Many modern industrial chemical processes are optimised for raw materials from petrochemistry. Renewable raw materials can only serve as a viable alternative if alternative production processes are developed that are optimised to convert these biobased feedstocks. In the CatchBio (Catalysis for Sustainable Chemicals from Biomass) programme, Wageningen Food & Biobased Research has investigated a number of these processes.
Fossil feedstocks such as crude oil and natural gas were created by the geological breakdown of biomass over extended periods of time at high pressures and temperatures, causing nearly all of the chemically reactive groups to disappear. After (oil) refinery, reactive groups such as alcohols or acids are introduced in various chemical processes, which requires a lot of energy and results in the production of waste.
Fresh biomass, on the other hand, is too rich in functional groups for many practical applications. “In most cases breaking down biomass until it resembles petroleum by removing all reactive groups, and then adding them again in existing industrial processes, is not very efficient,” says Daan van Es, project leader at Wageningen Food & Biobased Research. “What could be effective, however, is to develop an alternative processes in which the undesired functionalities are removed selectively, while the desired ones are kept (selective defunctionalisation).” To develop these types of processes, Wageningen Food & Biobased Research participated in several sub-projects of the CatchBio programme.
Together with Utrecht University, scientists from Wageningen Food & Biobased Research developed catalysts to make better biofuels and raw materials for products such as detergents from unsaturated fatty acids from waste oils and fats without adding hydrogen. They contributed knowledge on vegetable oils and gained more insight into catalysts and the effects of unsaturated fatty acids on the processes. Using new tungsten and molybdenum carbide catalysts it was shown that both fuels and the desired chemicals could be produced. Moreover, although the process still requires hydrogen, it allows for the production of higher value chemicals. Further development of the new catalysts and processes is necessary to achieve commercialisation.
Alternative route to butadiene
An alternative route to 1,3-butadiene based on biomass was the goal of the second project. Butadiene is a starting material for synthetic rubber, among other things, and is much in demand in the chemical industry. Agricultural waste materials contain many non-digestible pentose sugars. Together with Utrecht University, Wageningen Food & Biobased Research explored the possibilities of shortening these sugars by one carbon atom, then removing all oxygen to produce butadiene. Although it proved possible to produce butadiene using this approach, it is currently too expensive to compete commercially with crude oil. The research by Wageningen Food & Biobased Research did result in new insights into methods to selectively cut down sugars and produce other industrially relevant building blocks such as ethylene glycol.
Selective deconstruction of lignin
Another project that Wageningen Food & Biobased Research was involved in, focused on the selective breakdown of lignin. In woody crops such as trees and grasses, lignin provides firmness and flexibility by acting as a kind of glue between the cellulose fibres and the hemicellulose. By treating wood or straw with acids or alkalis in hot water, the cellulose can be separated from the lignin. “The paper and pulp industry has been interested in lignin for decades,” confirms Van Es. “It consists of precursors to aromatic building blocks that are much in demand in the chemical sector. Currently, the majority of the lignin is incinerated to generate electricity and heat. Conversion into aromatic building blocks for plastics such as polycarbonate, PET or polystyrene increases its value and sustainability.”
Research into lignin is challenging, however. One reason for this is that the lignin which is obtained from pulping processes has undergone significant chemical changes during processing making it a less than ideal raw material for producing pure chemicals. Whereas a lot of research into the chemical deconstruction of lignin is focused on making liquid fuels, Wageningen Food & Biobased Research is mainly looking at conversion into high-value aromatic chemicals. While this is extra challenging, major progress has been achieved. One benefit is that the Wageningen process is performed in water, significantly reducing the steps in the process as the extraction of fibres from the cellulose slurry in the paper industry is also water-based. The use of water also makes the process far safer compared to flammable solvents such as alcohols.
The development of the process is still ongoing. Van Es: “Lignin is tricky. If you’re not careful, it turns into a sort of bakelite – which is not the intention. But we’re headed in the right direction. The lignin research is already being followed up in several new projects.” These studies are increasingly focused on adapting the processes to remove lignin from pulp; the milder the process, the better the lignin quality.
During the chemical conversion of sugars complex substances called humins are formed. A good example is the caramelisation of sugar, which starts with brown discolouration and eventually results in a black insoluble mass. Humins are undesirable by-products in many processes that involve sugars. Together with Utrecht University, Wageningen Food & Biobased Research performed research into humins produced in industrial processes. A large part of the research focused on shedding light on the chemical structure of these humins, aiming to gain more insight into the formation of humins (and possibly reducing or preventing it in the future). In addition, the study looked at whether it was possible to, in analogy to lignin, produce high-value chemicals and materials via the chemical conversion of humins. This humin research is also being followed up in various new projects based on the developed analysis methods and chemical insights.
Application of new processes
The CatchBio programme has yet to result in immediately applicable processes, according to Wageningen Food & Biobased Research. But Van Es hadn’t really expected it to do so at this time. “We can’t build any plants yet. The petrochemical industry has been carrying out research into many processes for over 70 years, and they are still being developed further. In this framework, the research into large-scale industrial refinery for the production of chemicals is still in its infancy.”