Abstract
A process of much future-potential for upgrading of biofuels derived from hydrothermal liquefaction (HTL) is catalytic hydrotreatment. HTL bio-oil, manufactured from Chlorella microalgae in a reactor operating in continuous flow mode was processed via hydrotreatment using a bio-Pd/C catalyst. This catalyst comprises a bacterial biomass support decorated with Pd(0) nanoparticles. The hydrotreatment performance of commercial Pd/C catalyst and bio-Pd/C was compared in order to benchmark the latter catalyst preparation. Oil:catalyst ratio, time and temperature were investigated as three variables for optimization. Similar conversion was observed for both Pd/C (76% liquid yield, 4.2% O) and bio-Pd/C (77% liquid yield, 3.9% O) catalysts under equivalent conditions (4h reaction time, 5wt% Pd loading, 325°C). The oxygen content was reduced by 65%, whilst the nitrogen content decreased by 35%, with a bio-oil:catalyst ratio of 20, at a temperature of 325°C and reaction time of 4h. The upgraded oil was further studied by elemental analysis, Simulated Distillation and GC–MS, in order to quantify the improvement in fuel properties. The fresh and spent catalysts were analyzed using elemental analysis, TGA and ICP-MS, showing that the bio-oil yield was augmented by conversion of the biomass component from bio-Pd/C.
Highlights
In order to meet the demands of future fuel requirements, the large requirement for fossil fuels [1,2,3,4] could be progressively replaced by biofuels with reduced carbon footprint [5,6]
Singlestep biorefining of Pd from wastes into new catalysts has been shown in other work, with the biorefined catalyst proving comparable to chemical counterparts in fuel cells [37], in chemical catalysis [38], and in catalytic upgrading of Canadian heavy oil [39], where the economic case was argued [28]. These results show that a high quality fuel can be produced by upgrading hydrothermal liquefaction (HTL) bio-oil using a bio-Pd/C that can be prepared from wastes
The Fourier-Transform infrared (FT-IR) spectra was dominated by alkane peaks and had higher heteroatom functional groups (1750–1500 cm−1) in untreated bio-oil compared to Illinois shale oil
Summary
In order to meet the demands of future fuel requirements, the large requirement for fossil fuels [1,2,3,4] could be progressively replaced by biofuels with reduced carbon footprint [5,6]. Use of heterogeneous and homogeneous catalysts in-situ to achieve improved bio-oil quality is one of the most commonly reported research approach in this field [12,13]. Nanoparticles of palladium supported upon the surface of bacterial biomass (bio-Pd), for organic synthesis, while Hart et al [28] and Omajali et al [29] reported activity in catalytic upgrading of heavy oil. In each case the activity of the bio-catalyst was comparable to commercial equivalents These bio-catalysts use green and economical support material and metals can be recycled and reused from various waste sources [29]. The current investigation presents results for upgrading the low lipid microalga Chlorella bio-oil (produced from a continuous reactor) with nanosized bio-Pd/C catalyst. The results are discussed in context of potential replacement of commercial catalysts with alternative biobased Pd/ C catalyst
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