| dc.description.abstract | Environmental concerns and increased energy demand, has increased the need for sustainable fuel production using renewable feedstocks. Biomass has been identified as a potential net-zero CO2 emission and abundant raw material for bio-fuel production. Fast pyrolysis has been identified as a suitable method for producing fuel, however the produced bio-oil needs to be upgraded due to high acidity, oxygen content and low heating value. Catalytic vapor upgrading has been assessed as a promising route for bio-oil upgrading, and with removal of smaller oxygenates through ketonization and aldol condensation reactions the process can have a higher yield of transportation fuel range hydrocarbons in the final product.
In this project four noble-metal supported on metal oxide catalysts were tested for atmospheric upgrading of fast hydropyrolysis bio-oil in a pilot plant reactor. The aim was to synthesize four pellet sized in-house catalysts and determine if they were suitable for bio-oil c-c coupling upgrading under industrial conditions. The catalysts were synthesized using incipient wetness impregnation methods, with a target metal loading of 1wt%. The noble metals used were ruthenium and platinum and the metal oxides used were aluminum oxide and titanium oxide. In addition to activity tests, the catalyst were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF) N2-adsorption and temperature programmed reduction (TPR).
The XRD detected peaks attributable to the metallic phase in Ru/TiO2 and Ru/Al2O3, but not in the platinum catalyst, indicating that the ruthenium was not well dispersed, but the platinum was. N2-adsorption showed a decrease in pore volume and surface area for Ru/TiO2, Pt/TiO2 and Pt/Al2O3, but not for Ru/Al2O3. This indicates that smaller pores have been blocked by the active phase for three of the four catalysts. Changes to the synthesis methodology could help limit this blockage. XRF results indicated that Ru/TiO2, Ru/Al2O3 and Pt/Al2O3 did not retain the desired 1 wt% active material. Pt/TiO2 had higher than 1 wt% active material, possibly stemming from loss of support material during synthesis. TPR results showed ruthenium catalyst reducing between 150-200°C while the platinum catalysts did not display clear peaks in the temperature range.
Activity testing with the different catalysts were performed in a pilot scale setup with 500°C in the pyrolysis reactor, 400°C in the upgrading reactor, and a 1.5L/min H2 and 1.0 L/min N2 flow at atmospheric pressure. The feeding rate of biomass was 10g/hr with 20g of catalyst loaded, and each activity test was carried out for 6 hours. A liquid, gas and solid phase was formed from each experiment. The liquid consisted of two fractions, one oil and one aqueous, which was made up of over 50 different compounds. In the gas phase, CO2, CO, and C1-C6 carbonaceous gases were identified as products. The solid phase consisted of char and coke. The oil yield was found to be in decreasing order Pt/TiO2>Ru/TiO2>Ru/Al2O3>Pt/Al2O3, with the main components in the oil fraction being carbonyls, both cyclic and linear and phenolic compounds. For ketonization reactions the activity is therefore found to be in decreasing order Pt/TiO2>Ru/TiO2>Ru/Al2O3 >Pt/Al2O3.
The O/C ratio was successfully reduced for all catalyst from 0.65 to 0.20, while also increasing the H/C ratio from 1.45 to 1.6 for all but Pt/Al2O3. The higher heating value of the bio-oil was increased from 16.9MJ/kg to 38 MJ/kg for all catalyst, underpinning the capacity of the catalyst to remove oxygen, increase hydrogen and c-c couple smaller oxygenates. | |