers, commonly used in engineering practice for storage, handling and processing of fuels or organic fluids. Pyrolysis oil from microalgae was compared with pyrolysis oil from pine chips, which is almost commercially available, and for which larger data sets have been generated in the past. Finally, the results of the test campaign on the micro gas turbine are presented in chapter “Use of bio-oils in a modified micro gas turbine”. The possibility to feed a modified micro gas turbine, previously adapted to biofuels, was evaluated and the unit tested with two distinct pyrolysis oils; the first was of biogenic origin (pine chips), the second was obtained from the pyrolysis of scrap tires. Test results are discussed along with the challenges associated with feeding pyrolysis oils to a stationary engine for distributed power generation.