Cultivation of microalgae for biodiesel production:A review on upstream and downstream processing

Fluctuating market price of fossil fuel and overwhelming emission of greenhouse gases to the atmosphere have resulted in climate change and have been a global concern in this decade. Hence, biodiesel has become an alternative option to fossil diesel as it is renewable and environmentally friendly. Nevertheless, this alternative fuel that is usually derived from terrestrial oil crops will cause shortage in food supply and deforestation if mass production is realized. In recent years, cultivation of aquatic microorganism(particularly microalgae) to produce biodiesel is considered as a practical solution due to their high growth rate and ability to synthesize large quantity of lipid within their cell. However, the development of energy and cost-efficiency of microalgae cultivation system are the main issues in producing renewable microalgae biodiesel. Of late, wastewater or organic compost has been used as the cultivation medium as it can provide sufficient nutrients to sustain microalgae growth.Microalgae cultivation method and system are vitally important as these factors undoubtedly affect the final microalgae biomass and lipid yield. In this review, the cultivation system of microalgae, nutrients demanded for microalgae production, cell harvesting and drying, microalgae oil extraction, and utilization of microalgae biomass for biodiesel production are introduced and discussed. It is anticipated to convey clearer perspectives in upstream and downstream processes in microalgae-derived biodiesel production.

Effect of ethanedioic acid functionalization on Ni/Al_2O_3 catalytic hydrodeoxygenation and isomerization of octadec-9-enoic acid into biofuel: kinetics and Arrhenius parameters

The effect of ethanedioic acid（Ed A） functionalization on Al2O3 supported Ni catalyst was studied on the hydrodeoxygenation（HDO）, isomerization, kinetics and Arrhenius parameters of octadec-9-enoic acid（OA） into biofuel in this report. This was achieved via synthesis of two catalysts; the first, nickel alumina catalyst（Ni/Al2O3） was via the incorporation of inorganic Ni precursor into Al2O3; the second was via the incorporation nickel oxalate（Ni Ox） prepared by functionalization of Ni with Ed A into Al2O3 to obtain organometallic Ni Ox/Al2O3 catalyst. Their characterization results showed that Ni species present in Ni/Al2O3 and Ni Ox/Al2O3 were 8.2% and 9.3%, respectively according to the energy dispersive X-ray result. Ni Ox/Al2O3 has comparably higher Ni content due to the Ed A functionalization which also increases its acidity and guarantees high Ni dispersion with weaker metal-support-interaction leading to highly reducible Ni as seen in the X-ray diffraction, X-ray photoelectron spectroscopy, TPR and Raman spectroscopy results. Their activities tested on the HDO of OA showed that Ni Ox/Al2O3 did not only display the best catalytic and reusability abilities, but it also possesses isomerization ability due to its increased acidity. The Ni Ox/Al2O3 also has the highest rate constants evaluated using pseudo-first-order kinetics,but the least activation energy of 176 k J/mol in the biofuel formation step compared to 244 k J/mol evaluated when using Ni/Al2O3. The result is promising for future feasibility studies toward commercialization of catalytic HDO of OA into useful biofuel using organometallic catalysts.

Simultaneous harvesting and cell disruption of microalgae using ozone bubbles:optimization and characterization study for biodiesel production

In the present study, ozone was introduced as an alternative approach to harvest and disrupt microalgae cells (Chlorella vulgaris) simultaneously for biodiesel production. At the optimum ozonation conditions (6.14 g·h^(−1) ozone concentration, 30 min ozonation time, 1 L·min^(−1) of ozone flowrate at medium pH of 10 and temperature of 30℃), the sedimentation efficiency of microalgae cells increased significantly from 12.56% to 68.62%. It was observed that the microalgae cells aggregated to form flocs after pretreated with ozone due to the increment of surface charge from −20 to −6.59 mV. Besides, ozone had successfully disrupted the microalgae cells and resulted in efficient lipid extraction, which was 1.9 times higher than the control sample. The extracted microalgae lipid was mainly consisted of methyl palmitate (C16:0), methyl oleate (C18:1) and methyl linolenate (C18:3), making it suitable for biodiesel production. Finally, utilization of recycled culture media after ozonation pre-treatment showed robust growth of microalgae, in which the biomass yield was maintained in the range of 0.796 to 0.879 g ·h^(−1) for 5 cycles of cultivation.