Bio-hydrotreated fuel production from non-edible oil using supported Ni-based catalyst

Abstract

This thesis is dedicated to the investigation, and development of catalysts for catalytic hydrotreating of biomass-based oil with the aim of producing high quality liquid fuel from non-edible biomass.

Ni metal supported on alumina (Ni/γ-Al2O3) catalysts were prepared and tested for hydrotreating activity of algae bio-crude oil produced from hydrothermal liquefaction of Nannochloropsis sp. In addition, the effect of Cu and Re addition on γ-Al2O3 supported Ni catalyst were investigated for the same purpose. The reaction was performed in high pressure batch reactor setup at 350 ℃, 75 bar H2, and reaction time of 4 h, using the different Ni-based catalysts including Ni/γ-Al2O3, Ni-Cu/γ-Al2O3, Ni-Re/γ-Al2O3 and Ni-Cu-Re/γ-Al2O3, (10%Ni, 5%Cu, 2.5%Re) were used in upgrading of the bio-crude oil. Several characterization techniques including N2-physisorption, temperature program reduction (H2-TPR), X-ray diffraction (XRD), scanning electron microscope equipped with energy dispersion X-ray spectroscopy (SEM-EDS), and transmission electron microscopy (TEM) were employed to unravel the composition, morphology, and properties of the prepared catalysts. Upgraded bio-oil yield, elemental content (CHNS/O), and oil properties were here used to point out the activity of the catalysts. In addition, the chemical compositions of upgraded bio-oil were identified using GC-MS to address the effect of Cu and Re promotion on the catalytic activity and also selectivity.

Most catalytic systems could effectively eliminate S and decrease the N and O contents, and enhance more than 20% improvement in the higher heating value (HHV) of the bio-oil (34 to 41-45 MJ/kg). Ni-Cu-Re/γ-Al2O3 ternary alloy offered the best results on the overall performance, achieving the highest upgraded bio-oil yield of 58 wt. %. Moreover, the carbon efficiency and overall energy recovery (ERoverall) including ER from biomass algae to bio-crude oil (ERHTL) and ER from bio-crude oil to upgraded bio-oil (ERupgrade) are calculated. Finally, the reaction pathways for the formation of different hydrotreated products catalyzed by mono-, bi-, and tri metallic Ni-Cu-Re have been proposed.

The behavior of the prepared catalysts during the hydrotreating reaction was studied by performing in continuous down-flow packed-bed reactor. In this part, Pongamia pinnata (P. pinnata) oil was used, representing the non-edible triglyceride-based oil. All the catalysts revealed good deoxygenation and hydrogenation activity, which enabled liquid fuel yield of 65-77 % which are mainly in diesel boiling range product. The constantly 100% conversion of Pongamia pinnata oil along 15 h time on stream under 330 °C, LHSV 1 h-1, 50 bar H2 and continuously flow of hydrogen, demonstrating the high potential of prepared supported Ni catalysts in hydrodeoxygenation (HDO). The carbonaceous deposition occurred during the HDO, which could be a majority cause for loss of catalyst surface and active site toward catalyst deactivation. The addition of Cu and Re could inhibit the coke formation with their synergistic effect.

However, the process for testing and screening of numerous catalysts can be costly and time-consuming due to highly energy-intensive and required significant amount of feedstock and catalyst. Coking has been reported as the most prevalence cause of catalyst deactivation in other hydrodeoxygenation studies, and it was also evident in this work. Typically, the accelerated coking deactivation was performed via chemical or thermal aging. In this research, novel facile aging method was proposed by intermittent feed of hydrogen for hydrodeoxygenation reaction. The fresh and spent catalysts of continuous and intermittent hydrogen feed were analyzed by N2 sorption, XRD, and TGA-DTG-DSC, which exhibited that coke formation were a reason of this rapid catalyst deactivation. Moreover, this accelerated deactivation technique does not alter the reaction pathway as the contribution of DCOx and HDO reactions are almost the same.

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