Renewable fuels via catalytic pyrolysis of lignocellulose
Promotion date: May 14.
Promotor(s): Prof.dr. K. Seshan and Prof.dr.ir. Leon Lefferts
Fast pyrolysis is one of the most frequently used thermochemical processes for the conversion of lignocellulosic biomass to liquid fuels. Biomass is rapidly heated to temperatures around 500 °C, at atmospheric pressure, in the absence of oxygen; followed by a subsequent quenching to a liquid, termed bio-crude oil or bio-oil. Unfortunately this is not suitable for direct use in engines or even as feedstock in conventional oil refineries due to its poor quality, i.e.: high oxygen content, high acidity, low heating value and thermal instability.
Developing catalysts to make this conversion efficient and to improve the properties, is tremendously popular these days. This thesis focuses on the development of in-situ catalytic deoxygenation mainly. Two experimental set-ups have been used: 1) a fixed-bed reactor with an IR-oven for rapid heating of biomass and an electrical heater for separate heating of the catalytic bed; 2) a micro scale pyrolyser system, for mimicking a real fast pyrolysis process by heating to 500 °C within one second.
A catalyst screening was conducted. It was found that sodium modified amorphous silica alumin catalysts (Na/ASA) posses a mild acidity and lead to production of bio-oil with higher yields. Other alkali metals - including K, Cs, Ca and Mg – have positive influence on the deoxygenation, but none of them is able to solve all problems associated with bio-oil at once.
Cs/ASA showed a substantial influence on the production of hydrocarbons, formation of required furans and cracking of pyrolytic lignin. These are all positive aspects. The Cs/ASA showed a unique activity for the formation of aliphatic hydrocarbons which also influences the quality of bio-oil positively.
At last, a techno-economic and environmental assessment of catalytic pyrolysis processes was conducted. The economic viability of the pyrolysis process shows the minimum selling price to be 3,8 euro/litre for hydrotreated Cs/ASA. However, compared to fossil-based fuels Cs/ASA bio-oil leads to lower environmental impact and a net reduction in non-renewable energy use. The challenge to improve the yield of bio-oil still remains. Improving the yield may lead to a lower minimum selling price.
Was your PhD work application oriented or more fundamental in nature?
Using catalytic chemical reactions in pyrolysis processes of biomass - to increase the active reaction area’s and to lower the activation energy – is a major research topic for about ten years now. (The approach is different from more well known pyrolysis processes which are thermal in nature.) The research attempts focus on the development of (new types of) catalysts.
In my research two different scale equipments were used: one using gram capacity, the other using microgram capacity. The latter was aimed at catalyst screening.
The approach was in between fundamental and application oriented research, as we were very much inspired by commercial catalysts. We didn’t study the reaction schemes on small molecular scales in a fundamental way, but started our search from commercial catalysts - used in similar processes in petrochemical industry - in combination with scientific literature studies.
This approach resulted in ‘gaps’; we found that some classes of catalysts were not covered sufficiently in earlier research attempts. We narrowed down our catalyst candidates by comparing them to six criteria. From here six or seven serious catalysts remained. In the end we choose the cesium-based metal catalyst which showed great results and, on top of that, specific activities and characteristics, making this catalyst a very special one.
The information and performances we were able to characterize, are of practical use to explore future catalysts further. In my view, this is a promising direction of future research. To confirm this statement, we performed a technological and economic assessment study to finish the PhD work. Here we found that this catalytic process results in high quality bio-oil at a prize of about 3,5 euro per liter, making further improvements worthwhile.
Do you recall some special moments during your PhD working period?
The road of research as a whole was very fulfilling: choosing this new type of catalysts on good grounds, showing their special behavior, and being able to explain why this behavior occurred. Therefore, I strongly believe that this behavior can be implemented in future catalysts.
In what magazines did you manage to publish your findings?
Seven articles appeared in major journals: Bioresource Technology, Biomass & Bioenergy, ACS Catalysis, Journal of Carbon, Physical Chemistry, Fuel Processing Technology and Applied Catalysis A.
In what way did you develop as a scientist and researcher in these four years?
In comparison with my master work, I am now able to work according to a proper and sound methodology. Working systematically, thinking strategically, right from the beginning of the project, and using my analytical skills; these all will be of great help in finding future jobs.
What are your future plans?
I started working already, at BiChem, a medium sized company in Eindhoven. Here, research on renewable chemicals is a central theme. These chemicals are used in petrochemical industry and, in a modified form, also in additional fuel processing.
I like to contribute as a chemist to a more sustainable and renewable future. The experience built up my PhD project fitted very well in this new job. The skills I mentioned in my curriculum vita stood out when I applied on this research position.
Did you feel a member of the Mesa+ community working on your PhD thesis?
Mark Smithers and Gerard Kip were of crucial importance in my PhD work, as these fine technicians helped me out on using SEM, to characterize the catalysts, and XPS techniques. They performed highly specialized measurement in close collaboration and consultation with me.
The equipment Mesa+ houses for characterization purposes, is really impressive. It is special to note that all experts are very helpful in order for you to use the apparatus independently. This contributes to one’s experimental skills and makes you feel more confident in using these instruments.