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phd





Ph.D. studies (in English)  ph.d.-studies    |  Ph.d.-studium (på dansk)
My Ph.D thesis with the title "Catalytic production of biodiesel" was handed in on the 30th of June 2011 and defended on the 30th of September 2011. The research has been carried out at the Centre for Catalysis and Sustainable Chemistry at the Technical University of Denmark (DTU) in Lyngby.
The studies have been part of an innovation consortium, Waste-to-value", counting a handful of Danish companies with relation to biofuels (producers, tail-gas cleaners, car retailers, petroleum distributors). During my studies I visited the Proces Chemistry Group at Åbo Akademi, Turku, Finland.

Diesel from biomass may be produced in a handful of ways, but two of them are more technically developed than the others and are being produced on an increasing industrial scale around the world. Both of these use as their primary resource triglycerides (vegetable oils of all kinds, animals fats, etc.).



Esterification and transesterification of fatty feedstock
One of these is the acid-catalysed esterification of free fatty acids with methanol and the base/acid-catalysed transesterification of glycerides with methanol to yield fatty acid methyl esters (FAME). Technically only this fuel is referred to as biodiesel, while some would regards this a too narrow definition. In principle not only methanol, but all alcohols may be used in the ester reactions, however, methanol is cheapest and affords the fastest reaction on industrial scale. Normal mineral sulphuric acid (H2SO4) and potassium hydroxide (KOH) are used as the catalysts in industry since they are cheap and abundant. In Denmark about 150 kton/y biodiesel is produced in this way on Emmelev Mølle and Daka Biodiesel, starting from respectively rapeseed oil and animal waste fats. This constitutes about 7-8% of the demand for Diesel oil (2008 basis).

Our research team have investigtated a solid organic acid that has been immobilised on various porous support materials for the esterification of free fatty acids and the transesterification of glycerides. We have tested this material in the lab in batch mode and in flow reactors where it has shown some prominent properties regarding activity and flow properties. However, there is ample room for optimisation before this can be introduced technically. Use of suitable solid, insoluble catalysts in the industry would make for a more economical proces, easier purification and proces control.



Hydrodeoxygenation of fatty feedstock
Another route for diesel from biomass is the so-called deoxygenation of fats and oils using hydrogen to yield straight-chain alkanes. Hereby the chemical bound oxygen is removed as water or carbon oxides. The most suitable catalysts for this reaction are either supported noble metals or supported transition-metal sulfides, where the latter are installed at most petrochemical refineries already as desulphurisation catalysts for petroleum. The first refiner to have industrialised the deoxygenation of oils and fats is the Finnish company Neste Oil at their refinery in Porvoo, but other oil companies are following their lead, for instance Preem, PetroBras and ConocoPhilips.

During my ph.d.-studies I have investigated the deoxygenation of triglycerides and fatty acids over supported noble metal catalysts, mostly palladium and platinum, partly at DTU (in a batch reactor) and partly during my research visit at Åbo Akademi (in continuous a reactor). Employing noble metals as catalysts leads to more severe problems of catalyst deactication, most likely by formation of various heavy compounds or coke that cannot be flushed. The deactivation is suppressed in reducing atmosphere (presence of hydrogen), but hydrogen can lead to unwanted formation of methane. It is as yet unknown how to avoid the use of hydrogen, which would be highly desirable.



Alternatives not employing fats and oils
Both production methods have their pros and cons, but first and foremost the fats and oils needed as the main raw materials are indeed sparse compared to the global diesel consumption. It may be possible to increase production of various plant oils in a sustainable manner, for instance by using shrubs and oil-producing algae, but generally other raw materials should be used. Three other strategies for potential diesel fuel production have been suggested, and although these are more complicated in terms of raw materials, reaction conditions and proces layout, but they also allow a much larger and cheaper fraction of the available biomass to be converted to fuel.

1) Starting from carbohydrates, polyols and water-soluble organics, the group of James Dumesic at Un. of Madison-Wisconsin has pioneered a production method of both reforming and reducing organic compounds in the aqueous phase - so-called aqueous-phase reforming, APR. When these organics gets sufficiently reduced, either to alkanes or monofunctional hydrocabons of up to C6 length, they separate to a non-polar hydrocarbon phase. Upgrading the chain-length of intermediates to suit the Diesel pool can be achieved by ketonisations and aldol-condensations. Hydrogen for the reduction is delivered internally by the reforming of part of the carbohydrates.

2) Starting from straw, wood or various waste compounds, it is possible to obtain a bio-oil or bio-crude either by so-called flash pyrolysis (heat-induced degassing of condensible tars) or by a harsh boiling in near-critical water. Bio-oils cannot be used themselves as transportation fuels, but the bio-oils may be upgraded by reduction and deoxygenation (using) as with the fats and oils. However, due to the high content of oxygen functionalities in bio-oil compounds, a much higher consumption hydrogen is necessary for the complete reduction of the oils, and catalysts are as well much more prone to deactivation by coking on the catalyst surface - thus understanding the mechanisms of the upgrading becomes even more important.

3) The final option for biomass diesel is a "break down, build up" strategy, available With principally any type of biomass. First the biomass is gasified at high temperatures and with little or no oxygen present. The gasification yields a producer-gas that, after ample gas clean-up of tars and and adjustment, removal of some H2O and CO2, is worked up to so-called synthesis gas (or syn-gas) to CO and H2 in the ratio 1 : >2. The syn-gas be reacted to yield long-chain alkanes, well suited for use in the Diesel pool, in the so-called Fischer-Tropsch-synthesis, normally over supported iron or cobalt catalysts containing other elements as promotors. This strategy is investment-intensive, especially the gasifier, so it is thought as a centralised technology.








Sidst opdateret torsdag 16. februar 2012


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