Support effects on hydrotreating of soybean oil over NiMo carbide catalyst
Graphical abstract
Introduction
Due to volatility in the price of fossil fuels, world energy security and environmental concerns, economical techniques for the production of biofuels from alternative and renewable sources must be developed. It is well known that triglyceride based vegetable oils, animal fats, and recycled grease have the potential to be suitable sources of fuel under the right processing conditions.
Currently, lipid-based feedstocks can be converted into liquid hydrocarbon fuels by hydrotreating processes similar to those found in the oil and gas refining industry [1], [2]. Conventional γ-Al2O3 supported sulfided bimetallic catalysts (usually Mo- or W-based sulfides promoted with Ni or Co) are presently used for desulfurization of fossil diesel streams in a process requiring high energy consumption, high temperature, high pressure, and with large amounts of hydrogen [3]. The products obtained are essentially n-paraffins (n-C15 up to n-C18) solidifying at subzero temperatures and as such are unsuitable for high quality diesel fuels, kerosene and gasoline compounds [4]. The process is costly and the yield of product can be low because of coke formation, which causes catalyst deactivation and pressure build-up in the reactor [5]. More importantly, the base metals in these hydrocracking catalysts need to be maintained in their sulfided form in order to be active at process conditions, and therefore, a sulfurization co-feed needs to be added to the feedstock [6].
In order to address the above issues, a number of studies have been carried out to develop non-sulfided catalysts with high activity, good selectivity and long lifetime in a hydrotreating process [7], [8], [9], [10], [11], [12], [13]. Among them, the nitrides and carbides of early transition metals have been identified as a new class of hydrotreating catalysts that are competitive with the conventional bimetallic sulfided catalysts. These catalysts exhibit high activity similar to the noble metals because the introduction of carbon or nitrogen into the lattice of the early transition metals results in an increase of the lattice parameter a0 and an increase in the d-electron density [14]. Han et al. [11] reported that a transition metal carbide catalyst, Mo2C, supported on multi-walled carbon nanotubes, showed 90% conversion and 91% hydrocarbon selectivity for one-step conversion of vegetable oils into branched diesel-like hydrocarbons. Most recently, Han et al. [15] successfully prepared ordered mesoporous carbon (OMC)-supported molybdenum carbide catalysts. The catalysts exhibited high product selectivity and excellent resistance to leaching in the conversion of vegetable oils into diesel-like hydrocarbons. Nitrides of molybdenum, tungsten and vanadium supported on γ-Al2O3 were also used for hydrodeoxygenation of oleic acid and canola oil [12]. The oxygen removal exceeded 90% over the supported molybdenum catalyst for a long reaction duration (450 h) and the yield of middle distillate hydrocarbons (diesel fuel) ranged between 38 and 48 wt%. Moreover, bimetallic nitride and carbide catalysts were found to be much more active and stable than the mono-metallic ones [16], even though no application in the biomass hydrotreating process has been reported.
While the nitrides and carbides of early transition metals have been evaluated as hydrotreating catalysts to convert vegetable oils to biofuels, no systematic study exists on the effect of the support on the hydrotreating activity of the catalysts, even though the support plays an important role in the cracking function for hydrotreating catalysts [17], [18]. The support contributes to the cracking of the C–O or C–C bond and to the isomerization of the resultant n-olefins, that, after hydrogenation, are transformed into isoparaffins [10], [19]. Hence, the aim of this work is to investigate the effects of support on hydrotreating activity of bimetallic (NiMo) carbide catalysts.
In this study, the preparation of Al-SBA-15 with Si/Al = 80 and hydrotreating catalysts based on this mesoporous material along with commercialized γ-Al2O3, ZSM-5 (Si/Al ratio = 80), Zeolite β (Si/Al ratio = 38) and USY zeolite (Si/Al ratio = 80) are presented. Nickel and molybdenum were impregnated as active metals. The carbides of the catalysts were evaluated for hydrotreating of soybean oil in a bench-scale plug flow reactor.
Section snippets
Preparation of Al-SBA-15
Al-SBA-15 with Si/Al = 80 was synthesized following the procedure of Wu et al. [20]. A typical synthesis procedure was followed: 20 g of commercialized SBA-15 powder (ACS Materials, LLC, Medford, MA) were dispersed in 150 mL hexane. Then, 0.067 g aluminum isopropoxide dispersed in a small amount of hexane was added with stirring. After 10 min, the solution was diluted by adding more hexane (150 mL) and the stirring was continued for another 24 h at room temperature. The mixture was filtered and the
Catalyst characterization
Fig. 1 exhibits the nitrogen adsorption–desorption isotherms of the five supported NiMoC catalysts. According to De Boer’s theory the isotherm curve of NiMoC/Al-SBA-15 is type IV and the adsorption hysteresis loop is type A, which means that NiMoC/Al-SBA-15 has a meso porous structure with uniform regular channel distribution. The specific adsorption capacity is as high as 450 m2/g. NiMoC/γ-Al2O3 catalyst shows a type IV isotherm curve and the adsorption hysteresis loop is type E, indicating
Conclusions
The hydrotreating of soybean oils on supported NiMo carbide catalysts makes possible the production of gasoline to diesel range liquid hydrocarbons. Because of specific pore structures, all of the zeolite-supported catalysts have a strong cracking activity, producing more gaseous and gasoline products. The meso-porous γ-Al2O3 and Al-SBA-15 supported catalysts led to a higher production of green diesel, containing mostly C15–C18 hydrocarbons, which were mainly formed by
Acknowledgments
Financial support from the Department of Energy (Grant DE-FG36-05GO85005) and National Institute of Food and Agriculture (Grant MICW-2010-01534) for this research are gratefully acknowledged.
References (32)
- et al.
Hydroprocessed vegetable oils for diesel fuel improvement
Bioresource Technol
(1996) - et al.
Hydrodeoxygenation of oleic acid and canola oil over alumina-supported metal nitrides
Appl Catal A: Gen
(2010) Metal carbides and nitrides as potential catalysts for hydroprocessing
Appl Catal A: Gen
(2003)- et al.
Synthesis, characterization, and catalytic performance of mesoporous Al-SBA-15 for tert-butylation of phenol
Chin J Catal
(2006) - et al.
Synthesis, characterization, and catalytic properties of clean and oxygen-modified tungsten carbides
Catal Today
(1992) - et al.
Molybdenum carbide catalysts.1. Synthesis of unsupported powders
J Catal
(1987) - et al.
Synergies between bio- and oil refineries for the production of fuels from biomass
Angew Chem Int Ed
(2007) - Egeberg GR, Michaelsen HN, Skyum L. Novel hydrotreating technology for production of green diesel presented at ERTC;...
- Koivusalmi E, Piilola R, Aalto P. Process for producing branched hydrocarbons United States Patent, Publication...
- Egeberg RG, Knudsen K. Industrial-scale production of renewable diesel, Published in PTQ Q3;...
Hydrodeoxygenation of methyl palmitate over supported Ni catalysts for diesel-like fuel production
Energy Fuels
Catalytic deoxygenation of fatty acids and their derivatives
Energy Fuels
Catalytic deoxygenation of tall oil fatty acid over palladium supported on mesoporous carbon
Energy Fuels
Production of synthetic diesel by hydrotreatment of jatropha oils using Pt−Re/H-ZSM-5 catalyst
Energy Fuels
Renewable diesel production from the hydrotreating of rapeseed oil with Pt/zeolite and NiMo/Al2O3 catalysts
Ind Eng Chem Res
Nanostructured molybdenum carbides supported on carbon nanotubes as efficient catalysts for one-step hydrodeoxygenation and isomerization of vegetable oils
Green Chem
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