(48c) Catalytic Upgrading of Algae Bio-Oil from Hydrothermal Liquefaction on Ni-Based Catalyst : The Role of Support

Biofuels or bio-based fuels are one of the most promising alternative fuels. It can be derived from natural resources as biomass that is highly abundant availability, and carbon-neutral renewable energy resource. Among the biomass-based fuel, algae-base biofuel has much significant attention due to its ability to high lipid content, high growth rate, and fix CO₂ in atmosphere rapidly. In addition, cultivation of algae do not require fertile or agricultural land, thus no impact on food supply chains due to competition between food and energy sector. To convert algae to biofuels, hydrothermal liquefaction (HTL) is the promising process to produce biofuel from algae or wet-biomass feedstocks, which uses water or other solvent as reactant and reaction medium at sub- or supercritical temperature and pressure. Bio-oil obtained from HTL has high heating value around 31-39 MJ/kg and low water content of 5-10 wt%. Unfortunately, the crude bio-oil cannot use directly in automobile engine because of its negative properties such as high acidity, high viscosity, and high level of nitrogen and oxygen content. Consequently, the process of bio-oil treatment is essential for removing their oxygen and undesirable compound to obtain the high-grade bio-oil.

Catalytic hydroprocessing (including hydrodeoxygenation, hydrotreating, and hydrocracking) is presently considered as the most promising process for bio-oil upgrading due to high quality biofuel which higher heating value, high H/C ratio and low oxygen, nitrogen and other heteroatom content could be obtained. The catalytic hydroprocessing of crude bio-oil has been conducted under high temperature and high hydrogen pressure using heterogeneous catalysts. The most study of bio-oil upgrading has been reported on the effect of operating conditions, such as temperature, pressure and residence time. Moreover, types of catalysts are also importantly studied factor due to their influentially for heteroatoms (N, O, S and metal) removing.

Supported nickel based catalysts are found to be the promising catalyst for this purpose due to a profusion of nickel, and non-expensive. In addition, Ni-based catalyst on deoxygenation of fatty acid was proposed by Snare and co-worker (2006), and many report showed good activity for hydrodeoxygenation (HDO) of triglycerides-based and biomass-based (e.g. guaiacol, phenol etc.). However, the monometallic Ni catalysts are known to be active in methanation reaction which consume high amount of hydrogen and may cause the catalyst deactivation by carbon deposits. In addition, sintering is another factor that effect to stability of Ni catalyst due to high amount of Ni-metal loading. To solve this problem, the bimetallic Ni-based catalysts are investigated. NiCu catalyst was reported to be success in preventing coke formation, enhance hydrogenation activity, and decreasing the sintering of metal active phase. Moreover, there are other metals that could be used as a promoter to improve stability and resistance of Ni-based catalyst such as Re (enhanced HDO activity by increasing the dispersion of active phase) which are barely reported on algae bio-oil upgrading.

Based on authors’ experimental which compare the activity of hydrotreating of vegetable oil using mono-, bi-, and tri-metallic Ni supported on Al₂O₃, namely Ni, NiCu, and NiCuRe. The tri-metallic NiCuRe/Al₂O₃ demonstrated the highest activity of hydrotreating and stability which no deactivation was observed after 24 h time on stream. The purpose of this work is to investigate the activity of tri-metallic NiCuRe with difference supports for upgrading of algae bio-oil. The different supports, namely commercial Al₂O₃, high surface area CeO₂, ZrO₂ and mixed-oxide CeO₂-ZrO₂ were selected. The Al₂O₃ was selected, as it is commonly use and high surface area; however it can be deactivated by coke formation due to the presence of water in bio-oil. The CeO₂, and ZrO₂ were selected, as the promising support because their properties: the activation of oxygen compound on surface, water resistance, high thermal stability, and improving the dispersion of metal particle. In addition, the mixed oxide CeO₂-ZrO₂ has been reported to enhance thermal stability, surface area, and improve catalytic performance [1]. The CeO₂, ZrO₂ and mixed-oxide CeO₂-ZrO₂ were prepared by surfactant-assist co-precipitation method. Then, NiCuRe was load on the support by co-wetness impregnation. The textural properties of fresh and spent catalysts were characterized by N₂ physisorption (BET surface area), XRD, TPR, SEM and TGA. The hydrotreating of algae bio-oil produced from hydrothermal liquefaction (HTL) of Nannochloropsis sp. are performed in batch reactor at reaction condition of 350°C, hydrogen pressure of 5 MPa and reaction time of 4 h to determine the effect of support of catalyst on product properties and catalyst performance. Moreover, the operating parameters i.e. operating temperature, H₂ pressure, and reaction time will be investigated in order to find the suitable operating condition. To determine the activity of catalyst, the upgrading bio-oil yield and the comparison of chemical properties of feed and product were analyzed by gas-chromatographic method (GC-MS), FT-IR, and element analysis CHNS/O. Additionally, the properties of bio-oil in term of heating value, acidity and viscosity are also investigated. The relative activities of different reaction pathways among each supported catalyst are also discussed.

Reference

[1] M.A. Ebiad, D.R. Abd El-Hafiz, R.A. Elsalamony, L.S. Mohamed, Ni supported high surface area CeO2-ZrO2 catalysts for hydrogen production from ethanol steam reforming, RSC Adv. 2 (2012) 8145–8156. doi:10.1039/C2RA20258A.