Son Nguyen

Development of an efficient catalyst for the pyrolytic conversion of biomass into transport fuel

Promotion date: December 4.

Promotor(s): Prof. dr. ir. Leon Lefferts and Prof. dr. Kulathuiyer Seshan

Fast pyrolysis is a promising technique to convert biomass into a liquid fuel/fuel precursor, known as bio-oil. However, compared to conventional crude oil, bio-oil has a much higher oxygen content which results in various detrimental properties and limits its application. Thus it is important to develop an efficient catalyst to upgrade bio-oil into high quality fuel via de-oxygenation.

Compared to non-catalytic pyrolysis, catalytic upgrading in the presence of Na2CO3/γ-Al2O3 results in a higher level of selective de-oxygenation with the oxygen ending up in heterogeneous char or removed as COx. TGA and 23Na MAS NMR study suggested the formation of a new hydrated sodium phase, which is likely to be responsible for the high activity of the catalyst. This hydrated phase is supposed to be formed by the coordination between sodium ion and the hydroxyl group of alumina.

Dual-bed operation with two consecutive beds containing Na2CO3/γ-Al2O3 and Pt/γ-Al2O3 has shown to achieve the highest de-oxygenation level of bio-oil among all the catalytic systems. This was achieved via the removal of harmful carbonyls and enhancement of the desirable hydrocarbons, leading to a heating value higher than that of traditional fuel oil (42 MJ kg-1). N-butane was shown to possess similar performances compared to H2 as a hydrogen source for biomass hydro-pyrolysis. This opens new ways for economical hydrogen sources for bio-oil treating (for e.g. natural gas).

Apart from the fundamental issues, was your work application driven as well?

The use of catalysis for the conversion of biomass is widely under interest as biomass, and the resulting bio-oil, is not an optimal fuel precursor by nature. Our approach was quite unique: turning biomass into a fossil-compatible fuel precursor via pyrolysis and using catalysis as a way to make this process more efficient (reduce waste, save energy, etc.)

In the end we successfully developed a dual bed system, in which two catalysts were separated in two chambers; one catalyzed de-oxygenation reactions and the other facilitated hydrogenation. This system resulted in a bio-oil with a higher energy content compared to diesel.

Was collaboration a main part of your PhD work?

At the University of Twente two groups were involved in biomass-related studies: Catalytic Processes & Materials, and Sustainable Process Technologies. In this way we were able to work efficiently using different experimental set-ups simultaneously, and by profiting from the broad spectrum of expertise available.

The project was founded by STW and was part of the Green & Smart Process Technologies Program. A user group was involved and user meetings were organized once every year, to decide on the research direction. The communication was very good and only selectively the target of research was redirected.

A series of nice results and key moments occurred during my PhD period. I especially recall results of an experiment in which an alternative hydrogen source (n-butane gas) was successfully used to upgrade bio-oil via hydropyrolysis.

In what journals did you publish your results?

Articles were published in Bioresources Technology and in Biomass & Bioenergy Journal. Three more articles are submitted at this very moment. Also I was a speaker on the CatBIOR, Catalysis for Biorefineries Conference in Malaga, Spain.

In what way did you develop personally, as a researcher and scientist?
My approach towards research is much more pro-active now. In my home country the research lines were set by the professor leading the group. Here, it was valued greatly to bring in one’s own suggestions and ideas, and persuade the professor himself of its importance.

In the beginning it was not easy to learn this new way of thinking and working. By the time I was assured my professor and colleagues were really open for my suggestions, and willing to think along with me, I learned to appreciate their expertise as an invaluable source of information in a new way.

What are your future plans?

I prefer to go and work in industry, as I would like to perform applied research. In order to achieve this goal it is better for me not to stay focused on fundamental research too much. I prefer a R&D job in a big company. Here it will be possible to work on various topics in limited periods of time. The dynamics of these research groups appeal to me.

To start with, I am going to work as a post-doc at The University of Sydney on similar topics like the PhD-work of this past four years. Here I hope to learn extra new skills, especially on characterizing catalytic materials. This could very well be of importance to my future job.

In the post-doc project I am also managing my own project, learning management skills along the way. These might be very helpful as well.

Did you feel part of the Mesa+ community while working on your PhD project?

My daily work was more directed towards that of our Group: Catalytic Processes and Materials. The projects in our Group are divided: the materials scientists are more directed towards Mesa+, whereas the applied catalysts experts are more connected to other compartments within the University of Twente. I am very proud my PhD-work is taken further by the Group. So, they have really become interested in this new line of research.