ARTICLE pubs.acs.org/EF
Catalytic Deoxygenation of Tall Oil Fatty Acid over Palladium Supported on Mesoporous Carbon P€aivi M€aki-Arvela,† Bartosz Rozmyszowicz,†,‡ Siswati Lestari,†,§ Olga Simakova,†,|| Kari Er€anen,† Tapio Salmi,† and Dmitry Yu. Murzin*,† †
Process Chemistry Centre, Åbo Akademi University, 20500 Turku, Finland Faculty of Chemical Technology, Poznan University of Technology, 60-965 Poznan, Poland § ARC Centre of Excellence for Functional Nanomaterials, University of Queensland, Brisbane, Queensland 4072, Australia Boreskov Institute of Catalysis, Novosibirsk 630090, Russia
)
‡
ABSTRACT: Catalytic deoxygenation of tall oil fatty acids (TOFAs) was investigated over 1 wt % Pd/C Sibunit, which is a synthetic mesoporous carbon. The reactions were performed in a semi-batch reactor using dodecane as a solvent under 17 bar of total pressure. The main studied parameters were the reaction temperature, initial concentration of TOFA, effect of the reaction atmosphere, and metal loading. The temperature and initial concentration ranges were 300 350 °C and 0.15 0.6 mol/L, respectively. The total conversion of fatty acids increased, as expected, with increasing temperatures and decreasing initial TOFA concentrations. The main liquid-phase products were n-heptadecane and n-heptadecene. In addition to the desired linear C17 hydrocarbons, also aromatic C17 compounds, such as undecylbenzene, were formed. The best conditions for the formation of the desired C17 hydrocarbons were lower initial concentrations of TOFA, 300 325 °C, and the presence of hydrogen. An increase of the metal loading (4 wt %) led to an increase of the selectivity to linear C17 hydrocarbons.
1. INTRODUCTION Biofuels have potential to substitute part of the energy supply and contribute to the reduction of greenhouse gases. Currently, there are only a few types of biofuels that are commercially available for transportation uses. Bioethanol as such or in the form of ethyl tertiary butyl ether (ETBE) is an alternative fuel in the range of gasoline, usually derived from crops rich in sugar or starch via fermentation processes. The amount of both ethanol and ETBE that can be used without engine modification is limited by the flash point specification. Normally, up to 5 or 15% of ethanol (ETBE) is present in gasoline ethanol blends.1 In the range of diesel fuels, fatty acid methyl ester (FAME) is usually used as an alternative diesel fuel derived from biomass. FAME is the main product in the transesterification of triglycerides with alcohol, usually methanol, with alkaline catalysts in a mild reaction temperature range from 60 to 120 °C.2,3 The raw materials used in the transesterification process are varied depending upon the region; mostly soybean and rapeseed oil are used in the U.S. and Europe, respectively.4 The main drawbacks of the transesterification process are limited compatibility of the FAME product with conventional diesel engines and the formation of low-value glycerol as a byproduct, which thus requires a further separation process and the need to further use or valorize glycerol. Another type of alternative diesel fuel is a product of gas-toliquid (GTL) technology, which uses syngas in the Fischer Tropsch process. Use of biomass feed in this technology requires removal of impurities because the catalysts are highly sensitive to them. Gasification of biomass could also be challenging. At the same time, there are GTL processes using natural gas, and furthermore, transformation of coal to liquid is a well-known technology.5 r 2011 American Chemical Society
The public concern about the use of biodiesel is particularly related to using land, which could be dedicated for agricultural purposes, for energy plant generation. To overcome this issue, the research activities have been focused on developing the next generation of biofuels, which is characterized by at least two criteria: (i) produces a diesel-like hydrocarbon product and (ii) uses non-food raw materials. A novel method has been recently developed for converting fatty acids and their derivatives via catalytic deoxygenation.6 13 Recently, extensive research was performed to determine the most suitable catalyst and reaction conditions.14 20 It was proven that the reaction pathway over the Pd/C catalyst can be influenced by an increase of the hydrogen content in the reaction atmosphere and CO poisoning.14 An increase of the hydrogen pressure presence in the reactor system shifted the reaction selectivity from decarboxylation to decarbonylation, while CO addition caused a decrease of the decarboxylation rate by competitive inhibition over decarboxylation sites for CO and reactant. The conversion and hydrocarbon yield in deoxygenation of fatty acids over NiMo and Pd catalysts are dependent upon the hydrogen partial pressure.15 Recently, new catalysts were proposed for deoxygenation of fatty acids. Such catalysts could have an advantage by diminishing internal diffusion limitations (Pd on mesoporous SBA-1516 and Al2O317), as well as affording the production of branched hydrocarbons (Pd/SAPO-3118) and olefins (PtSnK/SiO219). Received: March 11, 2011 Revised: June 13, 2011 Published: June 14, 2011 2815
dx.doi.org/10.1021/ef200380w | Energy Fuels 2011, 25, 2815–2825
Energy & Fuels
ARTICLE
Table 1. BET Specific Surface Areas and the Relative Volume of the Pores of the Fresh and Spent 1 wt % Pd/C (Sibunit) Catalysts BET specific catalyst
surface area (m2/g)
>50 nm
50 10 nm
10 5 nm
5 2 nm
2 1.6 nm
1.6 0 nm
micropores
mesopores
(
