AbstractMicroalgae are a promising 3rd generation feedstock for biofuel production. However, their harvesting according to literature is uneconomical contributing up to 25% of the total cost of biofuel processing. In addition, the drying and solvent extraction step is energy intensive. Therefore, this research aimed at overcoming these challenges through the application of magnetic nanoparticles (MNPs) for algal separation, catalytic hydrothermal liquefaction and in ionic liquid (IL) lysis of magnetically separated microalgae. The MNPs were synthesized by co-precipitation and used to separate microalgae from culture medium at a separation efficiency of over 95%. The microalgae/MNPs slurry was subjected to HTL and IL treatment in separate experiments. In the HTL process, the microalgae/particle slurry was converted to biocrude oil and a biocrude yield of 37.1 wt.% was achieved in presence of MNPs while microalgae only yielded 23.2%. The percentage areas in the GC-MS chromatogram corresponding to hydrocarbons (HCs) in Zn-ferrite catalysed and uncatalysed biocrude were 46.5% and 19.9% respectively. Heteroatom compounds in the biocrude oil reduced substantially when liquefaction was done in the presence of Zn/Mg ferrites. The MNPs were recovered from solid residue by sonication and recycled. To further reduce N and O content of biocrude, the effect of HTL conditions on yield and biocrude composition was also investigated. HTL under 5 wt.% sulphuric acid reduced the nitrogen content of biocrude by 83 wt.%. In addition, increasing liquefaction time led to a gradual reduction in the N, O and S content of the biocrude. Moreover, HTL under 30 bar hydrogen atmospheres resulted in increased biocrude yield compared to HTL in absence of hydrogen.
ILs were also used for lysis of magnetically separated microalgae to efficiently extract lipids. GC-MS, FT-IR and 1H NMR analyse was done on the extracted lipids. The MNPs were recovered from algal residue by sonication in DI water. TGA analysis of recovered MNPs confirmed absence of algal biomass on the MNPs. These were then recycled to harvest more microalgae at a separation efficiency of 96%. The ILs were also recycled and 1HNMR, mass spectrometry and FT-IR analysis confirmed absence of structural alterations in the recycled IL. Finally, the effect of process conditions on yield of extracted lipids was also investigated. Application of MNPs in magnetic separation of microalgae, catalytic HTL and IL extraction will potentially reduce the processing cost of biofuels from microalgae. This would result in biofuels being more competitive with petroleum-derived fuels.
|Date of Award||2 Oct 2019|
|Supervisor||Pawel Plucinski (Supervisor) & Chris Chuck (Supervisor)|